Radioimmunoassay and immunocytochemical studies on the recovery of pineal innervation and function following unilateral denervation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in physiology at Massey University

Abstract

The sympathetic noradrenergic neurons of the superior cervical ganglia provide the major source of innervation to the pineal gland Studies described in this thesis were designed to further investigate the initial decline and subsequent recovery of pineal melatonin secretory capacity which has been reported in sheep after unilateral superior cervical ganglionectomy (Lapwood. 1993). Further to that, the compensatory mechanism proposed by Dornay, et al(1985), of re-innervation of denervated tissue by residual nerve fibres originating from the intact SCG, was investigated Melatonin sceretory capacity is advocated as a superior index of pineal function with direct measurement of pineal output Radioimmunoassay was used to measure dark period plasma levels of melatonin prior to and at 1,3,7, 14. 21 and 28 days after unilateral SCGX. Initial response to partial denervation was a reduction in secretory capacity by 80% of pre-operative levels, followed by a linear recovery to pre-operative levels at 21 days after surgery, which was sustained at 28days. Immunocytochemical localization of GAP-43 determined that nerve regeneration occurs in the pineal gland as a reponse to unilateral SCGX GAP-43 in nerve fibres was most prominent at 3 days after surgery after which followed a linear decline to pre-operative levels in measurements taken at 28 days. An association between nerve terminals and the membranes of pinealocytes was observed at 28 days, suggesting those cells were the target of new nerve growth. The presence of nerve growth maturity corresponded with the recovery in pineal function and for this reason the compensatory mechanism of re-innervation is reasoned to be responsible for that recovery. Immunocytochemical localization of alpha tubulin established the presence of that component of microtubules in the cytoplasm of pinealocytes, where it is suggested to function in ihe process of hormone secretion. No variance in the presence of alpha tubulin was measured in any treatment group indicating that cell integrity was maintained and that atrophy did not occur, despite partial denervation. The findings of this study have confirmed a role for re-innervation in the full recovery of pineal melatonin secretory capacity after unilateral SCGX and has demonstrated that the SCG-pineal complex is a very useful model for future studies correlating nerve growth and functional regeneration.