Differential effects of subcutaneous injection of formalin and bee venom on responses of wide-dynamic-range neurons in spinal dorsal horn of the rat

By using extracellular single unit recording technique, the effects of subcutaneous (s.c.) administration of formalin and bee venom on responses of wide-dynamic-range (WDR) neurons in the spinal dorsal horn were investigated in pentobarbital anaesthetised rats. Similar to the previous results, s.c. formalin injection into the cutaneous receptive field (RF) of WDR neurons produced a biphasic increase in spike response; however, s.c. bee venom injection into the RF produced a prolonged, monophasic increase in spike discharges over the background activity, suggesting that the two tonic pain models may have different underlying neural mechanisms.