This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.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 by systemic application of the 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.
Showing the most recent 10 out of 118 publications
