Maheedhar Kodali

Blood brain barrier dysfunction and delayed neurological deficits in mild traumatic brain injury induced by blast shock waves

Mild traumatic brain injury (mTBI) resulting from exposure to blast shock waves (BSWs) is one of the most predominant causes of illnesses among veterans who served in the recent Iraq and Afghanistan wars. Such mTBI can also happen to civilians if exposed to shock waves of bomb attacks by terrorists. While cognitive problems, memory dysfunction, depression, anxiety and diffuse white matter injury have been observed at both early and/or delayed time-points, an initial brain pathology resulting from exposure to BSWs appears to be the dysfunction or disruption of the blood-brain barrier (BBB). Studies in animal models suggest that exposure to relatively milder BSWs (123 kPa) initially induces free radical generating enzymes in and around brain capillaries, which enhances oxidative stress resulting in loss of tight junction (TJ) proteins, edema formation, and leakiness of BBB with disruption or loss of its components pericytes and astrocyte end-feet. On the other hand, exposure to more intense BSWs (145–323 kPa) causes acute disruption of the BBB with vascular lesions in the brain. Both of these scenarios lead to apoptosis of endothelial and neural cells and neuroinflammation in and around capillaries, which may progress into chronic traumatic encephalopathy (CTE) and/or a variety of neurological impairments, depending on brain regions that are afflicted with such lesions. This review discusses studies that examined alterations in the brain milieu causing dysfunction or disruption of the BBB and neuroinflammation following exposure to different intensities of BSWs. Furthermore, potential of early intervention strategies capable of easing oxidative stress, repairing the BBB or blocking inflammation for minimizing delayed neurological deficits resulting from exposure to BSWs is conferred.

Resveratrol Prevents Age-Related Memory and Mood Dysfunction with Increased Hippocampal Neurogenesis and Microvasculature, and Reduced Glial Activation

Greatly waned neurogenesis, diminished microvasculature, astrocyte hypertrophy and activated microglia are among the most conspicuous structural changes in the aged hippocampus. Because these alterations can contribute to age-related memory and mood impairments, strategies efficacious for mitigating these changes may preserve cognitive and mood function in old age. Resveratrol, a phytoalexin found in the skin of red grapes having angiogenic and antiinflammatory properties, appears ideal for easing these age-related changes. Hence, we examined the efficacy of resveratrol for counteracting age-related memory and mood impairments and the associated detrimental changes in the hippocampus. Two groups of male F344 rats in late middle-age having similar learning and memory abilities were chosen and treated with resveratrol or vehicle for four weeks. Analyses at ~25 months of age uncovered improved learning, memory and mood function in resveratrol-treated animals but impairments in vehicle-treated animals. Resveratrol-treated animals also displayed increased net neurogenesis and microvasculature, and diminished astrocyte hypertrophy and microglial activation in the hippocampus. These results provide novel evidence that resveratrol treatment in late middle age is efficacious for improving memory and mood function in old age. Modulation of the hippocampus plasticity and suppression of chronic low-level inflammation appear to underlie the functional benefits mediated by resveratrol.

Resveratrol Treatment after Status Epilepticus Restrains Neurodegeneration and Abnormal Neurogenesis with Suppression of Oxidative Stress and Inflammation.

Antiepileptic drug therapy, though beneficial for restraining seizures, cannot thwart status epilepticus (SE) induced neurodegeneration or down-stream detrimental changes. We investigated the efficacy of resveratrol (RESV) for preventing SE-induced neurodegeneration, abnormal neurogenesis, oxidative stress and inflammation in the hippocampus. We induced SE in young rats and treated with either vehicle or RESV, commencing an hour after SE induction and continuing every hour for three-hours on SE day and twice daily thereafter for 3 days. Seizures were terminated in both groups two-hours after SE with a diazepam injection. In contrast to the vehicle-treated group, the hippocampus of animals receiving RESV during and after SE presented no loss of glutamatergic neurons in hippocampal cell layers, diminished loss of inhibitory interneurons expressing parvalbumin, somatostatin and neuropeptide Y in the dentate gyrus, reduced aberrant neurogenesis with preservation of reelin + interneurons, lowered concentration of oxidative stress byproduct malondialdehyde and pro-inflammatory cytokine tumor necrosis factor-alpha, normalized expression of oxidative stress responsive genes and diminished numbers of activated microglia. Thus, 4 days of RESV treatment after SE is efficacious for thwarting glutamatergic neuron degeneration, alleviating interneuron loss and abnormal neurogenesis, and suppressing oxidative stress and inflammation. These results have implications for restraining SE-induced chronic temporal lobe epilepsy.

