Conclusion

In summary, the main limitation of the slice preparation is the massive loss of intrinsic and extrinsic connectivity.

FIGURE 4 A: Two-photon imaging of the CA1 region of a hippocampal slice from a mouse. Pyramidal cell somata are clearly visible in the pyramidal cell layer (P); interneurons are visible in stratum oriens (O) and stratum radiatum (R). Neurons are filled with a Ca2+ indicator, and variations in [Ca2+] are measured. Electrophysiologic properties of any individual neuron can also be recorded. For example, the inset shows the spontaneous activity recorded in a stratum oriens interneuron (Rosa Cossart, personal communication). B: Spatiotemporal patterns of neuronal activity evoked in the dentate gyrus in control and kainic acid (KA)-treated rat hippocampal slices. Level of neuronal activity is displayed according to the pseudocolor code (from background gray to highly activated red). (Adapted from Otsu et al., 2000.) (See color insert.)

FIGURE 4 A: Two-photon imaging of the CA1 region of a hippocampal slice from a mouse. Pyramidal cell somata are clearly visible in the pyramidal cell layer (P); interneurons are visible in stratum oriens (O) and stratum radiatum (R). Neurons are filled with a Ca2+ indicator, and variations in [Ca2+] are measured. Electrophysiologic properties of any individual neuron can also be recorded. For example, the inset shows the spontaneous activity recorded in a stratum oriens interneuron (Rosa Cossart, personal communication). B: Spatiotemporal patterns of neuronal activity evoked in the dentate gyrus in control and kainic acid (KA)-treated rat hippocampal slices. Level of neuronal activity is displayed according to the pseudocolor code (from background gray to highly activated red). (Adapted from Otsu et al., 2000.) (See color insert.)

Hence the main pitfall lies in the interpretation of the results and their applicability to epileptogenic conditions in intact systems. Slice preparations, however, can provide some insight into the connectivity and the transfer of information from one hippocampal subregion to another. Despite the issues of interpretation and applicability, comparing control and "epileptic" hippocampal slices has proven very useful for unraveling seizure-related modifications in network properties. Arguably the best use of the hippocam-pal slice preparation is for analysis of the reorganizations that take place within the various hippocampal networks during the latent period and the chronic phase of epilepsy as established within intact animal models. Such modifications give profound insights into epilepsy-associated brain plasticity. The future of this research focus lies, at least in part, in the simultaneous analysis of group and individual cell properties (e.g., with fluorescent dyes and patch-clamp recordings) in relevant models (e.g., a transgenic animal carrying the same mutation found in patients and displaying the same type of epilepsy). In this way the hippocampal slice constitutes an adjunctive approach to studying many of the models that are presented in other chapters in this volume.

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FIGURE 6—4 A: Two-photon imaging of the CA1 region of a hippocampal slice from a mouse. Pyramidal cell somata are clearly visible in the pyramidal cell layer (P); interneurons are visible in stratum oriens (O) and stratum radiatum (R). Neurons are filled with a Ca;+ indicator, and variations in [Ca2+]j are measured. Electrophysiologic properties of any individual neuron can also be recorded. For example, the inset shows the spontaneous activity recorded in a stratum oriens interneuron (Rosa Cossart. personal communication). B: Spatiotemporal patterns of neuronal activity evoked in the dentate gyrus in control and kainic acid (KA (-treated rat hippocampal slices. Level of neuronal activity is displayed according to the pseudocolor code (from background gray to highly activated red). (Adapted from Otsu et al., 2000.)

FIGURE 6—4 A: Two-photon imaging of the CA1 region of a hippocampal slice from a mouse. Pyramidal cell somata are clearly visible in the pyramidal cell layer (P); interneurons are visible in stratum oriens (O) and stratum radiatum (R). Neurons are filled with a Ca;+ indicator, and variations in [Ca2+]j are measured. Electrophysiologic properties of any individual neuron can also be recorded. For example, the inset shows the spontaneous activity recorded in a stratum oriens interneuron (Rosa Cossart. personal communication). B: Spatiotemporal patterns of neuronal activity evoked in the dentate gyrus in control and kainic acid (KA (-treated rat hippocampal slices. Level of neuronal activity is displayed according to the pseudocolor code (from background gray to highly activated red). (Adapted from Otsu et al., 2000.)

KArat 1 Normal f Calcium

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