Ipsilateral Nucleus Research Articles

Cytochemical investigation of binaurally converging connections in nuclei of the cat superior olive

Binaurally converging connections at the level of the superior olivary nuclei were investigated in anesthetized cats by the method of quantitative cytospectrophotometry. As a result of monaural stimulation for 2 h with burst of rhythmic noise a marked increase was observed in the content of cytoplasmic RNA in neurons of the ipsilateral and contralateral medial and lateral nuclei. The volume of functioning neurons of these nuclei either showed no significant change or was increased. Some idea of the character of the functional organization of binaurally convergent connections can be deduced from these results.

Projections from the lateral reticular nucleus to the cerebellar cortex and nuclei in the cat.

The fiber projection from the lateral reticular nucleus (LRN) to the cerebellum was examined in the cat. Electrolytic lesions were placed in a confined area of the LRN using a parapharyngeal approach, and the ensuing degeneration was studied in sections stained by the Nauta and the Fink-Heimer methods. Fibers from the LRN ascend the ipsilateral restiform body, terminating bilaterally but chiefly in the ipsilateral cerebellum. In the ipsilateral cortex projections were found to lobules I to V, with denser terminations in sublobules IVb to Ve. The projections are stronger in the intermediate-lateral zones than in the vermis proper. There is also a dense projection to sublobules VId and VIf and to the medialmost part of the simple lobule (HVI). Scanty termination was seen in the medialmost part of crus I. There is a moderate projection to the caudalmost folium of sublobule VIIb and to the rostral folia of sublobule VIIIa and the paramedian lobule. The contralateral projection by fibers crossed within the cerebellum is far less dense but clearcut in the anterior lobe, the rostral folia of lobule VI and the medial part of the simple lobule. In the ipsilateral nuclei strong projections were found to rostral portions of the medial nucleus (M) and the caudal two thirds of the anterior interpositus nucleus (IA) with predominance in the lateral part of the latter. A focal projection was found to rostrodorsal portions of the posterior interpositus nucleus (IP). No projection was found to the lateral nucleus (L). Contralaterally there is a weak projection to the rostral part of M and the medial parts of IA and IP.

Telencephalic projections in two teleost species.

The efferent pathways of the telencephalon were investigated in the percomorph Eugerres and the berycomorph Holocentrus. One telencephalic hemisphere was resected by suction and the animals were perfused 7-35 days thereafter. The brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink-Heimer ('67) technique for selective silver impregnation of degenerating axons and terminals. Some fibers emerging from the lesioned telencephalic hemisphere terminate upon the contralateral hemisphere. The large bulk of efferent fibers, however, descends into the ipsilateral diencephalon and gives off the so-called strio-tectal bundle (STB) as well as the medial forebrain bundle (MFB). The remaining contingent eventually splits into the so-called strio-lobar bundle (SLB) and the lateral forebrain (LFB), but, previous to splitting, it contributes most of the telencephalic projection to the optic tectum in Eugerres, and gives abundant terminals to the ipsilateral nucleus rotundus or prethalamicus in both Eugerres and Holocentrus. The STB conveys all telencephalo-tectal fibers in Holocentrus, and some of them in Eugerres. Telencephalic efferents teminate ipsilaterally in the middle level of the tectum's stratum griseum centrale; in Holocentrus there is also a small projection to the stratum opticum. The MFB terminates at the caudal hypothalamus and gives terminals all along its course. The LFB also gives terminals all along its course and terminates upon a nucleus located between the midline and the corpus glomerulosum. The SLB spreads out and terminates in the inferior lobe of the hypothalamus.

Effects of deafferentation on the development of the isthmo-optic nucleus in the duck ( Anas platyrhynchos)

The developmental pattern of the isthmo-optic nucleus following deafferentation was studied from Day 12 of incubation to a few days before hatching in duck embryos. Unilateral optic tectum lesions in ovo were performed on Day 5 of incubation age. No detectable changes could be observed in the ipsilateral nucleus following deafferentation until Day 17. It is concluded that cellular proliferation and migration proceeds independent of any kind of afferent influences. Marked reduction in cell number, cell size, and processes were observed in the affected nucleus from Days 18 through 25. The results indicate that intact afferent input is essential for normal neuronal differentiation and their subsequent maintenance. The possibility of afferent fibers bringing in some chemical substance(s) and its role in cytodifferentiation and normally occurring cell loss is also discussed.

