Afferent and efferent connections of the habenula in the rainbow trout (Oncorhynchus mykiss): An indocarbocyanine dye (DiI) study

The habenula is a conserved structure in the brain of vertebrates. With the aim of further understanding of the evolution of the habenular system in vertebrates, we studied the afferent and efferent connections of the habenula of the rainbow trout. Experiments included application of the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) into the habenula, telencephalon, pineal organ, posterior tubercle, and interpeduncular nucleus (IPN). The results obtained reveal a consistent pattern of habenular connections. Most afferents originate from three nuclei, one extending from the preoptic region to the rostral thalamus (the entopeduncular nucleus), the second located in the region of the hypothalamus-posterior tubercle and consisting of large bipolar cells (tuberculohabenular nucleus), and the third in the preoptic region (preoptic nucleus). A few large neurons of the locus coeruleus appeared to be labeled in some cases. The trout habenula also receives pineal and parapineal projections. Small labeled glial cells were observed in the thalamus around the fasciculus retroflexus and, sometimes, around the IPN. The most conspicuous efferents coursed in the fasciculus retroflexus to the IPN, the isthmal raphe, and the central gray. The existence of olfactohabenular or habenulotelencephalic projections is discussed. © 1996 Wiley-Liss, Inc.     

Afferent and efferent connections of the habenula in the larval sea lamprey (Petromyzon marinus L.): An experimental study

The habenula is an integrative center between the striatum and the limbic and motor systems. With the aim of achieving further understanding of the evolution of this structure in vertebrates, we carried out an experimental study of the afferent and efferent connections of the habenula of larval sea lamprey. Experimental procedures included in vivo and in vitro transport after injections of horseradish peroxidase (HRP) into the habenula, telencephalon, pineal organ, dorsal thalamus, and posterior tubercle as well as carbocyanine dye tracing (DiI). The combined results of these experiments showed that the pattern of habenular connections is very simple. Most afferents appear to originate from the lobus subhippocampalis and neighboring area, whereas the only efferents found coursed in the fasciculus retroflexus to the neuropil of the nucleus interpeduncularis. This neuropil comprises a commissural region in the rostral mesencephalon, two long bilateral areas extending in the basal mesencephalon and medulla oblongata to the trigeminal level, and, finally, a caudal commissural zone. The conspicuous habenular commissure contains interhemispheric fibers that appear to form occasional contacts within the habenulae. The lamprey habenula also receives a few immunocytochemically identified fibers (somatostatinergic, catecholaminergic, and serotoninergic fibers) from other sources. © 1994 Wiley-Liss, Inc.     

In vitro HRP-labeling of the fasciculus retroflexus in the lizard Gallotia galloti.

In order to test the usefulness of the in vitro HRP-labeling technique in the brains of small lizards, the fasciculus retroflexus was labeled in isolated brains of young specimens of the lizard Gallotia galloti by means of HRP applied with the tip of a micropipette located approximately midway along the descending course of the tract. Cells in the medial and lateral habenular nuclei were labeled retrogradely. Anterograde transport showed the course of the fasciculus retroflexus, first dorsoventrally into the paramedian prerubral tegmentum and then longitudinally into the isthmic nucleus interpeduncularis. Some fibers spread dorsally into the mesencephalic and isthmic tegmental fields. A substantial bundle continues caudally into nucleus raphe parvocellularis. Other fibers diverge rostral-wards from the point of inflexion of the fasciculus, coursing longitudinally in the medial forebrain bundle into the basal telencephalon. Some fibers course rostrally from the nucleus habenularis lateralis in the stria medullaris and could be followed to the dorsal septum.     

