Stickney, J. D., Morgan, M. M. 2021. Social housing promotes recovery of wheel running depressed by inflammatory pain and morphine withdrawal in male rats. Behavioural Brain Research 396, 112912.

The increased use of opioids to treat pain has led to a dramatic increase in opioid abuse. Our previous data indicate that pain may facilitate the development of opioid abuse by increasing the magnitude and duration of opioid withdrawal. The present study tested the hypothesis that social housing would facilitate recovery of activity depressed by pain and opioid withdrawal. Male Sprague Dawley rats were housed either in pairs or alone and then moved to a cage with a running wheel for 6 h daily to assess pain- and opioid withdrawal-induced depression of wheel running. Rats were implanted with two morphine (75 mg each) or placebo pellets to induce opioid dependence and were simultaneously injected with Complete Freund’s Adjuvant or saline into the right hind paw to induce persistent inflammatory pain. Hind paw inflammation depressed wheel running whether rats were implanted with a morphine or placebo pellet. Pair-housed rats showed greater recovery of wheel running than individually housed rats. Spontaneous morphine withdrawal precipitated by removal of the morphine pellets caused a reduction in wheel running that was greater in rats with hind paw inflammation compared to pain free rats. Social housing facilitated recovery from withdrawal in rats with hind paw inflammation, but slowed recovery in pain free rats. These data suggest that social housing facilitates recovery by reducing pain both before and during opioid withdrawal. Our findings are consistent with previous studies showing that social buffering reduces pain-evoked responses.

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