The long-term goal of the proposed research is to understand the psychobiological bases of mammalian maternal behavior. The maternal behavior of Norway rats provides a good model for this goal because it consists of a rich repertoire of maternal behaviors that are displayed frequently and because it has been well-studied. The proposed research focuses on the sensorimotor regulation of maternal behavior in rats, and its interactions with neurochemical influences and motivational expression. The major hypothesis is that this behavior consists of a complex reflex chain, the components of which have separate stimuli. The motorically- active components, such as retrieval and licking of pups, are under perioral trigeminal control, whereas the crouching posture during nursing is under ventral somatosensory control; this posture is characterized by immobility, splayed legs to accommodate the litter, and ventroflexion resulting in a pronounced dorsal arch. During the period of requested support, this hypothesis will be explored further by (1) assessing the maintenance, onset, and (hormonal and non-hormonal) induction of maternal responsiveness following desensitization of the anterior snout with bilateral trigeminal sensory denervations (infraorbital in upper jaw, inferior alveolar in lower jaw); (2) examining the afferent control of pup retrieval in detail, including interaction of somatosensory and distal inputs; (3 analyzing the afferent control of the crouching response with detailed videotaped observations, artificial stimulation, and acute and chronic ventrum desensitization; (4) determining with spinal transactions the sensorimotor pathways mediating the crouching response and the spinal vs. supraspinal control mechanisms; (5) determining how changes in reproductive state and afferent input affect the frequency and duration of nesting and nursing bouts; (6) characterizing the enhancement of the crouching response to pups in maternally-naive rats treated with a dopamine receptor antagonist, haloperidol, as a function of gender and hormonal state; (7) determining the neurochemical specificity and neural sites of action whereby dopaminergic antagonism inhibits the expression of motorically-active components of maternal behavior while enhancing the immobile crouching posture; (8) establishing that maternal motivation can be expressed by instrumental responding (bar-pressing) for access to a nest box with pups; and (9) studying how maternal motivation is affected by various manipulations, including changes in afferent input.
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