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PubMed1982

Amygdalopetal projections in the cat. II. Subcortical afferent connections. A study with retrograde tracing techniques.

The subcortical afferent connections of the amygdaloid complex of the cat were studied by means of retrograde tracing of horseradish peroxidase and the fluorescent substances bisbenzimid and nuclear yellow. The results of the present study indicate that structures in the basal forebrain, hypothalamus, brainstem, and thalamus project in a topographical manner to the various amygdaloid nuclei. Within the basal forebrain "ventral pallidal" structures project to the lateral and basolateral amygdaloid nuclei. The nucleus of the horizontal limb of the diagonal band and the medial part of the bed nucleus of the stria terminalis project predominantly to the medial and the medial central amygdaloid nuclei. Fibers from the substantia innominata distribute to nearly the entire expanse of the amygdaloid complex. The medial preoptic area and medial hypothalamic nuclei, including the paraventricular, ventromedial, arcuate, premammillary, and supramammillary nuclei, project most heavily to a region of the amygdala which includes the medial and the medial central nuclei. The caudal part of the lateral hypothalamic area sends strong projections to the medial central amygdaloid nucleus and more weakly projects to the basolateral nucleus. Brainstem neurons located in the cell groups A8 and A10, the dorsal raphe nucleus, the locus coeruleus, and the parabrachial nucleus project mainly to the medial central amygdaloid nucleus. Fibers originating in the medial part of the parabrachial nucleus in addition have a dense termination in the anterior amygdaloid area. Of the various midline nuclei of the thalamus which project to the amygdaloid complex, the paraventricular and ventral reuniens nuclei distribute fibers to the medial central and basolateral nuclei. The parataenial and the interventral nuclei project only to the medial central amygdaloid nucleus. Fibers from the interanteromedial nucleus exclusively reach the basolateral nucleus of the amygdala. Caudally in the ventral thalamus the subparafascicular and peripeduncular nuclei have been found to project to the medial, central, lateral, and cortical nuclei. In the posterior thalamus the medial part of the medial geniculate nucleus and the nucleus mediolateralis-suprageniculate complex give rise to fibers which reach the lateral central amygdaloid nucleus.

Afferent Pathways↗
PubMed1983

Corticothalamic projections from postcruciate area 4 in the dog.

Corticothalamic projections from postcruciate area 4, located on the rostral part of the posterior sigmoid gyrus, were traced with the autoradiographic technique in the dog. Injections of tritiated amino acids were made into the lateral and medial parts of area 4 in regions corresponding to the forelimb and hindlimb areas of the primary motor cortex, respectively. In cases with injections placed in the lateral part of area 4, dense accumulations of label were present in the lateral part of the ventral anterior nucleus (VA), the central part of the ventral lateral nucleus (VL), the ventral half of the ventral posterior inferior nucleus (VPI), the caudal part of the central lateral nucleus (CL), and the centrum medianum (CM). Lighter label was also present in the lateral part of the cytoarchitectonically distinct VL region bordering the ventrobasal complex (VB), as well as in the ventrolateral part of the mediodorsal nucleus (MD), and in the lateral posterior nucleus (LP). In one case in which the injection site involved an adjacent part of area 3a, label was also seen ventrally in the medial division of the posterior nuclear group (POm). However, no detectable differences in VL, MD, or intralaminar labeling patterns were noted between this case and the four other cases with injections confined to the lateral part of area 4. In two cases with injections restricted to the medial part of area 4, dense label was present in the lateralmost part of VL, the ventral part of VPI, the caudal part of CL, and CM. Lighter label was also present in the VL region bordering the dorsolateral edge of VB and in LP. An additional case in which the injection also involved the rostral border of area 3a showed a similar pattern of thalamic labeling. Projections from both the lateral and medial parts of area 4 were also noted in the subthalamic nucleus, zona incerta, and nucleus of Darkschewitsch. These results suggest that corticothalamic projections from postcruciate area 4 to VL are organized topographically such that projections from the lateral part of area 4 project centrally within VL while those from the medial part of area 4 project more laterally. Both parts of area 4 also project topographically to a cytoarchitectonically distinct region of VL located immediately adjacent to VB. In contrast, the projections to the intralaminar nuclei do not appear to be topographically organized. The data from cases involving spread of the injection into area 3a suggest that projection patterns from area 3a to ventral, intralaminar, and medial thalamic nuclei are similar to those from area 4. However, it appears that at least the lateral part of area 3a also projects to POm.

