Thermal preference behavior following clonidine, norepinephrine, isoproterenol, and ephedrine

A thermal gradient (temperature range 7-45 degrees C) was used to assess am bient temperature (T-a) preferences of rats following treatment with clonid ine (25 mu g/kg), norepinephrine (NE, 250 mu g/kg), isoproterenol (ISO, 50 mu g/kg), and ephedrine (EPH, 10 mg/kg). Clonidine produced a preference fo r a temperature (31.5 degrees C) slightly warmer than that preferred after saline (28.3 degrees C), but this resulted in no significant change in post test colonic temperature (T-c). NE, ISO and EPH produced a preference for a colder region of the gradient (20-22 degrees C) compared to saline (24.5-2 8.9 degrees C). Posttest T-c was reduced significantly from 37.7-37.9 degre es C after saline to 37.2 degrees C (NE), 37.3 degrees C (ISO), and 36.8 de grees C (EPH). Thus, given the opportunity to select an environmental tempe rature, the animals selected a T-a that resulted in significantly lower bod y temperatures after NE, ISO, and EPH. This suggests that paradoxical therm oregulatory effects of these thermogenic adrenergic agonists are due, at le ast in part, to a preference for a lower body temperature. (C) 1999 Elsevie r Science Inc.