180 CATALYZING INQUIRY
FIGURE 5.16 Bursting in the pre-Botzinger complex.
Panel 1: Example of voltage-dependent properties of pre-Bötzinger complex (pre-BötC) inspiratory bursting neu-
rons. Traces show whole-cell patch-clamp recordings from a single candidate pacemaker neuron in the pre-BötC of
a 400-μm-thick neonatal rat transverse medullary slice with rhythmically active respiratory network. Recordings
in A and B were obtained respectively before and after block of synaptic transmission by low Ca2+ conditions
identical to those described in Johnson et al. (1994) (i.e., 0.2 mM Ca2+, 4 mM Mg2+, 9 mM K+ in slice bathing
solution). Patch pipette solution and procedure for whole-cell recording were as described previously (Smith et al.
1991, 1992). Before block of synaptic transmission, the neuron bursts in synchrony with the inspiratory phase of
network activity as monitored by the inspiratory discharge recorded on the hypoglossal (XII) nerve (Smith et al.
1991). After block of synaptic activity (30 minutes under low-Ca2+ conditions), the cell exhibits intrinsic voltage-
dependent oscillatory behavior. As the cell is depolarized by constant applied current, it undergoes a transition
from silence (baseline potential below 65 mV, left) to oscillatory bursting to beating (baseline potential above 45
mV, right). In the bursting regime, the burst period and duration decreases (see expanded time-base traces in B) as
the baseline membrane potential is depolarized. SOURCE: Reprinted by permission from R.J. Butera, Jr., J. Rinzel,
and J.C. Smith, “Models of Respiratory Rhythm Generation in the Pre-Bötzinger Complex. I. Bursting Pacemaker
Neurons,” Journal of Neurophysiology 82(1):382-397, 1999. Copyright 1999 American Physiological Society.
continuedPANEL 1