Co-localization of midbrain projections, progestin receptors, and mating-induced fos in the hypothalamic ventromedial nucleus of the female rat

In female rats, sexual behavior requires the convergence of ovarian hormone signals, namely estradiol and progesterone, and sensory cues from the male on a motor output pathway. Estrogen and progestin receptors (ER and PR) are found in neurons in the hypothalamic ventromedial nucleus (VMH), a brain region necessary for lordosis, the stereotypic female copulatory posture. A subset of VMH neurons sends axonal projections to the periaqueductal gray (PAG) to initiate a motor output relay, and some of these projection neurons express PR. Previous studies showed that VMH neurons are activated during mating, based on the expression of the immediate early gene Fos. Many of the activated neurons expressed ER; however, it is not known if such activated neurons co-express PR. Fluorogold, a retrograde tracer, was injected into the PAG of ovariectomized rats to label neurons projecting from the VMH. Hormone-treated animals then were mated, and their brains were immunohistochemically stained for PR and Fos. Of the Fos-positive neurons, 33% were double-labeled for PR, 19% were double-labeled with Fluorogold, and 5% were triple-labeled for Fos, PR, and the retrograde tracer. The majority of triple-labeled neurons were found in the rostral, rather than caudal, portion of the VMH. These results show that PR-containing neurons are engaged during sexual behavior, which suggests that these neurons are the loci of hormonal-sensory convergence and hormonal-motor integration.     

Orphanin FQ in the mediobasal hypothalamus facilitates sexual receptivity through the deactivation of medial preoptic nucleus mu-opioid receptors

Sexual receptivity, lordosis, can be induced by sequential estradiol and progesterone or extended exposure to high levels of estradiol in the female rat. In both cases estradiol initially inhibits lordosis through activation of β-endorphin (β-END) neurons of the arcuate nucleus of the hypothalamus (ARH) that activate μ-opioid receptors (MOP) in the medial preoptic nucleus (MPN). Subsequent progesterone or extended estradiol exposure deactivates MPN MOP to facilitate lordosis. Opioid receptor-like receptor-1 (ORL-1) is expressed in ARH and ventromedial hypothalamus (VMH). Infusions of its endogenous ligand, orphanin FQ (OFQ/N, aka nociceptin), into VMH–ARH region facilitate lordosis. Whether OFQ/N acts in ARH and/or VMH and whether OFQ/N is necessary for steroid facilitation of lordosis are unclear. In Exp I, OFQ/N infusions in VMH and ARH that facilitated lordosis also deactivated MPN MOP indicating that OFQ/N facilitation of lordosis requires deactivation of ascending ARH-MPN projections by directly inhibiting ARH β-END neurons and/or through inhibition of excitatory VMH–ARH pathways to proopiomelanocortin neurons. It is unclear whether OFQ/N activates the VMH output motor pathways directly or via the deactivation of MPN MOP. In Exp II we tested whether ORL-1 activation is necessary for estradiol-only or estradiol + progesterone lordosis facilitation. Blocking ORL-1 with UFP-101 inhibited estradiol-only lordosis and MPN MOP deactivation but had no effect on estradiol + progesterone facilitation of lordosis and MOP deactivation. In conclusion, steroid facilitation of lordosis inhibits ARH β-END neurons to deactivate MPN MOP, but estradiol-only and estradiol + progesterone treatments appear to use different neurotransmitter systems to inhibit ARH-MPN signaling.     

