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A.J. Valjakka, J. Ahonen, L. Pitkänen, K. Gurevicius, A. Urtti; The Consequences of Light-Induced Retinal Lesion on the Time-Gain Dynamics of Field Potential Generation by Flashes in the Retina-to-Superior Colliculus Track of Freely Moving Rats . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4120.
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Purpose: The properties, and retinal photoreceptor layer-mediated control, of the time-size dynamics of flash-evoked field potentials in the retina and conjointly in the superficial layers of the contralateral superior colliculus (SC) in freely moving albino rats were studied. Methods: The reproducible electroretinograms from the conjunctival surface of the eye were recorded with a novel device developed for the present experiment. Results: The following issues were established: (1) the biphasic saturation function of both the implicit amplitude maxima and latency of evoked responses by the stimulus intensity in both the retina (a- and b-wave) and SC (peak-1 and -2), (2) the integration of discrete non-linearities of corresponding response functions forming the two major groupings of increased values, below and above the intermediate level of stimulus intensity, (3) about fourfold magnification of the dynamic variation range of amplitude of peak-1 and -2 in the SC when compared to that of the a-wave in the retina, (4) differing response latency-vs-stimulus intensity functions between the opposite polarization phases of peak-1 and -2 of the SC and the a-wave of the retina, (5) appearance of peak-1 of the SC before the a-wave peak that in turn invariably preceded peak-2 of the SC, and (6) the relative consistency of duration between peak-2 and peak-1 in relation to the moment of its appearance or timing of the a-wave peak by the variation of flash intensity. The two-week exposure of rats to constant light, which demonstrably damaged the retinal photoreceptor layer, caused principal alterations of noteably only points 1-3: i.e. reduction (and delay) of evoked responsiveness that involved differential dampings in amplitudes of the a-wave and peak-1/-2, and the change of associated biphasic response-functions to a single-phase type. Conclusions: These data point to (A) two complementary mechanisms of light intensity reception by the retina, dependent on the photoreceptor layer and retinal integrity, (B) contribution of retinal composite processes of the a-wave to the induction of biphasic responses of peak-1 and -2 in the SC, and (C) the adaptive, stimulus intensity-dependent and time-constrained foldings of non-linearly and individually modulated polarization phases of evoked responses in the retina and SC. The developed system enables one to determine the condition of retina, optic nerve, and vision track structures in freely behaving and conscious animals, in subchronic/chronic studies.
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