The research interests of this laboratory center on the physiological properties of neurons of the mammalian central nervous system (CNS), developmental expression of these properties, and the mechanisms by which drugs of abuse or CNS disease and injury alter neuronal physiology and viability. To address these issues we use electrophysiological techniques (whole cell current clamp, voltage clamp and single channel recordings), fura-2 based microscopic imaging of intracellular calcium, biochemical analyses, immunohistochemical techniques, and in vitro model systems (primary cultures of CNS neurons and acutely isolated brain slices). Some of the current areas of research are outlined below.
Immune System-CNS Interactions. Several lines of evidence indicate that the immune system can influence the normal activities of the CNS. Cells of the immune system are present in the CNS where they show increased chemical activities under conditions of CNS inflammation and disease. Cytokines and chemokines, chemical factors secreted by immune cells, are likely mediators of immune cell-CNS interactions under normal conditions and in diseased states. Elevated levels of cytokines, including interleukin-6 (IL-6), and chemokines, CXCL0 (previously called IP-10) and CCL2 (MCP-1), occur in the CNS in several diseases associated with CNS neuropathology, for example human immunodeficiency virus (HIV) infection and Alzheimer's disease. Elevated levels of IL-6 are also observed in diseases associated with developmental disorders. IL-6 and cilliary neurotrophic factor (CNTF), a neuronal growth factor, share the same intracellular receptor, suggesting that IL-6 may influence the nervous system via pathways normally used by growth factors. Relatively little is known about the effect of IL-6 or chemokines on CNS neurons, the transduction mechanism linked to IL-6 or chemokine receptors, or the pathways involved in IL-6 or chemokine induced neuropathology. To address these questions we are studying the effects of elevated levels of IL-6 and chemokines on CNS neuronal development, function and viability using in vitro culture model systems and transgenic mouse models that overexpress IL-6 in their CNS.
Calcium Regulation of Gene Expression. Neuronal activity produces dynamic changes in cellular calcium that play a central role in the regulation of a number of cellular functions including gene expression. Recently we demonstrated that early developing cerebellar Purkinje neurons express a membrane-to-nucleus somatic calcium signaling pathway that is driven by endogenously generated electrical activity at a developmentally significant stage, just prior to dendritic expression. Our results show that activation of this signaling pathway produces cytosolic and nuclear calcium signals that activate transcription factors and induced changes in the level of cellular proteins. We hypothesize that the endogenously generated activity that drives this pathway in the immature Purkinje neurons is a developmentally relevant signal and that one role for this activity is to induce changes in gene expression necessary for initiation of the next developmental stage, expression of functional dendrites. To test this hypothesis, we are applying gene array microanalysis to acutely isolated Purkinje neurons subjected to various stimulation paradigms at the relevant developmental stage. We will use this information in combination with other approaches (e.g., analysis of protein expression, functional analysis using electrophysiological techniques and calcium imaging) to gain an understanding of the impact of calcium-regulated gene expression at a specific developmental stage.
Neuroregulation by steroids. Regulation of neuronal excitability is essential for normal CNS function. One class of endogenous neurochemicals, the neurosteroids, has recently emerged as a potentially important addition to the known classes neuroregulators. Interest in CNS actions of neurosteroids developed over the last ten years following the demonstration that steroids associated classically with adrenal and gonadal functions are actively synthesized in CNS, can modulate behavior, can alter neuronal excitability, and can influence learning and memory. These steroids are referred to as neurosteroids to distinguish them from other neuroactive steroids (e.g., corticosteroids) that are synthesized in the periphery but have CNS actions. The neurosteroids are synthesized in the glial cells and may be important signaling molecules in the flow of information from the glial to neuronal population. Our studies focus on the influence of neurosteroids on neurotransmission and neuroplasticity in the hippocampal region of the CNS and on interactions between neurosteroids and alcohol.
Liljelund, P., Netzeband, G. and Gruol, D.L. (2000) L-type calcium channels mediate calcium oscillations in early postnatal Purkinje neurons, Journal of Neuroscience 20:7394-7403.
Conroy, S. M. Nguyen, V., Quina, L.A., Blakely-Gonzales, P.K., Ur, C., Netzeband, J G., Prieto, A.L. and Gruol, D.L. (2004) Interleukin-6 produces neuronal loss in developing cerebellar granule neuron cultures, Journal of Neuroimmunology, 155:43-54.
Nelson, T.E. and Gruol, D.L. (2004) The chemokine CXCL10 modulates excitatory activity and intracellular calcium signaling in cultured hippocampal neurons, Journal of Neuroimmunology, 156:74-87.
Nelson, T.E. Netzeband, J.G. and Gruol, D.L. (2004) Chronic interleukin 6 exposure alters metabotropic glutamate receptor-mediated calcium signaling in cerebellar Purkinje neurons, European Journal of Neuroscience, 20:2387-2400.