THE LOCUST OVIPOSITOR OPENER MUSCLE: PROPERTIES OF THE NEUROMUSCULAR SYSTEM

Abstract

A new preparation for studying properties of neuromuscular transmission and neuromodulation in insects, the ventral opener muscle of the locust ovipositor, is described. It consists of the complete musculoskeletal apparatus of the ventral opener muscle and the associated abdominal ganglia containing the central pattern generator that drives oviposition digging. In this preparation it is possible to record simultaneously motoneurone activity, muscle electromyograms, intracellular muscle fibre activity and behaviourally relevant tension production. The muscle displays ultrastructural and physiological characteristics typical of insect intermediate-type fibres: abundant sarcoplasmic reticulum, active Ca2+-dependent membrane responses, phasic contractions when stimulated by high-potassium saline and a low twitch:tetanus ratio. Superfused glutamate (10–4 mol l- 1) and proctolin (10–8 mol l-1) induce contractions of the muscle, while GABA (10–4 mol l-1) reduces potassium-induced depolarizations. HPLC, bioassay and immunological methods show that proctolin is associated with all of the ventral ovipositor muscles, and combined back- filling/immunohistochemistry suggests that at least one of the ventral opener motoneurones is proctolinergic.