Axonal projections of medial preoptic and anterior hypothalamic neurons

Review of the cytology and connections of the lateral habenula, an avatar of adaptive behaving

The cytology and connections of the lateral habenula (LHb) are reviewed. The habenula is first introduced, after which the cytology of the LHb is discussed mainly with reference to cell types, general topography and descriptions of subnuclei. An overview of LHb afferent connections is given followed by some details about the projections to LHb from a number of structures. An overview of lateral habenula efferent connections is given followed by some details about the projections from LHb to a number of structures. In considering the afferent and efferent connections of the LHb some attention is given to the relative validity of regarding it as a bi-partite structure featuring 'limbic' and 'pallidal' parts. The paper ends with some concluding remarks about the relative place of the LHb in adaptive behaving.

Anthony Sclafani: Consummate scientist

In this article we review the scientific contributions of Anthony Sclafani, with specific emphasis on his early work on the neural substrate of the ventromedial hypothalamic (VMH) hyperphagia-obesity syndrome, and on the development of diet-induced obesity (DIO). Over a period of 20 years Sclafani systematically investigated the neuroanatomical basis of the VMH hyperphagia-obesity syndrome, and ultimately identified a longitudinal oxytocin-containing neural tract contributing to its expression. This tract has since been implicated in mediating the effects of at least two gastrointestinal satiety factors. Sclafani was one of the first investigators to demonstrate DIO in rats as a result of exposure to multiple palatable food items (the "supermarket diet"), and concluded that diet palatability was the primary factor responsible for DIO. Sclafani went on to investigate the potency of specific carbohydrate and fat stimuli for inducing hyperphagia, and in so doing discovered that post-ingestive nutrient effects contribute to the elevated intake of palatable food items. To further investigate this effect, he devised an intragastric infusion system which allowed the introduction of nutrients into the gut paired with the oral intake of flavored solutions, an apparatus her termed the "electronic esophagus". Sclafani coined the term "appetition" to describe the effect of intestinal nutrient sensing on post-ingestive appetite stimulation. Sclafani's productivity in the research areas he chose to investigate has been nothing short of extraordinary, and his studies are characterized by inventive hypothesizing and meticulous experimental design. His results and conclusions, to our knowledge, have never been contradicted.

AMPA/kainate receptors in the ventromedial hypothalamus mediate the effects of glutamate on estrus termination in the rat

Infusions of glutamate or its selective receptor agonists to the VMH of ovariectomized (OVX) female rats primed with estradiol benzoate (EB) and progesterone (P) inhibit both appetitive and consummatory aspects of sexual behavior whereas selective glutamate receptor antagonists facilitate these measures in females primed with EB alone. Because vaginocervical stimulation (VCS) activates glutamate neurons in the VMH, and induces a faster termination of estros behavior, the present study examined the effects of the AMPA/kainate receptor antagonist DNQX on the induction of estrus termination by manual VCS. Ovx, sexually-experienced rats were primed with EB and P and subsequently received either 1 or 50 distributed VCSs, over the course of an hour, 12 h before a test with sexually vigorous males. Half of the females in each stimulus group received bilateral infusions of 1 μl/side of either DNQX (19.8 mmol/μl) or saline aimed at the VMH immediately prior to VCS or sham stimulation. Saline-infused females given VCS had lower lordosis quotients compared to females given sham stimulation. In contrast, females infused with DNQX prior to VCS displayed more appetitive behaviors and higher lordosis quotients and magnitudes compared to females infused with saline. These data indicate that activation of AMPA/kainate receptors in the VMH by increased glutamate transmission induced by VCS mediates estrus termination.

The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis

All animals evaluate the salience of external stimuli and integrate them with internal physiological information into adaptive behavior. Natural and sexual selection impinge on these processes, yet our understanding of behavioral decision-making mechanisms and their evolution is still very limited. Insights from mammals indicate that two neural circuits are of crucial importance in this context: the social behavior network and the mesolimbic reward system. Here we review evidence from neurochemical, tract-tracing, developmental, and functional lesion/stimulation studies that delineates homology relationships for most of the nodes of these two circuits across the five major vertebrate lineages: mammals, birds, reptiles, amphibians, and teleost fish. We provide for the first time a comprehensive comparative analysis of the two neural circuits and conclude that they were already present in early vertebrates. We also propose that these circuits form a larger social decision-making (SDM) network that regulates adaptive behavior. Our synthesis thus provides an important foundation for understanding the evolution of the neural mechanisms underlying reward processing and behavioral regulation.

Alpha-oestrogen and progestin receptor expression in the hypothalamus and preoptic area dopaminergic neurones during oestrous in cycling rats

A secretory surge of prolactin occurs on the afternoon of oestrous in cycling rats. Although prolactin is regulated by ovarian steroids, plasma oestradiol and progesterone levels do not vary during oestrous. Because prolactin release is tonically inhibited by hypothalamic dopamine and modulated by dopamine transmission in the preoptic area (POA), the present study aimed to evaluate whether oestrogen receptor (ER)-alpha and progestin receptor (PR) expression in the dopaminergic neurones of arcuate (ARC), periventricular, anteroventral periventricular (AVPe) and ventromedial preoptic (VMPO) nuclei changes during the day of oestrous. Cycling rats were perfused every 2 h from 10-20 h on oestrous. Brain sections were double-labelled to ERalpha or PR and tyrosine hydroxylase (TH). The number of TH-immunoreactive (ir) neurones did not vary significantly in any area evaluated. ERalpha expression in TH-ir neurones increased at 14 and 16 h in the rostral-ARC and dorsomedial-ARC, 14 h in the caudal-ARC and 16 h in the VMPO, whereas it was unaltered in the ventrolateral-ARC, periventricular and AVPe. PR expression in TH-ir neurones of the periventricular and rostral, dorsomedial, ventrolateral and caudal-ARC decreased transitorily during the afternoon, showing the lowest levels between 14 and 16 h; but it did not vary in the AVPe and VMPO. Plasma oestradiol and progesterone concentrations were low and unaltered during oestrous, indicating that the changes in receptors expression were probably not due to variation in ligand levels. Thus, our data suggest that variations in ERalpha and PR expression may promote changes in the activity of medial basal hypothalamus and POA dopaminergic neurones, even under unaltered secretion of ovarian steroids, which could facilitate the occurrence and modulate the magnitude of the prolactin surge on oestrous.

