Epilepsy and mental retardation constitute the major causes of childhood disability. Their pathogenesis is poorly understood because, in part, of our limited understanding of early brain and neuronal maturation. Since Ca2+ influx through voltage-dependent Ca2+ channels (VDCC) is critical to early neuronal function, signalling, and differentiation, we have chosen to study its postnatal development and regulation. Electrophysiological studies have identified four classes of neuronal Ca2+ channels, designated T, L, N and P. This ensemble of currents is not present in early neuronal life. Each subtype arises in a differential sequence over time. Using whole-cell patch recording techniques in the rat hippocampal slice preparation, we will characterize this progression and the nature of each current subtype in the postnatal period. Fluorescent analogs of selective channel ligands will enable visualization of VDCC sites on developing hippocampal neurons and in situ hybridization will be used to analyze the synthesis of these channels. Factors that regulate VDCC expression will also be studied. Using organotypic cultures of the hippocampus we will alter the growth conditions to which immature neurons are exposed and observe the effects on VDCC expression, neuronal morphology and adaptive properties of the neurons. In addition, the above techniques will be used to examine the developmental role of Ca2+ currents on models of learning and memory and epilepsy in cultured hippocampal slices. This combined approach of electrophysiology, fluorescent imaging and in situ hybridization will provide essential information about normal Ca2+ channel development and regulation during early neuronal maturation. Disturbances in Ca2+ channel expression may explain the increased learning problems and seizure susceptibility that occur in the young.
