Abstract
The functions of central amines, norepinephrine (NE) and 5-hydroxytryptamine (5-HT), during changes in adaptation to temperature have not been determined. Likewise, central activation of thermogenesis by monoamines has not been studied to any extent. Paradoxical functions do occur after central injection of monoamines in many species in the thermal neutral zone. Thus, 5-HT lowers rectal temperature in rabbits, sheep, and goats, but raises it in the cat and monkey, whereas the opposite function or lack of effect holds for NE injection (1, 2). Below the lower critical temperature of species studied, central injection of amines apparently decreases internal temperature (3). In cold-adapted guinea pigs, injection of NE into the anterior hypothalamic area caused a calorigenic effect, while 5-HT injection in similar amounts did not (4). The present work investigated to what extent varying doses of NE and 5-HT injected into the anterior hypothalamus in a cold environment influence body temperature and heat production mechanisms in cold- and warm-adapted rabbits.
Methods. Male, Dutch belted rabbits (2.1-2.5 kg) were used in this study. Stainless-steel guide tubes (21 gauge) for unilateral hypothalamic injection cannulas were implanted stereotaxically (A 1.0 mm, L 1.5 mm, H 10-15 mm) according to the atlas of Sawyer et al. (5) under pentobarbital anesthesia. Additional guide tubes (20 gauge) for recording brain temperature were placed 2 mm posterior to each injection cannula guide. The injection sites are within an area in the anterior hypothalamus which has a high concentration of thermosensitive neurons (6). After surgery and a 1-week recovery period, the rabbits were kept at 30° (range 29-31°, RH 67%) or 5° (range 3-7°, RH 90-100%). The rabbits were exposed in each environment for a minimum of 40 days prior to experimentation and returned to the same temperature room after each experiment.
Get full access to this article
View all access options for this article.