Objective

To study effects of vitreous injecting M(1)-selective muscarinic antagonist, pirenzepine, on expression of M(1) and M(4) receptor in retina, choroid, sclera and iris-ciliary body of guinea pig with form-deprived myopia.

Methods

Twenty-four 1 - 2 week-old pigmented guinea pigs were randomly divided into four groups. Group1: normal control (N) (n = 6); group 2: simple form-deprived myopia (FDM) (n = 6); group 3: drug control (S) (n = 6); group 4: pirenzepine (P) (n = 6). Expression changes of M(1) and M(4) muscarinic receptors at mRNA level were detected by semi-quantitative RT-PCR in retina, choroid, sclera and iris-ciliary body.

Result

1. After 21 days' treatment, FDM group produced relative myopia of -4.92 D and an axial length of 0.29 mm with significance (P < 0.001), compared with N group. Compared with group S, the relative refractive error in group P was +0.88 D, and axial length decreased 0.30 mm with respectively significance (P < 0.001). Differences in refractive error between group S and group FDM were not significant, but in axial length were significant (0.08 mm vs. 0.29 mm) (P < 0.05). 2. Semi-quantitative RT-PCR: M(1) and M(4) mRNA expression showed no significant differences in the retina, choroid and iris-ciliary body of group P compared with group S (P > 0.05). Of interest, in the posterior sclera, mRNA expression of group P was significantly greater than that of group S for the M(1) (P < 0.05) and M(4) subtypes (P < 0.05). The M(1) and M(4) subtype in group P was increased by +19.16% and +64.29% respectively.

Conclusion

M(1)-selective muscarinic antagonist, pirenzepine, can effectively inhibit form-deprived myopia in guinea pig. M(1) and M(4) subtype in sclera and their cholinergic signaling may participate in muscarinic antagonist inhibition of myopic development.