In order to assess the importance of maternal thermal cues in controlling the acute USV responses of rat pups to contact with her body (the contact comfort response) and to separation from her, we drastically altered maternal temperature by inducing severe hypothermia so that maternal rectal and flank temperatures averaged more than 20 degrees C below normal and 10 degrees C below ambient levels during testing. Isolated 12- to 13-day-old pups showed reductions in USV when these cold dams were presented and brisk USV accelerations when the cold dams were removed from the test chamber. These responses closely resembled those of other pups tested with warm (36 degrees C) anesthetized dams. No significant differences were found in pups' USV contact comfort responses to cold and warm dams. For acute separation, prior maternal thermal properties and other factors were found to modulate the relative intensity of the marked USV increase elicited by this event.
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Hofer et al. (1993) studied this question.