Visualization of Respiratory Neuron Activity in the Ventral Medulla from a Newborn Rodent

Abstract

We visualized respiratory neuron network activity in the medulla of the rat and mouse in vitro by optical recordings using voltage-sensitive dye. The brainstem and spinal cord of 0- to 1-day-old Wistar rats and 0-day-old mice isolated under deep ether anaesthesia were incubated in a modified Krebs solution containing a fluorescent voltage-sensitive dye. Fluorescence signals corresponding to respiratory activity were detected by a CCD image sensor. Pre-inspiratory neuron activity appeared in the limited region of the rostral ventrolateral medulla [i.e. para-facial respiratory group (pFRG) region], preceding the onset of inspiratory activity by about 500 ms. During the inspiratory phase, plateau activity appeared in the more caudal ventrolateral medulla at the level of most rostral roots of the XIIth nerve (i.e. the pre-Botzinger complex level). We found that pre-inspiratory neurons which were a predominant subtype of the pFRG neurons were located in the area immediately beneath the ventral pia mater at the level of the facial nucleus. We also analyzed respiratory neuron activity in the wild type and two kinds of knock-out mice that exhibit respiratory failure leading to neonatal death due to dysfunction of central respiratory neuron activity. The optical recordings clearly detected the difference in the spatio-temporal pattern between the wild type and both knockout mice.