LESIONS OF THE VENTRAL STRIATUM MIMIC THE EFFECT OF OLFACTORY BULBECTOMY TO PREVENT SHORT PHOTOPERIOD-INDUCED TESTICULAR REGRESSION IN GOLDEN-HAMSTERS

Bilateral olfactory bulbectomy (BX) or bilateral transection of the ro stral lateral olfactory tract (LOT) at the level of the anterior olfac tory nucleus markedly increases gonadotropin secretion and prevents th e testicular regression associated with maintenance on short photoperi od in golden hamsters. In an effort to further elucidate the neural tr acts involved in this influence on gonadotropin secretion, lesions wer e placed in several potential pathways. Hamsters underwent sham surger y (SH), bilateral BX, or electrolytic or radiofrequency lesions of the : medial nucleus of the amygdala (MeX) caudal LOT just rostral to the medial nucleus of the amygdala (LOTX); or ventral striatum (VSX). Lesi ons were either bilateral or unilateral with contralateral olfactory b ulbectomy. All animals were then placed on short photoperiod (LD 10:14 ) for 10 weeks and testicular size and body weight were assessed at we ekly intervals. Lesion placement was assessed in brain sections staine d with cresyl violet and animals with misplaced lesions mere excluded. The following represent the number of animals in each group undergoin g testicular regression in response to short photoperiod: SH: 32/35: B X: 8/31 (P < 0.01 vs. SH). MeX: 5/5; caudal LOTX: 8/9 and VSX: 3/8 (P < 0.05 vs. SH). Serum LH, FSH and testosterone at the end of the study correlated with the testicular regression data. These results suggest that the tonic inhibitory effect of the olfactory bulbs on gonadotrop in secretion is mediated by fibers that exit the LOT rostral to the am ygdala and project medially, either passing through or synapsing in th e ventral striatum.