The role of purinergic receptors in neural repair and regeneration after spinal cord injury

Spinal cord injury is a serious injury of the central nervous system that results in neurological deficits. The pathophysiological mechanisms underlying spinal cord injury, as well as the mechanisms involved in neural repair and regeneration, are highly complex. Although there have been many studies on these mechanisms, there is no effective intervention for such injury. In spinal cord injury, neural repair and regeneration is an important part of improving neurological function after injury, although the low regenerative ability of nerve cells and the difficulty in axonal and myelin regeneration after spinal cord injury hamper functional recovery. Large amounts of ATP and its metabolites are released after spinal cord injury and participate in various aspects of functional regulation by acting on purinergic receptors which are widely expressed in the spinal cord. These processes mediate intracellular and extracellular signalling pathways to improve neural repair and regeneration after spinal cord injury. This article reviews research on the mechanistic roles of purinergic receptors in spinal cord injury, highlighting the potential role of purinergic receptors as interventional targets for neural repair and regeneration after spinal cord injury.

Spinal cord injury causes insulin resistance associated with PI3K signaling pathway in hypothalamus

Spinal cord injury (SCI) is an independent risk factor for type 2 diabetes, and may induce insulin resistance that leads to this disease. Studies have shown that greater phosphoinositide 3-kinase (PI3K) activation in the hypothalamus leads to activation of the anti-inflammatory pathway, and the anti-inflammatory reflex may protect against insulin resistance and type 2 diabetes. However, the importance of this phenomenon in type 2 diabetes pathogenesis after SCI remains elusive. In the present study, the expression of c-Fos in the hypothalamus of rats with SCI was elevated, and the hypothalamus injury was observer following SCI. Then we showed that SCI could induce increased levels of blood glucose and glucose tolerance in rats. Also, we found that SCI could damage the liver, adipocyte and pancreas, and led to lipid position in liver. Western blots were used to detect the level of PI3K and p-Akt in the hypothalamus, and the results showed a significant downregulation of PI3K and p-Akt after SCI. Furthermore, to verify the activity of the PI3K signaling pathway, immunofluorescence was used to examine the expression of neurons positive for p-S6 (a marker of PI3K activation) after SCI. The results showed that the expression of p-S6-positive neurons decreased after SCI. In addition, the effect of SCI on peripheral inflammation was also investigated. Following SCI, the serum levels of tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 increased. Collectively, our results suggest abnormality in glucose metabolism after SCI, and demonstrate that SCI may impair activation of the PI3K signaling pathway in the hypothalamus. The reduced activity of the PI3K signaling pathway in the hypothalamus may lead to peripheral inflammation, which might be the mechanism underlying the development of insulin resistance and type 2 diabetes following SCI.

What drives progressive motor deficits in patients with acute pontine infarction?

Progressive motor deficits are relatively common in acute pontine infarction and frequently associated with increased functional disability. However, the factors that affect the progression of clinical motor weakness are largely unknown. Previous studies have suggested that pontine infarctions are caused mainly by basilar artery stenosis and penetrating artery disease. Recently, lower pons lesions in patients with acute pontine infarctions have been reported to be related to progressive motor deficits, and ensuing that damage to the corticospinal tracts may be responsible for the worsening of neurological symptoms. Here, we review studies on motor weakness progression in pontine infarction and discuss the mechanisms that may underlie the neurologic worsening.

