DIVISION OF PSYCHOLOGY: INFANTILE HANDLING AND BODY TEMPERATURE CHANGE IN THE RAT. III. EARLY TEMPERATURE CHANGE AND ITS IMPLICATIONS FOR LATER RESPONSES*

Abstract

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,

Mechanisms mediating the production of environmentally induced brain changes.

“…Furthermore, there is evidence suggesting that the relationship between amount of cooling and subsequent emotionality is of an inverted U type (Hutchings, 1967;Mclver, Jeffrey, Stevenson, & Nielson, 1968). Several previously puzzling findings would then be explicable using the arousal hypothesis, since almost any form of experimental manipulation would present a host of major novel stimuli against the background of the relatively stimulus poor laboratory nesting cage.…”

"Infantile stimulation" in rodents: A consideration of possible mechanisms.

“…The implication seems to be that typical handling procedures applied to the older pup (Week 2 and later) are not effective in producing hypothermia, owing to the development of the capacity for relatively efficient thermo-regulation. Mclver et al (1968) have examined this notion by subjecting pups to low ambient temperatures of an order (predetermined empirically) sufficient to reduce their rectal temperatures by 3 C C. even during the second and third weeks. These temperatures must necessarily be considerably lower than the ambient temperatures normally obtaining in conventional handling studies.…”

“…In view of these kinds of considerations it seems unlikely, then, that the cooling hypothesis can be made to account for all the effects reported. Indeed, in order to be able to explain both the fact that (a) under some circumstances handling in the absence of cooling is not an effective treatment (Hutchings, 196S, 1967;Mclver & Camp, 1966;Nielson & Mclver, 1966;Schaefer, 1963) and (/;) handling can be effective even when the amount of hypothermia involved is nil (Mclver et al, 1968) or likely to be extremely small (Denenberg & Smith, 1963;Meyers, 196S), it seems necessary to assume that at least two mechanisms are involved. One of these must be based on cooling, with the nature of the second being unclear but possibly involving some form of direct action.…”

Infantile stimulation and ultrasonic signaling: A possible mediator of early handling phenomena

“…He failed to find a handling effect when a reduction in body temperature was prevented from occurring during handling (1963), and showed that if degree of body temperature is varied quantitatively, adrenal ascorbic acid (AAA) depletion to cold stress is a U-shaped function of degree of temperature loss. However, McIver, Jeffrey, Stevenson, and Nielson (1968) report that both handled-cooled and handled-noncooled HANDLING AND ULTRASONIC SIGNALING 183 animals differed from nonhandled animals in open field activity, in blood glucose level, and in basal resistance level following the open field testing. Furthermore, although handling early during the preweaning period appears to have greater effects than postweaning handling (Levine & Otis, 1968), handling later in life does appear to influence body weight (Weininger, 1956), maze learning (Bernstein, 1952), and emotionality as measured by latency for cage emergence (Meyers, 1965).…”

“…He failed to find a handling effect when a reduction in body temperature was prevented from occurring during handling (1963), and showed that if degree of body temperature is varied quantitatively, adrenal ascorbic acid (AAA) depletion to cold stress is a U-shaped function of degree of temperature loss. However, McIver, Jeffrey, Stevenson, and Nielson (1968) (Levine & Otis, 1968), handling later in life does appear to influence body weight (Weininger, 1956), maze learning (Bernstein, 1952), and emotionality as measured by latency for cage emergence (Meyers, 1965). Since the rat and mouse are homeothermic by weaning, temperature reduction does not appear to be an adequate explanation of all infantile stimulation studies, although it may be one important variable associated with infantile handling.…”