Glutamic Acid Decarboxylase and Glutamate Receptor Changes during Tolerance and Dependence to Benzodiazepines

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 98; no. 6; pp. 3483 - 3488
• Main Authors: Izzo, Emanuela, Auta, James, Impagnatiello, Francesco, Pesold, Christine, Guidotti, Alessandro, Costa, Erminio
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 13.03.2001; National Acad Sciences; The National Academy of Sciences
• Subjects: Animals; Antibodies; Biological Sciences; Brain - drug effects; Brain - metabolism; Dendrites; Diazepam - pharmacology; Drug therapy; Drug Tolerance; Frontal Lobe - drug effects; Frontal Lobe - metabolism; GABA Modulators - pharmacology; Gene Expression Profiling; Glutamate Decarboxylase - genetics; Glutamate Decarboxylase - metabolism; Hippocampus; Hippocampus - drug effects; Hippocampus - metabolism; Isoenzymes - genetics; Isoenzymes - metabolism; Ligands; Male; Messenger RNA; N methyl D aspartate receptors; Neurological disorders; Neurology; Occipital Lobe - drug effects; Occipital Lobe - metabolism; Rats; Rats, Inbred F344; Receptors; Receptors, AMPA - genetics; Receptors, AMPA - metabolism; RNA, Messenger; Seizures; Substance-Related Disorders; Time Factors; Vehicles
• DOI: 10.1073/pnas.051628698
• ISSN: 0027-8424

Protracted administration of diazepam elicits tolerance, whereas discontinuation of treatment results in signs of dependence. Tolerance to the anticonvulsant action of diazepam is present in an early phase (6, 24, and 36 h) but disappears in a late phase (72-96 h) of withdrawal. In contrast, signs of dependence such as decrease in open-arm entries on an elevated plus-maze and increased susceptibility to pentylenetetrazol-induced seizures were apparent 96 h (but not 12, 24, or 48 h) after diazepam withdrawal. During the first 72 h of withdrawal, tolerance is associated with changes in the expression of GABAA (γ-aminobutyric acid type A) receptor subunits (decrease in γ2 and α1; increase in α5) and with an increase of mRNA expression of the most abundant form of glutamic acid decarboxylase (GAD), GAD67. In contrast, DL-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor GluR1 subunit mRNA and cognate protein, which are normal during the early phase of diazepam withdrawal, increase by approximately 30% in cortex and hippocampus in association with the appearance of signs of dependence 96 h after diazepam withdrawal. Immuno-histochemical studies of GluR1 subunit expression with gold-immunolabeling technique reveal that the increase of GluR1 subunit protein is localized to layer V pyramidal neurons and their apical dendrites in the cortex, and to pyramidal neurons and in their dendritic fields in hippocampus. The results suggest an involvement of GABA-mediated processes in the development and maintenance of tolerance to diazepam, whereas excitatory amino acid-related processes (presumably via AMPA receptors) may be involved in the expression of signs of dependence after withdrawal.