Topography of the dopamine neurons in the arcuate nucleus of the mouse hypothalamus.

The distribution of the dopamine (DA) cell bodies was elucidated within the mouse arcuate nucleus by fluorescence histochemistry. The arcuate nucleus was divided into five regions; heterogeneity in distribution and different amounts of DA among the regional areas were demonstrated. The DA cell bodies containing a large amount of DA, observable even in the arcuate nucleus of the intact mice, distributed in the medial areas of the anterio-central and the middle-central regions and in the dorsal area of the posterior-central region. On the other hand, those containing probably as small amount of DA distributed in the medial area of the rostral region and in the ventral areas of the anterior-central and middle-central regions. They were not observed in the intact mice, but found in the mice treated with nialamide plus alpha-methyldopa. No DA cells were found in the caudal region.     

Immunocytochemical identification of vasopressinergic and oxytocinergic neurons in the hypothalamus of the cat

Our immunocytochemical investigation of the magnocellular neuroendocrine cells in the cat hypothalamus reveals a mixture of vasopressin (VP)- and oxytocin (OT)-containing neurons in the supraoptic (NSO), the paraventricular (NPV) and in five accessory nuclei (NAC). We describe the lateral hypothalamic nucleus (NLH), a new accessory nucleus, lying at the junction of the internal capsule and pallidum, and possibly involved in drinking behavior. Previously characterized incompletely in mammals, the four other accessory nuclei consist of the circularis (NC), anterior fornical (NAF), posterior fornical (NPF) and retrochiasmatic (NRC). The two peptidergic cell types, VP and OT, are equally mixed in the NPV and the NAC, but in the NSO VP neurons predominate. The perikarya of these VP and OT neurons do not show distinct morphological differences at the level of light microscopy. The organization of magnocellular neuroscretory neurons in the cat hypothalamus closely resembles that described in other mammals with the exception of the unique presence of the lateral hypothalamic accessory nucleus.     

Activation of vasopressinergic and oxytocinergic neurons during aging in the Wistar rat

The activity of the hypothalamo-neurohypophyseal system (HNS) was determined in male Wistar rats from 3 to 32 months of age. Plasma levels of vasopressin (AVP) and oxytocin (OXT) were measured by means of a radioimmunoassay. In addition, the distribution of the Golgi apparatus marker enzyme thiamine-pyrophosphatase (TPP-ase) was measured as a parameter for neurosecretory activity in the hypothalamic supraoptic and paraventricular nuclei (SON and PVN). Plasma levels of radioimmunoassayable AVP were increased in the 32-month-old animals. Plasma levels of radioimmunoassayable OXT in 32-month-old animals did not differe from the levels found in the youngest group, but were higher than in 11-month-old animals. Neurosecretory activity in the SON was similar in 3- and 32-month-old animals, whereas in the PVN neurosecretory activity was increased in the 32-month-old animals. Urine excretion decreased between 6 and 11 months of age and remained on the same level until 32 months of age. In other words, instead of a loss of HNS function as has been suggested in the literature, an increased neurosecretory activity was observed in aged rats.     

Glucose-sensing neurons of the hypothalamus

Specialized subgroups of hypothalamic neurons exhibit specific excitatory or inhibitory electrical responses to changes in extracellular levels of glucose. Glucose-excited neurons were traditionally assumed to employ a 'beta-cell' glucose-sensing strategy, where glucose elevates cytosolic ATP, which closes KATP channels containing Kir6.2 subunits, causing depolarization and increased excitability. Recent findings indicate that although elements of this canonical model are functional in some hypothalamic cells, this pathway is not universally essential for excitation of glucose-sensing neurons by glucose. Thus glucose-induced excitation of arcuate nucleus neurons was recently reported in mice lacking Kir6.2, and no significant increases in cytosolic ATP levels could be detected in hypothalamic neurons after changes in extracellular glucose. Possible alternative glucose-sensing strategies include electrogenic glucose entry, glucose-induced release of glial lactate, and extracellular glucose receptors. Glucose-induced electrical inhibition is much less understood than excitation, and has been proposed to involve reduction in the depolarizing activity of the Na+/K+ pump, or activation of a hyperpolarizing Cl- current. Investigations of neurotransmitter identities of glucose-sensing neurons are beginning to provide detailed information about their physiological roles. In the mouse lateral hypothalamus, orexin/hypocretin neurons (which promote wakefulness, locomotor activity and foraging) are glucose-inhibited, whereas melanin-concentrating hormone neurons (which promote sleep and energy conservation) are glucose-excited. In the hypothalamic arcuate nucleus, excitatory actions of glucose on anorexigenic POMC neurons in mice have been reported, while the appetite-promoting NPY neurons may be directly inhibited by glucose. These results stress the fundamental importance of hypothalamic glucose-sensing neurons in orchestrating sleep-wake cycles, energy expenditure and feeding behaviour.     

