Effects of early monocular lid suture upon neurons in the cat's medial interlaminar nucleus

Single unit extracellular recordings, cell size measurements, and cell packing density measurements were made in the medial interlaminar nucleus (MIN) of nine adult cats that had been monocularly deprived by lid suture prior to natural eye opening. The electrophysiological properties of neurons in the nondeprived regions of MIN (areas receiving input from the non-deprived eye) remained unaffected by monocular lid suture. The latencies to optic chiasm stimulation and receptive field properties, including receptive field center size, were essentially the same as those found for MIN neurons of normal adult cats. In contrast, cells in the deprived regions were severely affected by monocular deprivation. We encountered in the deprived regions of MIN only about one half as many active neurons per mm of electrode penetration as we did in the nondeprived regions. Of the physiologically active cells remaining, about one half had abnormal receptive field and/or response properties. This resulted in a sampling density of 5.1 normal Y-cells per mm of penetration in nondeprived regions of MIN compared to 1.0 normal Y-cell per mm in deprived regions of MIN. Histological effects of deprivation were also seen. Deprived regions of MIN were distinguished from nondeprived regions in four cats by autoradiography following intravitreal injection of tritiated proline into the deprived or non-deprived eye (2 cats each). The mean cell size of deprived regions of MIN was 34% smaller than that of nondeprived regions. We did not find a difference in cell packing density between these two regions. It appears that the effects of monocular lid suture upon MIN are in most respects similar to the effects of monocular lid suture previously reported for the A laminae. Since MIN is composed solely of Y-cells, these data support the idea that the Y-pathways are more severely affected by visual deprivation than are the X-pathways. Further, since MIN projects largely outside the striate cortex, these data give the first demonstration of a primary effect of early lid suture upon extrastriate visual pathways.