Ontogeny of REM sleep in rats: possible implications for endogenous depression

Nine neonatal Long-Evans rats had continuous (24 h/day) polysomnography for 2 weeks, from age 14 days through age 27 days. A new finding was that six more or less independent measures of REM sleep occurrence decreased in para llel from age 14 days to age 27 days. The measures included parallel decrea ses of four measures of 24-h REM duration (tonic REM sleep, phasic REM slee p, mean REM period duration, and number of REM periods) along with parallel increases of two measures of REM delay (REM latency and percent of nonslee p onset REM periods). A parsimonious interpretation of the correlated chang es is that a common developmental REM sleep inhibitory process accounts for the six parallel changes over time. This hypothesis can be tested empirica lly by studying inhibitory processes that operate on the pedunculopontine t egmental/latero-dorsal tegmental nuclei, the generators of REM sleep. The s tudy also noted that compared with (same species) normal adults, endogenous depressives had the same distinctive REM sleep characteristics as neonatal rats. The similarity suggests that an underdeveloped, relatively weak REM sleep inhibitory process may account for the REM sleep peculiarities of end ogenous depression. This hypothesis can be tested in adult rats made "depre ssed" by neonatal treatment with antidepressant drugs. Thus, the ontogeny o f REM sleep suggests a developmental process that may be altered in humans predisposed to endogenous depression, and may account for the (life-long) R EM sleep abnormalities of the disorder. (C) 2000 Elsevier Science Inc. All rights reserved.