Temperature reduction during handling in the first week of life was reported by Schaeferl to be a critical variable in producing later differences between rats handled o r not handled in infancy. Hutchings2 presented supporting evidence and hypothesized a curvilinear relationship between magnitude of reduction and later response differences. Also, rate of change rather than absolute change may be crucial.3 Investigating the generality of these hypotheses seemed important since they have implications for handling research. Do temperature changes underlie effects reported for early treatments other than handling ?4 Homeothermy increases with age in young rats; could a given treatment have l e s s effect on temperature with increasing age ? Could certain critical period findings5,G be an artifact of differential temperature change at different ages ?The present studies explored relationships between temperature change, treatment age, and later effects by varying ambient temperature (AT) during treatment to produce the same rectal temperature (RT) change in preweanling rats of different ages.
Experiment IATs required to reduce a pup's (Ss) RT 3" o r 7" (all temperatures in Centigrade) in three minutes were determined empirically for each of the first three weeks of life. These reductions were selected to replicate previous studies.2 A three-minute exposure, typical of many studies, was used to produce a relatively rapid reduction rate.3Thirty-five litters of eight Wistar Ss were reared under constant temperature and humidity (25.5" -26.5" and 45-55%, respectively) in plastic boxes, 13.5 X 17.5 X 6 inches, on 3 to 4 inches of wood shavings. For 12 litters RT was measured before and after a three-minute exposure on seven successive days. Of these, six each were exposed to ATs selected to produce RT reductions of either 3" o r 7". These litters were subdivided; two each were mea-*This paper was the third of three papers presented at a meeting of the Division on k h i v e r s i t y of California,
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