Distribution of 5-hydroxytryptamine (serotonin) in the brain of the teleost Gasterosteus aculeatus L

The distributions of serotoninergic neurons in the brain of the three-spined stickleback was demonstrated with the indirect peroxidase-antiperoxidase (PAP) immunohistochemical method with antibodies against serotonin. Serotoninergic perikarya were demonstrated in the brainstem reticular formation (nucleus raphe dorsalis, nucleus raphe medialis, and nucleus tegmenti dorsalis lateralis) and in the periventricular ventral thalamus and hypothalamus (nucleus ventromedialis thalami, nucleus posterioris periventricularis, nucleus recessus lateralis, and nucleus recessus posterioris). After pharmacological pretreatment of the animals with a monoamine oxidase inhibitor, serotoninergic perikarya were also visualized in area praetectalis and in the medial brainstem, caudal to nucleus raphe medialis. Whereas the cell groups of the brainstem give rise to both ascending and descending pathways, it was not possible to analyze the distribution of efferent projections from the diencephalic cell groups. Distribution of serotoninergic axons showed marked regional differences. Only scattered varicose fibers were demonstrated in the cerebellum, the facial lobes, and the lateral line lobes. In the mesencephalon, the dorsal periventricular tegmentum and the central gray receive only small numbers of serotoninergic axons, while torus semicircularis and the visual layers of tectum opticum are profusely innervated. In the diencephalon, the hypothalamus and ventral thalamus generally display the highest density of serotoninergic axons. Exceptions are found in nucleus glomerulosus and the ventromedial portion of lobus inferioris, where densities are low. In the telencephalon, the density of serotoninergic axons is very high in area dorsalis pars medialis and pars lateralis dorsalis, but low in area dorsalis pars dorsalis and pars lateralis ventralis, and intermediate in area ventralis.     

Projections of the retinorecipient pretectal nuclei in the pigeon (Columba livia)

We have used anterograde autoradiographic and retrograde HRP techniques to investigate the efferent connections of the retinorecipient pretectal nuclei in the pigeon. In the accompanying paper we identified these nuclei in the pigeon as the nucleus lentiformis mesencephali--pars lateralis and pars medialis, the tectal gray, the area pretectalis, and pretectalis diffusus. Although there are reports of a few of the projections of these nuclei, they had not previously been the subject of a detailed study. We found that different cell types in the lentiformis mesencephali, pars medialis and the lentiformis mesencephali, pars lateralis have descending projections to different targets. These targets include the inferior olive, the cerebellum, the lateral pontine nucleus, the nucleus papillioformis, the nucleus of the basal optic root, the nucleus mesencephalicus profundus, pars ventralis, the nucleus principalis precommissuralis, and the stratum cellulare externum. We found that a few cells in the lentiformis mesencephali project to the medial pontine nucleus, but that a much heavier projection arises from the nucleus laminaris precommissuralis, which is medial to the nucleus lentiformis mesencephali, pars medialis. The tectal gray has predominantly ascending projections to the diencephalon. The nuclei that it projects to are the nucleus intercalatus thalami, the nucleus of the ventral supraoptic decussation, the nucleus posteroventralis, the ventral lateral geniculate nucleus, the nucleus dorsolateralis medialis, and the nucleus dorsolateralis anterior. The tectal gray also projects topographically to layers 4 and 8-13 of the optic tectum. Area pretectalis has both ascending and descending projections. It has ipsilateral ascending projections to the nucleus dorsolateralis anterior, pars magnocellularis, the nucleus lateralis anterior, and the nucleus ventrolateralis thalami. It has ipsilateral descending projections to the central gray, the nucleus of the basal optic root, pars dorsalis, the lateral pontine nucleus, and the deep layers of the optic tectum. It has contralateral projections to the area pretectalis, the nucleus Campi Foreli, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, the cerebellum, and the Edinger-Westphal nucleus. The efferent projections of pretectalis diffusus are limited. It projects contralaterally to the pretectalis diffusus, and ipsilaterally to the nucleus of the ventral supraoptic decussation, the lateral pons, and the cerebellum.4     

