1. 1.

    The monosynaptic connexion between the trochanteral hairplate afferents and the motoneurone D8 was investigated pharmacologically.

  2. 2.

    Electrical stimulation of the hairplate produced a 1:1 reflex activation of D8 which was blocked by saline containing 50 mM-Mg2+.

  3. 3.

    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.

  4. 4.

    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).

  5. 5.

    These results are consistent with the hypothesis that ACh is a sensory transmitter in the insect CNS.

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