Comparison of fluorescent voltage-sensitive dyes for multisite optical recording in hamster cerebral cortex by measurement of bicuculline-induced epileptiform events.

Two fluorescent voltage-sensitive dyes, RH795 and DI-2-ANEPPQ, were compared for in vivo multisite optical recording from the gustatory insular cortex of the golden Syrian hamster, the first reported use of DI-2-ANEPPQ in a mammalian brain preparation. The exposed cortex of the anesthetized hamster was stained with a 500 microM solution of either dye, and the cortical surface was imaged onto a 124-element photodiode array by an epifluorescence microscope equipped with a 2.5x objective (0.08 na) and appropriate excitation and emission filters for each dye. Background fluorescence was recorded with amplifiers in DC-coupled mode, and the bathing solution changed to one containing 100 microM bicuculline methiodide. Large, widespread epileptiform events were recorded optically, and with a surface electrode, within 2 min. Three experiments were carried out with each dye. The 10 recorded events from each experiment (and five detector records from each of these 10) having the largest signals were selected for comparison. Five measures were derived from the data: (1) The ratio of peak signal fluorescence to background fluorescence (delta F/F), (2) signal-to-noise power ratio (S/N), (3) root mean square noise (RMS noise), (4) an amplitude ratio (AR) consisting of the signal height divided by RMS noise, and (5) the peak value of the surface electrode record (SER). The results indicate a twofold increase in delta F/F and a fivefold increase in S/N (twofold increase in AR) with DI-2-ANEPPQ. No significant difference was found between dyes in the RMS noise or SERs. In addition, signals did not decline detectably over time with DI-2-ANEPPQ, but declined about 25%/h with RH795.