Abstract
Ionotropic gamma-aminobutyric acid (GABA) receptors are known to mediate excitation in neonatal neurones as a crucial developmental factor. In the present study we employed calcium imaging techniques with the calcium indicator Fura-2-AM to study the pharmacology of GABA-induced calcium responses in cultures prepared from neonatal rat superficial superior colliculus (SC), after immunocytochemical labelling confirmed the presence of GABA C ρ 1 subunits in 35% of neurones. Rises in neuronal intracellular calcium were obtained in response to GABA and also to the subtype-specific GABA A agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol. However, the GABA C agonist cis-4-aminocrotonic acid induced calcium response only at unspecifically high concentrations (500 μM). Co-application of GABA antagonists revealed that both GABA A&C agonists’ actions could be blocked by the GABA A antagonist bicuculline but not the GABA C antagonists 1,2,5,6-tetrahydro-(pyridin-4-yl) methylphosphinic acid. This suggests that activation of GABA A but not GABA C receptors contributes to excitatory GABA responses and related calcium signals in neonatal SC neurones.
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