Differential effects of scopolamine on 3 forms of stress analgesia.

We have previously reported that non-opioid stress analgesia and two forms of opioid stress analgesia can be differentially produced in rats by varying the severity or temporal pattern of inescapable footshock. In this study, we investigated the role of muscarinic cholinergic mechanisms in mediating these 3 forms of stress analgesia. Whereas the muscarinic anticholinergic drug, scopolamine, had no effect on either non-opioid stress analgesia or opioid stress analgesia from 1 min of continuous 2.5-mA footshock, it significantly attenuated opioid analgesia from 20 min of intermittent footshock at this same intensity. The data are discussed in reference to other similarities and differences between these two forms of opioid stress analgesia.