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PubMed1983

Brainstem projections to the facial nucleus of the opossum. A study using axonal transport techniques.

The horseradish peroxidase and autoradiographic techniques have been used to determine the origin and intranuclear termination of brainstem axons projecting to the facial nucleus of the opossum and to define networks which could be utilized in some oral-facial behaviors. Two regions of the midbrain have dense projections to the facial nucleus. One region is the ventral periaqueductal gray and adjacent interstitial nucleus of the medial longitudinal fasciculus which project bilaterally to those areas of the facial nucleus supplying auricular and cervical musculature. A second is the paralemniscal zone of the caudolateral midbrain which innervates the same areas of the contralateral facial nucleus. The red nucleus and/or the adjacent tegmentum send a less dense projection to those regions of the contralateral facial nucleus which innervate buccolabial and zygomatic muscles. The dorsolateral pons (the parabrachial complex, the nucleus locus coeruleus, pars alpha, and the nucleus sensorius n. trigemini, pars dorsalis) projects densely to those areas of the ipsilateral facial nucleus which innervate buccolabial and zygomatic musculature. In contrast, the nucleus reticularis pontis, pars ventralis, projects bilaterally to parts of the facial nucleus supplying auricular and cervical muscles. There was evidence of some rostral to caudal organization in the latter projection. Neurons in medial parts of the lateral reticular formation project bilaterally to the facial nucleus. Those within the nucleus reticularis parvocellularis and the rostral nucleus reticularis medullae oblongatae ventralis innervate areas supplying buccolabial and zygomatic muscles. Neurons in the nucleus reticularis medullae oblongatae ventralis located caudal to the obex favor regions of the facial nuclei which supply auricular and cervical muscles. Neurons in the nucleus reticularis medullae oblongatae dorsalis and lamina V of the medullary and spinal dorsal horns project ipsilaterally to the facial nucleus in a manner suggesting that information from specific cutaneous areas reaches neurons supplying the muscles deep to them. The brainstem-facial connections are discussed in relation to the functionally diverse roles served by the facial nucleus in oral-facial behavior.

Animals↗
PubMed1984

Mesencephalic projections to the facial nucleus in the cat. An autoradiographical tracing study.

In 33 cats the projections of different parts of the mesencephalon to the facial nucleus were studied with the aid of the autoradiographical tracing method. The results indicate the existence of many different mesencephalo-facial pathways. The dorsomedial facial subnucleus, containing motoneurons innervating ear muscles, receives afferents from 4 different mesencephalic areas: a, the most rostral mesencephalic reticular formation; b, the nucleus of Darkschewitsch and/or the ventral part of the rostral PAG; c, the interstitial nucleus of Cajal and/or the mesencephalic tegmentum dorsomedial to the red nucleus. These areas project bilaterally by way of an ipsilateral medial tegmental pathway. The medial part of the deep tectum. This area projects bilaterally by way of the tecto-spinal tract. The lateral mesencephalic tegmentum close to the parabigeminal nucleus. This area projects mainly contralaterally by way of a separate contralateral lateral tegmental fiber bundle. The mesencephalic tegmentum just dorsolateral to the red nucleus and perhaps from the dorsolateral red nucleus itself. This area projects contralaterally by way of the rubrospinal tract. The intermediate facial subnucleus containing motoneurons innervating the muscle around the eye, receives afferents from two different mesencephalic areas: The dorsal part of the rostral as well as caudal red nucleus (but not from its caudal pole) and from the dorsally adjoining mesencephalic tegmentum including the area of the nucleus of Darkschewitsch and the interstitial nucleus of Cajal. These areas project contralaterally by way of the contralateral rubrospinal tract. The nucleus of the optic tract and/or the olivary pretectal nucleus. This area projects contralaterally by way of a contralateral medial tegmental pathway. The lateral and ventrolateral facial subnuclei containing motoneurons innervating the muscles around the mouth receive afferents from two different mesencephalic areas: The lateral part of the deep tectal layers. This area projects contralaterally by way of the tecto-spinal tract. The nucleus raphe dorsalis and perhaps the nucleus centralis superior. This area projects by way of the lateral tegmentum of caudal pons and medulla.

