Heterogeneous distribution of benzodiazepine receptors among rat neostriatal neurones.

1. The effects of benzodiazepine receptor (BZR) agonist were investigated in dissociated rat neostriatal neurones by a conventional whole-cell patch recording configuration at room temperature. 2. The dissociated neurones, with a longest somatic diameter of larger than 25 microns, were classified as 'large neurones', while those having soma measuring less than 15 microns were described as 'small neurones'. Large neurones were intensely positive for acetylcholinesterase staining, whereas the small ones were not. 3. CL218,872 enhanced the GABA response in both the large and small neurones with similar EC50S. However, the potentiation efficacy of CL218,872 in large neurones was larger than that of small ones. 4. Zolpidem also potentiated the GABA response in both neuronal populations with similar EC50S. This compound also enhanced the GABA response more strongly in large neurones than in small ones. 5. Zopiclone exerted a prominent potentiation in large neurones, although no difference was seen in the EC50S in the large and small neurones. 6. It was concluded that the BZR in large neurones had a different pharmacological property from that in small ones and that the BZR agonists showed a prominent difference, not in EC50, but in the potentiation efficacy between these neuronal populations.