Spontaneous and evoked (orthodromic and antidromic) activities of 115 trigeminal ganglion neurons were studied. Three percent of cells stimulated at low frequency (less than 10 Hz) and 96% of cells stimulated at high frequencies (10 to 100 Hz) demonstrated ectopic action potentials (regardless of whether stimuli were anti- or orthodromic). However, this phenomenon was maximal in response to moderate-frequency stimuli (20 to 30 Hz) following periods of high-frequency stimulation. Collision experiments demonstrated that these extra spikes arose from the neurons' peripheral axons, and persisted after transection of the retrogasserian root. Both conditioning antidromic action potentials and subthreshold orthodromic stimuli were found to increase greatly the incidence of extra spikes produced by low-frequency orthodromic and antidromic stimuli, respectively. Repetitive firing was abolished by cooling of the neurons' receptive fields. This repetitive firing appears to be generated from the peripheral axon, possibly its terminal myelinated segment. The theoretical basis of this phenomenon has implications for the mechanism of trigeminal neuralgia.
ASJC Scopus subject areas
- Developmental Neuroscience