COM4S_M.TTF

Research Focus

Clues to the possible functions of astrocytes, and for that matter any cell type, come from the identification of the proteins expressed by that cell type. However, because of the complex arrangement of cell types within a tissue it is a technical challenge to determine what genes are expressed by astrocytes. After Dr. Kimelberg had demonstrated the existence of several functional neurotransmitter receptors on cultured astrocytes I undertook the study of which metabotropic glutamate receptors are expressed on astrocytes in vivo. For this study we dissociated live astrocytes from rat brain slices and immediately collected individual cells for gene expression analysis. The transcripts of expressed genes in single cells were amplified in process called reverse transcription-polymerase chain reaction (RT-PCR) so that detection of specific mGluR gene sequences indicated expression of that gene.

Cell type specific marker expression in combination with electrophysiological studies by Dr. Min Zhou enabled us to re-classify a cell type that had previously been thought to be an astrocyte. We found that the freshly isolated hippocampal glial cell with “complex” current voltage relationships expressed NG2, a marker for a cell type which lacks many commonly-accepted astrocyte properties and possesses several additional attributes. Because of these major differences NG2 positive cells likely have functions that are distinct from those of astrocytes.

Recently, we have used a live brain slice model to study the properties of astrocytes in situ. This experimental model enabled us to study the postnatal development of the astrocytic syncytium, or the system of coupled cells through which relatively small molecules may diffuse. We found that the astrocyte-to-astrocyte dye coupling is not entirely responsible for the “passive” character, meaning current flow directly proportional to the magnitude and polarity of the voltage across the cell membrane, nature of the astrocyte in the mature hippocampus.

Another interest is in the roles of astrocytes in both protecting and damaging neurons during stroke. Pathological fluxes of water and amino acids across various barriers in the brain are responsible for a great deal of the tissue damage caused by stroke. Therefore, it is important to understand the routes of water in and out of cells and also if these same routes allow the passage of other molecules. I am currently studying the role of a brain-expressed water channel protein, called aquaporin 9, which is also permeable to several other small molecules, some of which may be protective if they are able to diffuse from astrocytes to energy-starved neurons during stroke. The goal of the study is to determine the net effect of aquaporin 9 expression on the brain damage volume in an animal model of stroke.

Selected Publications

• Schools GP, Zhou M, Kimelberg HK (2006) Development of gap junctions in hippocampal astrocytes: evidence that whole cell electrophysiological phenotype is an intrinsic property of the individual cell. J Neurophysiol 96(3):1383-1392.
• Abdullaev IF, Rudkouskaya A, Schools GP, Kimelberg HK, Mongin AA (2006) Pharmacological comparison of swelling-activated excitatory amino acid release and Cl- currents in cultured rat astrocytes. J Physiol 572:677-689.
• Zhou M, Schools GP, Kimelberg HK (2006) Development of “>NG2 glia in rat hippocampus CA1: mature astrocytes are electrophysiologically passive. J Neurophysiol 95(1):134-143.
• Schools GP, Zhou M, Kimelberg HK (2003) Electrophysiologically “Complex” Glial Cells Freshly Isolated From the Hippocampus Are Immunopositive For the Chondroitin Sulfate Proteoglycan NG2. J Neurosci Res. 73:765-777.
• Schools GP, Kimelberg HK (2001) Metabotropic glutamate receptors in freshly isolated astrocytes from rat hippocampus. Chapter 25 of Progress in Brain Research Vol.:32, B. Castellano Lopez and M. Nieto-Sampedro (Eds)
• Cai Z, Schools GP, Kimelberg HK (2000) Metabotropic glutamate receptors in acutely isolated hippocampal astrocytes: developmental changes of mGluR5 mRNA and functional expression. Glia 29:70-80.
• Schools GP, Kimelberg HK (1999) mGluR3 and mGluR5 are the Predominant Metabotropic Glutamate Receptor mRNAs Expressed in Hippocampal Astrocytes Acutely Isolated From Young Rats. J Neuroscience Res 58:533-543.
• Crawford DR, Lauzon RJ, Wang Y, Mazurkiewicz JE, Schools GP, Davies KJ (1997) 16S mitochondrial ribosomal RNA degradation is associated with apoptosis. Free Radical Biology & Medicine 22:1295-1300.