Ventromedial Part Research Articles

Superior colliculus projections to midline and intralaminar thalamic nuclei of the rat.

The superior colliculus (SC) projections to the midline and intralaminar thalamic nuclei were examined in the rat. The retrograde tracer cholera toxin beta (CTb) was injected into one of the midline thalamic nuclei-paraventricular, intermediodorsal, rhomboid, reuniens, submedius, mediodorsal, paratenial, anteroventral, caudal ventromedial, or parvicellular part of the ventral posteriomedial nucleus-or into one of the intralaminar thalamic nuclei-medial parafascicular, lateral parafascicular, central medial, paracentral, oval paracentral, or central lateral nucleus. After 10-14 days, the brains from these animals were processed histochemically, and the retrogradely labeled neurons in the SC were mapped. The lateral sector of the intermediate gray and white layers of the SC send axonal projections to the medial and lateral parafascicular, central lateral, paracentral, central medial, rhomboid, reuniens, and submedius nuclei. The medial sector of the intermediate and deep SC layers project to the parafascicular and central lateral thalamic nuclei. The paraventricular thalamic nucleus is innervated almost exclusively by the medial sectors of the deep SC layers. The superficial gray and optic layers of the SC do not project to any of these thalamic areas. The discussion focuses on the role these SC-thalamic inputs may have on forebrain circuits controlling orienting and defense (i.e., fight-or-flight) reactions.

Immunohistochemical evidence and ultrastructural compartmentalization of a new antioxidant enzyme in the rat substantia nigra.

We previously described in the rat the presence of dehydroascorbate reductase, an enzyme regenerating ascorbic acid, which is constantly lost during oxidative processes occurring at a fast rate within the central nervous system. In the present study, we specifically evaluate the occurrence of this enzyme in the rat substantia nigra by using immunohistochemistry, and by analyzing the neuronal compartmentalization of dehydroascorbate reductase within nigral neurons by immunoblotting and transmission electron microscopy coupled with immunocytochemistry. The enzyme occurs in various portions of the substantia nigra, but it is more abundant in the ventromedial part extending through the ventral tegmental area, and the dorsal portion, involving the pars compacta. Within nigral neurons, the cytosolic enzyme is present in a perinuclear position, close to mitochondria, and in the nuclear membrane; we also found the enzyme in nigral axons close to the myelin sheath. In addition, dehydroascorbate reductase was present in the nucleus of nigral neurons. The nuclear occurrence of the enzyme was confirmed by immunocytochemical labelling and immunoblotting of isolated nuclei. The nuclear enzyme was constantly evident as clusters of immunogold particles on chromatin. This localization suggests new roles for dehydroascorbate reductase (eg. prevention of DNA oxidative damage and regulation of gene transcription).

The Vestibular Nuclei and Vestibuloreticular Connections in the Mallard (Anas platyrhynchos L.)

The vestibular apparatus provides information about the position and movements of the head. Craniocervical muscles position the head with respect to the upper part of the neck. Motoneurons innervating these muscles are located in the supraspinal nucleus and ventral horn of the rostral cervical cord. Premotor neurons of craniocervical muscles have been found in the medial two-thirds of the medullary reticular formation: the ventromedial part of the parvocellular reticular formation and the gigantocellular reticular formation. In the present study, projections from vestibular nuclei upon craniocervical premotor neurons were investigated using anterograde and retrograde tracers. Vestibulospinal fibers run bilaterally in the medial vestibulospinal tract and ipsilaterally in the lateral vestibulospinal tract. Vestibuloreticular projections are mainly ipsilateral, and originate from the n. vestibularis lateralis pars ventralis and pars dorsalis, and from the n. vestibularis descendens. Terminal labeling is found in the border zone between the parvocellular and gigantocellular reticular formation. These projections show that in addition to direct bilateral vestibulo-craniocervical projections an indirect vestibular pathway to craniocervical motor nuclei exists. The direct pathway probably is the neural substrate for the vestibulocollic reflex, whereas the vestibular projection upon the reticular formation might influence head orientation during various kinds of activities, such as pecking, preening and so on.

Vasopressin (V1a) receptor binding, mRNA expression and transcriptional regulation by androgen in the Syrian hamster brain.

