Imaging of Hippocampal Circuits in Epilepsy

Excerpt

This chapter describes the principles and applications of multiple dynamic imaging techniques that facilitate the elucidation of hippocampal circuit function in animal models of epilepsy. The first section outlines the benefits and the challenges of various techniques such as voltage sensitive dye (VSD) imaging, calcium imaging, and the related optical microcopies. In the second section, we summarize findings on dentate gyrus (DG) gating function. In naïve tissue, VSD imaging demonstrated that stimulation of the afferent to the DG, the perforant path, elicited a strong excitatory response in the inner molecular layer and cell body layer of the DG, as well as in the proximal hilus, but only minimally activated the CA3 pyramidal cell layer, illustrating the inhibition-dependent ‘gating’ aspect of DG function. The lack of dentate granule cell firing was verified using calcium imaging. Further experiments revealed that this DG ‘gating’ function was markedly disrupted in hippocampal slices prepared 1 week after pilocarpine-induced status epilepticus, during the latent period. In the third section, we briefly discuss the capability of calcium imaging in resolving individual cellular activities of hundreds of cells in spontaneously bursting network. The combined approach of multiple imaging modalities has significant promise in furthering our understanding of the mechanisms underlying epilepsy.