Upon focal ischemia in adult brains, a large number of new cells migrate from the subventricular zone (SVZ) to the injured striatum, where they potentially participate in neuronal regeneration. We have found that inflammatory cytokines, such as IL-6 and IL-1β can promote neuronal differentiation of adult neural stem cells (see Barkho et al 2006). We are currently investigating how adult neural stem cells behave in response to brain injuries and the underlying molecular mechanisms. Our long-term goal is to establish a molecular basis for utilizing adult neurogenesis and adult neural stem cells in brain repair. We are using a combination of cell biology, molecular biology, and brain imaging approaches in this project. This work is funded by NIH/COBRE.

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Mesial temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults and can be caused by a variety of insults.  Specific loss of entorhinal cortex (EC) Layer 3 (L3) pyramidal neurons (PNs) and hyperexcitability of L5 PNs are characteristic for early stages of the disease while damage elsewhere, as in the hippocampus follows after prolonged accumulation of seizures.  This projects studies the cellular and synaptic changes that occur in the entorhinal cortex in the early stages of TLE evolution, poorly understood at present. The research utilizes the pilocarpine model of TLE to examine early mechanisms of EC L5 hyperexcitability. In this model, status epilepticus (SE) is evoked in rats by systemic application of the cholinergic-muscarinic agonist pilocarpine and terminated after one hour by benzodiazepines. After a silent period of 2 – 4 weeks spontaneous seizures occur. Resulting seizures (both pilocarpine-induced and spontaneous) originate in EC-L5, and then spread to L2 and on into the hippocampus.  Pathologic release of endogenous acetylcholine may also initiate similar status epilepticus, as a consequence of the dense cholinergic innervation of all layers of the entorhinal cortex by convergence of cholinergic fibers from the basal ganglia, the forebrain nuclei and the septum.
 

Studies in this project test the hypothesis that deficiencies in synaptic inhibition of EC-L5 pyramidal neurons cause TLE, and address key mechanisms underlying EC-L5 hyperexcitability. Most studies compare preparations from control and pilocarpine treated rats 2 and 3 weeks after SE, to determine a) changes in neuronal Cl^--transporters (compromising GABAergic synaptic inhibition), b) vesicular release probability changes for glutamatergic excitatory and GABAergic inhibitory synaptic terminals, c) excitability changes in neuronal synaptic networks due to changes in synaptic efficacy and circuit structure, and d) local disturbance in neuronal [Ca²⁺]_i-homeostasis mechanisms as a trigger for cell death of L3 pyramidal neurons and loss of excitation to inhibitory neurons. This issues are studied using sharp electrode and patch clamp recording, immunocytochemistry, two-photon laser scan fluorescence microscopy of presynaptic vesicular release and intracellular Ca²⁺-concentration and diode-array imaging of excitability spread in neuronal tissue.

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The mitogen activated protein kinases (MAPKs) are expressed ubiquitously in the central nervous system. They participate in diverse physiological processes, including neuronal maturation and survival, learning and memory as well as neuronal cell death. Multiple lines of evidence strongly indicate that MAPK pathways are also involved in the pathophysiology of alzheimer’s disease, parkinson’s disease, schizophrenia and stroke. This raises the questions as to how they can participate in such diverse patho-physiological processes? Growing evidence suggests that the magnitude and duration of MAP kinase activation are important in determining a particular biological outcome. But how cells determine the duration of MAP kinase signaling is still unclear. The fact that MAPKs are activated by a single kinase but inactivated by several phosphatases, indicate that diverse signals are probably integrated at the phosphatase level. The primary goal of our laboratory is to elucidate the role of the protein tyrosine phosphatases, STEP  (striatal-enriched tyrosine phosphatase) and PTP-SL (STEP like tyrosine phosphatase) in the regulation of the MAP kinase signaling pathways under different patho-physiological condition.

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