Animals↗
PubMed1983

Cytology of periolivary cells and the organization of their projections in the cat.

Projections of cells located near principal nuclei of the superior olive, periolivary cells, were studied by injecting horseradish peroxidase or fluorescent tracers into the cochlea, cochlear nucleus, and inferior colliculus. At least two distinct cytological classes of periolivary cells were found to project to each of these structures. "Large" and "small" olivocochlear cells were labelled. Their cytology and locations were found to be as had been previously described. Some olivocochlear cells also project to the cochlear nucleus. Other major periolivary cell classes that project to the cochlear nucleus include a lateral group of multipolar cells whose members are located around the ipsilateral lateral superior olive and have coarse, darkly staining Nissl substance. The other major periolivary cell class that projects to the cochlear nucleus is the small cell of the ventral nucleus of the trapezoid body. This cell is characterized by its size and by only one or two intensely staining clumps of Nissl substance. Projections of these cells to the cochlear nucleus is from both sides. Periolivary cells that project to the inferior colliculus include medial and lateral groups. Cells of the lateral group project from both sides. These cells are multipolar in shape and contain lightly staining, flocculent Nissl substance. They are predominantly located immediately ventral to the lateral superior olive. Projections from the medial group are predominantly ipsilateral and arise from the region medial to the medial superior olive. The cells are multipolar and contain clumped Nissl substance. They often lie near "large" olivocochlear cells, which they resemble in Nissl material, but are distinguished from the latter in Protargol material by having ring-type axosomatic endings. The appearance and locations of these six classes of periolivary cells make it possible to recognize them in nonexperimental material and to infer with confidence what their projections are. These results show considerable organization of these previously little understood structures.

Animals↗
PubMed1983

Neocortical projections of the suprageniculate and posterior thalamic nuclei in the marsupial brush-tailed possum, Trichosurus vulpecula (Phalangeridae), with a comparative commentary on the organization of the posterior thalamus in marsupial and placental mammals.

Axonal transport methods were used to determine the extent and organisation of neocortical projections from the suprageniculate (SG) and posterior (PO) thalamic nuclei in the brush-tailed possum. Our findings show that SG projects extensively to the auditory cortex, overlapping the cortical projection field of the medial geniculate nucleus, and to the immediately neighbouring association cortex. Though the input relationships of SG appear similar to those reported for other mammals, placental and marsupial, a strong SG projection to auditory cortex has not been reported previously. Neocortical relationships of PO are characterised by an orderly point-to-point projection to all but the most rostral parts of the motor-somaesthetic cortex. There is also a substantial projection to the entire posterior parietal association cortex. The PO-neocortex projection is reciprocally organised. The PO-neocortical projection in the possum is similar to that reported in the Virginia opossum, rat, and several other mammals. There is a major difference in organisation in comparison with certain monkeys where the PO projection is much more restricted and does not involve the motor and somaesthetic cortex. We conclude that PO is similarly organised in many, though not all, mammals, including the marsupials, rodents, insectivores, and prosimian primates. The possum SG, on the other hand, is clearly distinct from other mammals in its extensive projection to auditory cortex, though we cannot say at present whether this a general property of marsupial mammals or a peculiarity restricted to this species and possibly its close relatives.

Animals↗
PubMed1983

Transient cerebrocerebellar projections in kittens: postnatal development and topography.

