title: GABA induces activity dependent delayed-onset uncoupling of GABA/benzodiazepine site interactions in neocortical neurons.
abstract: Changes in the function of type A gamma-aminobutyric acid receptors (GABA(A)Rs) are associated with neuronal development and tolerance to the sedative-hypnotic effects of GABA(A)R positive modulators. Persistent activation of GABA(A)Rs by millimolar concentrations of GABA occurs under physiological conditions as GABAergic fast-spiking neurons in neocortex and cerebellum exhibit basal firing rates of 5 to 50 Hz and intermittent rates up to 250 Hz, leaving a substantial fraction of synaptic receptors occupied persistently by GABA. Persistent exposure of neurons to GABA has been shown to cause a down-regulation of receptor number and an uncoupling of GABA/benzodiazepine (BZD) site interactions with a half-life of approximately 24 h. Here, we report that a single brief exposure of neocortical neurons in primary culture to GABA for 5-10 min (t(1/2) = 3.2 +/- 0.2 min) initiates a process that results in uncoupling hours later (t(1/2) = 12.1 +/- 2.2 h). Initiation of delayed-onset uncoupling is blocked by co-incubation with picrotoxin or alpha-amanitin but is insensitive to nifedipine, indicating that uncoupling is contingent upon receptor activation and transcription but is not dependent on voltage-gated Ca2+ influx. Delayed-onset uncoupling occurs without a change in receptor number or a change in the proportion of alpha1 subunit pharmacology, as zolpidem binding affinity is unaltered. Such activity dependent latent modulation of GABA(A)R function that manifests as delayed-onset uncoupling may be relevant to physiological, pathophysiological, and pharmacological conditions where synaptic receptors are transiently exposed to GABA agonists for several minutes.
authors.affiliation: Laboratory of Molecular Neurobiology, Department of Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
authors.forename: María C
authors.initials: MC
authors.lastname: Gravielle
authors.forename: Ramona
authors.initials: R
authors.lastname: Faris
authors.forename: Shelley J
authors.initials: SJ
authors.lastname: Russek
authors.forename: David H
authors.initials: DH
authors.lastname: Farb
mesh_terms: D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D001569:Benzodiazepines / Q000737:chemistry; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009995:Osmosis; D010852:Picrotoxin / Q000494:pharmacology; D011485:Protein Binding; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000737:chemistry / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014158:Transcription, Genetic; D000077334:Zolpidem; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D000546:Amanitins; D001569:Benzodiazepines; D002118:Calcium; D018076:DNA, Complementary; D009543:Nifedipine; D010852:Picrotoxin; D011725:Pyridines; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D000077334:Zolpidem; D005680:gamma-Aminobutyric Acid