Immunohistochemistry and Protein Secretion in the Rat Lacrimal Gland: a Morphophysiological Study

Abstract

The secretion of tears by the lacrimal glands is regulated by the parasympathetic and sympathetic nerves of the autonomic nervous system (Bothelho, 1964; Bromberg, 1981). The autonomic nerves innervate the secretory acini, the duct and the blood vessels and they play important roles in the control of lacrimation and blood flow (Dartt,1989). The parasympathetic nerves form the majority of the structural and functional innervation and control mainly hypersecretion of tears. On the other hand the sympathetic innervation appears to be relatively sparse around the secretory acini but the main sites appear near the lacrimal blood vessels (Nikkinen et al,1985). Activation of both cholinergic and adrenergic nerves can elicit protein secretion from the lacrimal and these responses can be mimicked by the respective agonists (Dartt, 1989; Muller et al, 1985). Recent studies have shown that peptidergic nerves may also control lacrimal secretion and the putative neurotransmitter released by the nerve is vasoactive intestinal polypeptide (VIP) (Dartt et al, 1984; Hussain and Singh, 1988; Matsumoto et al, 1992). However, the involvement of other neurotransmitters and mast cell mediators such as substance P, dopamine, serotonin and histamine in the control of lacrimal gland function is less understood. Thus, this investigation was designed to undertake a morphophysiological study measuring protein secretion and employing immunohistochemistry to confirm the involvement of serotonergic, dopaminergic, peptidergic and histaminergic elements in the control of protein secretion in the rat lacrimal gland.