Large variation of vacancy formation energies in the surface of crystalline ice

Resolving the atomic structure of the surface of ice particles within clouds, over the temperature range encountered in the atmosphere and relevant to understanding heterogeneous catalysis on ice, remains an experimental challenge. By using first-principles calculations, we show that the surface of crystalline ice exhibits a remarkable variance in vacancy formation energies, akin to an amorphous material. We find vacancy formation energies as low as similar to 0.1-0.2 eV, which leads to a higher than expected vacancy concentration. Because a vacancy's reactivity correlates with its formation energy, ice particles may be more reactive than previously thought. We also show that vacancies significantly reduce the formation energy of neighbouring vacancies, thus facilitating pitting and contributing to pre-melting and quasi-liquid layer formation. These surface properties arise from proton disorder and the relaxation of geometric constraints, which suggests that other frustrated materials may possess unusual surface characteristics

Behavioral and neurochemical changes induced by oxycodone differ between adolescent and adult mice.

Nonmedical use of the prescription opioid analgesic oxycodone is a major problem in the United States, particularly among adolescents and young adults. This study characterized self-administration of oxycodone by adolescent and adult mice, and how this affects striatal dopamine levels. Male C57BL/6J mice (4 or 10 weeks old) were allowed to acquire oxycodone self-administration (0.25 mg/kg per infusion) for 9 days, and then tested with varying doses of oxycodone (0, 0.125, 0.25, 0.5, and 0.75 mg/kg per infusion). On completion of the self-administration study, a guide cannula was implanted into the striatum of these mice. Six days later, microdialysis was conducted on the freely moving mouse. After collection of baseline samples, oxycodone was administered i.p. (1.25, 2.5, and 5.0 mg/kg) and samples were collected for 1 h after each dose. Adult mice self-administered significantly more oxycodone across the doses tested. After 1 week, basal striatal dopamine levels were lower in mice of both ages that had self-administered oxycodone than in yoked saline controls. Oxycodone challenge increased striatal dopamine levels in a dose-dependent manner in both age groups. Of interest, the lowest dose of oxycodone led to increased striatal dopamine levels in the mice that had self-administered oxycodone during adolescence but not those that self-administered it as adults. The lower number of infusions of oxycodone self-administered by adolescent mice, and their later increased striatal dopamine in response to the lowest dose of oxycodone (not found in adults), suggest differential sensitivity to the reinforcing and neurobiological effects of oxycodone in the younger mice

Evidence for a Role of Progesterone in Menstrual Cycle-Related Variability in Prepulse Inhibition in Healthy Young Women

Prepulse inhibition (PPI) of the startle response is sensitive to sex, with healthy young women showing less PPI compared with age-matched men, and varies according to the menstrual cycle phase in women. Relatively less is known regarding sex and hormonal influences in prepulse facilitation (PPF). Menstrual phase-related variability in PPI is suggested to be mediated by fluctuating estrogen level, based on the observations of more PPI in women during the follicular, relative to the luteal, phase. No study has directly assessed the relationship between fluctuating hormones and PPI or PPF levels over the human ovarian cycle. To examine the roles of circulating ovarian hormones in PPI and PPF, 16 non-smoking regularly menstruating healthy women were tested during both the follicular and luteal phases on PPI and PPF and provided saliva samples for measurement of 17β-estradiol (estrogen), progesterone and testosterone. The results showed higher levels of 17β-estradiol and progesterone during the luteal, relative to the follicular, phase; and more PPI during the follicular phase and more PPF during the luteal phase with comparable startle amplitude and habituation during the two phases. A larger increase in progesterone was associated with a smaller decrease in PPI from the follicular to the luteal phase. No significant associations were found between changes in PPI/PPF and estrogen levels. The findings confirm lower PPI during the luteal, compared with the follicular, phase and suggest a role for progesterone, more specifically an antipsychotic-like PPI-restoration action of progesterone, during the luteal phase in PPI of young women