Distribution and characterization of neuropeptide Y-like immunoreactivity in the brain of the crested newt

The newt brain represents a simplified model for the increasingly complex vertebrate neuronal organization. The localization of neuropeptide Y-like (NPY-like) containing neurons in the brain of Triturus cristatus was studied by means of indirect immunofluorescence, peroxidase-antiperoxidase, and avidin-biotin techniques using a highly specific antiserum. NPY-like positive cell bodies were observed in several areas, most notably in the telencephalon (primordium hippocampi and amygdaloid complex), the preoptic and suprachiasmatic areas, the hypothalamus, the dorsal thalamus, the tegmentum, and the rhombencephalon (laterolateral grey column and raphe area). Nerve fibres were particularly abundant in the pallium, striatum, septum, amygdaloid, preoptic neuropils, and pars intercalaris diencephali. Bundles of NPY-immunoreactive fibres also were visualized in the dorsal thalamus and in the posterior hypothalamus. The pars intermedia lacked any NPY-like positive fibres. Neuronal processes also were found in the tectum mesencephali and in the body of the cerebellum. A prominent NPY-like fibre network was observed in the octavolateralis. Concentrations of NPY measured by means of a specific radioimmunoassay were threefold higher in the hypothalamus (15.2 +/- 1.3 ng/mg proteins) than in the rhombencephalon (4.9 +/- 0.3) and the mesencephalon (4.3 +/- 0.2). The concentration found in the telencephalon was 2.1 +/- 0.3 ng/mg proteins. Sephadex G-50 gel chromatography of whole brain extracts indicated the presence of high molecular weight forms of NPY-like material in addition to the authentic peptide. Both amphibian and mammalian NPY peptides had an apparent molecular weight of 4,000 daltons, as evidenced by immunoblotting analysis. High-performance liquid chromatography demonstrated, however, that the newt peptide was slightly less hydrophobic than porcine NPY. The present findings indicate that NPY-immunoreactive neurons are widely distributed in the brain of urodeles. Our data indicate that the NPY molecule has been relatively well preserved during evolution.     

Distribution of choline acetyltransferase (ChAT) immunoreactivity in the central nervous system of a chondrostean, the siberian sturgeon (Acipenser baeri)

All studies to date of cholinergic systems of bony fishes have been done in teleosts. To gain further insight into the evolution of the cholinergic systems of bony fishes, we have studied the brain of a chondrostean fish, the Siberian sturgeon (Acipenser baeri, Brandt), by using an antibody against choline acetyltransferase (ChAT). This study showed the presence of ChAT-immunoreactive (ChAT-ir) neurons in the preoptic region (parvocellular and magnocellular preoptic nuclei and suprachiasmatic nucleus), the periventricular and tuberal hypothalamus, the saccus vasculosus, the dorsal thalamus, and the habenula. The mesencephalic tegmentum contained ChAT-ir cells in the torus semicircularis and torus lateralis. The isthmus contained several cholinergic populations: the nucleus isthmi, the lateral nucleus of the valvula, the secondary visceral nucleus, and the dorsal tegmental nucleus. The motor neurons of the cranial nerves and the spinal motor column were strongly immunoreactive. The medial (sensory) trigeminal nucleus also contained a ChAT-ir neuronal population. The distribution of ChAT-ir neurons in the sturgeon brain showed some notable differences with that observed in teleosts, such as the absence of cholinergic cells in the telencephalon and the optic tectum. Several brain regions were richly innervated by ChAT-ir fibers, particularly the telencephalon, optic tectum, thalamus, posterior tubercle, and interpeduncular nucleus. The hypothalamo-hypophyseal tract, the tract of the saccus vasculosus, the fasciculus retroflexus, and an isthmo-mesencephalo-thalamic tract were the most conspicuous cholinergic bundles. Comparative analysis of these results suggests that teleosts have conserved most traits of the cholinergic system of the sturgeon, having acquired new cholinergic populations during evolution.     

Cholinergic systems in the rat brain: II. Projections to the interpeduncular nucleus

