Activity‐dependent changes in eye influence during monocular blockade: Increases in the effects of visual stimulation on 2‐DG uptake in the adult rat geniculostriate system

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Abstract
We examined the effects of loss of monocular retinal activity 2‐deoxyglucose (2‐DG) uptake in the adult rat geniculostriate system. Of particular interest was whether the influence of the normally functioning eye changed during long‐term contralateral retinal silence. Group 1 rats were subjected to short‐term (24 hours) and group 2 rats to long‐term (21–90 days) monocular tetrodotoxin (TTX) blockade, and metabolic activity was assessed during exposure to square‐wave gratings. Group 1 rats exhibited patterns of cortical glucose utilization commensurate with complete monocular loss of retinal activity: minimal 2‐DG uptake in contralateral monocular area 17 and dorsal lateral geniculate nucleus (LGN), and a bilateral depression in the binocular regions; 2‐DG uptake was highest in the monocular regions fed by the stimulated normal eye (in both area 17 and the LGN) and these regions appeared unaffected by the monocular blockade. After repeated injections of TTX (group 2), metabolic activity in binocular area 17 and binocular LGN increased bilaterally relative to the metabolically active monocular regions contralateral to the normal eye. Group 3 rats were monocularly TTX‐injected for 30 or 60 days, and, 24 hours before 2‐DG, all retinal activity was eliminated by means of binocular TTX injections or binocular enucleation. Glucose utilization in the binocular regions of both area 17 and the LGN in these rats was depressed to levels seen in monocular area 17 after complete and recent loss of activity from the contralateral eye, indicating that the metabolic increase which occurred in the binocular regions during long‐term monocular retinal blockade was dependent upon the neuronal processing of retinal information from the non‐TTX eye. We conclude that, in the adult rat, an activity‐dependent, physiologically based shift in ocular influence occurred in the binocular geniculostriate system during long‐term monocular retinal inactivation.