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Modulation of transmitter release from the locust forewing stretch receptor neuron by GABAergic interneurons activated via muscarinic receptors

Lookup NU author(s): Dr Sarah Judge

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Abstract

The role of muscarinic receptors in the down-regulation of acetylcholine (ACh) release from the locust forewing stretch receptor neuron (fSR) terminals has been investigated. Electrical stimulation of the fSR evokes monosynaptic excitatory postsynaptic potentials (EPSPs) in the first basalar motoneuron (BA1), produced mainly by the activation of postsynaptic nicotinic cholinergic receptors. The general muscarinic antagonists scopolamine (10(-6) M) and atropine (10(-8) to 10(-6) M) caused a reversible increase in the amplitude of electrically evoked EPSPs. However, scopolamine (10(-6) M) caused a slight depression in the amplitude of responses to ACh pressure-applied to the soma of BA1. These observations indicate that the EPSP amplitude enhancement is due to the blockade of muscarinic receptors on neurons presynaptic to BA1. The muscarinic receptors may be located on the fSR itself and act as autoreceptors, and/or they may be located on GABAergic interneurons which inhibit ACh release from the fSR. Electron microscopical immunocytochemistry has revealed that GABA-immunoreactive neurons make presynaptic inputs to the fSR. The GABA antagonist picrotoxin (10(-6) M) caused a reversible increase in the EPSP amplitude, which does not appear to be due to an increase in sensitivity of BA1 to ACh, as picrotoxin (10(-6) M) slightly decreased ACh responses recorded from BA1. Application of scopolamine (10(-6) M) to a preparation preincubated with picrotoxin did not cause the EPSP amplitude enhancement normally seen in control experiments; in fact, it caused a slight depression. This indicates that at least some of the presynaptic muscarinic receptors are located on GABAergic interneurons that modulate transmission at the fSR/BA1 synapse.


Publication metadata

Author(s): Judge S, Leitch B

Publication type: Article

Publication status: Published

Journal: Journal of Neurobiology

Year: 1999

Volume: 40

Issue: 3

Pages: 420-431

Print publication date: 05/09/1999

ISSN (print): 0022-3034

ISSN (electronic): 1097-4695

Publisher: John Wiley & Sons, Inc.

URL: http://dx.doi.org/10.1002/(SICI)1097-4695(19990905)40:3<420::AID-NEU13>3.0.CO;2-R

DOI: 10.1002/(SICI)1097-4695(19990905)40:3<420::AID-NEU13>3.0.CO;2-R

PubMed id: 10440741


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