Axonal regeneration is compromised in NFH-LacZ transgenic mice but not in NFH-GFP mice

Neurofilaments in health and Charcot-Marie-Tooth disease

Neurofilaments (NFs) are the most abundant component of mature neurons, that interconnect with actin and microtubules to form the cytoskeleton. Specifically expressed in the nervous system, NFs present the particularity within the Intermediate Filament family of being formed by four subunits, the neurofilament light (NF-L), medium (NF-M), heavy (NF-H) proteins and α-internexin or peripherin. Here, we review the current knowledge on NF proteins and neurofilaments, from their domain structures and their model of assembly to the dynamics of their transport and degradation along the axon. The formation of the filament and its behaviour are regulated by various determinants, including post-transcriptional (miRNA and RBP proteins) and post-translational (phosphorylation and ubiquitination) modifiers. Altogether, the complex set of modifications enable the neuron to establish a stable but elastic NF array constituting the structural scaffold of the axon, while permitting the local expression of NF proteins and providing the dynamics necessary to fulfil local demands and respond to stimuli and injury. Thus, in addition to their roles in mechano-resistance, radial axonal outgrowth and nerve conduction, NFs control microtubule dynamics, organelle distribution and neurotransmission at the synapse. We discuss how the studies of neurodegenerative diseases with NF aggregation shed light on the biology of NFs. In particular, the NEFL and NEFH genes are mutated in Charcot-Marie-Tooth (CMT) disease, the most common inherited neurological disorder of the peripheral nervous system. The clinical features of the CMT forms (axonal CMT2E, CMT2CC; demyelinating CMT1F; intermediate I-CMT) with symptoms affecting the central nervous system (CNS) will allow us to further investigate the physiological roles of NFs in the brain. Thus, NF-CMT mouse models exhibit various degrees of sensory-motor deficits associated with CNS symptoms. Cellular systems brought findings regarding the dominant effect of NF-L mutants on NF aggregation and transport, although these have been recently challenged. Neurofilament detection without NF-L in recessive CMT is puzzling, calling for a re-examination of the current model in which NF-L is indispensable for NF assembly. Overall, we discuss how the fundamental and translational fields are feeding each-other to increase but also challenge our knowledge of NF biology, and to develop therapeutic avenues for CMT and neurodegenerative diseases with NF aggregation.

The dazzling rise of neurofilaments: Physiological functions and roles as biomarkers

In the last two years, neurofilaments (NFs) have become one of the most blazing topics in clinical neuroscience. NFs are major cytoskeletal constituents of neurons, can be detected in body fluids, and have recently emerged as universal biomarkers of neuronal injury and neurological diseases. This review will examine the evolving landscape of NFs, from their specific cellular functions within neurons to their broad clinical value as biomarkers. Particular attention will be given to the dynamic nature of the NF network and its novel roles in microtubule regulation, neurotransmission, and nanomedicine. Building from the initial evidence of causative mutations in NF genes in Charcot-Marie-Tooth diseases, the latest advances at the frontiers of basic and clinical sciences have expanded the scope and relevance of NFs for human health remarkably and have poised to fuel innovation in cell biology and neuroscience.

Effects of Tianeptine on Adult Rats Following Prenatal Stress

Objective

Exposing a pregnant female to stress during the critical period of embryonic fetal brain development increases the risk of psychiatric disorders in the offspring. The objective of this study was to investigate the effect of antidepressant tianeptine on prenatally stressed (PNS) rats.

Methods

In this study, a repeated variable stress paradigm was applied to pregnant rats during the last week of gestation. To investigate the effects of antidepressant tianeptine on PNS rats, behavioral and protein expression analyses were performed. Forced swim test, open field test, and social interaction test were performed to determine changes in PNS rats compared to non-stressed offspring. Haloperidol was used as a positive control as an antipsychotic drug based on previous studies.

Results

Behavioral changes were restored after treatment with tianeptine or haloperidol. Western blot and immunohistochemical analyses of the prefrontal cortex revealed downregulation of several neurodevelopmental proteins in PNS rats. After treatment with tianeptine or haloperidol, their expression levels were increased.

Conclusion

Downregulation of several proteins in PNS rats might have caused subsequent behavioral changes in PNS rats. After tianeptine or haloperidol treatment, behavioral changes in PNS rats were restored. Therefore, tianeptine might decrease incidence of prenatal stress related-psychiatric disorders such as depression and schizophrenia.

