Microtubule-associated protein 2 (MAP2) expression during synaptic plasticity in the guinea pig cochlea

The Missing Piece? A Case for Microglia's Prominent Role in the Therapeutic Action of Anesthetics, Ketamine, and Psychedelics

There is much excitement surrounding recent research of promising, mechanistically novel psychotherapeutics - psychedelic, anesthetic, and dissociative agents - as they have demonstrated surprising efficacy in treating central nervous system (CNS) disorders, such as mood disorders and addiction. However, the mechanisms by which these drugs provide such profound psychological benefits are still to be fully elucidated. Microglia, the CNS's resident innate immune cells, are emerging as a cellular target for psychiatric disorders because of their critical role in regulating neuroplasticity and the inflammatory environment of the brain. The following paper is a review of recent literature surrounding these neuropharmacological therapies and their demonstrated or hypothesized interactions with microglia. Through investigating the mechanism of action of psychedelics, such as psilocybin and lysergic acid diethylamide, ketamine, and propofol, we demonstrate a largely under-investigated role for microglia in much of the emerging research surrounding these pharmacological agents. Among others, we detail sigma-1 receptors, serotonergic and γ-aminobutyric acid signalling, and tryptophan metabolism as pathways through which these agents modulate microglial phagocytic activity and inflammatory mediator release, inducing their therapeutic effects. The current review includes a discussion on future directions in the field of microglial pharmacology and covers bidirectional implications of microglia and these novel pharmacological agents in aging and age-related disease, glial cell heterogeneity, and state-of-the-art methodologies in microglial research.

Neural presbycusis at ultra-high frequency in aged common marmosets and rhesus monkeys

The aging of the population and environmental noise have contributed to high rates of presbycusis, also known as age-related hearing loss (ARHL). Because mice have a relatively short life span, murine models have not been suitable for determining the mechanism of presbycusis development and methods of diagnosis. Although the common marmoset, a non-human primate (NHP), is an ideal animal model for studying age-related diseases, its auditory spectrum has not been systematically studied. Auditory brainstem responses (ABRs) from 38 marmosets of different ages demonstrated that auditory function correlated with age. Hearing loss in geriatric common marmosets started at ultra-high frequency (>16 kHz), then extended to lower frequencies. Despite age-related deterioration of ABR threshold and amplitude in marmosets, outer hair cell (OHC) function remained stable at all ages. Spiral ganglion neurons (SGNs), which are the first auditory neurons in the auditory system, were found to degenerate distinctly in aged common marmosets, indicating that neural degeneration caused presbycusis in these animals. Similarly, age-associated ABR deterioration without loss of OHC function was observed in another NHP, rhesus monkeys. Audiometry results from these two species of NHP suggested that NHPs were ideal for studying ARHL and that neural presbycusis at high frequency may be prevalent in primates.

Recent development of AAV-based gene therapies for inner ear disorders

Gene therapy for auditory diseases is gradually maturing. Recent progress in gene therapy treatments for genetic and acquired hearing loss has demonstrated the feasibility in animal models. However, a number of hurdles, such as lack of safe viral vector with high efficiency and specificity, robust deafness large animal models, translating animal studies to clinic etc., still remain to be solved. It is necessary to overcome these challenges in order to effectively recover auditory function in human patients. Here, we review the progress made in our group, especially our efforts to make more effective and cell type-specific viral vectors for targeting cochlea cells.

Effects of neuritin on the differentiation of bone marrow‑derived mesenchymal stem cells into neuron‑like cells

While the neurotrophic factor neuritin is known to be involved in neurodevelopment, the effects of this compound on cell differentiation remain unclear. The present study demonstrated that neuritin treatment induced the differentiation of rat bone marrow-derived mesenchymal stem cells (rBM-MSCs) into neuron-like (NL) cells. For these analyses, rBM-MSCs were incubated with 0.5 µg/ml neuritin for 24 h. Following induction, 27% of the rBM-MSCs exhibited typical NL cell morphologies. Subsequently, NL cells were characterized by examining the expression of neuronal markers and by analysis of cell functions. The findings demonstrated that the NL cells produced by neuritin treatment expressed the neuronal markers neuron-specific enolase and microtubule associate protein 2, and secreted the neurotransmitter 5-hydroxytryptamine. Furthermore, the NL cells exhibited certain partial neural-electrophysiological functions. In conclusion, neuritin treatment may be an effective method for inducing the differentiation of BM-MSCs towards NL cells. This may provide an alternative, potentially complementary tool for disease modeling and the development of cell-based therapies.