Studies of suspected neurotransmitters in the vestibuloocular pathways

Isolated fresh cat trochlear and oculomotor nuclei, which contain the axon terminals of inhibitory neurons whose cell bodies are in the superior vestibular nucleus (SVN), actively synthesize and store [3H]GABA, [14C]acetylcholine, [3H]dopamine and [3H]tyramine from labeled precursors of these compounds. Twelve to 14 days following lesions of the ipsilateral superior vestibular nucleus or its efferent pathway to the oculomotor and trochlear nuclei, at a time when there is extensive degeneration of superior vestibular nucleus axon terminals in these nuclei, the synthesis and storage of GABA in the ipsilateral trochlear nucleus is markedly reduced compared to that in the contralateral trochlear nucleus; the synthesis of acetylcholine, dopamine and tyramine is not measurably affected. The oculomotor nuclei, which unlike the trochlear nuclei receive a heavy bilateral projection from the SVN, show no asymmetric decrease after SVN lesions in their ability to synthesize any of the compounds tested. The data support the identity of GABA as an inhibitory transmitter in the superior vestibular nucleus-trochlear nucleus pathway.

Electron microscopic observations on the retino-preoptic pathway of Rana temporaria L.

Electron microscopic observations confirm the presence of optic terminals of retinal origin in the preoptic area of Rana temporaria. After unilateral section of the optic nerve, degenerating axon terminals were observed among the neurosecretory cells of the preoptic nucleus, both ipsilaterally and contralaterally. The retino-preoptic terminals apparently establish axo-dendritic synapses with non-neurosecretory neurons. Many more degenerating fibres were seen in the ipsilateral preoptic nucleus than in the contralateral nucleus. These are presumed to pass through and to cross in the dorsal posterior part of the optic chiasm.

Efferent projections of the superior olivary nucleus in the frog, Rana catesbeiana.

Following electrolytic lesions of the superior olivary nucleus (SO) of the bullfrog, Rana catesbeiana, the efferent pathways of this nucleus were studied with silver impregnation methods. The major projection was to the ipsilateral principal nucleus of the torus semicircularis. Less conspicuous degeneration was traced to the nuclei magnocellularis and commissuralis of the torus. No contribution was made to the tectum or nucleus isthmi. Other projections of the SO include a sma-ler contralateral projection to these same nuclei and to the ipsilateral nucleus lateralis profundus mesencephali. A system of connections between the acoustic nuclei was invariably interrupted with these lesions and the degeneration seen in the more dorsal acoustic areas was not entirely due to the destruction of SO neurons.

Striate cortex projections to the lateral geniculate and other thalamic nuclei: a study using degeneration and autoradiographic tracing methods in the marmoset Callithrix.

Abstract The thalamic projections of the striate cortex were investigated in the New World primate Callithrix jacchus with the experimental-anatomical method of anterograde fiber degeneration after cortical destruction and with autoradiography of tritiated proteins transported by axoplasmic flow after injection of [ 3 H]proline into area 17. The findings of both methods were in accord with respect to the target loci: fibers of striate cortex origin were found to terminate in the ipsilateral nucleus geniculatus lateralis (LGN), nucleus praegeniculatus, nucleus reticularis thalami, nucleus pulvinaris lateralis, nucleus pulvinaris inferior, and nucleus posterior thalami. The projection upon the LGN appeared to be the most pronounced of the corticofugal projections of area 17. A characteristics finding in the autoradiographs of the LGN was a distinct labeling of the neuronal perikarya and of the walls of blood vessels within the focus of radioactivity. Since similar features were observed in the LGN after intraocular injection of [ 3 H]proline, this neuronal labeling very probably was not due to retrograde transport but no a transneuronal transfer of labeled material.

