Abstract
The influence of kinin and opioid receptor blockade in the paratrigeminal nucleus (Pa5) on the somatosensory reflex (SSR) to sciatic nerve stimulation (SNS) was assessed in anaesthetized–paralyzed rats. SNS (square 1 ms pulses at 0.6 mA and 20 Hz for 10 s) increased mean arterial pressure from 87 ± 3 to 106 ± 3 mmHg. Pressor responses to SNS were reduced 40–60% by HOE-140 and LF 16-0687 (B 2 receptor antagonists; 20 and 100 pmol respectively), CTOP or nor-binaltorphimine (mu and kappa opioid receptor antagonists, respectively; 1 μg) but potentiated by naltrindole (delta opioid receptor antagonist) receptor antagonist microinjections into the contralateral (but not ipsilateral) Pa5. The SSR to sciatic nerve stimulation was not changed by B 1 kinin receptor or NK 1, NK 2 and NK 3 tachykinin receptor antagonists administered to the Pa5. Capsaicin pretreatment (40 mg/kg/day, 3 days) abolished the effects of the opioid receptor antagonists, but did not change the effect of kinin B 2 receptor blockade on the SSR. Thus, the activity of B 2 and opioid receptor-operated mechanisms in the Pa5 contribute to the SSR in the rat, suggesting a role for these endogenous peptides in the cardiovascular responses to SNS.
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