EVIDENCE FOR SPECIFIC INVOLVEMENT OF 5-HT1A AND 5-HT2A C RECEPTORS INTHE EXPRESSION OF PATTERNS OF SPONTANEOUS MOTOR-ACTIVITY OF THE RAT/

The 5-HT1A and the 5-HT2A/C receptor agonists 8-hydroxy-2-(di-n-propyl amino)tetralin (8-OH-DPAT) (0.006-0.4 mg kg(-1) s.c.) and +/-)-1-(2,5- dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (0.05-4.0 mg kg(-1) s.c.) , respectively, produced a similar stereotyped forward locomotion in r ats, although the intensity of the behavioral change was considerably less with DOI. The stereotyped forward locomotion was accompanied by a slight decrease in total activity, suppression of rearing behavior an d an increased activity in the periphery of the open-field arena. In s upport of receptor specificity, the effects of 8-OH-DPAT and DOI could be antagonised by pretreatment with the 5-HT1A/B and the 5-HT2A/C rec eptor antagonists (-)-pindolol(2 mg kg(-1) s.c.) and ritanserin (2 mg kg(-1) s.c.), respectively. In addition, (-)-pindolol, but not the sel ective beta-adrenoceptor antagonist betaxolol, markedly enhanced the b ehavioral effects produced by DOI. The nature of these specific action s and interactions in terms of pre- and post-synaptic serotonergic mec hanisms remains an important question.