Overexpression of STIM1 in neurons in mouse brain improves contextual learning and impairs long-term depression

STIM1 is an endoplasmic reticulum calcium sensor that is involved in several processes in neurons, including store-operated calcium entry. STIM1 also inhibits voltage-gated calcium channels, such as Ca_v1.2 and Ca_v3.1, and is thus considered a multifunctional protein. The aim of this work was to investigate the ways in which transgenic neuronal overexpression of STIM1 in FVB/NJ mice affects animal behavior and the electrophysiological properties of neurons in acute hippocampal slices. We overexpressed STIM1 from the Thy1.2 promoter and verified neuronal expression by quantitative reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry. Mature primary hippocampal cultures expressed STIM1 but exhibited no changes in calcium homeostasis. Basal synaptic transmission efficiency and short-term plasticity were comparable in slices that were isolated from transgenic mice, similarly as the magnitude of long-term potentiation. However, long-term depression that was induced by the glutamate receptor 1/5 agonist (S)-3,5-dihydroxyphenylglycine was impaired in STIM1 slices. Interestingly, transgenic mice exhibited a decrease in anxiety-like behavior and improvements in contextual learning. In summary, our data indicate that STIM1 overexpression in neurons in the brain perturbs metabotropic glutamate receptor signaling, leading to impairments in long-term depression and alterations in animal behavior. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

The effect of glycogen phosphorolysis on basal glutaminergic transmission

Astrocytic glycogen metabolism sustains neuronal activity but its impact on basal glutamatergic synaptic transmission is not clear. To address this issue, we have compared the effect of glycogen breakdown inhibition on miniature excitatory postsynaptic currents (mEPSCs) in rat hippocampal pure neuronal culture (PNC) and in astrocyte-neuronal co-cultures (ANCC). Amplitudes of mEPSC in ANCC were nearly twice as large as in PNC with no difference in current kinetics. Inhibition of glycogen phosphorylase reduced mEPSC amplitude by roughly 40% in ANCC being ineffective in PNC. Altogether, these data indicate that astrocyte-neuronal interaction enhances basal mEPSCs in ANCC mainly due to astrocytic glycogen metabolism.

Calcium and fos involvement in brain-derived Ca(2+)-binding protein (S100)-dependent apoptosis in rat phaeochromocytoma cells

Brain-derived calcium-binding protein S100 induces apoptosis in a significant fraction of rat phaeochromocytoma (PC12) cells. We used single cell techniques (patch clamp, videomicroscopy and immunocytochemistry) to clarify some of the specific aspects of S100-induced apoptosis, the modality(ies) of early intracellular Ca2+ concentration increase and the expression of some classes of genes (c-fos, c-jun, bax, bcl-x, p-15, p-21) known to be implicated in apoptosis of different cells. The results show that S100: (1) causes an increase of [Ca2+]i due to an increased conductance of L-type Ca2+ channels; (2) induces a sustained increase of the Fos levels which is evident since the first time point tested (3 h) and remains elevated until to the last time point (72 h). All these data suggest that S100-derived apoptosis in PC12 cells may be the consequence of a system involving an increase in L-type Ca2+ channel conductance with consequent [Ca2+]i increase which up-regulates, directly or indirectly, the expression of Fos.