The cholinergic innervation of the interpeduncular nucleus was investigated by use of fluorescent tracer histology in combination with choline-O-acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. Following propidium iodide or Evans Blue infusion into the interpeduncular nucleus, brains were processed for co-localization of transported fluorescent label and ChAT and AChE. Control infusions of tracers were made into the ventral tegmental area. In order to delimit the course of putative cholinergic afferents to the interpeduncular nucleus from extra-habenular sources, knife cuts surrounding the habenular nuclei were performed. Somata containing propidium iodide that were highly immunoreactive for ChAT were found primarily in the vertical and horizontal limbs of the diagonal band, the magnocellular preoptic area, and the dorsolateral tegmental nucleus, also referred to as the laterodorsal tegmental nucleus. A few such co-labeled somata were also detected in the medial septal nucleus, substantia innominata, nucleus basalis, and pedunculopontine tegmental nucleus. A good correlation was observed between intensely-staining, AChE-containing and ChAT-positive neurons projecting to the interpeduncular nucleus from the aforementioned structures. Although the medial habenula contained numerous cells demonstrating transported label following interpeduncular infusion of fluorescent tracers, the ChAT-positivity associated with somata in that nucleus was weak compared to ChAT-like immunoreactivity in known cholinergic neurons in the basal forebrain and brainstem. Knife cuts that separated the habenular nuclei from the stria medullaris and neural regions lateral and posterior to those nuclei while leaving the fasciculus retroflexus intact resulted in a reduction of ChAT-like immunoreactivity in the medial habenular nucleus, fasciculus retroflexus, and interpeduncular nucleus. These data suggest (1) that the cholinergic innervation of the interpeduncular nucleus derives primarily from ChAT-positive cells in the basal forebrain and dorsolateral tegmental nucleus and (2) that putative cholinergic fibers having their origin in the medial habenula, if they exist, constitute a minor portion of the cholinergic input to the interpeduncular nucleus.     

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16,21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN...     

Organization of tyrosine-hydroxylase immunopositive neurons in the brain of the crested newt, Triturus cristatus carnifex

The localization of neurons, fibers, and terminals containing tyrosine hydroxylase (TH)-like immunoreactivity was studied in the brain of the crested newt by using an antiserum to rat phaeochromocytoma tyrosine hydroxylase. Immunoreactive cells and fibers were found in the spinal cord, the medulla oblongata (lateral periventricular areas), and the acousticolateral area. In the tegmentum mesencephali, two bilateral clusters of labelled cells were localized in the ventrolateral periventricular gray extending toward the caudal hypothalamus. In the hypothalamic tuberal lobes, the TH-like reactive neurons, frequently of CSF-contacting type, lined the dorsal wall of the lateral infundibular recesses. A thick network of TH-like reactive nerve fibers and terminals was observed in the perivascular zone of the median eminence and in the adenohypophysial pars intermedia. A number of labelled cell bodies were also found in the dorsal thalamus (pars intercalaris diencephali), the paraventricular organ, and the ventral wall of the preoptic recess. In the telencephalon, immunoreactive innervation was identified in the striatum, together with immunopositive cell bodies in the olfactory bulbs. The pattern of organization of TH-immunoreactive systems in the newt showed, except for some peculiarities (e.g., the labelled cell bodies in dorsal thalamus), close similarities to the arrangement typical of mammals.     

Somatostatin-like immunoreactivity in the brain of the urodele amphibian Pleurodeles waltl. Colocalization with catecholamines and nitric oxide

The neuronal structures with somatostatin-like immunoreactivity have been studied in the brain of the urodele amphibian Pleurodeles waltl. Intense immunoreactivity was observed in neurons and fibers distributed throughout the brain. Within the telencephalon, the subpallial regions were densely labeled containing both cells and fibers, primarily in the striatum and amygdala. The majority of the somatostatin immunoreactive neurons were located in the preoptic area and hypothalamus, although less numerous cells were also found in the thalamus. A conspicuous innervation of the median eminence was revealed, which arises from the hypothalamic cell populations. In the brainstem, intense fiber labeling was present in the tectum and tegmentum, whereas cell bodies were located only in the tegmentum of the mesencephalon and in the interpeduncular, raphe and reticular nuclei of the rhombencephalon. Longitudinal fiber tracts throughout the brainstem were observed and they continued into the spinal cord in the laterodorsal funiculus. The localization of somatostatin in catecholaminergic and nitrergic neurons was studied by double labeling techniques with antisera against tyrosine hydroxylase and nitric oxide synthase. Catecholamines and somatostatin only colocalized in a cell population in the ventral preoptic area. In turn, the striatum and amygdala contained neurons with somatostatin and nitric oxide synthase. Our results demonstrated that the somatostatin neuronal system in the brain of Pleurodeles waltl is consistent with that observed in anuran amphibians and shares many characteristics with those of amniotes. Colocalization of somatostatin with catecholamines and nitric oxide is very restricted in the urodele brain, but in places that can be easily compared to those reported for mammals, suggesting that interactions between these neurotransmitter systems are a primitive feature shared by tetrapod vertebrates.     

