Optical imaging of dynamic horizontal spread of excitation in rat auditory cortex slices

Optical recordings using a voltage-sensitive dye (RH482) were conducted in brain slice preparations to investigate spatiotemporal patterns of excitation in the rat auditory cortex. Electrical stimulation of the border between the white matter and layer VI evoked vertical as well as horizontal spreading responses. While velocities of vertical and horizontal propagation of excitation were similar to those reported in non-disinhibited preparations, the horizontal propagation was widespread and strong especially in layers II/III in auditory cortex slices. This horizontal spread was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but not by D-2-amino-5-phosphonopentanoic acid (D-AP5). These results suggest that the horizontal responses, especially in layers II/III, are prominent and are mediated primarily by non-N-methyl-D-aspartic acid (NMDA) receptors in the auditory cortex.