Fibrotic scar model and TGF-β1 differently modulate action potential firing and voltage-dependent ion currents in hippocampal neurons in primary culture

Transforming growth factor-beta 1 enhances discharge activity of cortical neurons

JOURNAL/nrgr/04.03/01300535-202502000-00031/figure1/v/2024-05-28T214302Z/r/image-tiff Transforming growth factor-beta 1 (TGF-β1) has been extensively studied for its pleiotropic effects on central nervous system diseases. The neuroprotective or neurotoxic effects of TGF-β1 in specific brain areas may depend on the pathological process and cell types involved. Voltage-gated sodium channels (VGSCs) are essential ion channels for the generation of action potentials in neurons, and are involved in various neuroexcitation-related diseases. However, the effects of TGF-β1 on the functional properties of VGSCs and firing properties in cortical neurons remain unclear. In this study, we investigated the effects of TGF-β1 on VGSC function and firing properties in primary cortical neurons from mice. We found that TGF-β1 increased VGSC current density in a dose- and time-dependent manner, which was attributable to the upregulation of Nav1.3 expression. Increased VGSC current density and Nav1.3 expression were significantly abolished by preincubation with inhibitors of mitogen-activated protein kinase kinase (PD98059), p38 mitogen-activated protein kinase (SB203580), and Jun NH2-terminal kinase 1/2 inhibitor (SP600125). Interestingly, TGF-β1 significantly increased the firing threshold of action potentials but did not change their firing rate in cortical neurons. These findings suggest that TGF-β1 can increase Nav1.3 expression through activation of the ERK1/2-JNK-MAPK pathway, which leads to a decrease in the firing threshold of action potentials in cortical neurons under pathological conditions. Thus, this contributes to the occurrence and progression of neuroexcitatory-related diseases of the central nervous system.

The Role of Neuroinflammatory Mediators in the Pathogenesis of Traumatic Brain Injury: A Narrative Review

Traumatic brain injury (TBI) is a debilitating acquired neurological disorder that afflicts nearly 74 million people worldwide annually. TBI has been classified as more than just a single insult because of its associated risk toward various long-term neurological and neurodegenerative disorders. This risk may be triggered by a series of postinjury secondary molecular and cellular pathology, which may be dependent on the severity of the TBI. Among the secondary injury mechanisms, neuroinflammation may be the most crucial as it may exacerbate brain damage and lead to fatal consequences when prolonged. This Review aimed to elucidate the influence of neuroinflammatory mediators on the TBI functional and pathological outcomes, particularly focusing on inflammatory cytokines which were associated with neuronal dysfunctions in the acute and chronic stages of TBI. These cytokines include interleukins (IL) such as IL-1(beta)β, IL-4, IL-6, IL8, IL-10, IL-18, IL-33 and tumor necrosis factor alpha (TNF-α), which have been extensively studied. Apart from these, IL-2, interferon gamma (IFN-γ), and transforming growth factor-beta (TGF-β) may also play a significant role in the pathogenesis of TBI. These neuroinflammatory mediators may trigger a series of pathological events such as cell death, microglial suppression, and increased catecholaminergic activity. Interestingly, in the acute phase of TBI, most of these mediators may also play a neuroprotective role by displaying anti-inflammatory properties, which may convert to a pro-inflammatory action in the chronic stages post TBI. Early identification and treatment of these mediators may help the development of more effective treatment options for TBI.

Delta-opioid receptor-mediated modulation of excitability of individual hippocampal neurons: mechanisms involved

BACKGROUND

Delta-opioid receptor (DOR)-mediated modulation of hippocampal neural networks is involved in emotions, cognition, and in pathophysiology and treatment of mood disorders. In this study, we examined the effects of DOR agonist (SNC80) and antagonist (naltrindole) on the excitability of individual hippocampal neurons.

METHODS

Primary neuronal cultures were prepared from hippocampi of newborn rats and cultivated in vitro for 8-14 days (DIV8-14). The effects of SNC80 naltrindole on evoked and spontaneous action potentials (APs) were measured at DIV8-9 and DIV13-14, respectively.

RESULTS

SNC80 (100 µM) potentiated spontaneous AP firing and stimulated sodium current; naltrindole had opposite effects. The stimulatory effect of 100 µM of SNC80 was revoked by pre-administration of 1 µM of naltrindole. SNC80 and naltrindole induced similar inhibitory effects on the evoked AP firing and on the calcium current. Further, SNC80 inhibited both peak and sustained potassium currents. Naltrindole had no effect on potassium currents.

CONCLUSION

We suggest that the effects of naltrindole and high concentration of SNC80 on the sodium currents are mediated via DORs and underlying the changes in spontaneous activity. The inhibitory effects of SNC80 on calcium and potassium currents might also be DOR-dependent; these currents might mediate SNC80 effect on the evoked AP firing. The inhibitory effects of naltrindole on calcium and of low doses of SNC80 on sodium currents might be however DOR independent. The behavioral effects of SNC80 and naltrindole, observed in previous studies, might be mediated, at least in part, via the modulatory effect of these ligands on the excitability of hippocampal neurons.

Role of proteoglycans in neuro-inflammation and central nervous system fibrosis

Fibrosis is defined as the thickening and scarring of connective tissue, usually as a consequence of tissue damage. The central nervous system (CNS) is special in the sense that fibrogenic cells are restricted to vascular and meningeal areas. Inflammation and the disruption of the blood-brain barrier can lead to the infiltration of fibroblasts and trigger fibrotic response. While the initial function of the fibrotic tissue is to restore the blood-brain barrier and to limit the site of injury, it also demolishes the structure of extracellular matrix and impedes the healing process by producing inhibitory molecules and forming a physical and biochemical barrier that prevents axon regeneration. As a major constituent in the extracellular matrix, proteoglycans participate in the neuro-inflammation, modulating the fibrotic process. In this review, we will discuss the pathophysiology of fibrosis during acute injuries of the CNS, as well as during chronic neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and age-related neurodegeneration with focus on the functional roles of proteoglycans.