Acetylcholine Receptors on the Cell Body Membrane of Giant Interneurone 2 in the Cockroach, Periplaneta Americana

Abstract

1. Ionophoresis of acetylcholine (ACh) onto the cell body membrane of an identified giant interneurone (GI2) in the central nervous system of the cockroach Periplaneta americana induced a depolarizing response at resting potential which was attributed to a population of extrasynaptic ACh receptors. 2. The sensitivity of the cell body membrane of GI 2 to ionophoresis of ACh was determined. 3. Perfusion of 1.0 × 10−6M neostigmine, an inhibitor of acetylcholinesterase, potentiated the ACh sensitivity of the cell body membrane of GI2. This indicated that a high acetylcholinesterase activity was present in the periphery of the sixth abdominal ganglion (A6). 4. The nicotinic antagonist, α-bungarotoxin (at a concentration of 1.0 × 10−7M) was found to block the ACh response of the cell body membrane of GI2. By contrast, the muscarinic antagonist, quinuclidinyl benzilate, (at concentrations up to 1.0 × 10−5 M) had no detectable effect on the ACh response. 5. It is suggested that an extrasynaptic nicotinic type of ACh receptor is present on the cell body membrane of GI2.

α-Bungarotoxin Blocks Excitatory Synaptic Transmission Between Cercal Sensory Neurones and Giant Interneurone 2 of the Cockroach,Periplaneta Americana

“…Recently, in studies on the extrasynaptic cell body membrane of GI 2, the depolarizing response to ionophoretically-applied acetylcholine was blocked by a-bungarotoxin (Harrow & Sattelle, 1983). Since the cell body membranes of neurones in the cockroach sixth abdominal ganglion appear to be devoid of synapses (Smith & Treherne, 1965), a presynaptic action of the toxin appears to be ruled out in this case.…”

“…The dense binding of 1Z5 I-a-bungarotoxin noted in the peripheral regions of the ganglion, part of which is non-specific, contrasts with the previously reported absence of binding in the peripheral regions of ganglia in Drosophila melanogaster (Hall & Teng, 1975;Schmidt-Nielsen et al 1977) and Manduca sexta (Hildebrand, Hall & Osmond, 1979) but is consistent with findings for other insects such as the cricket Acheta domesticus (L. M. Hall, B. C. Osmond & J. G. Hildebrand, unpublished observations). Part of the specific binding in peripheral regions of the cockroach terminal abdominal ganglion is probably due to a-bungarotoxin-sensitive cholinergic receptors on the somal membranes of neurones (Harrow & Sattelle, 1983). T h i possibility that a-bungarotoxin is binding to glial cells cannot be excluded.…”

“…For this study we chose, instead, giant interneurone 2 (GI 2) whose axon is more readily dissected than that of any other giant interneurone in the cockroach and is therefore well suited for pharmacological studies using the oil-gap, single-fibre technique. Also, the cell body of GI 2 is located conveniently for microelectrode impalements, thereby enabling comparative studies on the pharmacology of synaptic and extrasynaptic acetylcholine receptors of the same identified neurone (Harrow & Sattelle, 1983).…”