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  • Title: Proportion of glutamate- and aspartate-immunoreactive neurons in the efferent pathways of the rat visual cortex varies according to the target.
    Author: Dori I, Dinopoulos A, Cavanagh ME, Parnavelas JG.
    Journal: J Comp Neurol; 1992 May 08; 319(2):191-204. PubMed ID: 1381727.
    Abstract:
    Immunohistochemistry, with antisera directed against glutamate (Glu) or aspartate (Asp), was combined with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) histochemistry to examine the distribution, morphology, and proportions of Glu- and Asp-containing neurons that give rise to corticofugal and callosal projections of the rat visual cortex. WGA-HRP injections in the dorsal lateral geniculate nucleus resulted in retrograde labelling of small and medium-sized cells throughout layer VI of the visual cortex. Of these cells, 60% were also Glu-immunoreactive and 61% Asp-positive. WGA-HRP injections in the superior colliculus labelled large and medium-sized neurons in the upper portion of layer V of the visual cortex. Of these cells, 46% were also stained for Glu and 66% for Asp. Injections in the pontine nuclei resulted in retrograde labelling of cells in the deeper part of cortical layer V. Retrogradely labelled cells, which were also immunoreactive for Glu or Asp, were large pyramidal cells. Corticopontine neurons, which were also Glu-positive, accounted for 42% of the total number of WGA-HRP labelled cells, whilst for Asp-positive neurons this percentage was 51%. Finally, after injections in the visual cortex, retrogradely labelled small and medium-sized cells were found throughout layers II-VI in the contralateral visual cortex. Of these neurons, 38% were also labelled for Glu while 49% were also Asp-immunoreactive. The present results demonstrate that substantial proportions of projection neurons in the rat visual cortex are immunoreactive for Glu or Asp, suggesting that these excitatory amino acids are the major transmitters used by the cortical efferent systems examined. Furthermore, the proportions of these immunoreactive neurons in the efferent pathways vary according to the target.
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