Fiber connections of the inferior lobe in a percomorph teleost, Thamnaconus (Navodon) modestus

Afferent and efferent fiber connections of the lobus inferior (LI) were studied in a percomorph teleost, Thamnaconus (Navodon) modestus. The LI of Thamnaconus is composed of the nucleus diffusus lobi inferioris (NDLI), the nucleus recessus lateralis pars lateralis et medialis (NRLl and NRLm), and the nucleus centralis lobi inferioris pars anterior et posterior (NCa and NCp). The NDLI receives projections from the secondary gustatory nucleus, preglomerular tertiary gustatory nucleus, corpus glomerulosum, dorsal region of the area dorsalis telencephali pars medialis (dDm), and area dorsalis telencephali pars lateralis. Different subdivisions of the dorsal telencephalon project to discrete regions of the NDLI. The NDLI projects to the corpus mamillare, NRLl, NCa, and NCp. Thus the NDLI could be regarded as an intrahypothalamic relay nucleus. The NCa receives projections from the NDLI and projects to the preglomerular tertiary gustatory nucleus, secondary gustatory nucleus, nucleus lateralis valvulae, and NRLl. The NCa appears to be primarily an extrahypothalamic projection nucleus. The NCp receives projections from the NDLI. Efferent connections of the NCp remain to be studied. The NRLl receives projections from the NDLI, and projects to the nucleus ruber (NR) of Goldstein [1905] and the preglomerular tertiary gustatory nucleus. Dense projections of the NR to the stratum opticum and stratum fibrosum et griseum superficiale of the optic tectum are demonstrated. The NRLm receives projections from the medial part of the dDm. Efferent connections of the NRLm remain unclear. The LI as a whole receives projections from the locus coeruleus and nucleus raphe superior. These results suggest that the LI receives gustatory and/or general visceral information from the secondary and tertiary gustatory nuclei, visual and somatosensory inputs from the corpus glomerulosum. Inputs from the dorsal telencephalic subdivisions could be of various modalities (e.g. visual, acousticolateral, gustatory and/or general visceral). The present study also suggests that information processed in the LI is transmitted to the optic tectum via the NR, to the corpus mamillare, to the secondary and tertiary gustatory nuclei, and to the cerebellum via the nucleus lateralis valvulae.     

Telencephalic afferent nuclei in the Carp diencephalon, with special reference to fiber connections of the nucleus preglomerulosus pars lateralis

Fiber connections of the nucleus preglomerulosus pars lateralis (PGl), which primarily provides afferent inputs to the telencephalon, were examined in carp by means of horseradish peroxidase tracing methods. The major afferent sources of PGl are the bilateral nucleus tuberis anterior and a few projections are found deriving from the ipsilateral nucleus ventromedialis thalami, nucleus centralis posterior, dorsal periventricular hypothalamus, and torus semicircularis. Axons arising in the PGl can be traced to the area dorsalis pars centralis of the ipsilateral telencephalon, nucleus centralis posterior and the nucleus ventromedialis thalami. In addition, another 5 telencephalic afferent nuclei are found in the diencephalon; the nucleus subrotundus of Sheldon, nucleus preglomerulosus pars anterior, nucleus ventromedialis thalami, nucleus centralis posterior and nucleus posterior thalami.     

An HRP study of afferent connections of the supracommissural ventral telencephalon and the medial preoptic area in himé salmon (landlocked red salmon, Oncorhynchus nerka)

