Confocal calcium imaging analysis of respiratory-related burst activity in the parafacial region

•Phox2b is a good genetic marker of parafacial neurons in the rostral medulla.•It is not clear what percentage of Phox2b-expressing cells show rhythmic burst activity.•We used transgenic rats in which Phox2b-positive cells expressed EYFP.•We analyzed the activity of EYFP-expressing cells by confocal calcium imaging.•More than 60% of the EYFP-expressing cells showed respiratory burst activity. The parafacial respiratory group (pFRG) surrounding the ventrolateral part of the facial motor nucleus is one of respiratory rhythm generators that consists of pre-inspiratory (Pre-I) neurons. Previous studies showed that most of the Pre-I neurons locating in the Phox2b cluster of the rostral ventral medulla were also Phox2b positive and intrinsically CO2 sensitive. However, it is not clear what percentage of Phox2b-expressing cells in the pFRG of the ventral medulla are Pre-I neurons. To address this issue, we analyzed the activity of Phox2b-positive cells by calcium imaging using a confocal laser microscope in transgenic rats in which Phox2b-positive cells expressed EYFP. We found that more than 60% of the EYFP/Phox2b-positive cells showed Pre-I neuron-like rhythmic burst activity in the parafacial region of newborn rat.