Orthograde and retrograde labeling techniques were used to study the ontogenesis of transient cerebrocerebellar projections in kittens. Tritiated amino-acid or horseradish peroxidase injections were made into the coronal gyrus of the primary somatosensory cortex of kittens 1-70 postnatal days old. Orthogradely labeled axons were observed bilaterally in the superior and inferior cerebellar peduncles in kittens between 6 and 49 postnatal days of age. Most cerebrocerebellar axons labeled on the ipsilateral side arise from the pyramidal tract as it courses through the pontine nuclei. These axons descend through the pontine tegmentum as a diffusely organized corticotegmental tract and enter the ipsilateral superior cerebellar peduncle. Fewer cerebrocerebellar axons leave the pyramidal tract caudal to the pontine nuclei and project into the contralateral superior cerebellar peduncle. Cerebrocerebellar projections through the superior cerebellar peduncles terminate primarily in the cerebellar nuclei, where they are localized in the interpositus nuclei and in immediately adjacent areas of the dentate and fastigial nuclei. More caudally, labeled axons exit from the pyramidal tract and take a superficial route around the ventrolateral brainstem into the inferior cerebellar peduncles bilaterally. These projections are more numerous contralaterally and are directed primarily to the internal granule cell layer of the posterolateral folia of the anterior lobe, the posteromedial simplex lobule, and the dorsal paramedian lobule. Horseradish peroxidase injections were made into the cerebellar posterior lobe and deep nuclei and the results from these cases showed that the cerebrocerebellar pathway originates from pyramidal neurons in layer V primarily in the coronal, the precoronal, and the anterior and posterior sigmoid gyri on both sides. In these gyri, many of the HRP-positive neurons were found in clusters of two to five neurons, aligned in anterior-posterior strips. The results from all experiments provide evidence about the ontogeny of cerebrocerebellar projections. Projections through the superior cerebellar peduncles generally develop at 6-8 postnatal days of age, whereas projections through the inferior cerebellar peduncles first are seen at 8-10 days postnatally. Cerebrocerebellar projections reach their maximum development in the second postnatal week but sharply decrease in density during the third postnatal week. No cerebrocerebellar projections were observed after the seventh postnatal week of development. Possible functional implications for this transient projection are discussed.

Animals↗
PubMed1984

The organization of projections from the cortex, amygdala, and hypothalamus to the nucleus of the solitary tract in rat.

Direct projections from the forebrain to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus in the rat medulla were mapped in detail using both retrograde axonal transport of the fluorescent tracer True Blue and anterograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). In the retrograde tracing studies, cell groups in the medial prefrontal cortex, lateral prefrontal cortex (primarily ventral and posterior agranular insular cortex), bed nucleus of the stria terminalis, central nucleus of the amygdala, paraventricular, arcuate, and posterolateral areas of the hypothalamus were shown to project to the NTS and in some cases also to the dorsal motor nucleus of the vagus. The prefrontal cortical areas projecting to the NTS apparently overlap to a large degree with those cortical areas receiving mediodorsal thalamic and dopaminergic input. The retrogradely labeled cortical cells were situated in deep layers of the rat prefrontal cortex. The anterograde tracing studies revealed a prominent topography in the mediolateral termination pattern of forebrain projections to the rostral part of the NTS and to the dorsal pons. The projections to the NTS were generally bilateral, except for projections from the central nucleus of the amygdala and bed nucleus of the stria terminalis which were predominantly ipsilateral. The prefrontal cortical projections to the NTS travel through the cerebral peduncle and pyramidal tract and terminate throughout the rostrocaudal extent of the NTS. Specifically, the prefrontal cortex innervates dorsal portions of the NTS (lateral part of the dorsal division of the medial solitary nucleus, dorsal part of the lateral solitary nucleus and the caudal midline region of the commissural nucleus), areas which receive relatively sparse subcortical projections. These dorsal portions of the NTS receive major primary afferent projections from the vagal and glossopharyngeal nerves. In contrast, the subcortical projections, which travel through the midbrain and pontine tegmentum, terminate most heavily in the ventral portions of the NTS, i.e., the area immediately dorsal and lateral to the dorsal motor nucleus of the vagus. Only the paraventricular hypothalamic nucleus has substantial terminals throughout the dorsal motor nucleus of the vagus. Hypothalamic cell groups innervate the area postrema and, along with the prefrontal cortex, innervate the zone subjacent to the area postrema.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1984

Cortical projections to nuclei adjacent to the oculomotor complex in the medial dien-mesencephalic tegmentum in the monkey.

