Hypothalamic control of thyroid gland activity and gonadal activity in the goldfish, Carassius auratus

Abstract

A stereotaxic method for placement of electrodes in the goldfish hypothalamus was described. Electrolytic lesions in the nucleus preopticus (NP), or bilaterally in the NP-hypophyseal tract, did not effect thyroid activity or gonadal activity. Lesions that destroyed the nucleus lateralis tuberis (NLT) pars anterior in the region anterior of the pituitary stalk made the animals hyperthyroid, but they had no effect on gonadal activity. Lesions that destroyed the NLT pars posterior and the posterior part of the NLT pars anterior significantly increased thyroid activity and significantly decreased gonadal activity. Lesions in the pituitary stalk, without destruction of any nuclear region of the hypothalamus, also induced hyperthyroidism and decreased gonadal activity. Lesions in the posterior hypothalamus, dorsal hypothalamus, and epithalamus had no significant effects in terms of these parameters. The results provide direct evidence for hypothalamic control of thyroid gland activity in the goldfish. The hyperthyroid response of some of the groups of lesioned fish indicates that this control is mediated by a factor which normally inhibits the secretion of thyrotropin by the pituitary gland and may be called the thyrotropin inhibitory factor (TIF). Viewed together, the lesions identify the NLT pars anterior and NLT pars posterior as the TIF hypophysiotropic center. The results provide direct evidence also for hypothalamic control of gonadal activity in the goldfish. This control is mediated by a factor which stimulates the secretion of gonadotropin and may be called the gonadotropin-releasing factor (GFR). The lesions identify the NLT pars posterior and the posterior part of the NLT pars anterior as the GRF hypophysiotropic center.