Histamine-immunoreactive neurons in the hypothalamus of cats

The localization of histaminergic neurons in the cat brain was determined immunohistochemically with an antibody against histamine. We found that histamine-immunoreactive neurons are observed exclusively in the posterior hypothalamus of colchicine treated cats. The larger group of neurons was found in the ventrolateral part of the posterior hypothalamus, including the tuberomammillary nucleus. Histamine-positive neurons were also observed in the supramammillary area and adjacent posterior hypothalamic area, as well as in the peri- and premammillary regions. In addition, numerous histamine immunoreactive fibers were detected, not only in the posterior hypothalamus, but also in other brain areas, such as the preoptic area of the anterior hypothalamus.     

Progestin receptors in substance P-immunoreactive neurons in the hypothalamus of male guinea pigs after behaviorally effective estradiol pulse treatment.

Pulsatile administration of estradiol effectively primes orchidectomized (ORCH) male guinea pigs to display progesterone-facilitated lordosis. In contrast, a single injection of estradiol benzoate (EB) is not behaviorally effective. In ovariectomized female guinea pigs, estradiol pulses induce progestin receptors selectively in substance P neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes females to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P neurons in the VLH in males, ORCH animals received a single injection of EB 40 h before, or two pulses of estradiol-17 beta, 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. The only difference found between the two estradiol treatment groups was a higher number of progestin receptor-immunoreactive (PR-IR) cells in the rostral VLH of estradiol pulse-treated males. There were no significant differences in the number of PR-IR cells in the mid- or caudal VLH, nor in the number of substance P-immunoreactive (SP-IR) neurons in the VLH/ventromedial hypothalamus (VMH) of animals receiving the two estradiol treatments. Furthermore, the percentage of PR-IR cells in the VLH also immunoreactive for SP did not differ between the estradiol pulse- (22%-25%) and the EB-injected animals (22%-32%). These data do not support the hypothesis that administration of behaviorally effective estradiol pulses, as compared to behaviorally ineffective EB injections, induce progestin receptors selectively in substance P neurons in the VLH of male guinea pigs.     

CRF-containing neurons of the rat hypothalamus

Summary The immunoreactive CRF-neurons of the rat hypothalamus have been examined immunohistochemically employing anti-rat CRF serum. These neurons are confined to the paraventricular nucleus, dorsomedial-lateral hypothalamic area, and suprachiasmatic nucleus, and are, respectively, also immunoreactive to anti-Met-enk, -alpha-MSH, and -VIP sera. Intraventricular administration of colchicine (50 g/5 l/rat) induces a dramatic enhancement of the immunostainability of the cell somata, and also accelerates the development of immunoreactivity of other stored peptides, especially in the paraventricular nucleus.The CRF-neurons respond to adrenalectomy by showing increased immunoreactivity and an increase in the number of cell bodies; in the dorsomedial-lateral area and suprachiasmatic nucleus, there is also an enhanced immunoreactivity for alpha-MSH and VIP, respectively. CRF-cells in the paraventricular nucleus become markedly hypertrophied, but do not show any enhanced immunoreactivity for Met-enk. Since the axons of the paraventricular neurons run to the median eminence, it is probable that they are involved with the endocrine control of hypophysial ACTH release. It is concluded that the CRF-containing neurons in rat hypothalamus consist of three types which are functionally and morphologically different.     

