Generation of Interspike Intervals of Rat Carotid Body Chemoreceptors

Abstract

Hypoxia is well established to stimulate carotid body chemoreceptors leading to an increase in sinus nerve activity, but the mechanism by which the nerve activity increases is unresolved. It is generally assumed that spike initiation is solely dependent on presynaptic transmitter secretion, but, synaptic blockade with low calcium solutions causes little change in baseline nerve activity (although it does eliminate the hypoxia response) (Donnelly & Kholwadwala, 1992). This suggests that the nerve endings can initiate action potentials independent of glomus cell secretion. However, it is difficult to study this directly because of the small size of the nerve terminals and uncertainty regarding the site of action potential generation. The present study was undertaken to better understand the process of spike initiation by examination of the interspike interval pattern from rat chemoreceptors. The results show that spike generation during normoxia and during hypoxia stimulation is a Poisson-type random process, and this generator characteristic is highly sensitive to the Na⁺ channel agonist, veratridine.