Animals↗
PubMed1985

Connections and oculomotor projections of the superior vestibular nucleus and cell group 'y'.

Attempts were made to determine brainstem and cerebellar afferent and efferent projections of the superior vestibular nucleus (SVN) and cell group 'y' ('y') in the cat using axoplasmic tracers. Injections of HRP, WGA-HRP and [3H]amino acids were made into SVN and 'y' using two different infratentorial stereotaxic approaches. Controls were provided by unilateral HRP injections involving the oculomotor nuclear complex (OMC), the interstitial nucleus of Cajal (INC) and the deep cerebellar nuclei (DCN). Large injections of SVN almost invariably involved 'y' and dorsal parts of the lateral vestibular nucleus (LVN). Smaller injections involved central and ventral peripheral parts of SVN. Discrete injections of 'y' involved small dorsal parts of LVN. Afferents to SVN are derived mainly from the vestibular nuclei (VN) and parts of the vestibulocerebellum. SVN receives afferents: bilaterally from caudal portions of the medial (MVN) and inferior (IVN) vestibular nuclei and 'y'; contralaterally from ventral and lateral parts of SVN and rostral MVN; and ipsilaterally from the nodulus, uvula and medial parts of the flocculus. Purkinje cells (PC) in medial parts of the flocculus project to central regions of SVN, while PC in the nodulus and uvula appear to project mainly to dorsal peripheral regions of SVN. SVN receives sparse projections from the ipsilateral INC, the contralateral central cervical nucleus (CCN) and virtually no projections from the reticular formation. SVN projects via the medial longitudinal fasciculus (MLF) to the ipsilateral trochlear nucleus (TN), the inferior rectus subdivision of the OMC, the INC, the nucleus of Darkschewitsch (ND) and the rostral interstitial nucleus of the MLF (RiMLF). Contralateral projections of SVN cross in the ventral tegmentum caudal to most of the decussating fibers of the superior cerebellar peduncle and terminate in the dorsal rim of the TN and the superior rectus and inferior oblique subdivisions of the OMC; sparse crossed projections enter the INC and the ND. Cerebellar projections of SVN end as mossy fibers in the ipsilateral nodulus, uvula and in medial parts of the flocculus bilaterally. Retrograde transport from unilateral injections of the OMC indicate that afferents from SVN arise ipsilaterally from central and dorsal regions and contralaterally from dorsal peripheral regions. Ventral cell group 'y' receives small numbers of afferent fibers from caudal central parts of the ipsilateral flocculus. No fibers from ventral 'y' could be traced to other vestibular nuclei, the OMC or the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1986

Origin of ascending auditory projections to the nucleus mesencephalicus lateralis pars dorsalis in the chicken.

Ascending auditory projections to the nucleus mesencephalicus lateralis pars dorsalis (MLd) were studied in white Leghorn chickens by means of unilateral injections of horseradish peroxidase into the MLd and by injections of tritiated leucine into nucleus angularis or the combined nucleus magnocellularis and nucleus laminaris. The experiments showed that nucleus angularis sends an extensive projection to the contralateral MLd and a smaller projection to the rostral pole of the ipsilateral MLd; the lagenar region contributes to these bilateral connections. Nucleus angularis also projects bilaterally to the superior olive and nucleus ventralis lemnisci lateralis and to the contralateral nucleus lemnisci lateralis pars ventralis and dorsal nucleus of the lateral lemniscus. Projections from nucleus laminaris were demonstrated to the ipsilateral superior olive, to the contralateral lemniscal nuclei and a small medial region in MLd bilaterally; the contralateral projection is much denser than the ipsilateral one. Other nuclei having ascending connections with MLd include the contralateral superior olive, the ipsilateral nucleus lemnisci lateralis pars ventralis, the contralateral nucleus ventralis lemnisci lateralis and the contralateral MLd. The ipsilateral superior olive and nucleus ventralis lemnisci lateralis also project to MLd but much more sparsely than in their contralateral projection. Although several of these findings correspond with auditory connections previously shown in the pigeon brainstem, they differ fundamentally in that we find both nucleus angularis and nucleus laminaris projecting to different areas of the MLd on both sides of the brain. In particular, our observation that the cochlear nucleus has bilateral connections with MLd demonstrates an important avian similarity with the brainstem auditory pathways of other terrestrial vertebrates.

