Comparative pharmacological properties of muscle function in the foregut and the hindgut of the cockroach Leucophaea maderae

1. 5-Hydroxytryptamine (4 × 10 −8 M) consistently caused an increase in the frequency and amplitude of spontaneous contractions of the foregut of Leucophaea maderae. The hindgut showed similar responses to this indolalkylamine, but the threshold ranged from 4 × 10 −8 M to 4 × 10 −6 M. 2. Tyramine (5 × 10 −6 M) produced a marked suppression of muscular activity in both organs and served as an antagonist of 5-hydroxytryptamine, glutamate and proctolin. 3. Monosodium glutamate (4 × 10 −5 M) generally evoked a large phasic contraction in hindguts. However, glutamate (1 × 10 −4 M) had either no effect on foreguts or induced a suppression of contractile activity. 4. Although the pentapeptide proctolin stimulated rhythmic activity in both the foregut and the hindgut, the threshold for activation of the hindgut (3 × 10 −11 M) was lower than the foregut (3 × 10 −8 M). 5. The results suggests that a dichotomy exists between the neurochemical mechanisms controlling these two organs in L. maderae.