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

PURPOSE. TO re-evaluate the hypothesis that the expression of the calcium-b inding protein parvalbumin (PV) in a subpopulation of gamma-aminobutyric ac id (GABA)ergic neurons is an appropriate molecular marker for the effect on ocular dominance plasticity of monocular deprivation during the postnatal sensitive period. METHODS. Long-Evans rats underwent monocular enucleation immediately before eye opening (postnatal day [P] 14). Immunohistochemical analysis using ant i-PV antibody was performed on the superior colliculus (SC) and lateral gen iculate nucleus (LGN) at P45. In the visual cortex (VC) developmental chang es 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. RESULTS. PV-immunoreactive neurons were present in the SC and VC, whereas o nly a few were found in the LGN. The monocular enucleation at the onset of the sensitive period markedly reduced PV immunoreactivity in the neuropil o f 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 pe riod. The expression of PV mRNA in these central visual structures was not affected by early monocular enucleation. CONCLUSIONS. Expression of PV is developmentally regulated, and marked chan ges in its protein expression in the SC can be induced by monocular enuclea tion. Contrary to the original hypothesis, monocular enucleation did not co nsistently affect the expression of PV in the rat VC. The expression of PV is probably regulated by multiple factors, not merely by binocular competit ion.