Serotonergic Modulation of the Locust Mandibular Closer Muscle

Abstract

Within the suboesophageal ganglion of the locust there is a group of 14 anterior-midline cell bodies that stain with antibody to 5-hydroxytryptamine (5HT, serotonin). Six of these cell bodies have previously been termed “the satellite neurones” because their axons run along side the ventrally-directed peripheral nerves of the ganglion forming putative neurohaemal endings in the sheaths (Bråunig, 1987). The other 8 neurones, termed “the link nerve neurones”, have similar endings, however, these terminate along the more anterior of the peripheral nerves, in particular the upper reaches of nerve 1D, which contains the motor axons of the mandibular closer muscle. Labelling with anti-5HT also reveals axons among the mandibular closer muscle fibres. The present study demonstrates that 1) 5HT modulates neurally-evoked contractions of the mandibular closer muscle in a similar manner to that of octopamine in the extensor tibiae, 2) drugs that artificially elevate cAMP levels in the mandibular closer muscle mimic the effect of 5HT, and 3) inhibition of adenylate cyclase by adenosine alters the action of 5HT.