Activation and odor conditioning of suckling behavior in 3-day-old albino rats

The circumstances under which a novel odor could elicit nipple attachment behavior in 3-day-old albino rats were investigated. In Experiment 1, rats suckled washed nipples scented with citral (a lemon odor) only if they either had received tactile stimulation (by stroking with a soft artist's brush) or had been administered amphetamine in the presence of citral prior to the suckling test. Pups stimulated in citral's absence or simply exposed to citral without stimulation failed to suckle such nipples. In Experiment 2, rats stimulated in a benzaldehyde (an almond odor) ambience suckled washed nipples scented with benzaldehyde but not those with citral scent. The opposite held for rats stimulated in a citral-rich environment. The stimulus conditions that support this conditioning were investigated in Experiment 3. Simultaneously increasing citral concentration and raising ambient temperature markedly attenuated the phenomenon. Experiment 4 demonstrated that not all classes of stimulation produced conditioning. Caffeine, in a wide range of doses, did not allow citral to elicit suckling on washed nipples. These findings are discussed within a framework of higher order conditioning. They may provide a mechanism by which naturally occurring stimuli come to elicit the species- and age-typical behavior of suckling.