Possible involvement of the GABAergic system in dopaminergic-cholinergic interactions in electroacupuncture-induced analgesia.

The involvement of the GABA system in dopamine-acetylcholine interactions in electroacupuncture induced analgesia (EAA), measured in terms of tail flick latency (TFL) test, was studied with administration of the GABA receptor agonist, muscimol (1 mg/kg, i.p.); antagonist, bicuculline (2 mg/kg, i.p.); GABAmimetic drug, ethanolamine-O-sulfate (EOS) (2 mg/kg, s.c.) or the drugs stimulating or inhibiting acetylcholine and dopamine receptors activity to rats exposed to electroacupunture (EA). All the drugs were administered prior to EA (10 Hz, 1 volt) exposure (2-15 min). Results observed under the above conditions suggest that the cholinergic system has a direct inhibitory role on EAA and the dopaminergic system mediates its action via the cholinergic system. A decrease in EAA with both the GABA receptor agonist and antagonist and tremendous increase of EAA with the gabamimetic drug, EOS, showed that GABA receptors may not be directly involved in EAA. Further (a) gradual withdrawal of muscimol, bicuculline or physostigmine induced decrease in EAA with the increase in duration of EA exposure; (b) the characteristic changes in EAA observed with the coadministration of (i) L-DOPA + carbidopa + muscimol (ii) atropine + muscimol; and (c) no significant change in bicuculline + physostigmine induced inhibition of EAA with the increase in duration of EA exposure suggest that some inhibitory substance(s) may be released during EA which may inhibit the GABA system and finally cholinergic activity through the activation of dopaminergic neurone.