LOCALIZATION AND CHANGES IN DISTRIBUTION OF BRAIN ALPHA(2)-ADRENOCEPTOR AND BETA-ADRENOCEPTOR IN RESPONSE TO ACCLIMATION STATE IN THE AMERICAN BULLFROG (RANA-CATESBEIANA)

Alpha (alpha)- and beta (beta)-adrenoceptors regulate physiological pr ocesses in vertebrates. This study determined the location of alpha(2) - and beta-adrenoceptors in the brain of the American bullfrog, Rana c atesbeiana, using autoradiography As the density of receptors may be a ffected by environmental temperature, a comparative numerical analysis of adrenoceptors in the areas of localization with respect to warm an d cold acclimation was also carried out. Areas of greatest concentrati on of alpha(2)-adrenoceptors were the accessory olfactory bulb, medial pallium, and olfactory bulb. Adrenoceptor numbers were significantly decreased in the accessory olfactory bulb and medial pallium in cold-a cclimated animals. beta-adrenoceptors were localized in the thalamus, cerebellum, medial pallium, and amygdala/striatum. Cold acclimation de creased adrenoceptor density in medial pallium and torus semicirculari s and increased adrenoceptor density in the thalamus and hypothalamic preoptic areas. Among the alpha(2)- and beta-adrenoceptors, only four regions of overlap existed, the medial pallium, hypothalamic preoptic area, optic tact, and isthmic tegmentum. Otherwise, where there were a lpha(2)-adrenoceptors, there were few or no beta-adrenoceptors. No alp ha(2)- or beta-adrenoceptors were found in the pituitary and optic chi asm. The distribution of adrenoceptors in particular areas of the brai n may have functional significance with respect to physiological chang es which occur in response to hibernation. (C) 1998 Academic Press.