Aromatase in axonal processes of early postnatal hypothalamic and limbic areas including the cingulate cortex

It has been shown that sexual dimorphic morphology of certain hypothalamic and limbic areas underlie gender-specific sexual behavior and neuroendocrine mechanisms. The key role played by locally formed estrogen in these developmental events has been revealed during a critical perinatal period. In this study, we aimed to document the presence of estrogen-synthetase (aromatase)-immunoreactive elements in the involved limbic system and hypothalamus of the developing rat brain. On postnatal day 5, animals of both sexes were perfusion-fixed, and sections from the forebrain and hypothalamus were immunolabelled for aromatase using an antiserum that was generated against a 20 amino acid sequence of placental aromatase. Aromatase-immunoreactivity was present in neuronal perikarya and axonal processes in the following limbic structures: the central and medial nuclei of the amygdala, stria terminalis, bed nucleus of the stria terminalis (BNST), lateral septum, medial septum, diagonal band of Broca, lateral habenula and all areas of the limbic (cingulate) cortex. In the hypothalamus, the most robust labelling was observed in the medial preoptic area, periventricular regions, ventromedial and arcuate nuclei. The most striking feature of the immunostaining with this antiserum was its intracellular distribution. In contrast to the heavy perikaryal labelling that can be observed with most of the currently available aromatase antisera, in the present experiments, immunoperoxidase was predominantly localized to axons and axon terminals. All the regions with fiber staining corresponded to the projection fields of neuron populations that have previously been found to express perikaryal aromatase. Our results confirm the presence of aromatase-immunoreactivity in developing limbic and hypothalamic areas. The massive expression of aromatase in axonal processes raises the possibility that estrogen formed locally by aromatase may not only regulate the growth, pathfinding and target recognition of its host neuronal processes, but may also exert paracrine actions on structures in close proximity, including the target cells.     

Noradrenergic innervation of the hypothalamus of rhesus monkeys: distribution of dopamine-beta-hydroxylase immunoreactive fibers and quantitative analysis of varicosities in the paraventricular nucleus

The distribution of noradrenergic processes within the hypothalamus of rhesus monkeys (Macaca mulatta) was examined by immunohistochemistry with an antibody against dopamine-beta-hydroxylase. The results revealed that the pattern of dopamine-beta-hydroxylase immunoreactivity varied systematically throughout the rhesus monkey hypothalamus. Extremely high densities of dopamine-beta-hydroxylase-immunoreactive processes were observed in the paraventricular and supraoptic nuclei, while relatively lower levels were found in the arcuate and dorsomedial nuclei and in the medial preoptic, perifornical, and suprachiasmatic areas. Moderate levels of dopamine-beta-hydroxylase immunoreactivity were found throughout the lateral hypothalamic area and in the internal lamina of the median eminence. Very few immunoreactive processes were found in the ventromedial nucleus or in the mammillary complex. Other midline diencephalic structures were found to have high densities of dopamine-beta-hydroxylase immunoreactivity, including the paraventricular nucleus of the thalamus and a discrete subregion of nucleus reuniens, the magnocellular subfascicular nucleus. A moderate density of dopamine-beta-hydroxylase immunoreactive processes were found in the rhomboid nucleus and zona incerta whereas little dopamine-beta-hydroxylase immunoreactivity was found in the fields of Forel, nucleus reuniens, or subthalamic nucleus. The differential distribution of dopamine-beta-hydroxylase-immunoreactive processes may reflect a potential role of norepinephrine as a regulator of a variety of functions associated with the nuclei that are most heavily innervated, e.g., neuroendocrine release from the paraventricular and supraoptic nuclei, and gonadotropin release from the medial preoptic area and mediobasal hypothalamus. Additionally, quantitative analysis of dopamine-beta-hydroxylase-immunoreactive varicosities was performed on a laser scanning microscope in both magnocellular and parvicellular regions of the paraventricular nucleus of the hypothalamus. The methodology employed in this study allowed for the high resolution of immunoreactive profiles through the volume of tissue being analyzed, and was more accurate than conventional light microscopy in terms of varicosity quantification. Quantitatively, a significant difference in the density of dopamine-beta-hydroxylase-immunoreactive varicosities was found between magnocellular and parvicellular regions, suggesting that parvicellular neurons received a denser noradrenergic input. These differential patterns may reflect an important functional role for norepinephrine in the regulation of anterior pituitary secretion through the hypothalamic-pituitary-adrenal stress axis.     

