Direct effects of endogenous pyrogen on medullary temperature-responsive neurons in rabbits

Interleukin-1 beta induces histamine release in the rat hypothalamus in vivo

We have previously demonstrated the increase of histidine decarboxylase activity and histamine content in the murine hypothalamus after intracerebroventricular injection of lipopolysaccharide possibly due to inducible interleukin-1 beta (IL-1 beta). Therefore, we investigated the effects of IL-1 beta on brain histamine dynamics by directly injecting it into the tuberomammillary nucleus of the rat hypothalamus (TM) using an in vivo microdialysis method. Injection of artificial cerebrospinal fluid or recombinant murine IL-1 beta at 0.1 ng into the TM did not evoke a significant change in core temperature, however, a significant monophasic febrile response was observed following injection of IL-beta at more than 1 ng per animal. Histamine release in the anterior hypothalamic area in vivo was significantly augmented from 140 min to 360 min following injection of IL-1 beta at 10 ng dose. These results suggest the possibility that interrelationship between histamine and IL-1 beta may modulate the acute phase reaction in the central nervous system.

Neural mechanisms in the pyrogenic and acute-phase responses to interleukin-1

It has become increasingly apparent over the past several decades that the hypothalamus, among other brain regions, plays an important part in the modulation of the immune system (reviewed in Korneva et al., 1985; Roszman & Brooks, 1985; Jankovic & Spector, 1986; Cotman et al., 1987). Since the hypothalamus also mediates the fever and various other acute-phase responses characteristic of the early stages of infection (reviewed in Hellon & Townsend, 1983; Blatteis, 1984, 1985; Cooper, 1987), it is possible that the localization within a common brain region of the controllers of several, different host defense reactions is not a happenstance, but represents a highly organized neuronal network serving to coordinate them. Indeed, pyrogenic, inflammatory, and immune responses do interact in the defense of the host against infection (reviewed in Dinarello, 1984). It is not yet known how immune responses are integrated centrally, but some data are available on the neural mechanisms controlling fever and certain components of the acute-phase reaction. The purpose of this paper is to review these briefly in the hope that a background can be provided against which features that may be common to neuroimmunomodulation and to the control of acute-phase reactions might be revealed.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

Interaction between the effects of centrally administered arecoline and leucocyte pyrogen on the activity of posterior hypothalamic neurons in the rabbit

In experiments with urethane-anesthetized rabbits, the alteration in the activity of posterior hypothalamic neurons resulting from intracerebroventricular injection of leucocyte pyrogen was attenuated by subsequent administration of arecoline. Atropine failed to alter the neuronal response to leucocyte pyrogen but abolished the effect of arecoline. The neuronal response to arecoline was reversed in the absence of leucocyte pyrogen.

Comparison of the action of prostaglandin with endotoxin on thermoregulatory response thresholds

Prostaglandin E2 (PGE2) and lipopolysaccharide (LPS) derived from E. coli were injected into the lateral cerebral ventricle of rabbits at 30 degrees C ambient temperature. The threshold core temperatures for ear cutaneous vasoconstriction (Thv) and shivering (Thsh) were determined by whole-body cooling with an intestinal thermode. Each threshold, as determined at the plateau phase of LPS fever and PGE2 hyperthermia respectively, were compared with the control values before LPS and PGE2 injection. Thsh was not changed by the injection of LPS, while Thv was increased. After PGE2 injection both Thsh and Thv were increased in comparison to their control levels. These changes paralleled the elevation of core temperature. The present study does not exclude prostaglandins as humoral mediators involved in some of the central processes generating fever, but suggest at the same time that there are additional properties of LPS fever for which prostaglandins do not account.

Molecular mechanisms in endotoxin fever

Two important concepts are presented in this review. First, endotoxin fever, like all fevers, is mediated by a host product, leukocytic pyrogen (LP). The mechanism by which LP production is initiated by endotoxin is discussed and evidence is provided which clearly distinguishes the biological and physical differences between LP and endotoxins. The second concept is that many of the molecular and neurochemical mechanisms by which LP causes fever by its action on the hypothalamic thermoregulatory center are also observed when endotoxins are introduced into the central nervous system. Thus, there may be experimental and clinical situations in which endotoxins can directly affect the hypothalamus and initiate fever. Although this bi-modal effect of endotoxin on the production of fever can occur, the importance of LP in mediating endotoxin and other fevers cannot be overstated.