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PubMed1985

The retinal projection to the cat pretectum.

Retinal ganglion cells were labeled retrogradely by localized injections of HRP into different regions of the pretectum, tectum, and optic tract in 26 cats. Retinal projection zones in the pretectum were labeled anterogradely in the same cats by intravitreal injections of 3H-proline. This allowed the HRP injection sites to be located with respect to the retinal termination zones. The form of the projection zones from retina to pretectum was determined from serial reconstructions of either coronal or horizontal sections. The zones are best distinguished in horizontal sections, where they are seen as four roughly parallel strips on either side of the brain. They are more-or-less parallel to the anterior border of the tectum, and appear to traverse the entire width of the retinal projection to the tectum. Each zone is similar in form for the ipsilateral and contralateral projections, although the contralateral projection is thicker and denser. Binocular injections of 3H-proline showed that the projections from the two eyes were in register and did not interdigitate. Cells labeled by HRP injections in the anteromedial end of the pretectum were concentrated in the lower nasal quadrant of the contralateral retina, and the lower temporal quadrant of the ipsilateral retina. Posterolateral injections labeled cells in the upper quadrants. There is thus a rough retinotopic mapping along the elongated axis of the pretectum. When the distributions of ganglion cells labeled by HRP injections to different parts of the pretectum are combined, they show a concentration in both the visual streak and area centralis, and thereby reflect, at least qualitatively, the relative spatial distribution of the entire ganglion-cell population. About 85% of the retinal projection to the pretectum is contralateral. For all of the HRP injections, the spatial density of labeled cells was always low, accounting for no more than 3% of the total spatial density of ganglion cells in any retinal region. Several types of ganglion cells were labeled following injections to most regions of the pretectum; these included alpha, beta, and epsilon cells, as well as small-bodied cells showing a variety of morphologic forms. Alpha cells were labeled mainly from the anterolateral end of the pretectum, but other cell types were labeled from all injected regions. In the peripheral retina, 2% of the labeled cells were alpha cells, 32% were beta cells, 19% were epsilon cells, and the remaining 47% were small cells whose dendrites only occasionally filled to any significant extent.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Trigeminocerebellar, trigeminotectal, and trigeminothalamic projections: a double retrograde axonal tracing study in the mouse.

Double retrograde axonal tracing experiments were carried out in order to reveal potential patterns of divergence in axonal projections from the two major sensory nuclei of the mouse brainstem trigeminal complex: the principal sensory and spinal trigeminal nuclei (oralis, interpolaris, and caudalis divisions). The tracers wheat germ agglutinin, N-[acetyl-3H] and horseradish peroxidase were used in paired injection strategies within portions of the cerebellum, superior colliculus, and thalamic ventrobasal complex and/or posterior group of adult ICR white mice. Trigeminal neurons with projections to tactile areas of the cerebellar cortex or underlying deep cerebellar nuclei were found scattered throughout the principal sensory nucleus and interpolaris division, and mainly in dorsal regions of the oralis division of the spinal trigeminal nucleus. Injections of either tracer which involved lateral portions of the rostral half of the superior colliculus labeled trigeminotectal neurons mainly in the contralateral interpolaris division, ventral half of the oralis division, and a ventral region of the principal sensory nucleus near the oralis border. Fewer trigeminotectal neurons were found scattered throughout the principal sensory nucleus and the magnocellular layer of the caudalis divisions, although an occasional labeled neuron wa also found in the marginal layer. Contralaterally projecting trigeminothalamic neurons were observed throughout the principal sensory nucleus, interpolaris division, and within the marginal and magnocellular layers of caudalis. Double-labeled neurons were observed only after paired injections of the tracers in the thalamus and ipsilateral superior colliculus, and they were found within the caudoventral portion of the principal sensory nucleus near the oralis border, throughout the interpolaris division, within the magnocellular layer of caudalis, and only a few double-labeled neurons were also found within the marginal layer. After such injections, 50% of the labeled tectum-projecting neurons in the principal sensory nucleus, 64% in the interpolaris division, and 57% in the caudalis division are branched neurons which have collateralized projections to both the superior colliculus and thalamus. These projections, which have not been described before, appear to arise from more than one class of projection neuron which is differentially distributed within different regions of the trigeminus.

