Developmental loss of GABA- and glycine-induced depolarization and Ca2+ transients in embryonic rat dorsal horn neurons in culture.
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.
Wang
J
J
Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032.
Reichling
D B
DB
Kyrozis
A
A
MacDermott
A B
AB
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D005998:Glycine / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009118:Muscimol / Q000494:pharmacology; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D009467:Neuromuscular Depolarizing Agents; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D005998:Glycine; D001640:Bicuculline