Arginine vasopressin plays an important role in the regulation of social behaviours in rodents. In the Syrian hamster, vasopressin injected directly into the brain stimulates scent marking and aggressive behaviour in a steroid dependent manner and is therefore a useful model for investigating steroid-peptide-behaviour interactions. In this study, we used in situ hybridization and radioligand binding assays on adjacent sections of hamster brains to compare the relative distribution of vasopressin (V1a) receptor mRNA and V1a receptor binding. V1a receptor mRNA and binding are abundant in the lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus, anterodorsal thalamus and suprachiasmatic nucleus. Moderate receptor binding and low levels of receptor mRNA are present in the central nucleus of the amygdala and a lateral zone from the medial preoptic area through the anterior hypothalamus. V1a receptor mRNA is anatomically more restricted in several areas compared to the ligand binding pattern, which is consistent with significant spread of receptor protein along neuronal processes. Comparison of V1a receptor ligand binding and mRNA in intact, castrated, and castrated-testosterone treated animals reveals that V1a receptors in the medial preoptic nucleus are regulated by androgen, most likely by an upregulation of V1a receptor gene expression in a cluster of neurones concentrated in the ventromedial part of this nucleus. This study confirms the presence of the V1a subtype of vasopressin receptors in behaviourally important regions of the hamster brain and suggests that transcriptional regulation by gonadal steroids may play a role in modulating behavioural sensitivity to vasopressin.

Limited participation of 5-HT 1A and 5-HT 2A/2C receptors in the clozapine-induced Fos-protein expression in rat forebrain regions

Through the development of tolerance following long-term clozapine treatment, we investigated whether 5-HT 1A and 5-HT 2A/2C receptors participate in the clozapine-induced Fos-protein expression in the rat forebrain. Tolerance exists when the acutely increased Fos responses to a challenge dose of the 5-HT 1A and 5-HT 2A/2C agonists 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane-hydrochloride (DOI) and 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT), respectively, given simultaneously to rats, are attenuated after 3-week clozapine (20 mg kg −1 day −1 i.p.) pretreatment. As compared to the acute effects of clozapine, the Fos responses to concomitant administration of the 5-HT receptor agonists DOI (2.5 mg kg −1 i.p.) and 8-OH-DPAT (2.5 mg kg −1 i.p.) were more pronounced in the prefrontal cortex, the nucleus accumbens core and the dorsomedial and ventromedial striatum, areas in which clozapine (20 mg kg −1 i.p.) exhibited marginal effects. In the hypothalamic paraventricular nucleus, both clozapine and DOI/8-OH-DPAT induced a remarkably high number of Fos-positive nuclei. Long-term clozapine pretreatment attenuated the acutely induced Fos expression of the 5-HT receptor agonists in the nucleus accumbens core, the dorsomedial and ventromedial parts of the striatum and the lateral septum, indicating (partial) common sites of action of the agents in these brain regions. No tolerance was found in the nucleus accumbens shell and the hypothalamic paraventricular nucleus and the central amygdala, suggesting that the clozapine-induced Fos responses, though distinct in these regions, are independent of 5-HT receptors. The prefrontal cortex and the dorsolateral striatum indicated only a tendency towards tolerance. In addition, the involvement of the tested 5-HT receptor agonists in the clozapine-enhanced release of plasma corticosterone became apparent. The present results indicate that the clozapine-induced patterns of Fos expression in the rat forebrain can only be in part attributed to an interaction with 5-HT 1A/2A/2C receptors.

Neural circuits and topographic organization of the basal ganglia and related regions.

The present review was attempted to analyze the multiple channels of basal ganglia-thalamocortical connections, and the connections of their related nuclei. The prefrontal and motor areas consist of a number of modules, which seem to provide multiple subloops of the basal ganglia-thalamocortical connections in subhuman primates. There may be a great degree of convergence of the limbic, associative and motor loops at the level of the striatum, substantia nigra, pallidum, and the subthalamic nucleus as well as the pedunculopontine nucleus. Nigral dopaminergic neurons receive limbic input directly as well as indirectly through the striosomes in the striatum. Dopamine contributes to behavioral learning by signaling motivation and reinforcement. The pedunculopontine nucleus might be involved in behavioral state control, learning and reinforcement processes, locomotion and autonomic functions. Each subdivision of the motor areas receives a mixed and weighted transthalamic input from both the cerebellum and basal ganglia. In particular, based on the author's data, the hand/arm motor area and adjacent premotor area receive strong superficial basal ganglia-thalamocortical projections as well as the deep cerebello-thalamocortical projections. These areas, have very dense corticocotrical connections with other cortical areas, receive polymodal afferents from the parietal and temporal cortices, and integrated information, via multiple routes, from the prefrontal cortex. The author suggests that the ventrolateral part of the caudal medial pallidal segment (GPi) and the ventromedial part of the GPi are linked directly to these areas by ways of the oral part of ventral lateral nucleus (VLo) and the ventral part of the parvicellular part of ventral anterior nucleus (VApc), respectively. These connections are thought to be involved in the acquisition and coordination of motor sequences.