Physiological characteristics of the projection pathway from the medial preoptic to the nucleus raphe magnus of the rat and its modulation by the periaqueductal gray

Anatomical studies have shown a strong projection from the medial preoptic nucleus of the hypothalamus (MPO) to both the periaqueductal gray (PAG) and nucleus raphe magnus (NRM). In this study, we examined the physiological characteristics of MPO to NRM connections and examined how blockade of neuronal transmission and of the glutamatergic system within the PAG modifies this pathway. In deeply anesthetized rats, recordings were made from NRM neurons that were identified by their response to peripheral mechanical stimulation and designated as "E", "I", or "N" if they were excited, inhibited, or not activated by noxious stimulation. In addition, cells were identified as spinally projecting if they could be antidromically activated by stimulation of the dorsolateral funiculus at the thoracic level. The responses of 204 NRM neurons to electrical and 87 cells to both chemical and electrical stimulation of MPO were recorded. The response of NRM neurons to MPO stimulation was highly dependent on the sensory class of these cells. Chemical stimulation of MPO inhibited 50% (16/32) and excited 16% (5/32) of the I-cells. In contrast, 23% (9/39) of the E-cells were inhibited and 49% (19/39) were excited by chemical stimulation of MPO. Electrical stimulation at intensities below 80 microA at 100Hz had similar effects on the two classes of cells; 62% (24/39) of the E-cells and 31% (10/32) of the I cells were excited, and 31% (12/39) of the E-cells and 59% (19/32) of the I-cells were inhibited. The excitatory response to chemical stimulation lasted for an average of 136.8+/-73.2s and inhibitory response lasted for an average of 143.8+/-102.1s. Electrical stimulation of MPO at 1Hz excited 27%, inhibited 3%, and had no effect on 70% of NRM cells. The mean latency to peak excitation was 9.6+/-6.6ms. Antidromic activation of MPO neurons by NRM stimulation showed an average latency of 6.3+/-3.4ms. Blocking the glutamatergic transmission within the PAG (by injecting kynurenic acid (KYN) into the PAG) blocked the inhibitory response of 40% (6/15) of the I-cells and inhibitory response of 43% (3/7) of the E-cells. The excitatory response of 27% (3/11) of the I-cells and the excitatory response of 14% (1/7) of the E-cells were blocked by kynurenic injection into the PAG. It is concluded that: (1) in response to chemical stimulation of MPO, the number of I-cells that were inhibited was more than three times the number of I-cells that were excited; in contrast, the number of E-cells that were excited was more than twice the number of E-cells that were inhibited. (2) The interaction between MPO and NRM can be modulated by blockade of the neuronal transmission or blockade of the glutamatergic system in the PAG. (3) Simultaneous activity of many synapses is required for activation of the MPO-NRM pathway. (4) MPO to NRM interaction is mediated by fibers with a conduction velocity of less than 1m/s.

Cardiovascular responses to subseptic doses of endotoxin contribute to differential neuronal activation in rat brain

The contribution of cardiovascular activity in the early central responses to systemic inflammation was assessed in rats following intravenous administration of subseptic doses of lipopolysaccharide (LPS). LPS at 12.5 microg/kg increased heart rate (HR) but did not alter mean arterial pressure (MAP), and induced interleukin-1 beta (IL-1 beta) gene expression at 1 h in circumventricular organs (CVOs), choroid plexus, meninges, blood vessels, and pituitary gland. IL-1 beta mRNA levels were attenuated at 2 h in most regions studied. LPS at 50 microg/kg caused a biphasic change in MAP, increased HR, increased levels of arginine vasopressin heteronuclear RNA in the hypothalamic paraventricular nucleus (PVN), and induced IL-1 beta gene expression in the nucleus of the solitary tract (NTS) at 1 h. LPS (both doses) induced Fos-like immunoreactivity (FLI) in the area postrema, organum vasculosum of the lamina terminalis, NTS, preoptic area, supraoptic nucleus, and PVN at 1 h. In the PVN, neurons with FLI were found primarily in the dorsal and dorsal medial parvocellular divisions after 12.5 microg/kg of LPS whereas neurons with FLI were found throughout the PVN after 50 microg/kg of LPS. After 2 h, FLI was widespread throughout the brain. Plasma ACTH levels were elevated at 1 and 2 h in response to both doses of LPS, and levels of CRF mRNA were increased after 2 h in the parvocellular PVN. Our results reveal that central responses to increasing doses of LPS show different patterns which are related to activation of distinct immune and viscerosensory pathways, and that cardiovascular responses contribute to early neuronal activation as LPS concentrations are increased.

The organization of preoptic-medullary circuits in the male rat: evidence for interconnectivity of neural structures involved in reproductive behavior, antinociception and cardiovascular regulation

The present studies used anatomical tract-tracing techniques to delineate the organization of pathways linking the medial preoptic area and the ventral medulla, two key regions involved in neuroendocrine, autonomic and sensory regulation. Wheatgerm agglutinin-horseradish peroxidase injections into the ventromedial medulla retrogradely labeled a large number of neurons in the medial preoptic area, including both the median and medial preoptic nuclei. The termination pattern of preoptic projections to the medulla was mapped using the anterograde tracers Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine. Tracer injections into the preoptic area produced a dense plexus of labeled fibers and terminals in the ventromedial and ventrolateral pons and medulla. Within the caudal pons/rostral medulla, medial preoptic projections terminated heavily in the nucleus raphe magnus; strong anterograde labeling was also present in the pontine reticular field. At mid-medullary levels, labeled fibers focally targeted the nucleus paragigantocellularis, in addition to the heavy fiber labeling present in the midline raphe nuclei. By contrast, very little labeling was observed in the caudal third of the medulla. Experiments were also conducted to map the distribution of ventral pontine and medullary neurons that project to the medial preoptic area. Wheatgerm agglutinin-horseradish peroxidase injections in the preoptic area retrogradely labeled a significant population of neurons in the ventromedial and ventrolateral medulla. Ascending projections from the medulla to the preoptic area were organized along rostral-caudal, medial-lateral gradients. In the caudal pons/rostral medulla, retrogradely labeled cells were aggregated along the midline raphe nuclei; no retrograde labeling was present laterally at this level. By contrast, in the caudal half of the medulla, cells retrogradely labeled from the medial preoptic area were concentrated as a discrete zone dorsal to the lateral reticular nucleus; labeled cells were not present in the ventromedial medulla at this level. The present findings suggest that the medial preoptic area and ventral midline raphe nuclei share reciprocal connections that are organized in a highly symmetrical fashion. By contrast, preoptic-lateral medullary pathways are not reciprocal. These preoptic-brainstem circuits may participate in antinociceptive, autonomic and reproductive behaviors.

