Role of striatal GABAergic neuron system in learning behavior

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The striatum has been suggested to be involved not only in the sensory or motor control but also in cognitive function such as memory and learning. We have investigated the effects of striatal kainic acid lesions, which induce selective neuronal cell death in the striatum, on various kinds of learning behavior. Rats with striatal lesions showed severe deficits in spatial learning tasks though they did not show any deficits in discrimination learning and classical conditioning. The present study investigated the mechanism of learning deficits in these animals and the role of striatal neurons, especially striatal GABAergic neurons, in learning and memory.GABA_A agonist systemically administered before each trial significantly improved the performance of Morris water maze and radial maze tasks in rats with striatal kainic acid lesions, while GABA_B agonist did not. This suggests that GABA_A receptors in the brain are involved in the learning deficits of striatal lesioned animals. Since there are three areas to which striatal GABA neurons project, we then tested the effects of microinjection of GABA_A antagonist on radial maze behavior using normal rats previously trained in this task. As a result, injection into the substantia nigra pars reticulata most distinctly increased the number of errors, and injection into the striatum also had significant effects. Taken together it was suggested that a neural circuit containing the striatum, especially the strionigral GABAergic neuron system, plays an important role in performance of spatial memory tasks.