Ventromedial Preoptic Area Research Articles

Activation of neurons projecting to the paraventricular hypothalamic nucleus by intravenous lipopolysaccharide.

The central nervous system interacts with the immune system to coordinate several components of the acute phase response, although the specific neuroanatomical pathways that mediate these responses are still uncharacterized. However, neurons in both the autonomic and endocrine components of the paraventricular hypothalamic nucleus (PVH) are characteristically activated in different models of immune stimulation. In the current study, we have used intravenous administration of lipopolysaccharide (LPS; 5 or 125 micrograms/kg) to induce the acute phase response. We subsequently coupled immunohistochemistry for Fos (as a marker of neuronal activation) with retrograde transport of the neuroanatomical tracer cholera toxin-b from the PVH. Several of the activated cell groups directly projected to the paraventricular nucleus, including the visceromotor (infralimbic) cortex, median preoptic nucleus, ventromedial preoptic area, bed nucleus of the stria terminalis, parabrachial nucleus, ventrolateral medulla, and nucleus of the solitary tract. These findings indicate that immune system stimulation activates cell groups from multiple nervous system levels that project to the paraventricular nucleus. We hypothesize that the activation of specific autonomic and endocrine elements of the PVH may be due to the activity of distinct afferents that converge on the PVH from multiple components of the central autonomic control system. Our results are consistent with the hypothesis that the PVH plays a key role in integrating diverse physiological cues into the varied manifestations that constitute the cerebral component of the acute phase response.

Ventromedial Preoptic Prostaglandin E2 Activates Fever-Producing Autonomic Pathways

Fever is thought to be initiated by pyrogenic cytokines inducing the production of prostaglandin E2 (PGE2) in the preoptic area (POA); PGE2 may act as a paracrine mediator that stimulates the neural pathways that raise body temperature. This essential role for prostaglandins in fever first was proposed 25 years ago, but the specific preoptic cell groups at which PGE2 acts and the pathways through which fever is produced remain poorly understood. To better define the role of preoptic PGE2 in fever, we developed a new method for combining acute brain injections with Fos immunohistochemistry. We microinjected a threshold dose of PGE2 to construct an anatomically detailed map of fever-producing preoptic sites. The most pyrogenic preoptic sites were clustered along the ventromedial aspect of the POA, surrounding and just anterior to the organum vasculosum of the lamina terminalis. We then used Fos immunohistochemistry to identify the pattern of neural activation induced by fever-producing preoptic injections of PGE2 and compared it with the Fos pattern seen after systemic immune stimulation. PGE2 fever was accompanied by Fos induction in the ventromedial POA and the parvicellular subnuclei of the paraventricular nucleus of the hypothalamus (PVH). In contrast to the Fos pattern seen after intravenous lipopolysaccharide administration, PGE2 injection did not induce Fos in the circumventricular organs or the magnocellular subnuclei of the PVH. These observations establish a potential site of PGE2 action during fever and help define candidate pathways through which fever occurs.

Distribution of Fos-like immunoreactivity in the rat brain following intravenous lipopolysaccharide administration.

The central nervous system, particularly the hypothalamus, is intimately involved in the coordination of various aspects of the inflammatory response, including the generation of fever. We used intravenous injections of bacterial cell wall lipopolysaccharide (LPS; 5 or 125 micrograms/kg) to stimulate the acute phase response and mapped the resultant distribution of Fos-like immunoreactivity in the rat brain. In addition, we compared the patterns of Fos distribution with the thermoregulatory responses elicited by the LPS. Administration of LPS resulted in a dose- and time-dependent pattern of Fos-like immunoreactivity throughout the rat brain consistent with a coordinated autonomic, endocrine, and behavioral response to the LPS challenge that was most pronounced 2 hours following injection. Specifically, Fos-like immunoreactivity was observed in key autonomic regulatory nuclear groups, including the insular and prelimbic cortices, paraventricular hypothalamic nucleus, parabrachial nucleus, nucleus of the solitary tract, and the rostral and caudal levels of the ventrolateral medulla. In addition, a significant sustained elevation of Fos-like immunoreactivity was observed in a cell group adjacent to the organum vasculosum of the lamina terminalis, which we termed the ventromedial preoptic area. This sustained elevation of Fos-like immunoreactivity coupled with the alterations in body temperature elicited by LPS leads us to hypothesize that the ventromedial preoptic area may be a key site for the initiation of fever during endotoxemia.

