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B. A. Ekesten, P. Gouras; A Fast Response Complex in Murine Striate Cortex. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1434.
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To understand the source of a light-driven, fast response complex (FRC) comprised by a short latency spike-like potential of brief duration (10 ms) and relatively large amplitude (1 mV) followed by a series of oscillations, unpredictably detected in murine striate cortex.
Glass microelectrodes were used to record local responses to diffuse light pulses from striate cortex of pentobarbithal-anesthetized mice. Variations in the light stimulus wavelength and intensity, as well as the presence and absence of selective chromatic adaptation were used to assess the contribution of UV- and M-cones to the FRC in different areas and depths of V1.
We encounter the FRC in about 10% of penetrations into murine striate cortex and only with glass microelectrodes. It seems confined to local areas being often lost with small movements of the pipette. There are two forms: a spike-like negative wave followed by prolonged oscillations and its mirror image, a positive spike-like response with reversed polarity oscillations. Impulses of small amplitude ride on the spike-like responses. The negative spike seems more common in upper, the positive spike in deeper layers. Light stimulation of the UV- and M-cone opsins influence the response similarly in most areas of striate. Selective chromatic adaptation shows that orange light often suppresses the response to UV stimuli, implying co-expression of both cone opsins in the cones affecting this response. The latency of the FRC is about 30-40 ms, reflecting the earliest event to reach the cortex. It has several unique aspects. One is that the FRC can occur spontaneously. The second is an asymmetry in the rising and falling phases of the spike-like response and the oscillations where very fast voltage changes occur. The third is an all or none like behavior of the spike-like component of the FRC.
An unusual evoked response exists in murine striate cortex that is larger and faster than that reported for light-evoked cortical responses of mice. Whether this response represents a unique structure or an unusual synchrony of neuronal discharges in either the LGN input or postsynaptic responsive neurons in striate cortex remains to be determined.
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