Effects of Thyroxine on Locomotor Activity and Carbon Dioxide Release in the Toad, Bufo japonicus : Endocrinology

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To elucidate a role of thyroxine (T_4) in toad migration during the breeding season, we studied effects of administration of T4 on locomotor activity and CO_2 release using normal and thyroidectomized adults of both sexes which were captured before hibernation. All the experiments were performed during the breeding season under laboratory conditions. Locomotor activity was estimated by passage of infrared beams in an activity box and CO_2 release was estimated comparing CO_2 contents in inflow air to the activity box and outflow air from the activity box. Locomotor activity was significantly suppressed (to 9%) by T4 treatment (10μg/day for 2 weeks) in intact males. T_4 also suppressed CO_2 release in intact males at moving states, while T_4 enhanced CO_2 release at resting states, T_4 had no effect on either locomotor activity or CO_2 release in female toads. Thyroidectomy in males resulted in a 3-fold increase in locomotor activity and T4 administration suppressed activity in dose-dependent fashion (1 to 100 ng/g BW/day for 3 weeks). Neither thyroidectomy nor T_4 administration had any effect in females. These results suggest that thyroxine can not be the factor which induces breeding migration to the pond in the toad. If the sedative effect of thyroxine is physiological, it is probable that thyroxine initiates the post-breeding inactive stage.
社団法人日本動物学会の論文
1990-04-15