Neurotransmitter effects on body temperature are modified with increasing age

Antipyretic activity of Guduchi Ghrita formulations in albino rats

The present pharmacological investigation was undertaken to study the anti-pyretic activity of Guduchi ghrita formulations in albino rats against yeast induced pyrexia. Seven groups of six animals were used for the experiment. The yeast induced pyrexia method was standardized first by injecting 12.5% yeast suspension (s.c) followed by recording the rectal temperature at regular intervals. Then the evaluation of anti-pyretic activity of Guduchi ghrita formulations was carried out by using this standard procedure. Both the Guduchi ghrita samples including vehicle significantly attenuated the raise in temperature after three hours of yeast injection. After 6 and 9 hours of yeast injection also both the Guduchi ghrita samples attenuated the raise in temperature in a highly significant manner in comparison to both yeast control and vehicle control groups. The data generated during study shows that both the Guduchi ghrita formulations having significant anti-pyretic activity.

Baker yeast-induced fever in young rats: Characterization and validation of an animal model for antipyretics screening

In this study we describe a low-cost and reliable method for inducing fever in young male rats (28-30 days of age, 75-90 g), which seems suitable for the screening of new antipyretics. The effects of temperature measuring procedure-induced stress on the basal rectal temperature and on Baker yeast-induced hyperthermia was assessed. Rectal temperature (T) was recorded every hour for 12 h (07:00-19:00 h) with a lubricated thermistor probe. The animals were injected intraperitoneally with baker yeast (0.25, 0.135, 0.05 g/kg) or the equivalent volume of saline at 7:00 h. The administration of 0.135 g/kg baker yeast induced a sustained increase in rectal temperature for 4 h. Classical (dipyrone and acetaminophen) and novel (MPCA and FPCA) antipyretics, at doses that had no effect per se, reverted baker yeast-induced fever. The method presented induces a clear-cut fever, which is reverted by antipyretics commonly used in human beings and selected novel antipyretics in small animals. The method also allows antipyretic evaluation with low amount of drugs, due to the use of small animals and to the small variability of the pyretic response, which ultimately causes a significant reduction in the number of animals necessary for antipyretic evaluation. Therefore, this study describes an animal model of fever that is not only advantageous from the economical and technical point of view, but that also bears ethical concerns.

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.

Thermal biology of the laboratory rat

The purpose of this paper is to thoroughly review the literature and present a data base of the basic thermoregulatory parameters of the laboratory rat. This review surveys the pertinent papers dealing with various aspects of the thermal biology of the laboratory rat, including: metabolism, thermoneutrality, core and brain temperature, thermal tolerance, thermal conductance and insulation, thermoregulatory effectors (i.e., thermogenesis, peripheral vasomotor tone, evaporation, and behavior), thermal acclimation, growth and reproduction, ontogeny, aging, motor activity and exercise, circadian rhythm and sleep, gender differences, and other parameters. It is shown that many facets of the thermoregulatory system of the laboratory rat are typical to that of most homeothermic species. However, is several instances the rat exhibits unique thermoregulatory responses which are not comparable to other species.

Changes in body composition, brown adipose tissue activity and thermogenic capacity in BN/BiRij rats undergoing senescence

Metabolic rate, thermogenesis, brown adipose tissue (BAT) activity, and body composition were followed in ageing rats (female BN/BiRij) at 3 to 35.5 months of age. Colonic temperatures were similar in rats at 3 to 23 months of age (37.1-37.6 degrees C), but significantly reduced (36.3 degrees C) in those aged 36 months. Resting oxygen consumption (VO2), corrected for body size, was comparable in all groups, but the thermogenic response to noradrenaline was significantly reduced with age. BAT mass was unaffected by age, but brown fat protein content, specific mitochondrial cytochrome oxidase activity, and thermogenic activity (assessed from mitochondrial purine nucleotide binding) all declined markedly with age. Carcass analysis revealed a fall in body protein in very old (35.5 month) rats, but body fat content increased up to 23 months of age and thereafter declined.

Temperature as a dependent variable in the study of cholinergic mechanisms

1. Change in core temperature over time can be used as a dependent variable when studying the effects of manipulations on neurotransmitter systems. This article focuses on the measurement of core temperature as a strategy for detecting changes in the status of cholinergic systems. 2. Cholinergic neurons participate in the process of thermoregulation and interventions affecting them alter the thermal response to cholinomimetics. For example, chronic treatment with amitriptyline, chronic swim stress and inescapable footshock supersensitize rats to the hypothermic effects of oxotremorine. 3. This is consistent with the hypothesis that the pathophysiologies of tricyclic antidepressant withdrawal phenomena and stress involve supersensitivity of muscarinic mechanisms. 4. Uses of thermoregulation paradigms for investigating the actions of lithium ion, electroconvulsive shock and substances of abuse on muscarinic mechanisms are discussed. Applications to problems in the arena of clinical research are highlighted.

Characteristics of pyrogen fevers are altered in the aged rabbit

The febrile response to both intravenous and intracerebral administration of pyrogens was investigated in young and old male New Zealand White rabbits. Intravenous bacterial pyrogen evoked biphasic fevers in both groups of animals. However, the fevers in the group of older rabbits were significantly less than in younger animals. In contrast, intravenous injection of endogenous pyrogen produced identical fevers in the two groups. Bacterial and endogenous pyrogens injected into a lateral cerebral ventricle evoked marked febrile responses of long duration in both young and old rabbits. The responses of the old rabbits were significantly less than those of the younger ones. Finally, direct microinjection of prostaglandin E1 into tissue sites within the anterior hypothalamic preoptic area elicited short latency hyperthermic responses which were significantly less in the older rabbits. Analysis of ear skin temperatures during fever demonstrated that some of the differences may, in part, be due to altered vasoconstrictor responses in the peripheral vasculature. Thus, these data indicate that the febrile response is altered with increasing age in the rabbit.

Differences in behavioral responses to oxotremorine and physostigmine in New Zealand black (NZB/BlNJ) and C57BL/6 mice

The NZB/BlNJ (NZB) mice are an autoimmune-prone strain, known to develop brain-reactive antibodies in serum at much earlier chronological ages than normal mice. Measurement of locomotor activity in 8-10 month old C57BL/6 (C57) mice following the administration of either oxotremorine or physostigmine, revealed a biphasic response consisting of inhibition at small doses, but increased motor activity at large doses. In contrast, age-matched NZB mice exhibited little inhibition at the smaller doses, but had much greater increases in activity after the larger doses. Similarly, when compared to C57 mice, NZB mice were less sensitive to oxotremorine-induced salivation, diarrhea and visible tremors. Moreover, oxotremorine-induced hypothermia occurred at smaller doses in C57 mice than in NZB mice and was of a greater magnitude. Thus, at an age when NZB mice possess high levels of brain-reactive antibodies, and exhibit impairment in tests of learning/memory, these mice also show diminished responses in several tests of cholinomimetic-induced behavior and physiological alterations.