Abstract
We have examined the properties of neurons from the visual cortex of postnatal Long Evans rats in dissociated cell culture. Visual cortex from rat pups 1–15 d old was subjected to enzymatic and mechanical dissociation to yield a suspension of single cells. Neurons plated onto collagen or a feeder layer of astrocytes rapidly extended processes and survived for 4–10 weeks. Antisera to glutamic acid decarboxylase, choline acetyltransferase, and vasoactive intestinal polypeptide stained 22 +/- 2, 2.3 +/- 0.3, and 2.4 +/- 0.2% of all neurons, respectively, suggesting that different neuronal classes survived roughly in proportion to their number in vivo. In order to study a particular identified class of cortical neurons, we prelabeled cells in vivo by retrograde transport of a fluorescent tracer. Neurons in layer V of visual cortex that project to the superior colliculus were labeled after injecting fluorescent latex microspheres into the colliculus. Retrogradely labeled neurons were readily identified immediately after dissociation and throughout the period in vitro. After 2 weeks in culture, labeled cells exhibited many ultrastructural features characteristic of pyramidal neurons in vivo. Intracellular recording techniques were used to evaluate the response properties of labeled layer V neurons, as well as other, unlabeled neurons, to excitatory amino acid agonists and antagonists. Glutamate and aspartate--as well as the synthetic agonists N-methyl-D-aspartate (NMDA), kainate, and quisqualate--excited every cortical neuron tested. The antagonist 2- amino-5-phosphonovaleric acid had no effect on responses to quisqualate and kainate but completely blocked depolarizations due to NMDA and aspartate and reduced depolarizations elicited by low concentrations of glutamate. Kynurenic acid, piperidine dicarboxylic acid, and gamma-D- glutamylglycine antagonized responses to all 5 of the agonists. These results provide evidence that corticocollicular neurons in culture express both NMDA-type and non-NMDA receptors for excitatory amino acids.
