Inhibition of myopia development in chicks using himbacine:: a role for M4 receptors?

The success of the M-1-selective muscarinic antagonist pirenzepine in preventing myopia development in animal models implicates a role for the M-1 receptor. However, the relatively high dose of pirenzepine required may indicate that the drug acts through another receptor subtype. This study examined whether the M-4-selective antagonist, himbacine, could also prevent myopia. Daily intravitreal injections of himbacine inhibited the inducement of myopia in chick eyes in a dose-dependent manner. Doses less than or equal to 200 mug caused no significant inhibition of induced myopia compared to controls (-13.7 +/-2.3 vs -16.2 +/-0.9D, ANOVA p=0.37), whilst a dose of 800 mug almost completely inhibited the induced myopia(-2.4 +/-2.0, p<0.01). Findings demonstrate himbacine is effective at preventing the development of myopia in chick and implicates a role for the M-4 receptor. NeuroReport 12:2453-2456 (C) 2001 Lippincott Williams & Wilkins.