Amphetamine elevates phosphorylation of eukaryotic initiation factor 2α (eIF2α) in the rat forebrain via activating dopamine D1 and D2 receptors

Dopamine D2 receptor antagonists alter autophosphorylation of focal adhesion kinases in the mouse forebrain in vivo

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase expressed in neurons of the developing and adult brain in addition to non-neuronal cells. Activation of FAK is initiated by autophosphorylation of the kinase at tyrosine 397 (Y397). Active FAK transmits extracellular signals inside neurons to integrate cytoskeletal rearrangements and modulate synaptic transmission and plasticity. Here we investigated roles of dopamine receptors, i.e., Gαs/olf-coupled D1 and Gαi/o-coupled D2 subtypes, in regulation of FAK autophosphorylation in two major dopamine-innervated areas of the mouse brain in vivo. We found that acute systemic administration of a dopamine D1 or D2 receptor agonist had no effect on basal FAK autophosphorylation at Y397 in the striatum and medial prefrontal cortex (mPFC). Similarly, a D1 receptor antagonist did not alter striatal and cortical Y397 phosphorylation. However, acute injection of a D2 receptor antagonist (eticlopride or haloperidol) induced a marked increase in Y397 phosphorylation in the striatum and mPFC. The eticlopride-induced Y397 phosphorylation can be seen in the two striatal subdivisions, the caudate putamen and nucleus accumbens, and was induced at two effective doses (0.1 and 0.5 mg/kg). All drug treatments caused insignificant changes in cellular FAK protein expression. These results reveal an existence of a tonic inhibitory tone of dopamine D2 receptors over basal FAK autophosphorylation in the mouse striatum and mPFC.

Acteoside Attenuates Oxidative Stress and Neuronal Apoptosis in Rats with Focal Cerebral Ischemia-Reperfusion Injury

Acteoside (ACT) has been shown to exert antioxidant and neuroprotective effects in neurodegenerative diseases. However, the effect of ACT on cerebral ischemia-reperfusion (I/R) injury is not yet clear. In this study, we found that ACT administration reduced infarct volume and brain edema, and improved neurological deficits, as indicated by the decreased modified neurological severity score. Administration of ACT strikingly reduced oxidative stress, accompanied by decreased levels of reactive oxygen species and malondialdehyde and increased levels of superoxide dismutase and catalase in a rat model of middle cerebral artery occlusion/reperfusion (MCAO/R). Furthermore, ACT administration reduced the number of terminal deoxynucleotidyl transferase uridine 5'-triphosphate (UTP) nick-end labeling-positive cells in the cerebral cortex of ischemic side of MCAO/R rats, accompanied by downregulation of B cell lymphoma 2 (Bcl-2) associated X protein and cleaved caspase-3 proteins and upregulation of Bcl-2 protein. Additionally, ACT treatment inhibited the protein kinase R/eukaryotic initiation factor-2α stress pathway in the brains of MCAO/R rats. Our results demonstrated that ACT attenuates oxidative stress and neuronal apoptosis in MCAO/R rats, suggesting that ACT may serve as a novel therapeutic candidate for the treatment of I/R brain injury.

Amphetamine activates non-receptor tyrosine kinase Fyn and stimulates ERK phosphorylation in the rat striatum in vivo

The psychostimulant amphetamine (AMPH) has an impact on a variety of cellular activities in striatal neurons, although underlying signaling mechanisms are incompletely understood. The Src family kinase (SFK) is among key signaling molecules enriched in striatal neurons and is involved in the regulation of a set of discrete downstream targets. Given the likelihood that AMPH may regulate SFKs, we investigated and characterized the effect of AMPH on SFK phosphorylation and enzymatic activity in rat striatal neurons in vivo. We found that AMPH elevated SFK Y416 phosphorylation in striatal slices and the adult rat striatum. This elevation was concentration- and time-dependent and occurred in all subdivisions of the striatum, including the caudate putamen and nucleus accumbens (core and shell). The dopamine D₁ receptor antagonist SCH23390 blocked the effect of AMPH. Between Fyn and Src, AMPH elevated phosphorylation of immunoprecipitated Fyn but not Src and increased Fyn kinase activity in the striatum. In parallel with SFKs, striatal ERK phosphorylation was increased by AMPH. This increase in ERK phosphorylation was reduced by the SFK inhibitor PP2. These results demonstrate that AMPH is able to activate SFKs (mainly Fyn) in striatal neurons via a D₁ receptor-dependent mechanism. Activated SFKs participate in processing the concomitant ERK response to AMPH.