THE EFFECTS OF SEROTONIN AND DOPAMINE ON SALIVARY SECRETION BY ISOLATED COCKROACH SALIVARY-GLANDS

We have studied the effects of 3-hydroxytyramine (dopamine) and 5-hydr oxyr:ryptamine (serotonin) on (1) the rates of salivation from isolate d salivary glands of the cockroach Periplaneta americana, (2) the prot ein content of the saliva, and (3) the ultrastructure of the salivary gland epithelium. The rates of neurotransmitter-induced salivation var ied in a dose-dependent manner within the concentration range 10(-9) t o 10(-4) moll(-1), Half-maximal secretory rates were induced by 6x10(- 7) moll(-1) serotonin and 1.1x10(-7) moll(-1) dopamine. Stimulation of the glands by serotonin resulted in the production of a protein-rich saliva, whereas saliva was protein-free after stimulation by dopamine. Electron microscopic studies revealed that the central cells, which a re believed to produce the proteinacepis components of the salivia, se crete their vesicular content after stimulation by 10(-6) moll(-1) ser otonin for 20 min. In contrast, no morphological changes could be dete cted after stimulation by 10(-6)moll(-1) dopamine. These data indicate that dopamine stimulates only the secretion of the fluid component of the saliva, whereas serotonin is necessary to stimulate secretion of the proteinaceous components.