Neurotransmitter released from neurons is known to signal to neighbouring neurons and glia. Here we demonstrate an additional signalling pathway in which glutamate is released from astrocytes and causes an NMDA (N-methyl-D-aspartate) receptor-mediated increase in neuronal calcium. Internal calcium was elevated and glutamate release stimulated by application of the neuroligand bradykinin to cultured astrocytes. Elevation of astrocyte internal calcium was also sufficient to induce glutamate release. To determine whether this released glutamate signals to neurons, we studied astrocyte-neuron co-cultures. Bradykinin significantly increased calcium levels in neurons co-cultured with astrocytes, but not in solitary neurons. The glutamate receptor antagonists D-2-amino-5-phosphonopentanoic acid and D-glutamylglycine prevented bradykinin-induced neuronal calcium elevation. When single astrocytes were directly stimulated to increase internal calcium and release glutamate, calcium levels of adjacent neurons were increased; this increase could be blocked by D-glutamylglycine. Thus, astrocytes regulate neuronal calcium levels through the calcium-dependent release of glutamate.

An MCM-41 type mesoporous silica nanosphere-based (MSN) controlled-release delivery system has been synthesized and characterized using surface-derivatized cadmium sulfide (CdS) nanocrystals as chemically removable caps to encapsulate several pharmaceutical drug molecules and neurotransmitters inside the organically functionalized MSN mesoporous framework. We studied the stimuli-responsive release profiles of vancomycin- and adenosine triphosphate (ATP)-loaded MSN delivery systems by using disulfide bond-reducing molecules, such as dithiothreitol (DTT) and mercaptoethanol (ME), as release triggers. The biocompatibility and delivery efficiency of the MSN system with neuroglial cells (astrocytes) in vitro were demonstrated. In contrast to many current delivery systems, the molecules of interest were encapsulated inside the porous framework of the MSN not by adsorption or sol-gel types of entrapment but by capping the openings of the mesoporous channels with size-defined CdS nanoparticles to physically block the drugs/neurotransmitters of certain sizes from leaching out. We envision that this new MSN system could play a significant role in developing new generations of site-selective, controlled-release delivery nanodevices.

We synthesized a MCM-41-type mesoporous silica nanosphere (MSN)-based gene transfection system, where second generation (G2) polyamidoamines (PAMAMs) were covalently attached to the surface of MSN. The G2-PAMAM-capped MSN material (G2-MSN) was used to complex with a plasmid DNA (pEGFP-C1) that encodes for an enhanced green fluorescence protein. The gene transfection efficacy, uptake mechanism, and biocompatibility of the G2-MSN system with various cell types, such as neural glia (astrocytes), human cervical cancer (HeLa), and Chinese hamster ovarian (CHO) cells, were investigated. The mesoporous structure of the MSN material allows membrane-impermeable molecules, such as pharmaceutical drugs and fluorescent dyes, to be encapsulated inside the MSN channels. The system renders the possibility to serve as a universal transmembrane carrier for intracellular drug delivery and imaging applications.

ATP caused a dose-dependent, receptor-mediated increase in the release of glutamate and aspartate from cultured astrocytes. Using calcium imaging in combination HPLC we found that the increase in intracellular calcium coincided with an increase in glutamate and aspartate release.

Earlier studies in live pancreatic acinar cells identified new cellular structures at the cell plasma membrane called 'pits' and 'depressions', where membrane-bound secretory vesicles dock and fuse to release vesicular contents. In the current study, using atomic force microscopy we identify similar structures at the plasma membrane of GH-secreting cells of the pituitary and implicate their involvement in hormone release. Pits containing 100-200 nm in diameter depressions or fusion pores were identified in resting GH-secreting cells. Following stimulation of secretion the size of depression enlarged and gold-tagged GH antibody were found to bind to the pit structures in the stimulated GH cells. This study documents for the first time the presence of these structures and their involvement in secretions in a neuroendocrine cell.