Animals↗
PubMed1987

Topographical distribution of Purkinje cells in the uvula and the nodulus projecting to the vestibular nuclei in cats.

The localization of the Purkinje cells in the uvula and nodulus projecting to the vestibular nuclei and the prepositus hypoglossal nucleus (PH) was studied by means of retrograde axonal transport of horseradish peroxidase in cats. Findings indicate a zonal organization in the uvula and nodulus projecting to the vestibular nuclei as follows; the Purkinje cells located in the medial half of the uvula except for the area along the posterolateral fissure project to the middle part of the inferior vestibular nucleus (IV) (middle IV zone); those in the lateral half of the uvula other than the laterocaudal part project to the caudal part of the IV (caudal IV zone); those in the mediorostral part of the nodulus and the middle part of the nodulus project to the middle part of the medial vestibular nucleus (MV) (middle MV zone); those in the lateral part of the nodulus project to the caudal part of the MV (caudal MV zone); those in the medial part of the uvula and nodulus along the posterolateral fissure project to the dorsal peripheral part of the superior vestibular nucleus (SV) (SV zone). There is no specific projection zone in the uvula and nodulus projecting to the lateral vestibular nucleus, the ventral peripheral and the central part of the SV, the rostral part of the MV, the rostral part and the caudal pole of the IV, the caudal one-third of the group f, the group x and the PH.

Animals↗
PubMed1988

Visual thalamocortical projections in normal and enucleated rats: HRP and fluorescent dye studies.

Visual thalamocortical projections of neonatally enucleated and control rats were studied after tracer injections into the striate and peristriate areas of adult pigmented rats. The distribution of retrogradely labeled neurons in the visual thalamic nuclei was mapped after (a) small localized injections of horseradish peroxidase into either area 17, 18, or 18a and (b) simultaneous injections of three different retrograde tracers (fast blue, HRP, and diamidino yellow) into the anterior, medial, and posterior regions of area 17. It was shown in both normal and neonatally enucleated rats, that the dorsal lateral geniculate nucleus projects to the striate cortex (area 17), whereas the laterodorsal thalamic nucleus of the lateral thalamus projects to the medial peristriate area 18, and the lateral posterior thalamic nucleus has a projection to the lateral peristriate area 18a. Additionally, both extrageniculate visual thalamic nuclei project to area 17. Neurons in the dorsoanterior region of the dorsal lateral geniculate nucleus project to the posterior part of area 17, while neurons in the ventroposterior region of the nucleus send their axons to the anterior part of area 17. A similarly inverted projection of anterior and posterior divisions of the lateral posterior thalamic nucleus to visual area 18a was detected. In enucleated rats, the general topography of the projections from the thalamic neurons to the striate and peristriate cortices was indistinguishable from that in the controls. Nonetheless, there was noticeable shrinkage of the dorsal lateral geniculate nucleus and lateral thalamus and a significant decrease in the size of the somata of projecting neurons. Mean somal area of the HRP-labeled neurons in the dorsal lateral geniculate nucleus of enucleated rats was reduced by 19.0% and the mean maximum cell diameter by 14.3% compared with controls.

Amidines↗
PubMed1983

The development and restriction of the ipsilateral retinofugal projection in the chick.

