Central mechanism of domato-parasympathetic reflex vasodilatation

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We measured the changes in lower lip blood flow and systemic arterial blood pressure (SABP) evoked by lingual nerve (LN) or trigeminal spinal nucleus (Vsp) stimulation to gain an insight into the brainstem integration of sympathetic and parasympathetic responses to nociceptive stimulation. We used artificially ventilated, cervically vago-sympathectomized cats deeply anesthetized with a-chloralose and urethane. A lip blood flow (LBF) increase occurred in an intensity- and frequency-dependent manner following electrical stimulation of Vsp or LN regardless of whether SABP increased or decreased. In contrast, there was no apparent optimal frequency for the changes in SABP elicited by electrical stimulation of Vsp or LN. No relationship was found between the amplitude of the LBF increase and that of the SABP change. Microinjection of lidocaine or kainic acid into the Vsp evoked, respectively, reversible and irreversible inhibition of the LBF increase and SABP change evoked by LN stimulation … More . When microinjected unilaterally directly into the ipsilateral Vsp, the GABA agonist muscimol abolished the LN-evoked increase in lip blood flow and changes in SABP without changing basal SABP, suggesting the presence in the Vsp of a GABAergic system modulating both the parasympathetically mediated LBF increase and the sympathetically mediated SABP change. Lidocaine microinjection into the salivatory nucleus caused a significant attenuation of the LN-induced blood flow increase, but had no effect on the LN-induced SABP change. Thus, the neural pathway mediating the LN-induced LBF increase seems to be simple, requiring a minimum of four neurons : trigeminal afferent - Vsp parasympathetic pre-ganglionic neurons with cell body located in the inferior salivatory nucleus - otic postganglionic neuron. On the other hand, the pathway underlying the evoked SABP changes, presumably mediated via altered sympathetic activity, seems to be more complicated and could be affected by more numerous factors. Less