1992 Volume 11 Issue 1-2 Pages 1-2_21-1-2_31
The spontaneously epileptic rat (zi/zi, tm/tm: SER), a double mutant obtained by mating tremor rats (+/+, tm/tm) and zitter rats (zi/zi, +/+), exihibits characteristic absence-like seizures and tonic convulsions without external stimuli. These epileptic rats have extensive spongy changes in the brain including the brainstem. These findings stimulated us to perform further morphological and functional studies on the visual organ in these mutants.
Five males each of tremor rats, zitter rats, SER and Kyo: Wistar rats (control), 6 and 10 to 12 weeks of age, were subjected to eye examination.
No remarkable change was observed in SERs or tremor rats in ophthalmoscopic examination. Zitter rats showed mild tortuosity and narrowness of the retinal artery.
ERGs revealed prolongation of b-wave latency, increase of a- and b-waves amplitude, splitting and indistinctness of oscillatory potential were recorded in zitter rats and SERs. In biochemical examination, the dopamine content in the retina was significantly decreased in zitter rats compared with that in Kyo: Wistar rats. The dopamine content in the retina of SERs was lower, though not statistically significant, than that of Kyo: Wistar rats. Histopathological examination revealed abundunt vacuole-like gaps between the external plexiform and outer granular layers in the retina in zitter rats and similar gaps in the inner granular layer in SERs. In addition, hypomyelinization was observed in the optic nerve in SERs and zitter rats.
Tremor rats, however, showed no remarkable change in ERG findings, dopamine contents, and histopathological examinations.
Thus, we concluded that the retinal abnormality observed in SERs was ascribable to the zi/zi gene from the zitter rat; however, the changes in the retina were more marked in zitter rats than in SERs.