Although it is generally believed that the central projections of the retina in birds are entirely crossed, using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) as an anterograde tracer, we have found that in normal posthatched chicks there is a small ipsilateral retinofugal projection to the diencephalon and midbrain. Most of the ipsilateral fibers appear to be directed to the lateral anterior and dorsolateral anterior nuclei of the thalamus, to the pretectal region, and to the ectomammillary nucleus and the adjoining nucleus externus. Even in the best preparations the numbers of ipsilateral fibers are so small that it is hardly surprising that they have been overlooked in previous axonal degeneration and autoradiographic experiments. A significantly larger ipsilateral retinal projection develops during the second week of incubation. The ipsilaterally directed fibers can be first seen on the fifth day of incubation and their numbers appear to increase until about embryonic day 12. At this stage the projection involves substantially more fibers than at hatching and is also more extensive in its distribution; in fact, in its general organization (but not its size) it closely parallels the normal crossed retinofugal system, contributing fibers to essentially all the primary visual relay nuclei in the diencephalon and midbrain and to much of the optic tectum, where the densest projection is to its caudomedial aspect. During the second week of incubation there is also a small number of retinal fibers, which after crossing in the optic chiasm, recross the midline in the posterior and tectal commissures (and also in the tectal roof plate), before ending in the pretectal region of the ipsilateral side. In addition, there is a markedly aberrant projection from the retina into the contralateral optic nerve. Most of the ipsilateral retinal fibers are eliminated between the twelfth and sixteenth days of incubation, and by day 17 the ipsilateral projection is reduced to its mature form. The progressive reduction in the ipsilateral projection occurs at a time when it is known (from other studies) that there is an appreciable loss of retinal ganglion cells; but whether the reduction is due to neuronal death or to the selective elimination of ipsilateral axon collaterals remains to be determined. The existence of a significant ipsilateral retinofugal component early in development, probably accounts, in part, for the distinctive and persistent ipsilateral projection that occurs if one eye is removed during the first few days of incubation.

Animals↗
PubMed1985

The organization of cerebellar afferent projections to the paramedian lobule in neonatal cats.

This study sought to determine whether cerebellar afferent pathways, that are topographically organized in adult cats, are similarly ordered during the postnatal development and maturation of the cortex, or whether the projections are first distributed randomly in the cortex before becoming organized. Injections of wheat germ agglutinin-horseradish peroxidase were made into dorsal (dPML) or ventral (vPML) divisions of the paramedian lobule (PML) in neonatal (0- to 21-days-old) and adult cats and the ensuing distributions of retrogradely labeled neurons in the lateral reticular nuclei, the inferior olive and the pontine nuclei were compared. Magnocellular and parvicellular neurons in the dorsomedial and dorsolateral parts of the ipsilateral lateral reticular nuclei project respectively to dPML and vPML in all neonatal and adult cats. Olivocerebellar projections were entirely crossed, in most cases, with neurons projecting to the dPML more rostral and medial in the dorsal and medial accessory nuclei and in the principal olive than neurons which project to the vPML. A parasagittal zonal organization of olivocerebellar projections was present in newborn cats. Neurons were labeled in the ipsilateral inferior olive following dPML injections in 1- to 4-day-old kittens, but not in older kittens or in adult cats. Pontocerebellar projections were bilateral with a contralateral predominance. In adult and neonatal cats, labeled neurons were clustered together and formed rostral-caudal oriented columns dorsomedial and ventromedial to the pyramidal tract after injections in the contralateral dPML and vPML and bilaterally in the dorsolateral pons after dPML injections. These results show that lateral reticulo-, olivo- and pontocerebellar projections to the PML which are topographically organized in adult cats are organized similarly in newborn cats. Studies in prenatal cats are required in order to determine whether these cerebellar afferents are ever randomly distributed in the cerebellar anlage or whether these projections are ordered as they grow into the cerebellum.

Afferent Pathways↗
PubMed1986

The effects of neonatal monocular enucleation on the organization of ipsilateral and contralateral retinothalamic projections in the rabbit.

Autoradiographic methods were used to compare the ipsilateral and contralateral retinothalamic projections in pigmented Dutch-Belted rabbits that had neonatal monocular enucleation with the projections found in normally reared rabbits. In the normal adult rabbit, there is dense label throughout the dorsal lateral geniculate nucleus (LGd) except for a decreased label density in the region corresponding to the ipsilateral input. Following neonatal monocular enucleation, the contralateral projection fills in the part of the LGd corresponding to the ipsilateral input. Our data indicate that following monocular enucleation, two processes occur: an arrest of the segregation process and an expansion of the contralateral projection into the space normally containing the terminals of the ipsilateral projection. In addition, this filling in of the terminal space occurs relatively rapidly and is completed by day 14. No changes, however, were observed in the ipsilateral projection to the LGd. Unlike the LGd, the ventral lateral geniculate nucleus and the intergeniculate leaflet showed increases in the size of the ipsilateral projection region, and no changes in the contralateral projection. The present findings suggest that there may be different mechanisms governing whether alterations in the distribution of retinothalamic projections will occur in either the ipsilateral or contralateral nucleus.

