The developmental regulation of glutamate receptor-mediated calcium signaling in primary cultured rat hippocampal neurons

Androgens Regulate Tau Phosphorylation Through Phosphatidylinositol 3-Kinase-Protein Kinase B-Glycogen Synthase Kinase 3β Signaling

Age-related testosterone depletion in men is a risk factor for Alzheimer's disease (AD). How testosterone modulates AD risk remains to be fully elucidated, although regulation of tau phosphorylation has been suggested as a contributing protective action. To investigate the relationship between testosterone and tau phosphorylation, we first evaluated the effect of androgen status on tau phosphorylation in 3xTg-AD mice. Depletion of endogenous androgens via gonadectomy resulted in increased tau phosphorylation that was prevented by acute testosterone treatment. Parallel alterations in the phosphorylation of both glycogen synthase kinase 3β (GSK3β) and protein kinase B (Akt) suggest possible components of the underlying signaling pathway. To further explore mechanism, primary cultured neurons were treated with a physiological concentration of testosterone or its active metabolite dihydrotestosterone (DHT). Results showed that testosterone and DHT induced significant decreases in phosphorylated tau and significant increases in phosphorylation of Akt and GSK3β. Pharmacological inhibition of phosphatidylinositol 3-kinase (PI3K) effectively inhibited androgen-induced increases in Akt and GSK3β phosphorylation, and decreases in tau phosphorylation. In addition, androgen receptor (AR) knock-down by small interfering RNA prevented androgen-induced changes in the phosphorylation of Akt, GSK3β and tau, suggesting an AR-dependent mechanism. Additional experiments demonstrated androgen-induced changes in Akt, GSK3β and tau phosphorylation in AR-expressing PC12 cells but not in AR-negative PC12 cells. Together, these results suggest an AR-dependent pathway involving PI3K-Akt-GSK3β signaling through which androgens can reduce tau phosphorylation. These findings identify an additional protective mechanism of androgens that can improve neural health and inhibit development of AD.

Reduced expression of GluN2A induces a delay in neuron maturation

NMDA receptors (NMDARs) play an important role in synaptic plasticity both in physiological and pathological conditions. GluN2A and GluN2B are the most expressed NMDAR regulatory subunits, in the hippocampus and other cognitive-related brain structures. GluN2B is characteristic of immature structures and GluN2A of mature ones. Changes in GluN2A expression were associated with complex phenotypes that led to complex neurodevelopmental disorders, including the occurrence of seizures. However, little is known about the role of GluN2A in these phenotypes. In this work, we reduced GluN2A expression in mature neuronal cultures and observed an altered GluN2A/GluN2B ratio. Furthermore, those neurons exhibit an increase in immature dendritic spines and dendritic branching, as well as an increased response to glutamate stimulus. This phenotype (considering GluN2A/GluN2B ratio, index branching and glutamate response) resembles those observed at immature neuronal stages in vitro. We propose that this immature phenotype led to a higher response to glutamate stimulus which, in vivo, would be the basis of reduced threshold for seizure onset in GluN2A-pathological conditions.

High Frequency Electromagnetic Radiation Stimulates Neuronal Growth and Hippocampal Synaptic Transmission

Terahertz waves lie within the rotation and oscillation energy levels of biomolecules, and can directly couple with biomolecules to excite nonlinear resonance effects, thus causing conformational or configuration changes in biomolecules. Based on this mechanism, we investigated the effect pattern of 0.138 THz radiation on the dynamic growth of neurons and synaptic transmission efficiency, while explaining the phenomenon at a more microscopic level. We found that cumulative 0.138 THz radiation not only did not cause neuronal death, but that it promoted the dynamic growth of neuronal cytosol and protrusions. Additionally, there was a cumulative effect of terahertz radiation on the promotion of neuronal growth. Furthermore, in electrophysiological terms, 0.138 THz waves improved synaptic transmission efficiency in the hippocampal CA1 region, and this was a slow and continuous process. This is consistent with the morphological results. This phenomenon can continue for more than 10 min after terahertz radiation ends, and these phenomena were associated with an increase in dendritic spine density. In summary, our study shows that 0.138 THz waves can modulate dynamic neuronal growth and synaptic transmission. Therefore, 0.138 terahertz waves may become a novel neuromodulation technique for modulating neuron structure and function.

