Comparison of infant and adult rats in exploratory activity, diurnal patterns, and responses to novel and anxiety-provoking environments.
Infant rats emerge from the maternal nest at Postnatal Day 17-18 to have their first critical environmental experiences; they may be particularly sensitive to experiences or experimental interventions that can affect their adult capacity. The authors address open questions on 2 components of normative environmental exploration, locomotor activity and response to anxiety-provoking locations, in Postnatal Day 18 infant and Postnatal Day 60 adult rats. The authors compare diurnal patterns of locomotor activity, wheel running, novel and familiar open-field activity, and 2 measures of anxiety. Infants have an equivalent capacity to adults for locomotor activity and wheel running and a fundamentally adult-like diurnal rhythm, except that they do not anticipate light-dark transitions, are more perturbable at their most somnolent, and are more or less active during specific limited phases than adults. Infants initially have a lower rate of locomotor activity in novel environments and have a greater willingness to be active in anxiety-provoking locations. Such differences may allow enhanced gathering of environmental information by the infant and are important to consider in the design of experiments using infants.
Smith
Kiersten S
KS
Center for Molecular and Behavioral Neuroscience, Rutgers University, Newark, NJ 07102, US. kismith@pegasus.rutgers.edu
Morrell
Joan I
JI
D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001007:Anxiety / Q000503:physiopathology*; D001522:Behavior, Animal; D002940:Circadian Rhythm / Q000502:physiology*; D004777:Environment; D005106:Exploratory Behavior / Q000502:physiology*; D005260:Female; D009043:Motor Activity / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley