Feeding elicited in sheep by intrahypothalamic injections of PGE 1

Leptin stimulates prostaglandin E2 and F2alpha, but not nitric oxide production in neonatal rat hypothalamus

Leptin, an adipocyte-derived 16 kDa polypeptide hormone, has been found to regulate food intake and thermogenesis by modulating stimulatory and inhibitory pathways in the feeding circuitry of the hypothalamus, among which corticotropin releasing hormone (CRH). Nitric oxide (NO) and prostaglandins have been shown to be involved in both CRH neurosecretion and feeding regulation. We have investigated the role of NO, prostaglandin E2 and prostaglandin F2alpha as mediators of the hypothalamic effects of leptin and their possible involvement in leptin-stimulated CRH secretion. Using primary cultures of neonatal (5- to 6-day-old) rat hypothalamic cells, we confirmed that leptin (0.1-10 nM) stimulates CRH secretion. This effect was not blocked by L-N(G)-nitro-methyl-arginine (L-NAME, 100 microM), a NO-synthase competitive inhibitor; and leptin did not stimulate NO production. Cyclooxygenase inhibition by indomethacin (10 microM) did not modify leptin-induced CRH secretion, while leptin stimulated prostaglandin E2, and prostaglandin F2alpha secretion. In conclusion, leptin-induced hypothalamic CRH secretion is not modulated by NO-synthase- or cyclooxygenase-mediated mechanisms; leptin does not stimulate NO production, but it stimulates prostaglandin E2 and F2alpha production, which could add to the growing list of mediators of leptin signaling in the hypothalamus.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Effect of prostaglandin E1 and its biosynthesis inhibitor indomethacin on drinking in the rat

In the rat, injection of prostaglandin E1 (PGE1) 0.5, 1.0 or 2.0 microgram into the 3rd brain ventricle (3rd b.v.) inhibited the water deprivation-induced water intake in a dose-related fashion. The 1.0 microgram dose of PGE1 also inhibited the intake of 1.8% sodium chloride in rats depleted of body sodium by intraperitoneal dialysis, and of food in food deprived rats during a 60 min test period. Prostaglandin E1 (1 microgram) depressed the dipsogenic effect of angiotensin II (AII) or carbachol injected through the same cannula. Water-deprived rats pretreated with the PG synthetase inhibitor indomethacin, in two different doses, showed enhanced water intake. The pretreatment with indomethacin also enhanced the dipsogenic effect of various doses of AII injected into the 3rd b.v. The antagonistic action of PGE1 on water-deprivation, or AII-induced water intake, and the enhancement of water intake after blocking PGs synthesis, suggests the involvement of PG in the regulation of thirst.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents

This survey, the second in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of cholinergic agonists and antagonists, histamine and H1- and H2-receptor antagonists, narcotic analgesics and antagonists in both non-tolerant and tolerant subjects and of prostaglandins and related agents. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.

Effect of prostaglandin, pyrogen and noradrenaline, injected into the hypothalamus, on thermoregulation in newborn lambs

Thirteen newborn lambs were implanted stereotaxically with an array of 4 guide tubes positioned bilaterally so that their tips lay above various hypothalamic loci. At postnatal ages 50-70 h, rectal temperature was monitored, and bilateral 1 microliter injections were made into the hypothalamus. Prostaglandin E1 (0.2 microgram) and prostaglandin E2 (0.2-2.0 microgram) did not cause fever on any occasion though injections were made into 44 sites throughout the hypothalamus. Nevertheless, lambs that did not develop fever following central injection were often, if sensitized by bacterial pyrogen given earlier able to develop fever after intravenous injection of bacterial pyrogen. Infusion of a bacterial pyrogen (S. abortus equi, 0.2 microgram) into these same sites caused fever only when injections were made into the anterior hypothalamic/preoptic area (AH/POA). Eight lambs were placed in a 10 degrees C environment and noradrenaline was injected. Rectal temperature fell by 0.5-1.4 degrees C after 7 bilateral injections into the AH/POA, but 9 injections into other hypothalamic areas caused little temperature change. When 6 lambs were placed at a temperature of 30 degrees C and noradrenaline was injected, no consistent temperature changes were observed after microinjection into the AH/POA or other parts of the hypothalamus.

Dopamine efflux from the brain stem of the rat during feeding, drinking and lever-pressing for food

To determine whether endogenous dopamine (DA) is involved in the control of feeding and drinking, the cerebral activity of 14C-DA was examined in the rat while the animal consumed food or water. A push-pull guide tube was implanted above sites either adjacent to the third ventricle, the anterior hypothalamus or the substantia nigra in each of 41 rats. After the endogenous stores of DA at specific sites were labelled by a microinjection of 0.5 to 2.0 muCi of 14C-DA, an artificial CSF was perfused at half-hour intervals at a rate of 20-23 mul/min in these sites in the food deprived rat. After a 14C-washout curve of radioactivity in the perfusate was derived for successive control samples, the food-deprived rat was offered food or water which was ingested during the course of one or more perfusions. As the rat consumed food, 14C-DA was released in some experiments from circumscribed sites in the nucleus reuniens and the zona incerta. The efflux of 14C-DA from certain sites in the circumscribed sites in the nucleus reuniens and the zona incerta. The efflux of 14C-DA from certain sites in the ventromedial and dorsomedial hypothalamus as well as from the substantia nigra also was enhanced as the rat depressed a lever to obtain food pellets. Since 14C-DA was also released from the zona incerta, perifornical hypothalamus, and into the third ventricle as the rat drank water, these results suggest that dopaminergic neurons in the brain stem play some part in the motor component of ingestive behavior rather than feeding per se.