Pharmacological Analysis of A Monosynaptic Reflex in the Cockroach, Periplaneta Americana

Abstract

The monosynaptic connexion between the trochanteral hairplate afferents and the motoneurone D₈ was investigated pharmacologically. Electrical stimulation of the hairplate produced a 1:1 reflex activation of D₈ which was blocked by saline containing 50 mM-Mg²⁺. Changes in the hairplate-to-D₈ reflex and in the tonic activity of D₈ were monitored during perfusion of drugs known to affect cholinergic transmission. The reflex response was blocked by cholinergic antagonists (atropine, d-tubocurarine, α-bungarotoxin, hexamethonium, decamethonium and TMA); and by an inhibitor of ACh synthesis (hemicholinium-3); it was blocked and desensitized by agonists (carbachol and nicotine) and depolarized and blocked by an AChE inhibitor (eserine). These results are consistent with the hypothesis that ACh is a sensory transmitter in the insect CNS.