ACTION OF PROCTOLIN AND L-GLUTAMIC ACID ON THE VISCERAL MUSCLES OF THE HINDGUT OF THE COCKROACH LEUCOPHAEA-MADERAE

1. Response of the hindgut of Leucophaea maderae to glutamate (2 × 10-5 M) resembles contractions evoked by brief neural stimulation. The action of proctolin (3 × 10-10 M) approximates the response of the hindgut to recurrent neural stimulation but not to continous stimulation. 2. Neurally evoked contractions were graded and increased with the frequency of stimulation. Exposure of the hindgut to increasing concentrations of either glutamate or proctolin cause a graded response in deganglionated preparations. 3. The threshold for activation with proctolin on the hindgut of Periplaneta americana was about 4 × 10-11 M. At a concentration of 6 × 10-11 M, the response continued for 20 min. 4. Both glutamate (1.5 × 10-6 M) and proctolin (2 × 10-10 M) potentiated neurally evoked events in L. maderae, but glutamate at 2 × 10-5 M or higher often suppressed contractions. This later circumstance resulted in part from a blockade of axonal transmission. Proctolin at elevated concentrations (10-7 M) did not disrupt synaptic transmission. 5. Tyramine (10-7 M) suppressed the action of proctolin and glutamate. The results suggest that glutamate might serve as a transmitter and that proctolin might function as a modulator in the hindgut of L. maderae. © 1979.