Object location and object recognition memory impairments, motivation deficits and depression in a model of Gulf War illness

Memory and mood deficits are the enduring brain-related symptoms in Gulf War illness (GWI). Both animal model and epidemiological investigations have indicated that these impairments in a majority of GW veterans are linked to exposures to chemicals such as pyridostigmine bromide (PB, an antinerve gas drug), permethrin (PM, an insecticide) and DEET (a mosquito repellant) encountered during the Persian Gulf War-1. Our previous study in a rat model has shown that combined exposures to low doses of GWI-related (GWIR) chemicals PB, PM, and DEET with or without 5-min of restraint stress (a mild stress paradigm) causes hippocampus-dependent spatial memory dysfunction in a water maze test (WMT) and increased depressive-like behavior in a forced swim test (FST). In this study, using a larger cohort of rats exposed to GWIR-chemicals and stress, we investigated whether the memory deficiency identified earlier in a WMT is reproducible with an alternative and stress free hippocampus-dependent memory test such as the object location test (OLT). We also ascertained the possible co-existence of hippocampus-independent memory dysfunction using a novel object recognition test (NORT), and alterations in mood function with additional tests for motivation and depression. Our results provide new evidence that exposure to low doses of GWIR-chemicals and mild stress for 4 weeks causes deficits in hippocampus-dependent object location memory and perirhinal cortex-dependent novel object recognition memory. An open field test performed prior to other behavioral analyses revealed that memory impairments were not associated with increased anxiety or deficits in general motor ability. However, behavioral tests for mood function such as a voluntary physical exercise paradigm and a novelty suppressed feeding test (NSFT) demonstrated decreased motivation levels and depression. Thus, exposure to GWIR-chemicals and stress causes both hippocampus-dependent and hippocampus-independent memory impairments as well as mood dysfunction in a rat model.

Voluntary Running Exercise-Mediated Enhanced Neurogenesis Does Not Obliterate Retrograde Spatial Memory

Running exercise (RE) improves cognition, formation of anterograde memories, and mood, alongside enhancing hippocampal neurogenesis. A previous investigation in a mouse model showed that RE-induced increased neurogenesis erases retrograde memory (Akers et al., 2014). However, it is unknown whether RE-induced forgetting is common to all species. We ascertained whether voluntary RE-induced enhanced neurogenesis interferes with the recall of spatial memory in rats. Young rats assigned to either sedentary (SED) or running exercise (RE) groups were first subjected to eight learning sessions in a water maze. A probe test (PT) conducted 24 h after the final training session confirmed that animals in either group had a similar ability for the recall of short-term memory. Following this, rats in the RE group were housed in larger cages fitted with running wheels, whereas rats in the SED group remained in standard cages. Animals in the RE group ran an average of 78 km in 4 weeks. A second PT performed 4 weeks after the first PT revealed comparable ability for memory recall between animals in the RE and SED groups, which was evidenced through multiple measures of memory retrieval function. The RE group displayed a 1.5- to 2.1-fold higher hippocampal neurogenesis than SED rats. Additionally, both moderate and brisk RE did not interfere with the recall of memory, although increasing amounts of RE proportionally enhanced neurogenesis. In conclusion, RE does not impair memory recall ability in a rat model despite substantially increasing neurogenesis. SIGNIFICANCE STATEMENT Running exercise (RE) improves new memory formation along with an increased neurogenesis in the hippocampus. In view of a recent study showing that RE-mediated increased hippocampal neurogenesis promotes forgetfulness in a mouse model, we ascertained whether a similar adverse phenomenon exists in a rat model. Memory recall ability examined 4 weeks after learning confirmed that animals that had run a mean of 78 km and displayed a 1.5- to 2.1-fold increase in hippocampal neurogenesis demonstrated similar proficiency for memory recall as animals that had remained sedentary. Furthermore, both moderate and brisk RE did not interfere with memory recall, although increasing amounts of RE proportionally enhanced neurogenesis, implying that RE has no adverse effects on memory recall.

