Spatial and visual discrimination reversals in adult and geriatric rats exposed during gestation to methylmercury and n−3 polyunsaturated fatty acids

Fish contain essential long chain polyunsaturated fatty acids (PUFAs), particularly docosahexaenoic acid (DHA), an omega-3 (or n-3) PUFA, but are also the main source of exposure to methylmercury (MeHg), a potent developmental neurotoxicant. Since n-3 PUFAs support neural development and function, benefits deriving from a diet rich in n-3s have been hypothesized to protect against deleterious effects of gestational MeHg exposure. To determine whether protection occurs at the behavioral level, female Long-Evans rats were exposed, in utero, to 0, 0.5, or 5 ppm of Hg as MeHg via drinking water, approximating exposures of 0, 40, and 400 μg Hg/kg/day and producing 0, 0.29, and 5.50 ppm of total Hg in the brains of siblings at birth. They also received pre- and postnatal exposure to one of two diets, both based on the AIN-93 semipurified formulation. A “fish-oil” diet was high in, and a “coconut-oil” diet was devoid of, DHA. Diets were approximately equal in α-linolenic acid and n-6 PUFAs. As adults, the rats were first assessed with a spatial discrimination reversal (SDR) procedure and later with a visual (nonspatial) discrimination reversal (VDR) procedure. MeHg increased the number of errors to criterion for both SDR and VDR during the first reversal, but effects were smaller or nonexistent on the original discrimination and on later reversals. No such MeHg-related deficits were seen when the rats were retested on SDR after two years of age. These results are consistent with previous reports and hypotheses that gestational MeHg exposure produces perseverative responding. No interactions between Diet and MeHg were found, suggesting that n-3 PUFAs do not guard against these behavioral effects. Brain Hg concentrations did not differ between the diets, either. In geriatric rats, failures to respond were less common and response latencies were shorter for rats fed the fish oil diet, suggesting that exposure to a diet rich in n-3s may lessen the impact of age-related declines in response initiation

Anxiety symptom severity differentiates HPA acute stress reactivity in children

Rationale/statement of the problem : Considerable research has focused on the relationship of anxiety with alterations in the hypothalamic-pituitary-adrenal (HPA) acute stress response. Findings, however, differ among studies on adults and children, and among different types of anxiety. This study investigates the relationship of anxiety symptom severity with HPA reactivity to the cold pressor task (CPT) in preadolescent children. We hypothesize that children with increased symptoms of anxiety will have increased cortisol (HPA) reactivity to the CPT. Methods : A social-evaluative adaptation of the CPT was used to elicit HPA acute stress reactivity among 42 children (26 female, 16 male) aged 8–12 years (mean age, 10 years) recruited from a child anxiety disorders clinic (n=20) and from the community at large (n=22). Repeated saliva samples were assayed for cortisol to determine maximum task response (TR) and area under the curve with respect to the increase from baseline (AUCi). Multi-dimensional anxiety measures included the Screen for Anxiety and Related Disorders (SCARED: parent and child report); State Trait Anxiety Inventory-Trait (STAI-T), and Children's Anxiety Sensitivity Index (CASI). Subjects were grouped according to recruitment source and high/low symptom measures (all subjects by anxiety measure median split); groups were compared via independent samples t-tests. Results : Maximum cortisol TR and AUCi did not differ between children recruited from the anxiety disorders clinic and the community. Among all subjects, maximum TR was significantly greater for those with high anxiety symptoms on the STAI-T (p=0.006), SCARED-C (p=0.012), and SCARED-P (p=0.031), and approached significance on the CASI (p=0.056), compared to those with low symptoms on these measures. AUCi was greater among those with high symptoms on the SCARED-C (p=0.01) and SCARED-P (p=0.011), but not on the STAI-T (p=0.113) or CASI (p=0.072). Conclusion : Results suggest that increased anxiety symptom severity is associated with greater cortisol reactivity to acute stress in preadolescent children. Moreover, findings were similar among youth recruited from the clinic and the community, thus providing additional evidence of the high prevalence of anxiety in children and the potential associated risk of alterations in physiological stress reactivity among those with more severe symptoms

Seasonal influences on sleep and executive function in the migratory White-crowned Sparrow (<it>Zonotrichia leucophrys gambelii</it>)

Abstract Background We have previously shown that the White-crowned Sparrow (WCS) decreases sleep by 60% during a period of migratory restlessness relative to a non-migratory period when housed in a 12 h light: 12 h dark cycle. Despite this sleep reduction, accuracy of operant performance was not impaired, and in fact rates of responding were elevated during the migratory period, effects opposite to those routinely observed following enforced sleep deprivation. To determine whether the previously observed increases in operant responding were due to improved performance or to the effects of migration on activity level, here we assessed operant performance using a task in which optimal performance depends on the bird's ability to withhold a response for a fixed interval of time (differential-reinforcement-of-low-rate-behavior, or DRL); elevated response rates ultimately impair performance by decreasing access to food reward. To determine the influence of seasonal changes in day length on sleep and behavioral patterns, we recorded sleep and assessed operant performance across 4 distinct seasons (winter, spring, summer and fall) under a changing photoperiod. Results Sleep amount changed in response to photoperiod in winter and summer, with longest sleep duration in the winter. Sleep duration in the spring and fall migratory periods were similar to what we previously reported, and were comparable to sleep duration observed in summer. The most striking difference in sleep during the migratory periods compared to non-migratory periods was the change from discrete day-night temporal organization to an almost complete temporal fragmentation of sleep. The birds' ability to perform on the DRL task was significantly impaired during both migratory periods, but optimal performance was sustained during the two non-migratory periods. Conclusions Birds showed dramatic changes in sleep duration across seasons, related to day length and migratory status. Migration was associated with changes in sleep amount and diurnal distribution pattern, whereas duration of sleep in the non-migratory periods was largely influenced by the light-dark cycle. Elevated response rates on the DRL task were observed during migration but not during the short sleep duration of summer, suggesting that the migratory periods may be associated with decreased inhibition/increased impulsivity. Although their daily sleep amounts and patterns may vary by season, birds are susceptible to sleep loss throughout the year, as evidenced by decreased responding rates following enforced sleep deprivation.</p