During the early postpartum period or following estrogen/progesterone administration, pups elicit maternal behavior accompanied by a robust dopamine (DA) response in the nucleus accumbens (NAC) of female rats (Afonso et al., 2009). To determine whether DA responds to ostensibly "salient" stimuli in the absence of consummatory behaviors, we examined NAC shell DA responses during restricted (stimuli placed in a perforated box), and unrestricted access to pup and food stimuli. Microdialysis samples were collected from female rats that were either cycling and postpartum (Experiment 1), or after ovariectomy and treated with empty and hormone-filled capsules (Experiment 2). Relative to nonprimed controls, hormonally primed females had suppressed basal DA concentrations and facilitated pup-evoked DA responses, regardless of stimulus access condition. In contrast, food-evoked DA responses were unchanged by hormonal priming and were greater when females consumed food compared with distal (restricted) exposure to food. During pup and food restriction conditions, the lack of any "appetitive" behavioral differences, even in pup experienced postpartum females, was surprising. In Experiment 3, we confirmed that postpartum dams allocated time equivalently to restricted pup and food stimuli, even after pup deprivation. This was in sharp contrast to the effects of deprivation during the unrestricted access phase. Together, our data demonstrated that, in hormonally primed females, distal pup cues could evoke DA responses without prior stimulus experience, ongoing maternal (behavioral) responses, or clear evidence of robust pup saliency. The results suggest that NAC DA response reflects a state of responsiveness related to basal DA suppression in the hormonally primed female rat.

No abstract

No abstract

Estrogen has been shown to enhance the effects of antipsychotics in humans. To investigate the mechanisms of how this may occur, the current study examined estradiol's effects on dopaminergic transmission and behavior in amphetamine-sensitized and non-sensitized female rats. Sixty-four ovariectomized female Sprague-Dawley rats were used for this study. Half of the rats were sensitized to four once-daily injections of 1 mg/kg amphetamine and the other half served as controls. Rats received chronic administration of either low-dose haloperidol (0.25 mg/kg/day) or saline vehicle via osmotic minipumps implanted subcutaneously. The groups were further subdivided with respect to estradiol treatment: low chronic estrogen (subcutaneous estradiol implant, 0.36 mg/pellet: 90-day release, plus an additional oil vehicle injection every second day) and high pulsatile estrogen (subcutaneous estradiol implant plus an additional 10 μg/kg estradiol injection every second day). Motor activity was assessed at day 2 and day 12 during haloperidol treatment, while nucleus accumbens dopamine availability was assessed via microdialysis 10 days into antipsychotic treatment. Haloperidol treatment along with high, but not low, estradiol replacement was effective in reducing amphetamine-induced locomotor activity in sensitized rats. High estradiol treatment also augmented the effects of chronic haloperidol in reducing dopaminergic release in sensitized rats. These data suggest that estradiol levels affect both the behavioral and the dopamine responses to chronic antipsychotic treatment.

Studies in both rodents and humans have made much progress in shedding light on how fluctuations in ovarian hormones can affect memory in women across the lifespan. Specifically, advances in neuroscience have identified multiple memory systems that are each mediated by different brain areas. Two memory systems used to navigate an environment are 'place' and 'response' memory. They are defined as either using an allocentric strategy: using a spatial or cognitive map of the surroundings, or an egocentric strategy: using habitual-turns/ movements, respectively. Studies in neuroendocrinology have shown that estrogen levels can bias a female to use one memory system over another to solve a task, such that high estrogen levels are associated with using place memory and low levels with using response memory. Furthermore, recent advances in identifying and localizing estrogen receptors in the rodent brain are uncovering which brain regions are affected by estrogen and providing insight into how hormonal fluctuations during the menstrual cycle, pregnancy, and menopause might affect which memory system is facilitated or impaired in women at different life stages. These studies can help point the way to improving cognitive health in women. Estrogen and cognitionModern Western society is not only marked by longer life expectancies, but young women are also waiting longer to have children and having fewer of them, therefore having more menstrual cycles in their lifetimes than ever before. Progesterone (P) and 17β-estradiol (E2; the most potent of the estrogens during reproductive years) vary across the menstrual cycle in a consistent and fluctuating manner.During the first half of the cycle, or follicular phase, E2 and P levels are low; E2 levels then start to increase steadily at the end of menstruation, reaching a peak in the middle of the menstrual cycle, right before ovulation occurs. This is followed by the luteal phase, when E2 levels plateau while P levels increase and peak until menstruation begins again (Figure 1). Thus, E2 and P work hand in hand across a woman's cycle to orchestrate menstruation, ovulation, and conception.However, these hormones appear to be exerting other effects on the female brain, which could be subject to subtle changes as hormone levels fluctuate over time. human menstrual cycle (top panel) and the ~4 day rat estrous cycle (bottom panel). Human menstrual cycle begins with a follicular (mentrual and preovulatory) phase, followed by ovulation, and ends with a luteal phase (spanning end of ovulation to pre-menstrual phase).