Fig. 1.

Preparation and definition of rhythmic versus nonrhythmic neurons of the ventral respiratory group (VRG).A, Schematic representation of the transverse slice containing the pre-Bötzinger complex (pBC;gray area), a region in the VRG that is presumably the site for respiratory rhythm generation. The right panelshows a video image obtained from the VRG. The image contains neurons that were visualized with infrared Nomarski optics. The electrode tip is visible and points to the voltage-clamp recording shown inC. B, Extracellular recording obtained from the rhythmically active hypoglossal rootlet (XII,bottom trace) and its integrated signal (top trace). C, Burst activity in the integrated XII recording (top trace) corresponds to rhythmic inward currents in the whole-cell patch recording (bottom trace). A neuron with this property is defined as rhythmic (R). D, Burst activity in the integrated XII recording (top trace) is not correlated with synaptic activity in the intracellularly recorded VRG neuron (bottom trace). A neuron with this characteristic is defined as nonrhythmic (nR). IO, Inferior olive; NA, nucleus ambiguus; NTS, nucleus tractus solitarius; Sp5, spinal trigeminal nucleus;XII, hypoglossus motor nucleus; XII nerve, XII rootlet.