Effective loci and roles of acetylcholine in temperature regulation of goldfish

Microinjections of acetylcholine (ACh) and carbachol were made into discrete forebrain loci in goldfish (Carassius auratus) to evaluate the importance of cholinergic mechanisms for behavioral thermoregulation. Injections of 5, 10, 25, and 50 μg ACh into the far anterior nucleus preopticus periventricularis (NPP) (R. Peter and V. Gill. J. Comp. Neurol. 159: 69-102, 1975) and immediately adjacent ventral telencephalon led to consistent dose-dependent decreases in selected temperature. No effect was observed following injections of 2 μg ACh or 0.7% NaCl. Injections of ACh into a different portion of the ventral telencephalon led to increases in the selected temperature. Lower doses of carbachol (0.5 and 1.0 μg) injected into the NPP produced decreases in selected temperature similar to the highest doses of ACh. Injections of ACh into loci other than those mentioned above either had no thermoregulatory effect or had lesser thermoregulatory effects which, in comparison with injections into the most effective sites, were inconsistent and required larger doses to obtain. The site where cholinergic stimulation led to decreases in the selected temperature exactly overlapped the effective site of ethanol hypothermia in the goldfish.