The supracommissural ventral telencephalon and the medial preoptic area have been shown to play important roles in the sexual behavior of himé salmon (landlocked red salmon, Oncorhynchus nerka). In the present study, the sites of neurons projecting to these regions were examined by means of the retrograde horseradish peroxidase (HRP) tracing method. The morphology of neurons in these sites of origin was also studied by means of the Golgi method. The nucleus preopticus periventricularis and the rostral part of nucleus preopticus (NPP-rNPO) received bilateral projections from the middle parts of the area ventralis telencephali pars ventralis (Vv) and the area ventralis telencephali pars dorsalis (Vd), NPP and lateral part of the preoptic area (LPOA), ipsilateral projections from the caudal part of Vv, nucleus anterioris periventricularis (NAPv), nucleus ventromedialis thalami (NVM) at the level of the posterior commissure, nucleus lateralis tuberis pars medialis (NLTm), nucleus anterior tuberis (NAT), nucleus saccus vasculosus (NSV), nucleus recessus posterioris (NRP) and midbrain tegmentum (TG), and a projection from the nucleus posterior tuberis (NPT), which is situated on the midline of the brain. The area ventralis telencephali pars supracommissuralis and neighboring caudal ventral telencephalon (Vs-cV) received ipsilateral projections from almost all parts of the Vv, the middle and caudal parts of Vd, almost all parts of the NNP, the NPO at the level between the habenula and the posterior commissure, and the rostral part of the nucleus dorsomedialis thalami (NDM). The Vs-cV also received a projection from NPT. These findings seem to give anatomical bases for understanding the neural mechanisms involved in sexual behavior as well as neuroendocrine functions.     

Telencephalic ascending gustatory system in a cichlid fish,Oreochromis (Tilapia) niloticus

Central fiber connections of the gustatory system were examined in a percomorph fish Oreochromis (Tilapia) niloticus by means of the horseradish peroxidase (HRP), biocytin, and carbocyanine dye tracing methods. The primary gustatory areas in tilapia are the facial, glossopharyngeal, and vagal lobes of the medulla. The secondary gustatory nucleus (SGN) is a dumb-bell-shaped structure located in the isthmic region. In the SGN, there are two or three layers of neurons lining the ventromedial periphery of the nucleus and a molecular layer constituting of the major part of the nucleus. The SGN receives bilateral projections from the facial lobes and ipsilateral projections from the glossopharyngeal and vagal lobes. Ascending fibers originating from the SGN form the ipsilateral tertiary gustatory tract. A major part of the tract courses rostrally and terminates ipsilaterally in several diencephalic nuclei: the preglomerular tertiary gustatory nucleus (pTGN), the posterior thalamic nucleus, the nucleus diffusus lobi inferioris, the nucleus centralis of inferior lobe, and the nucleus recessus lateralis. The remaining small fiber bundle enters the medial and lateral forebrain bundles and terminates directly in two telencephalic regions; the area ventralis pars intermedia (Vi) and the area dorsalis pars posterior (Dp). Ascending fibers from the pTGN pass through the lateral forebrain bundle and terminate ipsilaterally in the dorsal region of area dorsalis pars medialis (dDm) of the telencephalon. Following biocytin injections into the dDm, small, round cells were labeled in the pTGN. After biocytin injections into the Vi and Dp of the telencephalon, retrogradely labeled cells were found in the ipsilateral SGN. The results show that the ascending fiber connections of the central gustatory system in the percomorph teleost tilapia are essentially similar to those of mammals. That is, the pathway from the primary gustatory areas (facial, glossopharyngeal, and vagal lobes) through the SGN and pTGN to the dDm in tilapia corresponds with the mammalian gustatory pathway from the solitary nucleus through the pontine taste areas (nucleus parabrachialis) and the thalamic relay nucleus (ventral posteromedial nucleus) to gustatory neocortices. In addition, the pathway from the primary gustatory areas through the SGN to the Vi and Dp in tilapia corresponds with the pathway from the solitary nucleus through the pontine taste areas to the amygdala in mammals. J. Comp. Neurol. 392:209–226, 1998. © 1998 Wiley-Liss, Inc.     