The medial preoptic area modulates the increase in plasma glucose and free fatty acid mobilization induced by acute cold exposure

The effect of cold exposure (0 degrees C, 1 h) on free fatty acid (FFA) mobilization and plasma glucose was studied in freely moving male rats injected with adrenergic blockers (phentolamine or propranolol) into the medial preoptic area (MPOA). The rats were implanted with chronic jugular catheters for blood sampling and with unilateral intracerebral cannulas placed just above the MPOA. Blood samples were taken 2 min before and 10, 20, 40 and 60 min after cold exposure. After cold exposure plasma glucose and plasma FFA levels rose rapidly, reaching a peak at 20 min post-stimulus. Previous administration of phentolamine (50 nmol), but not propranolol (100 nmol), into the MPOA blocked the glycemic response to cold exposure. On the other hand, previous administration of propranolol, but not phentolamine, into the MPOA blocked the increased FFA mobilization in response to cold exposure. On the basis of these results, we propose that MPOA alpha-adrenergic synapses relay impulses activating the sympathetic outflow expressed by neurally mediated hyperglycemia, and beta-adrenergic synapses relay impulses activating the sympathetic outflow to the adipose tissue, increasing FFA acid mobilization.

Modulation of plasma glucose by the medial preoptic area in freely moving rats

The effect of norepinephrine (NE) injection into the medial preoptic area (MPOA) on plasma glucose was studied in freely moving male rats. The rats were implanted with chronic jugular catheters for blood sampling and with unilateral intracerebral cannulas placed just above the MPOA. Blood samples were taken immediately before and 5, 10, 15, and 30 min after NE injection. As early as 5 min after NE injection, plasma glucose levels rose rapidly, reaching a peak at 15 min poststimulus. The hyperglycemic response to NE injection into the MPOA was dose-related within the range of doses tested (10, 20, and 40 nmol). Previous administration of phentolamine (50 nmol), but not propranolol (100 nmol), into the MPOA blocked the hyperglycemic response to NE injection into the MPOA. The increase of plasma glucose induced by NE into the MPOA and the blockade of the hyperglycemic response to NE by phentolamine suggest the involvement of an alpha-adrenergic mechanism in MPOA-mediated hyperglycemia. On the basis of these and previous results, we propose that MPOA alpha-adrenergic synapses relay impulses activating the sympathetic outflow expressed by neurally mediated hyperglycemia.

Immunohistochemical mapping of neuropeptides in the premamillary region of the hypothalamus in rats

The topographical distribution of neuropeptide-containing cell bodies, fibers and terminals was studied in the premamillary region of the rat hypothalamus using light microscopic immunohistochemistry. Alternate coronal sections through the posterior third of the hypothalamus of normal and colchicine-treated male rats were immunostained for 19 different neuropeptides and their distributions were mapped throughout the following structures: the ventral and dorsal premamillary, the supramamillary, the tuberomamillary and the posterior hypothalamic nuclei, as well as the premamillary portion of the arcuate nucleus and the postinfundibular median eminence. Seventeen of the investigated neuropeptides were present in neuronal perikarya, nerve fibers and terminals while the gonadotropin associated peptide and vasopressin occurred only in fibers and terminals. Growth hormone-releasing hormone-, somatostatin-, alpha-melanocyte stimulating hormone-, adrenocorticotropin-, beta-endorphin- and neuropeptide Y-immunoreactive neurons were seen exclusively in the premamillary portion of the arcuate nucleus. Thyrotropin-releasing hormone-, dynorphin A- and galanin-containing neurons were distributed mainly in the arcuate and the tuberomamillary nuclei. A high number of methionine- and leucine-enkephalin-immunoreactive cells were detected in the arcuate and dorsal premamillary nuclei, as well as in the area ventrolateral to the fornix. Substance P-immunoreactive perikarya were present in very high number within the entire region, in particular in the ventral and dorsal premamillary nuclei. Cell bodies labelled with cholecystokinin- and calcitonin gene-related peptide antisera were found predominantly in the supramamillary and the terete nuclei, respectively. Corticotropin-releasing hormone-, vasoactive intestinal polypeptide- and neurotensin-immunoreactive neurons were scattered randomly in low number, mostly in the arcuate and the ventral and dorsal premamillary nuclei. Peptidergic fibers were distributed unevenly throughout the whole region, with each peptide showing an individual distribution pattern. The highest density of immunoreactive fibers was presented in the ventral half of the region including the arcuate, the ventral premamillary and the tuberomamillary nuclei. The supramamillary nucleus showed moderately dense fiber networks, while the dorsal premamillary and the posterior hypothalamic nuclei were poor in peptidergic fibers.

Hypothalamic modulation of splenic natural killer cell activity in rats

1. The cytotoxic activity of splenic natural killer cells measured by a standard chromium release assay in urethane and alpha-chloralose-anaesthetized rats was significantly suppressed 20 min after bilateral ablation of the medial part of the preoptic hypothalamus (MPO). The suppression was completely blocked by prior splenic denervation. The splenic natural killer cell activity of MPO sham-lesioned rats or thalamus-lesioned rats, both having an intact splenic innervation, were not different from that of a non-treated control group. 2. Electrical stimulation of the bilateral MPO (0.1 ms, 0.1-0.3 mA, 5-100 Hz) suppressed the efferent activity of the splenic nerve in all six rats examined. The reduction of the nerve activity was accompanied by a transient fall in blood pressure. An I.V. injection of phenylephrine (3 micrograms/0.3 ml) also evoked a suppression of the nerve activity, which was accompanied by transient hypertension, suggesting that the suppressive effect of the MPO stimulation was independent of changes in blood pressure. On the other hand, a bilateral lesion of the MPO resulted in a sustained increase in the electrical activity of the splenic sympathetic nerve filaments which lasted for more than 2 h. 3. Microinjection of monosodium-L-glutamate (0.1 and 0.01 M in 0.1 microliters saline) unilaterally into the MPO evoked a transient suppression of the efferent discharge rate of the splenic nerve activity within 1 min, which was also accompanied by a decrease in blood pressure. The injection of saline (0.1 microliter) into the MPO had no effect. The microinjection of recombinant human interferon-alpha (200 and 2000 U in 0.1 microliter saline) into the MPO dose dependently increased the splenic nerve activity without any change in blood pressure. 4. In contrast, microinjection of interferon-alpha into the paraventricular nucleus of the hypothalamus (PVN) had no effect on splenic nerve activity, although an injection of glutamate increased the nerve activity. 5. The present results, taken together with previous reports, suggest that the neuronal networks between the MPO and the splenic sympathetic nerve, which may be activated by centrally administered interferon-alpha, are important in the suppression of the splenic cellular immunity.

