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Wang J, Reichling DB, Kyrozis A, MacDermott AB: Developmental loss of GABA- and glycine-induced depolarization and Ca2+ transients in embryonic rat dorsal horn neurons in culture. Hear Res. 2000 Feb;140(1-2):126-36.
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 early in development and play a role in postmitotic differentiation. |
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