Fig. 4 |. A circuit that generates and modulates sighs.

a | Gastrin-releasing peptide (GRP) and neuromedin B (NMB)-expressing neurons of the parafacial nucleus (pF) project to preBötzinger Complex (preBötC) neurons that express GRP receptors (GRPRs), NMB receptors (NMBRs) or both. b | Breathing patterns in an anaesthetized adult rat showing tidal volume (V_T; maximal excursion 5 ml), annotated to differentiate an eupnoeic breath from a sigh, and diaphragmatic electromyography (Dia trace shows raw recording; ∫Dia trace shows integrated activity, in arbitrary units). c | Time- compressed recordings of V_T and ∫ Dia. Thick baseline reflects continuous eupnoea. Large periodic spikes are sighs, which increase in frequency following infusion of NMB. LRN, lateral reticular nucleus; NA, nucleus ambiguus; pF_V, ventral parafacial nucleus; PiCo, postinspiratory complex; rVRG, rostral ventral respiratory group; VII, facial motor nucleus; vIRT, ventral intermediate reticular formation. Part a and c are adapted from ref. ¹⁸⁹, Macmillan Publishers Limited. Part b is adapted with permission from ref. ¹⁹², Elsevier.