Increased excitatory synaptic input to granule cells from hilar and CA3 regions in a rat model of temporal lobe epilepsy.
One potential mechanism of temporal lobe epilepsy is recurrent excitation of dentate granule cells through aberrant sprouting of their axons (mossy fibers), which is found in many patients and animal models. However, correlations between the extent of mossy fiber sprouting and seizure frequency are weak. Additional potential sources of granule cell recurrent excitation that would not have been detected by markers of mossy fiber sprouting in previous studies include surviving mossy cells and proximal CA3 pyramidal cells. To test those possibilities in hippocampal slices from epileptic pilocarpine-treated rats, laser-scanning glutamate uncaging was used to randomly and focally activate neurons in the granule cell layer, hilus, and proximal CA3 pyramidal cell layer while measuring evoked EPSCs in normotopic granule cells. Consistent with mossy fiber sprouting, a higher proportion of glutamate-uncaging spots in the granule cell layer evoked EPSCs in epileptic rats compared with controls. In addition, stimulation spots in the hilus and proximal CA3 pyramidal cell layer were more likely to evoke EPSCs in epileptic rats, despite significant neuron loss in those regions. Furthermore, synaptic strength of recurrent excitatory inputs to granule cells from CA3 pyramidal cells and other granule cells was increased in epileptic rats. These findings reveal substantial levels of excessive, recurrent, excitatory synaptic input to granule cells from neurons in the hilus and proximal CA3 field. The aberrant development of these additional positive-feedback circuits might contribute to epileptogenesis in temporal lobe epilepsy.
The Journal of neuroscience : the official journal of the Society for Neuroscience
January 25, 2012
Agency: NINDS NIH HHS, Id: P01 NS012151
Agency: NINDS NIH HHS, Id: P50 NS012151
Agency: NINDS NIH HHS, Id: P50 NS012151-31
Agency: NINDS NIH HHS, Id: R01 NS034774
Agency: NINDS NIH HHS, Id: R01 NS040276
Agency: NINDS NIH HHS, Id: R01 NS040276-12
CA3 Region, Hippocampal
Disease Models, Animal
Epilepsy, Temporal Lobe
Excitatory Postsynaptic Potentials
Organ Culture Techniques
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