The effects of nerve growth factor and anti-nerve growth factor antibody on the neuroendocrine reproductive system in the European starling Sturnus vulgaris

Thyroidectomy of starlings causes them to remain in breeding condition indefinitely; deactivation of gonadotrophin-releasing hormone neurons that is characteristic of photorefractoriness does not occur. We hypothesise that a neurotrophin, whose presence or ability to function is dependent upon thyroid hormones, is somehow involved in this termination of gonadotrophin-releasing hormone release. Nerve growth factor is one such candidate. Mouse 7S-nerve growth factor dissolved in artificial cerebro-spinal fluid was therefore infused into the lateral ventricle of thyroidectomised male starlings held on long days four times daily for 21 days and 31 days, in separate experiments, to see if photorefractoriness would occur. The result was significant gonadal regression in the treatment groups during the infusion period, with no change in testicular volume in the control groups. Testicular recrudescence occurred after the end of the treatment period. To see if this was a non-specific effect, or progression towards photorefractoriness per se, we used castrated, photorefractory starlings held on long days. Anti-nerve growth factor antibody was infused into the lateral ventricle at increasing concentrations and frequency. There was a significant rise in circulating luteinising hormone levels in the treatment groups as compared to controls, increasing with antibody dosage.