Animals↗
PubMed1985

Cutaneous projections from the rat hindlimb foot to the substantia gelatinosa of the spinal cord studied by transganglionic transport of WGA-HRP conjugate.

The somatotopic organization of cutaneous afferent fibers from the hindlimb foot in the substantia gelatinosa of the spinal cord was investigated in adult Sprague Dawley rats following intracutaneous injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). The different parts of the foot were found to project in a precise manner to the medial two-thirds of the substantia gelatinosa of the spinal cord segments L3-L5. The projections from the digits were arranged in a consecutive row rostrocaudally, with the most medial digit in caudal L3 and the most lateral digit in caudal L4 or rostral L5. The plantar skin was found to project both rostral and caudal to the projection of the digits. The dorsal foot skin projects lateral to the digits, neighboured by the medial edge of the foot rostrally and the lateral edge caudally. Within the projection of a particular digit, the plantar skin was found medially and the dorsal skin laterally. A certain degree of overlap for the projections from the different foot skin areas was found.

Afferent Pathways↗
PubMed1985

Development of the spinal-medullary projection from the mouse barrel field.

Neurons in layer V of the murine posteromedial barrel subfield (PMBSF) project to structures at or caudal to the spinal-medullary junction. During postnatal development a reduction occurs in the density of the neurons which form this projection. In principle, three processes might be expected to contribute to this reduction: cell death, tissue growth, and axon pruning. Three different paradigms in which cells of origin of the projection are labeled retrogradely with True Blue, injected into the spinal-medullary junction, taken together with an estimate of the relative growth of layer V, provide separate estimates of the magnitude and rate of reduction consequent to these different processes during the first 3 postnatal weeks. The density of neurons in an index sector of layer V of the PMBSF which contribute to the projection at varied ages is estimated by injections made at a range of ages from postnatal day 1 (P1) to P16, with a survival of 4 days in each instance. Overall reduction in density is 80%. The component due primarily to axon pruning is estimated to be 50% by injections delivered at graded ages from P1 to P16 with survival to P20 in each instance. The component of the reduction attributable to increase in volume is estimated at 30% by a series of injections delivered at P1 with graded survival times from P5 through P20. A reduction due to cell death is not identified. The reduction in density due to tissue growth is essentially linear through the interval P5-P11. At all ages, neuronal somata of origin of the spinal-medullary projection are located within layer V. Subsequent to P15 they are confined to sublayer Vb; at earlier ages somata in Va and Vc also contribute axons to the projection. Although volume increase due to growth of the neuropil reduces the density of the population contributing to the projection equally in all three sublayers, final elimination of all contributions from Va and Vc depends upon axon pruning.

Animals↗
PubMed1985

Transient tectogeniculate projections in neonatal kittens: an autoradiographic study.

By using anterograde transport autoradiography, the present experiments demonstrated that the pattern of tectogeniculate projections in young (birth-14 postnatal days) kittens is strikingly different from that present in adult cats. Rather than being confined to the ventral C laminae, the neonatal projection extended across all layers of the lateral geniculate nucleus. This projection, like that in the adult cat, originates from cells in superficial laminae and is visuotopically organized. Thus, labeling only a portion of the superior colliculus with tritiated leucine produced a topographically appropriate strip of labeling in the ipsilateral lateral geniculate nucleus that encompassed all laminae and was especially dense in all interlaminar zones. Transported label also invaded the medial interlaminar nucleus (MIN). The loss of tectogeniculate projections in the neonate from MIN and the dorsal laminae and interlaminar zones of the lateral geniculate nucleus does not appear to begin until 1-2 weeks postnatal. Once initiated, however, the process is nearly completed by 21 days postnatal. It is not yet known whether the loss of these "anomalous" projections is due to the pruning of axonal collaterals, cell death, or a combination of the two processes. However, by comparing these data with those from other laboratories, it does appear that the loss of tectogeniculate projections depends on the presence of the two eyes and may reflect the differential laminar distribution of W-, X-, and Y-cell types. The protracted postnatal anatomical maturation of tectogeniculate projections differs substantially from the earlier maturing patterns apparent in all other tectofugal pathways.

