Absolute and relative sensitivity of the scotopic system of rat: Electroretinography and behavior

Abstract

The goal of the present study was to relate the dark and light-adapted flash sensitivity of the scotopic threshold response (STR) and rod b-wave of the electroretinogram (ERG) to behaviorally measured rod increment threshold responses. Small amplitudes of the dark-adapted STR and b-wave, the latter after application of NMDA, were found to increase in proportion to flash intensity. The value obtained for the sensitivity of the b-wave would be expected if signals from rods were summed linearly by the rod bipolar cell. The sensitivity of the STR could not be accounted for in terms of rod signal convergence as the source of this ERG component is still unknown. Increment threshold responses of rats were measured behaviorally in an operant conditioning chamber. At absolute threshold, on average I in 2400 rods were activated by the test flash. Comparison of the adaptive effects of background lights on behaviorally measured scotopic sensitivity and rod ERG sensitivity suggest that the increment threshold sensitivity of rat is regulated at three different sites in the retina.

Controlling the Gain of Rod-Mediated Signals in the Mammalian Retina

“…6). These backgrounds are substantially higher than those required to halve the sensitivity of the ERG scotopic threshold response (a signal originating at unknown sites in the inner retina) (Frishman and Sieving 1995;Naarendorp et al, 2001;Saszik et al, 2002) and the sensitivity of spike responses of cat retinal ganglion cells measured in vivo (Barlow and Levick, 1969;Enroth-Cugell and Shapley, 1973). Furthermore, weak backgrounds decrease the gain of the scotopic threshold response but not the ERG b-wave (attributed to activity of rod bipolar cells).…”

“…Possible differences between in vivo and in vitro preparations do not appear to be caused by slicing the retina because the sensitivity of ganglion cells in our slice and flatmount preparations are consistent with each other and with other studies of mouse ganglion cells (see Materials and Methods). Second, in vivo recordings from cat ganglion cells (Barlow and Levick, 1969;Enroth-Cugell and Shapley, 1973) and measurements of the scotopic threshold response (Frishman and Sieving, 1995;Naarendorp et al, 2001;Saszik et al, 2002) show decreases in gain for weaker backgrounds than those required to reduce the gain of the AII amacrine responses. Species differences likely contribute to this difference, because the backgrounds required to reduce the gain of the scotopic threshold response differ by a factor of ϳ5 between cat and mouse (Frishman and Sieving, 1995;Saszik et al, 2002).…”

“…Past work has established that the saturation threatened by convergence and amplification is prevented by gain control mechanisms operating within the inner retina, i.e., by interactions between bipolar, amacrine, and ganglion cells (Dowling, 1967;Barlow and Levick, 1969; Enroth-Cugell and Shapley, 1973;Frishman and Sieving, 1995;Naarendorp et al, 2001). However, it is not known how or where in the inner retina gain is controlled.…”

Detection of Visual Activation in the Rat Brain Using 2-deoxy-2-[18F]fluoro-d-glucose and Statistical Parametric Mapping (SPM)

“…Sensitivity to light stimulation in albino and pigmented rodents has been studied using behavioral and electrophysiological techniques [7][8][9][10][11][12]; however, there are no studies using in vivo imaging techniques.…”

Light response differences in the superior colliculus of albino and pigmented rats

“…The light sensitivity in albino and pigmented rodents has been studied using behavioral and electrophysiological techniques [1][2][3]7,8,10,[14][15][16]19]. There are differences in opinion regarding the visual sensitivity of albino rodents.…”