Chronic oxidative stress, mitochondrial dysfunction, Nrf2 activation and inflammation in the hippocampus accompany heightened systemic inflammation and oxidative stress in an animal model of Gulf war illness

Memory and mood dysfunction are the key symptoms of Gulf war illness (GWI), a lingering multi-symptom ailment afflicting >200,000 veterans who served in the Persian Gulf War-1. Research probing the source of the disease has demonstrated that concomitant exposures to anti-nerve gas agent pyridostigmine bromide (PB), pesticides, and war-related stress are among the chief causes of GWI. Indeed, exposures to GWI-related chemicals (GWIR-Cs) and mild stress in animal models cause memory and mood impairments alongside reduced neurogenesis and chronic low-level inflammation in the hippocampus. In the current study, we examined whether exposure to GWIR-Cs and stress causes chronic changes in the expression of genes related to increased oxidative stress, mitochondrial dysfunction, and inflammation in the hippocampus. We also investigated whether GWI is linked with chronically increased activation of Nrf2 (a master regulator of antioxidant response) in the hippocampus, and inflammation and enhanced oxidative stress at the systemic level. Adult male rats were exposed daily to low-doses of PB and pesticides (DEET and permethrin), in combination with 5 min of restraint stress for 4 weeks. Analysis of the hippocampus performed 6 months after the exposure revealed increased expression of many genes related to oxidative stress response and/or antioxidant activity (Hmox1, Sepp1, and Srxn1), reactive oxygen species metabolism (Fmo2, Sod2, and Ucp2) and oxygen transport (Ift172 and Slc38a1). Furthermore, multiple genes relevant to mitochondrial respiration (Atp6a1, Cox6a1, Cox7a2L, Ndufs7, Ndufv1, Lhpp, Slc25a10, and Ucp1) and neuroinflammation (Nfkb1, Bcl6, Csf2, IL6, Mapk1, Mapk3, Ngf, N-pac, and Prkaca) were up-regulated, alongside 73–88% reduction in the expression of anti-inflammatory genes IL4 and IL10, and nuclear translocation and increased expression of Nrf2 protein. These hippocampal changes were associated with elevated levels of pro-inflammatory cytokines and chemokines (Tnfa, IL1b, IL1a, Tgfb, and Fgf2) and lipid peroxidation byproduct malondialdehyde in the serum, suggesting the presence of an incessant systemic inflammation and elevated oxidative stress. These results imply that chronic oxidative stress, inflammation, and mitochondrial dysfunction in the hippocampus, and heightened systemic inflammation and oxidative stress likely underlie the persistent memory and mood dysfunction observed in GWI.

Neural Stem Cell or Human Induced Pluripotent Stem Cell–Derived GABA‐ergic Progenitor Cell Grafting in an Animal Model of Chronic Temporal Lobe Epilepsy

Grafting of neural stem cells (NSCs) or GABA-ergic progenitor cells (GPCs) into the hippocampus could offer an alternative therapy to hippocampal resection in patients with drug-resistant chronic epilepsy, which afflicts >30% of temporal lobe epilepsy (TLE) cases. Multipotent, self-renewing NSCs could be expanded from multiple regions of the developing and adult brain, human embryonic stem cells (hESCs), and human induced pluripotent stem cells (hiPSCs). On the other hand, GPCs could be generated from the medial and lateral ganglionic eminences of the embryonic brain and from hESCs and hiPSCs. To provide comprehensive methodologies involved in testing the efficacy of transplantation of NSCs and GPCs in a rat model of chronic TLE, NSCs derived from the rat medial ganglionic eminence (MGE) and MGE-like GPCs derived from hiPSCs are taken as examples in this unit. The topics comprise description of the required materials, reagents and equipment, methods for obtaining rat MGE-NSCs and hiPSC-derived MGE-like GPCs in culture, generation of chronically epileptic rats, intrahippocampal grafting procedure, post-grafting evaluation of the effects of grafts on spontaneous recurrent seizures and cognitive and mood impairments, analyses of the yield and the fate of graft-derived cells, and the effects of grafts on the host hippocampus.

