Increased glutamate, GABA and glutamine in lateral geniculate nucleus but not in medial geniculate nucleus caused by visual attention to novelty

This study is concerned with cortico-thalamic neural mechanisms underlying attentional phenomena, Previous results from this laboratory demonstrated t hat the visual sector of the GABAergic thalamic reticular nucleus is select ively c-fos activated in rats that are naturally paying attention to featur es of a novel-complex environment, and that this activation is dependent on top-down glutamatergic inputs from the primary visual cortex. By contrast, the acoustic sector of the thalamic reticular nucleus is not activated des pite noise generated by exploration and c-fos activation of brainstem acous tic centers (e.g. dorsal cochlear nucleus, inferior colliculus). A predicti on of these results is that the levels of the neurotransmitters glutamate a nd GABA, and the glutamate-related amino acid glutamine, will be increased in the lateral geniculate nucleus (LGN), but not in the medial geniculate n ucleus (MGN) of rats that explore a novel-complex environment in comparison to levels of these amino acids in control rats. By means of neurochemical analysis of these amino acids (HPLC) the results of this study confirmed th is prediction. The results are consistent with the previously proposed 'foc al attention' hypothesis postulating that a focus of attention in the prima ry visual cortex generates top-down center-surround facilitatory-inhibitory effects on geniculocortical transmission via corticoreticulogeniculate pat hways. The results also supports the notion that a main function of cortico thalamic pathways to relay thalamic nuclei is attention-dependent modulatio n of thalamocortical transmission. (C) 2001 Elsevier Science B.V. All right s reserved.