The parahippocampal gyrus in Alzheimer's disease. Clinical and preclinical neuroanatomical correlates.

The human parahippocampal gyrus forms a large part of the limbic lobe along the ventromedial part of the temporal cortical mantle. It is a variable and complicated cortex in terms of structure, and the latter is aggravated further by interfaces with the anterior insula anteriorly and the cingulate gyrus and occipital lobe posteriorly. Additional complications relate to its lateral border with the temporal cortex and especially the sulcal configurations that define this junction. The rhinal sulcus, which separates parahippocampal and temporal cortices in other species, including the anthropoid apes, is either lacking or rudimentary in the human brain. Thus, defining this junction requires cytoarchitectural examination and precludes the use of mere inspection of sulcal existing patterns. The cortical areas that form the parahippocampal gyrus are vulnerable to pathological changes in Alzheimer's disease (AD), and its entorhinal and perirhinal subdivisions are both the most heavily damaged cortical areas and the focus for disease onset. The neurons that acquire neurofibrillary tangles (NFTs) occupy the junction of the isocortical mantle with the limbic cortical mantle, but share, or partially share, a vulnerability phenotype with large neurons in both domains. The differential expression of this phenotype across time creates the false impression of NFT spread in cross-sectional comparisons of AD brains. The questions of what this phenotype is and why it is expressed first in the perirhinal and entorhinal cortices of the parahippocampal gyrus are the central molecular biological/neuroanatomical questions in understanding the etiology of AD.

Effects of neurotensin receptor antagonists on the firing rate of rat ventral pallidum neurons.

Using anaesthetized adult rats, we compared the effects of i.v. injections of neurotensin receptor antagonists (SR48692 and SR142948), haloperidol and clozapine on neuronal firing rate in the two ventral pallidal areas. SR48692 (0.5, 1 and 2 mg/kg, i.v.) induced a dose-dependent inhibition of firing rate in two thirds of neurons in the ventromedial part without any effect in the ventrolateral part. These effects are in keeping with the preferential neurotensin immunoreactivity distribution reported in the ventral pallidum. The classical antipsychotic drug haloperidol (0.5 mg/kg, i.v.) induced an inhibition of neuronal firing rate in both ventral pallidal areas whereas the atypical antipsychotic drug clozapine (20 mg/kg, i.v.), like the neurotensin receptor antagonist SR48692, inhibited cell firing only in the ventromedial part.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immmunohistochemistry for tyrosine hydroxylase, dopamine-ß-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus, the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (A1 group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

Orexin-A and -B activate the neuronal activity in the ventromedial part of the rat arcuate nucleus

Orexin-A and -B activate the neuronal activity in the ventromedial part of the rat arcuate nucleus

Effect of amphetamine on the expression of the metabotropic glutamate receptor 5 mRNA in developing rat brain.

Mechanisms underlying the acute effects of amphetamine (AMP) were examined by monitoring the expression of metabotropic glutamate receptor 5 (mGluR5) and specific 3H-glutamate binding in the developing rat brain. Each of the postnatal day (P) 4, P21 and P60 rats received one intraperitoneal injection of AMP, 5 mg/kg or saline and were sacrificed one hour later. In situ hybridization analysis revealed that the AMP treatment raised the levels of the mGluR5 mRNA by 9-28% in the neurons of the layer 5 of motor and somatosensory cortices, whereas reduced the levels by 12-28% in the layer 5 of perirhinal cortex and the ventromedial part of caudate-putamen of the 3 ages. In the layer 2/3 neurons of cingular cortex, an 18% higher and 14% and 22% lower than control levels of the mRNA were detected in the P4 and in the P21 and P60 rats injected with AMP. Moreover, the levels of mGluR5 mRNA in the hippocampi and dentate gyri were elevated by AMP to 110-151% of controls in the rats of 3 ages. Reversible 3H-glutamate binding assay showed an increase of 25% and a 12% decrease in the binding levels in the cortices of AMP-treated P4 and P21 rats. The AMP administration also produced a 27% reduction and 62% elevation in the binding of the hippocampi of P4 and P60 rats. The results reveal age- and region-dependent changes in the expression of the glutamate receptors induced by AMP and may indicate differential plastic capability of the neurons to the drug perturbation.

