The effects of intraventricular injections of bombesin on temperature selection in the rat

Bombesin-induced hypothermia in rats tested at normal ambient temperatures: contribution of the sympathetic nervous system

Rats infused centrally with bombesin become hypothermic at normal ambient temperatures when acutely deprived of food, but not while allowed unrestrained access to food. Ad lib-fed rats, tested at normal ambient temperatures, become hypothermic after receiving intracerebroventricular (ICV) bombesin when they have ventromedial hypothalamic lesions or when administered insulin or 2-deoxy-D-glucose peripherally. All of these conditions have been linked to reductions of sympathetic nervous system activity to brown adipose tissue (BAT), a major thermogenic mechanism of many homeotherms. A between group design was used to examine the effects of ICV bombesin infusions on the response to peripheral injections of a) the sympathetic ganglionic blocker chlorisondamine (2.5 mg/kg, IP) in ad lib-fed rats, b) the nonspecific beta-agonist isoproterenol (30 mg/kg, IP) in food-deprived rats, and c) the combination of isoproterenol and chlorisondamine in ad lib-fed rats. Ad lib-fed rats receiving ICV bombesin (100 ng/5 microliters), in combination with peripheral chlorisondamine injection, became hypothermic 60 min postbombesin administration (-2.84 +/- 0.33 degrees C), while ad lib-fed rats receiving ICV bombesin infusion and peripheral injections of saline did not (-0.08 +/- 0.37 degrees C). Isoproterenol blocked hyperthermia in ad lib-fed rats injected with chlorisondamine and ICV bombesin. Food-derived rats receiving ICV bombesin infusion and peripheral saline injection exhibited hypothermia 60 min postbombesin administration (-2.51 +/- 0.29 degrees C). Peripheral injections of isoproterenol prevented bombesin-induced hypothermia in food-deprived rats. These data suggest that bombesin induces hypothermia at normal ambient temperatures when the sympathetic nervous system drive to BAT cannot be (or is not) activated.

Food deprivation does not influence body or selection temperature in rats receiving intraventricular bombesin

Bombesin (BBS), a tetradecapeptide, has been found to have potent hypothermic effects when centrally administered. This study was designed to investigate the relationship between food-deprivation and BBS-induced hypothermia in a temperature selection paradigm. Food-deprived and satiated male Sprague-Dawley rats were given intracerebroventricular (ICV) injections of several doses of BBS and control vehicle. Selection temperature data and changes in core body temperature were measured. BBS produced a significant hypothermia and decrease in selection temperatures in all doses but one. No significant differences in body temperature or selection temperatures were found between food-deprived and satiated animals. The results are consistent with the hypothesis that BBS acts centrally to decrease body temperature set point.

Bombesin reduces alcohol choice in nutritive expectancy and limited-access procedures

Bombesin is a bioactive tetradecapeptide found in nerves of the brain and gut and previously shown to inhibit intake of ethanol in forced-choice, one-bottle tests in water-deprived rats. In the present experiments, intraperitoneal bombesin (4-100 micrograms/kg) reduced selection of alcohol in two-bottle choice tests with water. In an application of the "nutritive expectancy" procedure, weight-reduced rats received access to 4% w/v ethanol and water. Bombesin injection suppressed the intake of ethanol, but not of water, in rats with prior ethanol experience. In an application of the "limited access" procedure, nondeprived rats received access to 6% w/v ethanol and water in nonhome cages during either the light or the dark phase of a 12:12 h lighting cycle. Bombesin injection lowered the intake of ethanol, but not of water, in both phases of the lighting cycle and in both sexes. Water deprivation is not necessary for bombesin to inhibit alcohol intake and this effect cannot be explained by hypodipsia, nonspecific debilitation, or conditioned aversion. Endogenous bombesin-like neuropeptides may specifically reduce choice of alcohol by signaling satiation with ethanol.

Destruction of different fiber tracts underlies development of lateral hypothalamic lesion-induced hyperthermia and loss of bombesin-induced hypothermia

The relative roles of lateral hypothalamic cell bodies and fibers of passage were assessed in the development of lesion-induced hyperthermia and bombesin-induced hypothermia. Electrolytic lesions or discrete fiber transections were combined with intracisternal bombesin injection to show that each of these two thermoregulatory effects involves fibers crossing the borders of the lateral hypothalamus; however, the two effects primarily involve fibers crossing different borders. Thus, the hyperthermia and the abolition of bombesin-induced hypothermia which follow lateral hypothalamic damage appear to result from disruption of separate thermoregulatory pathways.

An inexpensive gradient for temperature selection in rodents

The construction of a horizontal temperature gradient is described in detail. The apparatus is built from readily available and inexpensive materials. The chamber is built from PVC tubing, fitted with an aluminum floor, and placed in a sound-attenuated box. A temperature gradient is formed by placing solid CO2 at one end and a hot plate at the opposite end of an aluminum floor. The apparatus described is reliable, dependable, and has proven to be very suitable for use with small rodents.