Animals↗
PubMed1989

Absence of impulse activity in cortical neurons with transient projections to the cerebellum.

During the second postnatal week of development in cats, neurons in layer V of the primary sensorimotor cortex project transiently, by way of collaterals of pyramidal tract axons, to the cerebellum. All cerebrocerebellar collaterals are subsequently eliminated, while the collaterals in the pyramidal tract persist into the adult. To determine if the transience of the projection to the cerebellum could be due to the lack of functional activity in cerebrocerebellar projection neurons, single-unit extracellular recordings were made from neurons in the primary somatosensory cortex (S-I) in 8-14-day-old kittens. Projection neurons were identified by their antidromic activation from pyramidal tract or cerebellum. Collision experiments confirmed that some neurons had collateral projections to both structures. Recordings from both generally anesthetized as well as locally anesthetized, but awake preparations, indicated that pyramidal tract and cerebrocerebellar projection neurons never fired action potentials spontaneously or were orthodromically activated following stimulation of the medial lemniscus. Stimulation of the medial lemniscus did synaptically activate neurons in the cortex, but these were always located superficial to the antidromically activated projection neurons. These findings indicate that pyramidal tract and/or cerebrocerebellar S-I projection neurons are physiologically silent during the period of development that cortical axons are transiently present in the cerebellum, suggesting that cerebrocerebellar projections may be eliminated because of the lack of impulse activity.

Animals↗
PubMed1988

Topographic organization and collateralization of the projections of the anterior and laterodorsal thalamic nuclei to cingulate areas 24 and 29 in the rat.

Fast blue and Rhodamine microspheres were used to analyze the topography and collateralization of the limbic nuclei of the thalamus to 4 defined areas of the cingulate gyrus (anterior 24, posterior 24, anterior 29, and posterior 29). The anterodorsal nucleus and the anteroventral nucleus project to posterior area 24 and all of area 29. The anteromedial nucleus projects generally to both areas 24 and 29, but principally to anterior area 24. The laterodorsal nucleus projects only to area 29. The anterior and posterior portions of the thalamic nuclei topographically project to the anterior and posterior regions of the cingulate gyrus, respectively. Neurons in the medial region of the anterior nuclei project to the anterior area of the cingulate gyrus while neurons located in the lateral region project to posterior areas. Collaterals (9-13%) from the anteromedial nucleus project diffusely to areas 24 and 29, while collaterals from other nuclei project primarily to areas adjacent to each other. Modulation of limbic system functions probably occurs via these projection fibers. Furthermore, the idea appears to be reinforced that at least a dual and coupled function exists for these direct thalamocingulate connections.

Amidines↗
PubMed1992

An autoradiographic study of cortical projections from motor thalamic nuclei in the macaque monkey.

The special areal and laminar distributions of cortical afferent connections from various thalamic nuclei in the monkey (Macaca fuscata) were studied by using the anterograde axonal transport technique of autoradiography. The following findings were obtained. The superficial thalamocortical (T-C) projections, terminating in the (superficial half of) cortical layer I, arise mainly from the nucleus ventralis anterior, pars principalis (VApc) and nucleus ventralis lateralis, pars oralis (VLo), and possibly from the nucleus ventralis lateralis, pars medialis (VLm) and nucleus ventralis anterior, pars magnocellularis (VAmc). The VApc gives rise to the superficial T-C and deep T-C projections onto the postarcuate premotor area around the arcuate genu and spur, and onto the dorsomedial part of the caudal premotor area as well as the supplementary motor area (SMA). The VApc also gives rise to only deep T-C projections onto the remaining premotor area and onto the rostral bank of the arcuate sulcus as well as the ventral bank of the cingulate sulcus at the level of the premotor area. The VLo gives rise to the superficial T-C projections onto the ventrolateral part of the motor area (mainly to the forelimb motor area) and onto the dorsomedial part to the mesial cortex at the rostral level of the motor area. The VAmc gives rise to the superficial T-C projections onto the banks of the arcuate genu and adjacent region of area 8. Area X, the nucleus ventralis posterolateralis, pars oralis (VPLo), nucleus ventralis posterolateralis, pars caudalis (VPLc), nucleus ventralis posteromedialis (VPM) and possibly the nucleus ventralis lateralis, pars caudalis (VLc) send only deep T-C projections. The dorsal and medial parts of the VLc project onto the premotor area, the rostral part of the motor area and the SMA, and also the ventral bank of the cingulate sulcus. Area X projects onto the premotor area, the SMA, and the caudal part of area 8. The thalamic relay nuclei projecting onto the frontal association cortex were found to be the VAmc, medial VLc and area X.

