Neuroendocrinology of maternal behavior in the rabbit

Rabbit maternal behavior consists of building an underground nest of straw and body hair during late pregnancy and displaying, with circadian periodic ity, a single 3-min nursing bout/day across lactation. Estrogen, androgen, progesterone, and prolactin regulate specific aspects of nest-building and promote the onset of maternal responsiveness. However, the maintenance of t his behavior relies on stimuli from the litter: by preventing mother/young contact at parturition or during early lactation maternal responsiveness is altered or abolished. The brain areas controlling the expression of nest-b uilding and nursing were investigated by implanting estradiol, locating the distribution of estrogen and prolactin receptors, quantifying the expressi on of immediate-early genes, and lesioning structures of the olfactory syst em. These studies revealed that: (a) estrogen receptor-a, alpha, present in the preoptic region, may mediate the stimulation of nest-building by estra diol; (b) prolactin binding sites, located mainly in periventricular struct ures, are more abundant in late pregnancy and early lactation; (c) the numb er of FOS-immunoreactive neurons increases in the lateral septum, but not i n the mediobasal hypothalamus, following nursing; (d) the accessory olfacto ry bulb tonically inhibits the expression of maternal behavior because its removal promotes maternal responsiveness in virgins, which are otherwise un responsive to daily pup exposure. In summary, rabbits rely on the same horm onal and extrahormonal factors that stimulate maternal behavior in other ma mmals, yet the way in which such factors promote elaborate nest-building an d the unfailing display of circadian nursing is unique to rabbits and warra nts future investigation. (C) 2001 Academic Press.