Patterns of activity-dependent conduction velocity changes differentiate classes of unmyelinated mechano-insensitive afferents including cold nociceptors, in pig and in human.
Activity-dependent slowing of conduction velocity (ADS) differs between classes of human nociceptors. These differences likely reflect particular expression and use-dependent slow inactivation of axonal ion channels and other mechanisms governing axonal excitability. In this study, we compared ADS of porcine and human cutaneous C-fibers. Extracellular recordings were performed from peripheral nerves, using teased fiber technique in pigs and microneurography in humans. We assessed electrically-induced conduction changes and responsiveness to natural stimuli. In both species, the group of mechano-insensitive C-fibers showed the largest conduction slowing ( approximately 30%) upon electrical stimulation (2Hz for 3min). In addition, we found mechano-insensitive cold nociceptors in pig that slowed only minimally (<10% at 2Hz), and a similar slowing pattern was found in some human C-fibers. Mechano-sensitive afferents showed an intermediate conduction slowing upon 2Hz stimulation (pig: 14%, human 23%), whereas sympathetic efferent fibers in pig and human slowed only minimally (5% and 9%, respectively). In fiber classes with more pronounced slowing, conduction latencies recovered slower; i.e. mechano-insensitive afferents recovered the slowest, followed by mechano-sensitive afferents whereas cold nociceptors and sympathetic efferents recovered the fastest. We conclude that mechano-insensitive C-fiber nociceptors can be differentiated by their characteristic pattern of ADS which are alike in pig and human. Notably, cold nociceptors with a distinct ADS pattern were first detected in pig. Our results therefore suggest that the pig is a suitable model to study nociceptor class-specific changes of ADS.
Obreja
Otilia
O
Department of Anesthesiology Mannheim, University of Heidelberg, Germany Department of Neurosurgery, Johns Hopkins University, Baltimore, USA Department of Physiology, University of Erlangen, Germany.
Ringkamp
Matthias
M
Namer
Barbara
B
Forsch
Elmar
E
Klusch
Andreas
A
Rukwied
Roman
R
Petersen
Marlen
M
Schmelz
Martin
M
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000344:Afferent Pathways / Q000503:physiopathology; D000818:Animals; D001703:Biophysics / Q000379:methods; D003080:Cold Temperature; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D017288:Pain Threshold / Q000502:physiology*; D013552:Swine / Q000033:anatomy & histology*