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B.V. Bui, B. Fortune, J.C. Morrison, G.A. Cioffi; Ganglion Cell Contribution to the Rat Full Field Electroretinogram . Invest. Ophthalmol. Vis. Sci. 2003;44(13):36.
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Purpose: The current study considered the contribution of ganglion cell responses to the rat ERG by assessing function following optic nerve (ON) transection or tetrodotoxin (TTX) application. Methods: ERGs were obtained from adult Brown Norway rats anaesthetized using a mixture of ketamine, xylazine and acepromazine (55:5:1 mg/kg). Simultaneous recording from both eyes were made between silver chloride electrodes on the cornea and reference rings on the sclera 2 mm behind the limbus. White discharge flashes were delivered via a Ganzfeld sphere with luminous energies ranging from –6.1 to 2.7 log cd.s/m2 under fully dark-adapted conditions. Following scotopic ERGs, signals were collected (0.9 to 2.7 log cd.s/m2) on a rod suppressing background (200 cd/m2). Four animals had ERGs measured 1, 3 and 4 weeks after retrobulbar optic nerve transection. Damage to the retinal vasculature was ruled out with ophthalmoscopy. A separate co-hort of five animals had ERGs assessed 60 minutes following 2 µL intravitreal injection of TTX (~6 µM) or vehicle (BSS) in treated and control eyes respectively. ERG parameters are expressed as a mean (±SEM) percentage reduction relative to control eyes Results: The scotopic threshold response (STR) was significantly reduced one week following ON transection (p < 0.05). The positive component (pSTR, 64 ± 13%) was relatively more attenuated compared with the negative response (nSTR, 55 ± 12%) at -4.7 log cd.s/m2, where both pSTR and nSTR were prominent in control eyes. By three and four weeks following ON transection the pSTR and nSTR had declined further to (89 ± 3%, 79 ± 6%) and (68 ± 3%, 58 ± 2%) respectively. The photopic b-wave measured at the highest stimulus energy was significantly reduced post-transection (week 1; 35 ± 6%, week 3; 23 ± 11%, week 4; 20 ± 6%), whereas photopic oscillatory potentials (OPs, p = 0.12(0.2)) were not significantly altered. Scotopic a-wave (p = 0.24(0.2)), b-wave (p = 0.51(0.1)) and OP (p = 0.61(0.5)) amplitudes at 2.7 log cd.s/m2 were not significantly changed by ON transection. TTX application resulted in loss of component(s) of the rat STR similar to that observed with ON transection. TTX significantly reduced photopic b-wave (35 ± 6%) and OP amplitudes (85 ± 3%), but did not affect scotopic a-wave (p = 0.21(0.2)), b-wave (p = 0.62(0.1)) or OP (p = 0.19(0.3)) amplitudes. Conclusions: The rat full field ERG contains contributions from ganglion cells, which were greatest for the STR, photopic b-wave and OPs, but negligible for scotopic a-waves, b-waves and OPs.
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