Cortical projections to cell groups surrounding the oculomotor complex were studied by using the retrograde and anterograde capabilities of the horseradish peroxidase (HRP) technique in old and new world monkeys. Fluid HRP injections or transcannular solid polyacrylamide HRP gel implants were made into the oculomotor nucleus (OMN) and adjacent nuclei to label retrogradely corticofugal neurons that project to this region, and cortical HRP gel implants were made in various areas of the frontal lobe to label anterogradely the trajectories and terminations of cortico-paraoculomotor projections and thus to confirm the retrograde findings. Projections to the paraoculomotor cell groups in the medial dien-mesencephalic tegmentum originate almost exclusively from the frontal lobe. Both retrograde and anterograde studies confirmed that the prearcuate cortex in the concavity of the arcuate sulcus, including the frontal eye field, and, to a lesser extent, suprarcuate rostral dorsal area 6 cortex and the dorsomedial convexity (area 9), project to the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the dorsal region of the prerubral field, nucleus of Darkschewitsch (ND), medial accessory nucleus of Bechterew (NB) and dorsomedial parvocellular red nucleus (dmPRN). The premotor area 6 and motor area 4 cortex, on the other hand, give rise to projections that target a larger portion of the parvocellular red nucleus, extending rostrally into the ventral region of the prerubral field, and a rather intense projection to the ND. The interstitial nucleus of Cajal (IC) was distinguished more by its light, or lack of, projections from the frontal cortex. The inferior parietal lobule (IPL, area 7) which has certain common physiological properties with the frontal eye field (FEF area 8) related to the oculomotor system, lacked retrogradely labeled neurons in all cases where transcannular gel implants into the OMN eliminated the possibility of HRP uptake in the corpus callosum or other structures traversed in needle injections, suggesting that the IPL affects eye movement primarily through its rostrally directed corticocortical associational connections with the FEF. In additional cases, the ND-NB-dmPRN configuration of cells that receives FEF input is shown to project to the inferior olivary complex (i.e., is pre-olivo-cerebellar), whereas riMLF and IC give rise to descending projections in the MLF, which target extraocular muscle motor nuclei, vestibular complex, and spinal cord. The results are discussed in terms of the potential role of the cerebral cortex in eye movement mechanisms.

Animals↗
PubMed1984

Telencephalic connections in lizards. I. Projections to cortex.

The afferent connections to five cortical regions in two distantly related species of lizards (Gekko gecko and Iguana iguana) were studied by means of retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin. Each of the five cortical regions is characterized by a specific pattern of projections from telencephalic, thalamic, hypothalamic, and brainstem regions. Subdivisions within the five cortical regions also receive different patterns of projections. The thalamo-cortical projections are as follows: The small-celled mediodorsal cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The large-celled mediodorsal cortex receives projections from nucleus dorsolateralis anterior pars parvicellularis and pars magnocellularis. The dorsal cortex receives a projection from nucleus dorsolateralis anterior pars parvicellularis. The lateral cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The pallial thickening receives projections from nucleus dorsomedialis and nucleus intercalatus. The latter nucleus receives a direct retinal projection. Thus, the pallial thickening is the recipient of a retino-thalamocortical projection. To date, comparisons of data from experimental studies have suggested that the cortical regions in lizards and turtles may be organized differently. However, the results of the present study suggest that the organization of cortical regions among reptiles is more similar than previously realized.

Afferent Pathways↗
PubMed1984

Amygdalo-cortical projections in the monkey (Macaca fascicularis).

Amygdalo-cortical projections were analyzed in the macaque monkey (Macaca fascicularis) in a series of experiments in which 3H-amino acids were injected into each of the major divisions of the amygdaloid complex and the anterogradely transported label was demonstrated autoradiographically. Projections to widespread regions of frontal, insular, temporal, and occipital cortices have been observed. The heaviest projections to frontal cortex terminated in medial and orbital regions which included areas 24, 25, and 32 on the medial surface and areas 14, 13a, and 12 on the orbital surface. Lighter projections were also seen in areas 45, 46, 6, 9, and 10. The heaviest projection to the insula terminated in the agranular insular cortex with a decreasing gradient of innervation to the more caudally placed dysgranular and granular insular areas. The projection to this region continues around the dorsal limiting sulcus to terminate in the somatosensory fields 3, 1-2, and SII. Essentially all major divisions of the temporal neocortex receive a projection from the amygdaloid complex with the most prominent projections ending in the cortex of the temporal pole (area TG) and the perirhinal cortex. The entire rostrocaudal extent of the inferotemporal cortex (areas TE and TEO) is also in receipt of an amygdaloid projection. While the rostral superior temporal gyrus (area TA) is heavily labeled in several of the experiments (with light labeling continuing into AI and adjacent auditory association regions) there was little indication of labeling in the caudal reaches of area TA. There was a surprisingly strong projection to prestriate regions of the occipital lobe and, in at least one case, clear-cut labeling in areas OB and 17. Labeling in the parietal cortex was primarily observed in the depths of the intraparietal sulcus. In all cortical fields, label was heaviest at the border between layers I and II and in some regions layers V and VI also had above background levels of silver grains.

