Non-genomic Actions of Methylprednisolone Differentially Influence GABA and Glutamate Release From Isolated Nerve Terminals of the Rat Hippocampus

Activation of Galanin Receptor 1 with M617 Attenuates Neuronal Apoptosis via ERK/GSK-3β/TIP60 Pathway After Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease. Neuronal apoptosis plays an important pathological role in early brain injury after SAH. Galanin receptor 1 (GalR1) activation was recently shown to be anti-apoptotic in the setting of ischemic stroke. This study aimed to explore the anti-neuronal apoptosis effect of GalR1 activation after SAH, as well as the underlying mechanisms. GalR1 CRISPR and GalR1 selective agonist, M617, was administered, respectively. Extracellular-signal-regulated kinase (ERK) inhibitor (U0126) and glycogen synthase kinase 3-beta (GSK3-β) CRISPR were administered to investigate the involvement of the ERK/GSK3-β pathway in GalR1-mediated neuroprotection after SAH. Outcome assessments included neurobehavioral tests, western blot, and immunohistochemistry. The results showed that endogenous ligand galanin (Gal) and GalR1 were markedly increased in the ipsilateral brain hemisphere at 12 h and 24 h after SAH. GalR1 were expressed mainly in neurons, but expression was also observed in some astrocytes and microglia. GalR1 CRISPR knockdown exacerbated neurological deficits and neuronal apoptosis 24 h after SAH. Moreover, activation of GalR1 with M617 significantly improved short- and long-term neurological deficits but decreased neuronal apoptosis after SAH. Furthermore, GalR1 activation dysregulated the protein levels of phosphorylated ERK and GSK-3β, but downregulated the phosphorylated Tat-interactive protein 60 (TIP60) and cleaved caspase-3 at 24 h after SAH. GalR1 CRISPR, U0126, and GSK-3β CRISPR abolished the beneficial effects of GalR1 activation at 24 h after SAH in rats. Collectively, the present study demonstrated that activation of GalR1 using M617 attenuated neuronal apoptosis through the ERK/GSK-3β/TIP60 pathway after SAH in rats. GalR1 may serve as a promising therapeutic target for SAH patients.

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.