Sustained Treatment with Insulin Detemir in Mice Alters Brain Activity and Locomotion

Falling Short: The Contribution of Central Insulin Receptors to Gait Dysregulation in Brain Aging

Insulin resistance, which manifests as a reduction of insulin receptor signaling, is known to correlate with pathological changes in peripheral tissues as well as in the brain. Central insulin resistance has been associated with impaired cognitive performance, decreased neuronal health, and reduced brain metabolism; however, the mechanisms underlying central insulin resistance and its impact on brain regions outside of those associated with cognition remain unclear. Falls are a leading cause of both fatal and non-fatal injuries in the older population. Despite this, there is a paucity of work focused on age-dependent alterations in brain regions associated with ambulatory control or potential therapeutic approaches to target these processes. Here, we discuss age-dependent alterations in central modalities that may contribute to gait dysregulation, summarize current data supporting the role of insulin signaling in the brain, and highlight key findings that suggest insulin receptor sensitivity may be preserved in the aged brain. Finally, we present novel results showing that administration of insulin to the somatosensory cortex of aged animals can alter neuronal communication, cerebral blood flow, and the motivation to ambulate, emphasizing the need for further investigations of intranasal insulin as a clinical management strategy in the older population.

Sensitivity of the S1 neuronal calcium network to insulin and Bay-K 8644 in vivo: Relationship to gait, motivation, and aging processes

Neuronal hippocampal Ca²⁺ dysregulation is a critical component of cognitive decline in brain aging and Alzheimer's disease and is suggested to impact communication and excitability through the activation of a larger after hyperpolarization. However, few studies have tested for the presence of Ca²⁺ dysregulation in vivo, how it manifests, and whether it impacts network function across hundreds of neurons. Here, we tested for neuronal Ca²⁺ network dysregulation in vivo in the primary somatosensory cortex (S1) of anesthetized young and aged male Fisher 344 rats using single‐cell resolution techniques. Because S1 is involved in sensory discrimination and proprioception, we tested for alterations in ambulatory performance in the aged animal and investigated two potential pathways underlying these central aging‐ and Ca²⁺‐dependent changes. Compared to young, aged animals displayed increased overall activity and connectivity of the network as well as decreased ambulatory speed. In aged animals, intranasal insulin (INI) increased network synchronicity and ambulatory speed. Importantly, in young animals, delivery of the L‐type voltage‐gated Ca²⁺ channel modifier Bay‐K 8644 altered network properties, replicating some of the changes seen in the older animal. These results suggest that hippocampal Ca²⁺ dysregulation may be generalizable to other areas, such as S1, and might engage modalities that are associated with locomotor stability and motivation to ambulate. Further, given the safety profile of INI in the clinic and the evidence presented here showing that this central dysregulation is sensitive to insulin, we suggest that these processes can be targeted to potentially increase motivation and coordination while also reducing fall frequency with age.

Novel Noninvasive Approaches to the Treatment of Obesity: From Pharmacotherapy to Gene Therapy

Recent insights into the pathophysiologic underlying mechanisms of obesity have led to the discovery of several promising drug targets and novel therapeutic strategies to address the global obesity epidemic and its comorbidities. Current pharmacologic options for obesity management are largely limited in number and of modest efficacy/safety profile. Therefore, the need for safe and more efficacious new agents is urgent. Drugs that are currently under investigation modulate targets across a broad range of systems and tissues, including the central nervous system, gastrointestinal hormones, adipose tissue, kidney, liver, and skeletal muscle. Beyond pharmacotherapeutics, other potential antiobesity strategies are being explored, including novel drug delivery systems, vaccines, modulation of the gut microbiome, and gene therapy. The present review summarizes the pathophysiology of energy homeostasis and highlights pathways being explored in the effort to develop novel antiobesity medications and interventions but does not cover devices and bariatric methods. Emerging pharmacologic agents and alternative approaches targeting these pathways and relevant research in both animals and humans are presented in detail. Special emphasis is given to treatment options at the end of the development pipeline and closer to the clinic (ie, compounds that have a higher chance to be added to our therapeutic armamentarium in the near future). Ultimately, advancements in our understanding of the pathophysiology and interindividual variation of obesity may lead to multimodal and personalized approaches to obesity treatment that will result in safe, effective, and sustainable weight loss until the root causes of the problem are identified and addressed.

Putative Anti-Immobility Action of Acute Insulin Is Attributable to an Increase in Locomotor Activity in Healthy Wistar Rats

BACKGROUND/AIMS

Anti-immobility actions of insulin in diabetic rats that are subjected to the forced swim test (FST) have been reported. In this test, low doses of antidepressants exert actions after long-term treatment, without affecting locomotor activity in healthy rats. Few studies have compared acute and chronic actions of insulin with antidepressants in healthy rats.

METHODS

We hypothesized that if insulin exerts a true anti-immobility action, then its effects must be comparable to fluoxetine in both a 1-day treatment regimen and a 21-day treatment regimen in healthy, gonadally intact female Wistar rats.

