Effects of acupuncture on microglial polarization and the TLR4/TRIF/MyD88 pathway in a rat model of traumatic brain injury

OBJECTIVE

Neuroinflammation caused by traumatic brain injury (TBI) can lead to neurological deficits. Acupuncture can inhibit neuroinflammation and promote nerve repair; however, the specific mechanism is still unclear. The purpose of this study was to explore whether acupuncture could modulate the M1 and M2 phenotypic polarization of microglia in a rat model of TBI via the toll-like receptor 4 (TLR4)/intracellular toll-interleukin-1 receptor (TIR) domain-containing adaptor inducing interferon-β (TRIF)/myeloid differentiation factor 88 (MyD88) pathway.

METHODS

A total of 90 adult male Sprague-Dawley (SD) rats, SPF grade, were randomly divided into a normal group, model group and acupuncture group. Each group was further divided into three subgroups (first, third, and fifth day groups) according to the treatment time (n = 10 rats/subgroup). We used the modified neurological severity score (mNSS) method to quantify neurological deficits before and after modeling. We used Nissl staining to observe the pathological changes in brain tissue, flow cytometry to detect the proportion of M1 and M2 polarized microglia in the injured area on the first, third and fifth day, and co-immunoprecipitation (Co-IP) to examine TLR4/TRIF/MyD88 expression in microglia on the first, third and fifth day, as well as expression of the amount of binding of TLR4 with TRIF and MyD88.

RESULTS

Compared to the model group, mNSS in the acupuncture group gradually decreased and pathological morphology improved. The proportion of CD11b/CD86 positive cells was decreased, while that of CD11b/CD206 was increased in the acupuncture group. Expression of IP TLR4, IP TRIF and IP MyD88 also decreased in the acupuncture group.

CONCLUSION

The results of this study demonstrate that one of the mechanisms through which acupuncture mitigates neuroinflammation and promotes nerve repair in TBI rats may be inhibition of M1 phenotypic polarization and promotion of M2 phenotypic polarization through inhibition of the TLR4/TRIF/MyD88 signaling pathway.

Early postnatal alcohol exposure produced long-term deficits in brain weight, but not the number of neurons in the locus coeruleus

The locus coeruleus (LC), a small nucleus in the pontine tegmentum with clusters of norepinephrine (NE) containing neurons, projects to more brain regions than any other nucleus in the central nervous system. Therefore, any neuroanatomical deficits in the LC may have wide-ranging functional implications. Previous studies have shown that heavy alcohol exposure during development can damage several brain regions receiving extensive innervation from the LC (e.g., cerebellum and olfactory bulb). In this study, we examined the effects of early alcohol exposure during development on neuronal numbers in the LC of the adult rat. Sprague-Dawley rat pups were reared using artificial rearing techniques during the brain growth spurt period (part of the third trimester equivalent). The pups in the alcohol group received 4.5 g/kg per day in two of their 12 daily feedings from postnatal days (PDs) 4-9. Gastrostomy and suckle control groups were also included. On PD 90, the animals were sacrificed and their brains were processed for stereological cell counting. Whole brain weight, the number of neurons in the LC, the volume and neuronal density of the LC were assessed. There was a significant reduction in whole brain weight of the alcohol group compared with that of the gastrostomy control group, demonstrating a long lasting effect of alcohol on overall brain growth. Nevertheless, there were no differences in neuronal number, density and volume of the LC between alcohol and gastrostomy groups. Results were discussed in relation to the issues of temporal and regional vulnerabilities.

Cocaine-induced somatic growth deficit during the brain growth spurt is prevented by artificial-rearing

The brain growth spurt is a dynamic period of central nervous system development that has been shown to be particularly vulnerable to a variety of insults. This study was designed to assess the effects of various doses of cocaine during this potentially vulnerable period on survival rate, somatic growth, and brain development, utilizing an artificial-rearing paradigm. Three cocaine-treated groups received SC administration of either 40, 60, or 80 mg/kg/day of cocaine HCl from postnatal days 4 through 9. There were significant differences in survival rates among 60 and 80 mg/kg/day cocaine-treated animals as compared with gastrostomy controls. No statistically significant differences were found with regard to body and brain weights between the various cocaine-treated groups and the gastrostomy control group. Additionally, there was no evidence of cocaine's effect on forebrain, cerebellum, or brainstem weights when compared with individually corresponding controls. Taken together with our previous results, these data suggest that cocaine administration during the brain growth spurt period produces a dose-related increase in lethality, and the use of artificial-rearing method seems to lower the lethal threshold of cocaine among these neonates. However, no statistically significant effects of cocaine exposure on brain weight measures were obtained. The most important finding was that the cocaine-induced somatic growth retardation observed previously under normal-rearing conditions was eliminated by using a nutritionally controlled artificial-rearing paradigm, suggesting that cocaine-induced restriction of somatic growth may be a function of interference with normal feeding behavior, and therefore, a secondary effect of cocaine exposure during development.