Neonatal and 21-day-old (P21) rats: P3 rat pups were anaesthetized and a syringe containing 0.5 μl of 0.9 % saline with 2.2 μCi of 3[H]Gabazine was inserted intrathecally. The compound was injected and 10min post injection the animals were terminally anaesthetized with sodium pentobarbitone. Injections of 3H-gabazine in the L4-L5 region at P3 confirmed that gabazine binding was restricted to the lumbar spinal cord. The effects of spinalization were consistent with gabazine facilitation of ventral root potentials observed in isolated neonatal spinal cord.

Gabazine totally blocked evoked inhibitory postsynaptic currents (IPSCs) in CA3 pyramidal cells. The application of guanidinoethanesulfonic acid, an uptake inhibitor of beta-alanine and taurine, induced strychnine-sensitive chloride current in the presence of gabazine. To determine whether glycine receptors, which are expressed most strongly on CA3 pyramidal cells, are involved in synaptic transmission, it was characterized the pharmacological profile of the receptors mediating IPSCs evoked by brief extracellular stimulation (100 μs, single current pulse up to 30 μA) in the stratum radiatum of the CA3 region in the presence of CNQX (40 μm), CPP (40 μm) and CGP 62349 (5 μm). First, the sensitivity of the IPSC to GABAA receptor blockade by gabazine was tested. Evoked IPSCs and responses to GABA puffs were alternately induced. The degree of GABAA receptor blockade was monitored by examining the effect of gabazine on responses induced by GABA puffs, whose peak amplitudes were adjusted to match those of the alternately evoked IPSCs. Bath application of gabazine (10 μm) completely blocked the IPSC and inhibited the GABA-induced currents by 98.7 ± 0.3 % (n = 7). Application of gabazine also abolished spontaneous IPSCs. The incomplete blockade of responses to exogenous GABA by the competitive antagonist gabazine probably reflects the prolonged presence of GABA resulting from the puff applications, which may saturate GABA transporters, since even with the addition of gabazine to the GABA application pipette, GABA-induced currents could not be blocked completely.