Stratified organization and disorganization of inner plexiform layer revealed by TNAP activity in healthy and diabetic rat retina.

Tissue non-specific alkaline phosphatase (TNAP), an abundant ectophosphatase, is present in various organs including the brain and retina of several vertebrate species. Evidence is emerging that TNAP influences neural functions in multiple ways. In rat, strong TNAP activity has been found in retinal vessels, photoreceptors, and both synaptic layers. In the present study, we identified eleven strata of the inner plexiform layer (IPL) by using TNAP histochemistry alone. The TNAP strata corresponded exactly to the strata seen after combined immunohistochemistry with four canonical IPL markers Therefore, as described in other mammalian species, our data support the existence of multiple morphologically and functionally discernible IPL strata in rats. Remarkably, the stratification pattern of the IPL was severely disrupted in a diabetic rat model, even before changes in the canonical IPL markers were detectable. These findings indicate that TNAP histochemistry offers a more straightforward, but also more sensitive, method for investigating retinal strata and their diabetes-induced degeneration.

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