An HRP study of afferent connections of the supracommissural ventral telencephalon and the medial preoptic area in hime´salmon (landlocked red salmon,oncorhynchus nerka)

The supracommissural ventral telencephalon and the medial preoptic area have been shown to play important roles in the sexual behavior of hime´salmon (landlocked red salamon,Oncorhynchus nerka). In the present study, the sites of neurons projecting to these regions were examined by means of the retrograde horseradish peroxidase (HRP) tracing method. The morphology of neurons in these sites of origin was also studied by means of the Golgi method. The nucleus preopticus periventricularis and the rostral part of nucleus preopticus (NPP-rNPO) received bilateral projections from the middle parts of the area ventralis telencephali pars ventralis (Vv) and the area ventralis telencephali pars dorsalis (Vd), NPP and lateral part of the preoptic area (LPOA), ipsilateral projections from the caulal part of Vv, nucleus anteriors periventricularis (NAPv), nucleus ventromedialis thalami (NVM) at the level of the posterior commissure, nucleus lateralis tuberis pars medialis (NLTm), nucleus anterior tuberis (NAT), nucleus saccus vasculosus (NSV), nucleus recessus posterioris (NRP) and midbrain tegmentum (TG), and a projection from the nucleus posterior tuberis (NPT), which is situated on the midline of the brain. The area ventralis telencephali pars supracommissuralis and neighboring caudal ventral telencephalon (Vs-cV) received ipsilateral projections from almost all parts of the Vv, the middle and caudal parts of Vd, almost all parts of the NNP, the NPO at the level between the habenula and the posterior commisure, and the rostral part of the nucleus dorsomedialis thalami (NDM). The Vs-cV also received a projection from NPT. These findings seem to give anatomical bases for understanding the neural mechanisms involved in sexual behavior as well as neuroendocrine functions.     

Thalamic fiber connections in a teleost (Sebastiscus marmoratus): visual somatosensory, octavolateral, and cerebellar relay region to the telencephalon

Fiber connections of the nucleus ventromedialis thalami (VM) of Schnitzlein (J. Comp. Neurol. 118:225-267, '62) in a teleost (Sebastiscus marmoratus) were examined by means of the horseradish peroxidase (HRP) tracing method. This nucleus receives fibers from the ipsilateral telencephalon (area dorsalis pars centralis), contralateral retina, contralateral VM, ipsilateral optic tectum, ipsilateral torus semicircularis, contralateral corpus cerebelli, contralateral sensory nucleus of the trigeminal nerve, bilateral bulbospinal reticular formation, contralateral obex region, and contralateral dorsal portion of upper spinal segments. In turn, axons arising from VM terminate in the dorsal telencephalic areas (pars centralis, pars dorsalis, and pars medialis) ipsilaterally, ventral telencephalic area (pars supracommissuralis) bilaterally, nucleus prethalamicus of Meader (J. Comp. Neurol. 60:361-407, '34) bilaterally, nucleus dorsomedialis thalami bilaterally, VM contralaterally, optic tectum bilaterally, torus semicircularis bilaterally, and nucleus lateralis valvulae ipsilaterally. Based on the cytoarchitecture and fiber connections, VM is subdivided into rostral and caudal components. The caudal part of VM in Sebastiscus is considered to be a multimodal thalamic complex that contains some cells that constitute the dorsal thalamus in other vertebrate groups.     

Horseradish peroxidase study of tectal afferents in Xenopus laevis with special emphasis on their relationship to the lateral-line system