Amygdala↗
PubMed1984

Prenatal and postnatal development of retinogeniculate and retinocollicular projections in the mouse.

The development of retinal projections to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) has been studied in fetal and neonatal mice of the pigmented C57BL/6 strain, using the anterograde transport of tritiated proline and horseradish peroxidase (HRP). Retinal efferents are present contralaterally just beyond the chiasm at E14. By E16 they have grown into both dLGN and SC. Ipsilateral fibers are limited to the proximal optic tract at E16; their growth into dLGN and SC is delayed until E18-birth. During the first 2 postnatal days, an early population of ipsilateral fibers invades the dLGN. Most of these fibers grow in or around the medio-dorsal sector of the dLGN, i.e., the future binocular segment. Fibers are also present, but at lower densities, in the ventral half of the nucleus and thereafter become dispersed or are lost, without at any stage becoming dense. Some denser labeling is also present ipsilaterally in the outer rim of dLGN, just below the optic tract, and later disappears. On the third postnatal day, the ipsilateral fibers establish a deep and denser projection along the medial and dorsal borders of dLGN; this projection overlaps part of the crossed projection, which at this age extends to the whole nucleus. The segregation of each projection starts on the fourth postnatal day, when crossed fibers begin to disappear from the small region of uncrossed projection. This process goes on for another 4 days. During this period, the ipsilateral fibers withdraw from the deepest layer of dLGN, and their terminal density increases gradually; by the eighth postnatal day, both projections are already well separated. Dense crossed projections first appear near the surface of the SC at birth. Prior to this, retinal fibers course throughout neurons of the collicular plate and underneath the pia. The uncrossed fibers invade the SC between birth and P3. They are located preferentially in the anterior and medial aspect of the SC. Subsequently, there occurs a diminution in the laminar and tangential extent of these projections, simultaneously with an intensification of the ipsilateral input to several small, longitudinally oriented clusters located deep to the crossed projections.

Animals↗
PubMed1985

Projection patterns of individual X- and Y-cell axons from the lateral geniculate nucleus to cortical area 17 in the cat.

Horseradish peroxidase was injected intracellularly into single, physiologically-identified X- and Y-cell geniculocortical axons projecting to area 17 of the cat. This injection anterogradely labeled the axon terminal fields in cortex and retrogradely labeled the somata of these same axons in laminae A and A1 of the lateral geniculate nucleus (LGN). The laminar projections of 21 X- and 15 Y-cell axons were analyzed. For these, the laminar terminations of ten X- and seven Y-cell axons were also related to their cells' positions in the A-laminae. The terminal fields of X- and Y-cell axons overlapped substantially in layers IV and VI of area 17. Some X-cells terminated mainly in IVb, others mainly in IVa, and still others throughout IVa and IVb. The latter two groups also projected up to 100 micron into lower layer III. Y-cells terminated primarily in layer IVa and projected up to 200 microns into lower layer III. Some also arborized throughout the depth of layer IVb. Both X- and Y-cell axons terminated throughout the depth of layer VI, although more so in the upper half. We found no relationship between the diameter of the parent axon and its sublaminar projection within layer IV. Within layer IV, X-cell axons generally terminated within a single, continuous clump and had surface areas of 0.6 to 0.9 mm2. Axons of Y-cells often terminated in two to three separate clumps, separated by terminal free gaps 400 to 600 micron wide. Their total surface areas, including gaps, were 1.0 to 1.8 mm2, roughly 1.6 times the surface areas of X-cell axons. Despite considerable overlap, Y-cell arbors contained significantly more boutons than did X-cell arbors. The sublaminar projections of the X- and Y-cell axons within layer IV reflected the locations of the cells' somata within the depth of the A-laminae. X-cells located in the dorsal or ventral thirds of the depths of the laminae projected mainly to layer IVa or throughout layer IV in cortex. Those located in the central thirds projected mainly to layer IVb. Y-cells showed a similar positional relationship, but they appeared to follow different rules. Y-cells in the outer thirds of the A-laminae projected mainly to layer IVa; those in the central thirds, in addition, expanded their projections to include layer IVb. In general, larger sized somata in the LGN gave rise to more widely spreading terminal arbors and greater numbers of boutons in cortex than did smaller somata.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Central projections of cat retinal ganglion cells.

