Influence of selective opiate antagonists on striatal acetylcholine and dopamine release

In the present study the effect of selective opiate antagonists on the release of acetylcholine (ACh) and dopamine (DA) was studied in striatal slices. beta-funaltrexamine (beta-FNA) a mu receptor antagonist, naltrindole (NTI) a delta receptor antagonist and a kappa receptor antagonist nor-binaltorphimine (nor-BNI) were used to selectively block the different opioid receptor subpopulations located on the axon terminals. The receptor activation was examined on superfused slices from rat striatum previously labelled with [3H]choline or [3H]dopamine. We found that both beta-FNA and NTI significantly enhanced the evoked release of ACh using electrical field stimulation but it occurred only in those cases when dopaminergic input was impaired either by lesion of the nigrostriatal tract or by D2 dopamine receptor blocade. By contrast, under these conditions the opiate antagonists had no modulatory effect on the release of DA. Our data suggest that the release of ACh in the striatum is under the tonic control of endogenous opioid peptides. This effect is mediated via mu and delta opioid receptors. However the striatal DA release does not seem to be controlled tonically by opioid peptides.