Siniscalchi_1993_Eur.Neuropsychopharmacol_3_511

Acetylcholine (ACh) release from the cerebral cortex was studied in freely moving guinea pigs, implanted with epidural cups. A single dose of either 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT, 0.1 mg/kg s.c.) or 5-hydroxytryptamine (5-HT, 250 micrograms i.c.v.) increased cortical ACh release, both in male and in female guinea pigs. In female guinea pigs chronically treated with 8-OHDPAT (0.1 mg/kg daily s.c., for 14 days) the facilitatory effect of 8-OHDPAT and 5-HT was maintained. In chronically 8-OHDPAT-treated male guinea pigs, 8-OHDPAT no longer modified ACh release, while 5-HT inhibited it. The inhibition was prevented by the 5-HT3 antagonist MDL 72222 1 mg/kg s.c. These results indicate that differences exist between male and female guinea pigs in the adaptive responses to prolonged treatment with the selective 5-HT1A agonist 8-OHDPAT.