Amino acids as central synaptic transmitters or modulators in mammalian thermoregulation

Of the amino acids that affect the activity of central neurons, aspartate and glutamate (which exert generally excitatory influences) and glycine, taurine, and gamma-aminobutyric acid (GABA) (which generally exert inhibitory influences) are the strongest neurotransmitter candidates. As with other putative transmitter substances, their effects on body temperature when injected into the cerebral ventricles or the preoptic hypothalamus tend to vary within and between species. These effects are uninterpretable without accompanying information regarding effector activity changes and the influences of dose and ambient temperature. Observations necessary for analysis of apparent action have been made in studies of the effects of intracerebroventricular injections of these amino acids into sheep. Aspartate and glutamate have similar excitatory effects on the neural pathways that activate both heat production and heat loss effectors. Glycine appears to be without effect.