Afferents to the hippocampus of the rat studied with the method of retrograde transport of horseradish peroxidase

Horseradish peroxidase (HRP) injected into rat hippocampus was transported to the perikarya of neurons which project to the hippocampus. HRP-labeled cells were present in both medial and lateral entorhinal cortex; cells of the medial entorhinal cortex appeared to be topographically organized. The mediaal septal nucleus contained stained cells; its mediaal aspect was labeled after dorsal hippocampal injections, while ventral hippocampal injections resulted in the labeling of more laterally located cells. Stained cells were also observed in the ipsilateral nucleus locus coeruleus, dorsal and median raphe nuclei and areas CA3–4 of the contralateral hippocampus. In additions, cells in the supramammillary region, an area not previously recognized to project to the hippocampus, were labeled. Finally, the mossy fiber terminal zone and the CA3–4 terminal zone in the dentate molecular layer of the ipsilateral hippocampus demonstrated HRP activity, presumably the result of orthograde axonal transport from the injection site.

The central distribution of VIII nerve afferents in larval Petromyzon marinus.

In larval lampreys (body length 30–80 mm), the central projection of VIII nerve afferents was traced with selective silver methods for degenerating axoplasm. In 30–40 mm animals, lateral regions, described by Rudeberg as ''migration A'', are filled with degenerated terminals. In 50–80 mm animals, the ipsilateral nucleus intermedialis and nucleus cerebelli are so filled. These regions are the adult derivatives of ''migration A'', suggesting the maintenance of functional connections during neural development.

Central projections of the statoacoustic nerve in Caiman crocodilus.

The central distribution of primary afferent fibers of the eighth cranial nerve was analyzed in the common South American caiman by comparison of patterns of anterograde fiber degeneration resulting from differential lesions of the nerve. Degenerating fibers from the papilla basilaris project only to ipsilateral nuclei angularis, magnocellularis medialis and lateralis, and to the neuropil above laminaris. Discrete electrolytic lesions suggest a spatial ordering of this auditory projection within the ''cochlear'' nuclei. Primary afferents from vestibular endorgans distribute to six nuclei ipsilaterally: ventrolateralis, ventromedialis, descendens, tangentialis, dorsolateralis, and a previously unrecognized group labeled here ''dorsomedialis''. Analysis of differential degeneration patterns indicate that nerves from specific semicircular canals project to restricted regions within the vestibular nuclear complex. For example, the dorsal subdivision of ventrolateralis receives fibers chiefly from the posterior crista, while the anterior and horizontal canal nerves project to the ventral and medial subdivisions. Primary vestibular fibers also project bilaterally to the granular layer of the cerebellum at more rostral levels.

Nucleus of the accessory optic tract. Light and electron microscopic study in normal monkeys and after eye enucleation

The fine morphology and synaptic organization of the accessory optic tract nucleus was investigated in monkeys ( Macaca mulatta) by light and electron microscopic methods. Nissl stains delineated the wedge-shaped nucleus between the brachium of the inferior colliculus and the medial lemniscus. Most of the neurons are of medium size with dark coarse Nissl bodies. Smaller and paler cells are also present. Golgi material revealed the two classic type I and II neurons, the former with early bifurcating dendrites exhibiting numerous spines. Electron microscopy showed mostly medium size neurons with relatively frequent occurrence of somatic spines. The dendritic profiles have a thick smooth initial protion followed by the appearance of increasing number of spines. The dendrites bifurcate close to the soma and finally end in brushlike fashion. Axon terminals make synaptic contacts with the soma, dendrites (spines and trunk) and dendritic endings. The latter articulations appear as “glomeruli”. At this level, profiles of ambiguous nature, possibly dendrites of Golgi type II cells, containing synaptic vesicles are frequently seen. Following eye enucleation, both the contralateral and ipsilateral nuclei showed terminal boutons in different stages of degeneration depending on the survival time. The optic fibers terminate on the soma as well as on the proximal spineless part of the dendrites and at the dendritic bifurcations. There are no optic terminals participating in the “glomeruli”. This nucleus receives direct retinal fibers and the system is both crossed and uncrossed. The presence of abundant axosomatic contacts of optic terminals as well as the absence of such endings in the glomeruli suggest a very different functional mechanism than that of the geniculate pathway. The nucleus receives many more afferents of unknown origin.

