Effect of Gestational Nicotine Treatment on Newborn Rat Retina: a Histopathological and Morphometric Analysis

Background: Smoking is a significant risk factor in several debilitating and fatal diseases. It has been implicated in bilateral tobacco-toxic and Leber's hereditary optic neuropathies. Although it has been demonstrated that smoking has a cumulative effect on retinal and optic nerve functions and causes diffuse and localised retinal sensitivity decrease in healthy chronic heavy smokers, the affected retinal layer has not been identified and there is no experimental study investigating the effect of nicotine exposure during gestation on the newborn rat retina.

Purpose: This experimental investigation evaluated histologically the influence in vivo of maternal nicotine treatment during pregnancy on the newborn rat retina. Different dosages of the test compound simulated the range of low, moderate, and heavy smokers in humans.

Methods: Experimentally naive, adult female Wistar-albino rats weighing 200-250 g were mated with adult male rats over 2 days for copulation in the proportion of two females for every male animal. After confirming pregnancy with vaginal smear method, 40 gravid rats (dams) were then randomly assigned into four equal groups (three experimental and one control; n = 10 in each). On day 9 of gestation, groups 1, 2, and 3 experimental dams were treated with intraperitoneal (i.p.) (-)-nicotine tartrate at doses of 0.5, 1, and 2 mg kg body weight-1 day-1, respectively during pregnancy from gestational day 9-21. Group 4 control dams were given i.p. saline solution daily for the same period. After normal delivery, the newborn litters were sacrificed at postnatal day 1 or day 30. The eyes were enucleated for histopathologic and morphometric analysis of the retinas. Nicotine-induced neuronal changes were measured by morphometric analyses on cell counts of ganglion cell layer (linear cell density in number per unit length of retina) and thickness of the various retinal layers.

Results: The litters in control group 4, and experimental groups 1 and 2 had normal retinal findings. On the other hand, morphometric analysis of retinal sections in experimental group 3 eyes demonstrated a 20.7% decrease in the number of surviving ganglion cells (40.7 +/- 2.0) compared with controls (51.3 +/- 1.1; p < 0.001). The thickness of whole retina (126.6 +/- 5.4 microm) was also reduced by 13.5% compared with controls (146.3 +/- 4.5 microm; p = 0.007). The main site of retinal atrophy was the inner plexiform layer (30.1 +/- 1.6 microm vs 43.5 +/- 1.3 microm; p < 0.001) with almost no change in the other retinal layers.

Conclusions: Gestational nicotine treatment induces marked changes in the organisation of the developing retina in newborn rats histopathologically. Quantitative morphometric analysis clearly demonstrated that the two most affected structures were the retinal ganglion cells and the inner plexiform layer, both of which are supplied by central retinal artery.