Aims: To document the expression of vasoactive intestinal polypeptide (VIP) in the visual cortex-17 of kittens with anisometropic amblyopia, and to investigate the relationship between VIP and the development of the visual system.
Methods: Sixteen normal kittens (4-wk of age) were randomly divided into two groups: control and amblyopic. Amblyopia was produced by atropinization of one eye in eight kittens. Four (2 normal and 2 amblyopia) kittens were sacrificed at weeks 3, 6, 9, or 12 post-treatment respectively. Expression of VIP-mRNA in the visual cortex-17 was detected through in-situ hybridization. Neurons in the visual cortex were visualized by transmission electron microscopy (TEM). The number of neurons was analyzed via light microscopy (LM).
Results: VIP-mRNA expression was increased with age in control kittens but remained nearly static in age-matched anisometropic amblyopic kittens (p < 0.05). The number of VIP-positive cells of amblyopic kittens decreased dramatically when compared to normal age-matched kittens (p < 0.05). The total comparison between different positive ranks suggested a significant difference. The degree of expression between these two groups was significantly different. Ultrastructurally, in the control group, the nuclear membrane of most neurons was discernable and chromatin was evenly distributed within the nucleus. Abundant cytoplasm and tubular-shaped mitochondria were observed. These cells were also rich in Golgi bodies, ribosomes, and endoplasmic reticulum. In amblyopic kittens, nuclei of most neurons were aggregated, the number of ribosomes and Golgi bodies was reduced, mitochondria were swollen, and mitochondrial cristae were shortened or even absent. The endoplasmic reticulum was distended and reduced in magnitude.
Conclusions: VIP appears to play an important role in visual development, and its mRNA expression is affected by visual experiences. Visual dysfunction may down-regulate the expression of VIP-mRNA by impairing the structure and function of the neurons in the visual cortex, finally leading to amblyopia.