Quantitative assessment of early and discontinuous estradiol-induced effects on ventromedial hypothalamic and preoptic area proteins in female rat brain.

In this study, changes in individual proteins in the ventromedial hypothalamus (VMN) and the preoptic area (POA) of the female rat brain were quantitatively assessed following either a short treatment (2 h) or a discontinuous schedule of estradiol. Ovariectomized (OVX) rats were implanted with estradiol capsules or sham-implanted for the appropriate paradigm and sacrificed by decapitation. Punches of brain tissue containing the VMN and POA were incubated with 35S-methionine and 35S-cysteine, and the labeled proteins separated by two-dimensional gel electrophoresis. Estradiol-induced changes were quantitatively assessed by computerized optical densitometry and subjected to a normalization procedure between pairs of estradiol-treated and OVX control gels. A number of proteins within the VMN and POA were found to be positively or negatively affected in labeling after either hormone administration paradigm. In both brain regions, the population of proteins affected in labeling after 2 h of estradiol treatment were markedly different from those affected after the discontinuous hormone paradigm. Comparison of the VMN and POA also indicated that the populations of proteins affected in labeling by either hormone treatment paradigm were different, with there being only 3 proteins (from a total of 39) affected in the same direction and 2 affected in the opposite direction by the hormone in both regions. These findings lend support to the hypothesis that administration of estradiol results in a molecular cascade of events within brain regions involved in the control of reproductive behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Projection of fibers immunoreactive to an antiserum against gonadoliberin (LHRH) into the pineal stalk of the white-crowned sparrow, Zonotrichia leucophrys gambelii

We have demonstrated a bundle of fibers, immunoreactive to an antiserum against gonadoliberin (luteinizing hormone-releasing hormone), that projects into the pineal stalk of photostimulated male Z. l. gambelii, a photoperiodic passerine species. These fibers have their origin in the dorsal division of the column of gonadoliberin-positive perikarya that extends caudodorsally from the ventromedial preoptic area to the level of the anterior commissure. After entering the habenula these fibers can be traced into the pineal stalk. This bundle is of interest because it apparently has not previously been reported in birds, and further, because the pineal body of this species is not known to have a role in the photoperiodic induction of increased rates of release of gonadotropins. Relationships of this bundle to other components of the gonadoliberin system are described briefly.

Courtship stimulates aromatase activity in preoptic area of brain in male ring doves.

Aromatase activity was quantified in vitro in different regions of the basal forebrain of male ring doves at various times after the initiation of courtship. By 24 h after the introduction of a female dove into the cage of a male, there was a significant, nearly two-fold, increase in aromatase activity which was confined to the ventromedial preoptic area (VM-POA) where enzyme activity was concentrated. This increase in aromatase activity, which was sustained through day 5 of courtship, presumably serves to activate nest-oriented behavior.

Luteinizing hormone-releasing hormone peptidase activities in the female rat: Characterization by an assay based on high-performance liquid chromatography

So far, the presence of two peptidase activities which degrade luteinizing hormone-releasing hormone (LHRH) have been found in hypothalamic tissue: an endopeptidase and a postproline cleaving enzyme (PPCE). Although it is possible that degradation of LHRH plays a physiological role in the control of gonadotropin secretion, evidence in favor of this hypothesis remains controversial, since only indirect measurements of peptidase activity have been reported. The present paper describes an assay that directly estimates LHRH degradation. This includes fractionation of the degradation products of LHRH by high-performance liquid chromatography (HPLC) and the use of digital integration to measure the disappearance of the LHRH molecule and account for the products deriving from its cleavage. The assay allows for measurement of total LHRH peptidase activity in discrete hypothalamic regions, such as median eminence (ME) and ventromedial preoptic area (POA), of individual animals. These peptidase activities are linear with respect to tissue concentration and time of incubation for up to 40 min for POA and anterior pituitary (AP) and for 2–2.5 h for ME. The major degradation product after HPLC separation and amino acid analysis is the LHRH 1–5 fragment whose appearance in the incubation medium is highly correlated with the disappearance of the LHRH molecule. With the use of this assay, various inhibitors of this activity were examined; the sulfhydryl reagents PCMS and ZnCl 2, the peptide antibiotic bacitracin, and the metalloendopeptidase inhibitor, 1,10-phenanthroline were the most effective.

In vivo biosynthesis of hypothalamic luteinizing hormone releasing hormone in individual free-running female rats.