Aging↗
PubMed1985

The cerebellar and vestibular nuclear complexes in the turtle. I. Projections to mesencephalon, rhombencephalon, and spinal cord.

Cerebellar and vestibular projections were investigated in the turtle Pseudemys scripta elegans following injection of 35S-methionine into the cerebellar and vestibular nuclear complexes at various locations. Fibers arising from the cerebellar nuclei were traced via the cerebellar commissure to the contralateral vestibular nuclear complex (particularly the n. vestibularis inferior and n. vestibularis ventrolateralis) and caudal rhombencephalic tegmentum. Ascending projections crossing the midline in the ventral isthmomesencephalic tegmentum terminated in the contralateral red nucleus and nuclei of the fasciculus longitudinalis medialis (f lm). Vestibular projections ascending mainly via the f lm terminated in the nuclei of the f lm, the nuclei of the posterior commissure, and particularly the extraocular motor nuclei. Vestibulo-ocular projections arising from the rostral vestibular nuclear complex were almost exclusively ipsilateral; those from the caudal vestibular nuclear complex were bilateral. Evidence for a topographic organization of the projections to the trochlear and oculomotor nuclei was also obtained. There were some vestibular projections to the contralateral rhombencephalic tegmentum and n. vestibularis inferior. Spinal projections coursing within the ipsilateral ventral descending tract and the ipsilateral fasciculus longitudinalis medialis were found to arise from both rostral and caudal vestibular regions. The caudal vestibular nuclear complex in addition gave rise to fibers descending in the contralateral fasciculus longitudinalis medialis. Evidence for the existence of labeled fibers crossing at spinal levels was also obtained. Vestibulospinal terminations appeared restricted to the ventral horn.

Animals↗
PubMed1986

Cholinergic and GABAergic afferents to the olfactory bulb in the rat with special emphasis on the projection neurons in the nucleus of the horizontal limb of the diagonal band.

We have examined the location of cholinergic and GABAergic neurons that project to the rat main olfactory bulb by combining choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) immunohistochemistry with retrograde fluorescent tracing. Since many of the projection neurons are located in subcortical basal forebrain structures, where the delineation of individual regions is difficult, particular care was taken to localize projection neurons with respect to such landmarks as the ventral pallidum (identified on the basis of GAD immunoreactivity), the diagonal band, and medial forebrain bundle. In addition, sections with fluorescent tracers or immunofluorescence were counterstained for Nissl substance in order to correlate tracer or immunopositive neurons with the cytoarchitecture of the basal forebrain. The majority of the cholinergic bulbopetal neurons are located in the medial half of the nucleus of the horizontal limb of the diagonal band (HDB), whereas only a few are located in its lateral half. A substantial number of cholinergic bulbopetal cells are also found in the sublenticular substantia innominata. A small number of cholinergic bulbopetal neurons, finally, are located in the ventrolateral portion of the nucleus of the vertical limb of the diagonal band. At the level of the crossing of the anterior commissure, approximately 17% of the bulbopetal neurons in the HDB are ChAT-positive. The noncholinergic bulbopetal cells are located mainly in the lateral half of the HDB. GAD-containing bulbopetal neurons are primarily located in the caudal part of the HDB, especially in its lateral part. About 30% of the bulbopetal projection neurons in the HDB are GAD-positive. A few GAD-positive bulbopetal cells, furthermore, are located in the ventral pallidum, anterior amygdaloid area, deep olfactory cortex, nucleus of the lateral olfactory tract, lateral hypothalamic area, and tuberomamillary nucleus. The topography of bulbopetal neurons was compared to other projection neurons in the HDB. After multiple injections of fluorescent tracer in the neocortex, retrogradely labeled neurons were concentrated in the most medial part of the HDB, while neurons projecting to the olfactory and entorhinal cortices were located in the ventral part of the HDB. These results show that the cells of the HDB can be divided into subpopulations based upon projection target as well as transmitter content. Furthermore, these subpopulations correspond, at least to a considerable extent, to areas that can be defined on cyto- and fibroarchitectural grounds.

Animals↗
PubMed1986

Projections to the superior temporal sulcus from the central and peripheral field representations of V1 and V2.

