Origin of Nerve Terminals on Glomus Cells in Cat Carotid Body: A Study of Axoplasmic Movement of Labeled Material Along Sensory Neurons of the Petrosal Ganglion

Abstract

The site of termination of chemosensory fibers in the carotid body, once considered to be well established by the pioneering studies of de Castro (3), has been the object of renewed interest and speculation. De Castro concluded that sensory fibers in the cat carotid nerve terminate on glomus (type I) cells in the carotid body, because he observed that such nerve endings were unaltered following intracranial Sect, of the glossopharyngeal (IXth) nerve root central to its sensory ganglion (deefferentation). These findings have been challenged, however, by the more recent ultrastructure studies of Biscoe and coworkers (1). They repeated de Castro’s original experiment and claimed that the synapses between carotid nerve terminals and glomus cells are efferent, not afferent; it appeared to them that the nerve endings did degenerate with deefferentation of the carotid nerve. This interpretation was supported by the concurrent discovery by Neil and 0’Regan (11) of an efferent control of chemoreceptor discharge by fibers passing along the carotid nerve. This issue was complicated by the curious finding that the time course of nerve ending degeneration following decentralization was sometimes as much as 1 year, a finding that Biscoe et al. (1) compared to similarly long degeneration times for neurons in certain areas of the central nervous system.