Glutamic Acid Decarboxylase Concentration Changes in Response to Stress and Altered Availability of Glutamic Acid in Rabbit (Oryctolagus cuniculus) Brain Limbic Structures

Abstract

Glutamic acid decarboxylase (GAD) is an enzyme that catalyses the formation of γ-aminobutyric acid (GABA), the most important inhibitory neurotransmitter, from glutamic acid (Glu), which is considered the most important excitatory transmitter in the central and peripheral nervous systems. GAD is a key enzyme that provides a balance between Glu and GABA concentration. Hence, it can be assumed that if the GAD executes the synthesis of GABA from Glu, it is important in the stress response, and thus also in triggering the emotional states of the body that accompany stress. The aim of the study was to investigate the concentration of the GAD in motivational structures in the brain of the rabbit (Oryctolagus cuniculus) under altered homeostatic conditions caused by stress and variable availability of Glu. Summarising, the experimental results clearly showed variable concentrations of GAD in the motivational structures of the rabbit brain. The highest concentration of GAD was found in the hypothalamus, which suggests a strong effect of Glu and GABA on the activity of this brain structure. The GAD concentrations in individual experimental groups depended to a greater extent on blocking the activity of glutamate receptors than on the effects of a single stress exposure. The results obtained clearly support the possibility that a rapid change in the concentration of GAD could shift bodily responses to quickly achieve homeostasis, especially in this species. Further studies are necessary to reveal the role of the Glu–GAD–GABA system in the modulation of stress situations as well as in body homeostasis.

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“…DA of the mesocortical and mesolimbic pathways is involved in memory, learning and emotional processes (30). Stress increases DA concentrations in the frontal cortex, local changes in DA after stressors in limbic cortex fields may be associated with changes in behavior in response to stress stimuli (17,31).…”

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“…[ 70 ] GABAergic system closely interacts with the dopaminergic, serotonergic and cholinergic neurotransmitter systems. [ 70 ] GABA signalling is controlled by levels of GAD67, the major isozymes responsible for GABA content in the PFC. The PFC is been found to be involved in the alteration of neurocognitive functions following binge alcohol consumption.…”

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“…Molecular oxygen and Cu might contribute to this inhibition through various mechanisms, including S-glutathionylation. The vulnerabilities of GAD65 and GAD67 to oxidative stress further complicate the interplay within the GABAergic system (5,39).…”