Improving and accelerating drug development for nervous system disorders.

Advances in the neurosciences have placed the field in the position where it is poised to significantly reduce the burden of nervous system disorders. However, drug discovery, development, and translation for nervous system disorders still pose many unique challenges. The key scientific challenges can be summarized as follows: mechanisms of disease, target identification and validation, predictive models, biomarkers for patient stratification and as endpoints for clinical trials, clear regulatory pathways, reliability and reproducibility of published data, and data sharing and collaboration. To accelerate nervous system drug development, the Institute of Medicine's Forum on Neuroscience and Nervous System Disorders has hosted a series of public workshops that brought together representatives of industry, government (including both research funding and regulatory agencies), academia, and patient groups to discuss these challenges and offer potential strategies to improve the translational neuroscience.

Caloric restriction experience reprograms stress and orexigenic pathways and promotes binge eating.

Long-term weight management by dieting has a high failure rate. Pharmacological targets have focused on appetite reduction, although less is understood as to the potential contributions of the stress state during dieting in long-term behavioral modification. In a mouse model of moderate caloric restriction in which a 10-15% weight loss similar to human dieting is produced, we examined physiological and behavioral stress measures. After 3 weeks of restriction, mice showed significant increases in immobile time in a tail suspension test and stress-induced corticosterone levels. Increased stress was associated with brain region-specific alterations of corticotropin-releasing factor expression and promoter methylation, changes that were not normalized with refeeding. Similar outcomes were produced by high-fat diet withdrawal, an additional component of human dieting. In examination of long-term behavioral consequences, previously restricted mice showed a significant increase in binge eating of a palatable high-fat food during stress exposure. Orexigenic hormones, melanin-concentrating hormone (MCH) and orexin, were significantly elevated in response to the high-fat diet only in previously restricted mice. Furthermore, administration of the MCH receptor-1 antagonist GSK-856464 [4-(4-ethyl-5-methylsulfanyl-1,2,4-triazol-3-yl)pyridine] significantly reduced total caloric intake in these mice during high-fat access. These results reveal reprogramming of key central pathways involved in regulating stress responsivity and orexigenic drives by moderate caloric restriction experience. In humans, such changes would be expected to reduce treatment success by promoting behaviors resulting in weight regain, and suggest that management of stress during dieting may be beneficial in long-term maintenance.

Prenatal stress programming of offspring feeding behavior and energy balance begins early in pregnancy.

To examine the long-term effects of stress experienced early in gestation on the programming of offspring feeding behaviors and energy balance, pregnant mice were exposed to stress during early pregnancy (days 1-7) and adult offspring examined on chow and high fat diets for long-term outcomes. Placental 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2) and insulin-like growth factor 2 (IGF-2) expression was measured to determine the possible sex-specific contribution of prenatal stress (PNS) on fetal programming of embryo growth and development during early pregnancy. PNS mice showed a basal hyperphagia when on chow diet. Prenatal treatment differences were ameliorated when adult mice were on a high fat diet. Interestingly, PNS male mice also had significantly reduced body weights compared to control males on both chow and high fat diets. Body composition analyses revealed reduced body fat and increased lean mass in PNS mice on the high fat diet, but no differences were detected in plasma leptin or insulin-like growth factor 1 (IGF-1) levels. Mechanistic examination of gene expression in embryonic day 12 placentas found that early PNS was associated with increased IGF-2 expression and sex-dependent effects of stress on 11 beta-HSD2, supporting specific aspects of early pregnancy. These studies suggest that the long-term effects of stress during pregnancy on programming of feeding behavior and energy homeostasis begin much earlier in development than previously thought.

Stress and sex influences on food-seeking behaviors.

