Microdialysis of a non-NMDA receptor antagonist into the L7 dorsal horn attenuates the pressor response to static muscle contraction but not passive stretch in cats

Mean arterial pressure (MAP) and heart rate (HR) were measured during static contraction or passive stretch of the triceps surae muscle of chloralose-anaesthetized cats. MAP and HR increased by 46 +/- 5 mmHg and 17 +/- 3 beats min(-1), respectively, during a 1 min contraction. Passive stretch of the same muscle for 1 min reflexly increased MAP and HR by 40 +/- 7 mmHg and 14 +/- 3 beats min(-1), respectively. Microdialysis of 2 mM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, into the dorsal horn at the L7 spinal level attenuated the reflex presser response to static contraction (2h of dialysis: Delta MAP = 23 +/- mmHg, Delta HR = 8 +/- 2 beats min(-1)). By contrast, there was no attenuation of the presser response to passive stretch at 2 h of CNQX perfusion. However, the simultaneous microdialysis of 2 mM CNQX into the L6 and S1 levels blunted the presser and tachycardic responses to contraction and stretch. These data show that the reflex presser response to static muscle contraction is partly mediated by activation of non-NMDA receptors at the level of afferent fibre entry into the dorsal horn and through collateral pathways. Further, it appears that the afferent pathways within the dorsal horn for the signal transduction arising from static muscle contraction and passive stretch of the hindlimb are dissimilar.