Afferent projections to the tectum opticum of the clawed toad Xenopus laevis were studied by injections of horseradish peroxidase (HRP) into the tectum. Cells were labelled in the following nuclei, listed from rostral to caudal: nucleus entopeduncularis anterior, nucleus anterior thalami, nucleus posterior thalami, nucleus ventromedialis thalami, nucleus ventrolateralis thalami pars dorsalis, nucleus lateralis thalami pars posterodorsalis, nucleus neuropilis postthalamici, nucleus lentiformis mesencephali, nucleus praetectalis, nucleus laminaris tori semicircularis, nucleus principalis tori semicircularis, nucleus magnocellularis tori semicircularis, nucleus profundus mesencephali, nucleus anterodorsalis tegmenti, nucleus posterodorsalis tegmenti, nucleus posteroventralis tegmenti, nucleus isthmi, nucleus lineae lateralis pars rostralis, nucleus lineae lateralis pars caudalis, nucleus intermedius, nucleus lateralis nervi octavi, nucleus descendens nervi trigemini, nucleus reticularis superior, nucleus reticularis medius, nucleus reticularis inferior, nucleus reticularis lateralis, nucleus cuneatus and area dorsalis medullae spinalis. Four of these nuclei can be associated with lateral-line processing: the nuclei lineae lateralis rostralis and caudalis of the medulla and the centrolateral nuclei magnocellularis and principalis of the torus semicircularis. The toric input is particularly prominent; it is topologically organized in that central parts of the torus project to the medial tectum, and lateral parts of the torus project to the rostrolateral tectum. For comparison, the torotectal connection was also examined in several anuran species that lose their lateral line at metamorphosis. In these animals, this projection is less well developed than in Xenopus. Therefore, it is argued that the torotectal connection primarily conveys lateral-line information.     

Anterior thalamic afferents from the mamillary body and the limbic cortex in the rat

Anterior thalamic afferents from the mamillary body and the limbic cortex were studied by using single and double retrograde transport methods in the rat. The medial mamillary nucleus was divided on the basis of the cytoarchitecture into four subnuclei: the pars medialis centralis, pars medialis dorsalis, pars lateralis, and pars basalis. Extensive connections were seen between each of these subdivisions of the mamillary body and the anterior thalamic nuclei, topographically organized so that the anteromedial thalamic nucleus receives projections exclusively from the pars medialis centralis, while the anteroventral thalamic nucleus receives projections from the pars medialis dorsalis and pars lateralis. Nuclei in the dorsal half of these two mamillary subdivisions project predominantly to the medial half of the anteroventral thalamic nucleus, and those in the ventral half to the lateral half of the nucleus. The pars basalis was found to have numerous projections to the magnocellular part of the anteroventral nucleus. All limbic cortical areas send projections bilaterally to all regions of the anteromedial nucleus as well as to the parvicellular parts of the anteroventral thalamic nucleus, while the anterodorsal nucleus receives ipsilateral projections originating exclusively from the preagranular, anterior limbic, and cingular regions. The magnocellular part of the anteroventral nucleus, however, receives only ipsilateral projections from all of the limbic cortex. Some neurons in the infralimbic region also project bilaterally to all of the anterior thalamic nuclei except the anterodorsal nucleus. All of these cortical projections to the anterior thalamus originate in layers V and VI of the limbic cortex.     

Telencephalic ascending acousticolateral system in a teleost (Sebastiscus marmoratus), with special reference to the fiber connections of the nucleus preglomerulosus

Acousticolateral systems were examined by means of the horseradish peroxidase tracing method in a teleost (Sebastiscus marmoratus). The torus semicircularis projected bilaterally to the optic tectum, nucleus ventromedialis thalami of Schnitzlein ('62), and reticular formation; contralaterally to the torus semicircularis; and ipsilaterally to the nucleus preglomerulosus of Schnitzlein ('62) and the inferior olive. No topographic organization was detected between the torus semicircularis and the nucleus preglomerulosus. Ipsilateral inputs to the torus were from dorsal telencephalic areas (pars centralis, Dc; pars dorsalis, Dd; and the dorsal part of pars medialis, dDm) and the optic tectum. Contralateral inputs to the torus were from the torus semicircularis, a caudal part of the cerebellum, and a portion of the trigeminal complex. The torus also received bilateral input from the nucleus ventromedialis thalami, nucleus of lemniscus lateralis, nucleus medialis, anterior octaval nucleus, descending octaval nucleus, and the reticular formation. Retrogradely labeled cells in the octaval nuclei were seen predominantly subsequent to HRP injections in the medial torus, while cells in the nucleus medialis were retrogradely labeled following injections into the lateral torus. HRP injections into the nucleus preglomerulosus labeled cells in the superficial region of the torus, while injections into the nucleus ventromedialis thalami labeled cells in the deep region. The nucleus preglomerulosus received inputs bilaterally from the nucleus of the lemniscus lateralis and reticular formation and ipsilaterally from the dorsal telencephalic areas (Dc, Dd, and dDm) and the torus semicircularis. In turn the nucleus preglomerulosus projected to Dd and Dm. Fibers arising in the nucleus ventromedialis thalami ended in Dc, Dd, Dm, and area ventralis pars supracommissuralis (Vs). Homology between the nucleus preglomerulosus and the central thalamic nucleus in amphibians, the nucleus reuniens in reptiles, the nucleus ovoidalis in birds, and the medial geniculate body in mammals is discussed.     

