THE AMINERGIC CONTROL OF LOCUST (LOCUSTA-MIGRATORIA) SALIVARY-GLANDS - EVIDENCE FOR DOPAMINERGIC AND SEROTONERGIC INNERVATION

Tyrosine hydroxylase-like immunoreactivity and serotonin-like immunoreactivity of the subesophageal ganglion of the locust, Locusta migratoria, reveals several pairs of cells. One pair of tyrosine hydroxylase-like positive cells (SN1) and one pair of serotonin-like positive cells (SN2) both project through nerve 7b to the salivary glands, where they branch extensively over the acini. Individual acini receive innervation from both SN1 and SN2. Co-localization of immunoreactivity was never observed. Neurons that stain positively for tyrosine hydroxylase-like immunoreactivity are considered to be catecholaminergic since tyrosine hydroxylase is the first and rate limiting enzyme in the pathway for the production of catecholamines. High-performance liquid chromatography of the salivary glands reveals the presence of dopamine and serotonin. Both dopamine and serotonin induce an elevation of cyclic AMP in salivary glands of adult male locusts in a dose-dependent manner. Thus it appears that cyclic AMP is a second messenger for the action of dopamine and serotonin on salivary glands. The presence of distinct dopamine and serotonin receptors on the glands was shown via the ability of the receptor antagonists, SCH-23390 and ketanserin, to inhibit the elevation of cyclic AMP levels induced by dopamine and serotonin, respectively.