Changes in protein synthesis underlying functional plasticity in immature monkey visual system.

Abstract

Local rates of cerebral protein synthesis were determined in newborn rhesus monkeys subjected to either acute or chronic monocular visual deprivation. Chronic monocular deprivation resulted in decreased rates of protein synthesis in the laminae ofthe lateral geniculate nuclei innervated by the deprived eye whereas rates of protein synthesis were normal in geniculate laminae innervated by the functioning eye. Acute monocular deprivation produced no differential changes in rates ofprotein synthesis in any of the geniculate laminae.In animals with binocular vision the projections from the retinae of the two eyes are partly crossed at the optic chiasma in such a manner that the retinal outputs representing the right and left visual fields of both eyes are collected and' distributed more or less exclusively to the left and right geniculate bodies, respectively. However, the information from the two eyes remains segregated, and the optic tracts terminate in six well-defined cellular laminae in each ofthe lateral geniculate bodies: laminae 1, 4, and &receive input from the contralateral eye, and laminae 2, 3, and 5 are served by the ipsilateral eye. The segregation of the information from the two eyes and for both visual fields is retained in the organization of the pathways' from the lateral geniculate bodies to the striate cortex.'Each geniculate body projects to the ipsilateral striate cortex consigning the information for each visual field to the contralateral visual cortex. The cell bodies in the laminae' of each geniculate body project to the ipsilateral striate cortex in an organized pattern in which the information for, a given point in the visual field converges to two adjacent visual cortical columns, one pair of columns for each point in the visual field and one column for each of the two eyes. These so-called ocular dominance columns are most prominent and discrete in layer 4 ofthe striate cortex but are perpendicularly arranged and traverse all the other cytoarchitectural layers (1). In the young adult rhesus monkey they are approximately 400 Am in width (1).

Regional Rates of Cerebral Protein Synthesis Measured with l-[1-11C]Leucine and PET in Conscious, Young Adult Men: Normal Values, Variability, and Reproducibility

“…Studies in rodents have demonstrated that rCPS changes during the process of aging (Ingvar et al , 1985) and during brain development (Sun et al , 1995). Activity-dependent protein synthesis is thought to be an integral step in many forms of synaptic plasticity (Nguyen et al , 1994), and, in a study of developmental plasticity in monkeys, we found regionally selective changes in rCPS (Kennedy et al , 1981). Variations in rCPS likely reflect adaptive processes taking place over a longer period of time compared with the acute physiological changes signaled by positron emission tomography (PET) measurements of regional cerebral metabolic rate for glucose or cerebral blood flow.…”

“…The l -[1- 11 C]leucine PET method for the quantitative measurement of rCPS in human subjects provides us with a new and potentially powerful tool to investigate adaptive CNS responses in humans. In animal models, conditions such as sleep, hibernation, axonal injury with subsequent regeneration, synaptic plasticity in the visual system, and ischemia are all associated with altered rCPS compared with appropriate controls (Frerichs et al , 1998; Kennedy et al , 1981; Nakanishi et al , 1997; Smith et al , 1984; Widmann et al , 1991). The l -[1- 11 C]leucine PET method can be used to track changes in rCPS and/or Λ across regions and over time.…”

Measurement of Regional Rates of Cerebral Protein Synthesis with L-[1-11C]leucine and PET with Correction for Recycling of Tissue Amino Acids: II. Validation in Rhesus Monkeys

“…Further decreases occur during the more prolonged process of aging (Smith et al, 1995). Regional rates of cerebral protein synthesis are also affected by changes in synaptic input during development as seen in a study of plasticity in the developing monkey visual system (Kennedy et al, 1981). Studies in monkeys show a positive correlation between rCPS and deep sleep (Nakanishi et al, 1997), and during hibernation in ground squirrels rCPS is suppressed to less than 1% of normal (Frerichs et al, 1998).…”

Molecular substrates of plasticity in the developing visual cortex

“…Downstream signaling events are not well understood, but the many instances of activity-dependent protein synthesis documented suggest that translation of proteins is required for normal plasticity. Multiple plasticity-related genes show visually driven increases in protein levels, including oCaMKII (Wu et al, 1998) and the calcium/cyclicAMP-response element binding protein (Pham et al, 1999), and lengthy MD can alter gross levels of protein synthesis in the lateral geniculate nucleus (LGN: Kennedy et al, 1981). Neurotrophins and their receptors are regulated in an activity-dependent fashion in vitro and in vivo (Zafra et al, 1992;Schoups et al, 1995;Androutsellis-Theotokis et al, 1996;Lein and Shatz, 2000) and have potent effects upon synaptic plasticity in the visual cortex (Cabelli et al, 1995;McAllister et al, 1995;Hanover et al, 1999;Gillespie et al, 2000).…”