Training‐induced changes in the expression of GABA_A‐associated genes in the amygdala after the acquisition and extinction of Pavlovian fear

Abstract

Previous work suggests the γ-aminobutyric acid (GABA)ergic system may be dynamically regulated during emotional learning. In the current study we examined training-induced changes in the expression of GABA A -related genes and the binding of GABA receptor radioligands in the amygdala after the acquisition and extinction of Pavlovian fear. Using in situ hybridization, we examined the expression pattern changes of mRNAs for GABAergic markers in the lateral, basolateral and central subdivisions of the amygdala in C57Bl/6J mice. These markers included GABA-synthesizing enzymes (GAD67 and GAD65), major GABA A receptor subunits (α1, α2, α3, α5, β2 and γ2) and the expression of mRNAs that are involved in a variety of GABA-related intracellular processes, including GABA transporter-1 (GAT1), GABA A receptor-associated protein and the GABA A clustering protein, gephyrin. With fear conditioning, we found decreased mRNA levels of α1, α5 and GAD67, as well as deceased benzodiazepine binding in the amygdala. Fear extinction induced an increase in mRNA levels of α2, β2, GAD67 and gephyrin, as well as a decrease in GAT1. Together, these findings indicate that the acquisition of fear induced a downregulation of mRNA markers related to a decrease in amygdala GABAergic function, whereas the acquisition of fear extinction produced an upregulation of GABAergic markers related to enhanced GABAergic transmission.

Glutamic Acid Decarboxylase 65: A Link Between GABAergic Synaptic Plasticity in the Lateral Amygdala and Conditioned Fear Generalization

“…In fact, GAD expression is regulated upon both stress (Bowers et al, 1998) and fear conditioning (Bergado-Acosta et al, 2008;Heldt and Ressler, 2007). While GAD67 is the cytosolic isoform controlling metabolic GABA synthesis (Kaufman et al 1991), it has been suggested on the basis of subcellular localization, membrane, and cofactor association studies that GAD65 is the synaptically localized isoform generating GABA in an activity-dependent manner required for rapid synaptic release (Kaufman et al, 1991;Patel et al, 2006).…”

“…However, these conditions are known to regulate also GAD67 expression (Heldt and Ressler, 2007), which may functionally compensate for GAD65 (Asada et al, 1996;Kash et al, 1997). This appears unlikely because fear training with high shock intensities mimicked both the synaptic and behavioral phenotypes in Gad65 À / À , whereas the gross synaptic network structure and function displayed no severe abnormalities, and glutamatergic transmission was not affected.…”

“…GAD67 is typically distributed throughout the neuron and almost all of it exists in its active cofactor-bound form, whereas GAD65 is predominantly found in synaptic terminals and much of it is in the form of an inactive apoenzyme (Kaufman et al, 1991;Martin and Rimvall, 1993). Both GAD enzymes are highly expressed in the amygdala, where fear training results in a transient decrease in GAD67 and GAD65 mRNA levels in the basolateral complex (BergadoAcosta et al, 2008;Heldt and Ressler, 2007). Gad65-null mice show an increase in anxiety and altered responsiveness to anxiolytics (Kash et al, 1999), a generalization of learned fear responses (Bergado-Acosta et al, 2008), and an impairment of fear extinction (Sangha et al, 2009;Sangha et al, 2012).…”

Cell-type specific deletion of GABA(A)α1 in corticotropin-releasing factor-containing neurons enhances anxiety and disrupts fear extinction

“…Research has pointed to an important role for the α1 subunit of the GABA(A) receptor in anxiety and fear memory. Fear training decreases GABA(A)α1 subunit containing neurons (19) and disruption of the GABA(A)α1 subunit receptor leads to enhanced synaptic plasticity in the lateral nucleus of the amygdala and enhanced auditory fear memory (20). GABA(A)α1 neurons can be found within the amygdala (21), BNST, and PVN (22), areas that also strongly express CRF.…”

The role of mediodorsal thalamic nucleus in fear extinction

“…Thus, extinction training induced an increased gene and protein expression for the GABA(A) receptor clustering protein, gephyrin (Chhatwal et al, 2005), an upregulation of gamma-aminobutyric acid (GABA)ergic markers related to enhanced GABAergic transmission (Heldt and Ressler, 2007), and an increased amplitude of GABAergic miniature inhibitory postsynaptic currents (Lin et al, 2009). Fear extinction increased perisomatic parvalbumin and GAD67 around perisomatic inhibitory synapses originating from parvalbumin and cholecystokinin-positive interneurons and silenced fear conditioning-activated neurons in the BL (Trouche et al, 2013).…”