Thermoregulatory responses following injection of 5-hydroxytryptamine into the septohippocampal complex in rats

The present study investigated the change in thermoregulatory responses following microinjection of 5-hydroxytryptamine (5-HT) into the lateral septum and the hippocampus of unanesthetized, unrestrained rats. Intraseptal injection of 5-HT (5 to 20 micrograms) caused a dose-related fall in core temperature (Tb), which was associated with a decrease in heat production (HP). As the decrease in HP can not completely account for the magnitude of the decrease in Tb, increase in heat loss may also be involved in the 5-HT-induced hypothermia. In contrast to observed changes following intraseptal injection, no significant change in either Tb or HP was observed after microinjection of the same doses of 5-HT into the hippocampal areas, indicating that the hypothermic response to intraseptal injection of 5-HT is site specific. Further, the hypothermic response to intraseptal injection of 5-HT was only attenuated by systemic pretreatment with cyproheptadine, but not by naloxone or scopolamine, indicating that the hypothermic response is mediated by 5-HT receptor, but not by endogenous opioid and cholinergic systems.

Differential projections of the anterior and posterior regions of the medial amygdaloid nucleus in the Syrian hamster

The medial nucleus of the amygdala is important for the neural control of reproductive behavior in the adult male Syrian hamster. Two types of signals are essential for this behavior, chemosensory stimuli and gonadal steroids; these signals appear to be received in different parts of the medial nucleus. The anterior region receives input from olfactory and vomeronasal systems, both of which are required for this behavior, whereas the posterior region receives gonadal hormone inputs. Behavioral studies have also suggested a functional differentiation of these two areas; electrolytic lesions of the anterior, but not the posterior, part eliminates normal sexual behavior. In this study, the efferent projections of the anterior and posterior divisions of the medial nucleus of the amygdala in the Syrian hamster were analyzed throughout the forebrain after injections of the anterograde neuronal tracer, Phaseolus vulgaris-leucoagglutinin. Neurons of the anterior, but not the posterior, medial nucleus, were found to project to numerous olfactory bulb projection areas and to the ventral striatopallidal complex. Within areas of the chemosensory circuitry that control reproductive behavior, the anterior region of the medial nucleus projects to the intermediate part of the posterior bed nucleus of the stria terminalis and the lateral part of the medial preoptic area, whereas the posterior region of the medial nucleus projects to the medial parts of these areas. Differences in targets were also observed in the ventromedial nucleus of the hypothalamus where the anterior region projects to the core while the posterior part projects to the shell of this nucleus. Furthermore, reciprocal projections between the anterior and posterior regions of the medial nucleus were observed. Taken together, these studies support the hypothesis that the anterior and posterior regions of the medial amygdaloid nucleus provide substantially different contributions to the control of reproductive behaviors.

A subset of progesterone target neurons have axonal projections to the midbrain

Progestin-concentrating neurons in the preoptic area and hypothalamus that project to the midbrain in the female rat were identified using the combined steroid hormone autoradiography-retrograde axonal tracing technique. Progesterone target neurons were most abundant in the periventricular preoptic area and the medial preoptic nucleus, and in the ventromedial and arcuate nuclei of the hypothalamus. In the medial preoptic area as a whole, about 14% of the progestin-concentrating cells were afferent to the midbrain. More specifically, 23% of medial preoptic nucleus progesterone target neurons communicated directly with midbrain cell groups, whereas a much smaller percentage (2%) of periventricular preoptic target neurons projected to the midbrain. In the medial basal hypothalamus as a whole, 11% of the progestin-concentrating cells detected sent axons to the midbrain. This proportion was slightly higher in the ventromedial nucleus (15%), and much lower in the arcuate nucleus (3%). In the dorsal and lateral hypothalamic areas, close to 30% of the progesterone target neurons sent axons to the midbrain, although the total number and density of target cells in the two latter areas was low. These data support the idea that transduction by forebrain target neurons of the progesterone signal into altered synaptic transmission in the midbrain is one route through which progesterone can influence a variety of behaviors.

Involvement of organum vasculosum of lamina terminalis and preoptic area in interleukin 1 beta-induced ACTH release

Intravenous administration of recombinant human interleukin 1 beta (IL-1 beta, 1 micrograms/100 g body wt) resulted in a marked elevation of plasma adrenocorticotropic hormone (ACTH) levels, with peak levels at 10 min, in conscious unrestrained rats. One week after the placement of a lesion by radiofrequency or microinjection of kainic acid in the organum vasculosum of lamina terminalis (OVLT) but not in subfornical organ, ACTH response to intravenous IL-1 beta was enhanced, whereas both radiofrequency-induced lesion and kainic acid in the preoptic area (POA) suppressed the response. Indomethacin or a prostaglandin E (PGE) antagonist microinjected into the OVLT or POA suppressed or abolished the response. On the other hand, PGE, but not PGD2, microinjected into the POA increased plasma ACTH levels. These results suggest an important role for the OVLT, which lacks blood-brain barrier, as a possible site of entry of blood-borne IL-1 beta into the brain and for the POA, which may contain the neurons required for the response. Involvement of PGE in the OVLT and POA in the ACTH response to intravenous IL-1 beta is also suggested.

CNS connections with the median raphe nucleus: retrograde tracing with WGA-apoHRP-Gold complex in the rat

In this work we examined the neuronal input to one of the serotoninergic centers in the brain, median raphe nucleus (MR). Special consideration is given to projections of the hypothalamus. To describe the afferents to MR, a retrograde transport technique was used after microinjection of WGA-apoHRP-Gold complex under pressure and subsequent gold-silver intensification on formaldehyde-fixed rat brain sections. Optimal conditions were obtained when the coordinates of the injection site were A +/- 1.5, L +/- 0.15, and H +/- 2.7 according to Paxinos and Watson (The Rat Brain in Stereotaxic Coordinates. New York: Academic Press, '82). Results obtained under these conditions show a heterogeneous distribution of labeled neurons throughout the brain, including a large proportion (+/- 65%) of hypothalamic neurons. Extra-hypothalamic neurons projecting to MR were from the prefrontal cortex, lateral and medial habenular nuclei, the pontine area of the central grey, interpeduncular nucleus, dorsal raphe nucleus, oculomotor and trochlear nuclei, dorsal and laterodorsal tegmental nuclei, parabrachial nuclei, and lateral and interpositus cerebellar nuclei. Hypothalamic neurons connected to MR were found to be from medial and lateral preoptic areas, lateral hypothalamus, dorsomedian nucleus, the perifornical area, and the complex of mammillary bodies. Many other discrete regions contained different densities of labeled perikarya: the medial preoptic nucleus, paraventricular nucleus, retrochiasmatic area, arcuate nucleus, lateral magnocellular nucleus, and the posterior area. The MR appears as an integrative center receiving many neuroanatomically and functionally heterogeneous inputs from the whole brain.

