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JN Hokoc, ML Almeida, AD Silveira, RC A Guedes, AB Martinez; Ultrastructural Deficits in Malnourished Rat Optic Nerve . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2704.
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Purpose: It is known that malnutrition produces deficits in the central nervous system particularly in the initial period of development. These deficits can alter several important events during development, including nerve myelination. The purpose of this study was to analyze the optic nerve (ON) ultrastructure of adult rats and during post-natal development after the administration of a low protein diet. Methods: We used ON tissue from adult and post-natal (P13, P21, P30 and P60) albino rats from litters whose mothers underwent malnutrition during the lactation period until 60 post-natal days. The animals were divided in two groups. One group was treated with a diet containing only 8% protein and the second group with a normal diet containing 23 % protein. The low protein diet was similar to the Basic Regional Diet (BRD) that is used by the poor population of the Zona da Mata de Pernambuco, Brazil. The two groups had free access to water as well as to the diet. After the suckling period, animals were anesthetized, perfused, and ON segments from control and experimental groups were processed for transmission electron microscopy. Results: Ultrastructure of the ON revealed substantial changes in the myelin pattern of the malnourished animals compared to the control group. These changes were evidenced by a decrease of the myelin sheath thickness and fibers without glial sheaths. The quantitative analysis was performed so as to compare two developmental ages, P21 and P60. As expected, the percentage of myelinated fibers (MF) increases (from 67% to 86%) and the percentage of unmyelinated fibers (UF) decreases (from 19.8% to 6.5%) in the control group. In the malnourished group the percentage of MF was lower than the control group (19% and 40%) at all ages. The percentage of UF decreased as development proceeded (from 32.6% to 9.8%), however remained high when compared to the control group. There was a percentage of fibers with structural anomalies (SA) in the myelin sheath that remained almost unchanged during development in the control group (10% and 7.7%), but were more frequent in the malnourished group (48% and 50%). Conclusion: During development, myelination occurs in a lower rate in malnourished animals and MF does not reach the high percentage of the control group. Malnourished animals show a significantly high percentage of SA in the myelin sheath, suggesting that BRD, in the lactation period, leads to dysfunction of visual capacity.
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