Release into ventriculo-cisternal perfusate of beta-endorphin- and Met-enkephalin-immunoreactivity: effects of electrical stimulation in the arcuate nucleus and periaqueductal gray of the rat

To examine the resting and evoked release of the endogenous opioid peptides beta-endorphin and Met-enkephalin from brain, we examined the levels of the respective immunoreactivities in the lateral ventricle-cisterna magna perfusate of the halothane-anesthetized rat. Ten Hz but not 100 Hz stimulation in the arcuate nucleus (ARC) of the hypothalamus released beta-endorphin immunoreactivity (beta-EPir) to the perfusate, whereas 100 Hz but not 10 Hz stimulation in the periaqueductal gray (PAG) of the mid brain released Met-enkephalin immunoreactivity (MEir). MEir was not released by stimulation in ARC and beta-EPir was not released by stimulation in PAG. Characterization of the released beta-EPir and MEir by high performance liquid chromatography showed that authentic beta-endorphin and Met-enkephalin were the major constituents of beta-EPir and MEir, respectively. Systemic administration of the dopaminergic antagonist haloperidol increased plasma, but not perfusate levels of beta-EPir. Both the opioid antagonist naloxone and the NMDA antagonist MK-801 failed to affect beta-EPir or MEir release. ARC and PAG stimulated inhibited a nociceptive reflex (tail-dip in 52.5 degrees C water), and naloxone did not reliably reverse this inhibition. These data support the previously suggested possibility of opioid mediation of stimulation induced analgesia, although we were unable to confirm the theory by naloxone reversibility in this study. Furthermore, the data support the assumption that measurement of opioid peptides in cerebrospinal fluid is a relevant approach in research aimed at elucidating the physiological and pathophysiological roles of endogenous opioid peptides.     

Patterns of induction of the immediate-early genes c-fos and egr-1 in the female rat brain following differential amounts of mating stimulation

Vaginocervical stimulation received either during mating or by artificial mechanical means has been shown to induce FOS expression in medial amygdala, preoptic area, hypothalamus, and midbrain of female rats. While mating-induced increases in FOS-like immunoreactivity (FOS-IR) have been shown to require intromissive stimulation from males, the pattern of FOS-IR in animals receiving numbers of intromissions across a range relevant to the induction of the prolactin surges of early pregnancy has not been explored. Experiment 1 examined brain FOS-IR following 15 mounts without intromission or 5, 10, or 15 intromissions in ovariectomized females treated with estrogen and progesterone; these treatments are known to be less than or more than sufficient to trigger prolactin surges in cycling females. FOS was expressed in a graded fashion in the medial amygdala with respect to the numbers of intromissions received and in an all-or-nothing manner in preoptic area, bed nucleus of the stria terminalis, and ventromedial nucleus of the hypothalamus. In experiment 2, 15 intromissions induced expression of another immediate-early gene, egr-1, in each of these same areas as well as in a second division of the bed nucleus of the stria terminalis and in the paraventricular nucleus of the hypothalamus. These studies demonstrate that mating is differentially effective in inducing FOS expression in responsive brain areas and point to the medial amygdala as a site in which summation of intromissive stimulation may occur. Furthermore, the induction of EGR-1 may be a more sensitive marker for mating-induced neural activation in these areas than is FOS.     

Projections of the estrogen receptor-immunoreactive ventrolateral hypothalamus to other estrogen receptor-immunoreactive sites in female guinea pig brain

