The pupillary light reflex in normal and innate microstrabismic cats, I: Behavior and receptive-field analysis in the nucleus praetectalis olivaris

Abstract

Neurons in the nucleus praetectalis olivaris (NPO) were antidromically identified by electrical stimulation of the nucleus of Edinger-Westphal (EW), the location of preganglionic pupilloconstrictor motoneurons. Electrical stimulation within the NPO leads to bilateral pupil constriction. Single neurons recorded in the NPO respond tonically to light stimuli, and their discharge frequency increases linearly with logarithmic increase in light intensity. This characteristic identifies NPO neurons as luminance detectors. They have large receptive fields mostly lying in the upper and contralateral quadrant of the visual field.Cats with impaired binocular vision show a significantly reduced binocular summation of the pupillary light reflex (BSP), i.e. the increase of pupil constriction during binocular illumination when compared to monocular illumination is less than in normal animals. The investigation of ocular dominance and subthreshold binocular interactions in the NPO of normal and innate microstrabismic cats revealed two possible mechanisms for BSP and its reduction in strabismic subjects. First, the percentage of neurons increasing their discharge rate by illuminating either eye is significantly reduced in the NPO of innate microstrabismic cats (6.6%) when compared to normal cats (22% of all neurons tested). Second, in most NPO neurons of normal cats the subthreshold influence of the ipsilateral eye leads to an increase in neuronal activity during binocular stimulation when compared to monocular stimulation of the contralateral eye (binocular summation). The subthreshold influence of the ipsilateral eye in most NPO neurons of microstrabismic cats, however, is inhibitory, i.e. the neuronal discharge rate during binocular stimulation is decreased when compared to monocular stimulation of the contralateral eye (binocular inhibition). However, there is no significant correlation between BSP and binocularity in the NPO in individual animals. This suggests that BSP may be additionally influenced by visual structures other than NPO.

Transneuronal retinal input to the primate Edinger-Westphal nucleus

“…In transverse sections, the olivary nuclei could be recognized easily in every animal. Neurons in the olivary nucleus respond to changes in retinal illuminance, and microstimulation of the olivary nucleus produces pupil constriction (Trejo and Cicerone, 1984;Clarke and Ikeda, 1985;Distler and Hoffmann, 1989;Gamlin et al, 1995). These experiments, coupled with anatomical evidence for a direct retinal projection, leave little doubt that the olivary nucleus serves the pupillary light reflex.…”

Interactive Events Subserving the Pupillary Light Reflex in Pigmented and Albino Rats

“…Engel, 1967;ten Doesschate and Alpern, 1967). Now with a clear hindsight of the anatomical substrates underlying the PLR (Campbell and Lieberman, 1985;Clarke and Ikeda, 1985;Distler and Hoffmann, 1989a;Young and Lund, 1994) and the use of invasive techniques in animal models, we have re-addressed the problem with a new perspective, using animals with different decussation patterns, selective pretectal nucleus lesions and employing an improved pupillometry system.…”

The effect of pupil size on binocular summation at suprathreshold conditions

“…31 The discrepancy between our results on binocular summation at suprathreshold and those reported by Collier 11 and Campbell & Green 13 at the threshold, can be explained by assuming that, at the threshold, these mechanisms present no significant activity, as might occur under suprathreshold conditions. It noteworthy that Dinse and Krüger 49 found in peristriate cortical regions, where eye control is processed, [4][5][6]41 signal-to-noise thresholds higher than near and striate areas. Similarly, in pupillogram studies, when stimuli were just above the threshold, pupil reflexes were weaker, the speed of response was slower, and latency increased in comparison to responses for clearly visible stimuli.…”

“…18,19,[24][25][26] In the present study, this form of expression could not be appropriate because it is assumed that different VRTs could produce equal summation ratios, obviating the difficulty of the task. To avoid these problems, we propose that summation ratios can be better defined for each experimental condition in the natural-and artificialpupil conditions by an expression similar to that used by Distler & Hoffman 41 for binocular summation of the pupillary light reflex, adapted to the present VRT experiments: (1) where VRT R , VRT L , VRT B refer to the mean visual-reaction time for the right eye, the left eye and binocular vision, respectively. Expression (1) is thus a performance parameter per se.…”