Gulf war illness-related chemicals increase CD11b/c+ monocyte infiltration into the liver and aggravate hepatic cholestasis in a rodent model

Gulf War Illness (GWI) is a chronic multisymptom disorder affecting veterans of the 1990–91 Gulf war. GWI was linked with exposure to chemicals including the nerve gas prophylactic drug pyridostigmine-bromide (PB) and pesticides (DEET, permethrin). Veterans with GWI exhibit prolonged, low-level systemic inflammation, though whether this impacts the liver is unknown. While no evidence exists that GWI-related chemicals are hepatotoxic, the prolonged inflammation may alter the liver’s response to insults such as cholestatic injury. We assessed the effects of GWI-related chemicals on macrophage infiltration and its subsequent influence on hepatic cholestasis. Sprague Dawley rats were treated daily with PB, DEET and permethrin followed by 15 minutes of restraint stress for 28 days. Ten weeks afterward, GWI rats or naïve age-matched controls underwent bile duct ligation (BDL) or sham surgeries. Exposure to GWI-related chemicals alone increased IL-6, and CD11b+F4/80− macrophages in the liver, with no effect on biliary mass or hepatic fibrosis. However, pre-exposure to GWI-related chemicals enhanced biliary hyperplasia and fibrogenesis caused by BDL, compared to naïve rats undergoing the same surgery. These data suggest that GWI patients could be predisposed to developing worse liver pathology due to sustained low-level inflammation of the liver when compared to patients without GWI.

Rhythms of Core Clock Genes and Spontaneous Locomotor Activity in Post-Status Epilepticus Model of Mesial Temporal Lobe Epilepsy

The interaction of Mesial Temporal Lobe Epilepsy (mTLE) with the circadian system control is apparent from an oscillatory pattern of limbic seizures, daytimes effect on seizure onset and the efficacy of antiepileptic drugs. Moreover, seizures per se can interfere with the biological rhythm output, including circadian oscillation of body temperature, locomotor activity, EEG pattern as well as the transcriptome. However, the molecular mechanisms underlying this cross-talk remain unclear. In this study, we systematically evaluated the temporal expression of seven core circadian transcripts (Bmal1, Clock, Cry1, Cry2, Per1, Per2, and Per3) and the spontaneous locomotor activity (SLA) in post-status epilepticus (SE) model of mTLE. Twenty-four hour oscillating SLA remained intact in post-SE groups although the circadian phase and the amount and intensity of activity were changed in early post-SE and epileptic phases. The acrophase of the SLA rhythm was delayed during epileptogenesis, a fragmented 24 h rhythmicity and extended active phase length appeared in the epileptic phase. The temporal expression of circadian transcripts Bmal1, Cry1, Cry2, Per1, Per2, and Per3 was also substantially altered. The oscillatory expression of Bmal1 was maintained in rats imperiled to SE, but with lower amplitude (A = 0.2) and an advanced acrophase in the epileptic phase. The diurnal rhythm of Cry1 and Cry2 was absent in the early post-SE but was recovered in the epileptic phase. Per1 and Per2 rhythmic expression were disrupted in post-SE groups while Per3 presented an arrhythmic profile in the epileptic phase, only. The expression of Clock did not display rhythmic pattern in any condition. These oscillating patterns of core clock genes may contribute to hippocampal 24 h cycling and, consequently to seizure periodicity. Furthermore, by using a pool of samples collected at 6 different Zeitgeber Times (ZT), we found that all clock transcripts were significantly dysregulated after SE induction, except Per3 and Per2. Collectively, altered SLA rhythm in early post-SE and epileptic phases implies a possible role for seizure as a nonphotic cue, which is likely linked to activation of hippocampal–accumbens pathway. On the other hand, altered temporal expression of the clock genes after SE suggests their involvement in the MTLE.