SELECTIVE EXPRESSION AND RAPID REGULATION OF GABA(A) RECEPTOR SUBUNITS IN GENICULOCORTICAL NEURONS OF MACAQUE DORSAL LATERAL GENICULATE-NUCLEUS

Monocular deprivation in adult macaques produces a rapid down-regulati on in GABA and GABA(A) receptor subunit immunoreactivity in deprived-e ye columns of primary visual cortex (V1) but a significantly delayed G ABA reduction in deprived layers of the dorsal lateral geniculate nucl eus (LGN). These findings, suggesting that normal inhibitory neurotran smission persists in LGN at a time when V1 inhibitory mechanisms are g reatly altered, are consistent with physiological studies that have de monstrated a greater degree of functional plasticity in V1 than in LGN . Nonetheless, functional adaptation to partial loss of visual input h as been detected in the LGN, indicating that synaptic plasticity takes place in this nucleus. In the present study, evidence for early chang es in inhibitory neurotransmission were examined with immunocytochemic al methods to determine if, in the absence of early GABA regulation, G ABA(A) receptor subunits in macaque LGN are affected by adult deprivat ion. Immunoreactivity for alpha 1 and beta 2/3 subunits of the GABA(A) receptor was intense within the magnocellular layers and more modest in the parvocellular layers and intercalated layers. In all layers, im munoreactivity was present in the cytoplasm and along the surfaces of relatively large somata and in dense tangles of processes in the neuro pil. Double-labeling experiments demonstrated that somata and processe s immunoreactive for alpha 1 and beta 2/3 were surrounded by GABA term inals but no cell intensely immunoreactive for either subunit expresse d immunoreactivity for GABA, itself. Following periods of monocular de privation by tetrodotoxin (TTX) injection for 4 days or longer, layers deprived of visual activity displayed levels of alpha 1 and beta 2/3 immunoreactivity markedly lower than those displayed by the adjacent, normally active layers. Such changes were greater as the period of dep rivation increased. The changes included a loss of immunostaining in a nd around somata and in many neuropil elements of deprived layers. The se data indicate that GABA and GABA(A) receptor subunits alpha 1 and b eta 2/3 are expressed by separate populations of neurons in macaque LG N that are differentially regulated by visual activity. The findings s uggest that rapid, activity-dependent regulation of postsynaptic recep tors represents one mechanism for altering synaptic strength in the ad ult macaque visual system.