Orphanin FQ in the mediobasal hypothalamus facilitates sexual receptivity through the deactivation of medial preoptic nucleus mu-opioid receptors

Sexual receptivity, lordosis, can be induced by sequential estradiol and progesterone or extended exposure to high levels of estradiol in the female rat. In both cases estradiol initially inhibits lordosis through activation of β-endorphin (β-END) neurons of the arcuate nucleus of the hypothalamus (ARH) that activate μ-opioid receptors (MOP) in the medial preoptic nucleus (MPN). Subsequent progesterone or extended estradiol exposure deactivates MPN MOP to facilitate lordosis. Opioid receptor-like receptor-1 (ORL-1) is expressed in ARH and ventromedial hypothalamus (VMH). Infusions of its endogenous ligand, orphanin FQ (OFQ/N, aka nociceptin), into VMH–ARH region facilitate lordosis. Whether OFQ/N acts in ARH and/or VMH and whether OFQ/N is necessary for steroid facilitation of lordosis are unclear. In Exp I, OFQ/N infusions in VMH and ARH that facilitated lordosis also deactivated MPN MOP indicating that OFQ/N facilitation of lordosis requires deactivation of ascending ARH-MPN projections by directly inhibiting ARH β-END neurons and/or through inhibition of excitatory VMH–ARH pathways to proopiomelanocortin neurons. It is unclear whether OFQ/N activates the VMH output motor pathways directly or via the deactivation of MPN MOP. In Exp II we tested whether ORL-1 activation is necessary for estradiol-only or estradiol + progesterone lordosis facilitation. Blocking ORL-1 with UFP-101 inhibited estradiol-only lordosis and MPN MOP deactivation but had no effect on estradiol + progesterone facilitation of lordosis and MOP deactivation. In conclusion, steroid facilitation of lordosis inhibits ARH β-END neurons to deactivate MPN MOP, but estradiol-only and estradiol + progesterone treatments appear to use different neurotransmitter systems to inhibit ARH-MPN signaling.     

Lesions of the anterior forebrain song control pathway in female canaries affect song perception in an operant task

Sexual behavior in female rats, typified by the lordosis reflex, is dependent upon estrogen action in the ventromedial nucleus of the hypothalamus (VMH) and its surrounding neuropil. However, the synaptic organization of this brain region remains unclear. Pseudorabies virus (PRV) was used to transneuronally label the neural network that innervates the lumbar epaxial muscles that execute the lordosis response. PRV-labeled neurons were identified within and subjacent to the VMH four days after injection of PRV into the back muscles. The pattern of labeling was defined in relation to three landmarks: the VMH core, as defined by Crystal Violet staining; the shell, as defined by the oxytocin fiber tract; and the cluster of estrogen receptor-containing cell nuclei. The pattern of PRV labeling in the VMH displayed a striking rostral-caudal gradient. In general, many of the PRV-labeled neurons were found in the oxytocin fiber tract, with far fewer in the core of the VMH. Furthermore, PRV-labeled neurons were rarely found in the cluster of estrogen receptor-containing neurons, and less than 3% of the PRV-labeled neurons were double labeled for estrogen receptor. The results suggest that oxytocin may directly influence these lordosis-relevant VMH projection neurons, whereas estrogen may have transsynaptic effects.     

Functionally‐defined compartments of the lordosis neural circuit in the ventromedial hypothalamus in female rats

Sexual behavior in female rats, typified by the lordosis reflex, is dependent upon estrogen action in the ventromedial nucleus of the hypothalamus (VMH) and its surrounding neuropil. However, the synaptic organization of this brain region remains unclear. Pseudorabies virus (PRV) was used to transneuronally label the neural network that innervates the lumbar epaxial muscles that execute the lordosis response. PRV‐labeled neurons were identified within and subjacent to the VMH four days after injection of PRV into the back muscles. The pattern of labeling was defined in relation to three landmarks: the VMH core, as defined by Crystal Violet staining; the shell, as defined by the oxytocin fiber tract; and the cluster of estrogen receptor‐containing cell nuclei. The pattern of PRV labeling in the VMH displayed a striking rostral‐caudal gradient. In general, many of the PRV‐labeled neurons were found in the oxytocin fiber tract, with far fewer in the core of the VMH. Furthermore, PRV‐labeled neurons were rarely found in the cluster of estrogen receptor‐containing neurons, and less than 3% of the PRV‐labeled neurons were double labeled for estrogen receptor. The results suggest that oxytocin may directly influence these lordosis‐relevant VMH projection neurons, whereas estrogen may have transsynaptic effects. © 2000 John Wiley & Sons, Inc. J Neurobiol 45: 1–13, 2000     