Indomethacin-induced antipyresis in the rat: role of vasopressin receptors

Infusion of 15 micrograms/microliters (approximately 120 micrograms/kg/h) of indomethacin within the ventral septal area of the rat brain significantly reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. A bolus injection of a V1 receptor antagonist, d(CH2)5Try(Me)AVP, (200, 2000, or 20,000 pmol) within the ventral septal area had no effect of body temperature alone but did suppress the PGE1-induced fever. Similar bolus injections of the V1 receptor antagonist within the ventral septal area failed to alter the antipyretic action of indomethacin on the hyperthermia resulting from centrally administered PGE1. Central injections of a V2 receptor antagonist failed to alter either the PGE1-induced fever or the indomethacin-evoked antipyresis. The results suggest that the V1 receptor antagonist may exert non-specific neurodepressant effects which may interfere with the expression or production of PGE1 hyperthermia and may further mask any contribution of arginine vasopressin to the antipyretic effects of indomethacin.

Blockade of prostaglandin E1 hyperthermia by sodium salicylate given into the ventral septal area of the rat brain

1. Sodium salicylate (30.0 micrograms microliter-1) or artificial cerebrospinal fluid (ACSF) was infused bilaterally into the ventral septal area (v.s.a.) of the unrestrained rat for 1 h before and 1 h after the injection of prostaglandin E1 at a concentration of 20.0 ng microliter-1 into a lateral cerebral ventricle. 2. During control (ACSF) infusions, 200.0 ng of prostaglandin E1 evoked a hyperthermic response (0.95 +/- 0.16 degrees C). During sodium salicylate infusions, the prostaglandin E1-evoked hyperthermia was significantly reduced (P less than 0.025) to 0.31 +/- 0.16 degrees C. 3. The fever index (degrees C h for 1.0 h) during the infusion of sodium salicylate was reduced 66% below that of control infusions (P less than 0.01). 4. These data indicate that sodium salicylate infused in the v.s.a. of rats can antagonize a prostaglandin E-evoked hyperthermia. This suggests that there may be an additional mechanism of action for sodium salicylate antipyresis other than inhibition of prostaglandin E synthesis.

Effects of neural stimuli on paraventricular nucleus neurones

The electrical activity of 122 neurones mostly located within the parvocellular components of the hypothalamic paraventricular nucleus (PVN) was recorded in urethane-anaesthetized male rats. Spontaneous activity and responses to single-shock stimulation of the following sites were recorded: median eminence (ME), neurohypophysis (PIT), preoptic area (POA), nucleus accumbens (ACB), subiculum (SUB), sciatic nerve (ScN), and photic (Ph) stimulation. Stimulation of ME antidromically invaded 14% of the cells recorded, the spontaneous firing rate of these neurones was significantly slower than that of the rest of the population. The responses of the neurones identified as projecting to ME, to the above stimuli, were generally found to be in the same direction as for the whole population but the proportions of the majority responses were greater. Identified cells mainly responded with orthodromic excitation following POA, SUB, ScN, and Ph stimulation whereas ACB stimulation produced a greater proportion of inhibitiory responses. High degrees of convergence were found following afferent stimuli. The possibility that some of the neurones projecting to ME may be candidates for the corticotropin-releasing factor (CRF-) cells, is discussed.

Central nervous regulation of body temperature in vertebrates: comparative aspects

Thermal fluctuations affect, and are responded to by, nearly all forms of life. The basic vertebrate template has guided and shaped the ways that animals in this subphylum cope with thermal challenges. This has led to a situation where there are major similarities in the neuronal mechanisms which sense temperature and control the responses to temperature change in all vertebrates, from fish to mammals. The PO/AH is the most important single integration site for temperature regulation and (except for birds) is also important in the sensing of core temperature. Other portions of the brainstem as well as the spinal cord are also involved in thermal control and can sense, integrate, and produce appropriate efferent signals to varying degrees. Peripheral thermal input to the hypothalamic areas is via the brainstem reticular areas. A number of studies has related the thermal response characteristics of CNS single neurons to the thermoregulatory output of intact animals. These studies have been performed on neurons in whole animal, brain slice, and tissue culture preparation. These neurophysiological studies of central neurons are informative, but are sometimes difficult to interpret because of the chronic lack of definite criteria to differentiate generalized thermal sensitivity from thermal sensitivity utilized for regulating body temperature. Recent neuroanatomical work has illustrated that many areas previously implicated in the thermoregulatory network (such as the septum, various hypothalamic nuclei, the midbrain reticular formation, and the midbrain raphé nuclei) receive direct projections from PO/AH neurons. When compared, the neurophysiological and neuroanatomical characteristics of the preoptic nucleus and anterior hypothalamic area are similar, but not identical. The broad differences in the responses that vertebrates utilize to deal with thermal change is largely determined by the respiratory medium (water or air) and whether metabolic energy (endothermy) or ambient temperature (ectothermy) is of primary importance in the determination of internal temperature. A number of physiological systems are perturbed in water breathing ectotherms when the ambient temperature is altered. In these vertebrates long-term acclimation is very important and has a major effect on temperature selection. Air breathing ectotherms are less adversely affected by temperature change; long-term thermal acclimation is less important and has little effect upon temperature selection; large thermal changes are often initiated by these animals. Endotherms rely on insulation and a high, variable metabolic rate to maintain a constant internal temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of forebrain neurons which project directly to the medulla and spinal cord of the rat by retrograde tracing with wheat germ agglutinin

