Ontogeny of behavioral arousal in rats: Effect of maternal and sibling presence.

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Abstract
In 2 experiments, spontaneous locomotor activity of 132 5-30 day old Sprague-Dawley rats housed either alone or in the presence of components of the normal nest and litter stimuli was recorded by time-lapse videography. Developing Ss observed alone showed a sharp increase in total daily locomotor activity from Day 5 to Day 15 followed by a rapid decline from Day 15 to Day 30. Individual Ss observed in the context of the normal litter environment showed a different pattern of development. They were relatively inactive during the 1st 15 days of life and then began a gradual increase of activity which continued for the next 15 days. The heightened activity characteristic of the isolated 15-day-old S was also inhibited by the presence of 4 siblings, an anesthetized lactating female, or an anesthetized adult male. Thermal conditions, including heating of the floor to approximately nest temperature or the presence of a heated tube in one corner of the test apparatus, did not inhibit heightened activity. Results question the generality of the ontogenetic sequence of excitation and inhibition proposed by B. A. Campbell and his associates (1975, 1969)--at least a portion of the heightened activity seen around 15 days of age was the result of isolation distress, not merely maturational changes in the brain. (21 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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