Lactation reduces Fos induction in the paraventricular and supraoptic nuclei of the hypothalamus after urethane administration in rats.

Both neuroendocrine and behavioral responses to stressors are reduced in lactating animals. In these studies we determined whether Fos induction following treatment with urethane would differ between nonlactating and lactating rats. Urethane treatment produced robust Fos expression in the central nucleus of the amygdala and the paraventricular and supraoptic nuclei of the hypothalamus 1 h after treatment. Fos expression in both the paraventricular and supraoptic nuclei was attenuated in lactating rats compared to that seen in nonlactating animals but Fos expression in the central nucleus of the amygdala did not differ between these two groups. Removing litters from lactating rats 48 h prior to urethane administration restored the Fos response in the parvocellular division of the paraventricular nucleus (PVN) to the level seen in nonlactating rats.