Cat retinal ganglion cell receptive-field alterations after 6-hydroxydopamine induced dopaminergic amacrine cell lesions.

Abstract

Optic tract single-unit recordings were used to study ganglion cell response functions of the intact cat eye after 6-hydroxydopamine (6-OHDA) lesioning of the dopaminergic amacrine cell (AC) population of the inner retina. The impairment of the dopaminergic AC was verified by high pressure-liquid chromatography (HPLC) with electrochemical detection of endogenous dopamine content and by [3H]dopamine high-affinity uptake; the dopaminergic ACs of the treated eyes demonstrated reduced endogenous dopamine content and reduced [3H]dopamine uptake compared with that of their matched controls. Normal appearing [3H]GABA and [3H]-glycine uptake in the treated retinas suggests the absence of any nonspecific action of the 6-OHDA on the neural retina. The impairment of the dopaminergic AC population was found to alter a number of response properties in off-center ganglion cells, but this impairment had only a modest effect on the on-center cells. An abnormally high proportion of the off-center ganglion cells in the 6-OHDA treated eyes possessed nonlinear, Y-type receptive fields. These cells also possessed shift-responses of greater than normal amplitude, altered intensity-response functions, reduced maintained activities, and more transient center responses. Of the on-center type cells, only the Y-type on-center cells were affected by 6-OHDA, possessing higher than normal maintained activities and altered intensity-response functions. The on-center X-cells were unaffected by 6-OHDA treatment. The dopaminergic AC of the photopically adapted cat retina therefore modulates a number of ganglion cell response properties and within the limits of this study is most prominent in off-center ganglion cell circuitry. When functioning normally, the dopaminergic AC of the cat's retina appears to make the receptive field of the off-center cell more sustained and may make its spatial summation characteristics more linear while adjusting the intensitive properties of neurons in both the on- and off-center pathways.