Abstracts

Gene therapy is emerging as a new promising strategy for treatment of epilepsy. In ex vivo gene therapy, cultured neural stem cell lines are transfected in vitro to express genes of interest, and then transplanted into the target area. On transplantation these cells can migrate and integrate into the host neuronal circuitry. Therefore, this strategy offers unique possibilities to replace lost cells and at the same time to deliver gene products into the diseased brain. To provide maximal symptomatic relief during seizures, one can hypothesize that the gene product should be released in a regulated and activity-dependent manner. Therefore, it is important to know whether and how formation of new afferent synaptic connection from host to transplanted neural stem cells occurs and if these synapses display various forms of synaptic plasticity., Using whole-cell patch-clamp technique, we studied electrophysiological characteristics, and functional and synaptic integration of GFP-labeled RN33B neuronal progenitor cells transplanted into the intact rat hippocampus., 4 weeks after transplantation, RN33B cells differentiated into neurons with axonal and dendritic processes and were incorporated within the granule cell layer of the hippocampal dentate gyrus as well as the pyramidal cell layers of CA3 and CA1 area. These cells displayed intrinsic membrane properties of endogenous granule cells and pyramidal cells, respectively. Moreover, mature RN33B cells received region specific afferent inputs resembling the hippocampal trisynaptic circuitry, recapitulating patterns of synaptic connectivity with remarkable accuracy, and exhibited short-term synaptic plasticity as shown by paired-pulse stimulation. Excitatory synapses formed on transplanted cells also exhibited activity-dependent long-term potentiation (LTP), demonstrating, for the first time, that such newly formed synapses can undergo long-lasting synaptic changes., The striking similarity in functional synaptic integration between transplanted neural stem cells and host neurons provide further evidence that cell replacement strategies and ex vivo gene therapy could be valuable approaches for future treatment of epilepsy., (Supported by Swedish Research Council, Segerfalk[apos]s, Crafoord[apos]s and Kock[apos]s Foundation.)