Wheat germ agglutinin (WGA) in a slow-release polyacrylamide gel pellet was implanted in the medulla or spinal cord of the rat. Large numbers of retrogradely labeled cells were visualized by immunocytochemical procedures in specific nuclei of the forebrain mainly ipsilateral to the implant site following implants as far caudal as the sacral segments of the spinal cord. Total average number of labeled forebrain cells (three brains per category; 100 micron per 150 micron of brain tissue were examined microscopically): medulla, 2,115; cervical, 1,878; lumbar, 1,017; sacral, 385. After WGA-gel implants in the medulla or cervical cord the majority of retrogradely labeled neurons were seen in the lateral hypothalamic area, the zona incerta, and in subdivisions of the paraventricular nucleus. A continuum of labeled cells extended from the caudal part of the paraventricular nucleus into the posterior hypothalamus and into the central gray of the midbrain. Labeled cells were also seen in the medial basal hypothalamus and the rostral part of the bed nucleus of the stria terminalis. A few labeled cells were observed in the medial and lateral preoptic areas, the rostral part of the paraventricular nucleus, and in the arcuate nucleus. Following WGA-gel implants in the lumbar or sacral cord many retrogradely labeled cells were observed mainly in the paraventricular nucleus, the lateral hypothalamus, zona incerta, medial basal hypothalamus, and posterior hypothalamic area. The continuum of labeled cells described above was also seen following these implants. Our data indicate that the lateral hypothalamus and zona incerta, as well as specific parts of the paraventricular nucleus, are major loci of neurons which project directly to the medulla and spinal cord of the rat. The consistency with which labeled cells were localized across all brains examined within categories of implant sites and the large numbers of labeled cells counted within these areas appeared to verify the sensitivity of our retrograde tracing method. Therefore, we interpret the paucity or absence of labeled cells in particular brain regions to indicate that cells of these regions do not project to the medulla or spinal cord.

Medial hypothalamic lesions and play fighting in juvenile rats

The effects of medial preoptic area (MPOA), anterior hypothalamic (AH) and ventromedial hypothalamic (VMH) lesions on play fighting were studied in juvenile rats that were housed and observed in heterosexual groups of 6-8 animals. Overall males engaged in play fighting more frequently than females and none of the lesions reliably affected this measure. Males also initiated more play fights. AH and VMH lesions reduced the frequency of play initiation in both sexes, but MPOA lesions had no reliable effect in either sex.

Effect of testosterone on medial preoptic/anterior hypothalamic neurone responses to stimulation of the lateral septum

Electrophysiological recordings were made from medial preoptic/anterior hypothalamic (MPOAH) neurones which could be orthodromically excited from the lateral septum (LS) in gonadally intact and castrated male rats. Castration significantly reduced the mean percentage of MPOAH neurones which responded reliably to 0.6 Hz stimulation (from 81.1% to 54.1%) and this could be reversed by testosterone propionate (from 52.5% to 90.1%). Both in the gonadally intact (58.1%) and castrated (53.8%) groups these MPOAH neurones with LS inputs also had inputs from the contralateral fimbria (CFIMB). A further experiment investigated whether these MPOAH neurones responding to LS stimulation had connections with the arcuate/median eminence (ARC/ME) region or the medial forebrain bundle (MFB). Altogether, 23.2% projected directly into the MFB and 9.5% into the ARC/ME. A further 28.4% and 31.6% of these MPOAH neurones received inputs from these respective brain regions. A small population of MPOAH neurones were also found which could be driven antidromically both from the LS and the MFB. Results show that testosterone alters the responsiveness of MPOAH neurones to stimulation of the LS. Since subpopulations of these neurones project to the MFB and ARC/ME the effects of castration on them may reflect both changes in sexual behavior and, for example, gonadotropin release.

Multiple connections of medial hypothalamic neurons in the rat

The responses of 700 single neurons in the hypothalamus to electrical stimulation of the preoptic area, limbic structures, and midbrain were studied to determine the location of neurons with multiple inputs and to identify by antidromic activation the projection areas of those neurons. Converging excitatory inputs, observed in 134 responsive hypothalamic neurons, were principally derived from the preoptic, limbic, and midbrain areas. Inputs from separate nuclei of the amygdala were noted in the response of individual hypothalamic neurons. Two classes of short latency transsynaptic responses to amygdala stimulation were defined, indicating either separate pathways from the amygdala to the medial hypothalamus or two types of fibers conducting at different velocities. Stimulation of single or multiple sites in the preoptic and limbic areas, as well as in the arcuate nucleus and medial forebrain bundle produced inhibition of hypothalamic neuronal activity. Most antidromically identified medial hypothalamic neurons projected to the preoptic area, median eminence (tuberoinfundibular neurons), or midbrain. Evidence is presented for collateral projections of tuberoinfundibular neurons to the preoptic area and reticular formation. Medial hypothalamic neurons received inputs from the preoptic area, lateral septal nucleus, amygdala, ventral hippocampus (subiculum), and fornix. These findings illustrate a pattern of reciprocal connections between the medial hypothalamus and limbic and midbrain structures. It was concluded that the hypothalamus contains a type of neuron that is equipped to perform complex integrations and to coordinate directly the behavior of neurons in a diversity of anatomical regions.

Stimulatory role for medial preoptic/anterior hypothalamic area neurones in growth hormone and prolactin secretion. A kainic acid study

The role of preoptic/anterior hypothalamic area (PO/AHA) neurones in the regulation of basal patterns of growth hormone (GH) and prolactin (Prl) secretion was investigated in unanesthetized male rats prepared with chronic indwelling venous cannulae. PO/AHA injections of the neurotoxin kainic acid (KA) substantially reduced both GH and Prl secretion. Histological examination of tissue sections indicated that KA treatment had produced extensive neuronal loss and gliosis in the medial (m) but not the periventricular (p) PO/AHA. These findings suggest that m-PO/AHA neurones are facilitatory to the basal secretion of both GH and Prl. It is proposed that GH-facilitatory m-PO/AHA neurones provide an inhibitory input to the GH release-inhibiting factor neurones which are known to reside in the p-PO/AHA. Prl-facilitatory m-PO/AHA neurones may secrete, or stimulate the secretion of a Prl releasing factor.

Male vole urine changes luteinizing hormone-releasing hormone and norepinephrine in female olfactory bulb

Female prairie voles (Microtus ochrogaster) exposed to a single drop of male urine on the upper lip showed changes in concentrations of luteinizing hormone-releasing hormone (LHRH) and norepinephrine in olfactory bulb tissue; no such changes occurred in dopamine concentration. The changes were measured in the posterior but not the anterior olfactory bulb tissue of females within 1 hour after they were exposed to urine. These females also showed rapid increases in serum concentrations of luteinizing hormone. Females exposed to water on the upper lip showed none of these changes. These results suggest that in this species LHRH and norepinephrine in the olfactory bulb may mediate luteinizing hormone release in response to external (pheromonal) chemical cues.