Experience-dependent refinement of the inhibitory axons projecting to the medial superior olive

Neurons in the medial superior olive (MSO) analyze interaural time differences (ITDs) by comparing the arrival times of the two excitatory inputs from each ear using a coincidence detection mechanism. They also receive a prominent inhibitory, glycinergic projection from the ipsilateral medial nucleus of the trapezoid body (MNTB), which contributes to the fine-tuning of ITD analysis. Here, we investigated developmental changes of the axonal arborisation pattern of single Microruby-labeled MNTB neurons projecting to the MSO region. During the first 2 weeks after hearing onset, the axonal arborisation of MNTB neurons was significantly refined resulting in a narrowed projection area across the tonotopic axis of the MSO and a redistribution of the axonal endsegments to a mostly somatic location. Rearing the animals in omnidirectional noise prevented the structural changes of single MNTB projections. These results indicate that the functional elimination of inhibitory inputs on MSO neurons after hearing onset, as described previously, is paralleled by a structural, site-specific refinement of the inputs and is dependent on the normal acoustic experience of the animal.     

Opiocortin and catecholamine projections to raphe nuclei

Afferent projections to the nucleus raphe magnus (NRM) and dorsal raphe nucleus (DRN) were identified using retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA). Neurons were labeled in important nociceptive regions including periaqueductal gray (PAG), arcuate nucleus, lateral hypothalamus and medial thalamic nuclei following both injections. We have immunocytochemically identified opiocortin/WGA neurons in the arcuate nucleus following NRM and DRN injections. Dual stained catecholamine/WGA perikarya were found in zona incerta, locus coeruleus, substantia nigra, nucleus tractus solitarius and adjacent A2, C2 and C3, lateral paragigantocellular reticular nucleus/C1 and lateral reticular nucleus/A1 following DRN injections and in zona incerta, substantia nigra, nucleus tractus solitarius/A2 and lateral reticular nucleus/A1 after NRM injections. These results provide further evidence for opiocortin and catecholamine modulation of analgesia.     

Induction of CCK mRNA levels in the limbic-hypothalamic circuit: Time course and site-specific effects of estrogen

Estrogenic regulation of cholecystokinin (CCK) and its receptors is correlated with the initiation and termination of lordosis behavior. To understand the effect of circulating estrogen concentration on the temporal aspects of CCK mRNA expression in the posterodorsal medial amygdaloid nucleus (MeApd) and the central part of the medial preoptic nucleus (MPNc) of the limbic-hypothalamic circuit, ovariectomized female rats were treated with a 10 mm Silastic™ capsule filled with estradiol, a bolus injection of 50 μg estradiol benzoate or 2 μg estradiol benzoate every 4 days for five “cycles.” In situ hybridization was used to compare the relative changes of CCK mRNA levels at 0 h to levels measured at 6, 12, 24, 48, 72, or 96 h after estrogen administration. In the MPNc and the MeApd, the 10-mm capsule significantly increased and maintained CCK mRNA levels from 6 to 96 h. The range of the increase was 3.0–5.1-fold in the MPNc and 2.8–5.0 in the MeApd. The 50-μg injections significantly increased and maintained CCK mRNA levels in the MPNc from 12 to 96 h (range of the increase 2.4–4.1-fold) and in the MeApd from 24 to 96 h (range of the increase 2.2–2.8-fold). The repeated administration of 2 μg estrogen induced a significant increase of message levels in the MPNc at 12 and 24 h that were 4.2- and 4.7-fold, respectively. In the MeApd this estrogen treatment did not significantly increase CCK mRNA. These studies demonstrate that small doses (2 μg) of estrogen that mimic the pattern and circulating levels of estrogen dramatically stimulate CCK mRNA levels in the limbic-hypothalamic circuit. To further study this steroid stimulation, ovariectomized female rats were implanted with estradiol-filled cannulae into the bed nucleus of the stria terminalis or MeA. Estrogen elevated CCK mRNA levels locally in each nucleus. Implants in the bed nucleus also elevated CCK mRNA levels in the MeApd indicating that physiologic estrogen stimulation of CCK in the MeApd is the result of both local and distal transsynaptic elevation of CCK mRNA levels. The site-specific induction of CCK mRNA levels within the limbic-hypothalamic nuclei provides another important facet of estrogenic modulation of CCK induction. © 1996 John Wiley & Sons, Inc.     

