The dopamine and 5-hydroxytryptamine content of locust and cockroach salivary neurones

The salivary glands of the cockroach and locust are innervated primarily from two pairs of motoneurones, designated SN1 and SN2, in the suboesophageal ganglion. Intracellular cobalt fills and subsequent silver intensification were used to reveal the morphology of these cells in both species. Fluorescent microscopy, following treatment of the ganglion with glyoxylic acid, showed that in both species only the SN1 neurones contained catecholamines. A radioenzymatic assay for dopamine, performed on the locust SN1 neurones, confirmed that this catecholamine was present. A radioenzymatic assay for 5-hydroxytryptamine (5-HT), performed on both pairs of salivary neurones in the locust, revealed small quantities of this amine in the SN2 neurones, but no significant amount in the SN1 neurones. In the cockroach, 5-HT was assayed in the SN2 neurones only. In contrast to the locust, however, the 5-HT content of these cells was not significantly above that of control cells taken from other ganglia. These observations demonstrate that only the SN1 neurones are the source of the catecholaminergic fibres investing the locust and cockroach salivary glands. The difference in neurotransmitter content between the SN1 and SN2 neurones suggests that these neurones have separate functions in the control of salivary secretion.