The neuropeptide calcitonin gene-related peptide (CGRP) is known to play a pro-nociceptive role after peripheral nerve injury upon its release from primary afferent neurons in preclinical models of neuropathic pain. We previously demonstrated a critical role for spinal cord microglial CD40 in the development of spinal nerve L5 transection (L5Tx)-induced mechanical hypersensitivity. Herein, we investigated whether CGRP is involved in the CD40-mediated behavioral hypersensitivity. First, L5Tx was found to significantly induce CGRP expression in wild-type (WT) mice up to 14 days post-L5Tx. This increase in CGRP expression was reduced in CD40 knockout (KO) mice at day 14 post-L5Tx. Intrathecal injection of the CGRP antagonist CGRP8-37 significantly blocked L5Tx-induced mechanical hypersensitivity. In vitro, CGRP induced glial IL-6 and CCL2 production, and CD40 stimulation added to the effects of CGRP in neonatal glia. Further, there was decreased CCL2 production in CD40 KO mice compared to WT mice 21 days post-L5Tx. However, CGRP8-37 did not significantly affect spinal cord CCL2 production following L5Tx in WT mice. Altogether, these data suggest that CD40 contributes to the maintenance of behavioral hypersensitivity following peripheral nerve injury in part through two distinct pathways, the enhancement of CGRP expression and spinal cord CCL2 production.
Vinpocetine has long been used for cerebrovascular disorders and cognitive impairment. Based on the evidence that the translocator protein (TSPO, 18 kDa) was expressed in activated microglia, while Vinpocetine was able to bind TSPO, we explored the role of Vinpocetine on microglia treated with lipopolysaccharide (LPS) and oxygen-glucose deprivation (OGD) in vitro. Our results show that both LPS and OGD induced the up-regulation of TSPO expression on BV-2 microglia by RT-PCR, western blot and immunocytochemistry. Vinpocetine inhibited the production of nitrite oxide and inflammatory factors such as interleukin-1β (IL-1β), IL-6 and tumour necrosis factor-α (TNF-α) in BV-2 microglia, in which cells were treated with LPS or exposed to OGD, regardless of the time Vinpocetine was added. Next, we measured cell death-related molecules Akt, Junk and p38 as well as inflammation-related molecules nuclear factor-κB (NF-κB) and activator protein-1 (AP-1). Vinpocetine did not change cell death-related molecules, but inhibited the expression of NF-κB and AP-1 in LPS-stimulated microglia, indicating that Vinpocetine has an anti-inflammatory effect by partly targeting NF-κB/AP-1. Next, conditioned medium from Vinpocetine-treated microglia protected from primary neurons. As compared with in vitro, the administration of Vinpocetine in hypoxic mice also inhibited inflammatory molecules, indicating that Vinpocetine as a unique anti-inflammatory agent may be beneficial for the treatment of neuroinflammatory diseases.
Modulation of astroglial components involved in reactive postlesional responses in the rat cerebral cortex was analyzed following exposure to environmental enrichment (EE) condition prior to injury. For this purpose, changes in % immunoreactive (IR) area of GFAP, vimentin, EAAT1 and ezrin were evaluated in the perilesional zone after placing a cortical stab wound in the visual cerebral cortex of adult rats. GFAP-IR postlesional reactive astrocytosis in the perilesional cortex was significantly lower in the animal group exposed to EE during postnatal development. This GFAP-IR reaction seems to be associated with existing astroglia, because neither BrdU- nor endogenous Ki-67-labeled nuclei were found in the perilesional cortex analyzed. Increased ezrin-IR area in the visual cortex of rats exposed to EE condition suggests the formation of new synapses or the enhancement of astroglial involvement in the existing ones. No effects of EE were found on either EAAT1- or vimentin-IR area. Results suggest that exposure to EE conditions prior to injury attenuates the postlesional astroglia GFAP-response in the perilesional cortex of rats. Whether this attenuated postlesional astroglia GFAP-response promotes or not protective effects on the cortical neuropil remains to be explored in futures studies.
Previously studied for its role in processing olfactory information in the antennal lobe, GABA also may shape development of the olfactory pathway, acting either through or on glial cells. Early in development, the dendrites of GABAergic neurons extend to the glial border that surrounds the nascent olfactory lobe neuropil. These neuropil glia express both GABAA and GABAB receptors, about half of the glia in acute cultures responded to GABA with small outward currents, and about a third responded with small transient increases in intracellular calcium. The neuronal classes that express GABA in vivo, the local interneurons and a subset of projection neurons, also do so in culture. Exposure to GABA in culture increased the size and complexity of local interneurons, but had no effect on glial morphology. The presence of glia alone did not affect neuronal morphology, but in the presence of both glia and GABA, the growth-enhancing effects of GABA on cultured antennal lobe neurons were eliminated. Contact between the glial cells and the neurons was not necessary. Operating in vivo, these antagonistic effects, one direct and one glia mediated, could help to sculpt the densely branched, tufted arbors that are characteristic of neurons innervating olfactory glomeruli.
Evidence indicates that children with autism spectrum disorder (ASD) suffer from an ongoing neuroinflammatory process in different regions of the brain involving microglial activation. When microglia remain activated for an extended period, the production of mediators is sustained longer than usual and this increase in mediators contributes to loss of synaptic connections and neuronal cell death. Microglial activation can then result in a loss of connections or underconnectivity. Underconnectivity is reported in many studies in autism. One way to control neuroinflammation is to reduce or inhibit microglial activation. It is plausible that by reducing brain inflammation and microglial activation, the neurodestructive effects of chronic inflammation could be reduced and allow for improved developmental outcomes. Future studies that examine treatments that may reduce microglial activation and neuroinflammation, and ultimately help to mitigate symptoms in ASD, are warranted.
