THE EFFECTS OF REM SLEEP-INHIBITING DRUGS IN NEONATAL RATS - EVIDENCEFOR A DISTINCTION BETWEEN NEONATAL ACTIVE SLEEP AND REM-SLEEP

Neonatal active sleep (AS) has been considered to be homologous and co ntinuous with rapid-eye-movement (REM) sleep in adult animals. We have recently proposed an alternative view that AS is an undifferentiated sleep state distinct from REM sleep. To test these opposing views on t he relationship of AS and REM sleep, neonatal rats (P11, P14 and P20) were systemically injected with compounds that inhibit REM sleep in ad ults. Zimelidine (ZMI) and desipramine (DMI) are monoamine uptake inhi bitors which increase synaptic concentrations of serotonin and norepin ephrine, respectively. Serotonin and norepinephrine inhibit brainstem cholinergic neurons important in REM sleep generation. Atropine (ATR) is a muscarinic receptor antagonist that blocks the post-synaptic effe cts of cholinergic projections. Only DMI (5 mg/kg) suppressed AS at P1 1. ZMI (6 mg/kg) and ATR (6 mg/kg) did not suppress AS until P14. Thes e data suggest that serotonergic and cholinergic regulation of AS are absent before P14. The fact that AS in P11 rats is not affected by cho linergic antagonists supports the hypothesis that AS and REM sleep rep resent different sleep states. (C) 1997 Elsevier Science B.V.