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J. Pan, T. Nguyen, Y. Umino, D. Everhart, R. Barlow; Glycemic Modulation of Mouse Retinal Sensitivity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):889.
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Examine the effect of chronic versus acute hypoglycemia on retinal sensitivity in mice.
We used wild type C57BL/6J mice and a mutant strain (Gcgr–/–), rendered chronically hypoglycemic. We modulated their blood glucose levels by fasting, supplemental glucose or Humalog insulin IP injection (1.25U/kg) and measured their retinal sensitivity (ERG) under Nembutal (5mg/ml: 60mg/kg) anesthesia. Scotopic ERG (100gain, 0.3–300 Hz) responses were recorded to a range of test flash intensities (0.10–2.8 x 104 photons/um2/flash). The blood glucose level was monitored by sampling tail vein blood, and the ERG was measured at the peak effect of insulin, glucose ingestion, or fasting (48 hr). Body temperature was maintained constant at 370C with a heating pad during ERG recordings.
Chronically hypoglycemic mice (Gcgr–/–) have blood glucose levels between 80mg/dl to 100mg/dl, while wild type mice have blood glucose levels between 140mg/dl to 160mg/dl. Chronically hypoglycemic (Gcgr–/–) mice have decreased retinal sensitivity (ERG b–wave) compared to age–matched wild type mice, but acutely hypoglycemic mice (blood glucose of 40–60mg/dl) have near normal retinal sensitivity. Inducing hypoglycemia in wild type mice by fasting yields similar results as insulin administration, but inducing hypoglycemia in Gcgr–/– mice by fasting yields lowering retinal sensitivity (ERG b–wave).
The chronic metabolic stress of hypoglycemia decreases retinal sensitivity in mice, while acute hypoglycemia appears to have little effect.
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