In a series of three studies, we have begun to explore the sequence of visual information processing along the pathway from striate cortex (V1), through MT, into the parietal lobe. In this first study, we sought to establish the relationships among MT, the heavily myelinated zone of the superior temporal sulcus (STS), and the V1 and V2 projection fields in the STS. Autoradiographic material from seven hemispheres of six macaques injected with tritiated amino acids into either V1 or V2 was analyzed in detail, and the results were plotted onto two-dimensional reconstructions of the STS. Autoradiographic material from eight additional macaques with V2 injections was also examined. The results indicate that the central visual field representations of both V1 and V2 project into the heavily myelinated zone in the lower bank and floor of the STS, confirming prior studies, whereas the far peripheral representations of both V1 and V2 project into the cortex medial to this zone on the upper bank of the sulcus. There is no evidence that this medial cortex is a separate area that receives projections from V1 and V2 in parallel with the projections these areas send to the heavily myelinated zone. Rather, there seems to be a single projection field of V1 and V2 whose central representation lies within the heavily myelinated zone and whose most peripheral representation lies medial to it. Because of the difference in myelination between the central and peripheral field representations as well as visuotopic anomalies between them, we retain the term "MT" for the heavily myelinated zone and apply the term "MTp" to the far peripheral projection zone. Both MT and MTp are required to process the complete outputs of V1 and V2 within the STS and thus should probably be regarded as two distinctive parts of a single visual area. The difference in myelination between MT and MTp suggests that there is a difference in visual processing between the central and peripheral visual fields. The average size of MT is estimated to be 62 mm2, and the average size of MT and MTp combined to be 76 mm2, which is consistent with estimates derived from several other studies.

Amino Acids↗
PubMed1987

Efferent projections of the suprachiasmatic nucleus: II. Studies using retrograde transport of fluorescent dyes and simultaneous peptide immunohistochemistry in the rat.

In a previous study (Watts et al., '87) we reexamined the projections of the suprachiasmatic nucleus (SCh) with the PHA-L method and found that they could be divided conveniently into six groups of fibers. By far the densest projection ends just dorsal to the SCh in a comma-shaped region designated the "subparaventricular zone," although some fibers continue on through the paraventricular nucleus of the hypothalamus to end in the overlying midline thalamus, and others continue on to end in the dorsomedial nucleus, the region around the ventromedial nucleus, and the posterior hypothalamic area. Other relatively sparse projections from the SCh were also described to the preoptic region, lateral septal nucleus, parataenial and paraventricular nuclei of the thalamus, and ventral lateral geniculate nucleus. In addition, the same method was used to show that the subparaventricular zone projects in turn massively to these same regions, as well as back to the SCh itself and to the periaqueductal gray. The present series of experiments was designed to confirm these observations with retrograde tracer injections and to investigate the cellular and possible neurotransmitter organization of the major projections from the SCh and subparaventricular zone with a combined retrograde tracer-immunohistochemical method. For this, the distribution of neuronal cell bodies within the SCh that stain with antisera to vasopressin, vasoactive intestinal polypeptide (VIP), corticotropin-releasing factor, bombesin, substance P, neurotensin, somatostatin, thyrotropin-releasing hormone, and angiotensin II was described in detail first. Then the distribution of retrogradely labeled neurons that were also stained for one or another of these peptides was described after injections of true blue, or in some cases SITS, into the regions of the subparaventricular zone, the paraventricular and parataenial nuclei of the thalamus, the ventromedial nucleus, the dorsomedial nucleus, and the periaqueductal gray. The results confirm previous immunohistochemical and anterograde tracing studies and in addition indicate that cells in dorsal as well as ventral parts of the SCh project to each of the terminal fields examined, as do many cells in surrounding areas, including the subparaventricular zone. Our results also suggest that, at the very least, vasopressin-, VIP-, and neurotensin-stained cells in the SCh project to the subparaventricular zone, midline thalamus, and dorsomedial nucleus, and that the vasopressin and VIP-stained fiber systems are partially segregated at the level of the subparaventricular zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II↗
PubMed1987

Organization of postcranial kinesthetic projections to the ventrobasal thalamus in raccoons.

