Cardiorespiratory effects of intertrigeminal area stimulation in vagotomized rats

It has been recently shown that the pontine intertrigeminal region (ITR) plays an important role in respiratory regulation, including vagally mediated apneic reflexes. Neurons of the ITR have connections with the nucleus tractus solitarius and projections to the ventrolateral medulla. However, the functional targets of these projections are not fully defined. Stimulation of ITR neurons produced respiratory effects, but cardiovascular responses have not been explored. We investigated impact of bilateral vagotomy on respiratory and cardiovascular responses to glutamate microinjections within the ITR in ketamine/xylazine anesthetized rats. Cardiorespiratory indices, including breath duration (TT), tidal volume (VT), mean cardiac intervals (RR), systolic blood pressure (SBP), pulse pressure (PP) and their coefficients of variation (CVTT, CVVT, CVSBP, CVPP, respectively) were analyzed in 30 s segments before and after injection of glutamate (10 mM, 30 L) into the ITR. This assessment was carried out both before and after bilateral vagotomy. Glutamate injection evoked apnea and increased CVTT, but these responses were not altered by bilateral vagotomy. In contrast, removing vagal pathways significantly increased volume variability (CVVT), making tidal volume more vulnerable to perturbation from the ITR. Vagotomy prolonged the increase of mean systolic blood pressure observed after glutamate injection and unmasked a delayed but sustained elevation of PP and CVPP after ITR stimulation. The present findings indicate a broad involvement of the ITR in autonomic regulation, including at least cardiovascular and respiratory effects.