DETERMINATION OF THE DETAILED HYPOTHALAMIC ROUTE OF THE MILK-EJECTION REFLEX IN THE GUINEA-PIG

SUMMARY The effect of various types of surgical damage to the forebrain on the release of oxytocin in response to electrical stimulation of the discrete ascending milk-ejection reflex pathway in the mid-brain was investigated in 99 anaesthetized lactating guinea-pigs. Oxytocin release was measured by comparison of experimental milk-ejection responses with the response to i.v. injection of known amounts of synthetic oxytocin. Removal of the entire telencephalon, including cerebral cortex, hippocampi, amygdalae and forebrain rostral to the hypothalamus, did not affect the subsequent release of oxytocin after electrical stimulation of the pathway in the mid-brain, from which it was concluded that the reflex pathway within the forebrain is entirely diencephalic. Transection of the hypothalamus immediately rostral to the paraventricular (PV) nuclei was without effect, while transection immediately caudal to the PV nuclei blocked the release of oxytocin. Destruction of the PV nuclei by a radiofrequency lesion which spared the supraoptic (SO) nuclei blocked the release of oxytocin. Undercutting both PV nuclei so as to isolate them from the ventral hypothalamus blocked the release of oxytocin. Undercutting the PV nucleus ipsilateral to the stimulated side of the mid-brain blocked the release of oxytocin, while undercutting the contralateral PV nucleus had no effect. The PV nuclei, therefore, lie on the ascending path of the milk-ejection reflex, the SO nuclei do not, and, from the mid-brain forwards, the ascending pathway remains uncrossed. The course of the reflex pathway was traced rostrally from the mesodiencephalic junction by making narrow transverse knife-cuts and determining which cuts reduced or blocked the release of oxytocin after mid-brain stimulation. At this level, the pathway on each side of the brain is represented by separate dorsal and ventral paths and in the present study it was found that the ventral path is more important than the dorsal path in terms of oxytocin release. The ventral path passes forward in the medial forebrain bundle, in the far-lateral hypothalamus, while the dorsal path enters the posterior hypothalamus dorsally in the periventricular region at the top of the third ventricle and impinges on the thalamic reuniens nucleus. Shortly afterwards the dorsal path swings abruptly in the lateral direction to join the ventral path in the lateral hypothalamus. The reunited pathway then moves forward in this position until it is level with the PV nuclei, where it swings dorsomedially to relay with the lateral tip of the ipsilateral PV nucleus, and in doing so intermingles with the descending neurosecretory fibres from this nucleus.

Retinal projections in Iguana iguana and Anolis carolinensis

The retinal projections were studied experimentally in Iguana iguana and Anolis carolinensis using the Fink-Heimer and Roth modifications of the Nauta silver impregnation technique for degenerating fibers. The retinal projections were similar in the two species. The following results were obtained: (1) Retinal fibers project to nucleus geniculatus lateralis, pars dorsalis, of the thalamus. The fiber terminations are more dense in the medial half of the nucleus. (2) The nucleus geniculatus lateralis, pars ventralis, receives retinal projections in the lateral neuropil and to a lesser extent in the medial cell plate. (3) Fibers of passage were seen in nucleus ventrolateralis, pars ventralis, of Senn, but fiber terminations in that nucleus could not be confirmed. (4) The nucleus dorsolateralis anterior was completely free of degeneration. (5) Pretectal nuclei which receive retinal projections are nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterdorsalis, and nucleus pretectalis. (6) Retinal fibers project to layers 8–14 of Ramo´n in the optic tectum, the stratum opticum and stratum fibrosum et griseum superficiale. (7) The nucleus opticus tegmenti receives retinal fibers via the basal optic tract; no projection to the ipsilateral nucleus was seen. (8) There is a sparse ipsilateral projection to the lateral half of the nucleus geniculatus lateralis, pars dorsalis.

