Physiological release of striatal acetylcholine (in vivo): effect of somatostatin on dopaminergic-cholinergic interaction.
The effects of somatostatin (SOM) on the release of acetylcholine (ACh) and dopamine (DA) from striatum of freely moving rats were studied by transversal microdialysis. Acetylcholine (ACh) and dopamine (DA) were detected by high performance liquid chromatography (HPLC) with electrochemical detection. Somatostatin (0.1, 0.5 and 1 microM), administered locally through the microdialysis probe to the striatum, was able to release dose-dependently ACh from the cholinergic neurons of the striatum. The increase in the extracellular levels of ACh produced by 1 microM SOM in the striatum reached a maximum of 200%. ACh-releasing effect of SOM was completely inhibited by tetrodotoxin indicating that neuronal firing is involved in its effect. Local infusion of sulpiride, 10 microM, D(2) receptor antagonist, potentiated (about 100%) the SOM (1 microM)-induced release of ACh. SOM, 1 microM, was more effective in enhancing the release of ACh in the striatum (two-fold increase) after degeneration of the nigrostriatal DA pathway with 6-hydroxydopamine (6-OHDA) (250 microg/animal, i.c.v.). The D(2) receptor agonists bromcriptine, 10 microM, or apomorphine, 10 microM, completely antagonize SOM-induced release. SOM, 1 microM, enhanced the release of DA (about 400%). These findings indicate that SOM is capable of releasing both ACh and DA in the striatum, however, its effect on ACh release is partially masked unless the D(2) receptor-mediated tonic inhibitory effect of released DA from the nigro-striatal pathway is attenuated.
D000109:Acetylcholine / Q000378:metabolism*; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003714:Denervation; D004298:Dopamine / Q000378:metabolism*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions / Q000502:physiology; D008297:Male; D017072:Neostriatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016627:Oxidopamine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013004:Somatostatin / Q000378:metabolism* / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017448:Receptors, Dopamine D2; D026941:Sodium Channel Blockers; D013004:Somatostatin; D016627:Oxidopamine; D000109:Acetylcholine; D004298:Dopamine