CENTRAL 5-HT1A MODULATION OF CARDIOVASCULAR-RESPONSES TO TIBIAL NERVESTIMULATION-EVOKED MUSCLE-CONTRACTION

The effects of administering 8-hydroxy-2-(di-n-propylamine) tetralin [ 8-OH-DPAT, a serotonin 1A (5-HT1A) receptor agonist] into the rostral ventrolateral medulla (RVLM) on cardiovascular responses during tibial nerve stimulation-evoked muscle contraction were investigated using a nesthetized rats. Stimulation of the tibial nerve (3 times motor thres hold, 0.1 ms, 40 Hz) for 30 s increased mean arterial pressure (MAP), heart rate (HR), and muscle tension by 25 +/- 3 mmHg, 24 +/- 4 beats/m in, and 299 +/- 35 g, respectively. Bilateral microdialysis of 8-OH-DP AT (10 mM) for 30 min attenuated the stimulation-evoked increases in M AP (8 +/- 2 mmHg) and HR (11 +/- 5 beats/min), without a change in mus cle tension (292 +/- 30 g). However, administration of 1 mM 8-OH-DPAT had no effect on the cardiovascular responses. Thirty minutes of micro dialysis of 8-OH-DPAT (10 mM) into the caudal ventrolateral medulla pr oduced no effect on cardiovascular responses during muscle contraction . Prior administration of 10 mM thoxyphenyl]-4-[4-(2-phthalimido)-buty l]piperazine (NAN-190), a 6-HT1A receptor antagonist, for 30 min into the RVLM blocked the attenuating effects of subsequent microdialysis o f 8-OH-DPAT (10 mM). Results suggest that activation of 5-HT1A recepto rs within the RVLM inhibit cardiovascular responses elicited during st atic muscle contraction.