| Abstract: | Rat pups aged 10 to 19 days were implanted with chronic electrodes and recorded while freely moving in the litter situation, during nursing and throughout naturally occurring maternal absences. Heart rates were significantly higher in the mother's presence (p<.01) while respiratory rates and percent of time spent active were identical under the 2 conditions. Pups' inactive heart rates progressively increased during the 20 min of nursing, while no such time trends were evident in other measures. Inactive heart rates decreased significantly (p<.01) as a function of age; respiratory rates and activity during nursing showed similar trends. A histogram of number of periods of activity bursts of different durations while pups were nursing showed a preponderance of 1- to 5-sec bursts which were observed to be associated with active sucking and pawing movements. This pattern of short bursts of spontaneous activity was repeated almost identically when the mother was absent, although the behavior was qualitatively different. In a second experiment, increases in pups' body temperature of .2°C to 1.0°C were found to accompany active nursing. If such increases were imposed by an artificial heat source, heart rates of pups actually fell slightly. In a third study, heart rates were recorded from nursing mothers and found to be relatively unaffected by stimulation from the pups. |
