The effect of various biogenic amines on the activity of the foregut of the cockroach, Blaberus giganteus

A differential transformer displacement transducer recorded the activity of the visceral muscle of Blaberus giganteus (L.) with a high degree of sensitivity. The denervated foregut proved to have myogenic properties with certain specific pacemaker regions. Nevertheless, stimulation of the oesophageal nerve innervating the region of the crop caused a slow type of graded contraction in the longitudinal muscles. Preparations of both the innervated and the denervated foregut were sensitive to 5-hydroxytryptamine (10 −7 M), noradrenaline (10 −6 M), and acetylcholine (5 × 10 −6 M). Also, Factor S, a biogenic amine of uncertain structure found in arthropods, caused an excitatory response in innervated foreguts and an inhibitory response in denervated foreguts. Denervated foreguts had a greater sensitivity to l-glutamic acid than innervated preparations. The neurochemical divergence between the control of visceral and somatic musculature of insects is discussed in relation to the pharmacology of these biogenic amines.