Connections of brainstem respiratory nuclei studied by the retrograde horseradish peroxidase axon transport method

Intrabulbar connections of respiratory nuclei and the medullary reticular formation and also descending pathways from these structures in the spinal cord were studied by the retrograde horseradish peroxidase axonal transport method in cats. Neurons of the nucleus ambiguus and nucleus retroambigualis (ventral respiratory group) and of the ventrolateral part of the nucleus of the tractus solitarius (dorsal respiratory group) were shown to form direct two-way connections with each other and with the medial region of the medulla. Neurons of the pneumotaxic center send uncrossed axons to the nucleus ambiguus and to the medial medullary reticular formation. Neurons of the contralateral homonymous nucleus and neurons of the nucleus of the tractus solitarius are sources of projections of the locus coeruleus. A well developed system of direct connections was found between neurons of respiratory nuclei of the two halves of the brain. The possible role of these nuclear formations in genesis of the respiratory rhythm and regulation of the respiratory and other motor functions of the reticular formation is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 149–157, March–April, 1982.     

The organization of cholinergic neurons in the mesencephalon of the eel,Anguilla anguilla,as determined by choline acetyltransferase immunohistochemistry and acetylcholinesterase enzyme histochemistry

Cholinergic systems in the midbrain of the eel were identified by using histochemical procedures for the demonstration of the enzymes choline acetyltransferase (ChAT) and acetylcholinesterase. Neurons detected by both methods are located in the stratum periventriculare of the tectum, cranial motor nuclei III and IV, nucleus isthmi, nucleus gustatorius secundarius, nucleus reticularis superior, and nucleus lateralis valvulae. Some projections of these cell groups were studied by injecting horseradish peroxidase into selected brain regions. Cholinergic neurons make up about 10% of the neurons in the stratum periventriculare of the tectum and are a subset of the type-XIV neurons. Neurons in n. isthmi project primarily to the ipsilateral tectum; some cholinergic isthmal neurons project to n. pretectalis superficialis. A few ChAT-positive axons, perhaps belonging to the tectopetal system, were observed in the optic nerve. The cholinergic neurons of n. gustatorius secundarious project to the inferior lobes of the hypothalamus. The neurons of the superior reticular nucleus are a cholinergic subset of the superior reticular formation. Their axons project rostrally, probably to the thalamus and pretectum. The findings are discussed in relation to functional features of the mesencephalon, particularly in relation to locomotory control.     

Development of the habenulointerpeduncular tract of rats

Development of the habenulointerpeduncular tract has been carried out on fixed brains obtained from 21 day rat embryos and from neonatal animals on the 0 and 9 days of postnatal development by DiI tracing method (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) along neuronal membranes. The marker was inserted into the nuclei of the habenula, the interpeduncular nucleus, and into the area of raphe nuclei. Neurons and fibers that contained DiI were identified on vibratome sections by fluorescent and confocal microscopy. We have found that reciprocal connections between the lateral habenular nucleus and raphe nuclei are formed in the prenatal period by stage E21. Raphe nuclei innervating neurons were located in dorso- and ventrocaudal parts of the lateral habenular nucleus. Projections of the medial habenular nucleus onto interpeduncular nucleus were found only in the postnatal period from P2. Neurons that provide a source of these projections form characteristic groups inside the medial habenular nucleus. Therefore, the present study for the first time describes heterogenic formation of different projection systems that are included in the habenulointerpeduncular tract of rats at perinatal ontogenesis.     

