LOW-DOSES OF NEUROTENSIN IN THE PREOPTIC AREA PRODUCE HYPERTHERMIA - COMPARISON WITH OTHER BRAIN SITES AND WITH NEUROTENSIN-INDUCED ANALGESIA

High amounts of neurotensin (NT) are found in the preoptic area of the hypothalamus, an area known to be involved in the regulation of body temperature. It is generally believed that NT is a peptide that produc es hypothermia, and several sites in the brain have been proposed to m ediate NT-induced hypothermia, including the preoptic area. However, t he doses of NT used in these experiments were always very high (microg ram order) whereas, according to Goedert, the total brain content of N T in the rat does not exceed 10 ng. We therefore reinvestigated the ef fects of microinjections of NT in the brain, using high (5 mu g) and l ow (50 and 5 ng) doses, into the preoptic area and other brain sites ( cerebral ventricles, posterior hypothalamus, and nucleus accumbens), a nd we also studied, as a comparison, the effects of high and low doses of NT on pain sensitivity in the same sites. The results show that th e preoptic area has unique properties in the regulation of body temper ature: low doses of NT in the preoptic area produce a hyperthermic res ponse, whereas high doses produce hypothermia. In comparison, NT produ ces hypothermia in the posterior hypothalamus whatever the dose, and N T has analgesic effects in the preoptic area only at high doses. Besid es, NT has no thermic effect, but does have an analgesic effect, in th e nucleus accumbens. The selectivity of the actions of high doses of N T, as well as the mechanism of action of NT (possibly an endogenous ne uroleptic), are discussed.