Neuron-specific expression of cationic amino acid transporter 3 in the adult rat brain

CAT3 (cationic amino acid transporter 3) is a member of the murine CAT family which bears a system y + transport activity. On the Northern blot of adult rat tissues, the expression of CAT3 is restricted to the brain. In the present study, cellular localization of CAT3 mRNA and protein in the adult rat brain sections was examined by in situ hybridization with cRNA and immunostaining with a CAT3-specific antiserum, respectively. CAT3 mRNA was present both in the cerebral and cerebellar gray matter but most prominently in the nuclei located in the ventromedial part of the brain. These included preoptic nucleus, hypothalamic nucleus, reticular nucleus of thalamus, substantia nigra, central gray around the third ventricle and amygdala. CAT3 protein was also detected both in the cerebral and cerebellar gray matter and strong immunostaining was obtained in the olfactory cortex, hippocampus and cerebellar granular and Purkinje cell layers. Observations at higher magnifications revealed that both mRNA and protein were expressed by neurons but neither by glial nor endothelial cells. These results confirm the neuron-specificity of CAT3 in the adult rat brain and indicate that CAT3 is responsible for the neuronal system y + activity. The discrepancy between the distribution of mRNA and its translation product suggests a regional difference in the translation rate of the CAT3 transcript.

Input-output relationships of the dorsal nucleus of the lateral lemniscus: Possible substrate for the processing of dynamic spatial cues

One organizing principle of the auditory system is the progressive representation of best tuning frequency. Superimposed on this tonotopy are nucleotopic organizations, some of which are related to the processing of different spatial cues. In the present study, we correlated asymmetries in the outputs of the dorsal nucleus of the lateral lemniscus (DNLL) to the two inferior colliculi (ICs), with asymmetries in the inputs to DNLL from the two lateral superior olives (LSOs). The positions of DNLL neurons with crossed and uncrossed projections were plotted from cases with unilateral injections of retrograde tracers in the IC. We found an orderly dorsal-to-ventral progression to the output that recapitulated the tonotopy of DNLL. In addition, we found a nucleotopic organization in the ventral (high-frequency) part of DNLL. Neurons with projections to the ventromedial (high-frequency) part of the contralateral IC were preferentially located ventrolaterally in DNLL; those with projections to the ventromedial part of the ipsilateral IC were preferentially located ventromedially in DNLL. This partial segregation of outputs corresponded with a partial segregation of inputs from the two LSOs in cases which received closely matched bilateral injections of anterograde tracers in LSO. The ventral part of DNLL received a heavy projection medially from the opposite LSO and a heavy projection laterally from the ipsilateral LSO. The findings suggest a direct relationship in the ventral part of the DNLL between inputs from the two LSOs and outputs to the two ICs. Possible roles for this segregation of pathways in DNLL are discussed in relation to the processing of static and dynamic spatial cues.

Alterations of second messenger systems in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle

We studied the sequential changes in second messenger systems in the striatum and substantia nigra (SN) after 6-hydroxydopamine lesions of the medial forebrain bundle in rats. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. [ 3H]Phorbol-12,13-dibutyrate (PDBu), [ 3H]forskolin and [ 3H]rolipram were used to label protein kinase C (PKC), adenylyl cyclase and calcium/calmodulin-independent cyclic-AMP phosphodiesterase, respectively. The degeneration of nigrostriatal pathway produced a significant increase in [ 3H]PDBu binding in the ventromedial part of the ipsilateral striatum from 2 to 8 weeks postlesion. In the contralateral side, [ 3H]PDBu binding showed a transient increase in the SN only 4 weeks after lesioning. [ 3H]Forskolin binding showed a significant increase in the ipsilateral and contralateral striatum from 2 to 4 weeks postlesion. In the ipsilateral SN, a significant increase in [ 3H]forskolin binding was observed at 4 weeks after lesioning. However, no significant change in [ 3H]forskolin binding was observed in the contralateral SN during postlesion. On the other hand, [ 3H]rolipram binding showed no conspicuous alteration in the brain during postlesion. These results demonstrate that rats made hemiparkinsonism by unilateral 6-hydroxydopamine injection have a significant increase in [ 3H]PDBu and [ 3H]forskolin binding in the striatum and/or SN, whereas no significant change in [ 3H]rolipram binding is observed in these areas during postlesion. Our findings also suggest that the increase in [ 3H]forskolin binding is more pronounced than that in [ 3H]PDBu binding in the brain after unilateral 6-hydroxydopamine injection. Thus, our studies may provide valuable information concerning degeneration of the nigrostriatal pathway such as Parkinson’s disease.

