Formalin-induced central sensitization in the rat: somatosensory evoked potential data.
Cortical somatosensory evoked potentials were used to measure secondary hyperaesthesia resulting from subcutaneous 1 and 5% formalin in unanesthetized rats with permanently implanted electrodes. Near field responses were evoked by contralateral non-noxious electrical stimulation of the middle third of the tail. 0.05 ml 5% formalin injected subcutaneously at the base of the tail increased the amplitude of P1-N1 a maximum of 158.5+/-10.91% and N2 a maximum of 150.4+/-21.40% compared to controls (P<0.05 and P<0.01). Amplitudes were increased from 5 min after injection to the end of the 70 min test period. The effect of 1% formalin was equivalent to 5% formalin. This increase was prevented by pretreatment with 5 mg/kg ketamine or 5 mg/kg morphine, in agreement with behavioral and electrophysiological data. Cortical somatosensory evoked potentials are objective measures of central sensitization which may usefully complement current behavioral models for the evaluation of analgesic drugs.
Lebrun
P
P
Laboratorium voor Fysiologie, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090, Brussels, Belgium. plebrun@fysp.vub.ac.be
Manil
J
J
Colin
F
F
D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology / Q000503:physiopathology; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005557:Formaldehyde / Q000633:toxicity*; D006941:Hyperesthesia / Q000139:chemically induced / Q000503:physiopathology* / Q000517:prevention & control; D007649:Ketamine / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology; D010146:Pain; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D005557:Formaldehyde; D007649:Ketamine; D009020:Morphine