The laws and effects of terahertz wave interactions with neurons

Introduction: Terahertz waves lie within the energy range of hydrogen bonding and van der Waals forces. They can couple directly with proteins to excite non-linear resonance effects in proteins, and thus affect the structure of neurons. However, it remains unclear which terahertz radiation protocols modulate the structure of neurons. Furthermore, guidelines and methods for selecting terahertz radiation parameters are lacking. Methods: In this study, the propagation and thermal effects of 0.3-3 THz wave interactions with neurons were modelled, and the field strength and temperature variations were used as evaluation criteria. On this basis, we experimentally investigated the effects of cumulative radiation from terahertz waves on neuron structure. Results: The results show that the frequency and power of terahertz waves are the main factors influencing field strength and temperature in neurons, and that there is a positive correlation between them. Appropriate reductions in radiation power can mitigate the rise in temperature in the neurons, and can also be used in the form of pulsed waves, limiting the duration of a single radiation to the millisecond level. Short bursts of cumulative radiation can also be used. Broadband trace terahertz (0.1-2 THz, maximum radiated power 100 μW) with short duration cumulative radiation (3 min/day, 3 days) does not cause neuronal death. This radiation protocol can also promote the growth of neuronal cytosomes and protrusions. Discussion: This paper provides guidelines and methods for terahertz radiation parameter selection in the study of terahertz neurobiological effects. Additionally, it verifies that the short-duration cumulative radiation can modulate the structure of neurons.

The analgesic effect of trans-resveratrol is regulated by calcium channels in the hippocampus of mice

Resveratrol has been widely studied in terms of it's potential to slow the progression of many diseases. But little is known about the mechanism of action in neuropathic pain. Neuropathic pain is the main type of chronic pain associated with tissue injury. Calcium channels and calcium/caffeine-sensitive pools are associated with analgesic pathway involving neuropathic pain. Our previous study suggested that the antinociceptive effect of resveratrol was involved in Ca²⁺/calmodulin-dependent signaling in the spinal cord of mice. The aim of this study was to explore the involvement of Ca²⁺ in analgesic effects of trans-resveratrol in neuropathic pain and signal pathway in hippocampus. Hot plate test was used to assess antinociceptive response when mice were treated with trans-resveratrol alone or in combination with Mk 801, nimodipine, CaCl₂, ryanodine or EGTA. The effects of trans-resveratrol and the combination on Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and BDNF (brain-derived neurotrophic factor) expression in hippocampus were also investigated. The results showed that trans-resveratrol increased paw withdraw latency in the hot plate test. The effect of resveratrol was enhanced by Mk 801 and nimodipine. Central administration of Ca²⁺, however, abolished the antinociceptive effects of resveratrol. In contrast, centrally administered EGTA or ryanodine improved trans-resveratrol induced antinociception. There was a significant increase in p-CaMKII and BDNF expression in the hippocampus when resveratrol were combined with Mk 801, nimodipine, ryanodine and EGTA. Administration of CaCl₂ blocked changes in p-CaMKII and BDNF levels in the hippocampus. These findings suggest that trans-resveratrol exerts the effects of antinociception through regulation of calcium channels and calcium/caffeine-sensitive pools.

Mitochondrial ATP-Mg/Pi carrier SCaMC-3/Slc25a23 counteracts PARP-1-dependent fall in mitochondrial ATP caused by excitotoxic insults in neurons

Glutamate excitotoxicity is caused by sustained activation of neuronal NMDA receptors causing a large Ca(2+) and Na(+) influx, activation of poly(ADP ribose) polymerase-1 (PARP-1), and delayed Ca(2+) deregulation. Mitochondria undergo early changes in membrane potential during excitotoxicity, but their precise role in these events is still controversial. Using primary cortical neurons derived from mice, we show that NMDA exposure results in a rapid fall in mitochondrial ATP in neurons deficient in SCaMC-3/Slc25a23, a Ca(2+)-regulated mitochondrial ATP-Mg/Pi carrier. This fall is associated with blunted increases in respiration and a delayed decrease in cytosolic ATP levels, which are prevented by PARP-1 inhibitors or by SCaMC-3 activity promoting adenine nucleotide uptake into mitochondria. SCaMC-3 KO neurons show an earlier delayed Ca(2+) deregulation, and SCaMC-3-deficient mitochondria incubated with ADP or ATP-Mg had reduced Ca(2+) retention capacity, suggesting a failure to maintain matrix adenine nucleotides as a cause for premature delayed Ca(2+) deregulation. SCaMC-3 KO neurons have higher vulnerability to in vitro excitotoxicity, and SCaMC-3 KO mice are more susceptible to kainate-induced seizures, showing that early PARP-1-dependent fall in mitochondrial ATP levels, counteracted by SCaMC-3, is an early step in the excitotoxic cascade.

