Evidence for two types of GABA-containing interneurons in the A-laminae of the cat lateral geniculate nucleus: a double-label HRP and GABA-immunocytochemical study.

Neurons containing GABA immunoreactivity were analyzed in the A-laminae of normal cat LGN and of LGN retrogradely labeled with HRP from the visual cortex. In contrast to retrograde labeling of relay cells, GABA+ cells were devoid of HRP label, providing additional evidence for the interneuronal nature of GABAergic cells in the cat LGN. Cell body area measurements showed that the population of GABA+ cells is composed of a large proportion of small (beta) cells and a smaller proportion of medium size (alpha) cells. The proportion of alpha GABA+ cells increases from medial to lateral parts of the A-laminae, resembling a similar medio-lateral increase of physiologically defined Y cells and of morphologically defined type 1 cells in these laminae. This suggests that the alpha and beta GABAergic cells are related to the Y and X geniculo-cortical relay cells, respectively.