Reactivity to Stress in Rats as a Function of Infantile Experience. ∗

Abstract

Levine(4) has suggested that rats stimulated during infancy may be more reactive to, but also recover more rapidly from, stress as adults than non-stimulated rats. These rats have a higher output of corticosterone and steroid production is greater in the 15-minute period following stress. Similarly, Bell, Reisner, and Linn(1) reported that recovery from electroconvulsive shock (ECS) is more rapid in rats handled the first 5 days of life, as compared with rats that were either handled or unhandled at later periods. They defined recovery from ECS by blood glucose levels taken 24 hours after ECS and immediately following ether anesthesia. Blood glucose levels did not differ for subjects handled the first five postnatal days that did or did not receive ECS. Furthermore, differences were found for subjects not so handled. Since ether anesthesia is a stressor in and of itself, however, 2 alternative conclusions could be drawn. Recovery from ECS may have been complete in all subjects 24 hours after ECS. Consequently, the difference between the rats handled the first 5 days of life and the other groups showed these rats less reactive to the immediate stress of ether anesthesia. Or, conversely, possibly none of the rats subjected to ECS had recovered within 24 hours. The rats handled the first 5 days of life may have been more reactive to the etherization.

To test Levine's hypothesis, but unconfounded with ether anesthesia, the following experiment was conducted. One hundred and ninety-one Sprague-Dawley rats, 99 females and 92 males, were either handled or unhandled from days 2 through 5 of life, and either stressed or not stressed in adulthood. The handling procedure was removal of the litter from the mother. Each pup was then placed in a small glass dish for 3 minutes before being returned to the mother.