The ventrolateral hypothalamus in female guinea pigs includes an estrogen receptor dense region adjacent to the ventromedial hypothalamus. This region is reciprocally connected with other estrogen receptor-containing areas suggesting that steroid hormone receptor-containing cells may be directly linked. Phaseolus vulgaris leucoagglutinin, an anterograde tract tracer, was specifically placed in this region with the aim of labeling some projections from estrogen receptor-containing neurons. These projections were colocalized immunocytochemically with the distribution of estrogen receptor-containing cells. Dense ventrolateral hypothalamic innervation was observed in some regions also containing a high concentration of estrogen receptor-containing cells. These regions included the medial preoptic area, the bed nucleus of the stria terminalis, the ventrolateral hypothalamus anterior and posterior to the injection site, and the midbrain central gray. A low density of ventrolateral hypothalamic fibers and terminals was observed in two regions rich in estrogen receptors, the amygdala and the arcuate nucleus. In general, ventrolateral hypothalamic fibers and terminals were present in all regions where estrogen receptors were found except the medial thalamus and habenular region. Labeled terminal boutons and perineuronal baskets were found around estrogen receptor-containing cells in most regions which contained estrogen receptor-containing cells. These close appositions were suggestive of synaptic contacts, suggesting that the ventrolateral hypothalamus may influence steroid-dependent behaviors via the modulation of estrogen receptor-containing cells. Furthermore, ventrolateral hypothalamic projections may include direct connections with estrogen receptor-containing cells, suggesting the presence of a network of interconnected estradiol-sensitive neurons involved in the regulation of estradiol-dependent functions.     

Endocytosis and recycling of neurokinin 1 receptors in enteric neurons

Neurotransmission depends on the availability of transmitter and on the presence of functional, high-affinity receptors at the plasma membrane that are capable of binding ligand. The pathway, mechanism and function of endocytosis and recycling of the substance P or neurokinin 1 receptor in enteric neurons were studied using fluorescent substance P, receptor antibodies and confocal microscopy. In both the soma and neurites, substance P induced rapid, clathrin-mediated internalization of the neurokinin 1 receptor into early endosomes, which also contained the transferrin receptor. After 4-8 h, there was a return in surface neurokinin 1 receptor immunoreactivity in the soma, which was not prevented by cycloheximide, and was thus independent of new protein synthesis. This return was prevented by acidotropic agents, therefore required endosomal acidification. This suggests that the neurokinin 1 receptor recycles in the soma. In contrast, in neurites, substance P and the neurokinin 1 receptor remained in endosomes and recycling was not detected. Neurons of the myenteric plexus were heavily innervated by substance P-containing nerve fibers, and K(+)-stimulated release of endogenous substance P from cultured neurons induced internalization of the neurokinin 1-receptor. Therefore, endogenous substance P may induce endocytosis of the neurokinin 1 receptor. In the soma, endocytosis and recycling correlated with loss and recovery of functional binding sites for substance P. suggesting that this process contributes to the regulation of peptidergic neurotransmission. Thus, ligand-induced endocytosis of the neurokinin 1 receptor in myenteric neurons is associated with a loss of surface receptors and functional binding sites. Since release of endogenous substance P induces neurokinin 1 receptor internalization, and neurokinin 1 receptor neurons are innervated by substance P-containing fibers, endocytosis of neuropeptide receptors may regulate neurotransmission.     

Morphologically heterogeneous met-enkephalin terminals form synapses with tyrosine hydroxylase-containing dendrites in the rat nucleus locus coeruleus

Physiological and anatomical studies have suggested that the endogenous opioid peptide, methionine-enkephalin (ENK), may directly modulate noradrenergic neurons. Additionally, chronic opiate administration has been shown to increase the levels of a number of G-proteins and phosphoproteins including the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH). We combined immunogold-silver localization of tyrosine hydroxylase and immunoperoxidase labeling for ENK in single sections through the nucleus locus coeruleus (LC) in the rostral pons to determine potential substrates for the divergent actions of this opioid peptide. Light microscopic analysis of ENK immunoreactivity in the LC area indicated that ENK fibers are dense and highly varicose. In coronal sections, ENK-immunoreactive processes were punctate and appeared to envelop LC-cell bodies. More rostrally, in the region of catecholamine-immunoreactive extranuclear dendrites, ENK-immunoreactive varicose processes were interdigitated with TH-labeled processes. Electron microscopy of this rostral region revealed that ENK-immunoreactive axon terminals contained small clear as well as large dense core vesicles. The large dense core vesicles (1-10/terminal) were consistently the most immunoreactive and were identified toward the periphery of the axon terminal distal to the active zone of the synapse. Unlabeled axon terminals and glial processes were the most commonly observed elements located adjacent to the plasmalemma of axons containing the labeled dense core vesicles. Axon terminals containing ENK immunoreactivity varied in size (0.3 micron to 2.0 microns) as well as formation of synaptic specializations (i.e., asymmetric versus symmetric). The ENK-labeled terminals formed synapses with dendrites with and without detectable TH immunoreactivity. These results provide the first direct ultrastructural evidence that morphologically heterogeneous terminals containing ENK immunoreactivity form synapses with catecholamine dendrites within the LC. The formation of asymmetric and symmetric synaptic specializations suggests that the opioid peptide, ENK, may be colocalized with other neurotransmitters. Furthermore, the distribution of ENK immunoreactivity in axon terminals apposed to other unlabeled afferents or astrocytic processes suggests that actions of ENK may also include presynaptic modulation of other transmitters and/or effects on astrocytes.     