Paraventricular organ of the lungfish Protopterus dolloi: morphology and projections of CSF-contacting neurons

The morphology and projections of neurons in the paraventricular organ (PVO) were studied by means of silver impregnation after intraocular application of cobaltous lysine in the lungfish Protopterus dolloi. Cobalt-labeled neurons were found exclusively in the PVO in the dorsal and infundibular hypothalamus. These bipolar neurons possess one CSF-contacting process that protrudes into the ventricular lumen with a club-shape ending and a thick, ramifying process directed into the hypothalamic neuropil; the ependymofugal processes form intra- and extrahypothalamic projections. Impregnated fibers from paraventricular neurons cross in infundibular and hypothalamic commissures, the commissure of the posterior tuberculum, the postoptic, the habenular, and the anterior commissures. Projections to the infundibulum and the median eminence are relatively sparse; no fibers are labeled in the pituitary gland. Ascending projections to the forebrain are extensive. Major targets include the dorsal hypothalamus, the periventricular preoptic nuclei, the habenula, the subhabenular region, the anterodorsal thalamus, and the medial telencephalic hemisphere (septum). Most ascending fibers follow the medial forebrain bundle; others course in the fasciculus retroflexus and terminate in rostral parts of the ipsilateral habenula. Descending fibers run caudally along the ventral floor of the brainstem. They terminate in the neuropil of the mesencephalic tegmentum, ventral tectum, isthmic region, ventral portions of the reticular formation throughout the rhombencephalon, and extend into the spinal cord. Intraocular application of cobaltous lysine results in selective impregnation of neurons in the PVO and their ascending and descending projections, presumably via uptake of tracer from vascular circulation. These projections do not represent retinofugal or retinopetal projections. We provide conclusive evidence for the existence of a PVO in Protopterus. On the basis of PVO location and acetylcholinesterase histochemistry, we propose subdivisions of the infundibular hypothalamus corresponding to those in amphibians. Ascending PVO projections appear to be particularly well developed in lungfish compared with other species and may be related to specialized endocrine mechanisms in this group of vertebrates.     

Nuclear organization of the bullfrog diencephalon

A cytoarchitectonic analysis was performed on the diencephalic nuclei of the bullfrog, Rana catesbeiana. The epithalamus contains two widely recognized habenular nuclei. The thalamus has three subdivisions: dorsal and ventral thalamus, and posterior tuberculum. The dorsal thalamus may be further parcelled into anterior, middle, and posterior zones. Connectional data from other studies support this zonation. The anterior zone projects to the telencephalic pallium. The middle zone nuclei receive a strong input from the midbrain roof and project to the telencephalic striatal complex. The posterior zone nuclei do not appear to project to the telencephalon; they may eventually be placed in the pretectum, a transitional area between the diencephalon and mesencephalon. Two of the ventral thalamic populations have been frequently placed in the dorsal thalamus and called the nucleus rotundus and the lateral geniculate nucleus. These terms imply homology with sauropsid dorsal thalamic nuclei, but our analysis and current connectional information do not support such homologies. We have given these populations more neutral names. The hypothalamus is divisible into a preoptic and infundibular hypothalamus, and the preoptic area can be further separated into anterior and posterior preoptic areas. The posterior area contains the magnocellular preoptic nucleus and a dorsal arm of this nucleus, often placed in the ventral thalamus, was recognized. We have tentatively placed the posterior entopeduncular nucleus in the hypothalamus.     

Projections of the olfactory bulb and nervus terminalis in the silver lamprey

The connections of the olfactory bulb were traced using horseradish peroxidase. A homologue of the medial olfactory tract in gnathostomes projects to the ipsilateral septal nucleus, preoptic area and, possibly, the rostral striatum. A homologue of the lateral olfactory tract projects to the ipsilateral lateral pallium, dorsal pallium and, possibly, the medial pallium, as well as to the posterior diencephalon. A component of the lateral olfactory tract decussates in the habenular and posterior commissures and distributes to the contralateral hemisphere and caudal diencephalon. A dorsal component of secondary olfactory fibers terminates, ipsilaterally, in a dorsomedially situated neuropil that has previously been interpreted as a single glomerulus of the olfactory bulb or as an accessory olfactory bulb, as well as in the contralateral olfactory bulb after decussation in the dorsal commissure. Afferents to the olfactory bulb arise from the ipsilateral dorsal pallium, lateral pallium, a cell-poor region adjacent to the preoptic area, and the midbrain tegmentum. The extent of the secondary olfactory projections in silver lampreys could be interpreted to support the phylogenetic hypothesis that all regions of the telencephalon received secondary olfactory projections in the earliest vertebrates, but this interpretation is not unequivocal, due to questions concerning the pallial homologues in lampreys and gnathostomes. Application of horseradish peroxidase to the olfactory epithelium revealed projections to the striatum, preoptic area, hypothalamus and posterior tuberculum that are comparable to projections of the nervus terminalis in other vertebrates.     