Visceral representation in the cat caudate nucleus

1. In response to stimulation of the splanchnic nerve, biphasic and multiphasic evoked potentials with relatively short (16–25 msec) and longer (30–54 msec) latent periods are recorded in the cat caudate nucleus. 2. Evoked potentials in response to stimulation of the splanchnic and tibial nerves and to clicks are not recorded from all points of the caudate nucleus, indicating its heterogeneity relative to representation of different afferent systems, including the visceral. 3. Extirpation of cortical somatosensory areas I and II, and also ablation of the neocortex, do not abolish evoked potentials in the ipsilateral caudate nucleus in response to splanchnic nerve stimulation.

Efferent fibers of the habenula and stria medullaris thalami in rats

Lesions were produced in the stria medullaris thalami and habenula of albino rats by the electrocoagulating method to study the efferent fibers of the habenula and stria medullaris thalami as well as the reciprocal fibers in the stria. Animals were killed on the fifth day after the operation by vascular perfusion with a 10% formol solution, and degenerating nerve fibers in the brain were traced by the Nauta-Gygax technique. Efferent fibers of these structures were distributed in the bilateral striae medullares thalami and habenulae. The fibers in the striae could be traced to the lateral preoptic and lateral hypothalamic areas of each side and were considered to be reciprocal fibers which take their course contrary to the main stream of fibers. Other regions receiving efferent fibers of the stria medullaris thalami and habenula were ipsilateral nucleus medialis dorsalis, ipsilateral nucleus parafascicularis, ipsilateral fasciculus retroxflexus, and nucleus interpeduncularis. It seemed that there was not so much difference between the distribution of efferent fibers of the stria medullaris thalami and that of the habenula.

Direct projections from the masseteric nerve to the mesencephalic nucleus.

AbstractThe caliber spectrum of the nerve to the masseter muscle of the cat was found to be unimodal, ranging from 1 to 16 μ, with the majority of the fibers in the 4‐8 μ range. The upper 25%, which includes the afferent propriococoptive fibers, averaged 10.4 μ. The nerve to the masseter was stimulated and evoked potentials were recorded from the ipsi‐ and contralateral mesencephalic nuclei of the trigeminus and from the contralateral nerve. The average latencies were 0.846, 0.935 and 1.46 msec respectively. The mesencephalic nucleus was stimulated and evoked potentials were recorded from the contrlateral nucleus with an average latency of 0.385 msec. Analysis of the latencies of the responses recorded from the ipsilateral nucleus suggested that about half of the fibers of the nerve to the masster projected directly and the other half projected by way of an intervening synapse. A similar distribution of the fibers to the contralateral nucleus was deduced from the recorded latencies. Potentials recorded in the nuclei as a result of stimulation of the contralateral nucleus demonstrated that there were direct internuclear pathways without intervening synapses. The latencies of potentials recorded in the nerve as a result of stimulation of the contralateral nerve indicated that there was always at least one synapse intervening. It was also shown that there were direct projections from the nerve of the masseter to the contralateral motor nucleus of V. The work confirms our earlier report of bilateral projections from a muscle of mastication to the mesencephalic nuclei and provides a pathway for bilteral simultaneous activation of the muscles of mastication resulting from stimulation of unilateral tension receptors.

The corticothalamic projection from the gyrus proreus and the medial wall of the rostral hemisphere in the cat. An experimental study with silver impregnation methods.

