Effect of maternal presence on the fear response to an unfamiliar environment as measured by heart rate in rats as a function of age

Abstract

Rats 16 to 60 days of age were placed in an unfamiliar environment either alone or in the presence of an anesthetized lactating dam. Rats of all ages show a dramatic increase in fear, as measured by heart rate (HR), when placed alone in an unfamiliar environment. Adult rats, however, show a rapid decline in heart rate during the course of a 90-min session, whereas 16-day-old rats show no significant decrease in HR during the same period. These results suggest that the adult rats become less fearful of the test environment over time, but that the 16-day-olds maintain a high level of fear throughout the 90-min test period. Twenty-three- and 30-day-old rats show an adultlike pattern of adaptation to the unfamiliar environment, i.e., their heart rates return partially but not completely to baseline levels within the 90-min session. When an anesthetized lactating dam is present in the test environment, a strikingly different pattern of results is obtained. Heart rate in the 16-day-old rat is immediately reduced to near baseline levels whereas in the young adult (60-day-old) rat the presence of the anesthetized dam has no effect on either initial HR or rate of adaptation. Again the 23- and 30-day-old rats showed an intermediate pattern of adaptation. In two follow-up experiments the effects of adding (Expt. 2) or removing (Expt. 3) an anesthetized dam on the 16-day-old rats' response to an unfamiliar environment was examined. Both experiments showed that animals were more fearful when the dam was absent from the environment than when it was present.

Emergence of conditioned cardiac responses to an olfactory CS paired with an acoustic startle UCS during development: Form and autonomic origins

“…The at least 20 hr prior to conditioning. Details of the electrode and its implantation can be found elsecylinders were mounted horizontally in a custombuilt sound-attenuating chamber with inner diwhere (Hunt et al, in press;Richardson, Siegel, & Campbell, 1988). In both the preweanlings and mensions measuring 66 ϫ 37 ϫ 81.5 cm.…”

“…Electrodes and leads were attached, and animals were allowed to adapt to main stream shortly before entering the Plexiglas chamber. The neutral airstream remained on at the testing chamber for 15 min prior to the first stimulus presentation (Richardson et al, 1988). all times except during the 10-s olfactory stimulus.…”

Delayed development of conditioned heart rate responses to auditory stimuli in the rat

“…Heart rate was recorded in the 75-day-olds by electrodes surgically implanted 20-48 hr prior to testing. A detailed description of this electrode and the minor surgical procedure needed to implant it can be found in Richardson, Siegel, and Campbell (1988). In both cases, the electrodes and attached leads (32 ga; Alpha Wire) did not appear to interfere appreciably with the subject's behavior.…”

Developmental constraints on the expression of behavioral and heart‐rate orienting responses: II. The role of ambient temperature

“…For the 12-and 18-day-old subjects the electrodes were made of 25-ga stainless steel wires shaped like safety pins. These electrodes were implanted transcutaneously at the specified dorsal and ventral location, and were identical to those used in previous studies with subjects 9-30 days of age (Hayne et al, 1991;Richardson, Siegel, & Campbell, 1988b;Siegel, Sananes, Gaddy, & Campbell, 1987). This procedure appears to produce no more distress than a simple subcutaneous injection.…”