Prefrontal cortical networks related to visceral function and mood.

At least twenty-two architectonic areas can be distinguished within the orbital and medial prefrontal cortex (OMPFC). Although each of these areas has a distinct structure and connections, they can be grouped into two "networks," defined by cortico-cortical connections that primarily interconnect areas within each network. The networks also have different connections to the striatum, medial thalamus, and other brain regions. The orbital network consists of most of the areas in the orbital cortex. It receives several sensory inputs (olfactory, gustatory, visceral afferent, somatic sensory, and visual) that appear to be related to feeding. It also receives many limbic inputs from the amygdala, entorhinal and perirhinal cortex, and subiculum, including a specific projection from the ventrolateral part of the basal amygdaloid nucleus. The orbital network may therefore serve as a substrate to integrate viscerosensory information with affective signals. The medial network consists of areas on the medial frontal surface together with a few select areas in the orbital cortex. These areas have few direct sensory inputs, and their limbic inputs are somewhat different than those to the orbital network (e.g., from the ventromedial part of the basal amygdaloid nucleus). However, they provide the major output from the OMPFC to the hypothalamus and brain stem (especially the periaqueductal gray). The medial network may therefore serve as a visceromotor system to provide frontal cortical influence over autonomic and endocrine function. Connections between the networks presumably allow information flow from viscerosensory to visceromotor systems. In addition to a probable role in eating behavior, this system appears to be involved in guiding behavior and regulation of mood. Lesions of the ventromedial prefrontal cortex result in sociopathic behavior and difficulty in making appropriate choices, whereas functional imaging studies indicate that subjects with unipolar and bipolar depression have abnormal activity in medial and orbital prefrontal areas. Many of these areas also show volume changes and decreased glial number and density in mood-disordered subjects.

Compartmental changes in expression of c-Fos and FosB proteins in intact and dopamine-depleted striatum after chronic apomorphine treatment

Chronic administration of dopaminergic agonists to rats with unilateral 6-OH-dopamine (6-OHDA) lesions of nigrostriatal pathway produces behavioral sensitization to subsequent agonist challenges and may serve as a model for DOPA-induced dyskinesias. In order to understand striatal mechanisms behind this long-term behavioral change we examined striatal c-Fos and FosB immunoreactivity induced by apomorphine challenge (5 mg/kg, s.c.) after 3 days of withdrawal following a 2-week administration (5 mg/kg, b.i.d., s.c.) both in intact and 6-OHDA-lesioned animals. In intact rats, c-Fos induction by acute apomorphine exposure showed a striosomal pattern, whereas FosB immunopositivity was diffusely distributed. Following chronic administration, FosB induction turned to a clear striosome dominant pattern similar to c-Fos expression. In denervated striatum, expression of both proteins was profoundly augmented in a homogeneous pattern after a single dose of apomorphine. A distinct striosomal patterning appeared after chronic apomorphine administration in ventromedial part of the denervated striatum with a down-regulation in the matrix and relative enhancement in striosomes. These results suggest that compartmental reorganization of striatal neuronal activity may play a role in long-term behavioral changes induced by chronic dopaminergic treatments both under normal and dopamine-depleted conditions.

Location of reticular premotor areas of a motor center innervating craniocervical muscles in the mallard (Anas platyrhynchos L.).

The supraspinal nucleus (SSp) in the mallard, which lies in the rostral spinal cord and caudal brainstem, is a motor nucleus that forms the rostral continuation of the ventral horn. It contains part of the motoneurons innervating the craniocervical muscles. Injections with horseradish peroxidase (HRP) and wheat germ agglutinin conjugated to HRP (WGA) in the SSp were used to localize the craniocervical premotor neurons in the medullary reticular formation. A mixture of WGA and HRP (WGA/HRP) or biotinylated dextran amine (BDA) were injected in the different reticular areas to test the results. Small numbers of craniocervical premotor neurons were found bilaterally in the ventromedial part of the parvocellular reticular formation (RPcvm) and in the caudal extension of RPcvm, the nucleus centralis dorsalis of the medulla oblongata, and the gigantocellular reticular formation (RGc). In a second series of experiments, WGA/HRP and BDA injections in these reticular areas were used to visualize afferent fibers and terminals in the SSp. The combination of the two types of experiments shows that RPcvm and RGc contain modest numbers of craniocervical premotor neurons. Because the reticular formation also contains jaw and tongue premotor neurons and receives a variety of sensory projections, the present results suggest that the medullary reticular formation plays a role in the coordination of complex movements (e.g., feeding). The pattern of afferent and efferent connections of the reticular formation is used to redefine its subdivisions in the myelencephalon of the mallard.

