Adrenoceptors and temperature regulation in goldfish

In goldfish, microinjections of norepinephrine (NE) into the anterior aspect of the nucleus preopticus periventricularis result in dose-dependent decreases in selected temperature (21). To determine the characteristics of the adrenoceptors involved in this response, noradrenergic antagonists were injected 10 min before an injection of 50 ng norepinephrine. In comparison to control injections, injections of 50 ng phentolamine, an α-antagonist, significantly attenuated the effect of NE. In contrast, 50 ng propranolol, a β-antagonist, produced a nonsignificant attenuation. These antagonists injected by themselves had no thermoregulatory effect. For noradrenergic agonists, thermoregulatory effects comparable to a dose of 10-25 ng NE were obtained at the following doses (in μg): 1.0 clonidine (α₂), 5.0 phenylephrine (α₁), and 25 isoproterenol (β). In fish, both α₁- and α₂-adrenoceptors appear to subserve the NE-induced decrease in selected temperature. Because antagonists injected by themselves do not have a thermoregulatory effect, NE may not have a role in the short-term regulation of body temperature in fish but rather may modulate this system in response to altered environmental conditions.