Anatomical distribution of brainstem sites where PGE1 induces hyperthermia in macaque species

Abstract

The neuroanatomical distribution of sites in the diencephalon and mesencephalon within which a prostaglandin (PG) of the E series elicits hyperthermia was characterized in Macaca mulatta and Macaca nemestrina. In 420 experiments undertaken in 13 animals, 225 loci were examined for their reactivity to PGE 1 microinjected in a dose of 30 or 100 ng given in a volume of 1.0–1.5 μL. The regions of the brainstem for injection extended rostrally from the thermosensitive cells of the anterior hypothalamic, preoptic area (AH/POA) to the caudal border of the mesencephalon. Colonic and skin temperatures of the monkeys were measured continuously by thermistor probes. A hyperthermic response of ≥0.5 °C and a latency of ≤45 min was evoked by PGE 1 within sites located primarily in the AH/POA. When PGE 1 was microinjected at loci located caudal to the AH/POA, the elevation in body temperature (T b) not only was less intense but rose at a slower rate. A higher concentration of PGE 1 in these caudal regions was required to induce hyperthermia comparable with that elicited at loci within the AH/POA. In a second series of experiments either 1.0–5.0 μg 5-hydroxytryptamine (serotonin) or a concentration of 10 8 organisms/mL of Escherichia coli was microinjected at PGE 1-reactive sites. A close anatomical concordance within the AH/POA of the animal was found in terms of the temporal characteristics and magnitude of the hyperthermia evoked by the indoleamine or lipopolysaccharide. The present results coincide with the reported neuroanatomical distribution of sites in the diencephalon and mesencephalon of other species in which PGE 1 causes hyperthermia. Furthermore, these findings support the concept that the local neuronal mechanism of action of a pyrogen in the brainstem of the primate may involve phasic changes in the endogenous activity of both the serotonergic pathway and cyclo-oxygenase system in the AH/POA. In turn, their commonality of action suggests a functional similarity in their effect of shifting the set point for T b.Key words: prostaglandin E 1, hyperthermia, serotonin, Escherichia coli, anterior hypothalamus, thermoregulation, bacterial pyrogen, preoptic area, neuroanatomical localization, Macaca nemestrina, Macaca mulatta.