Intravitreal kainic acid severely reduces the size of the developing optic tectum in newly hatched chickens

Abstract

Following a single intravitreal injection of 200 nmol of kainic acid (KA) to newly hatched chickens, there are acute and long-term effects on retinal ganglion cells in the chicken retina. Thirty min after injection, most ganglion cells showed cytoplasmic vacuolization. However, 14 days later, most ganglion cell soma appeared normal. Almost 60% of the cells in the ganglion cell layer (GCL) were lost, suggesting that displaced amacrine cells and not more than 40% of the ganglion cells had been eliminated. Following intravitreal injection of wheat germ agglutinin conjugated to horseradish peroxidase 14 days after the KA lesion, the amount of HRP reaction product was reduced to all retinorecipient layers, especially layers IIc and IId, of the tectum contralateral to the KA-treated eye. Fourteen days after the injection of kainic acid, during which the control tecta grow appreciably, all the superficial layers of the tectum contralateral to the kainic acid-lesioned eye, especially layers IIc and IId, were smaller than in controls, and did not differ in size from those seen ? contralateral to cut optic nerves. It is not clear whether this is a result of a developmental failure, or a shrinkage, or a combination of these factors. These results suggest that subtypes of ganglion cells may have a disproportionate influence in the maintenance of the cytoarchitectural integrity in the optic tectum. Alternatively the removal of the OFF-bipolar cells and amacrine cells presynaptic to ganglion cells may decrease their metabolism, and restrict the supply of trophic influences to the developing tectal cells.