Estrogen increases affinity of oxytocin receptors in the medial preoptic area-anterior hypothalamus

Analysis of binding data from saturation experiments using a radiolabeled oxytocin antagonist ([125I]OTA) demonstrated an increase in binding affinity after treatment with 5 micrograms estradiol benzoate (EB) for 3 days in membrane fractions from the medial preoptic area-anterior hypothalamus (MPOA-AH) of ovariectomized (OVX) rats. Analysis of data from competition experiments revealed high- and low-affinity [125I]OTA binding sites in the MPOA-AH, the medial basal hypothalamus (MBH), and hippocampus of OVX controls. Three days of EB treatment reduced low-affinity binding sites in the MPOA-AH and MBH, but not in the hippocampus. Treatment of membrane fractions from the MPOA-AH of oil-treated OVX rats in vitro with 100 nM OT or with estrogen or progesterone conjugated to bovine serum albumin (E-BSA and P-BSA) also reduced low-affinity [125I]OTA binding sites but BSA alone did not.     

Tachykinins in propranolol-augmented, hyperpnoea-induced bronchoconstriction in Taida guinea-pigs: effects of dimethylthiourea

The coexistence of molluscan cardioexcitatory neuropeptide (FMRFAMIDE) and luteinizing hormone-releasing hormone (LHRH) was studied in the nervous system of the big brown bat, Eptesicus fuscus, with immunocytochemistry. Within mammals, this is the first report of the coexistence of these neuropeptides in the terminal nerve. In juvenile and adult bats, both neuropeptides are distributed identically throughout the terminal nerve (tn), and they coexist in many parts of the prosencephalon from the olfactory bulb as far caudally as the interpeduncular nucleus. Peripherally, on the basal surface of the forebrain, fibers and a few perikarya, which may belong to the tn, form a loose plexus. Within the brain wall, regions of maximal immunoreactivity (ir) are the habenula, medial preoptic area, arcuate nucleus, and the infundibulum. Whereas in most areas of the prosencephalon (e.g., stria terminalis and bed nuclei, amygdaloid complex) fibers show stronger immunoreactivity to FMRFAMIDE, labeling of fibers in the habenula and infundibulum is largely identical for both neuropeptides. The arcuate nucleus contains a large number of perikarya and is the major source of both FMRFAMIDE- and LHRH-ir within the forebrain. A number of fibers run along the ependyma of the ventricular system and seem to terminate here; this is particularly evident in the median eminence and infundibular stalk. In the big brown bat, there seems to exist a continuum of FMRFAMIDE- and LHRH-ir throughout the tn and those structures of the forebrain that are known to be engaged in the control of mating behavior, reproduction, and rhythmicity. Concerning the hypothalamo-hypophyseal-gonadal axis, the arcuate nucleus may serve as a central hub between the olfactory/terminal input and superior areas including the limbic system. In contrast to LHRH immunoreactivity, FMRFAMIDE-like ir extends throughout the brainstem and cervical spinal cord. This system may also be involved in the processing and modulation of autonomic input via the parabrachial and solitary nuclei, the rhombencephalic central gray, and its projection into the hypothalamus (paraventricular nucleus), thus facilitating feed-back of gonadotropic influences of the terminal nerve and prosencephalon.     

