Involvement of the somatostatinergic interneurons of the lateral parafacial region in the generation of active expiration in mice.

Abstract

Expiration, under basal conditions, is a passive phenomenon, whereas, in situations of metabolic challenges such as hypercapnia, expiration becomes active, characterized by increased activity of the abdominal muscles, which favors the exhalation to increase pulmonary ventilation. Several studies have shown that rodents' lateral parafacial region (pFL) generates active expiration during hypercapnia. This region contains glutamatergic neurons that are silent under basal conditions, because of postsynaptic inhibition, and become active at the end of expiration under metabolically challenging conditions through postsynaptic disinhibition. It was also demonstrated the presence of inhibitory neurons in the parafacial region that express the peptide somatostatin (Sst) and that the inhibition of these neurons produced an increase in pulmonary ventilation. Furthermore, a portion of these somatostatinergic neurons is intrinsically inhibited by hypercapnia. However, the projections, electrophysiological properties, and contribution of these neurons to the generation of active expiration remain undetermined. In this sense, the hypotheses of the present Research Project are: i) the somatostatinergic interneurons of the pFL region, with local projections, inhibit active expiration in mice under basal conditions, and; ii) hypercapnia/acidosis produces inhibition of these neurons and induces active expiration in mice. Therefore, we will investigate the presence of somatostatinergic interneurons in the pFL region and the contribution of this neuronal population to the generation of inspiratory and expiratory motor activities and the control of pulmonary ventilation under basal and hypercapnic conditions. To evaluate the presence of somatostatinergic interneurons in the pFL region, we will use genetically modified mice that express the cre recombinase enzyme in somatostatinergic neurons (Sst-cre) and cre-dependent adeno-associated retrograde virus (AAV-rg). Next, a cre-dependent AAV-rg will be used to express a flippase (FLP) recombinase and a non-retrograde, cre- and FLP-dependent, AVVs to express Designer Receptors Exclusively Activated by Designer Drugs (DREADDs; hM3Dq or hM4Di) in somatostatinergic interneurons of the pFL region. The effect of stimulation (hM3Dq) and inhibition (hM4Di) of somatostatinergic interneurons in the pFL region in the generation of inspiratory and expiratory motor activities and the control of pulmonary ventilation will be evaluated during baseline and hypercapnic conditions in non-anesthetized mice (in vivo). Our data will reveal the existence of somatostatinergic interneurons in the pFL region and how they contribute to controlling active expiration under basal and metabolic challenges conditions in mice.