Afferent Pathways↗
PubMed1984

Axonal projections and peptide content of steroid hormone concentrating neurons.

The axonal projections of cell groups containing the most dense collections of steroid hormone concentrating cells have been demonstrated with retrograde neuroanatomical tracing methods. Horseradish peroxidase revealed large numbers of neurons in ventrolateral ventromedial nucleus (VL-VM) which project to dorsal midbrain. Wheat germ agglutinin (immunocytochemical recognition method) revealed large numbers of neurons in medial basal hypothalamus (MBH) and particular subdivisions of paraventricular nucleus (PVN) that project to dorsal caudal medulla or spinal cord. Fluorescent dyes revealed that many preoptic area (POA), anterior hypothalamic (AHA), and bed nucleus of the stria terminalis (BNST) neurons project to ventral tegmental area of Tsai (VTA). Also many neurons in POA and BNST project to amygdala. A method which enabled simultaneous demonstration of the steroid binding capacity and axonal projections of neurons in the same tissue section revealed that 26-36% estradiol (E2) concentrating cells in VL-VM project to dorsal midbrain. E2 concentrating neurons in POA and BNST project to amygdala and E2 concentrating POA neurons project to VTA. These neurons, which send their axons to cell groups located in different brain regions, are probably under the genomic-regulatory influence of E2. Using a method which allows simultaneous demonstration of peptide content and steroid hormone concentrating capacity of cells, many oxytocin-neurophysin and vasopressin-neurophysin containing magnocellular neurons in the caudal PVN were found to concentrate E2. About 4% of the beta-endorphin and about 6% of the dynorphin containing neurons in the MBH concentrate E2. In contrast, virtually none (less than 0.2%) of the LHRH containing hypothalamic neurons concentrate E2.

Amygdala↗
PubMed1983

Auditory cortical field projections to the basal ganglia of the cat.

Projections to the basal ganglia from four auditory cortical fields in the cat were studied by combining microelectrode-mapping of the neurons' best frequencies with autoradiographic and histochemical tract-tracing techniques. Each auditory field is a source of projections to the homolateral basal ganglia. The distribution of labeling within the basal ganglia is related to the cortical field in which the injection site is located. The dorsal portion of the putamen and adjacent caudate nucleus are connected with cortical fields situated anteriorly and dorsally, while the ventral portion of the putamen and adjacent lateral amygdaloid nucleus are related to auditory fields situated posteriorly and ventrally. Injections of two different tracers into different best-frequency loci of one cortical field provided evidence that low best-frequency neurons project medially within the basal ganglia while high best-frequency neurons project more laterally. We concluded that there was a basic similarity among patterns of terminations in the basal ganglia from axons that originate in different auditory cortical fields. When the source of a projection was confined to a restricted portion of an auditory cortical field, labeling appeared as dense patches of silver grains separated from each other by areas of less dense labeling. Often, these patches were distributed within a sheet of tissue, elongated both dorsoventrally and anteroposteriorly. Loci having the same best-frequency representation, but situated in different auditory cortical fields, project upon overlapping but not coextensive portions of a single sheet of tissue. Thus the projections from geographically distant cortical loci possessing similar best-frequency representations are notably distinguished on a topographic basis. By comparison, two adjacent sheets of tissue were labeled when two injections were made into the low best-frequency and high best-frequency representations of the same auditory field. Double-injection, double-tracer experiments revealed that adjacent sheets of tissue received projections from different best-frequency loci. These observations suggested a degree of tonotopic organization to this projection system which was equipoise to the evidence obtained for a topographic organization.

