The cockroach Periplaneta americana has acinar type salivary glands. The secretory acini consist of P-cells, responsible for electrolyte and water secretion and C-cells that secrete protein into the saliva. Salivation is controlled by the dopaminergic and GABAergic salivary neurons SN1 and SN2, and by several smaller serotonergic neurons.

Since tyramine receptors are expressed in the salivary gland complex, we looked for a tyraminergic and/or octopaminergic innervation. Furthermore we studied the physiological role of the GABAergic innervation and the actions of tyramine and octopamine on an isolated nerve-gland preparation. Using electrical salivary duct nerve (SDN) stimulation and simultaneous recording of the basolateral membrane potential (Vbl) from acinar cells we found: (1) GABA, tyramine and octopamine enhance Vbl-changes induced by electrical activity of the SDN and (2) these three transmitters act presynaptically. (3) Secretion measurements revealed that GABA enhances the rates of fluid and protein secretion significantly. (4) Pharmacological experiments indicate that GABAB-receptors are involved in mediating the excitatory GABA effect.

Supported by the DFG, GRK837 - Functional Insect Science