NEURONAL RELEASE OF ENDOGENOUS DOPAMINE FROM CORPUS OF GUINEA-PIG STOMACH

Neuronal release of endogenous dopamine was identified in mucosa-free preparations (muscle layer including intramural plexus) from guinea pi g stomach corpus by measuring tissue dopamine content and dopamine rel ease and by immunohistochemical methods using a dopamine antiserum. Do pamine content in mucosa-free preparations of guinea pig gastric corpu s was one-tenth of norepinephrine content. Electrical transmural stimu lation of mucosa-free preparations of gastric corpus increased the rel ease of endogenous dopamine in a frequency-dependent (3-20 Hz) manner. The stimulated release of dopamine was prevented by either removal of external Ca2+ or treatment with tetrodotoxin. Dopamine-immunopositive nerve fibers surrounding choline acetyltransferase-immunopositive gan glion cells were seen in the myenteric plexus of whole mount preparati ons of gastric corpus even after bilateral transection of the splanchn ic nerve proximal to the junction with the vagal nerve (section of ner ves between the celiac ganglion and stomach). Domperidone and sulpirid e potentiated the stimulated release of acetylcholine and reversed the dopamine-induced inhibition of acetylcholine release from mucosa-free preparations. These results indicate that dopamine is physiologically released from neurons and from possible dopaminergic nerve terminals and regulates cholinergic neuronal activity in the corpus of guinea pi g stomach.