Distribution of galaninlike immunoreactivity in the rat central nervous system

The localization of galanin (GAL) immunoreactive (IR) neuronal structures in the rat central nervous system has been investigated by using the indirect immunofluorescence technique. GAL-IR structures were seen in high concentrations in the hypothalamus, medulla oblongata, and spinal cord. Less extensive systems were detected in the telencephalon, thalamus, mesencephalon, and pons, while virtually no GAL-positive structures were seen in the olfactory bulb and cerebellum. Major populations of cell bodies staining for GAL-like material were seen in many areas. In the telencephalon somata were revealed in the bed nucleus of stria terminalis, in the nucleus of the diagonal band, medial septum, and in the medial aspects of the central amygdaloid nucleus, and in small numbers in cortical areas. The anterodorsal and periventricular nuclei of the thalamus contained positive cell bodies. In the hypothalamus GAL-IR somata were seen in the medial and lateral preoptic nuclei, arcuate nucleus, periventricular nucleus, in the dorsomedial nucleus, in the medial forebrain bundle area, in the tubular, caudal, accessory, supraoptic, and paraventricular magnocellular nuclei and lateral to the mammillary recess. The dorsal raphe nucleus hosted a large number of GAL-positive somata. Locus coeruleus of the pons contained a large number of GAL-IR perikarya. In the medulla oblongata positive somata were found in the caudal spinal trigeminal nucleus, the nucleus of the solitary tract, and in the ventral lateral area just rostral to area postrema. Small cell bodies were detected in the superficial layers of the dorsal horn of the spinal cord at all levels and in lamina X at lumbar levels. Analysis of GAL-positive fibers in the telencephalon revealed highly or medium-dense networks in the lateral septal nucleus, in the bed nucleus of stria terminalis, and in the central and medial amygdaloid nuclei. Positive fibers were found in the thalamus in and around the periventricular nucleus as well as in the lateral habenular nucleus and extending in a lateral, caudal direction from the third ventricle and fasciculus retroflexus to the lateral tip of the medial lemniscus. In the hypothalamus the external layer of the median eminence contained a very dense fiber network. Dense or medium-dense GAL-IR networks were detected in the periventricular nucleus, throughout the medial and lateral preoptic areas, in the medial forebrain bundle area, in the dorsomedial nucleus, and lateral to the mammillary recess. In the pons GAL-IR fibers were seen in the parabrachial nuclei, dorsal to the superior olive, and in the periaqueductal central gray.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cobalt injected into the right and left fasciculi retroflexes clarifies the organization of this pathway

A cobaltic lysine complex was injected separately into the right and left fasciculi retroflexes of the frog. This tracing technique labeled, in a Golgi-like manner, the neurons which initiate the fasciculi retroflexes and revealed details of their morphological pattern. The fasciculi retroflexes originate from various neurons distributed in the diencephalon and mesencephalon, but their main source is the habenular nuclei. In the frog there are dorsal and ventral habenulae which are homologous to the medial and lateral habenulae, respectively, of mammals. In the frog the dorsal habenulae are strikingly asymmetric. Our study shows that the fasciculus retroflexus is composed of several compact separated bundles of fibers and that the fibers originating from the dorsal habenular nuclei project to the interpeduncular nucleus, while those originating from the ventral habenular nuclei project beyond the interpeduncular nucleus, but so far we have not been able to show the exact site of their termination. The labeling of cells within the interpeduncular nucleus raises the possibility that the habenulo-interpeduncular tract is reciprocal in function. The finds support our previously reported hypothesis on the theoretical interpretation of the functional circuitry of the frog habenulo-interpeduncular system.     

