ABSTRACT
Animal conflict models have been used for years as a preclinical screen for predicting anxiolytic therapeutic efficacy. Anxiolytics, including benzodiazepines, increase punished responding. This suggests that the punished behavior may be mediated by the GABA receptor. To evaluate this hypothesis, we performed in situ hybridization histochemistry studies of GABA receptor subunits (alpha1-alpha4) and synthetic enzymes glutamic acid decarboxylase (GAD65 and GAD67) in four groups of rats: conflict (punishment), yoked controls (rats shocked without conflict training history), fixed interval only controls (rats that worked for food but were not shocked) and untreated controls. With conflict behavioral training, bilateral reduction of mRNA for the GABAA alpha1 subunit was seen relative to controls in the cortex, thalamus and hippocampus. In contrast, alteration of alpha2 mRNA levels appeared only in the yoked control group, with increased levels seen in the thalamus and cortex and decreased levels in the hippocampus. There were no differences in the alpha2 mRNA level between the control and the conflict behavioral trained animals. Further, no significant differences were found between groups in the mRNA levels for the alpha3 subunit, alpha4 subunit, GAD65, and GAD67. These results suggest that the behaviors related to conflict and uncontrollable aversive stimuli (yoked control group) are accompanied and perhaps mediated by selective changes in the GABAA alpha1 or alpha2 subunits, respectively. These findings highlight the potential usefulness of the conflict model as a means of elucidating the biological underpinnings of anxiety disorder. Published by Elsevier Science B.V. All rights reserved.
Subject(s)
Brain/metabolism , Conflict, Psychological , Glutamate Decarboxylase/biosynthesis , Neurons/metabolism , Receptors, GABA-A/biosynthesis , Transcription, Genetic , Animals , Cerebral Cortex/metabolism , Electroshock , Hippocampus/metabolism , Macromolecular Substances , Male , Organ Specificity , Punishment , Pyramidal Cells/metabolism , RNA, Messenger/biosynthesis , Rats , Rats, Sprague-Dawley , Reference Values , Thalamus/metabolismABSTRACT
We isolated a rat orphan nuclear hormone receptor from a brain cortex cDNA library. The sequence of the cDNA insert was 2154 bp with an open reading frame of 1794 bp encoding a putative protein of 598 amino acids and predicted molecular mass of 65 kDa. The deduced amino acid sequence showed a strong homology to the mouse nurr1 and human NOT1 orphan nuclear hormone receptors of the NGFI-B/nur77/NAK1 gene subfamily. We refer to this rat clone as r-nurr1. Northern blot analysis showed that r-nurr1 mRNA was highly expressed in the brain and moderately in the lung as a 4.0 kb transcript. A smaller transcript of 2.5 kb was also detected in the testes. The level of r-nurr1 transcript in the heart, skeletal muscle, liver, kidney and spleen was marginal. In situ hybridization showed that r-nurr1 mRNA was constitutively expressed in various regions of the CNS, particularly in the deeper layers (IV to VI) of the perirhinal cortex and area 2 of parietal cortex. We further evaluated the modulation of r-nurr1 expression in CNS by an electroconvulsive seizure (ECS) and by an amgydala-kindled seizure. A single ECS administered via earclip electrodes induced a rapid and transient increase of r-nurr1 mRNA in the granule cells of the dentate gyrus, being significant at 15 min after the seizure, maximal approximately 1 h and back to baseline at 4 h. The amygdala kindled seizure revealed a less robust and restricted nurr-1 induction in the CNS, as only two of the four kindled animals showed a unilateral induction of nurr1 mRNA in the dentate gyrus. These results suggest that r-nurr1 is an immediate-early gene that is differentially induced by ECS vs. kindled seizures. In addition, as r-nurr1 is prominently expressed in the specific brain sites associated with memory acquisition and consolidation, it may play a role in memory processing.
Subject(s)
Cerebral Cortex/metabolism , DNA-Binding Proteins , Dentate Gyrus/metabolism , Hippocampus/metabolism , Seizures/metabolism , Transcription Factors/metabolism , Animals , Base Sequence , Cloning, Molecular , Electroshock , Humans , In Situ Hybridization , Kindling, Neurologic , Male , Mice , Molecular Sequence Data , Nuclear Receptor Subfamily 4, Group A, Member 2 , Rats , Rats, Sprague-DawleyABSTRACT
The GABAergic system is sexually dimorphic in certain brain regions and can be regulated by testosterone (T). However, the contribution of T to sex-specific developmental processes in the brain is less clear. We have examined whether T regulates expression of GABA(A) receptor alpha2 subunit in the cerebral cortex of embryonic and postnatal female rats using in situ hybridization and Western blotting. We found that both alpha2 mRNA and protein levels are significantly increased by T treatment at embryonic day 20 (E20) and birth (P0). The observed modulation of the expression of GABA(A) receptor alpha2 subunit by T may be translated into changes in the levels or composition of GABA(A) receptor, either of which would be expected to alter neuronal functional response to GABA activation. As the effects of T are developmental-stage-specific, they may have an organizational impact on brain development.