Microbial degradation of tetraethyl lead in soil monitored by microcalorimetry

Fos immunohistochemistry was used to stain neurons in the caudal diencephalon, midbrain and hindbrain driven by rewarding stimulation of the lateral hypothalamus (LH). Increases in Fos-like immunoreactivity were most pronounced ipsilateral to the site of stimulation and tended to be confined within discrete structures such as the posterior LH, arcuate nucleus, ventral tegmental area (VTA), central gray, dorsal raphé, pedunculopontine area (PPTg), parabrachial nucleus, and locus coeruleus. At least two of these structures, the VTA and PPTg, have been implicated in medial forebrain bundle self-stimulation.     

Leptin receptors in estrogen receptor-containing neurons of the female rat hypothalamus

This study was undertaken to reveal whether integration of the peripheral signals, leptin and estradiol, that convey information on the metabolic state and gonadal function, respectively, might occur in the same hypothalamic neuronal perikarya. Light and electron microscopic immunolabeling for leptin receptors (LRs) and estrogen receptors (ERs) was carried out on hypothalamic sections of female rats. In the medial preoptic area, periventricular regions, including the parvicellular paraventricular nucleus, the arcuate nucleus and the ventromedial hypothalamic nucleus, all of the cells that expressed immunoreactivity for ERs were also immunopositive for LR. On the other hand, only a subpopulation of LR-containing cells was found to express ERs. The extensive colocalization of receptors for leptin and estrogen in neuronal perikarya of all parts of the hypothalamus suggests a closely coupled interaction between these peripheral signals in the regulation of a variety of behavioral and neuroendocrine mechanisms.     

Anatomical dissociation of the substrates of medial forebrain bundle self-stimulation and exploration.

The purpose of this research was to determine whether brain stimulation reward and exploration are induced by activation of the same set of neurons along the medial forebrain bundle. The behavioral version of the collision test was utilized with electrodes in the lateral hypothalamus (LH) and the ventral tegmental area (VTA). A collision effect obtained between LH and VTA in one behavior at the exclusion of the other was treated as evidence of the involvement of two different sets of fibers. In 4 rats, a collision effect was observed only in self-stimulation, whereas in 1 rat, a collision was obtained in exploration at the exclusion of self-stimulation. Three animals showed no collision in either behavior. These data suggest that coexistence of self-stimulation and exploration following medial forebrain bundle stimulation can be explained by current spread on two different sets of fibers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perseveration in two aphasic patients

In the present study a comparison was made between the distribution of Fos immunoreactivity in the brain of female and male rats following successive elements of sexual behavior. The distribution of Fos immunoreactivity following either mounting, eight intromissions or one or two ejaculations was compared with that in control animals. In both females, Fos immunoreactivity was induced in the medial preoptic nucleus, posteromedial part of the bed nucleus of the stria terminalis, posterodorsal part of the medial amygdala, and the parvicellular part of the subparafascicular thalamic nucleus. In addition, Fos immunoreactivity in females was induced in the ventrolateral part and the most caudoventral part of the ventromedial nucleus of the hypothalamus and in the premammillary nucleus. Differences between females and males were detected in the phases of sexual activity that resulted in Fos immunoreactivity in these brain areas, allowing more insight in the nature of the sensory and hormonal stimuli leading to the induction of Fos immunoreactivity. The posteromedial bed nucleus of the stria terminalis appears to be involved in chemosensory investigation, while specific distinct subregions are only activated following ejaculation. In addition, the parvicellular subparafascicular nucleus and the lateral part of the posterodorsal medial amygdala appear to be involved in the integration of viscero-sensory input. The neural circuitries underlying sexual behavior in males and females appear to be similar in terms of integration of sensory information. In males the medial preoptic nucleus may be regarded as the brain area where the integration of sensory and hormonal stimulation leads to the onset of male sexual behavior, while in females the ventrolateral part of the ventromedial hypothalamic nucleus appears to have this function. In addition, Fos immunoreactivity was distributed in distinct clusters in subregions with various brain areas in males and females. This was observed especially in the posteromedial bed nucleus of the stria terminalis and posterodorsal medial amygdala, but also in the parvicellular subparafascicular nucleus, ventromedial hypothalamic nucleus and ventral premammillary nucleus. It appears that relatively small subunits within these nuclei seem to be concerned with the integration of sensory and hormonal information and may play a critical role in sexual behavior.     

Destruction of the medial forebrain bundle caudal to the site of stimulation reduces rewarding efficacy but destruction rostrally does not.