Connections of the ventral telencephalon (subpallium) in the zebrafish (Danio rerio)

Connections of the medial precommissural subpallial ventral telencephalon, i.e., dorsal (Vd, interpreted as part of striatum) and ventral (Vv, interpreted as part of septum) nuclei of area ventralis telencephali, were studied in the zebrafish (Danio rerio) using two tracer substances (DiI or biocytin). The following major afferent nuclei to Vd/Vv were identified: medial and posterior pallial zones of dorsal telencephalic area, and the subpallial supracommissural and postcommissural nuclei of the ventral telencephalic area, the olfactory bulb, dorsal entopeduncular, anterior and posterior parvocellular preoptic and suprachiasmatic nuclei, anterior, dorsal and central posterior dorsal thalamic, as well as rostrolateral nuclei, periventricular nucleus of the posterior tuberculum, posterior tuberal nucleus, various tuberal hypothalamic nuclei, dorsal tegmental nucleus, superior reticular nucleus, locus coeruleus, and superior raphe nucleus. Efferent projections of the ventral telencephalon terminate in the supracommissural nucleus of area ventralis telencephali, the posterior zone of area dorsalis telencephali, habenula, periventricular pretectum, paracommissural nucleus, posterior dorsal thalamus, preoptic region, midline posterior tuberculum (especially the area dorsal to the posterior tuberal nucleus), tuberal (midline) hypothalamus and interpeduncular nucleus. Strong reciprocal interconnections likely exist between septum and preoptic region/midline hypothalamus and between striatum and dorsal thalamus (dopaminergic) posterior tuberculum. Regarding ascending activating/modulatory systems, the pallium shares with the subpallium inputs from the (noradrenergic) locus coeruleus, and the (serotoninergic) superior raphe, while the subpallium additionally receives such inputs from the (dopaminergic) posterior tuberculum, the (putative cholinergic) superior reticular nucleus, and the (putative histaminergic) caudal hypothamalic zone.     

Afferent and efferent connections of the diencephalic prepacemaker nucleus in the weakly electric fish,Eigenmannia virescens: interactions between the electromotor system and the neuroendocrine axis

The afferent and efferent connections of the gymnotiform central posterior nucleus of the dorsal thalamus and prepacemaker nucleus (CP/PPn) were examined by retrograde and anterograde transport of the small molecular weight tracer, Neurobiotin. The CP/PPn was identified by physiological assay and received a local iontophoretic injection of Neurobiotin. Retrogradely labeled somata were observed in the ventral telencephalon, hypothalamus, and the pretectal nucleus electrosensorius. Anterogradely labeled fibers were traced from the CP/PPn to the ventral telencephalon, the hypothalamus, the neuropil immediately adjacent to the most rostral subdivision of the nucleus electrosensorius, the optic tectum, and the pacemaker nucleus. Retrograde transport of tracer following injections into the ventral telencephalon, preoptic area, lateral hypothalamus, tectum, and pacemaker nucleus confirmed these efferent targets. A rostromedial subarea of the CP/PPn can be identified that projects to basal forebrain regions and to a lateral region of the CP/PPn that contains afferents to the pacemaker. Many of the targets, which are connected with the CP/PPn, have been linked to reproductive behavior or neuroendocrine control in other fishes. A comparative analysis reveals that the efferent pathways of the CP/PPn appear similar and may be homologous to efferent pathways of some components of the auditory thalamus among tetrapods. J. Comp. Neurol. 383:18–41, 1997. © 1997 Wiley-Liss, Inc.     

Neuroanatomical distribution of androgen and estrogen receptor-immunoreactive cells in the brain of the male roughskin newt

