Subarachnoidal Administration of the 5-HT uptake inhibitor citalopram points to the spinal role of 5-HT in morphine antinociception

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Abstract
The role of 5-hydroxytryptamine (5-HT) in morphine-induced antinociception was evaluated in mice and rats by means of the specific 5-HT uptake inhibitor citalopram. Systemic and subarachnoidal administration of the compounds was made and then the animals were tested in the grid-shock and hot plate model. In non-antinociceptive doses, systemically and subarachnoidally administered citalopram potentiated the effect of morphine given systemically. In contrast no potentiation was obtained with any of the 2 routes of administration of citalopram when morphine was injected subarachnoidally. The suggested importance of 5-HT terminals in mediation of the supraspinal but not the spinal contribution to morphine antinociception was suggested.