RESULTS

The results showed that low levels of glycemia were produced by all treatments, including fluoxetine, and glycemia was lower in proestrus-estrus than in diestrus-metestrus. None of the treatments or regimens produced actions on indicators of anxiety in the elevated plus maze. Insulin in the 1-day regimen increased the number of crossings and rearings in the open field test and caused a low cumulative immobility time in the FST. These actions disappeared in the 21-day regimen. Compared with the other treatments, fluoxetine treatment alone or combined with insulin produced a longer latency to the first period of immobility and a shorter immobility time in the chronic regimen in the FST, without affecting locomotor activity, and more pronounced actions were observed in proestrus-estrus (i.e., a true anti-immobility effect).

CONCLUSION

These results indicate that insulin does not produce a true antidepressant action in healthy rats. The purported antidepressant effects that were observed were instead attributable to an increase in locomotor activity only in the 1-day regimen.

Central actions of insulin during pregnancy and lactation

Pregnancy and lactation are highly metabolically demanding states. Maternal glucose is a key fuel source for the growth and development of the fetus, as well as for the production of milk during lactation. Hence, the maternal body undergoes major adaptations in the systems regulating glucose homeostasis to cope with the increased demand for glucose. As part of these changes, insulin levels are elevated during pregnancy and lower in lactation. The increased insulin secretion during pregnancy plays a vital role in the periphery; however, the potential effects of increased insulin action in the brain have not been widely investigated. In this review, we consider the impact of pregnancy on brain access and brain levels of insulin. Moreover, we explore the hypothesis that pregnancy is associated with site-specific central insulin resistance that is adaptive, allowing for the increases in peripheral insulin secretion without the consequences of increased central and peripheral insulin functions, such as to stimulate glucose uptake into maternal tissues or to inhibit food intake. Conversely, the loss of central insulin actions may impair other functions, such as insulin control of the autonomic nervous system. The potential role of low insulin in facilitating adaptive responses to lactation, such as hyperphagia and suppression of reproductive function, are also discussed. We end the review with a list of key research questions requiring resolution.

Delivery of bevacizumab by intracranial injection: assessment in glioma model

Background

Many reports have indicated that the intravenous administration of bevacizumab produces a number of systemic side effects. Therefore, we investigated the therapeutic effects of intratumoral bevacizumab administration using a glioma animal model.

Methods

The glioma cell lines U251 and U87 that carried luciferase were implanted into the brains of mice to develop glioma models. Glioma-bearing mice were treated with bevacizumab intravenously or intratumorally by Alzet micro-osmotic pumps, and the survival time of mice was monitored. Tumor volumes and location were observed by fluorescence imaging and histological analysis. Levels of microvessel marker, cancer stem cell marker as well as angiogenesis-, invasion-, and inflammation-related factors in tumors were examined by immunohistochemical staining.

Results

Mice treated with intratumoral low-dose bevacizumab had smaller tumor volumes, longer survival time, lower microvessel density, and fewer cancer stem cells as compared with untreated and intravenously treated mice. Furthermore, expression levels of inflammation-related factors increased signifiwhereas that of angiogenesis- and invasion-related factors decreased in intratumorally treated animals, compared with intravenously treated mice.

Conclusion

These results implied bevacizumab delivery by intratumoral injection via Alzet micro-osmotic pumps may be a more effective and safer protocol for treating gliomas.

Awake, long-term intranasal insulin treatment does not affect object memory, odor discrimination, or reversal learning in mice

Intranasal insulin delivery is currently being used in clinical trials to test for improvement in human memory and cognition, and in particular, for lessening memory loss attributed to neurodegenerative diseases. Studies have reported the effects of short-term intranasal insulin treatment on various behaviors, but less have examined long-term effects. The olfactory bulb contains the highest density of insulin receptors in conjunction with the highest level of insulin transport within the brain. Previous research from our laboratory has demonstrated that acute insulin intranasal delivery (IND) enhanced both short- and long-term memory as well as increased two-odor discrimination in a two-choice paradigm. Herein, we investigated the behavioral and physiological effects of chronic insulin IND. Adult, male C57BL6/J mice were intranasally treated with 5μg/μl of insulin twice daily for 30 and 60days. Metabolic assessment indicated no change in body weight, caloric intake, or energy expenditure following chronic insulin IND, but an increase in the frequency of meal bouts selectively in the dark cycle. Unlike acute insulin IND, which has been shown to cause enhanced performance in odor habituation/dishabituation and two-odor discrimination tasks in mice, chronic insulin IND did not enhance olfactometry-based odorant discrimination or olfactory reversal learning. In an object memory recognition task, insulin IND-treated mice did not perform differently than controls, regardless of task duration. Biochemical analyses of the olfactory bulb revealed a modest 1.3 fold increase in IR kinase phosphorylation but no significant increase in Kv1.3 phosphorylation. Substrate phosphorylation of IR kinase downstream effectors (MAPK/ERK and Akt signaling) proved to be highly variable. These data indicate that chronic administration of insulin IND in mice fails to enhance olfactory ability, object memory recognition, or a majority of systems physiology metabolic factors - as reported to elicit a modulatory effect with acute administration. This leads to two alternative interpretations regarding long-term insulin IND in mice: 1) It causes an initial stage of insulin resistance to dampen the behaviors that would normally be modulated under acute insulin IND, but ability to clear a glucose challenge is still retained, or 2) There is a lack of behavioral modulation at high concentration of insulin attributed to the twice daily intervals of hyperinsulinemia caused by insulin IND administration without any insulin resistance, per se.