Calcium elevation in astrocytes causes an NMDA receptor-dependent increase in the frequency of miniature synaptic currents in cultured hippocampal neurons

Tripartite synapses: glia, the unacknowledged partner

According to the classical view of the nervous system, the numerically superior glial cells have inferior roles in that they provide an ideal environment for neuronal-cell function. However, there is a wave of new information suggesting that glia are intimately involved in the active control of neuronal activity and synaptic neurotransmission. Recent evidence shows that glia respond to neuronal activity with an elevation of their internal Ca2+ concentration, which triggers the release of chemical transmitters from glia themselves and, in turn, causes feedback regulation of neuronal activity and synaptic strength. In view of these new insights, this article suggests that perisynaptic Schwann cells and synaptically associated astrocytes should be viewed as integral modulatory elements of tripartite synapses.

UV photolysis using a micromanipulated optical fiber to deliver UV energy directly to the sample

UV photolysis of caged molecules is a powerful method for studying cellular signaling. However, UV energy is often delivered through the microscope objective which can make certain experiments difficult. We have evaluated the utility of delivering UV pulses directly to the sample through an optical fiber. Visible (635 nm) and UV (337 nm) lasers were coupled into a UV transmitting optical fiber which was micromanipulated over the sample under investigation. Positioning of the fiber, and thus the photolysis beam, was achieved using the visible laser which acted much like a flashlight. By controlling the size of the optical fiber it is also possible to control the area of the sample which is exposed to UV light. After positioning the fiber we demonstrate that the UV beam exiting the optical fiber reliably photolysed NP-EGTA that had been loaded into cells, resulting in an elevation of intracellular calcium. Additionally, caged norepinephrine in the bathing saline was photo-released to activate receptor-operated calcium signaling pathways. Since the delivery of the UV energy is independent of microscope configuration, this approach can be readily incorporated into wide-field fluorescence imaging, confocal microscopy and electrophysiological applications.