Hippocampal slice extracellular recording

Hippocampal slices (400-500 frm) were quickly prepared from male Wistar rats (8- to 9-weeks-old) and maintained in a chamber at 35 °C, where they were continuously perfused with artificial cerebrospinal fluid as described in our previous paper [11]. A bipolar tungsten electrode was placed in the stratum radiatum to stimulate Schaffer collateral and commissural afferents. The evoked potential was extracellularly recorded from the pyramidal cell layer of the CA1 subfield with a glass capillary microelectrode. A single test stimulation (0.05 msec duration) was applied at intervals of 30 sec. Drugs were delivered by perfusion. To induce potentiation of the evoked potentials, tetanic stimulation was applied at the same intensity through the same stimulating electrode as used for the test stimulation. The magnitude of LTP was evaluated by the population spike amplitude 30 min after tetanic stimulation. 

A more direct approach is to assess the effects of PUFA on neuronal excitability. We tested the effects of DHA on seizures in vitro, using the zero-Mg2+ model (Stafstrom, Wang, and Jensen, unpublished data). Extracellular recordings were made from the CAl subfield in hippocampal slices of P14 rats. When the external Mg2+ was removed from the bathing medium, spontaneous interictal discharges and more prolonged, intense ictal bursts appeared (Fig. 3). Perfusion ofDHA (100 pM) eliminated those ictal bursts in a... 

It is important to consider the optimal time to perform an experiment Slice cultures change continuously in vitro. The development of the hippocampal slice in vitro has not been extensively studied. Extracellular recordings have shown that synaptic responses are substantially lai]ger at 21 than at 7 DIV (3). The mossy fiber pathway connecting dentate granule cells with CA3 pyramidal cells and hilar intemeurons forms entirely in vitro between 14 and 21 DIV (4,5,7). After 28 DIV, a steadily increasing proportion of cultures will be spontaneously epileptic see Note 14). As a result, we perform most experiments between 21-28 DIV. This permits mossy fiber development, yet avoids spontaneous epileptiform activity. 

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