Blockade of adenosine A2a receptors potentiates dopamine agonist-induced rotation in rats with unilateral 6-hydroxydopamine lesions of nigrostriatal pathway.

Previously we have reported that vascular nociceptive response evoked by intra-arterial injection of capsaicin is mediated b y peptidergic transmitters in the spinal cord.Other studies recently suggest that the activation of central nociceptive pathway evoked by capsaicin may be involved in tachykinin and excitatory animo acid receptors.In this study, we investigated the effect of intrathecal (i.t.) administration of NK-1, NK-2 and NMDA receptor antagonists on arterial capsaicin-evoked nociceptive response in conscious guinea pigs.I. t. pretreatment with CP-96,345 (50nmol), a selective NK-1 receptor antagonist, did not produce significant effects on capsaicin-evoked vocalization response (VOR).However, MEN-10,376 (40nmol), a selective NK-2 receptor antagonist, showed a significant and prolonged reduction of vocalization counts without affecting latency and duration for capsaicin-evoked VOR; 39.04 ± 9.61% (after 30min), 49.48 ± 11.10% (after 60min), 54.41 ± 15.47% (after 90min) and 55.06 ± 9.35% (after 120min) of the control value.Pretreatment with the NMDA receptor antagonist MK-801 (20nmol) resulted in a significant reduction of vocalization counts of capsaicin-evoked VOR with apparent shortening of duration; 65.63 ± 15.66% (after 10m in) and47.98 ± 15.49% (after 30m in) of the control value.These results indicate NK-2 and NMDA receptors in the spinal cord are involved in the transmission of nociceptive information evoked by arterial capsaicin.