Differences in insulin secretion and sensitivity in short-sleep insomnia.

OBJECTIVE: Short-sleep insomnia is associated with increased risk of diabetes. The role of altered insulin secretion and action in this association is poorly understood. DESIGN: Observational study. SETTING: Academic clinical research center. PARTICIPANTS: Nondiabetic individuals with insomnia (mean [standard deviation] age 48 [9] y, body mass index 25.6 [3.9] kg/m(2)) with ≤ 6 h (short sleep, n = 14) and > 6 h of sleep (n = 14) during overnight laboratory polysomnography. MEASUREMENTS AND RESULTS: Standard oral glucose testing was used to assess glucose tolerance, beta-cell function (homeostasis model assessment [HOMA-B]; second-phase insulin secretion) and insulin resistance (HOMA-IR; insulin sensitivity index). There was no significant difference in hemoglobin A1C and fasting or 2-h blood glucose concentrations between sleep groups. Short-sleep insomnia sufferers had lower fasting and postchallenge serum insulin concentrations associated with lower estimates of fasting and glucose-stimulated insulin secretion, and increased insulin sensitivity. CONCLUSIONS: Individuals with short-sleep insomnia appear to have higher indices of systemic insulin sensitivity and secrete less insulin without changes in overall glucose tolerance.

Mutation of the alpha2A-adrenoceptor impairs working memory performance and annuls cognitive enhancement by guanfacine.

Norepinephrine strengthens the working memory, behavioral inhibition, and attentional functions of the prefrontal cortex through actions at postsynaptic alpha2-adrenoceptors (alpha2-AR). The alpha2-AR agonist guanfacine enhances prefrontal cortical functions in rats, monkeys, and human beings and ameliorates prefrontal cortical deficits in patients with attention deficit hyperactivity disorder. The present study examined the subtype of alpha2-AR underlying these beneficial effects. Because there are no selective alpha2A-AR, alpha2B-AR, or alpha2C-AR agonists or antagonists, genetically altered mice were used to identify the molecular target of the action of guanfacine. Mice with a point mutation of the alpha2A-AR, which serves as a functional knock-out, were compared with wild-type animals and with previously published studies of alpha2C-AR knock-out mice (Tanila et al., 1999). Mice were adapted to handling on a T maze and trained on either a spatial delayed alternation task that is sensitive to prefrontal cortical damage or a spatial discrimination control task with similar motor and motivational demands but no dependence on prefrontal cortex. The effects of guanfacine on performance of the delayed alternation task were assessed in additional groups of wild-type versus alpha2A-AR mutant mice. We observed that functional loss of the alpha2A-AR subtype, unlike knock-out of the alpha2C-AR subtype, weakened performance of the prefrontal cortical task without affecting learning and resulted in loss of the beneficial response to guanfacine. These data demonstrate the importance of alpha2A-AR subtype stimulation for the cognitive functions of the prefrontal cortex and identify the molecular substrate for guanfacine and novel therapeutic interventions.