Picrotoxin but not bicuculline antagonizes 5-hydroxytryptamine-induced inhibition of cerebellar Purkinje neurons.
The inhibitory effects of iontophoretically applied serotonin (5-hydroxytryptamine) on Purkinje cells were examined in the presence of the GABA antagonists picrotoxin and bicuculline in in vivo and in vitro cerebellar preparations. Continuous application of the GABA-mediated chloride ionophore antagonist, picrotoxin, at currents that induced significant antagonism of GABA-elicited inhibition of Purkinje cells decreased the inhibitory effects of serotonin significantly in the same neurons. Bicuculline, an antagonist of GABA receptors, exerted different actions on serotonin-mediated inhibition of Purkinje cells. Continuous iontophoretic applications of bicuculline antagonized the inhibitory effects of GABA on Purkinje cells significantly, but failed to induce significant attenuation of serotonin-mediated inhibition. The inhibitory effects of serotonin on Purkinje cells were examined also in the presence of nipecotic acid, an inhibitor of GABA reuptake, and a low Ca2-high Mg2+ medium, which blocks synaptic transmission. Under these circumstances, serotonin-mediated inhibitions were not influenced significantly, indicating that its inhibitory effects do not involve release or reuptake of GABA. These results indicate that there might be a linkage between the actions of serotonin and GABA.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D009557:Nipecotic Acids / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology*; D011392:Proline / Q000031:analogs & derivatives*; D011689:Purkinje Cells / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*
D001640:Bicuculline; D002118:Calcium; D008274:Magnesium; D009557:Nipecotic Acids; D010852:Picrotoxin; D011392:Proline; D012701:Serotonin; C030278:nipecotic acid; C010983:homoproline