Depressor Effect of NO in Rat Parabrachial Nuclei and Its Mechanisms / 华中科技大学学报(医学版)

ABSTRACT

The Experiments were performed on 63 urethane anesthetized, suxamethonium chloride paralyzed and artificially ventilated rats. The results were as follows microinjection of L-Arg, NO precursor, into parabrachial nuclei (NPB) resulted in a marked decrease in the mean arterial pressure (MAP), but the heart rate had no significant change. Microinjection of N-nitro-L-arginine (L-NNA), NO synthase inhibitor, into NPB caused a significant increase in MAP. Preinjection of L-NNA and methylene blue into NPB separately blocked the depressor effect elicited by L-Arg. Preinjection of bicuculine, γ-aminobutyric acid (GABA) receptor antagonist, into NPB significantly reduced or abolished the depressor effect elicited by L-Arg. The above results indicated that (1) NO has depressor effect in NPB by activating guanylate cyclase; (2) Endogenous NO in NPB has tonic depressor effect and takes part in maintenance of normal blood pressure level; (3) The depressor effect evoked by NO in NPB is at least partly mediated by local GABA receptor.