Distribution and hypothalamic projection of tyrosine-hydroxylase containing neurons of the nucleus of the solitary tract in the pigeon.

The avian nucleus of the solitary tract has an extensive subnuclear organization. Several subnuclear cell groups can be distinguished on the basis of cytoarchitectonic criteria. In general, the subnuclei of the medial division of the nucleus of the solitary tract receive gastrointestinal afferents, whereas the subnuclei of the lateral division of the nucleus of the solitary tract receive cardiopulmonary afferents. Forebrain afferents to the nucleus of the solitary tract are segregated to medial and lateral subnuclei, which are located at the periphery of the nucleus. These peripheral subnuclei of the nucleus of the solitary tract are also the source of ascending axonal projections to the forebrain. In this study, the tyrosine hydroxylase (initial enzyme for catecholamine synthesis) content of the anteromedial hypothalamic projecting neurons of the nucleus of the solitary tract is determined by use of a combined retrograde fluorescent dye-immunofluorescence method. Fast Blue implanted into the anteromedial hypothalamus (in the region of the nucleus periventricularis magnocellularis) resulted in the retrograde labeling of neurons in the caudal two-thirds of the nucleus of the solitary tract. At levels rostral to the obex, dye-labeled cells were mostly observed in the dorsally located subnuclei medialis superficialis pars posterior and lateralis dorsalis pars posterior and in the ventrally located subnucleus medialis ventralis pars posterior. More centrally located subnuclei contained few labeled cells, if any. For example, subnucleus medialis intermedius pars posterior only had a few retrogradely labeled cells, whereas the centrally located subnucleus medialis dorsalis pars posterior was almost devoid of labeled cells. At levels caudal to the obex, many retrogradely labeled neurons of the nucleus of the solitary tract were observed. Neurons immunoreactively labeled for tyrosine hydroxylase were mostly found within subnuclei, which contain anteromedial hypothalamic projection neurons. In subnuclei medialis superficialis pars posterior and lateralis dorsalis pars posterior, 87% of the retrogradely dye-labeled cells were also immunoreactively labeled, whereas in the caudal nucleus of the solitary tract (at levels caudal to the obex), 68% of the retrogradely labeled cells were immunoreactively labeled. Not all tyrosine hydroxylase containing cells had projections to the implantation site in the anteromedial hypothalamus since only 40% of the immunoreactive cells in the caudal nucleus of the solitary tract and 59% of the immunoreactive cells in the subnucleus medialis superficialis pars posterior were retrogradely labeled with Fast Blue.(ABSTRACT TRUNCATED AT 400 WORDS)     

Telencephalic afferents in the goldfish: an anterograde degeneration study

Terminals of ascending afferents in the telencephalon of the goldfish were examined by the Fink-Heimer method, after the unilateral transection of the peduncular region containing the forebrain bundles. The ascending projections from the more caudal regions of the brain were seen mainly on the ipsilateral side of the lesion. The ascending forebrain bundles gave widely distributed terminals throughout the area dorsalis of the telencephalon, especially in the area dorsalis telencephali pars centralis (Dc) and in the area dorsalis telencephali pars lateralis (DI). They also gave sparse terminals to the preoptic area (POA).     

Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish

The secondary gustatory nucleus of teleost fishes receives ascending fibers from the primary gustatory center in the medulla and sends efferent fibers to several nuclei in the inferior lobe of the diencephalon. Similar to the corresponding parabrachial nucleus in birds and mammals, the secondary gustatory nucleus of catfish consists of several cytoarchitectonically distinct subnuclei which receive input from different portions of the primary gustatory nuclei. However, it is unclear how the subnuclear organization relates to the processing of gustatory information in the hindbrain and the subsequent transmission of that information to the forebrain. To determine whether cells within different subnuclei of the secondary gustatory nucleus of channel catfish project to different diencephalic targets, single cells were intracellularly labeled with biocytin. Three subnuclei have been identified in the secondary gustatory nucleus: a medial subnucleus spanning most of the rostrocaudal extent of the nucleus, a central subnucleus and a dorsal subnucleus, the latter two located in the rostrolateral portion of the complex. Cells throughout the secondary gustatory nucleus typically possessed similar collateral projections to several nuclei in the inferior lobe, although four of the six cells filled in the medial subnucleus projected only to nucleus centralis. The only apparent subnucleus-specific projection pattern involved cells at the rostral edge of the secondary gustatory nucleus and in the secondary visceral nucleus. Axons of these cells terminated only in restricted portions of nucleus lobobulbaris. These results suggest that efferents from different subnuclei of the secondary gustatory nucleus of catfish, like those of the parabrachial nucleus of birds and mammals, do not possess simple, topographical projections to target nuclei in the diencephalon. © 1996 Wiley-Liss, Inc.     

Distinct, parallel pathways link the medial mammillary bodies to the anterior thalamus in macaque monkeys

Mammillary body neurons projecting to the thalamus were identified by injecting retrograde tracers into the medial thalamus of macaque monkeys. The source of the thalamic projections from the medial mammillary nucleus showed strikingly different patterns of organization depending on the site of the injection within the two anterior thalamic nuclei, anterior medialis and anterior ventralis. These data reveal at least two distinct modes by which the primate medial mammillary bodies can regulate anterior thalamic function. Projections to the thalamic nucleus anterior medialis arise mainly from the pars lateralis of the medial mammillary nucleus. A particularly dense source is the dorsal cap in the posterior half of the pars lateralis, a subregion that has not previously been distinguished. In contrast, neurons spread evenly across the medial mammillary nucleus gave rise to projections more laterally in the anterior thalamic nuclei. A third pattern of medial mammillary neurons appeared to provide the source of projections to the rostral midline thalamic nuclei. In contrast, the labeled cells in the lateral mammillary nucleus were evenly spread across that nucleus, irrespective of injection site. In addition to the established projection to anterior dorsalis, the lateral mammillary nucleus appears to project lightly to a number of other thalamic nuclei, including lateralis dorsalis, anterior medialis, anterior ventralis, and the rostral midline nuclei, e.g. nucleus reuniens. These anatomical findings not only reveal novel ways of grouping the neurons within the medial mammillary nucleus, but also indicate that the mammillothalamic connections support cognition in multiple ways.     

Ascending projections of the brain stem reticular formation in a nonmammalian vertebrate (the lizard Varanus exanthematicus), with notes on the afferent connections of the forebrain