To determine the presence and organization of kinesthetic, as compared with other mechanosensory projection zones in the thalamus of raccoons, unit-cluster responses to mechanical stimulation of the postcranial body were mapped electrophysiologically in the thalami of 14 raccoons anesthetized with Dial-urethane. A distinct zone of kinesthetic projections (from receptive fields in muscles, tendons, and joints) was found in the rostral and dorsal aspects of the mechanosensory projection zone. These projections are somatotopically organized: those from axial structures lie dorsalmost and those from successively more distal limb regions are successively more caudoventral. The kinesthetic forelimb representation is large and lies rostrodorsal to a large central core of cutaneous projections from the forepaw digits. A few scattered kinesthetic projections were found at the caudal edge of the sensory thalamic region. The large, spatially and somatotopically distinct kinesthetic projection zone in the thalamus parallels those seen in the cortex and medulla of raccoons. Similar findings in monkeys, and suggestions from data in cats and humans support the hypothesis of a distinct pathway to the cortex for kinesthetic information in all mammals.

Afferent Pathways↗
PubMed1987

Spinocerebellar projections from the cervical enlargement in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The projection fields of spinocerebellar tracts arising from the cervical enlargement were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. Following injections of WGA-HRP into the C5-C8 or T1 segments, labeled terminals were seen in lobule I to sublobule Vf of the anterior lobe, and lobule VI, sublobule VIIb, lobules VIII and IX, the simple lobule, crus II, and the paramedian lobule of the posterior lobe. In the sagittal plane of sublobules Ib-Vf and sublobules VIf and VId, the labeled terminals were distributed mainly in the superficial two thirds of the apicobasal extent. The labeled terminals in the anterior lobe accounted for about 70% of the total labeled terminals; the great majority were in lobule IV (17-20%) and lobule V (40%). The labeled terminals in the posterior lobe accounted for 30% of the total labeled terminals; the majority were in sublobules VIf (11-15%) and VId (6%). In the mediolateral extent, more than 50% of the total labeled terminals in each lobule were concentrated within 1.0 mm from the midline (the vermis) and 70-80% within 2.0 mm from the midline (the vermis and the medial part of the intermediate regions). A smaller number were also present in the intermediate region. Cases with lateral cordotomies revealed that the projections were bilateral but predominantly ipsilateral to the cells or origin and that the quantity of the ipsilateral projection was 66.5-75% of the total in each of sublobules IVb, Va, and VIf. The projection to the paramedian lobule was also predominantly ipsilateral. Projection fields in the horizontal plane were reconstructed from a series of transverse sections through each lobule. In sublobules Va-VIf labeled terminals were distributed in three areas: area 1 located within 0.25 mm from the midline in zone A1 of Voogd; area 2 located between 0.5 and 0.75 mm lateral to the midline in zones A1 and A2; and area 3, which appeared to be located between 0.75 and 1.5 mm lateral to the midline in zones A2-B. These areas extended longitudinally in the apical two thirds of the lobules. From the present and previous retrograde HRP studies it was suggested that the neuronal groups in the cervical enlargement (the medial lamina VI group and the central lamina VII group) project to lobules I-V of the anterior lobe and lobule VI, sublobule VIIb, and lobule VIII of the posterior lobe. They have strong projections to caudal lobules of the anterior lobe (lobules III-Va) and lobules facing the primary fissure (sublobules Vd-Vf and sublobules VIf and VId).

Animals↗
PubMed1988

Development of projections from auditory to visual areas in the cat.

