Effect of infundibular lesions on GnRH and LH release in the frog, Rana temporaria, during hibernation.

The effects of lesions and deafferentations on accelerated hibernatory ovulation and on the concentration of GnRH in blood collected from the hypothalamo-pituitary area along with the blood and pituitary levels of luteinizing hormone (LH) in hibernating female frogs, Rana temporaria, were studied. The lesions to the caudal portion of the nucleus infundibularis ventralis resulted in: (1) an elevation in GnRH concentration in blood collected from the hypothalamo-pituitary area (x +/- SEM = 51 +/- 9.5 and 100 +/- 15 pg/ml in control and lesioned females, respectively), (2) an increase in plasma LH (from 11 +/- 1.3 to 14.7 +/- 2.5 ng/ml in controls to 73.1 +/- 12.0 and 74.2 +/- 15.8 ng/ml in lesioned females at 3 and 7 days), and (3) accelerated ovulations whose onset advanced as the hibernation season progressed. Histological and immunohistochemical analyses of the brains showed that GnRH seems to be stored during hibernation in the median eminence and suggested that the complete disruption of projections to the median eminence is prerequisite for accelerated ovulation. The influence of the hypothalamic inhibitory action on the release of GnRH and the way in which GnRH is transferred to the pituitary gland are discussed.