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Mother rabbits nurse once daily with circadian periodicity. The authors investigated brain structures involved in regulating this activity by quantifying c-FOS-immunoreactive (IR) cells in the forebrain of: (1) mothers killed on postpartum Day 1 (PPD 1) after nursing (Group 1) or not given pups (Group 2); (2) mothers killed on PPD 7 after nursing (Group 3) or not given pups on such day (Group 4); (3) unmated virgins (Group 5). Groups 1 through 4 showed similar numbers of c-FOS-IR cells in the preoptic area, an amount around three to fourfold larger than that found in virgins. Nursing increased, on PPD 1 and 7, c-FOS-IR cell number in the lateral septum and paraventricular and supraoptic nuclei. No differences were seen among Groups 1 through 5 in the suprachiasmatic nucleus. In the ventromedial hypothalamus virgins had more c-FOS-IR cells compared with Groups 1 and 2. Results suggest that specific forebrain structures participate in regulating particular aspects of rabbit maternal behavior: the POA and LS seem associated with the establishment of motherhood and the magnocellular nuclei with the occurrence of milk letdown.

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