In the present study an attempt has been made to analyze the ascending reticular projections in the lizard Varanus exanthematicus by means of the horseradish peroxidase (HRP) technique. Reticular projections ascending to the telencephalon were found to arise in the mesencephalon, but not caudal to the mesorhombencephalic border. HRP injections into the dorsal thalamus have demonstrated retrogradely labeled cells in the mesencephalic reticular formation, particularly at the level of the oculomotor nerve and in the medial magnocellular zone of the rhombencephalic reticular formation, predominantly rostrally. HRP infiltrations at the mesodiencephalic border damaged most of the fibers passing beyond this junction, resulting in the uptake of HRP by the damaged axons and subsequent labeling of the cell bodies or origin of ascending reticular projections to the diencephalon and telencephalon. From a comparison of cell-labeling patterns in cases of HRP injections of, respectively, the dorsal thalamus and the mesodiencephalic border, it seems likely that the nucleus reticularis medius and more sparsely the nucleus reticularis inferior project to ventral diencephalic structures (ventral thalamus and hypothalamus), whereas the midbrain reticular formation and the rostral parts of the rhombencephalic reticular formation (nuclei reticulares isthmi and superior) project to both the dorsal thalamus and more ventral diencephalic structures. Projections arising throughout the rhombencephalic reticular formation, but predominantly in the nucleus reticularis inferior, were found to ascend to the midbrain reticular formation. The present experimental data in the lizard Varanus exanthematicus are comparable to the findings in mammals, with the exception of the reticulo-oculomotor pathways which have not been analyzed so far in reptiles. In addition to the aforementioned ascending reticular projections, the present study has demonstrated projections ascending from monoamine cell groups, various diencephalics structures, as well as from neuronal groups involved in somatosensory, auditory, and gustatory systems. Projections were found from the locus coeruleus and the nucleus raphes superior to the telencephalon, as well as from the substantia nigra and the presumable reptilian homologue of the mammalian ventral tegmental area to the basal forebrain and the dorsal thalamus. Bilateral projections were demonstrated from the principal trigeminal nucleus to the telencephalon, reminiscent of the quintofrontal tract of birds. Ascending projections to the diencephalon were found to originate bilaterally in the descending trigeminal nucleus and the dorsal funicular nucleus. Auditory projections to the midbrain arise bilaterally in the superior olivary complex and in the cochlear nuclear complex. Finally, the ascending gustatory pathway arising in the nucleus of the solitary tract was found to project to the “parabrachial region”, which in its turn has extensive projections to the forebrain.     

Thalamic projections from the precentral motor cortex inMacaca fascicularis

Radioactive amino acids were injected into area 4 in 7 monkeys (Macaca fascicularis). Ipsilateral corticothalamic projections were traced to Olszewski's nucleus ventralis lateralis pars oralis and pars medialis, the nucleus ventralis posterior lateralis pars oralis, the nucleus ventralis posterior medialis and inferior and to the nucleus reticularis. Some fibers appeared to terminate in the ipsilateral nucleus ventralis lateralis pars caudalis, the nucleus lateralis posterior and the nucleus subthalamicus.A bilateral representation was found in the nucleus centrum medianum, possibly in the paracentralis-centralis lateralis complex and in the paralamellar portion of the nucleus medialis dorsalis. The contralateral labeling was due to fibers crossing via the massa intermedia and was most intense in the cases following injections into the motor face region.A somatotopic arrangement was clearly present in the nucleus ventralis lateralis pars oralis, the nucleus ventralis posterior lateralis pars oralis and the nucleus ventralis posterior medialis.The origin of the projections to the nucleus ventralis posterior medialis needs further clarification.     

GABA-like immunoreactivity of neurons in the chicken diencephalon and mesencephalon

The chick brain is a useful model system for studying the ontogeny and phylogeny of neural circuitry, especially that of the visual system. In this study the distribution of cells and processes showing GABA-like immunoreactivity (GABA+) in the diencephalon and mesencephalon of the posthatch chick was determined immunohistochemically with a polyclonal antibody to GABA and compared with the results of similar studies in mammals. Most of the small GABA+ cells were found in the chick visual centers such as the nucleus lateralis anterior, suprachiasmatic nucleus, ventral lateral geniculate, optic tract, dorsolateralis anterior pars lateralis, lentiformis mesencephali, ectomammillary nucleus, area pretectalis, and the optic tectum. Large GABA+ cells were found in the following nuclei: reticularis superior, posteroventralis thalami, subpretectalis, isthmi pars magnocellularis, interstitio-pretectosubpretectalis, mesencephalicus lateralis pars dorsalis. These large cell-containing nuclei receive projections from visual or auditory centers. GABA+ axons were found throughout the diencephalon and mesencephalon but were especially prominent in the ansa lenticularis, fasciculus medialis longitudinalis, and optic tract. The distribution of GABA+ cells in the chick is more widespread than in rodents and exhibits an increased association with the visual centers suggesting a correlation with the specialized visual requirements of the bird.