Effects of insulin-produced hypoglycemia in combination with ethanol on spontaneous motor activity in rats

Anxiety behavior and hypothalamic-pituitary-adrenal axis altered in a female rat model of vertical sleeve gastrectomy

Surgical weight loss results in a host of metabolic changes that culminate in net positive health benefit to the patients. However, the psychological impact of these surgeries has not been fully studied. On one hand, surgical weight loss has been reported to improve standard quality of life and resolution of symptoms of depression. But on the other hand, reports of self-harm and increased ER visits for self-harm suggest other psychological difficulties. Inability to handle anxiety following surgical weight loss has alarming potential ramifications for these gastric surgery patients. In the present study, we used models of diet-induced obesity and vertical sleeve gastrectomy (VSG) to ask whether anxiety behavior and hypothalamic-pituitary-adrenal (HPA) axis gene changes were affected by surgical weight loss under two diet regimens: i.e. low-fat diet (LFD) and high-fat diet (HFD). We show reduced exploratory behavior in the open field test but increased time in the open arms of the elevated plus maze. Furthermore, we show increased plasma levels of corticosterone in female VSG recipients in the estrus phase and increased levels of hypothalamic arginine-vasopressin (avp), pro-opiomelanocortin (pomc), and tyrosine hydroxylase (th). We report reduced dopamine receptor D1 (drd1) gene in prefrontal cortex (PFC) in VSG animals in comparison to Sham. Further we report diet-driven changes in stress-relevant gene targets in the hypothalamus (oxt, pomc, crhr1) and adrenal (nr3c1, nr3c2, mc2r). Taken together, these data suggest a significant impact of both surgical weight loss and diet on the HPA axis and further impact on behavior. Additional assessment is necessary to determine whether molecular and hormonal changes of surgical weight loss are the source of these findings.

Insulin attenuates the acquisition and expression of ethanol-induced locomotor sensitization in DBA/2J mice

AIM

Ethanol-induced locomotor sensitization is a behavioral manifestation of physiological responses to repeated ethanol exposures. While ethanol exerts direct effects on multiple neurotransmitter systems in the brain, ethanol-induced changes in metabolic state, including acute hyperglycemia and inhibition of insulin signaling, also have plausible roles in the expression of ethanol-related behaviors through direct and indirect effects on brain function. The current experiments examined whether insulin administration or the resultant hypoglycemia might attenuate the development of sensitization to the locomotor stimulant effect of ethanol.

MAIN METHODS

Male and female DBA/2J mice received daily injections of 5 or 10 IU/kg insulin before or after a stimulating dose of ethanol and subsequent testing in an automated activity monitor. Blood glucose levels were determined upon the completion of the experiments.

KEY FINDINGS

Insulin injected prior to ethanol blunted the acute stimulant response as well as the acquisition and expression of locomotor sensitization, while insulin given after ethanol did not affect the development of the sensitized response. In a separate experiment, mice given glucose concurrently with insulin developed ethanol-induced locomotor sensitization normally.

SIGNIFICANCE

These experiments suggest that insulin attenuates the development of ethanol-induced locomotor sensitization, and that blood glucose levels can largely account for this effect. Further studies of the role of ethanol-induced metabolic states should provide novel information on the expression of ethanol-related behaviors.

The effects of hypoglycemia and ethanol on rat performance in the radial-arm maze

A deficit in blood glucose (BG) (hypoglycemia, HG) causes a characteristic array of physiological sequelae, symptoms and cognitive impairment in human subjects. However, the performance of hypoglycemic animal subjects in the standard paradigms of behavioral pharmacology has received little research attention. The primary purpose of these experiments was to determine the effect of insulin-produced HG on spatial working memory in rats trained in the radial-arm maze (RAM), using a noninterrupted (win-shift) procedure. A second aim was to further investigate possible interaction between HG and ethanol administration since potentiation between the drugs' depressant effects has been reported for rat spontaneous motor activity (SMA). Insulin administration (resulting in BG levels approximately 65% of control levels) was combined factorially with ethanol treatment in two experiments. HG significantly increased time required to complete RAM trials in both experiments, but did not impair accuracy of arm choice. In the second experiment, ethanol was administered only once to minimize development of tolerance, and under these conditions, ethanol at 1500 mg/kg impaired arm-choice accuracy and marginally potentiated HG-produced slowing of running time. The current results appear somewhat similar to previously reported effects of HG on reaction time in human subjects.