Proposed pathways for vocal self-stimulation: Met-enkephalinergic projections linking the mibrain vocal nucleus,auditory-responsive thalamic vocal nucleus,auditory-responsive thalamic regions and neurosecretory hypothalamus

In this study, we have investigated the neuroanatomical pathways that may underlie the influence of a female bird's vocal behavior upon her own reproductive endocrine response. We traced the ascending efferent projections of the midbrain vocal control nucleus, the intercollicularis (ICo), using an anterograde tracer, PHAL, delivered by iontophoretic application. We found labelled terminal fields in the anterior regions of the hypothalamus that contained luteinizing hormone releasing hormone- (LHRH) immunoreactive neurons. We injected into the LHRH-rich anterior medial hypothalamus (AM) the retrograde tracer, fluorogold, to verify the results of PHAL anterograde tracing and exmine whether retrogradely labelled neurons in the ICo can be stained with met-enkephalin antiserum by the immunohistochemical method. Of the retrogradely labelled neurons in the medial division of ICo (mICo), between 5% and 15% were found to be met-enkephalin-immunoreactive positive perikarya. Our data suggest that axonal projections into the anterior medial hypothalamus may arise in part from enkephalin-immunoreactive neurons in the medial ICo. The mICo neurons distributed along the medial border of the midbrain auditory nucleus give rise to projections into the posterior medial hypothalamus (PMH) via synapses within the shell region of thalamic auditory nucleus, ovoidalis (Ov). We conclude that in the ring dove, the medial division of the vocal control nucleus, by virtue of its connection with the auditory thalamus and neurosecretory hypothalamus, is in a position to exert influence on endocrine response partly through enkephalinergic systems. Implications of similar connections in other species are discussed. 1994 John Wiley & Sons, Inc.     

Sex difference and response to testosterone in gabaergic cells of the medial preoptic nucleus and ventral bed nuclei of the stria terminalis in gerbils

The medial preoptic nucleus (MPN) and ventral bed nuclei of the stria terminalis (BST) are needed to maintain mating in sexually experienced male gerbils and rats. The gerbil ventral BST is also activated with mating, as assessed by Fos expression, as is the medial MPN (MPNm) of both species. In gerbils, many of those mating-activated cells contain glutamic acid decarboxylase (GAD), the enzyme that synthesizes γ-aminobutyric acid (GABA). Some of those cells are projection neurons, but others may release GABA locally. Through actions in the medial preoptic area, GABA inhibits and testosterone (T) promotes male sex behavior. Thus, T may promote mating, in part, by decreasing GAD in MPNm or ventral BST cells. In rats, T increases GAD mRNA in the central MPN (MPNc), where MPN GABAergic cells are densest, but mating behavior does not change in sexually experienced males when the MPNc is ablated. Therefore, this study focused on the MPNm and ventral BST to ask whether their GABAergic cells respond to T or are sexually dimorphic. This was done by visualizing cells immunoreactive (IR) for GAD₆₇, an isoform found primarily in cell bodies, in male and female gerbils and in castrated males with and without T. At both sites, males had more GAD₆₇-IR cells than females, and T decreased GAD₆₇-IR cell numbers in males. Thus, the MPNm and ventral BST have GABAergic cells that are sexually dimorphic and in which T decreases GAD, consistent with local effects of T and GABA on mating.     

Release of orphanin FQ/nociceptin in the medial preoptic nucleus and ventromedial nucleus of the hypothalamus facilitates lordosis

