Many maturational processes in the brain are at high levels prenatally as well as neonatally before eye-opening, when extrinsic sensory stimulation is limited. During these periods of rapid brain development, a large percentage of time is spent in rapid eye movement (REM) sleep, a state characterized by high levels of endogenously produced brain activity. The abundance of REM sleep in early life and its ensuing decline to lower levels in adulthood strongly suggest that REM sleep constitutes an integral part of the activity-dependent processes that enable normal physiological and structural brain development. We examined the effect of REM sleep deprivation during the critical period for visual development on the development of two calcium-binding proteins that are associated with developmental synaptic plasticity and are found in the lateral geniculate nucleus (LGN) and visual cortex. In this study, REM sleep deprivation was carried out utilizing a computer-controlled, cage-shaking apparatus that successfully suppressed REM sleep. Body weight data suggested that this method of REM sleep deprivation produced less stress than the classical multiple-platform-over-water method. In REM sleep-deprived animals with normal binocular vision, the number of parvalbumin-immunoreactive (PV) neurons in LGN was found to be lower compared with control animals but was not affected in visual cortex. The pattern of calbindin-immunoreactivity (CaB) was unchanged at either site after REM sleep deprivation. Parvalbumin-immunoreactivity develops later than calbindin-immunoreactivity in the LGN, and the REM sleep deprivation that we applied from postnatal day 42-49 delayed this essential step in the development of the kitten's visual system. These data suggest that in early postnatal brain development, REM sleep facilitates the usual time course of the expression of PV-immunoreactivity in LGN neurons.