Post-insult activity is a major cause of delayed neuronal death in organotypic hippocampal slices exposed to glutamate
Section snippets
Preparation of cultures
Organotypic cultures of the hippocampus were prepared according to the method of Stoppini et al. (1991). The rats were obtained from the Departmental animal house. Tranverse slices (thickness 350 μm) were cut from the dorsal two thirds (septal end) of hippocampi from P11–13 Wistar rats using a McIlwain tissue chopper. They were then placed for ∼1 h at 26°C in a bicarbonate-buffered Ringer solution containing (in mM) NaCl 124, KCl 3, CaCl2 2, NaHCO3 25, NaH2PO4 1.1, MgSO4 2 and glucose 10, and
The pattern of delayed pyramidal cell death
The standard bolus application of 10 mM glutamate for 30 min (see Experimental procedures) led to the following pattern of progressive cell damage within the hippocampus: at the earliest time points, 2–5 h after the insult (Fig. 1A), diffuse acute degeneration was observed all over the slice, including the cells in the hilus of the dentate gyrus. Delayed degeneration of hippocampal pyramidal cells started from the subicular (medial) end of the CA1 region by 15–17 h (Fig. 1B). Then it continued
Discussion
Earlier studies searching for hippocampal hyperexcitability after global brain ischemia have shown that in subsequent ex vivo slice experiments, increased spontaneous firing of the CA1 pyramidal cells (Kirino, 1992) or enhanced synaptic transmission at the CA3-CA1 synapse (Urban et al., 1989, Schurr et al., 1995) was present 1–24 h after the insult (but see Jensen et al., 1991). An attenuation of gross activity in CA1 was regularly observed after 48 h, preceding pyramidal cell death (Urban et
Acknowledgements
We thank Prof. Juha Voipio and Dr. Sebastian Schuchmann for constructive comments on the manuscript, and Sisko Laukola and Salme Ollikainen for skillful assistance in slice culturing. The study was supported by the Academy of Finland (Programme of Molecular Neurobiology), the Research and Science Foundation of Farmos, and the Sigrid Juselius and Ella and Georg Ehrnrooth Foundations.
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