The central projections of different groups of cat retinal ganglion cells were studied following small iontophoretic injections of horseradish peroxidase (HRP) into physiologically characterized sites. Analysis was restricted to labeled cells in the upper periphery of the nasal retina, contralateral to the injection site. Injections were made to the A lamina and C lamina of the dorsal lateral geniculate nucleus (LGNd-A,C), the geniculate wing (LGNd-W), the ventral lateral geniculate nucleus (LGNv), the pretectum (PT), and the superior colliculus (SC). The dendritic fields of alpha, beta, and epsilon cells were well labeled by the procedures we employed. A group, termed "g1," had somal sizes within the range of the smaller beta and epsilon cells, but dendritic morphologies distinct from either class. The g1 group may consist of a number of types, but our material provided no basis for further distinguishing them. Many cells were observed that had smaller somas; all had thin axons, and few had dendritic fields that labeled to any significant extent. We were not able to further distinguish these cells, and refer to this group, which may include a number of types, as "g2" cells. From the peripheral nasal retina, alpha cells project to LGNd-A, LGNd-C, PT, and SC. Beta cells project to LGNd-A, LGNd-C, and PT. Epsilon and g1 cells project to the LGNd-C, LGNd-W, LGNv, PT, and SC. We determined the total spatial density of cells in the region of the retina analyzed, using a Nissl-stained preparation. We then estimated the relative fraction of cells in each of the above groupings by injecting HRP throughout a cross section of the optic tract. Multiplying this relative fraction by the total spatial density gave an estimate of the spatial density of each of these groupings. From the spatial density of cells labeled from the injection site, we were able to estimate the fraction of cells of each retinal grouping that project to each of the zones investigated. By these calculations, almost all alpha cells from the upper nasal retina project to LGNd-A and LGNd-C; most project to SC, and about a third to PT. Beta cells, by contrast, project almost exclusively to LGNd-A, with about 10% going to LGNd-C, and about 1% to the PT. The great majority of epsilon cells, if not all, project to LGNd-W, and up to half of this population also project to the other zones noted above.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Projections of the entorhinal area to the striatum, nucleus accumbens, and cerebral cortex in the guinea pig.

A study of the efferent projections of the entorhinal area in the guinea pig, by using anterograde (autoradiographic tracing of tritiated amino acids) and retrograde (fluorochrome tracing) methods, revealed the following projections: (1) to nonhippocampal cortices: retrosplenial cortex (area 29), cingulate cortex (areas 23, 24), prelimbic cortex (area 32), infralimbic cortex (area 25), perirhinal cortex (areas 35, 36), prepyriform cortex (area 51B), and insular cortex (areas 13-16). All received direct projection; (2) to subcortical targets: distinct terminations were observed in the lateral thalamic nucleus, the striatum, and the accumbens nucleus. In retrograde experiments, the cells giving rise to the projections to the hippocampus were found to lie in layers II and III, those projecting to the nonhippocampal cortical regions to originate in layer IV, and those projecting to the striatum and the accumbens to lie in layers V and VI. Many of the efferent projections to the cerebral cortical regions are associated with reciprocal projections from these regions to the superficial layers (I-III) of the entorhinal cortex. The entorhinal efferent projections generally terminate ipsilaterally. A weak termination is, however, present at the contralateral side. The efferent projections of the entorhinal area represent a route for important caudally directed, nonfornical hippocampal output.

Animals↗
PubMed1985

An autoradiographic study of projections ascending from the midbrain central gray, and from the region lateral to it, in the rat.

