Does 5-carboxamidotryptamine-induced turning in guinea-pigs involve 5-HT1D autoreceptors?

Contralateral turning induced by unilateral injection of 5-carboxamidotryptamine (5-CT) into guinea-pig substantia nigra could result from unilaterally reduced inhibition of the dopaminergic pathway as a consequence of a decreased release of inhibitory 5-hydroxytryptamine (5-HT) through stimulation of 5-HT1D autoreceptors. This hypothesis was tested by administering 5-CT unilaterally to freely moving guinea pigs through a microdialysis probe, and simultaneously measuring extracellular 5-HT in the dialysate and rotation. A concentration of 250 mN 5-CT was required to produce significant turning. This also induced a massive increase in extracellular 5-HT, introduced as an impurity of the 5-CT. The presence of high concentrations of extracellular 5-HT makes it unlikely that 5-CT-induced rotation is mediated through decreased 5-HT release resulting from 5-HT1D autoreceptor stimulation.