Rapid gonadal recrudescence and body and lipid mass increases with hypothalamic lesions in photoregressed Siberian hamsters.

The effects of lesions (x) of the suprachiasmatic nucleus (SCN) or paraventricular nucleus (PVN), or pinealectomy (PINX) on gonadal recrudescence, body and fat pad weights, and food intake were examined in photoregressed male Siberian hamsters (Phodopus sungorus sungorus). Blood was sampled weekly for serum follicle-stimulating hormone (FSH) and prolactin (PRL) measurement. Lesions were classified as complete if greater than 80% of the nuclei were destroyed and designated as 'hits', whereas incomplete lesions were designated as 'misses'. Five weeks postlesion, hamsters with PVNx or SCNx hits and SCNx misses (lesions generally located caudal and dorsal to the SCN) had increased testes, epididymal white adipose tissue and body weights, increased food intake, and progressively increasing serum PRL, but not FSH concentrations compared with PINX, PVNx misses and intact short day controls. SCNx hamsters with complete lesions had sparse or arrhythmic locomotor activity patterns in subsequent tests under constant conditions. Although no single area was identified histologically as the locus for this effect, the hyperprolactinemia and rapid gonadal recrudescence was consistent with varied degrees of damage to the periventricular area. These results suggest a novel central control of PRL secretion by an area caudal and dorsal to the SCN, and extending to and including the PVN. This area may be involved with maintaining short day responses.