Ascending projections from the midbrain central gray (CG) and from the region lateral to it were traced in the rat using tritiated amino acid autoradiography. Leucine or a cocktail of amino acids (leucine, proline, lysine, histidine, and tyrosine) were used as tracers. In addition to projections within the midbrain, ascending fibers follow three trajectories. The ventral projection passes through the ventral tegmental region of Tsai and the medial forebrain bundle to reach the hypothalamus, preoptic area, caudoputamen, substantia innominata, stria terminalis, and amygdala. There are labeled fibers in the diagonal bands of Broca and medial septum, and terminal labeling in the lateral septum, nucleus accumbens, olfactory tubercle, and frontal cortex. The dorsal periventricular projection terminates in the midline and intralaminar thalamic nuclei. The ventral periventricular projection follows the ventral component of the third ventricle into the hypothalamus, passing primarily through the dorsal hypothalamic area and labeling the rostral hypothalamus and preoptic area. Projections from the region lateral to the CG are similar, but exhibit stronger proximal, and weaker distal, projections. Rostral levels of the CG send heavier projections to the fields of Forel and the zona incerta, but fewer fibers through the supraoptic decussation, than do caudal levels. Ascending projections from the CG are both strong and widespread. Strong projections to the limbic system and the intralaminar thalamic nuclei provide an anatomical substrate for CG involvement in nociception and affective responses.

Amino Acids↗
PubMed1986

Development of anomalous retinal projections to nonvisual thalamic nuclei in Syrian hamsters: a quantitative study.

When two of the principal targets of retinofugal axons, the superior colliculus and dorsal nucleus of the lateral geniculate body, are ablated in newborn hamsters and the somatosensory (ventrobasal) or auditory (medial geniculate) thalamic nuclei are partially deafferented, the optic axons form permanent, abnormal connections in the latter nuclei. The lateral posterior nucleus of the operated hamsters also receives an anomalously large retinal projection. Here, we report on the results of a quantitative study that was undertaken in order to elucidate how these abnormal connections are formed. In normal, newborn hamsters, there is a transient retinal projection to the ventrobasal nucleus that disappears 3-4 days postnatally. Our quantitative data show that postoperatively, the volume of the retino-ventrobasal projection increases proportionately more than the volume of the ventrobasal nucleus so that the retino-ventrobasal projection in operated adult hamsters is due both to the stabilization of the normally transient projection and to a reactive sprouting that increases the size of the projection. The retino-medial geniculate projection arises de novo by reactive sprouting of optic tract fibers that normally pass over and through the nucleus; in unoperated hamsters, terminating projections are never seen at any age. The quantitative data also show that the anomalously large retino-lateral posterior projection is due almost entirely to the reactive sprouting of the normal projection and/or normal fibers of passage that are already present on the day of birth, although it is possible that a minor component can be attributed to the stabilization of a small population of normally transient retino-lateral posterior axons. The present results demonstrate that the transient retino-ventrobasal axons in normal, newborn hamsters are capable of making permanent connections with ventrobasal neurons. This finding raises the important question of the cellular mechanisms that determine whether immature neuronal connections are stabilized or eliminated. The results also suggest that during both normal and abnormal development, the choice of a target by growing axons may depend upon the axons being in proximity to a potential terminal site just at the time when that site is capable of receiving afferents.

Animals↗
PubMed1987

The projection of the nucleus reticularis tegmenti pontis and adjacent regions of the pontine nuclei to the central cerebellar nuclei in the cat.

The projection of the nucleus reticularis tegmenti pontis (NRTP) and the pontine nuclei (NP) to the central cerebellar nuclei (CCN) was investigated by means of anterograde transport of tritiated leucine. Although termination was found in all the CCN, it was most pronounced in the lateral nucleus and the lateral aspect of the posterior interposed nucleus. The extreme lateral aspect of the anterior interposed nucleus and the caudal part of the fastigial nucleus received a projection of modest intensity. Termination in the infracerebellar nucleus and group Y is likely to be present but could not be confirmed with certainty from the light microscopical material. The contribution from the NP was small and originated from the dorsolateral and dorsal paramedian subdivisions of the NP. Within the NRTP the total area giving rise to projections to the CCN was extensive, and the origin of the projections to the individual CCN overlapped considerably. The projection of the NRTP to the ventrocaudal part of the lateral nucleus was found in conjunction with a projection to the ventrolateral part of the posterior interposed nucleus. Both projections seemed to branch off the fiber bundle terminating in the ventral paraflocculus. Similar correlations could be established in the projection of the NRTP to the dorsal paraflocculus and crus II of the ansiform lobule with other parts of the lateral and posterior interposed nuclei. It was concluded that the transverse, lobular organization of mossy fibers, which differs fundamentally from the longitudinal, modular organization of climbing fibers, is maintained in the collateral projection to the CCN. The results are further discussed in relation to the corticonuclear projection and the engagement of the NRTP and different parts of the CCN in pontocerebellar circuits.

