Effect of α7nAChR on learning and memory dysfunction in a rat model of diffuse axonal injury

Enhancing cognitive recovery in chronic traumatic brain injury through simultaneous allosteric modulation of α7 nicotinic acetylcholine and α5 GABAA receptors

Traumatic brain injury (TBI) leads to changes in the neural circuitry of the hippocampus that result in chronic learning and memory deficits. However, effective therapeutic strategies to ameliorate these chronic learning and memory impairments after TBI are limited. Two pharmacological targets for enhancing cognition are nicotinic acetylcholine receptors (nAChRs) and GABAA receptors (GABAARs), both of which regulate hippocampal network activity to form declarative memories. A promising compound, 522-054, both allosterically enhances α7 nAChRs and inhibits α5 subunit-containing GABAARs. Administration of 522-054 enhances long-term potentiation (LTP) and cognitive functioning in non-injured animals. In this study, we assessed the effects of 522-054 on hippocampal synaptic plasticity and learning and memory deficits in the chronic post-TBI recovery period. Adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury or sham surgery. At 12 wk after injury, we assessed basal synaptic transmission and LTP at the Schaffer collateral-CA1 synapse of the hippocampus. Bath application of 522-054 to hippocampal slices reduced deficits in basal synaptic transmission and recovered TBI-induced impairments in LTP. Moreover, treatment of animals with 522-054 at 12 wk post-TBI improved cue and contextual fear memory and water maze acquisition and retention without a measurable effect on cortical or hippocampal atrophy. These results suggest that dual allosteric modulation of α7 nAChR and α5 GABAAR signaling may be a potential therapy for treating cognitive deficits during chronic recovery from TBI.

Remimazolam Attenuates LPS-Derived Cognitive Dysfunction via Subdiaphragmatic Vagus Nerve Target α7nAChR-Mediated Nrf2/HO-1 Signal Pathway

Sepsis-induced neuroinflammation is significantly associated with sepsis-related brain dysfunction. Remimazolam is a novel ultra-short-acting benzodiazepine anesthetic with multiple organ protective effects. However, it is unknown whether remimazolam can ameliorate LPS-induced brain impairment. In this study, Lipopolysaccharide (5 mg/kg, LPS) severely impaired Sprague-Dawley rats spatial learning ability, memory, and cognitive function. However, remimazolam treatment showed a protective effect on LPS-induced cognitive dysfunction. Remimazolam partly reversed LPS-induced splenomegaly, decreased serum cytokine expression, suppressed hippocampal M1 microglial activation, and mitigated oxidative stress injury and neuroinflammation. Electroacupuncture (EA) or PNU282987 treatment improved LPS-induced cognitive dysfunction and also significantly inhibited neuroinflammation and systemic inflammation. However, MLA, ML385, or subdiaphragmatic vagus nerve (SDV) treatment abolished the protective effects of remimazolam. Further mechanistic studies showed that remimazolam induces protective effects by activating subdiaphragmatic vagus nerve target α7nAChR-mediated Nrf2/HO-1 signaling pathway. These results demonstrate that remimazolam can up-regulate α7nAChR, Cyto-Nrf2, HO-1, and cognitive-related (CREB, BDNF, PSD95) protein expressions, suppress M1 microglia, ameliorate neuroinflammation or systemic inflammation, and reverse cognitive dysfunction. Therefore, this study provides insight into a new therapeutic target for the treatment of sepsis-induced cerebral dysfunction.

Traumatic axonal injury (TAI): definitions, pathophysiology and imaging-a narrative review

Introduction

Traumatic axonal injury (TAI) is a condition defined as multiple, scattered, small hemorrhagic, and/or non-hemorrhagic lesions, alongside brain swelling, in a more confined white matter distribution on imaging studies, together with impaired axoplasmic transport, axonal swelling, and disconnection after traumatic brain injury (TBI). Ever since its description in the 1980s and the grading system by Adams et al., our understanding of the processes behind this entity has increased.

Methods

We performed a scoping systematic, narrative review by interrogating Ovid MEDLINE, Embase, and Google Scholar on the pathophysiology, biomarkers, and diagnostic tools of TAI patients until July 2020.

Results

We underline the misuse of the Adams classification on MRI without proper validation studies, and highlight the hiatus in the scientific literature and areas needing more research. In the past, the theory behind the pathophysiology relied on the inertial force exerted on the brain matter after severe TBI inducing a primary axotomy. This theory has now been partially abandoned in favor of a more refined theory involving biochemical processes such as protein cleavage and DNA breakdown, ultimately leading to an inflammation cascade and cell apoptosis, a process now described as secondary axotomy.

Conclusion

The difference in TAI definitions makes the comparison of studies that report outcomes, treatments, and prognostic factors a daunting task. An even more difficult task is isolating the outcomes of isolated TAI from the outcomes of severe TBI in general. Targeted bench-to-bedside studies are required in order to uncover further pathways involved in the pathophysiology of TAI and, ideally, new treatments.