Abstract
Purpose :
Infantile nystagmus syndrome (INS) is an eye movement disorder characterized by involuntary oscillations of the eyes starting in infancy. We recently showed decreased neuromuscular junction (NMJ) density as early as P10 in a mouse model of nystagmus (albino), as well as transient decreases in NMJ cross-sectional area. We now examine the development and maturation of the NMJs in three dimensions in albino EOMs.
Methods :
We examined NMJ formation and maturation in EOMs of P3, P7, P10, P14, P21 and 12 weeks (wks) old albino and littermate wildtype (WT) mice. In whole-mount EOMs, we stained acetylcholine receptors (AChRs) with α-bungarotoxin. NMJ development was assessed by measuring NMJ length, volume and morphology using Imaris software, and compared between WT and albino mice (n=2-6 animals per genotype for each time point). Data were analyzed using unpaired student’s t-test.
Results :
In WT, NMJs start as plaque-like structures at P3, become increasingly perforated and irregular in shape at P7 and P14, and are fully perforated, pretzel-like structures by P21, which further increase in size to adulthood. In albinos, at P3 NMJ length, volume and % of plaques were similar to wildtype. But at P7, albinos had less perforated, thin and long NMJ plaques but smaller average volume (228.36±21.5 vs 249.73±7.43 µm3 in WT). At P14, these NMJ plaques developed into irregular shape, thin structures with smaller average volume (477.58±21.5 vs 553.09±14.25 µm3 in WT). At P21, albino NMJs were irregular in shape, with smaller average volume (647.98±38.99 vs 910.39±29.1 µm3 in WT). In adulthood, albino NMJs were short, with smaller average length (37.70±1.2 vs 46.93±0.49 µm in WT) but equal volume. There was a greater proportion with immature morphology (27.24±0.02% vs 10.21±1.31% in WT) in adult albino EOMs compared to WT.
Conclusions :
In addition to a decreased density of NMJs in the EOMs of albino mice, the NMJs which are present are smaller and appear immature. Differences were noted as early as the second postnatal week, when albino mice EOMs show irregular NMJs. Altogether, the data suggest that irregular development of NMJs may contribute to the pathogenesis of INS in albino mice.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.