Type 2 diabetes mellitus (T2D) and Alzheimer’s disease (AD) are major public health burdens associated with aging. As the age of the population rapidly increases, a sheer increase in the incidence of these diseases is expected. Research has identified T2D as a risk factor for cognitive impairment and potentially AD, but the neurobiological pathways that are affected are only beginning to be understood. The rapid advances in neuroimaging in the past decade have added significant understanding to how T2D affects brain structure and function and possibly lead to AD. This article provides a review of studies that have utilized structural and functional neuroimaging to identify neural pathways that link T2D to impaired cognitive performance and potentially AD. A primary focus of this article is the potential for neuroimaging to assist in understanding the mechanistic pathways that may provide translational opportunities for clinical intervention.

Intracerebral microdialysis has proven useful for chemical monitoring in patients following traumatic brain injury. Recent studies in animals, however, have documented that insertion of microdialysis probes into brain tissues initiates a foreign-body response. Within a few days after probe insertion, the foreign body response impedes the use of microdialysis to monitor the K + and glucose transients associated with spreading depolarization, a potential mechanism for secondary brain injury. Herein, we show that perfusing microdialysis probes with dexamethasone, a potent anti-inflammatory glucocorticoid, suppresses the foreign body response and facilitates the monitoring of spontaneous spreading depolarizations for at least 10 days following controlled cortical injury in the rat. In addition to spreading depolarizations, results of this study suggest that a progressive, apparently permanent, decline in pericontusional interstitial glucose may be an additional sequela of brain injury. This study establishes extended dexamethasone-enhanced microdialysis in the injured rodent cortex as a new paradigm for investigating trauma-induced metabolic crisis.

Objective The development of type 1 diabetes (T1DM) within the first 7 years of life has been linked to poorer cognitive performance. Adults with T1DM have altered functional brain connectivity, but no studies have examined whether earlier age of T1DM onset is associated with functional connectivity later in life. Accordingly, we tested the relationship between age of onset and resting state functional connectivity in a cohort of middle-aged adults with childhood-onset T1DM. Methods Subjects were from a subsample of the Pittsburgh Epidemiology of Diabetes Complications cohort and included 66 adults (mean age = 47.54 years; 32 Male). Resting state blood oxygen level dependent activity was used to calculate mean connectivity for eight functional brain networks. A multivariate analysis of variance examined associations between age of onset and network connectivity. Diffusion tensor and fluid attenuated inversion recovery images were analyzed to identify microstructural alterations and white matter hyperintensity volumes. Results Later childhood onset of T1DM was associated with lower connectivity (F (8,57) = 2.40, p = .026). A significant interaction was present for current age such that an inverse association with age of onset for functional connectivity was present in older individuals (F (8,55) = 2.88, p = .035). Lower connectivity was associated with older age, increased white matter hyperintensity volume, and lower microstructural integrity. Conclusions Diagnosis of T1DM later in childhood may be associated with lower brain functional connectivity, particularly in those surviving into older ages. These alterations may be an early marker for subsequent cognitive decrements. Future studies are warranted to understand the pathways underlying these associations.

Cardiac arrest survival rates have improved with modern resuscitation techniques, but many survivors experience impairments associated with hypoxic-ischemic brain injury (HIBI). Currently, little is understood about chronic changes in striatal dopamine (DA) systems after HIBI. Given the common empiric clinical use of DA enhancing agents in neurorehabilitation, investigation evaluating dopaminergic alterations after cardiac arrest (CA) is necessary to optimize rehabilitation approaches. We hypothesized that striatal DA neurotransmission would be altered chronically after ventricular fibrillation cardiac arrest (VF-CA). Fast-scan cyclic voltammetry was used with median forebrain bundle (MFB) maximal electrical stimulations (60Hz, 10s) in rats to characterize presynaptic components of DA neurotransmission in the dorsal striatum (D-Str) and nucleus accumbens 14 days after a 5-min VF-CA when compared to Sham or Naïve. VF-CA increased D-Str-evoked overflow [DA], total [DA] released, and initial DA release rate versus controls, despite also increasing maximal velocity of DA reuptake (V ). Methylphenidate (10 mg/kg), a DA transporter inhibitor, was administered to VF-CA and Shams after establishing a baseline, pre-drug 60 Hz, 5 s stimulation response. Methylphenidate increased initial evoked overflow [DA] more-so in VF-CA versus Sham and reduced D-Str V in VF-CA but not Shams; these findings are consistent with upregulated striatal DA transporter in VF-CA versus Sham. Our work demonstrates that 5-min VF-CA increases electrically stimulated DA release with concomitant upregulation of DA reuptake 2 weeks after brief VF-CA insult. Future work should elucidate how CA insult duration, time after insult, and insult type influence striatal DA neurotransmission and related cognitive and motor functions.

Introduction: Cardiac arrest survival has improved with advances in resuscitation care, but survivors face impairments from the resulting hypoxic-ischemic brain injury (HIBI). Given the popular clinical use of DA modulators, despite limited understanding of disturbances in DA neurotransmission after HIBI, we characterized striatal DA signaling and behavioral deficits in a rat model of asphyxial cardiac arrest (ACA). Hypothesis: ACA-induced HIBI alters DA neurotransmission linked to behavioral deficits. Methods: Adult male Sprague-Dawley rats (n=41) underwent either Sham procedures (n=10) or 5-min no-flow ACA (n=28) insult. Fast-scan cyclic voltammetry (FSCV) and maximal medial forebrain bundle stimulations (60Hz, 10s) were used to characterize presynaptic DA signaling in dorsal striatum (D-Str). FSCV findings were compared with sensorimotor processing [acoustic startle responses (ASR)], open field exploration (total distance & exploratory zone entries), myoclonus, and anhedonia (sucrose preference testing). Results: ACA increased maximum evoked overflow (fig 1) and several DA release-based kinetic metrics. ACA hindered sensorimotor processing via increased ASR %change, elicited myoclonic responses to auditory stimuli, reduced mobility & exploration, and increased anhedonia. Many behavioral measures correlated with D-Str neurotransmission ( fig 2 ). Conclusions: ACA causes early hypodopaminergia that evolves to a hyperdopaminergic state by 2 weeks that is associated with behavioral dysfunction. Future work should further characterize striatal pathology post-ACA and identify treatments to resolve altered DA signaling and behavioral deficits.