Delayed reduction in GABA and GAD immunoreactivity of neurons in the adult monkey dorsal lateral geniculate nucleus following monocular deprivation or enucleation

GABA and glutamate decarboxylase (GAD) immunoreactivities were examined in dorsal lateral geniculate nuclei (LGN) of normal monkeys (Macaca fascicularis) and in monkeys that had one eye injected with tetrodotoxin (TTX) or one eye removed 5 days to 4 weeks prior to sacrifice. As seen in previous studies (Wong-Riley and Carroll 1984) monocular TTX injections or enucleation quickly reduced cytochrome oxidase (CO) staining in layers 2, 3 and 5 of the ipsilateral LGN and in layers 1,4 and 6 of the contralateral LGN. The reduction in CO staining was apparent at all survival times examined. By contrast, GABA and GAD immunostaining in the LGNs were qualitatively normal up to two weeks following enucleation or after 17 days of TTX injections. Quantitative and stereological analyses confirmed that the numerical density and proportion of GABA and GAD neurons do not change in the LGN following two weeks of denervation or deprivation, even though in the same monkeys a reduction in GABA immunostaining was found in deprived-eye columns of area 17. However, with longer survivals, of 3-4 weeks in duration, the number of GABA and GAD immunostained neurons in the deprived/denervated-eye laminae of the LGN was reduced by one-third. These findings demonstrate that the deprivation-induced reduction in GABA and GAD immunoreactivity is delayed in the LGN, by comparison with the visual cortex, and suggest that the effects in the LGN may be relayed through the cortex or that neurotransmitter levels may be regulated by different mechanisms in the two sites.