FIG. 3.
Spontaneous activity and evoked field potentials were recorded from a hippocampal slice using the SMEA. Before recording, an SMEA was subjected to 30 cycles of stretching to demonstrate its mechanical robustness. (A) A light micrograph of a hippocampal slice (5 DIV) on the SMEA (a nylon mesh holds the slice in place) and a schematic of the hippocampal anatomy. (B) Spontaneous activity of spikes was recorded using the SMEA, and the activity was diminished by 1 μM TTX. (Inset) Spontaneous activity before and after TTX from one electrode (E10). The peak-to-peak amplitude of spontaneous spikes ranged from 15 μV to more than 60 μV over a noise level of 1.86 μVrms. After 1 μM TTX was applied to the recording chamber, the firing rate monotonically decreased from approximately 8 Hz to 0 in 2 min. (C) Evoked field potentials were recorded from a hippocampal slice using the SMEA. A series of constant current, bipolar, biphasic stimuli (with increasing amplitude) was applied through two SMEA electrodes (E05 and E11) located within the DG region, and evoked field potentials were recorded from the other nine electrodes. The amplitude of evoked response in one channel (E10) located in the CA3 region was plotted versus intensity of applied stimuli (n = 3 each). The S/R curve was fitted with a sigmoidal function (dashed line). (Inset) An evoked field potential (at a stimulus intensity of 150 μA) recorded from one SMEA electrode (E10) before and after the cocktail was given. The response was essentially eliminated with a pharmacological cocktail of neuronal channel and receptor antagonists (1 μM TTX, 50 μM BIC, 100 μM APV, and 100 μM CNQX), and the remaining signal was attributed to stimulus artifact. The artifact was generated, in part, by the stimulator sync pulse and was present even when the stimulus intensity was set to 0.