The Journal of Neuroscience, February 15, 2003, 23(4):1114
BRIEF COMMUNICATION
Hippocampal Theta in the Newborn Rat Is Revealed under Conditions
That Promote REM Sleep
Karl Æ.
Karlsson and
Mark S.
Blumberg
Program in Behavioral and Cognitive Neuroscience, Department of
Psychology, University of Iowa, Iowa City, Iowa 52242
Hippocampal theta activity, a high-amplitude, slow (4-12 Hz)
oscillation that occurs in a variety of behavioral contexts, is thought
to emerge in infant rats only after 1 week of age. However, we report
here that unanesthetized 2- and 4-d-old rats with electrodes implanted
in the CA1 field of the hippocampus and tested in thermoneutral
conditions exhibit theta activity. Moreover, this infant theta is
characterized by the same neuronal bursting pattern and power spectrum
that characterize theta in adults. Simultaneous measures of behavior
and neck muscle tone indicated that bouts of theta occurred
predominantly during periods of muscle atonia (with or without
concurrent myoclonic twitching), indicative of REM sleep. In contrast,
sharp waves were accompanied by startles (i.e., simultaneous and
vigorous movement of all four limbs). These findings underscore the
need for comprehensive in vivo investigations of the
pharmacology, neural substrates, and behavioral correlates of
hippocampal field activity in neonates.
Key words:
REM sleep; hippocampus; sharp waves; muscle tone; myoclonic twitching; behavior; temperature; startle
Copyright © 2003 Society for Neuroscience 0270-6474/03/2341114-05$05.00/0