Spreading sensory excitation

Abstract

Integration and crosstalk between the signals carried by different primary afferent neurones occurs mainly in the CNS. In its simplest forms, this integration occurs as a result of the convergence of different axon terminals on the same second-order afferent neurones, or through axo–axonic synapses mediating presynaptic inhibition or excitation. A new concept has emerged recently, following the discovery that the electrical stimulation of peripheral branches of dorsal root ganglion (DRG) cells induced excitation of the soma not only of the stimulated neurones but also of neighbouring DRG cells within the same ganglion, despite lack of evidence for synaptic contacts between the somata of DRG cells. This phenomenon has been defined as cross-depolarization (CD) or cross-excitation. A recent study [ 1. Oh E.J. Weinreich D. Chemical communication between vagal afferent somata in nodose ganglia of the rat and the guinea-pig in vitro. J. Neurophysiol. 2002; 37: 2801-2807 Google Scholar ] now shows that ganglion cells associated with cranial nerves (e.g. the nodose ganglion associated with the vagal afferents) also display CD, demonstrating that this phenomenon is widespread among primary afferent neurones.