Presence and localization of immunoreactive luteinizing hormone-releasing hormone (LHRH) within the olfactory bulbs of adult male and female rats

A sensitive and specific radioimmunoassay was employed to measure the immunoreactive luteinizing hormone releasing hormone (LHRH) concentration from localized areas within the olfactory bulbs of adult male and female rats. Although no significant sex differences or lateralization were obtained, LHRH concentration within the posterior half of the olfactory bulb was significantly greater than that obtained in the anterior half for both males and females. The presence of LHRH within the olfactory bulbs and localization to areas involved in the chemical stimulation of reproductive processes suggests the possibility that this olfactory bulb LHRH may be involved in mediating pheromonally stimulated endocrinological responses.

The estrogen-sensitive neural system in the brain of female cats

Estrogens participate in the regulation of gonadotropin secretion and in the control of sexual and aggressive behavior. To elucidate the neuroanatomical substrate for these actions in the female cat, the topographical distribution of estrogen-concentrating cells in the brain was studied by autoradiography. One hour after the intravenous injection of 1 mCi (3 microgram) of 3H-estradiol in three adult ovariectomized cats, radioactivity was concentrated in the nuclei of neurons in several brain areas. Within the telencephalon, high concentrations of moderately to heavily labeled cells were found in the lateral and posterior septal nuclei (n.), bed n. of the stria terminalis (medial division), medial and central amygdaloid n., and amygdalo-hippocampal area. There were also many less strongly labeled cells in the ventral dentate gyrus. Within the diencephalon, many heavily labeled cells were distributed in the medial and periventricular preoptic n., anterior hypothalamic area, and infundibular, ventromedial, and periventricular hypothalamic n. In the brain stem, some labeled cells were located throughout the periaqueductal gray, and in the laminar spinal trigeminal n., n. of the solitary tract, n. incertus, marginal n. of the superior cerebellar peduncle, rostral linear n., and interfascicular n. Although minor differences were noted, the topographical distribution of estradiol-concentrating cells in the female cat brain agreed closely with that reported in other vertebrate species.

Role of the preoptic brain in the regulation of preovulatory gonadotropin surges in the hamster

These studies have examined the role of the preoptic-suprachiasmatic area (POA-SC) in brains of cyclic female hamsters in regulating proestrous preovulatory gonadotropin surges. The spontaneous release of LH and FSH which normally occurs on proestrous afternoon was blocked with phenobarbital. Temporal changes in serum LH and FSH were measured in such blocked animals after delivery of direct current (100 muA/60 s) to the POA-SC or that portion of the medial basal hypothalamus (MBH) which includes the arcuate nuclei and the median eminence. Bilateral dc treatment of MBH resulted in a 30-fold increase in serum LH and a 4-fold rise in serum FSH over basal concentrations. Unilateral MBH dc treatment produced a 12-fold increase in serum LH but FSH levels remained basal. In contrast, the delivery of dc to the POA-SC did not evoke any increase in serum LH or FSH. Sham electrode placement in the MBH or POA-SC also did not alter basal LH and FSH serum concentrations. These results suggest that, unlike the rat, passage of dc with concomitant production of an irritative lesion and deposition of ferrous ion does not activate structures responsible for preovulatory gonadotropin surges in hamsters. In a second study, discrete electrochemical lesions were produced in the basal anterior portion of the preoptic brain. These lesions did not involve the medial preoptic area or the suprachiasmatic nuclei. Following such brain destruction, spontaneous ovulation, LH surges, and 4-day vaginal cyclicity ceased. When the suprachiasmatic nuclei or extensive regions of the dorsal medial preoptic area, including the anterior commissure, were destroyed, vaginal cyclicity was disrupted for only 8-12 days. Thereafter, these animals had spontaneous preovulatory gonadotropin surges and ovulated. Seemingly, input from the medial basal anterior preoptic region (anterior to the SC) is essential for preovulatory LH and FSH surges to occur.

Electrophysiological analysis of pathways connecting the medial preoptic area with the mesencephalic central grey matter in rats

1. An electrophysiological study of ascending and descending connexions between the dorsal raphe region of the mesencephalic periaqueductal grey matter and the medial preoptic area has been performed in dioestrous female rats anaesthetized with urethane. 2. Extracellular action potentials recorded from 208 neurones in the medial preoptic area were analysed for a change in excitability following stimulation of the periaqueductal grey matter. 174 neurones were also tested for changes in excitability following stimulation of the mediobasal hypothalamus. 3. Stimulation of the periaqueductal grey matter at 1 Hz was rarely effective, but short trains of pulses (three at 100 Hz) usually caused an initial inhibition (62.5% of 208) of both projection identified and adjacent neurones of the medial preoptic area, at latencies of 5--90 msec (mean 34.1 +/- 1.4 msec). Inhibition following stimulation of the mediobasal hypothalamus occurred less frequently (34%) and at shorter latency (mean 12.0 +/- 1.8 msec; n = 48). 4. Less frequently (10.6%) periaqueductal grey matter stimulation caused an initial excitation of preoptic neurones at latencies of 15--180 msec, (mean 35.3 +/- 7.2). Initial excitation following mediobasal hypothalamus stimulation was stronger, occurred more frequently (29%) and at shorter latencies (range 3--60 msec, mean 13.1 +/- 1.5). Following such initial excitation, inhibition of spontaneous or ionophoretically evoked activity occurred more frequently following mediobasal hypothalamic stimulation, than after periaqueductal grey matter stimulation. 5. Twenty-four neurones displayed antidromic invasion following periaqueductal grey matter stimulation. Latencies for invasion ranged from 13 to 50 msec (mean 25.5 +/- 2.0 msec) and are suggestive of an unmyelinated projection. Occasionally an abrupt decrease in latency followed an increase in stimulus intensity. Antidromic invasion from mediobasal hypothalamus was characterized by a shorter latency (mean 12.5 +/- 0.7 msec; n = 43). A period of reduced excitability lasting 40--100 msec followed antidromic invasion from either site. 6. Antidromic responses to paired mediobasal hypothalamic or periaqueductal grey matter stimuli at 5 msec intervals revealed an increased latency of invasion of the second response, due to the partial refractory period of the neurone. Five cells showed a decreased latency of invasion at stimulus separations of 10--150 msec, interpreted as evidence of a supranormal period. Changes in conduction velocity during the supranormal period may give rise to a variable latency of invasion of spontaneously active cells. 7. These results provide evidence for direct, reciprocal connexions between the midbrain central grey and the medial preoptic area. These circuits may play a role in controlling neuroendocrine and behavioural aspects of reproductive functions.