OBJECTIVE: Stress increases the drive to consume calorically dense preferred foods suggesting an exogenous factor that may induce caloric overconsumption and weight gain. As females show heightened stress sensitivity and present with increased rates of obesity, we hypothesized that stress-induced increases in the motivation for preferred foods may be a sex-specific predisposing factor for weight gain. METHODS AND PROCEDURES: To investigate this hypothesis, we have developed a buried food paradigm that permits the measurement of sex differences and effects of chronic variable stress (CVS) on the latency to uncover and the consumption of a preferred food pellet without the requisite caloric restriction required in traditional operant conditioning tasks. RESULTS: In our studies, females consistently showed latencies that were twice as fast as males to locate the buried pellet in limited access tests. Interestingly, during stress exposure, male latencies decreased to that of control female levels. Male and female mice showed a significant effect of stress, three- and fourfold, respectively, on increased consumption of the preferred food during testing. DISCUSSION: These results support a basal sex difference in behaviors toward a preferred food, and a possible role of stress sensitivity in the drive and intake of such foods. Sex differences in the role stress plays in these behaviors may provide insight into underlying mechanisms related to an increased obesity risk.

Effect of vomeronasal organ removal from male mice on their preference for and neural Fos responses to female urinary odors.

Four experiments were conducted to determine whether vomeronasal organ (VNO) inputs in male mice mediate the rewarding properties of estrous female urinary odors. Sexually naive male mice with either an intact (VNOi) or lesioned (VNOx) VNO preferred to investigate female urine over water in Y-maze tests. Subsequently, VNOi males ran significantly more quickly and remained in nasal contact longer with estrous female urine than with male urine, whereas VNOx males investigated these odors equally. In home-cage habituation-dishabituation tests, VNOi males also investigated female urine significantly longer than did VNOx males, although both groups investigated female urine longer than other non-body odors. Finally, female urinary odors induced Fos in the nucleus accumbens core of VNOi males but not of VNOx males. Our results suggest that female urinary odors retain some incentive value in VNOx males. However, once direct nasal contact is made with female urine, VNO inputs further activate forebrain mechanisms that amplify the reward salience of this stimulus for the male mouse.

Accessory olfactory neural Fos responses to a conditioned environment are blocked in male mice by vomeronasal organ removal.

The ability of an anesthetized estrous female to induce a conditioned place preference (CPP) response was assessed in male mice from which the vomeronasal organ (VNO) had either been removed (VNOx) or left intact (VNOi) in an initial effort to assess the possible contribution of VNO-accessory olfactory inputs to the intrinsically rewarding properties of opposite-sex body odorants. Both VNOi and VNOx male mice acquired a CPP after repeated pairing of an initially non-preferred test chamber with an anesthetized estrous female mouse, suggesting that odorants detected by the main olfactory system and/or visual and tactile cues from the anesthetized estrous female can compensate for absent VNO inputs to establish a CPP. Subsequent exposure to this conditioning chamber alone caused significant increases in the number of Fos-immunoreactive cells in the mitral and granule cell layers of the accessory olfactory bulb as well as in the medial amygdala and ventral tegmental area of VNOi but not of VNOx males. These results suggest that activity in distal segments of the VNO-accessory olfactory pathway, in addition to the mesolimbic dopamine reward system, can be conditioned to respond to non-odor cues.

Olfactory sex discrimination persists, whereas the preference for urinary odorants from estrous females disappears in male mice after vomeronasal organ removal.

Based on observed changes in the social context for the display of ultrasonic vocalizations, scent marking, aggression, and mounting behavior by male mice with a null mutation of the transient receptor potential 2 ion channel, it was proposed recently that a primary function of the mouse vomeronasal organ (VNO)/accessory olfactory system is sex discrimination. We tested this hypothesis directly by studying the ability of male mice to discriminate between urinary odors of conspecifics of the two sexes and in different endocrine states using habituation-dishabituation tests. Male mice from which the VNO had been surgically removed (VNOx) resembled sham-operated controls (VNOi) in their ability to discriminate between volatile urinary odors from estrous females versus gonadally intact males, as well as between urinary odors from estrous versus ovariectomized females and from gonadally intact versus castrated males. When physical access to stimuli was permitted, VNOi control males strongly preferred to investigate volatile and nonvolatile urinary odorants from estrous females as opposed to intact males, whereas VNOx males showed no such preference. Mating performance in tests with estrous females was equivalent in VNOi and VNOx subjects. Both groups of males preferred to mount an estrous female instead of a castrated male. Our results suggest that the VNO is not required for sex discrimination but instead detects the nonvolatile components of opposite-sex urine that may be used to help prolong contact with individuals that produce these chemosignals.