Effects of Selective Neurotoxins on Eye Growth in the Young Chick

Molecular and Biochemical Aspects of the Retina on Refraction

“…In chickens, physiological and morphological changes in photoreceptors are associated with experimentally induced myopia [25]. In addition, differential eye growth under both normal and FD conditions in response to neurotoxins blocking responses from the photoreceptors [26], ON and OFF pathways [27, 28] and the inner retina [29] have been shown. Several retinal neurotransmitters such as dopamine (DA) [30, 31], glucagon [32], acetylcholine [33], nitric oxide [34, 35] and retinoic acid [36, 37] have also been implicated in defocus induced ocular growth in animals.…”

“…While blocking amacrine cell function using cell-specific neurotoxins, such as 6-hydroxy-dopamine (dopaminergic amacrine cells, [129]) and ethylcholine mustard aziridiniumion ion (cholinergic amacrine cells, [130]), does not alter refractive compensation to imposed defocus in chickens, other neurotoxins, like kainic acid [29, 131] causing a non-specific damage to the inner retina (including amacrine cells) at higher doses, lead to increased ocular growth (mostly in the posterior chamber) under normal conditions, and a reduction in myopic eye growth under form-deprived conditions. These findings warrant further investigation using amacrine cell knock out mutants [132].…”

Sonic Hedgehog Expression and Its Role in Form-Deprivation Myopia in Mice

“…26,28,29 Other agents that can influence eye growth when given to open eyes are a group of neurotoxins, such as colchicine, kainic acid, quisqualic acid, and N-methyl-D-aspartate, which act by destroying the normal structure of the retina. [44][45][46][47] Although the pathologic study revealed no changes in retinal morphology after administration of Shh-N or cyclopamine, it is difficult to determine whether the effects of both drugs are due to a receptor-mediated mechanism or retinal toxicity. Further research, using immunocytochemical markers or electroretinogram (ERG), for example, is needed.…”

Photoperiodic responses of broilers. II. Ocular development

“…Thus the close relationship between eye weight and eye dimensions, also observed by Ehrlich et al (1990), suggested that eye weight alone might be a simple indicator of ocular integrity.…”