Studies on How Early Maternal Separation Produces Behavioral Change in Young Rats

Abstract

Previously published studies point to the behavioral interaction between the mother and her litter as the origin of the processes responsible for the behavioral hyperactivity following maternal separation in 2-week-old rats. The following experiments explore (1) the time course over which behavioral hyperactivity develops, (2) environmental and social determinants, (3) the role of sensory stimulation in the regulation of behavior and (4) the olfactory sensory system as a mediator of separation effects. The hypotheses supported best by the data are (1) that tactile and olfactory stimulation repeatedly provided by the mother act to reduce levels of behavioral arousal of the infants and (2) that maternal separation exerts its effect by withdrawal of this regulating influence, allowing a new level of behavioral arousal, more intrinsic to the infant, to be revealed.

Physical stimulation reduces the body temperature of infant rats

“…This approach of isolating the young from the dam and litter was used to optimize the experimental conditions and uncover subtle effects of stimulation upon pups (Hofer, 1983). A similar approach has been used in most of the recent work on the effects of physical stimulation on pup physiology (Butler et al, 1968;Evoniuk et al, 1979;Kuhn et al, 1978;Hofer, 1983;Smotherman, 1983;Sullivan & Leon, 1986Wilson, Sullivan, & Leon, 1985Wilson, Wilner, Kurz, & Nadel, 1986) and behavior (Hall & Sullivan, 1988;Hofer, 1975Hofer, ,1983Pedersen, Williams, & Blass, 1982;Sullivan, Brake, Hofer, & Williams, 1986a;Sullivan, Hofer, & Brake, 1986b).…”

“…2) Shaking-the individual treatment container was continuously and gently rotated and shook for 30 sec every 1 min. This procedure was used to mimic nonspecific vestibular and tactile stimulation pups receive from the dam (Hofer, 1975;Wilson et al, 1986). 3) No-stimulation control-pups were left undisturbed in the treatment container.…”

“…Following recording of prestimulation rectal temperatures, pups were placed in a 32°C incubator with either a 1) normal humidity incubator (75%-78% relative humidity) or 2) high-humidity incubator (98%-100% relative humidity) for a 10-min habituation period, followed by a 5-min treatment procedure. During the 5-min treatment period pups were either: 1) stroked every 1 min for 15 sec, a schedule of stimulation which more closely approximates that which pups recceived from the dam (Barnett & Walker, 1974;Grota & Ader, 1969;Hofer, 1975Hofer, ,1983Hofer & Garbie, 1971;Moore & Powers, 1986), or 2) received no stimulation.…”

Physical stimulation reduces the brain temperature of infant rats

“…The types of stimulation used in this experiment were chosen because they are thought to approximate the type of stimulation pups receive from the dam (Barnett & Walker, 1974;Butler, Suskind, & Schanberg, 1968;Evoniuk, Kuhn, & Schanberg, 1979;Hofer, 1975Hofer, ,1983Kuhn, Butler, & Schanberg, 1978;Sullivan, Brake, Hofer, & Williams, 1986a;Sullivan, Hofer, & Brake, 1986b;Wilson, Sullivan, & Leon, 1985). Furthermore, pups were stimulated away from the nest and dam, in a thermally controlled environment.…”

“…2) Shaking-pups were left in their treatment container while the, container was continuously and gently rotated and shook. This treatment was done to mimic nonspecific tactile and vestibular stimulation pups recieve when they are jostled by the dam (Hofer, 1975;Wilson, Wilner, Kurz, & Nadel, 1986). 3) No-stimulation control, whose temperature was always used as a reference point for temperature changes which occurred in the stimulated pups.…”