Synaptic and Non-Synaptic Control of Membrane Potential Fluctuations in Bulbar Respiratory Neurons of Cats

Abstract

Bulbar respiratory neurons display rhythmic fluctuations of membrane potential in synchrony with the respiratory cycle. These undulatory potentials are largely dependent upon the periodically arriving synaptic activities. Intrinsic membrane properties also play a certain important role in the generation or modulation of these potentials. Several types of ionic conductance have been demonstrated in the presumed respiration-related neurons in the brainstem slices^{2, 3}. However, since these neurons in tissue slices usually lack the spontaneous rhythmic modulation in membrane potential, the identification of the neuron type based upon the spontaneous patterns of firing and membrane potential fluctuations is yet uncertain. Moreover, it is hard to know at what timing any specific ionic conductance becomes active in the respiratory cycle change in membrane potential observed in different types of the respiratory neuron. Nonetheless, an intact brainstem preparation has also an inherent drawback to exclude the contamination of ionic currents mediated by action potentials and postsynaptic potentials^{4, 5}. The coaxial multi-barrelled microelectrode technique⁶ can partly overcome these difficulties as it allows an in vivo intracellular recording of membrane potential in conjunction with an extracellular iontophoresis of drugs which could block action potentials and synaptic waves in the recorded neuron. The present study was aimed at elucidating the possible synaptic and non-synaptic mechanisms by which the periodic fluctuations of membrane potential are shaped in bulbar respiratory neurons of the ventral respiratory group.