Acquisition of a spatial navigation task in the padding pool induces an increase of GABA level in the hippocampus of Swiss mice

The balance between excitatory and inhibitory glutamatergic and GABAergic systems, respectively, is crucial for the maintenance of complex cognitive functions such as learning. Using Swiss mice as experimental model, the aims of the present study were to evaluate cognitive performance in a shallow water maze (SWM) and the effects of training in this spatial navigation task on hippocampal GABA and glutamate levels.  In addition, correlations between neurochemical and behavioural data, and between glutamate and GABA levels were assessed. Forty-six three-month-old mice were divided into three groups: Learning, n=18: animals submitted to the SWM task; Active, n=14: animals exposed to the SWM, without the demand of performing a cognitive task and Control, n=14: the animals were kept in the vivarium without contact with the SWM. There was significant training effect indicating that the Learning group animals have learned the task. Regarding neurochemical data, the findings of the present work show for the first time that the task learning process in SWM has a significant effect on GABA levels in the hippocampus. The relationship between the two neurotransmitters, observed in the control animals, was adjusted by a significant increase in hippocampal GABA levels caused by the spatial training performed by the animals from the Learning group. However, the relationship observed in control condition is disrupted by a subsequent exposure to the maze in the absence of a spatial cognitive demand, as was the case of the Active group.  These data open new perspectives to explore the involvement of the inhibitory and excitatory systems in the molecular mechanisms associated with different types and steps of learning processes.