Animals↗
PubMed1988

Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat.

The projections of the medial preoptic nucleus (MPN) were examined by making injections of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the MPN and charting the distribution of labeled fibers. The evidence indicates that the MPN projects extensively to widely distributed regions in both the forebrain and brainstem, most of which also supply inputs to the nucleus. An important neuroendocrine role for the MPN is underscored by its extensive projections to almost all parts of the periventricular zone of the hypothalamus, including the anteroventral periventricular, anterior part of the periventricular, paraventricular (PVH), and arcuate nuclei, and a role in autonomic mechanisms is indicated by projections to such regions as the dorsal and lateral parvicellular parts of the PVH, the lateral parabrachial nucleus, and the nucleus of the solitary tract. Other projections of the MPN suggest participation in the initiation of specific motivated behaviors. For example, inputs to two nuclei of the medial zone of the hypothalamus, the ventromedial and dorsomedial nuclei, may be related to the control of reproductive and ingestive behaviors, respectively, although the possible functional significance of a strong projection to the ventral premammillary nucleus is presently unclear. The execution of these behaviors may involve activation of somatomotor regions via projections to the substantia innominata, zona incerta, ventral tegmental area, and pedunculopontine nucleus. Similarly, inputs to other regions that project directly to the spinal cord, such as the periaqueductal gray, the laterodorsal tegmental nucleus, certain medullary raphe nuclei, and the magnocellular reticular nucleus may also be involved in modulating somatic and/or autonomic reflexes. Finally, the MPN may influence a wide variety of physiological mechanisms and behaviors through its massive projections to areas like the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the lateral hypothalamic area, the supramammillary nucleus, and the ventral tegmental area, all of which have extensive connections with regions along the medial forebrain bundle. Although the PHA-L method does not allow a clear demonstration of possible differential projections from each subdivision of the MPN, our results suggest that each of them does give rise to a unique pattern of outputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Characterization of transient cortical projections from auditory, somatosensory, and motor cortices to visual areas 17, 18, and 19 in the kitten.

We have examined the anatomical features of ipsilateral transient cortical projections to areas 17, 18, and 19 in the kitten with the use of axonal tracers Fast Blue and WGA-HRP. Injections of tracers in any of the three primary visual areas led to retrograde labeling in frontal, parietal, and temporal cortices. Retrogradely labeled cells were not randomly distributed, but instead occurred preferentially at certain loci. The pattern of retrograde labeling was not influenced by the area injected. The main locus of transiently projecting neurons was an isolated region in the ectosylvian gyrus, probably corresponding to auditory area A1. Other groups of transiently projecting neurons had more variable locations in the frontoparietal cortex. The laminar distribution of neurons sending a transient projection to the visual cortex is characteristic and different from that of parent neurons of other cortical pathways at the same age. In the frontoparietal cortex, transiently projecting neurons were located mainly in layer 1 and the upper part of layers 2 and 3. In the ectosylvian gyrus, nearly all the neurons are located in layers 2 and 3. In addition, a few transiently projecting neurons are found in layer 6 and in the white matter. Transiently projecting neurons have a pyramidal morphology except for the occasional spindle-shaped cell of layer 1 and multipolar cells observed in the white matter. Anterograde studies were used to investigate the location of transient fibers in the visual cortex. Injections of WGA-HRP at the site of origin of transient projections gave rise to few retrogradely labeled cells in areas 17, 18, and 19, demonstrating that transient projections to these areas are not reciprocal. Although labeled axons were found over a wide area of the posterior cortex, they were more numerous over certain regions, including areas 17, 18, and 19, and absent from other more lateral cortical regions. Transient projecting fibers were present in all cortical layers at birth. Plotting the location of transient fibers in numerous sections and at all ages showed that these fibers are not more plentiful in the white matter than they are in the gray matter. We found no evidence that the white/gray matter border constituted a physical barrier to the growth of transient axons. Comparison of the organization of this transient pathway to that of other transient connections is discussed with respect to the development of the cortex.

Aging↗