Spinal cord sensory systems after neonatal capsaicin.
Animals with a severe reduction in the number of afferent C-fibres as a consequence of neonatal administration of capsaicin, exhibit a number of neurological and behavioral deficits including increased nociceptive thresholds, altered somato-visceral and viscero-visceral reflexes, depressed cardiovascular and respiratory reflexes and changes in the organisation of spinal cord sensory systems. The reduction in the number of C-fibres produced by neonatal capsaicin does not cause a decrease of similar magnitude in the number of dorsal horn cells driven by the surviving C-fibres. Twenty-two per cent of dorsal horn neurones in capsaicin treated animals respond to electrical stimulation of the surviving afferent C-fibres: a reduction of only 50% from control values. Inhibitory controls on afferent C-fibre evoked responses of dorsal horn neurones are weaker in capsaicin treated rate than in control animals. The cutaneous receptive fields of some dorsal horn neurones can increase in size following stimulation of afferent C-fibres. Tonic descending inhibition on C-fibre evoked responses of dorsal horn neurones is reduced in capsaicin treated rats: fewer neurones show tonic descending inhibition in these animals and those that do are subjected to less powerful inhibitions than similar neurones from control animals. However, some central inhibitory mechanism are unchanged after neonatal capsaicin treatment, specially those that do not involve afferent C-fibres. We suggest that the nervous system develops central inhibition in response to and directed towards the excitations mediated by its afferent drives. Therefore reduced central inhibition in response to a decreased number of afferent C-fibres can compensate for the lost capacity in the signalling of peripheral noxious events.
Cervero
F
F
Department of Physiology, University of Bristol Medical School, United Kingdom.
Plenderleith
M B
MB
D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D002211:Capsaicin / Q000633:toxicity*; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012867:Skin / Q000294:innervation; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology
D002211:Capsaicin