Opioid regulation of reproduction has been widely studied. However, the role of opioid receptor-like 1 receptor (NOP; also referred to as ORL-1 and OP4) and its endogenous ligand orphanin FQ/nociceptin (OFQ/N) have received less attention despite their extensive distribution throughout nuclei of the limbic-hypothalamic system, a circuit that regulates reproductive behavior in the female rat. Significantly, the expression of both receptor and ligand is regulated in a number of these nuclei by estradiol and progesterone. Activation of NOP in the ventromedial nucleus of the hypothalamus (VMH) of estradiol-primed nonreceptive female rats facilitates lordosis. NOPs are also expressed in the medial preoptic nucleus (MPN), however, their roles in reproductive behavior have not been studied. The present experiments examined the role of NOP in the regulation of lordosis in the MPN and tested whether endogenous OFQ/N in the MPN and VMH mediates reproductive behavior. Activation of NOP by microinfusion of OFQ/N in the MPN facilitated lordosis in estradiol-primed sexually nonreceptive female rats. Passive immunoneutralization of OFQ/N in either the MPN or the VMH reduced lordosis in estradiol-primed females, but had no effect on lordosis in estradiol+progesterone-primed sexually receptive rats. These studies suggest that OFQ/N has a central role in estradiol-only induced sexual receptivity, and that progesterone appears to involve additional circuits that mediate estradiol+progesterone sexual receptivity.     

Androgen receptors are required for full masculinization of the ventromedial hypothalamus (VMH) in rats

The ventromedial hypothalamus (VMH) is one of several sexually dimorphic nuclei that regulate mating behavior, and is rich in steroid hormone receptors and aromatase activity. We looked at the contribution of the androgen receptor (AR) to the volume of the VMH in rats by measuring each of the four subdivisions of the VMH in 90 day old male, female, and XY male rats carrying a mutant AR allele (tfm), which renders animals largely unresponsive to androgens. Confirming published reports, total VMH volume was greater in wild-type males than in females (P<0.01). The mean total volume of the VMH in TFM males was intermediate, but not significantly different from either females or males (Ps>0.10). The sex difference in VMH volume was primarily accounted for by the ventrolateral subdivision (VMHvl), which in both females and TFM males was significantly smaller than in wild-type males (Ps<0.005). There was no significant sex difference in the volume of the other three subdivisions of the VMH. Neuronal somata were larger in males than females in VMHvl, central VMH (VMHc) and the dorsomedial VMH (VMHdm), with TFM males having feminine neuronal somata in the VMHdm and VMHc. These data suggest that AR plays a role during sexual differentiation of the VMH, imparting its greatest effect in the VMHvl. ARs may regulate aromatase expression or activity to affect estrogen receptor activation, or may act independently of estrogen receptors to influence VMH morphology.     

The distribution of cholinergic neurons in the human central nervous system

Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine, is presently the most specific marker for identifying cholinergic neurons in the central and peripheral nervous systems. The present article reviews immunohistochemical and in situ hybridization studies on the distribution of neurons expressing ChAT in the human central nervous system. Neurons with both immunoreactivity and in situ hybridization signals of ChAT are observed in the basal forebrain (diagonal band of Broca and nucleus basalis of Meynert), striatum (caudate nucleus, putamen and nucleus accumbens), cerebral cortex, mesopontine tegmental nuclei (pedunculopontine tegmental nucleus, laterodorsal tegmental nucleus and parabigeminal nucleus), cranial motor nuclei and spinal motor neurons. The cerebral cortex displays regional and laminal differences in the distribution of neurons with ChAT. The medial septal nucleus and medial habenular nucleus contain immunoreactive neurons for ChAT, which are devoid of ChAT mRNA signals. This is probably because there is a small number of cholinergic neurons with a low level of ChAT gene expression in these nuclei of human. Possible connections and speculated functions of these neurons are briefly summarized.     

A Population of Kisspeptin/Neurokinin B Neurons in the Arcuate Nucleus May Be the Central Target of the Male Effect Phenomenon in Goats