Animals↗
PubMed1985

Topographic organization of the cerebellothalamic projections in the rat. An autoradiographic study.

The topographical organization of the subnuclear projections towards the thalamus was studied with autographic methods in adult Wistar rats. The four cerebellar deep nuclei give rise to projections to the ventral region of the rostral thalamus. Most of the fibers end contralaterally, according to a topographical pattern; however, some fibers from each of the cerebellar nuclei recross the midline at the thalamic level and terminate ipsilaterally, within regions symmetric to those receiving the densest contralateral projection. These ipsilateral cerebellothalamic components arise in decreasing order from the caudal nucleus lateralis, the ventrocaudal nucleus medialis and the nucleus interpositus, respectively. The projections of the nucleus lateralis directed to the contralateral thalamus are topographically organized. (1) Within the nucleus ventralis lateralis, the rostral and caudal parts of the cerebellar nucleus lateralis project respectively to rostral and caudal regions; lateral and medial zones of the nucleus lateralis project, respectively, to medial and central aspects of the nucleus ventralis lateralis. (2) The nucleus ventralis medialis and particularly its caudal portion appears to receive the bulk of its afferents from the ventromedial portion of the nucleus lateralis including the "subnucleus lateralis parvocellularis". (3) The nucleus centralis lateralis receives fibers from most parts of the nucleus lateralis including the "dorsolateral hump". (4) The nucleus interpositus anterior projects to the dorsomedial aspect of the rostral nucleus ventralis lateralis. In the latter nucleus, the ventrolateral aspect of the central region receives projections in cases in which the nucleus interpositus posterior is largely involved. A particular emphasis is put on the different projections from the various subnuclear regions of the lateral nucleus. A comparison is attempted with the situation in the primates, particularly with regard to the question of the parvocellular subdivision of the lateral nucleus.

Animals↗
PubMed1988

Afferent projections to the dorsal thalamus of the rat as shown by retrograde lectin transport--I. The mediodorsal nucleus.

The topography of afferent projections to the mediodorsal thalamic nucleus of the rat has been studied using the retrograde transport of unconjugated wheat germ agglutinin as identified by immunocytochemistry. Inputs were defined according to the lateral, central or medial segments of the nucleus injected, and controlled by additional injections into the habenula, central medial and paraventricular nuclei of the thalamus. Cortical afferents to the lateral segment arose from anterior cingulate and prelimbic areas on the medial surface of the hemisphere, those to the central segment arose mainly from ventral orbital area, whilst those to the medial segment arose from the infra-limbic and agranular insular areas. This strict cortical topography was matched by the organization of afferents from the reticular thalamic nucleus; i.e. lateral, intermediate and medial reticular neurons from the rostral nucleus projected to lateral, central and medial segments of the mediodorsal thalamus respectively. In the basal forebrain ventral pallidum projected only to the medial segment, whilst magnocellular preoptic region projected only to the central segment. Lateral preoptic area projected to lateral and central segments and the diagonal band mainly to central segment. Projections from substantia innominata were found regardless of the area of mediodorsal nucleus injected. The paraventricular nucleus of thalamus, lateral habenula and substantia nigra reticulata projected to the lateral segment only, whilst central gray projected only to the medial segment. Projections from amygdala (mainly basolateral and central nucleus) were found only following central and medial segment injections. All regions of the mediodorsal nucleus injected received input from the lateral hypothalamus, the ventral tegmental area and the dorsal tegmental gray. The results are discussed and particular emphasis is placed on the possible functions of the thalamocortical connections and the role of the reticular thalamic nucleus as a potential regulator of thalamocortical activity.

Animals↗
PubMed1988

Distribution of inferior olivary projections to the vestibular nuclei of albino rabbits.

