Role of GABAB receptors in proepileptic and antiepileptic effects of an applied electric field in rat hippocampus in vitro.

The mechanisms underlying antiepileptic effects of deep brain stimulation (DBS) are complex and poorly understood. Studies on the effects of applied electric fields on epileptic nervous tissue could enable future advances in DBS treatments. Applied electric fields are known to inhibit or enhance epileptic activity in vitro through direct effects on local neurons, but it is unclear whether trans-synaptic effects participate in such actions. The present study investigates, in an epileptic brain slice model, the influence of GABAB receptor activation on excitatory and suppressive effects of a short-duration (10 ms) electric field in rat hippocampus. The results show that perfusion of the GABAB receptor antagonist, CGP 55845 (2 µM), could abolish applied-field induced suppression of orthodromic-stimulus evoked epileptiform afterdischarge activity in the CA1 region. GABAB receptor blockade was associated with an enhanced excitatory (proepileptic) effect of the applied field. However, the suppressive effect, observed in isolation using weak field stimuli, was left unchanged. The G-protein-activated inwardly rectifying K+ channel (GIRK) antagonist, tertiapin (30-50 nM), mimicked the effects of CGP 55845. The results suggest that the applied field activate (elements of) local interneurons to release GABA onto GABAB receptors. The resulting activation of postsynaptic GIRK channels inhibits neuronal activity thereby dampening the direct stimulatory effect of the applied field. The study indicates that local-stimulus induced GABAB receptor activation can serve a protective role under antiepileptic paradigms by preventing electrical stimulation from causing hyperexcitation.

Common Effects on Cancer Cells Exerted by a Random Positioning Machine and a 2D Clinostat.

In this study we focused on gravity-sensitive proteins of two human thyroid cancer cell lines (ML-1; RO82-W-1), which were exposed to a 2D clinostat (CLINO), a random positioning machine (RPM) and to normal 1g-conditions. After a three (3d)- or seven-day-culture (7d) on the two devices, we found both cell types growing three-dimensionally within multicellular spheroids (MCS) and also cells remaining adherent (AD) to the culture flask, while 1g-control cultures only formed adherent monolayers, unless the bottom of the culture dish was covered by agarose. In this case, the cytokines IL-6 and IL-8 facilitated the formation of MCS in both cell lines using the liquid-overlay technique at 1g. ML-1 cells grown on the RPM or the CLINO released amounts of IL-6 and MCP-1 into the supernatant, which were significantly elevated as compared to 1g-controls. Release of IL-4, IL-7, IL-8, IL-17, eotaxin-1 and VEGF increased time-dependently, but was not significantly influenced by the gravity conditions. After 3d on the RPM or the CLINO, an accumulation of F-actin around the cellular membrane was detectable in AD cells of both cell lines. IL-6 and IL-8 stimulation of ML-1 cells for 3d and 7d influenced the protein contents of ß1-integrin, talin-1, Ki-67, and beta-actin dose-dependently in adherent cells. The ß1-integrin content was significantly decreased in AD and MCS samples compared with 1g, while talin-1 was higher expressed in MCS than AD populations. The proliferation marker Ki-67 was elevated in AD samples compared with 1g and MCS samples. The ß-actin content of R082-W-1 cells remained unchanged. ML-1 cells exhibited no change in ß-actin in RPM cultures, but a reduction in CLINO samples. Thus, we concluded that simulated microgravity influences the release of cytokines in follicular thyroid cancer cells, and the production of ß1-integrin and talin-1 and predicts an identical effect under real microgravity conditions.