Cervical sympathectomy inhibits axonal transport of gonadotropin-releasing hormone during continuous exposure to light in male rats

Abstract

To examine the effects of cervical sympathectomy on the transport of gonadotropin-releasing hormone (GnRH) between the hypothalamic neurons and the median eminence, 16 male rats were assigned into four groups: control (C), light (L), light-sympathectomy (LS), and light-colchicine (LC). The C group was kept under a normal circadian rhythm for 2 weeks, and the L group was kept under continuous exposure to light for the same period. The LS group underwent bilateral cervical sympathectomy before being kept under continuous light conditions for 2 weeks. The LC group received colchicine into the cerebral ventricle after being kept under continuous light for 12 days; subsequently, this group was also housed for 2 days under continous light. After these procedures, blood was collected and serum luteinizing hormone (LH) levels were measured. All rats were perfused with a fixative, and GnRH neurons around the anterior commissure, as well as GnRH fibers and granules in the median eminence, were stained immunohistochemically. The L group showed a decreased number of GnRH neurons, increased concentrations of GnRH fibers and granules, and an increased LH level; however, in the LS and LC groups, these changes were not seen. The response in the LS group resembled that in the LC group. Considering the action of colchicine, which inhibits axonal transport, it is suggested that cervical sympathectomy also inhibits axonal transports of GnRH between the GnRH neurons and the median eminence during continuous exposure to light.