Reciprocal connectivity of the periaqueductal gray with the ponto-medullary respiratory network in rat

Abstract

AbstractSynaptic activities of the periaqueductal gray (PAG) can modulate or appropriate the respiratory motor activities in the context of behavior and emotion via descending projections to nucleus retroambiguus. However, alternative anatomical pathways for the mediation of PAG-evoked respiratory modulation via core nuclei of the brainstem respiratory network remains only partially described. We injected the retrograde tracer Cholera toxin subunit B (CT-B) in the pontine Kölliker-Fuse nucleus (KFn, n=5), medullary Bötzinger (BötC, n=3) and pre-Bötzinger complexes (pre-BötC; n=3), and the caudal raphé nuclei (n=3), and quantified the ascending and descending connectivity of the PAG. CT-B injections in the KFn, pre-BötC, and caudal raphé, but not in the BötC, resulted in CT-B-labeled neurons that were predominantly located in the lateral and ventrolateral PAG columns. In turn, CT-B injections into the lateral and ventrolateral PAG columns (n=4) yield the highest numbers of CT-B-labeled neurons in the KFn and far fewer numbers of labeled neurons in the pre-BötC and caudal raphé. Analysis of the relative projection strength revealed that the KFn shares the densest reciprocal connectivity with the PAG (ventrolateral and lateral columns, in particular). Overall, our data imply that the PAG may engage a distributed respiratory rhythm and pattern generating network beyond the nucleus retroambiguus to mediate downstream modulation of breathing. However, the reciprocal connectivity of the KFn and PAG suggests specific roles for synaptic interaction between these two nuclei that are most likely related to the regulation of upper airway patency during vocalization or other volitional orofacial behaviors.HighlightsThe lateral and ventrolateral PAG project to the primary respiratory network.The Kölliker-Fuse nucleus shares the densest reciprocal connectivity with the PAG.The Bötzinger complex appears to have very little connectivity with the PAG.