Electroacupuncture and A-317491 depress the transmission of pain on primary afferent mediated by the P2X3 receptor in rats with chronic neuropathic pain states

P2X is a family of ligand-gated ion channels that act through adenosine ATP. The P2X3 receptor plays a key role in the transmission of neuropathic pain at peripheral and spinal sites. Electroacupuncture (EA) has been used to treat neuropathic pain effectively. To determine the role of EA in neuropathic pain mediated through the P2X3 receptor in dorsal root ganglion neurons and the spinal cord, a chronic constriction injury (CCI) model was used. Sprague-Dawley rats were divided into four groups: sham CCI, CCI, CCI plus contralateral EA, and CCI plus ipsilateral EA. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were recorded. Furthermore, the expression of the P2X3 receptor was evaluated through Western blotting and immunofluorescence. The effects of EA and A-317491 were investigated through the whole-cell patch-clamp method and intrathecal administration. Our results show that the MWT and TWL of EA groups were higher than those in the CCI group, whereas the expression of the P2X3 receptor was lower than that in the CCI group. However, no significant difference was detected between the two EA groups. EA depressed the currents created by ATP and the upregulation of the P2X3 receptor in CCI rats. Additionally, EA was more potent in reducing mechanical allodynia and thermal hyperalgesia when combined with A-317491 through intrathecal administration. These results show that both contralateral and ipsilateral EA might inhibit the primary afferent transmission of neuropathic pain induced through the P2X3 receptor. In addition, EA and A-317491 might have an additive effect in inhibiting the transmission of pain mediated by the P2X3 receptor.

Effect of electroacupuncture on the pathomorphology of the sciatic nerve and the sensitization of P2X₃ receptors in the dorsal root ganglion in rats with chronic constrictive injury

OBJECTIVE

To explore the effect of electroacupuncture (EA) on the pathomorphology of the sciatic nerve and the role of P2X3 receptors in EA analgesia.

METHODS

The chronic constriction injury (CCI) model was adopted in this study. A total of 32 rats were randomly divided into four groups: sham CCI, CCI, CCI plus contralateral EA (CCI + conEA) and CCI plus ipsilateral EA (CCI + ipsEA). Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured. EA began at day 7 after the CCI operation and was applied to the Zusanli (ST 36) and Yanglingquan acupoints (GB 34). At day 14, the pathomorphologic changes of the operated sciatic nerve were demonstrated by hematoxylin and eosin staining. In addition, dorsal root ganglion (DRG) neurons isolated from rats were examined by electrophysiological recording to determine if the P2X3 receptor agonists, adenosine 5'-triphosphate disodium (ATP) and α,β-methylen-ATP (α,β-meATP) evoked inward currents.

RESULTS

Pain thresholds in the CCI group were obviously decreased post CCI surgery (P<0.01). In the EA groups, thermal and mechanical threshold values were increased after the last EA treatment (P<0.05, P<0.01). There was no significant difference in light microscopic examination among the four groups (P>0.05). Current amplitude after application of ATP and α,β-meATP in DRG neurons were much larger in the CCI group compared to those obtained in sham CCI (P<0.05). ATP and α, β-meATP invoked amplitudes in the CCI + EA groups were reduced. There was no signififi cant difference between the CCI + conEA group and the CCI + ipsEA group (P>0.05).

CONCLUSION

EA analgesia may be mediated by decreasing the response of P2X3 receptors to the agonists ATP and α,β-meATP in the DRG of rats with CCI. No pathological changes of the sciatic nerve of rats were observed after EA treatment.

DNA sequencing with dye-labeled terminators and T7 DNA polymerase: effect of dyes and dNTPs on incorporation of dye-terminators and probability analysis of termination fragments

The incorporation of fluorescently labeled dideoxynucleotides by T7 DNA polymerase is optimized by the use of Mn2+, fluorescein analogs and four 2'-deoxyribonucleoside 5'-O-(1-thiotriphosphates) (dNTP alpha S's). The one-tube extension protocol was tested on single-stranded templates, as well as PCR fragments which were made single-stranded by digestion with T7 gene 6 exonuclease. Dye primer sequencing using four dNTP alpha S's was shown to give uniform termination patterns which were comparable to four dNTPs. Efficiency of the polymerase also appeared to improve with the dNTP alpha S's. A mathematical model was developed to predict the pattern of termination based on enzyme activity and ratios of ddNTP/dNTPs. This method can be used to optimize sequencing reactions and to estimate enzyme discrimination constants of chain terminators.