Pharmacological modulation of the rod pathway in the cat retina

1. In the intact cat eye, the responses of ganglion cells to light stimulation were recorded extracellularly and the actions of iontophoretically applied 2-amino-4-phosphonobutyrate (APB), a potent agonist at ON-bipolars, and of strychnine, a glycine antagonist, were investigated. 2. Under light-adapted conditions, the activity of ON-center ganglion cells is decreased by APB but is increased by strychnine. APB and strychnine act independently of one another. 3. The activity of light-adapted OFF-center ganglion cells is increased by APB and by strychnine. The light response remains clearly modulated. Strychnine blocks the action of simultaneously applied APB. The results are in agreement with the action of a push-pull mechanism, according to which ON-cone-bipolars provide a glycinergic input into OFF-center ganglion cells. 4. Under dark-adapted conditions, APB blocks the light responses of both ON-center and OFF-center ganglion cells. The discharge rate of ON-center ganglion cells is completely suppressed; OFF-center ganglion cells show a high maintained discharge. 5. Strychnine blocks the scotopic light response of OFF-center ganglion cells and blocks the action of simultaneously applied APB. The light response of ON-center ganglion cells is hardly affected by strychnine. 6. The effects of strychnine on OFF-center ganglion cells are in agreement with the hypothesis that the glycinergic AII amacrine cells modulate the activity of the scotopic OFF-channel. 7. Intravitreally applied APB abolished the scotopic b-wave of the electroretinogram at concentrations of 100 microM. 8. Our data suggest that as in rabbit (10) the rod bipolars in cat retina are depolarizing (ON) bipolar cells.