Effects of monocular enucleation on parvalbumin in rat visual system during postnatal development

To evaluate the hypothesis that the expression of the calcium-binding protein parvalbumin (PV) in a subpopulation of gamma-aminobutyric acid (GABA)ergic neurons is an appropriate molecular marker for the effect on ocular dominance plasticity of monocular deprivation during the postnatal sensitive period.

Long-Evans rats underwent monocular enucleation immediately before eye opening (postnatal day [P] 14). Immunohistochemical analysis using anti-PV antibody was performed on the superior colliculus (SC) and lateral geniculate nucleus (LGN) at P45. In the visual cortex (VC) developmental changes in immunoreactivity were also examined at the ages of P17, P20, P27, and P45. Northern blot analysis for PV mRNA was also performed at P45. Changes in PV expression in the visual system of these rats were evaluated by use of a computer-based quantitative technique.

PV-immunoreactive neurons were present in the SC and VC, whereas only a few were found in the LGN. The monocular enucleation at the onset of the sensitive period markedly reduced PV immunoreactivity in the neuropil of the SC, contralateral to the enucleated eye when examined one month later. No consistent and significant change in PV immunoreactivity was found in either the LGN or the VC. The number of PV-immunoreactive neurons in the VC rapidly decreased to the adult level during the middle of the sensitive period. The expression of PV mRNA in these central visual structures was not affected by early monocular enucleation.

Expression of PV is developmentally regulated, and marked changes in its protein expression in the SC can be induced by monocular enucleation. Contrary to the original hypothesis, monocular enucleation did not consistently affect the expression of PV in the rat VC. The expression of PV is probably regulated by multiple factors, not merely by binocular competition.