Immunohistochemical Distribution of Neuropeptide Y-Related Substance in the Brain and Hypophysis of the Arctic Lamprey, Lethenteron japonica

The distribution of neuropeptide Y (NPY)-like immunoreactivity in the brain and hypophysis of the arctic lamprey, Lethenteron japonica, was studied by the use of polyclonal anti-synthetic porcine NPY antibody. Immunoreactivity was found throughout the brain, with varied densities among different areas. NPY-positive cell bodies were located in the dorsal pallium of the telencephalon; in the preoptic area, the thalamus, and the hypothalamus of the diencephalon; in the tegmentum of the mesencephalon; and in the octavolateralis nucleus, the middle reticular nucleus, and the vagal motor nucleus of the rhombencephalon. The majority of the NPY-positive cells in the thalamus and in the hypothalamus appeared as cerebrospinal fluid-contacting neurons. NPY-positive fibers were widely distributed in the brain and locally dense in the ventromedial part of the lateral pallium, in the posterior part of the interpeduncular nucleus, and in the raphe region. Conversely, they were less dense or well scattered in the olfactory bulb, the lateral pallium except for its ventromedial part, and the optic tectum. NPY-positive innervation in the neurohypophysis was evident, suggesting that involvement of NPY-related substance in the hypothalamo-hypophysial system had occurred in an early stage of vertebrate evolution.

A crossed projection from the optic tectum to craniocervical premotor areas in the brainstem reticular formation. An anterograde and retrograde tracing study in the mallard (Anas platyrhynchos L.).

The optic tectum in birds receives visual information from the contralateral retina. This information is passed through to other brain areas via the deep layers of the optic tectum. In the present study the crossed tectobulbar pathway is described in detail. This pathway forms the connection between the optic tectum and the premotor area of craniocervical muscles in the contralateral paramedian reticular formation. It originates predominantly from neurons in the ventromedial part of stratum griseum centrale and to a lesser extent from stratum album centrale. The fibers leave the tectum as a horizontal fiber bundle, and cross the midline through the caudal radix oculomotorius and rostral nucleus oculomotorius. On the contralateral side fibers turn to ventral and descend caudally in the contralateral paramedian reticular formation to the level of the obex. Labeled terminals are found in the ipsilateral medial mesencephalic reticular formation lateral to the radix and motor nucleus of the oculomotor nerve, and in the contralateral paramedian reticular formation, along the descending tract. Neurons in the medial mesencephalic reticular formation in turn project to the paramedian reticular formation. Through the crossed tectobulbar pathway visual information can influence the activity of craniocervical muscles via reticular premotor neurons.

Transcription Factor STAT3 in Leptin Target Neurons of the Rat Hypothalamus

Leptin is an adipose tissue-derived hormone that regulates body weight via interactions with hypothalamic neuronal circuitries expressing specific leptin receptors (Ob-R). The Ob-Rs act via the JAK-STAT (Janus kinase-signal transducers and activators of transcription) pathway of signal transduction. Recent evidence suggests that primarily the transcription factor STAT3 mediates leptin’s action in the hypothalamus. We have investigated the presence and cellular localization of STAT3 protein in the rat hypothalamus by means of indirect immunofluorescence histochemistry using a rabbit polyclonal STAT3 antiserum. The antiserum identified a 92-kDa protein using Western blotting on rat hypothalamic homogenates, corresponding to the expected size of STAT3. STAT3 immunoreactivity was demonstrated in Ob-R-containing neurons of the paraventricular nucleus (parvocellular part), periventricular nucleus, arcuate nucleus and in the lateral hypothalamic area. Direct double-labeling showed presence of STAT3 immunoreactivity in neuropeptide Y (NPY)-containing neurons of the ventromedial part of the arcuate nucleus and in proopiomelanocortin (POMC)-containing neurons of the ventrolateral part of the arcuate nucleus. The results provide an anatomical basis for a leptin action mediated by STAT3 in Ob-R-containing NPY and POMC neurons of the arcuate nucleus, as well as by Ob-R-containing neurons of the parvocellular paraventricular nucleus and lateral hypothalamic area.