Proliferation of lamellar whorls in arcuate neurons of the hypothalamus of male rats treated with estradiol benzoate or cyproterone acetate

Summary The arcuate nucleus of the hypothalamus (AH) of male rats which had been treated either with estradiol benzoate (E²B) or cyproterone acetate (CPA) was examined ultrastructurally for the presence of whorls of endoplasmic reticulum. The incidence of whorl containing neurons (WCN) was 2–4 times higher in the AH of animals treated for 2–3 weeks with E²B or for 2 weeks with CPA than in the AH of oil treated controls. CPA is a powerful anti-androgen while E²B acts both peripherally and centrally to limit testosterone production. These findings, together with previous evidence that whorls proliferate in AH of male rats deprived of androgen by morphine treatment or castration, suggest that steroid feedback (androgen alone or both androgen and estrogen) plays an important role in AH whorl proliferation. The possibility that WCN may be LH-RH containing neurons is suggested by the close correspondence between the number and location of WCN within AH as determined in this study and the distribution of LH-RH containing cells reported by others.The authors are indebted to Schering AG for supplying cyproterone acetate for this study. This work was supported by grants DA-00259, NS-09156 and MH-14677 from U.S.P.H.S.Research Scientist Development Award MH-38894Research Scientist Development Award MH-70180     

Leptin sensitive neurons in the hypothalamus.

A major paradigm in the field of obesity research is the existence of an adipose tissue-brain endocrine axis for the regulation of body weight. Leptin, the peptide mediator of this axis, is secreted by adipose cells. It lowers food intake and body weight by acting in the hypothalamus, a region expressing an abundance of leptin receptors and a variety of neuropeptides that influence food intake and energy balance. Among the most promising candidates for leptin-sensitive cells in the hypothalamus are arcuate nucleus neurons that co-express the anabolic neuropeptides, neuropeptide Y (NPY) and agouti-related peptide (AGRP), and those that express proopiomelanocortin (POMC), the precursor of the catabolic peptide, alphaMSH. These cell types contain mRNA encoding leptin receptors and show changes in neuropeptide gene expression in response to changes in food intake and circulating leptin levels. Decreased leptin signaling in the arcuate nucleus is hypothesized to increase the expression of NPY and AGRP. Levels of leptin receptor mRNA and leptin binding are increased in the arcuate nucleus during fasting, principally in NPY/AGRP neurons. These findings suggest that changes in leptin receptor expression in the arcuate nucleus are inversely associated with changes in leptin signaling, and that the arcuate nucleus is an important target of leptin action in the brain.     

Topography of catecholamine-containing neurons of the locus coeruleus in the cat

Topography of catecholamine-containing (CA) neurons of the cat locus coeruleus was studied using a combination of the catecholamine histofluorescence method and rapid embedding of the brain tissue into the paraffin wax. The distribution of CA neurons was examined at frontal and sagittal sections of the brain stem. Unlike that shown previously the quantity of CA neurons in the rostral pole of the locus coeruleus was somewhat higher while at the frontal level of P--2.0-P--4.0 the significant number of CA cells of the locus coeruleus was localized more ventromedially.     

Catechol estradiol induced implantation in the mouse

Induction of implantation is among the most sensitive responses to estrogens. The ability of catechol estradiols, 4-hydroxy-estradiol-17 beta (4-OH-E2) and 2-hydroxy-estradiol-17 beta (2-OH-E2), to induce implantation in ovariectomized pregnant mice was compared to that of estradiol-17 beta. Delayed implantation was maintained by the daily administration of 2 mg of progesterone. A single injection of 3 ng of estradiol-17 beta, 50 ng of 4-OH-E2, or 2,000 ng of 2-OH-32 consistently induce a full complement of implantation sites in all animals. Before the estrogenicity of the latter steroid can be established the lack of contaminating estrogens must be proved.     