The present studies examined the feasibility of performing in vivo biosynthetic studies of hypothalamic LHRH in preoptic area cannulated individual ovariectomized, estradiol benzoate (EB)-progesterone (P) treated rats. One day after EB treatment, rats were bilaterally cannulated in the anterior ventromedial preoptic area (POA). The following day, rats were treated with P, and a mix of 3H-proline and 3H-leucine (500 muCi) was continuously infused (for 8 hr) into the POA using an Alzet osmotic minipump delivery system at a rate of 1 microliter/h/cannula. 3H-LHRH was acid-extracted from discrete hypothalamic regions (POA, medial basal hypothalamus [MBH]and median eminence [ME]) and was purified to constant specific activity by sequential High Performance Liquid Chromatography. 3H-LHRH accounted for 0.010%, 0.018% and 1.6% of the total tissue 3H recovered in the POA, MBH and ME, respectively. These results demonstrate the feasibility of performing physiological studies on the biosynthesis and transport of hypothalamic LHRH using POA cannulated free-running female rats.

Luteinizing hormone-releasing hormone peptidase activities in discrete hypothalamic regions and anterior pituitary of the rat: apparent regulation during the prepubertal period and first estrous cycle at puberty.

Presently, two peptidase activities degrading LHRH have been observed in rat hypothalamic tissue: an endopeptidase and postproline cleaving enzyme (PPCE). Since no clear evidence for their physiological role in the onset of puberty has been presented, we examined the relationship between the content and degradation of LHRH by the median eminence (ME) and that by the ventromedial preoptic area (POA) during the prepubertal period and during the first estrous cycle at puberty. LHRH degradation by anterior pituitary during this period was also determined. Using kinetically optimized conditions, total LHRH degradation was measured by high performance liquid chromatographic estimation of the loss of synthetic LHRH catalyzed by low speed tissue supernatants, and PPCE activity was measured using a fluorogenic substrate (carbobenzoxy-1-glycl-1-prolyl-4- methylcourmarine-7-amide). The ME and POA LHRH content and serum levels of LH were estimated by RIA. During the prepubertal period, in animals killed between 22 and 30 days of age, the total LHRH-degrading activity in the ME remained constant (50 pmol LHRH degraded/μg protein- 30 min), while the LHRH content increased steadily. During the pubertal period (first estrous cycle), a high correlation between LHRH degradation and LHRH content in the ME was observed (r = 0.95). In animals killed between 34 and 38 days of age, total LHRH degradation increased from basal levels in anestrous animals to higher levels in early proestrous rats, reaching the highest value on the morning of late proestrous (300% increase). After the morning of late proestrus, LHRH degradation decreased (by 1300 h; P < 0.01) to reach prepubertal values on the first estrus, the following day. On diestrous day 1, both total LHRH degradation and LHRH content returned to early pubertal values. Cleavage at Pro9-Gly10 of LHRH (PPCE) was unchanged throughout the period studied. Both total LHRH degradation and postproline degrading activity on LHRH showed only minor fluctuations during the first estrous cycle in POA and anterior pituitary samples. The data suggest that LHRH degradation may contribute to the regulation of LHRH levels appropriate for gonadotropin release during the onset of puberty.

HYPOTHALAMIC REGULATION OF SLEEP IN RATS. AN EXPERIMENTAL STUDY

The essential role of the nervous system in the regulation of the sleep-waking rhythm of higher animals is now widely recognized. No less a person than von Economo, however, drew attention to the fact that the phenomenon of sleep cannot be accounted for by a mere functional change of the central nervous system from its condition during the waking state. It is indeed an important fact that the function of sleep, instead of being characteristic of higher animals, is also observed in organisms which do not possess a central nervous system, and even in several vegetable species. It is therefore impossible to attribute this mysterious function to any special organ. Since all experimental work on sleep has hitherto been confined to mammals, chiefly to cats and monkeys, practically no data concerning the comparative physiology of this phenomenon are available. Nevertheless, it seems probable that during the phylogenetic development the function of sleep, together with many other mechanisms, was progressively centralized into the nervous system from which organ all changes, characteristic of sleep, were ultimately effected. This centralization proceeded so far that the alternation of wake and sleep seems to be governed in mammals by a circumscribed area of the central nervous system, capable of determining physical and psychical activities. The existence of this “centre” for the regulation of sleep is generally accepted by students of this subject.