The corticothalamic projections from the gyrus proreus and the medial wall of the rostral hemisphere have been studied in the cat with the silver method of Nauta. The gyrus proreus projects upon the following nuclei (for abbreviations, see list on page 133), ipsilateral R, VA, VM, VL, MD, Pc, CL, CM, Pf, VPM, VPMpc. VPI and to the contralateral principal nucleus of the trigeminal nerve. The medial wall of the rostral hemisphere projects bilaterally upon R, VA, VM, VL, MD, Pc, CL, CM, Pf, VPM, VPMpc, VPI, VPL, the dorsal column nuclei and the principal nucleus of the trigeminal nerve. The ipsilateral thalamic projection is more abundant than the contralateral. The latter appears to increase in amount as the lesion is placed successively more ventrally on the medial wall of the rostral hemisphere. Some degenerating fibers cross in the corpus callosum and descend in the contralateral internal capsule but the majority cross in the dorsal part of the anterior commissure and reach the medial aspect of the anterior limb of the contralateral internal capsule. A somatotopical organization of the medial wall of the rostral hemisphere has been demonstrated. The rostrocaudal part projects upon the ipsilateral VPL lateralis (VPLl) and nucleus cuneatus and the contralateral nucleus gracilis and VPL medialis (VPLm). The caudal part of this cortical area sends fibers bilaterally to VPM, VPMpc, and the principal nucleus of the trigeminal nerve. The intermediate part, which also includes agranular cortex on the medial wall, projects upon ispsilateral VPLm and nucleus gracilis and upon contralateral VPLl and nucleus cuneatus. — The fibers to the ventro-basal complex, dorsal column nuclei and the principal nucleus of the trigeminal nerve are rather thick. The corticofugal fibers to the other thalamic nuclei are quite thin. — The findings are discussed in light of relevant anatomical and physiological observations in the literature and special emphasis has been laid on reported observations on the “supplementary motor” area.

The corticothalamic projection from the second somatosensory cortical area in the cat. An experimental study with silver impregnation methods.

The corticothalamic projection from the anterior ectosylvian gyrus in the cat has been studied with the silver impregnation method of Nauta. The second somatosensory cortical area (SII) projects upon the ipsilateral nucleus ventralis posterolateralis (VPL), nucleus ventralis posteromedialis (VPM), the posterior thalamic region (PO) and to a slight extent upon the reticular nucleus of the thalamus (R), the centrum medianum (CM), the parvocellular part of VPM (VPMpc) and the nucleus ventralis posterior inferior (VPI). A somatotopical arrangement in the projection upon the ventro-basal (VB) complex has been demonstrated and a topical arrangement in the corticothalamic fibers from SII to PO is also evident. The transitional area between SII and the second auditory cortex sends fibers mainly to the entire magnocellular part of the medial geniculate body (MGmc) and to a lesser degree to the principal division of this nucleus (MGp). The corticofugal fibers from SII follow various and rather complicated circuitous routes before they end in the different thalamic nuclei. The experimental findings are discussed in the light of recent anatomical and physiological observations. It is shown that zones B and C of SII which have been shown by Carreras and Andersson (1963) to possess a large number of place and modality specific neurons project upon the VB-complex. On the other hand, zone A which contains a majority of place and modality unspecific neurons sends its fibers exclusively to PO. Finally the problem of thalamocortical projections to SII is briefly discussed.

The characteristics of acetylcholine release mechanisms in the auditory cortex.

Abstract 1. The characteristics of the acetylcholine (ACh) release mechanism have been studied in the auditory cortex of rabbits on stimulation of the ipsilateral medial geniculate nucleus. 2. On stimulation of the medial geniculate nucleus the mean release of ACh from the auditory receiving cortex was 6·1 times the spontaneous release; the mean release from other parts of the cortex was 2·2 times the spontaneous release. 3. The frequency of stimulation most effective in evoking ACh release was found to be 10/sec. 4. Both the spontaneous and evoked release of ACh were reduced by 40-65% in the absence of calcium from the solution bathing the auditory cortex, and increased by 15-25% when the calcium concentration in the bathing solution was doubled. 5. The presence of low concentrations of magnesium in the fluid bathing the cortex was essential for the optimal release of ACh, but high magnesium concentrations lowered this release. 6. The presence of triethylcholine (TEC) in the fluid bathing the auditory cortex reduced both the spontaneous and evoked release of ACh. This reduction was reversed in the presence of choline. 7. The effects of calcium, magnesium and TEC on the ACh release mechanism in the cerebral cortex and at the neuromuscular junction are compared.