Inhibitory effects of insulin on GABAAcurrents modulated by the GABAAalpha subunit

Chronic neuroleptic treatment combined with a high fat diet elevated [3H] flunitrazepam binding in the cerebellum

Clinical and preclinical studies have shown dysfunctions in genetic expression and neurotransmission of γ-Aminobutyric acid (GABA), GABA_A receptor subunits, and GABA-synthesizing enzymes GAD₆₇ and GAD₆₅ in schizophrenia. It is well documented that there is significant weight gain after chronic neuroleptic treatment in humans. While there are limited studies on the effects of diet on GABA signaling directly, a change in diet has been used clinically as an adjunct to treatment for schizophrenic relief. In this study, rats chronically consumed either a chow diet (CD) or a 60% high-fat diet (HFD) and drank from bottles that contained one of the following solutions: water, haloperidol (1.5 mg/kg), or olanzapine (10 mg/kg) for four weeks. Rats were then euthanized and their brains were processed for GABA_A in-vitro receptor autoradiography using [³H] flunitrazepam. A chronic HFD treatment yielded significantly increased [³H] flunitrazepam binding in the rat cerebellum independent of neuroleptic treatment. The desynchronization between the prefrontal cortex and the cerebellum is associated with major cognitive and motor dysfunctions commonly found in schizophrenic symptomatology, such as slowed reaction time, motor dyscoordination, and prefrontal activations related to speech fluency and cognitive alertness. These data support the notion that there is a dietary effect on GABA signaling within the cerebellum, as well as the importance of considering nutritional intervention methods as an adjunct treatment for patients chronically treated with neuroleptics. Finally, we indicate that future studies involving the analysis of individual patient's genetic profiles will further assist towards a precision medicine approach to the treatment of schizophrenia.

Brain and behavioral correlates of insulin resistance in youth with depression and obesity

Depression, together with insulin resistance, is increasingly prevalent among youth. These conditions have traditionally been compartmentalized, but recent evidence suggests that a shared brain motivational network underlies their co-occurrence. We posit that, in the context of depressive symptoms, insulin resistance is associated with aberrant structure and functional connectivity in the Anterior Cingulate Cortex (ACC) and hippocampus. This motivational neural circuit underlies dysfunctional behavioral responses and increased sensitivity to rewarding aspects of ingesting high calorie food that lead to disinhibition of eating even when satiated. To investigate this shared mechanism, we evaluated a sample of forty-two depressed and overweight (BMI > 85th%) youth aged 9 to 17. Using ACC and hippocampus structural and seed-based regions of interest, we investigated associations between insulin resistance, depression, structure (ACC thickness, and ACC and hippocampal area), and resting-state functional connectivity (RSFC). We predicted that aberrant associations among these neural and behavioral characteristics would be stronger in insulin resistant compared to insulin sensitive youth. We found that youth with greater insulin resistance had higher levels of anhedonia and more food seeking behaviors, reduced hippocampal and ACC volumes, and greater levels of ACC and hippocampal dysconnectivity to fronto-limbic reward networks at rest. For youth with high levels of insulin resistance, thinner ACC and smaller hippocampal volumes were associated with more severe depressive symptoms, whereas the opposite was true for youth with low levels of insulin resistance. The ACC-hippocampal motivational network that subserves depression and insulin resistance separately, may represent a critical neural interaction that link these syndromes together.

Neural and Endocrine Correlates of Early Life Abuse in Youth With Depression and Obesity

Depression and insulin resistance are becoming increasingly prevalent in younger populations. The origin and consequence of insulin resistance in depressed youth may, in part, be rooted in exposure to environmental stressors, such as early life abuse, that may lead to aberrant brain motivational networks mediating maladaptive food-seeking behaviors and insipient insulin resistance. In this paper, we aimed to investigate the impact of early life abuse on the development of insulin resistance in depressed and overweight youth aged 9 to 17 years. We hypothesized that youth with the greatest burden of early life abuse would have the highest levels of insulin resistance and corresponding aberrant reward network connectivities. To test this hypothesis, we evaluated sixty-nine depressed and overweight youth aged 9 to 17, using multimodal assessments of early life abuse, food-seeking behavior, and insulin resistance. Based on results of the Childhood Trauma Questionnaire (CTQ), we separated our study participants into two groups: 35 youth who reported high levels of the sum of emotional, physical, or sexual abuse and 34 youth who reported insignificant or no levels of any abuse. Results of an oral glucose tolerance test (OGTT) and resting state functional connectivity (RSFC), using the amygdala, insula, and nucleus accumbens (NAcc) as seed-based reward network regions of interest, were analyzed for group differences between high abuse and low abuse groups. High abuse youth exhibited differences from low abuse youth in amygdala-precuneus, NAcc-paracingulate gyrus, and NAcc-prefrontal cortex connectivities, that correlated with levels of abuse experienced. The more different their connectivity from of that of low abuse youth, the higher were their fasting glucose and glucose at OGTT endpoint. Importantly, level of abuse moderated the relation between reward network connectivity and OGTT glucose response. In contrast, low abuse youth showed hyperinsulinemia and more insulin resistance than high abuse youth, and their higher OGTT insulin areas under the curve correlated with more negative insula-precuneus connectivity. Our findings suggest distinct neural and endocrine profiles of youth with depression and obesity based on their histories of early life abuse.