The efferent connections of the anterior hypothalamic area of the rat, cat and monkey

The general morphology and topographic relations of the anterior hypothalamic area (AHA) in the rat, cat and squirrel monkey have been described, and its efferent connections analyzed autoradiographically, after small injections of 3H-labeled amino acids into, or around, the area. In all three species the AHA is rather poorly separated from the surrounding preoptic and hypothalamic areas and nuclei but shows three distinct cellular condensations, located rostrally, centrally, and posterodorsally. Closely associated with the AHA are the retrochiasmatic area, the anterior periventricular nucleus and the scattered neurons usually referred to as the accessory supraoptic nucleus. The AHA has primarily short connections to the adjoining medial preoptic area, the lateral hypothalamic area, the periventricular nucleus, the dorsomedial nucleus, and to the "capsule" of the ventromedial nucleus. However, it also has certain more distant projections, rostrally to a narrow zone centered in the ventral part of the lateral septal nucleus, and caudally to the dorsal premammillary nuclei, the posterior hypothalamic area and the central gray. There is some evidence to suggest that the various subdivisions of the AHA have different efferent connections. Thus the posterodorsal cell condensation appears to give rise to the bilateral projection to the dorsal premammillary nuclei, while the projections to the septum, the posterior hypothalamic area and the central gray seem to have their origin in the central condensation. Similarly, the retrochiasmatic area sends its efferents through the ventral supraoptic commissure to the amygdala, the anterior periventricular nucleus contributes to the periventricular fiber system and to the external lamina of the median eminence, and the accessory supraoptic neurons project to the internal lamina of the median eminence.

Preoptic knife cuts and sexual behavior in male rats

Knife cuts aimed at severing either the medial-lateral or dorsal fiber connections of the medial preoptic-anterior hypothalamus (MPOAH) produced two clearly distinguishable patterns of copulatory deficits in male rats. On the other hand, transverse cuts, which were designed to destroy longitudinal connections on either the anterior or posterior end of the MPOAH, did not affect sexual behavior. Males with sagittal cuts exhibited deficits primarily in the initiation of copulation. In contrast, those with dorsal cuts showed alterations primarily in the execution of copulatory behavior. Combined behavioral and anatomical evidence was interpreted as suggesting that the MOPAH has at least two regulatory functions related to sex behavior: (1) it is involved in the mediation of the initiation of copulation through its lateral connections with the medial forebrain bundle, and (2) it influences the achievement of ejaculation and the subsequent refractory period through its dorsal connections with the amygdala and the hippocampus.

Preoptic-hypothalamic control of LH and prolactin release in male rats under pentobarbital anesthesia: differential responses to electrical stimulation

In acute experiments under pentobarbital anesthesia, the brains of adult male rats were stimulated bilaterally with trains of monophasic pulses at different frequencies and current intensities through bipolar, concentric, stainless steel electrodes. Stimulation of the POA-SQ region at 3, 10 (200 muA) or 200 Hz (100 muA) increased plasma prolactin levels within 30 min of the onset of stimulation. Stimulus parameters fully effective when applied to the POA-SQ or ARC-MED. EM. regions were ineffective when applied to the ARC-VMH region. Maximal effects were obtained with 10 Hz (200 muA) stimuli applied to the POA-SQ region. LH levels were increased after stimulation of any of the three regions--POA-SQ, ARC-VMH or ARC-MED. EM. Conversely to the prolactin response, LH levels did not rise after 3 Hz stimulation of the POA-SQ region. In male rats under pentobarbital anesthesia, LH levels seemed to be affected maximally with a stimulus frequency rate of about 50 Hz applied to the POA-SQ region. The results suggest a potential physiological role of frequency discrimination in the functional segregation of LH and prolactin release controls.

Afferent connections of the nucleus raphe dorsalis in the cat as visualized by the horseradish peroxidase technique

Using a retrograde tracer technique with protein horseradish peroxidase (HRP), attempts were made to determine afferent projections to the nucleus raphe dorsalis (NRD). As a control, the injection of the HRP was also made into one of the following structures adjacent to the NRD: (1) mesencephalic periaque ductal gray; (2) nucleus linearis intermedius; and (3) third cranial nucleus. The present results indicate that the NRD, particularly is rostral part, receives direct projections arising from: (1) locus coeruleus complex (locus coeruleus, locus coerulus alpha, and locus subcoeruleus); (2) parabrachial nuclei (nucleus parabrachialis lateralis and medialis); (3) nucleus laterodorsalis tegmenti; (4) griseum centrale pontis, particularly the caudal part of the nucleus incertus; (5) substantia nigra; (6) lateral habenular nucleus; (7) hypothalamic areas, particularly dorsal and lateral hypothalamic areas; (8) preoptic areas; (9) anarea dorso-lateral to the inferior olivary complex and medial to the lateral reticular nucleus; and (10) raphe nuclei; particularly nucleus linearis intermedius, centralis superior, pontis and magnus. The present findings thus confirm some previous reports on the afferent projections to the NRD described in the cat and rat, and further indicate the richness of afferent connections of the NRD. Some problems of the peroxidase technique have also been discussed.

Origin of glutamate-decarboxylase (GAD)-containing cells in discrete hypothalamic nuclei

Glutamate decarboxylase activity (GAD) was assayed in discrete hypothalamic nuclei in the rat following lesions of the major afferent pathways from hippocampus, amygdala, midbrain, septum, thalamus and globus pallidus. None of these lesions led to a marked decrease in GAD activity in selected nuclei. After total deafferentation of the medial-basal hypothalamus GAD remained unchanged in the median eminence but fell markedly in the ventromedial and arcuate nuclei. In these two nuclei a decrease of GAD still occurred following partial deafferentation from lateral and posterior hypothalamus, but not from anterior and preoptic areas. These results indicated that most GAD-containing cells have their origin inside of the hypothalamus. In this region GABAergic neurons are likely to be short interneurons providing intrahypothalamic connections. Such connections are suggested from lateral and posterior hypothalamus onto the medial basal nuclei.