Immunocytochemical localization of somatostatin-containing neurons in the rat hypothalamus

Summary The rat hypothalamus was studied at the light microscopic level with the use of single and double immunocytochemical staining methods. It was shown that the rat supraoptic and paraventricular hypothalamic nuclei, and their accessory neurosecretory nuclei, do not contain magnocellular somatostatin neurons. The distribution of the hypothalamic parvocellular somatostatin cells is described. The parvocellular component of the rat hypothalamic paraventricular nucleus is, at least partly, composed of somatostatin cells: they form a fairly well circumscribed periventricular cell mass. The rat suprachiasmatic nuclei contain separate somatostatin neurons and vasopressin neurons. Scattered somatostatin cells are present in the entire arcuate nucleus. In addition to the periventricular somatostatin cells located in the preopticanterior hypothalamic area and in the arcuate nucleus, the rat hypothalamus also contains numerous scattered somatostatin cells located distant from the third ventricle.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Electrophysiological effects of MCH on neurons in the hypothalamus

Melanin concentrating hormone (MCH) has been implicated in many brain functions and behaviors essential to the survival of animals. The hypothalamus is one of the primary targets where MCH-containing nerve fibers and MCH receptors are extensively expressed and its actions in the brain are exerted. Since the identification of MCH receptors as orphan G protein coupled receptors, the cellular effects of MCH have been revealed in many non-neuronal expression systems (including Xenopus oocytes and cell lines), however, the mechanism by which MCH modulates the activity in the neuronal circuitry of the brain is still under investigation. This review summarizes our current knowledge of electrophysiological effects of MCH on neurons in the hypothalamus, particularly in the lateral hypothalamus. Generally, MCH exerts inhibitory effects on neurons in this structure and may serve as a homeostatic regulator in the lateral hypothalamic area. Given the contrast between the limited data on cellular functions of MCH in the hypothalamus versus a fast growing body of evidence on the vital role of MCH in animal behavior, further investigations of the former are warranted.     

Prolactin-secreting neurons in the dorsolateral hypothalamus in Sprague-Dawley rats

By means of immunocytochemical techniques ovine prolactin like immunoreactivity (oPRL-LIR) has been demonstrated in the perikarya located around fornix in the dorso-lateral part of the rat hypothalamus. No PRL-LIR was observed in the arcuate n. perikarya. Immunoreactive fibers were present in the hypothalamus, medial thalamus, accumbens and amygdaloid nuclei.     

Effect of estradiol on the spontaneous activity of individual neurons in the arcuate area of the hypothalamus at different stages of the estrus cycle in rats

Microiontophoretic application of estradiol into the arcuate region of the hypothalamus increased the activity of single neurons in the majority of experiments. This reaction was more pronounced at the stage of dietrus-1 and diestrus-2 than during proestrus. It is supposed that the changes in the prevailing reactions of the arcuate region neurons to the estradiol administration in the course of the estrual cycle were determined by the level of the endogenous estrogens and gonadotropins of the hypophysis in the peripheral blood.     

Xylazine activates oxytocinergic but not vasopressinergic hypothalamic neurons under normal and hyperosmotic conditions in rats

Role of central alpha2-adrenoceptors in the regulation of hypothalamic magnocellular cells was studied under hyperosmotic challenge elicited by hypertonic saline (HS). Rats pretreated with receptor agonist, xylazine (XYL), were injected intraperitoneally with different (low: 0.375, moderate: 0.75, high: 1.5 M) HS 30 min later. The activity of the paraventricular (PVN) and supraoptic (SON) vasopressin and oxytocin perikarya was established by Fos-dual-immunohistochemistry 60 min after HS administration. Results showed that 1/XYL is a potent stimulus for oxytocin but not vasopressin magnocellular cells under basal and weak hyperosmotic conditions 2/highHS completely overlaps the effect of XYL. In addition, XYL partially suppressed Fos expression in the parvocellular PVN cells activated by highHS. The data suggest that alpha2-adrenoceptors may play an important role in the regulation of oxytocinergic PVN and SON neurons under basal and weak hyperosmotic conditions and that alpha2-adrenoceptors may also participate in the control of PVN parvocellular cells under intense osmotic challenge.