N-acetylcysteine treatment attenuates the cognitive impairment and synaptic plasticity loss induced by streptozotocin

Alzheimer's disease (AD) is a neurodegenerative disorder pathologically characterized by severe neuronal and glial structural changes and progressive cognitive decline. N-acetylcysteine (NAC) is a well-known pharmacological agent with pro-neurogenic properties and neuroprotective effects. In this study, we evaluated NAC protective effects on cognitive impairment and associated pathological markers in a streptozotocin (STZ)-induced sporadic dementia of AD type mice model. Animals were divided into six groups: I) Sham, II) NAC, III) physostigmine (PHY), IV) STZ, V) NAC + STZ and VI) PHY + NAC. NAC (5 mg/kg) and PHY (0.25 mg/kg) were administrated orally for 30 consecutive days and STZ (2.5 mg/kg) intracerebroventricularly at the first and third days. Novel object recognition (NOR, days 26-27) and Morris water maze (MWM, days 26-30) tasks were assessed to evaluate learning and memory. On the thirty-first day animals were euthanized and brains collected for biochemical analysis. Interestingly, our results showed that STZ treatment induced cognitive impairment in mice in the NOR and MWM tasks. Both NAC and PHY treatments prevented from this impairment. The increase in AChE activity and decrease in pTrkB and MnSOD levels caused by STZ in the cerebral cortex and hippocampus, were prevented by the NAC and PHY treatments. The decrease in SYN, MAP2 and GFAP expressions were also prevented by NAC and PHY treatments. In conclusion, NAC treatment prevented the cognitive impairment induced by STZ, normalizing the AChE activity and rescuing the synaptic plasticity loss. Our results suggest that NAC is a promising therapeutic strategy for the treatment of AD.

Oxidative stress, inflammation, and autophagic stress as the key mechanisms of premature age-related hearing loss in SAMP8 mouse Cochlea

AIMS

In our aging society, age-related hearing loss (ARHL) or presbycusis is increasingly important. Here, we study the mechanism of ARHL using the senescence-accelerated mouse prone 8 (SAMP8) which is a useful model to probe the effects of aging on biological processes.

RESULTS

We found that the SAMP8 strain displays premature hearing loss and cochlear degeneration recapitulating the processes observed in human presbycusis (i.e., strial, sensory, and neural degeneration). The molecular mechanisms associated with premature ARHL in SAMP8 mice involve oxidative stress, altered levels of antioxidant enzymes, and decreased activity of Complexes I, II, and IV, which in turn lead to chronic inflammation and triggering of apoptotic cell death pathways. In addition, spiral ganglion neurons (SGNs) also undergo autophagic stress and accumulated lipofuscin.

INNOVATION AND CONCLUSION

Our results provide evidence that targeting oxidative stress, chronic inflammation, or apoptotic pathways may have therapeutic potential. Modulation of autophagy may be another strategy. The fact that autophagic stress and protein aggregation occurred specifically in SGNs also offers promising perspectives for the prevention of neural presbycusis.

Physiology, pharmacology and plasticity at the inner hair cell synaptic complex

This report summarizes recent neuropharmacological data at the IHC afferent/efferent synaptic complex: the type of Glu receptors and transporter involved and the modulation of this fast synaptic transmission by the lateral efferents. Neuropharmacological data were obtained by coupling the recording of cochlear potentials and single unit of the auditory nerve with intra-cochlear applications of drugs (multi-barrel pipette). We also describe the IHC afferent/efferent functioning in pathological conditions. After acoustic trauma or ischemia, acute disruption of IHC-auditory dendrite synapses are seen. However, a re-growth of the nerve fibres and a re-afferentation of the IHC were completely done 5 days after injury. During this synaptic repair, multiple presynaptic bodies were commonly found, either linked to the membrane or "floating" in ectopic positions. In the meantime, the lateral efferents directly contact the IHCs. The demonstration that NMDA receptors blockade delayed the re-growth of neurites suggests a neurotrophic role of NMDA receptors in pathological conditions.