Fig. 9.

Effects of glutamatergic receptor antagonism in the parafacial respiratory group (pFRG) on the pattern of sympathetic activity during hypercapnia. A: cycle-triggered averages of integrated (∫) abdominal nerve (AbN), thoracic sympathetic nerve (tSN), and phrenic nerve (PN) activities of a representative preparation, showing the tSN burst pattern during eucapnia (basal, A), hypercapnia (8% CO₂), and after injections of kynurenic acid (Kyn) in the pFRG (8% CO₂ + Kyn) of in situ preparations (n = 7). Note that hypercapnia amplified tSN during inspiratory/postinspiratory periods and introduced a novel burst during late-expiration (late-E) phase (arrows). The latter was associated with the emergence of late-E bursts in abdominal activity (AbN). B–D: average values of tSN during inspiratory/postinspiratory and late-E phases and of perfusion pressure (PP) respectively. *Different from basal, P < 0.05; #different from CO₂, P < 0.05.