Rats with an electrode in the medial forebrain bundle (MFB) in or near the ventral tegmental area and another at the level of the rostral hypothalamus sustained large electrolytic lesions at either the rostral or the caudal electrode. The rewarding efficacy of stimulation through the other electrode was determined before and after the lesion. Massive damage to the MFB in the rostral lateral hypothalamus (LH) generally had little effect on the rewarding efficacy of more caudal stimulation, whereas large lesions in the caudal MFB generally reduced the rewarding efficacy of LH stimulation by 35–60%. Similar reductions were produced by knife cuts in the caudal MFB. These results appear to be inconsistent with the hypothesis that the reward fibers consist either of descending or ascending fibers coursing in or near the MFB. It is suggested that the reward fibers are collaterals from neurons with both their somata and their behaviorally significant terminals located primarily in the midbrain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Patchy and laminar terminations of medial geniculate axons in monkey auditory cortex

The object of this study was to identify the terminal distributions of thalamocortical axons arising in chemically characterized subdivisions of the medial geniculate complex. Large injections of wheat germ agglutinin-conjugated horseradish peroxidase or small injections of Phaseolus vulgaris leucoagglutinin were made in the medial geniculate complex of Macaca fuscata. The terminal distributions of labeled axons in the cortex were correlated with auditory cortical fields demonstrable by different intensities of immunoreactivity for parvalbumin. Fibers from the ventral nucleus terminated mainly in layer IV and deep portion of layer III (IIIB), with additional terminations in layers I-IIIA and in layer VI. In layers IIIB-IV, a major terminal plexus was formed by a small number of dense patches, 300-500 microns in diameter, surrounded by smaller satellite patches. The patches conformed to a similarly lobulated pattern of parvalbumin fiber immunoreactivity. Terminations of some individually labeled thalamocortical fibers were restricted to a single patch, whereas others innervated more than one patch by collateral branches. Fibers from the dorsal nuclei ending in areas of less dense parvalbumin immunoreactivity surrounding the primary auditory cortex formed much larger terminal patches centered largely in layer IIIB. Fibers from the magnocellular nucleus had relatively few terminal branches but innervated extremely wide areas by collaterals of single axons. Two types of axons arose from the magnocellular nucleus, one terminating preferentially in middle cortical layers and the other exclusively in layer I. These may arise respectively from parvalbumin- and calbindin-immunoreactive cell populations in the magnocellular nucleus.     

Chemical stimulation of the brain: Relationship between neural activity and water ingestion in the rat.

Implanted cannulae in the lateral septal nucleus, lateral hypothalamic area, or lateral caudate nucleus of 76 male Long-Evans rats. Ss then received injections of carbachol, atropine sulfate, or isotonic saline. Injecting carbachol into cholinergic drinking sites in the limbic system (septal nucleus or lateral hypothalamus) produced an immediate increase in neural firing at the stimulated site and at a contralateral nonstimulated site. The time course of the change in neural firing was similar to the time course of water ingestion. Increased neural firing was not produced by cholinergic stimulation of nondrinking caudate nucleus sites or by atropine or isotonic saline injection into the limbic system or caudate nucleus. Results suggest that drinking results from increased neural firing in a diffuse cholinergically coded circuit whose activity facilitates water ingestion. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An investigation of a possible direct projection from the medial nucleus of the cerebellum to the paraventricular nucleus of the hypothalamus in the rat: a study using retrograde WGA-HRP and Fluoro-Gold tracing techniques

Retrograde transport of lectin-conjugated horseradish peroxidase and Fluoro-Gold was used in an attempt to obtain data to confirm the existence, predicted from physiological studies, of a direct, monosynaptic projection from the medial nucleus of the cerebellum (MN) to the paraventricular nucleus of the hypothalamus (PVH) in the rat. Injections of these two tracers that included the PVH and surrounding diencephalic structures, or that in the case of Fluoro-Gold were localized to the PVH, resulted in retrograde neuronal labeling in widely separated nuclei known to project to the areas included in the injection sites. Thus, effective uptake and transport of both tracers occurred under the experimental conditions employed in this study. However, injections confined to the PVH and regions of the hypothalamus adjacent to it, or to the PVH alone, produced no retrograde neuronal labeling in the medial nucleus, indicating that the MN does not project directly to the PVH. Alternative explanations for the findings from physiological experiments were sought. The possibility that electrical stimulation of fibers of passage through the region of the MN might produce a monosynaptic response in the contralateral PVH was discarded, because retrogradely labeled neurons in nuclei such as the locus ceruleus and lateral parabrachial nucleus were distributed mainly ipsilateral to hypothalamic injection sites. However, tracer injections into the MN produced retrograde labeling of neurons in the same region of the lateral paragigantocellular nucleus (LPGi) in which labeled cells were found following tracers injections into the PVH. Axon collaterals of individual neurons in the LPGi might, therefore, project both to the MN and to the PVH. The possibility that such a circuit could, in the absence of a direct MN to PVH projection, provide the basis to explain the physiological findings is discussed.     