Exposure of females to a male pheromone accelerates pulsatile gonadotropin-releasing hormone (GnRH) secretion in goats. Recent evidence has suggested that neurons in the arcuate nucleus (ARC) containing kisspeptin and neurokinin B (NKB) play a pivotal role in the control of GnRH secretion. Therefore, we hypothesized that these neurons may be the central target of the male pheromone. To test this hypothesis, we examined whether NKB signaling is involved in the pheromone action, and whether ARC kisspeptin/NKB neurons receive input from the medial nucleus of the amygdala (MeA)—the nucleus suggested to relay pheromone signals. Ovariectomized goats were implanted with a recording electrode aimed at a population of ARC kisspeptin/NKB neurons, and GnRH pulse generator activity, represented by characteristic increases in multiple-unit activity (MUA) volleys, was measured. Pheromone exposure induced an MUA volley and luteinizing hormone (LH) pulse in control animals, whereas the MUA and LH responses to the pheromone were completely suppressed by the treatment with an NKB receptor antagonist. These results indicate that NKB signaling is a prerequisite for pheromone action. In ovariectomized goats, an anterograde tracer was injected into the MeA, and possible connections between the MeA and ARC kisspeptin/NKB neurons were examined. Histochemical observations demonstrated that a subset of ARC kisspeptin/NKB neurons receive efferent projections from the MeA. These results suggest that the male pheromone signal is conveyed via the MeA to ARC kisspeptin neurons, wherein the signal stimulates GnRH pulse generator activity through an NKB signaling-mediated mechanism in goats.     

Sources of thalamic afferents projecting to the suprasylvian gyrus of the black sea porpoise

Neurons sending fibers to different loci of the suprasylvian gyrus (SSG) of the porpoise(Phocaena phocaena) cortex were located in the thalamus by retrograde horseradish peroxidase transport and fluorescent tracing techniques. Horseradish peroxidase injection into the anterior section of the suprasylvian gyrus led to retrograde labelling of neurons in the lateral portion of the ventrobasal complex of nuclei and the ventroposteroinferior nucleus. A group of labelled cells was found in the ventral section of the main medial geniculate nucleus. Injecting bisbenzimide into different loci of the medial suprasylvian gyrus also led to retrograde labelling of neurons belonging to the ventral division of the main medial geniculate nucleus. Somewhat lower numbers of labelled cells were found in the inferior nucleus of the pulvinar. Small groups of labelled neurons were also found in the lateral nucleus of the pulvinar, the medioventral nucleus of the medial geniculate body, and the posterior complex of nuclei. A similar distribution of labelled cells was also observed after injecting bisbenzimide into the more caudal portion of the gyrus, although the location of labelled cells in the ventral division of the main medial geniculate nucleus and the lower pulvinar nucleus were shifted in a lateral direction.A. N. Severtsov Institute of Animal Evolutionary Moprhology and Ecology, Academy of Sciences of the USSR, Moscow. National University, Singapore. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 529–539, July–August, 1989.     

Spatial organization of vestibulospinal neurons in the guinea pig

Quantitative characteristics of spatial organization of neuron populations of vestibular nuclei, forming projections into the spinal cord, were obtained in experiments on guinea pigs by the retrograde axonal transport of horseradish peroxidase, injected unilaterally into the upper cervical and lower thoracic segments of the spinal cord, method. Neurons accumulating the enzyme were found ipsilaterally in the lateral vestibular nucleus and bilaterally in the descending and medial vestibular nuclei. The distribution of vestibulospinal neurons along the length of the spinal cord was studied. Neuron populations of the medial and descending vestibular nuclei whose projection regions coincide with those of fibers of the corticospinal and rubrospinal systems were discovered. The role of vestibulospinal systems in the structure of supra-segmental control of the neuronal apparatus of the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 353–362, May–June, 1991.     

Projections from neurons of the medial terminal nucleus of the accessory optic tract to the caudate nucleus in the cat revealed by combining techniques of retrograde axonal transport and experimentally induced degeneration

Neurons of the medial terminal nucleus of the accessory optic tract receiving direct retinal inputs were shown to project to the heat and body of the caudate nucleus in the cat using techniques of retrograde horseradish peroxidase axonal transport and experimentally induced degeneration. These primarily ipsilateral projections are evenly distributed throughout the aforementioned areas of the nucleus. Neurons of the medial terminal nucleus forming synaptic connections with caudate nucleus cells are distinguished by their varied shapes and sizes, ranging from 20 × 10 to 37.5 × 18 µm and are located in both the ventral and dorsal subdivisions of the nucleus. The supposed functional significance of these projections for the regulation of muscle tonus tension is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 214–219, March–April, 1986.