In newborn kittens, cortical auditory areas (including AI and AII) send transitory projections to ipsi- and contralateral visual areas 17 and 18. These projections originate mainly from neurons in supragranular layers but also from a few in infragranular layers (Innocenti and Clarke: Dev. Brain Res. 14:143-148, '84; Clarke and Innocenti: J. Comp. Neurol. 251:1-22, '86). The postnatal development of these projections was studied with injections of anterograde tracers (wheat germ agglutinin-horseradish peroxidase [WGA-HRP]) in AI and AII and of retrograde tracers (WGA-HRP, fast blue, diamidino yellow, rhodamine-labeled latex beads) in areas 17 and 18. It was found that the projections are nearly completely eliminated in development, this, by the end of the first postnatal month. Until then, most of the transitory axons seem to remain confined to the white matter and the depth of layer VI; a few enter it further but do not appear to form terminal arbors. As for other transitory cortical projections the disappearance of the transitory axons seems not to involve death of their neurons of origin. In kittens older than 1 month and in normal adult cats, retrograde tracer injections restricted to, or including, areas 17 and 18 label only a few neurons in areas AI and AII. Unlike the situation in the kitten, nearly all of these are restricted to layers V and VI. A similar distribution of neurons projecting from auditory to visual areas is found in adult cats bilaterally enucleated at birth, which suggests that the postnatal elimination of the auditory-to-visual projection is independent of visual experience and more generally of information coming from the retina.

Aging↗
PubMed1988

Onset and development of intersegmental projections in the chick embryo spinal cord.

The ontogeny of intersegmental (propriospinal) projections was studied in the chick embryo spinal cord between embryonic day 2.5 and day 6. Our goals were 1) to determine the earliest projections of intersegmental interneurons between specific spinal regions and to establish the cell types involved; and 2) to follow the ontogeny of these projections during the early formative stages of spinal cord development. Studies were carried out in vitro by using an isolated spinal cord/brainstem preparation. Horseradish peroxidase injections were made either uni- or bilaterally at various levels of the spinal cord along the rostrocaudal axis of the embryo. HRP histochemistry was done on Vibratome sections with diaminobenzidine as the chromogen. Following unilateral injections at day 2.5, labelled commissural interneurons were found contralaterally and were confined to the injected segment. Subsequently, labelled cells were found progressively further away from the injected segment. By day 4.5 reciprocal projections extended between lumbar and brachial regions. Interneurons with intersegmental axonal projections were often undifferentiated, consisting of primitive unipolar or bipolar cells with little, if any, dendritic development. In some cases migrating interneurons could be retrogradely labelled from two or three segments away from the location of their translocating cell body. Anterograde Golgi-like labelling of early undifferentiated cells revealed growing axons, axonal terminals, and growth cones. Five or six reasonably distinct classes of intersegmental interneurons were identified based on their location, axonal projections, and morphology of dendritic arbors. These appeared to be segmentally and bilaterally arranged along the rostrocaudal axis of the spinal cord. The axons of some of these types of interneurons exhibited preferences in their longitudinal projections within the ventral and ventrolateral marginal zone at the very onset of pathway formation. From the present observations it can be concluded that intersegmental connectivity precedes the development of ascending and descending supraspinal, as well as primary afferent connections in the chick embryo spinal cord.

Animals↗
PubMed1989

Forebrain projections from cholecystokininlike-immunoreactive neurons in the rat midbrain.

