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 c hloralose-anaesthetized cats. MAP and HR increased by 46 +/- 5 mmHg an d 17 +/- 3 beats min(-1), respectively, during a 1 min contraction. Pa ssive stretch of the same muscle for 1 min reflexly increased MAP and HR by 40 +/- 7 mmHg and 14 +/- 3 beats min(-1), respectively. Microdia lysis 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 atten uated the reflex presser response to static contraction (2h of dialysi s: Delta MAP = 23 +/- mmHg, Delta HR = 8 +/- 2 beats min(-1)). By cont rast, there was no attenuation of the presser response to passive stre tch at 2 h of CNQX perfusion. However, the simultaneous microdialysis of 2 mM CNQX into the L6 and S1 levels blunted the presser and tachyca rdic responses to contraction and stretch. These data show that the re flex presser response to static muscle contraction is partly mediated by activation of non-NMDA receptors at the level of afferent fibre ent ry into the dorsal horn and through collateral pathways. Further, it a ppears that the afferent pathways within the dorsal horn for the signa l transduction arising from static muscle contraction and passive stre tch of the hindlimb are dissimilar.