Cortical potentials evoked by nociceptive stimuli: their depression by a factor released during saphenous nerve stimulation in the rat.

1 The amplitudes of the first positive and the first negative waves of cortical potentials evoked by electrical stimulation of the dental pulp in the rat were decreased following electrical stimulation of the peripheral cut end of the saphenous nerve.2 This effect was greatly diminished when the stimulation of the saphenous nerve was performed with the saphenous or femoral veins ligated.3 During stimulation of the saphenous nerve of a donor rat, the subcutaneous tissue in the area supplied by the nerve was perfused; when the perfusate (in which a permeability-increasing factor was detected) was injected intravenously into a recipient animal, a decrease in the amplitude of the evoked cortical potential of the recipient rat was also observed.4 Intravenous injections of 5-hydroxytryptamine, histamine, bradykinin, prostaglandins or adenosine-triphosphate produced no effect on the evoked cortical potential, whereas large doses of acetylsalicylic acid caused a decrease.5 It is suggested that a humoral factor, released during sensory nerve stimulation, may help to modulate the processing of afferent inputs from pain receptors.