Transient cerebral ischemia induces active astrocytosis without distinct neuronal death in the gerbil main olfactory bulb: a long-term analysis

Parvalbumin-immunoreactive cells in the olfactory bulb of the pigeon: Comparison with the rat

The olfactory bulb (OB) shows special characteristics in its phylogenetic cortical structure and synaptic pattern. In the OB, gamma-aminobutyric acid (GABA), as an inhibitory neurotransmitter, is secreted from GABAergic neurons which contain parvalbumin (a calcium-binding protein). Many studies on the distribution of parvalbumin-immunoreactive neurons in the rodent OB have been published but poorly reported in the avian OB. Therefore, in this study, we compared the structure of the OB and distribution of parvalbumin-immunoreactive neurons in the OB between the rat and pigeon using cresyl violet staining and immunohistochemistry for parvalbumin, respectively. Fundamentally, the pigeon OB showed layers like those of the rat OB; however, some layers were not clear like in the rat OB. Parvalbumin-immunoreactive neurons in the pigeon OB were predominantly distributed in the external plexiform layer like that in the rat OB; however, the neurons did not have long processes like those in the rat. Furthermore, parvalbumin-immunoreactive fibres were abundant in some layers; this finding was not shown in the rat OB. In brief, parvalbumin-immunoreactive neurons were found like those in the rat OB; however, parvalbumin-immunoreactive fibres were significantly abundant in the pigeon OB compared to those in the rat OB.

Protective effect of Tanshinone IIA against infarct size and increased HMGB1, NFκB, GFAP and apoptosis consequent to transient middle cerebral artery occlusion

Acute inflammation plays an important role in brain damage following cerebral ischemia and reperfusion (I/R) injury. The present study employed a rat model of middle cerebral artery occlusion to explore the neuroprotective effects of tanshinone IIA (TSN), which is widely used in China for treating cerebrovascular and cardiovascular diseases. Rats were divided into a sham-operated group and I/R transiently occluded then reperfused groups. Some of the I/R animals were treated daily for 7 or 15 days with two different doses of TSN. After 15 days, triphenyl tetrazolium chloride staining revealed less unstained area indicating fewer lesions in the TSN-treated I/R group relative to the untreated corresponding I/R group. TSN treatment dramatically reduced infarct sizes and reduced content of high mobility group box 1 protein following I/R. Nuclear translocation of NFκB was also attenuated in I/R animals subsequently receiving TSN. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining revealed more apoptosis in the I/R model group and this was reduced in the I/R animals treated with TSN for 15 days. Thus, TSN mitigates the severity of damage effected by I/R.

Upregulation of glutamate transporter GLT-1 by mTOR-Akt-NF-кB cascade in astrocytic oxygen-glucose deprivation

Excessive extracellular glutamate leads to neuronal death in central nervous system. Excitatory glutamate transporter subtype 2 (GLT-1) carries bulk of glutamate reuptake in cerebral ischemia. Although GLT-1 expression fluctuates during the period of ischemia, little is known about its regulatory mechanism. Here we show an up-regulation of GLT-1 via mammalian target of rapamycin (mTOR)-Akt-nuclear factor-кB (NF-кB) signaling cascade in oxygen glucose deprivation (OGD). We found that brief rapamycin treatment significantly increased GLT-1 expression in cultured astrocytes. Rapamycin increased phosphorylation of raptor at Ser792 and decreased phosphorylation of rictor at Thr1135, suggesting that both mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) are involved in GLT-1 expression. This conclusion was further confirmed by raptor and rictor disruption experiments. Akt was activated by mTORC1 inhibition and required for GLT-1 expression because triciribine, a specific inhibitor of Akt, blocked the increase of GLT-1 expression. mTOR-Akt cascade then activated NF-кB and increased кB-motif-binding phosphoprotein (KBBP) expression and GLT-1 transcription. We next demonstrated that mTOR-Akt-NF-кB cascade was activated in OGD and subsequently caused the upregulation of GLT-1. Supporting evidence included: (1) inhibition of Akt or NF-кB occluded OGD-induced GLT-1 upregulation; (2) Raptor knock-down plus OGD did not add to the increase of GLT-1 expression; (3) Intact mTORC2 was required for GLT-1 enhancement. In summary, our data first showed that mTOR-Akt-NF-кB cascade played critical roles to up-regulate GLT-1 in OGD. This signaling cascade may work to promote glutamate uptake in brain ischemia and neurodegenerative diseases.