Effects of intraocular tetrodotoxin on the postnatal development of the dorsal lateral geniculate nucleus of the rat: a Golgi analysis.

The postnatal development of the rat dorsal lateral geniculate nucleus (dLGn) during tetrodotoxin (TTX)-induced monocular impulse blockade was investigated by quantitative Golgi techniques. Beyond 14 days postnatal (dpn), the effectiveness of TTX was monitored by loss of the pupillary light reflex. By 21 dpn, Golgi analysis indicated that TTX had no effect on the pattern of dendritic branching of class A or class B neurons, although the number of dendritic spinous protrusions was reduced. No evidence of any TTX-induced loss of optic axons or neuronal degeneration in the dLGn was found, despite a 16% decrease in the size of the nucleus, suggesting a reduction in the growth of neuropil. These data indicate that optic impulses are important in mediating the proper growth of postsynaptic specializations in the dLGn during ontogenesis, but that the postnatal development of the dendritic arbor of neurons in the dLGn appears to be independent of retinal impulse activity.