The purpose of the present study was to analyze the distribution of cholecystokininlike-immunoreactive (CCK-I) neurons within the rat ventral mesencephalon which project to several forebrain areas. The peroxidase-antiperoxidase immunocytochemical technique was used to examine the anatomical localization of CCK-I within the ventral midbrain and in the following forebrain regions: caudate-putamen, nucleus accumbens, olfactory tubercle, bed nucleus of the stria terminalis, septum, amygdala, and prefrontal, anterior cingulate, and piriform cortices. CCK-I perikarya were distributed throughout the substantia nigra, ventral tegmental area, and several midline raphe nuclei to a greater extent than previously reported, particularly in the substantia nigra pars compacta. Terminallike immunoreactivity for CCK was observed in all of the above forebrain sites. In addition, infrequent CCK-I cell bodies were localized in the caudate-putamen, nucleus accumbens, olfactory tubercle, septum, and bed nucleus of the stria terminalis. To analyze forebrain projections of the ventral midbrain CCK-I neurons, indirect immunofluorescence was combined with fluorescence retrograde tracing. CCK-I neurons of the substantia nigra and/or ventral tegmental area were found to project, to varying extents, to all of the above CCK-I forebrain terminal fields. The nucleus accumbens, olfactory tubercle, and septal and prefrontal cortical projections arose primarily from CCK-I perikarya in the ventral tegmental area whereas the projections to the caudate-putamen and anterior cingulate cortex arose predominantly from immunoreactive neurons in the substantia nigra pars compacta. The amygdala received innervation mainly from CCK-I cell bodies located in the substantia nigra pars lateralis. CCK-I afferents to the bed nucleus of the stria terminalis and piriform cortex originated from perikarya distributed approximately equally across the ventral tegmental area and substantia nigra pars compacta. The general topography of CCK-I forebrain innervation observed in this study is similar to that previously reported for the ascending dopaminergic projections from ventral mesencephalic neurons. CCK-I neurons of the midline raphe nuclei were found to provide relatively minor afferents to the caudate-putamen, bed nucleus of the stria terminalis, septum, and prefrontal cortex and more substantial projections to the amygdala. The results of this study demonstrate that CCK-I neurons of the ventral midbrain supply a much broader innervation of forebrain regions than previously appreciated.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Spinocerebellar projections from the upper lumbar segments in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The projection fields of the dorsal spinocerebellar tract (DSCT) arising from Clarke's column, marginal neurons of Clarke's column, and lamina V neurons in the upper lumbar segments were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. To label only these neuron groups with uncrossed ascending axons, the spinal cord was lesioned rostral and contralateral to the WGA-HRP injections. Following injections of WGA-HRP into the L1-L4 segments, labeled terminals were seen in sublobules Ia-VIc and VIIb-VIIIb, the simple lobule, the paramedian lobule, and the dorsal paraflocculus. About 70-80% and 20-30% of the total number of labeled terminals were in the anterior and the posterior lobe, respectively; the projections were predominantly ipsilateral to the cells of origin (about 87% or more labeled terminals of the total number in each of sublobules IIb-Va). The labeled terminals were abundant in sublobule IIb (6-11%), lobule III (12-27%), and sublobules IVa (14-17%) and IVb (14-21%). In the mediolateral extent of the lobules in the anterior lobe, the labeled terminals were most numerous between 1.1 and 3.0 mm lateral to the midline (45-75% of the total number of labeled terminals on the ipsilateral side). In the posterior lobe labeled terminals were numerous in sublobule VIIIb (13.6%) and sublobule C of the paramedian lobule (15-19%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross sections through each lobule. In the anterior lobe the labeled terminals were distributed in eight major areas. In sublobules IIb-III, areas 1-3 were located within 1.0 mm of the midline in zone A of Voogd; areas 4-6, between 1.0 and 2.5 mm lateral to the midline in zones B-C1; and areas 7 and 8, lateral to 3.0 mm from the midline in zones C2 and C3. Areas 1-6 extended apicobasally in the middle part of the lobules. In sublobule VIIIb projections were confined to three longitudinal areas whereas in the paramedian lobule the projection areas were less distinct. The projection pattern of the lumbar DSCT was different from that of the thoracic DSCT reported previously. In the anterior lobe the thoracic DSCT projects to five areas in the medial (zone A) and the lateral part (zone B) of the vermis and to four areas in the intermediate region of the hemisphere (zones C1-C3).

Animals↗
PubMed1989

Collateral projections of predorsal bundle cells of the superior colliculus in the rat.

The deep layers of the superior colliculus contain cells which are premotor in the sense that they respond prior to the onset of shifts in gaze and send axons, by way of a pathway called the predorsal bundle, to the contralateral brainstem gaze centers and cervical spinal cord. Previous studies have suggested that these cells also contribute to other efferent pathways which arise in the deep layers. The present study examines the contributions of the cells of origin of the predorsal bundle to these additional pathways as a step toward understanding their roles in gaze mechanisms. In one series of experiments, retrograde tracers were used to compare the laminar distribution of predorsal bundle cells with the distributions of the cells of origin of three other pathways: those that project to the intralaminar region of the dorsal thalamus, those that project to the contralateral superior colliculus, and those that project to the ipsilateral brainstem tegmentum. Predorsal bundle cells were found primarily in stratum griseum intermedium sublayer b. This distribution overlaps extensively with the distribution of colliculus cells that project to the intralaminar region of the thalamus. In contrast, the majority of the colliculus cells that project to either the contralateral superior colliculus or the ipsilateral brainstem tegmentum do not overlap extensively with the predorsal bundle cells; instead, they are primarily located dorsal or ventral to sublayer b of stratum griseum intermedium. In a second series of experiments, two regions were injected with different retrograde fluorescent traces in single animals in order to study the collateral projections of the cells of origin of these pathways. The results indicate that many predorsal bundle cells project to the intralaminar region of the dorsal thalamus but that only a few contribute to the tectotectal pathway. The results also indicate that few tectotectal cells contribute to the ipsilateral tectobulbar pathway.