Immunocytochemical localization of the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the hypothalamus of cattle

Immunocytochemical staining for the presence of catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, was used to characterize the regional distribution of catecholaminergic neurons in the hypothalamus and adjacent areas of domestic cattle, Bos taurus. In steers, heifers and cows, tyrosine hydroxylase-immunoreactive perikarya was located throughout periventricular regions of the third cerebral ventricle, in both anterior and retrochiasmatic divisions of the supraoptic nucleus, suprachiasmatic nucleus, and ventral and dorsolateral regions of the paraventricular nucleus, dorsal hypothalamus, ventrolateral aspects of the arcuate nucleus, along the ventral hypothalamic surface between the median eminence and optic tract, and in the posterior hypothalamus. Immunostained perikarya ranged from small (10-20 microns, parvicellular) to large (30-50 microns, magnocellular) and were of multiple shapes: round, triangular, fusiform or multipolar, often with 2-5 processes of branched arborization. There were no dopamine-beta-hydroxylase immunoreactive perikarya observed within the hypothalamus and adjacent structures. However, both tyrosine hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers and punctate varicosities were observed throughout regions of tyrosine hydroxylase immunoreactivity perikarya. Generally, the location and pattern of hypothalamic tyrosine hydroxylase immunoreactivity and dopamine-beta-hydroxylase immunoreactive were similar to those reported for most other large brain mammalian species, however, there were several differences with commonly used small laboratory animals. These included intense tyrosine hydroxylase immunoreactivity of perikarya within the retrochiasmatic division of the supraoptic nucleus (ventral A15 region), the absence of tyrosine hydroxylase immunoreactive perikarya below the anterior commissure or within the bed nucleus of stria terminalis (absence of the dorsal A15 region), an abundance of tyrosine hydroxylase immunoreactive perikarya within the ependymal layer of the median eminence, heavy innervation of the arcuate nucleus with dopamine-beta-hydroxylase immunoreactive fibers and varicosities, and the paucity of dopamine-beta-hydroxylase immunoreactive throughout the median eminence.     

Feeding behavior in the rat with isolated medial hypothalamus

After complete, unilateral, frontolateral, dorsal isolation of the medial hypothalamus, VMH included, or fornix section above the hypothalamus, total food consumption and diurnal pattern of food intake were followed 85 days postoperatively. It is suggested that the saftety signals are generated not only in VMH nucleus, but in a VMH-retrochiasmatic region located anteriorly to the VMH.     

Increase of extracellular glutamate and expression of Fos-like immunoreactivity in the ventral tegmental area in response to electrical stimulation of the prefrontal cortex

Electrical stimulation of the medial prefrontal cortex caused glutamate release in the ventral tegmental area (VTA) of freely moving animals. Cathodal stimulation was given through monopolar electrodes in 0.1-ms pulses at an intensity of 300 microA and frequencies of 4-120 Hz. Glutamate was measured in 10-min perfusate samples by HPLC coupled with fluorescence detection following precolumn derivatization with o-phthaldialdehyde/beta-mercaptoethanol. The stimulation-induced glutamate release was frequency dependent and was blocked by the infusion of the sodium channel blocker tetrodotoxin (10 microM) through the dialysis probe. The stimulation also induced bilateral Fos-like immunoreactivity in ventral tegmental neurons, with a significantly greater number of Fos-positive cells on the stimulated side. These findings add to a growing body of evidence suggesting that the medial prefrontal cortex regulates dopamine release in the nucleus accumbens via its projection to dopamine cell bodies in the VTA.