Examination of the subdiencephalic rat brain for sites mediating PGE1-induced pyrexia

The subdiencephalic rat brain was mapped for sites capable of mediating prostaglandin-induced pyrexia. In conscious rats, PGE1, 200 ng in a volume of 1 microliter, was injected unilaterally into 412 sites between the midmesencephalon and the caudal medulla. Injections into only 12 sites caused a reproducible, short-latency core temperature increase of at least 0.5 degrees C. None of these was located in the paramedian brainstem, which was considered a likely site of PGE1 action because of the presence there of thermosensitive and pyrogen-sensitive neurons. Rather, the reactive loci were found in the hippocampus (5 sites) and in the vicinity of the cochlear nuclei (7 sites). Injections into only 2 sites in the latter region failed to produce pyrexia. In the hippocampus, however, injections at 31 sites in the same frontal planes as the reactive loci produced no effect. The possibility that the active hippocampal sites were associated with a distribution of injectate to PGE1-sensitive neurons located within hippocampal cleavage planes rather than in a circumscribed region is discussed.