Pharmacologic evaluation of the discriminative stimulus of metachlorophenylpiperazine

A pharmacologic analysis of the discriminative stimulus of metachlorophenylpiperazine (mCPP) is reported. mCPP and m-trifluoromethylphenylpiperazine generalised, whereas 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl) -1H-indole, 6-chloro-2-(1-piperazinyl)-pyrazine, and mesulergine partially generalised to the mCPP discriminative cue. However, although mianserin, methiothepin, ritanserin, mesulergine and N-(1-methyl-5′-indolyl)- N′-(3-pyridyl)urea hydrochloride (SB 200646) all antagonised the effect of 5-hydroxytryptamine (5-HT) on IP 3 formation in the rat choroid plexus, they failed to antagonise the mCPP response in the drug discrimination studies. The 5-HT 3 receptor antagonist MDL 72222 neither generalised nor antagonised the mCPP cue. These data suggest that neither the 5-HT 1A, 5-HT 1B, 5-HT 1D, 5-HT 2A, 5-HT 2B, 5-HT 2C, 5-HT 3 5-HT 5, 5-HT 6, nor 5-HT 7 receptors are involved. The response does appear to be mediated by a postsynaptic 5-HT receptor, however, because fenfluramine generalised to the cue. Haloperidol generalises, and amphetamine partially antagonises the mCPP discriminative cue and low doses of apomorphine partially generalises to the mCPP cue, which suggests that a decrease in dopamine neurotransmission may also be involved.