Dynamic Expression of Serotonin Receptor 5-HT3A in Developing Sensory Innervation of the Lower Urinary Tract

Sensory afferent signaling is required for normal function of the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction and pelvic pain syndromes, few effective treatment options are available. Serotonin receptor 5-HT3A is a known mediator of visceral afferent signaling and has been implicated in bladder function. However, basic expression patterns for this gene and others among developing bladder sensory afferents that could be used to inform regenerative efforts aimed at treating deficiencies in pelvic innervation are lacking. To gain greater insight into the molecular characteristics of bladder sensory innervation, we conducted a thorough characterization of Htr3a expression in developing and adult bladder-projecting lumbosacral dorsal root ganglia (DRG) neurons. Using a transgenic Htr3a-EGFP reporter mouse line, we identified 5-HT3A expression at 10 days post coitus (dpc) in neural crest derivatives and in 12 dpc lumbosacral DRG. Using immunohistochemical co-localization we observed Htr3a-EGFP expression in developing lumbosacral DRG that partially coincides with neuropeptides CGRP and Substance P and capsaicin receptor TRPV1. A majority of Htr3a-EGFP+ DRG neurons also express a marker of myelinated Aδ neurons, NF200. There was no co-localization of 5-HT3A with the TRPV4 receptor. We employed retrograde tracing in adult Htr3a-EGFP mice to quantify the contribution of 5-HT3A+ DRG neurons to bladder afferent innervation. We found that 5-HT3A is expressed in a substantial proportion of retrograde traced DRG neurons in both rostral (L1, L2) and caudal (L6, S1) axial levels that supply bladder innervation. Most bladder-projecting Htr3a-EGFP+ neurons that co-express CGRP, Substance P, or TRPV1 are found in L1, L2 DRG, whereas Htr3a-EGFP+, NF200+ bladder-projecting neurons are from the L6, S1 axial levels. Our findings contribute much needed information regarding the development of LUT innervation and highlight the 5-HT3A serotonin receptor as a candidate for future studies of neurally mediated bladder control.

Influence of Panax ginseng on the offspring of adult rats exposed to prenatal stress

The exposure of pregnant females to stress during a critical period of fetal brain development is an environmental risk factor for the development of schizophrenia in adult offspring. Schizophrenia is a group of common mental disorders of unclear origin, affecting approximately 1% of the global population, showing a generally young age at onset. In the present study, a repeated variable stress paradigm was applied to pregnant rats during the final week of gestation. The effects of an extract of Panax ginseng C.A. Meyer (PG) on rats exposed to prenatal stress (PNS) were investigated in terms of behavioral activity and protein expression analyses. In the behavioral tests, grooming behavior in a social interaction test, line-crossing behavior in an open-field test and swimming activity in a forced-swim test were decreased in the rats exposed to PNS compared with the non-stressed offspring; the changes in behavioral activity were reversed upon oral treatment with PG (300 mg/kg). Subsequently, western blot analysis and immunohistochemical analyses of the prefrontal cortex and hippocampus revealed that the downregulation of several neurodevelopmental genes which occurred following exposure to PNS was reversed upon treatment with PG. The current findings demonstrate that the downregulation of several genes following exposure to PNS may affect subsequent behavioral changes, and that these phenomena are reversed following treatment with PG during pregnancy. Our results suggest that oral treatment with PG reduces the incidence of psychiatric disorders, such as schizophrenia.

Chronic proximal axonopathy in rats is associated with long-standing neurofilament depletion in neuromuscular junctions and behavioral deficits

In rodents exposed to 3,3'-iminodipropionitrile (IDPN), neurofilaments (NFs) accumulate in swollen proximal axon segments; this also occurs in motor neurons of patients with amyotrophic lateral sclerosis. We hypothesized that early loss of NFs in neuromuscular junctions (NMJs) in IDPN proximal neuropathy would result in neuromuscular dysfunction and lead to neuromuscular detachment. Adult male rats were given 0 or 15 mmol/L IDPN in drinking water for up to 1 year. The IDPN-exposed rats dragged their tails and had impaired endurance in a grip test. Neuromuscular junctions and distal axons were examined in the levator auris longus muscle after 3, 6, 9, and 12 months. Neuromuscular junctions showed a progressive reduction in NF immunolabeling, which became undetectable in up to 70% of the NMJs after 12 months. Neurofilament labeling was also reduced in preterminal axons and in a more proximal axon level within the muscle. Triple-label analysis with antisyntaxin demonstrated that the terminals remained in place and usually contained a few minute NF bundles. Electron microscopy revealed the disappearance of terminal NFs, reduced content in synaptic vesicles, and accumulation of multilamellar bodies, but scant degeneration. Thus, IDPN proximal neurofilamentous axonopathy is associated with NF depletion in motor terminals; motor weakness and structural changes in the NMJs suggest impaired synaptic function despite long-term preservation of the NMJs.