Immunohistochemistry was used to investigate the neuroanatomical distribution of androgen and estrogen receptors in brains of adult male roughskin newts, Taricha granulosa, collected during the breeding season. Immunoreactive cells were found to be widely distributed in specific brain areas of this urodele amphibian. Androgen receptor-immunoreactive (AR-ir) cells were observed in the olfactory bulbs, habenula, pineal body, preoptic area, hypothalamus, interpeduncular nucleus, area acusticolateralis, cerebellum, and motor nuclei of the medulla oblongata. Estrogen receptor-immunoreactive (ER-ir) cells were found in the lateral septum, amygdala pars lateralis, pallium, preoptic area, hypothalamus, and dorsal mesencephalic tegmentum. This immunocytochemical study of the newt brain reveals AR-ir and ER-ir cells in several regions that have not been previously reported to contain androgen and estrogen receptors in non-mammalian vertebrates. Additionally, the distribution of AR-ir and ER-ir cells in the newt brain, in general, is consistent with previous studies, suggesting that the distribution of sex steroid receptor-containing neurons in some brain regions is relatively conserved among vertebrates. © 1996 Wiley-Liss, Inc.     

Substance P containing and cholinergic projections from the habenula

Electrolytic lesions and surgical transection of the habenulo-interpeduncular-ventrotegmental tract have established the existence of separate habenulo-interpeduncular-ventrotegmental substance P and cholinergic projections. Micro-knife lesions separating the habenula nuclei showed the medial habenular nucleus to be the source of substance P fibres running via the fasciculus retroflexus to the ventral tegmental area. The lateral habenular nucleus receives a substance P projection from the medial habenular nucleus and is the source of cholinergic projection to the interpeduncular nucleus and to the medial habenular nucleus. Lesions of the ventrotegmental-interpeduncular area did not modify the levels of substance P and choline acetyltransferase in the habenula. These observations suggested that there are no substance P or ACh containing afferents to the habenula from the ventrotegmental-interpeduncular area and the accumulation of substance P and AChE proximal to but not caudal to transections of the fasciculus retroflexus confirmed this view.     

Efferent connections of the habenular nuclei in the rat.

The efferent connections of the medial (MHb) and lateral (LHb) habenular nuclei in the rat were demonstrated autoradiographically following small injections of tritiated amino acids localized within various parts of the habenular complex. Comparison of individual cases led to the following conclusions. MHb efferents form the core portion of the fasciculus retroflexus and pass to the interpeduncular nucleus (IP) in which they terminate in a topographic pattern that refects 90 degrees rotations such that dorsal MHb projects to lateral IP, medial MHb to ventral, and lateral MHb to dorsal IP. Most MHb fibers cross in the interpeduncular necleus in the "figure 8" pattern described by Cajal, and terminate throughout the width of IP with only moderate preference for the ipsilateral side. However, the most dorsal part of MHb projects almost exclusively to the most lateral IP zone in a cluster pattern that is particularly dense on the ipsilateral side. The MHb appears to have no other significant projections, but very sparse MHb fibers may pass to the supracommissural septum and to the median raphe nucleus. Except for some fibers passing ventrally into the mediodorsal nucleus, all of the LHb efferents enter the fasciculus retroflexus and compose the mantle portion of the bundle. No LHb projections follow the stria medullaris. In the ventral tegmental area LHb efferents become organized into groups that disperse in several directions: (a) Rostrally directed fibers follow the medial forebrain bundle to the lateral, posterior and dorsomedial hypothalamic nuclei, ventromedial thalamic nucleus, lateral preoptic area, substantia innominata and ventrolateral septum. (b) Fibers turning laterally distribute to the substantia nigra, pars compacta (SNC); a small number continue through SNC to adjacent tegmentum. (c) The largest contingent of LHb efferents passes dorsocaudally into paramedian midbrain regions including median and dorsal raphe nuclei, and to adjacent tegmental reticular formation. Sparse addition LHb projections pass to the pretectal area, superior colliculus, nucleus reticularis tegmenti pontis, parabrachial nuclei and locus coeruleus. No LHb projections appear to involve the interpeduncular nucleus. All of these connections are in varying degree bilateral, with decussations in the supramammillary region, ventral tegmental area and median raphe nucleus. On the basis of differential afferent and efferent connections, the LHb can be divided into a medial (M-LHb) and a lateral (L-LHb) portion. The M-LHb, receiving most of its afferents from limbic regions and only few from globus pallidus, projects mainly to the raphe nuclei, while L-LHb, afferented mainly by globus pallidus and in lesser degree by the limbic forebrain, projects predominantly to a large region of reticular formation alongside the median raphe nucleus. Both M-LHb and L-LHb, however, project to SNC. The reported data are discussed in correlation with recent histochemical findings.