Crayfish sensory terminals and motor neurones exhibit two distinct types of GABA receptors |
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Authors: | E Pearstein D Cattaert F Clarac |
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Institution: | (1) U.P.R. Neurobiologie et Mouvements, C.N.R.S.; 31, Ch. Joseph Aiguier, F-13402 Marseille Cedex 20, France Fax: (33)91775084, e-mail: edouard@lnf.cnrs-mrs.fr, FR |
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Abstract: | Motor neurones of the crayfish walking system display inhibitory responses evoked either by γ-amino butyric acid (GABA) or
glutamate, possibly involving the same receptor (Pearlstein et al. 1994). In order to test if this sensibility to both GABA
and glutamate was a specific property of crayfish GABA receptors, pharmacological characteristics of GABA-evoked responses
in both sensory terminals from CB chordotonal organ and motor neurones of the walking system have been compared. Both receptors
are GABA-gated Cl− channels activated by specific GABAA (muscimol, isoguvacine), GABAB (3-aminopropyl phosphinic acid), and GABAC (cis-4-amino crotonic acid) agonists, and blocked by competitive (β-guanidino propionic acid) and non-competitive (picrotoxin)
antagonists. They were insensitive to specific GABAA (bicuculline, SR-95531) and GABAB (phaclofen) antagonists. Furthermore, in both cases, nipecotic acid and the modulatory drug diazepam had no effect. However,
our results demonstrate that GABA receptors of sensory terminals are different from those of motor neurones. GABA-induced
desensitisation only occurred in sensory terminals. Moreover, glutamate was shown to activate GABA-gated Cl− channels in motor neurones, but not in sensory terminals. Therefore, GABA is likely to be the endogenous neurotransmitter
of presynaptic inhibition in sensory terminals, whereas inhibition between antagonistic motor neurones would be achieved by
glutamate.
Accepted: 10 July 1996 |
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Keywords: | GABA receptors Glutamate Sensory terminals Motor neurones Invertebrate |
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