THE IMMEDIATE-SHOCK DEFICIT AND POSTSHOCK ANALGESIA - IMPLICATIONS FOR THE RELATIONSHIP BETWEEN THE ANALGESIC CR AND UR

Rats received a 3-sec, l-mA footshock either immediately or 3 min afte r placement in a chamber. Postshock pain sensitivity was assessed with the formalin test, The animals that received the 3-min delay between placement and shock showed an analgesic response compared with no-shoc k controls. The immediate-shock animals did not. Thus the immediate sh ock deficit, previously reported for freezing and defecation, also occ urs for analgesia. This suggests that shock levels sufficient to condi tion analgesia are not necessarily sufficient to produce analgesia as an unconditional response. As with freezing, there is a dissociation b etween conditional and unconditional responses in the fear-conditionin g system. Increasing immediate shock levels to 6 sec, 2 mA produced a transient unconditional analgesia. For analgesia, a conditional respon se is more readily produced than an unconditional response.