|
pubmed:abstractText |
The activity of neurones in the zona compacta of the rat substantia nigra was recorded extracellularly in vitro. Dopamine produced a dose-dependent depression of firing, threshold doses being in the 3 microM range. The inhibitory effects of dopamine were antagonized by (-)-sulpiride (pA2 7.5), haloperidol (pA2 8.4) and cis-flupenthixol (pA2 6.9). The actions of gamma-aminobutyric acid (GABA) were not affected by these compounds. The gradients of Schild plots of data for (-)-sulpiride were less than unity while those for haloperidol and cis-flupenthixol were greater than unity, which suggests that the antagonism was not competitive. This is discussed with regard to the use of a bioassay system in the analysis of the effects of antagonists. Haloperidol and (-)-sulpiride were found to have similar potencies, as dopamine receptor antagonists, to those predicted from biochemical and clinical efficacy studies, but cis-flupenthixol was less potent than expected.
|
