Discriminative stimulus properties of the 5-HT1A receptor agonist BAY x 3702 in the rat.

The aminomethylchroman derivative BAY x 3702 (R-(-)-2-¿4-[(chroman-2-ylmethyl)-amino]-butyl¿-1,1-dioxo-benzo[d] isothiazolone HCl) has recently been characterized as a relatively selective, high affinity 5-HT1A receptor agonist with neuroprotective, anxiolytic- and antidepressant-like effects in animal models. It was the aim of the present study to further confirm its receptor binding profile in an in vivo assay. Rats were trained to discriminate BAY x 3702 (0.1 mg/kg, i.p.) from vehicle in a standard two-lever fixed ratio 10 food-reinforced procedure. All rats learned the discrimination, the median number of sessions to reach criterion being 38 (range: 22-58 sessions). Generalization tests with BAY x 3702 showed dose-dependent and complete generalization after different routes of administration; the ED50 values being: 0.030, 0.007 and 0.36 mg/kg, after i.p., i.v. and p.o. administration, respectively. Assessment of the duration of action after administration of 0.1 mg/kg BAY x 3702, i.p., resulted in a T1/2 of 65 min. Dose-dependent and complete generalization was also obtained with the 5-HT1A receptor agonists 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)-tetralin, ED50 in mg/kg, i.p.: 0.086), flesinoxan (0.30), SR 57746A ((4-(3-trifluoromethylphenyl)-N-(2-(naphth-2-yl)ethyl)-1,2,3,6-tet rahydropyridine HCl, 1.0), the (+)-enantiomer of BAY x 3702 (1.3) and ipsapirone (1.8); the ED50 values being closely correlated with their respective affinities for the 5-HT1A receptor. Pretreatment with the selective 5-HT1A receptor antagonist WAY-100635 ((N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N(2-pyridinyl) cyclohexane carboxamide trihydrochloride) dose-dependently and completely blocked the discriminative effects of 0.1 mg/kg BAY x 3702 (ID50: 0.013 mg/kg, i.p.). WAY-100635, prazosin, idazoxan, raclopride, paroxetine, (-)-BAY k 8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methyl-phenyl)-p yridine-5-carboxylate), ethanol, and the putative neuroprotectants MK-801 ((+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imin e), CNS 1102 (N-(1-naphthyl)-N'-(3-ethylphenyl)-N'-methyl-guanidine), CGS 19755 (cis-4-(phosphonomethyl) piperidine-2-carboxylic acid) and nimodipine did not induce more than 20% generalization. It is concluded that the BAY x 3702 cue is mediated by its agonistic activity at 5-HT1A receptors.