Effects of neuroactive substances on the morphine-induced respiratory depression; an in vitro study.

Effects of different neuroactive substances on morphine-induced respiratory depression were studied in medullary respiration-related structures using in vitro brainstem-spinal cord preparation from 1 to 4-day-old rats. Application of morphine (10 microM) reduced respiratory rhythm (fR) as measured by C4 ventral root activity. The depressant effects of morphine were reversed by acetylcholine (10 microM), substance P (50 nM), thyrotropin releasing hormone (TRH) (100 nM) and forskolin (10 microM). The adenosine receptor antagonist, theophylline (100 microM), the dopamine receptors antagonist, haloperidol (10 microM), the cyclooxygenase inhibitor, indomethacin (10 microM) and the phospholipase A(2) inhibitor, quinacrine (10 microM) had no effect on morphine-induced respiratory depression.