Neuronal pacemaker for breathing visualized in vitro

Breathing movements in mammals arise from a rhythmic pattern of neural acti vity, thought to originate in the pre-Botzinger complex(1) in the lower bra instem. The mechanisms generating the neural rhythm in this region are unkn own(2-5). The central question is whether the rhythm is generated by a netw ork of bursting pacemaker neurons coupled by excitatory synapses that synch ronize pacemaker activity. Here we visualized the activity of inspiratory p acemaker neurons at single-cell and population levels with calcium-sensitiv e dye. We developed methods to label these neurons retrogradely with the dy e in neonatal rodent brainstem slices that retain the rhythmically active r espiratory network We simultaneously used infrared structural imaging to al low patch-damp recording from the identified neurons, After we pharmacologi cally blocked glutamatergic synaptic transmission, a subpopulation of inspi ratory neurons continued to burst rhythmically but asynchronously. The intr insic bursting frequency of these pacemaker neurons depended on the baselin e membrane potential, providing a cellular mechanism for respiratory freque ncy control. These results provide evidence that the neuronal kernel for rh ythm generation consists of a network of synaptically-coupled pacemaker neu rons.