{alpha}1- and {alpha}2-adrenergic receptors in the retrotrapezoid nucleus differentially regulate breathing in anesthetized adult rats

Norepinephrine (NE) is a potent modulator of breathing that can increase/decrease respiratory activity by α₁-/ α₂-adrenergic receptors (AR) activation, respectively. The retrotrapezoid nucleus (RTN) is known to contribute to central chemoreception, inspiration and active expiration. Here we investigate the sources of catecholaminergic inputs to the RTN and identify respiratory effects produced by activation of ARs in this region. By injecting the retrograde tracer FluorGold into the RTN we identified back-labeled catecholaminergic neurons in the A7 region. In urethane-anesthetized, vagotomized and artificial ventilated male Wistar rats unilateral injection of NE or moxonidine (α₂-ARagonist) blunted Dia_EMG frequency and amplitude, without changing AbdEMG. Those inhibitory effects were reduced by pre-application of yohimbine (α2-AR antagonist) into the RTN. Conversely, unilateral RTN injection of phenylephrine (α₁-AR agonist) increased Dia_EMG amplitude, frequency and facilitated active expiration. This response was blocked by prior RTN injection of prazosin (α₁-AR antagonist). Interestingly, RTN injection of propranolol (β-AR antagonist) had no effect on respiratory inhibition elicited by applications of NE into the RTN, however, the combined blockade of α₂- and β-ARs (co-application of propranolol and yohimbine) revealed an α₁-AR-dependent excitatory response to NE that resulted in increase in Dia_EMG frequency and facilitation of active expiration. However, blockade of α₁-, α₂-, or β-ARs in the RTN had minimal effect on baseline respiratory activity, on central or peripheral chemoreflexes. These results suggest that NE signaling can modulate RTN chemoreceptor function; however, endogenous NE signaling does not contribute to baseline breathing or the ventilatory response to central or peripheral chemoreceptor activity in urethane-anesthetized rats.

from Physiology via xlomafota13 on Inoreader http://ift.tt/1Orjsm2
via IFTTT