Behavioral and neuroanatomical substrates contributing to motivation in the postpartum female rat:

The experiments described in this dissertation characterize the unique motivational state of the postpartum female rat. To effectively protect and care for offspring (pups), postpartum females must be strongly motivated to seek out and interact with pups. A combination of place preference studies, behavioral observations, and neurobiological interventions were used to explore females’ motivational state across the postpartum period.To challenge postpartum females’ maternal motivation, Chapter 1 presented females with a choice between chambers paired with pups and highly salient cocaine. While most late postpartum females preferred cocaine, many early postpartum females retained striking preference for the pup-paired chamber. To explore whether cocaine’s incentive value changed across the postpartum period, Chapter 2 examined females’ preference for cocaine- versus saline-paired chambers. Across a broad range of drug administration parameters, postpartum females consistently expressed similar, strong preference for the cocaine-paired chamber. Surprisingly, cocaine preference was stronger in postpartum females than virgin females or males. Females’ locomotor response to pup, cocaine, and saline stimuli predicted their preference for those stimuli. Chapter 3 revealed that the length of pup exposure and nature of female-pup interactions can even affect the motivational state of females that have not given birth. Virgin females were exposed to young pups for various lengths of time and then tested for pup-paired chamber preference. Striking pup-paired chamber preference emerged even in virgin females only briefly exposed to pups, matching the preference expressed by strongly motivated postpartum females. Experiments in Chapter 4 revealed that the ventral tegmental area (VTA), a brain region critical to motivated behavior, drives the incentive value of pup but not cocaine stimuli. Postpartum and virgin females were tested for their preference for pup- or cocaine-paired chambers, respectively, after transient VTA inactivation. Pup preference was abolished by VTA inactivation and restored after recovery. Cocaine preference remained intact despite VTA function.Maternal motivation is resilient to challenge during early postpartum and is at least partially driven by exposure to pups. As the choice of other salient stimuli (e.g., cocaine) during postpartum may jeopardize maternal motivation, females’ motivation to interact proactively with pups is critical to the offsprings’ survival and viability.Ph.D.Includes bibliographical references (p. 203-218)by Katharine M. Sei