NMDA and GABAAreceptors in the rat Kölliker‐Fuse area control cardiorespiratory responses evoked by trigeminal ethmoidal nerve stimulation

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Abstract
1 Electrical stimulation (10 s) of the ethmoidal nerve (EN5) evokes the nasotrigeminal reflex responses, including apnoea, bradycardia and rise in arterial blood pressure. In the present study, we examined the involvement of N-methyl-D-aspartate (NMDA), AMPA/kainate, (γ-aminobutyric acidA (GABAA) and glycine receptors in the Kölliker-Fuse (KF) nucleus in the mediation of the nasotrigeminal reflex responses. 2 Unilateral injections (n= 6) of 50-100 nl of the NMDA receptor antagonist AP5 into the KF area led to a significant blockade of the EN5-evoked respiratory depression and bradycardia. Injections placed into the midlevel of the KF area were most effective (80-90 % blockade). The rise in arterial blood pressure remained unaffected. 3 Unilateral injections (n= 6) of the AMPA/kainate receptor antagonist CNQX into the KF area failed to block EN5-evoked autonomic responses significantly. 4 Unilateral injections (n= 5) of the GABAA receptor antagonist bicuculline enhanced the EN5-evoked respiratory depression and bradycardia. The effect persisted for up to 30 s after stimulation. Bicuculline injections into the midlevel of the KF area were most effective. The increase in arterial blood pressure remained unaffected. 5 Unilateral injections (n= 5) of the glycine receptor antagonist strychnine into the KF area did not produce any significant effects on EN5-evoked autonomic responses. 6 Our results suggest that the KF area represents a mandatory relay for the nasotrigeminally induced apnoea and bradycardia which are predominantly mediated by NMDA receptors in the KF. Furthermore, it appears that KF neurons are under a potent GABAergic inhibitory control. The EN5-evoked rise in arterial blood pressure was not altered by any of the drugs and, therefore, appears not to be mediated via the KF.