Defects During Mecp2 Null Embryonic Cortex Development Precede the Onset of Overt Neurological Symptoms

MeCP2 is associated with several neurological disorders; of which, Rett syndrome undoubtedly represents the most frequent. Its molecular roles, however, are still unclear, and data from animal models often describe adult, symptomatic stages, while MeCP2 functions during embryonic development remain elusive. We describe the pattern and timing of Mecp2 expression in the embryonic neocortex highlighting its low but consistent expression in virtually all cells and show the unexpected occurrence of transcriptional defects in the Mecp2 null samples at a stage largely preceding the onset of overt symptoms. Through the deregulated expression of ionic channels and glutamatergic receptors, the lack of Mecp2 during early neuronal maturation leads to the reduction in the neuronal responsiveness to stimuli. We suggest that such features concur to morphological alterations that begin affecting Mecp2 null neurons around the perinatal age and become evident later in adulthood. We indicate MeCP2 as a key modulator of the transcriptional mechanisms regulating cerebral cortex development. Neurological phenotypes of MECP2 patients could thus be the cumulative result of different adverse events that are already present at stages when no obvious signs of the pathology are evident and are worsened by later impairments affecting the central nervous system during maturation and maintenance of its functionality.

Loss of α1,6-Fucosyltransferase Decreases Hippocampal Long Term Potentiation: IMPLICATIONS FOR CORE FUCOSYLATION IN THE REGULATION OF AMPA RECEPTOR HETEROMERIZATION AND CELLULAR SIGNALING

Core fucosylation is catalyzed by α1,6-fucosyltransferase (FUT8), which transfers a fucose residue to the innermost GlcNAc residue via α1,6-linkage on N-glycans in mammals. We previously reported that Fut8-knock-out (Fut8(-/-)) mice showed a schizophrenia-like phenotype and a decrease in working memory. To understand the underlying molecular mechanism, we analyzed early form long term potentiation (E-LTP), which is closely related to learning and memory in the hippocampus. The scale of E-LTP induced by high frequency stimulation was significantly decreased in Fut8(-/-) mice. Tetraethylammonium-induced LTP showed no significant differences, suggesting that the decline in E-LTP was caused by postsynaptic events. Unexpectedly, the phosphorylation levels of calcium/calmodulin-dependent protein kinase II (CaMKII), an important mediator of learning and memory in postsynapses, were greatly increased in Fut8(-/-) mice. The expression levels of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) in the postsynaptic density were enhanced in Fut8(-/-) mice, although there were no significant differences in the total expression levels, implicating that AMPARs without core fucosylation might exist in an active state. The activation of AMPARs was further confirmed by Fura-2 calcium imaging using primary cultured neurons. Taken together, loss of core fucosylation on AMPARs enhanced their heteromerization, which increase sensitivity for postsynaptic depolarization and persistently activate N-methyl-d-aspartate receptors as well as Ca(2+) influx and CaMKII and then impair LTP.

The major cholesterol metabolite cholestane-3β,5α,6β-triol functions as an endogenous neuroprotectant

Overstimulation of NMDA-type glutamate receptors is believed to be responsible for neuronal death of the CNS in various disorders, including cerebral and spinal cord ischemia. However, the intrinsic and physiological mechanisms of modulation of these receptors are essentially unknown. Here we report that cholestane-3β,5α,6β-triol (triol), a major metabolite of cholesterol, is an endogenous neuroprotectant and protects against neuronal injury both in vitro and in vivo via negative modulation of NMDA receptors. Treatment of cultured neurons with triol protects against glutamate-induced neurotoxicity, and administration of triol significantly decreases neuronal injury after spinal cord ischemia in rabbits and transient focal cerebral ischemia in rats. An inducible elevation of triol is associated with ischemic preconditioning and subsequent neuroprotection in the spinal cord of rabbits. This neuroprotection is effectively abolished by preadministration of a specific inhibitor of triol synthesis. Physiological concentrations of triol attenuate [Ca(2+)]i induced by glutamate and decrease inward NMDA-mediated currents in cultured cortical neurons and HEK-293 cells transiently transfected with NR1/NR2B NMDA receptors. Saturable binding of [(3)H]triol to cerebellar granule neurons and displacement of [(3)H]MK-801 binding to NMDA receptors by triol suggest that direct blockade of NMDA receptors may underlie the neuroprotective properties. Our findings suggest that the naturally occurring oxysterol, the major cholesterol metabolite triol, functions as an endogenous neuroprotectant in vivo, which may provide novel insights into understanding and developing potential therapeutics for disorders in the CNS.