This study analyses the course and topography of olivo-vestibular projections originating in the dorsal cap, ventrolateral outgrowth and beta nucleus of albino rabbits. Rabbits were given either single pressure-injections of [3H]L-leucine (20 microCi in 50 nl) or single or multiple injections of 3-acetylpyridine (0.2-0.25 microliter of 27.5 micrograms/microliter in saline) into the medial aspect of the inferior olive. Brains from the former animals were processed for autoradiography after 2-3 days survival; brains from the latter animals were stained for degeneration with cupric-silver methods after a 16-24 h survival. In addition, four rabbits with kainic acid lesions of the flocculus were used to document flocculo-vestibular projections. Olivo-vestibular projections from the dorsal cap ventrolateral outgrowth, beta nucleus and the medial accessory olive diverge from olivo-cerebellar projections at the caudal margin of the flocculus stalk, and course medially in a broad sheet. Fibers (1) ascend in the superior fascicle, with flocculo-vestibular projections, to the superior vestibular nucleus, (2) enter the medial fascicle, with flocculo-vestibular fibers, and course along the dorsolateral border of the 4th ventricle to innervate a distinct rostral subdivision of the medial vestibular nucleus, and (3) enter the lateral fascicle, with flocculo-vestibular fibers, to terminate in pars alpha and beta of the lateral vestibular nucleus and the caudal subdivision of the medial vestibular nucleus. Comparison of different injection cases indicate that the caudal half to two-thirds of the dorsal cap contributes projections to the rostral medial vestibular nucleus, centrolateral and dorsomedial aspects of the superior vestibular nucleus, and a projection to both central and dorsal aspects of the caudal medial vestibular nucleus. By contrast, the rostral third to half of the dorsal cap-ventrolateral outgrowth projects sparsely to the rostral medial vestibular nucleus, contributing dense projections to the central aspect of the superior vestibular nucleus and dorsomedial and lateral regions in the caudal medial vestibular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Embryonic entorhinal transplants project selectively to the deafferented entorhinal zone of adult mouse hippocampi, as demonstrated by the use of Thy-1 allelic immunohistochemistry. Effect of timing of transplantation in relation to deafferentation.

The mouse Thy-1.1/Thy-1.2 allelic marking system is used to show that transplanted embryonic entorhinal cortex can reinnervate adult host hippocampi. The projection is limited to the appropriate terminal zones--viz. the outer two-thirds of the stratum moleculare of the dentate gyrus, and the stratum lacunosum-moleculare of the hippocampus--and extends for up to about 2 mm into the denervated host terminal field. The reconstruction of the entorhinal projections to the host requires direct contact between the embryonic donor tissue and the denervated adult host terminal field, and is dependent upon removal of the ipsilateral host entorhinal area. In the absence of an overall deafferenting host entorhinal lesion the transplanted entorhinal area forms only small local projections which are confined to areas which would have been locally deafferented as a result of direct damage to the host entorhinal afferents (i.e. during their intrahippocampal course) by the hippocampal lesion caused at the time when the transplant was inserted. The correct relative timing of deafferentation and transplantation is vital for the formation of the transplant-to-host projection. The host dendrites can be made receptive to entorhinal transplant projections by removal of the host entorhinal area at the time of transplantation. When deafferentation is performed first and transplantation is delayed, it is found that the deafferented host dendrites retain this receptivity even when deafferentation has been performed as much as two months before transplantation. Reversing the order of transplantation and deafferentation, however, shows that the transplants have only a transient ability to project to the deafferented host territory. Thus, transplants inserted and allowed to become established for one week before host deafferentation make very much reduced projections to the host, and from two weeks onwards are incapable of any detectable response to subsequent removal of the host entorhinal area. Coextensive with the formation of transplant-to-host entorhinodentate projections, the host entorhinal lesion also induces an intensification of the acetylcholinesterase staining of the host septodentate afferents in the denervated outer dentate stratum moleculare. The findings demonstrate the accurate reconstruction of a lost projection in adult brain by transplanting the appropriate type of embryonic tissue, but the results of altering the relative timing of deafferentation and transplantation raise currently unsolved questions about the nature of the competitive interactions between transplant and host axons.(ABSTRACT TRUNCATED AT 400 WORDS)

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