Opiate microinjections in the locus coeruleus area of the cat enhance slow wave sleep.

The effects on sleep/wakefulness states of morphine, morphiceptin (specific mu agonist), DPDPE (delta agonist) and U-50,488H (kappa agonist) microinjections in the Locus coeruleus area (LC) were studied in cats. Morphine (0.8-1.75 nmols in 50 nl of saline) and morphiceptin (1.75 nmols) in LC significantly increased the total time spent in slow wave sleep (SWS) and the mean duration of SWS episodes. Prior naloxone administration blocked the morphine hypnogenic effects. The total time spent in SWS was unaffected by delivery of equimolar doses of DPDPE or U-50,488H in LC; however, the mean duration of the SWS episodes increased significantly after U-50,488H microinjections in LC. Thus, when acting in the LC, opiates have a SWS-enhancing effect and this effect appears to be mediated by mu receptors, although kappa receptors may have a subsidiary action.