| The properties of neurons from the visual cortex of postnatal Long Evans rats were examined in dissociated cell culture. Visual cortex from rat pups 1 to 15 days old was dissociated 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 {dollar}gamma{dollar}-aminobutyric acid, glutamic acid decarboxylase, choline acetyltransferase and vasoactive intestinal polypeptide stained 24 {dollar}pm{dollar} 5%, 22 {dollar}pm{dollar} 2%, 2.3 {dollar}pm{dollar} 0.3% and 2.4 {dollar}pm{dollar} 0.2% of all neurons, respectively, suggesting that different neuronal classes survived roughly in proportion to their number in vivo.; Prior to dissociation, neurons in layer V of visual cortex that project to the superior colliculus were labeled in vivo by retrograde transport of fluorescent latex microspheres--a permanent fluorescent marker. Retrogradely labeled neurons were readily identified immediately after dissociation and throughout the period in vitro. After two weeks in culture, labeled cells exhibited many ultrastructural features characteristic of pyramidal neurons in vivo.; Intracellular recording techniques were used to evaluate the pharmacology of responses of cortical neurons to excitatory amino acids as well as the pharmacology of epsps. Glutamate, aspartate, N-methyl-D-aspartate (NMDA), kainate, and quisqualate excited every cortical neuron tested. Kynurenic acid, piperidine dicarboxylic acid and {dollar}gamma{dollar}-D-glutamylglycine anatagonized responses to all five agonists. These 3 drugs also completely blocked monosynaptic epsps produced by corticocollicular neurons and by most other excitatory neurons. APV, 2-amino-5-phonovaleric acid, selectively antagonized responses to NMDA and reduced polysynaptic excitation. In Mg{dollar}sp{lcub}2+{rcub}{dollar} free medium, most epsps exhibited a slow component that was blocked by APV. These results suggest that most excitatory cortical neurons in culture use an excitatory amino acid neurotransmitter. Epsps are largely mediated by non-NMDA receptors, but in Mg{dollar}sp{lcub}+2{rcub}{dollar} free medium most epsps exhibit a slow, APV-sensitive component attributable to the NMDA receptor. |
