Action of ipsapirone and 8-OH-DPAT on exploratory behavior in hamsters (Mesocricetus auratus): effects of antagonists and p-CPA.

The effect of the serotonergic drugs 8-OH-DPAT (0.0625, 0.125, and 0.25 mg/kg) and ipsapirone (5.0 and 10.0 mg/kg) on the exploratory behavior shown by hamsters under light:dark conditions was studied. These drugs produced an increase in the number of transitions similar to that induced by diazepam (0.25, 0.5, and 1.0 mg/kg), suggesting an anxiolytic action. The antagonists, methiotepin (0.31 mg/kg), pindolol (2.0 mg/kg), and alprenolol (5.0 mg/kg), did not modify the number of transitions per se and were partially effective in reverting ipsapirone's action. Similarly, methiotepin and pindolol partially blocked 8-OH-DPAT actions, whereas alprenolol lacked an effect. Drug-induced increases in this behavior occurred despite the administration of p-CPA (400 mg/kg x 3 days). The neurochemical analysis revealed that this treatment decreased 5-HT levels (from 40% to 60%). Motor activity was assessed to control unspecific drug actions; 8-OH-DPAT produced an increase that was effectively blocked by methiotepin, but was unaffected by pindolol, alprenolol, or p-CPA. These results suggest that the increase in the number of transitions produced by 8-OH-DPAT cannot be interpreted on the basis of a reduced anxiety state. Data are discussed in terms of the similarities and differences between the actions of 5-HT1A drugs in hamsters when compared with rats and mice.