Glutamatergic and GABAergic inputs to the RVL mediate cardiovascular adjustments to noxious stimulation

Stimulation of cutaneous and muscle afferents induces several cardiovascula r adjustments such as hypertension, tachycardia, and muscle vasodilation. A lthough previous studies have demonstrated that the rostral ventrolateral m edulla (RVL) mediates sympathoexcitation and pressor responses to sciatic n erve stimulation (SNS), whether it also mediates blood flow adjustments rem ains unclear. Therefore, in the present study, we examined the role of the RVL in the vasodilation induced by SNS and the possible neurotransmitters i nvolved. In Urethane-anesthetized, paralyzed, and artificially ventilated r ats, SNS (square pulses, 1 ms, 20 Hz, 800-1200 muA, 10 s) produced increase s in blood pressure, heart rate, blood flow, and vascular conductance of th e stimulated limb. Unilateral microinjection of kainic acid (2 nmol/100 nl) into the RVL contralateral to the stimulated limb abolished cardiovascular adjustments to SNS. Unilateral microinjections of kynurenic acid (2 nmol/1 00 nl) selectively abolished the pressor response to SNS, whereas bicuculli ne (400 pmol/100 nl) abolished the increases in blood flow without changing the pressor response. These results suggest that glutamatergic synapses wi thin the RVL mediate pressor responses, whereas GABAergic synapses may medi ate the vasodilation to SNS.