Animals↗
PubMed1989

Mamillary body in the rat: topography and synaptology of projections from the subicular complex, prefrontal cortex, and midbrain tegmentum.

The retrograde and anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) has been used to trace afferent connections of the rat mamillary body (MB) at the light and electron microscopic levels. Injections of WGA-HRP into different parts of the MB resulted in heavy retrograde labeling in the subicular complex, medial prefrontal cortex, and dorsal and ventral tegmental nuclei. Injections of WGA-HRP into each of these brain regions, respectively, resulted in anterograde labeling with specific distributions and characteristic synaptic organizations in the MB. Projections from the rostrodorsal and caudoventral subiculum terminated in a topographically organized laminar fashion in the medial mamillary nucleus bilaterally, whereas afferent projections from the presubiculum and parasubiculum terminated only in the lateral mamillary nucleus. Labeled axon terminals which originated from the subicular complex were characterized by round vesicles and formed asymmetric synaptic junctions with small-diameter dendrites and dendritic spines in the medial and lateral mamillary nuclei. Projections from the prefrontal cortex originated mainly in the infralimbic area and to a lesser degree in the prelimbic and anterior cingulate areas. Injections of tracer into these brain regions gave rise to dense labeling of axon terminals in the medial mamillary nucleus, pars medianus, and in the anterior dorsomedial portion of the pars medialis. The labeled terminals were characterized by round vesicles and formed asymmetric synaptic junctions with small-diameter dendrites and dendritic spines. Projections from the dorsal tegmental nucleus terminated in the ipsilateral lateral mamillary nucleus, whereas afferent projections from the anterior and posterior subnuclei of the ventral tegmental nucleus terminated topographically in the medial mamillary nucleus. The ventral tegmental nucleus, pars anterior projected to the midline region of the medial nucleus and the dorsolateral and ventromedial subdivisions of the pars posterior projected to medial and lateral parts of the medial nucleus, respectively. In contrast to the synaptic morphology of subicular complex and medial prefrontal cortex axon terminals in the MB, labeled axon terminals in the MB which originated from the midbrain tegmentum were characterized by pleomorphic vesicles and formed symmetric synaptic junctions with neuronal somata and proximal dendrites as well as distal dendrites and dendritic spines.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1989

Enkephalin-immunoreactive neuronal projections from the medulla oblongata to the intermediolateral cell column: relationship to substance P-immunoreactive neurons.

The present study investigated the ventral medullary distribution of enkephalin-immunoreactive neurons that project to the intermediolateral cell column and the relationship of these neurons to substance P-immunoreactive neurons. Neurons that projected to the intermediolateral cell column were identified by the presence of rhodamine-labeled microspheres within the neuronal cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Enkephalin- and substance P-immunoreactivities were identified by dual-color immunohisto-chemistry. Enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were present in the raphe magnus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus, and the parapyramidal region. These neurons were present throughout the rostrocaudal extent of each of these nuclei. However, in the raphe magnus the greatest number was present at more rostral levels of the nucleus. The morphology and distribution of enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were similar to those of enkephalin-immunoreactive neurons that were not observed to contain rhodamine-labeled microspheres. Substance P- and enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were present in similar distributions in each of the nuclei studied, except the raphe magnus. The raphe magnus contained more enkephalin- than substance P-immunoreactive neurons at rostral levels and more substance P-immunoreactive neurons than enkephalin-immunoreactive neurons at caudal levels. Coexistence of substance P- and enkephalin-immunoreactivities in ventral medullary neurons that projected to the intermediolateral cell column was rarely seen. These studies support the hypothesis that ventral medullary enkephalinergic neurons project to the intermediolateral cell column where they could act to modulate preganglionic sympathetic activity.

Animals↗