Developmental Loss of GABA- and Glycine-induced Depolarization and Ca2+ Transients in Embryonic Rat Dorsal Horn Neurons in Culture |
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Authors: | Jian Wang David B Reichling reas Kyrozis Amy B MacDermott |
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Institution: | Department of Physiology and Cellular Biophysics and Center for Neurobiology and Behavior, Columbia University, 1106 Black Building, 630 W. 168th Street, New York, NY 10032, USA |
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Abstract: | More than 90% of dorsal horn neurons from embryonic day 15–16 rats responded to the inhibitory amino acids GABA and glycine by a transient elevation of intracellular Ca2+ concentration (Ca2+]i) when maintained in culture for <1 week. This Ca2+]i response has previously been shown to be due to depolarization and subsequent Ca2+ entry through voltage-gated Ca2+ channels following activation of bicuculline-sensitive GABAA receptors and strychnine-sensitive glycine receptors. Both the number of cells responding to GABA and glycine and the amplitude of the Ca2+]i response diminished over time in culture. By 30 days in culture, none of the cells responded to GABA, muscimol or glycine by elevation of Ca2+]i. The loss of the Ca2+]i response was not due to a change in the abundance or the properties of voltage-gated Ca2+ channels, since over the same period of time dorsal horn neurons showed a large increase in the amplitude of the Ca2+]i transient in response to 30 mM K+. Nor was the loss of the Ca2+]i response due to a loss of GABA and glycine receptors. Instead, the decrease in the Ca2+]i response over time paralleled a similar change in the electrophysiological responses. More than 90% of the neurons tested were depolarized in response to inhibitory amino acids during the first week in culture. After 30 days, all neurons tested responded to GABA and glycine with a hyperpolarization. These observations add support to the suggestion that GABA and glycine may excite dorsal horn neurons earlyin development and play a role in postmitotic differentiation. |
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Keywords: | development chloride voltage-gated Ca2+ channels spinal cord |
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