Sentence: Several lines of evidence implicate serotonin ( 5-HT ) as the mediator of this enhancement : ( 1 ) Tranyclypromine-enhanced nicotine reinforcement was blocked by the 5-HT₂ receptor antagonists , ritanserin and ketanserin ; ( 2 ) parachloroamphetamine ( PCA ) , a 5-HT releaser , also enhanced nicotine self-administration in animals in which MAO activity was inhibited ; ( 3 ) pretreatment with tranylcypromine increased PCA-induced 5-HT overflow in the nucleus accumbens .
Drug combination annotation:
[{'class': 'COMB', 'spans': ['nicotine', 'ketanserin'], 'is_context_needed': True}, {'class': 'COMB', 'spans': [2, 4], 'is_context_needed': True}, {'class': 'COMB', 'spans': [0, 5], 'is_context_needed': True}]