SPATIOTEMPORAL PATTERNS OF ONTOGENIC EXPRESSION OF PARVALBUMIN IN THESUPERIOR COLLICULI OF RATS AND RABBITS

We have examined the development of parvalbumin immunoreactivity in th e superior colliculi (SC) of the perinatal and mature rats and rabbits . In mature animals, parvalbumin-expressing cells (PECs) and neuropil in the retinorecipient layers were distributed in a continuous single band extending throughout the entire extent of the colliculus, whereas those in the intermediate layers formed distinct, radially oriented p atches. Parvalbumin was expressed for the first time on postconception al day 34 (PCD 34, postnatal day 12) and PCD 42 (postnatal day 11) in the SC of rat and rabbit, respectively. During ensuing development, bo th the thickness of the parvalbumin-expressing band in the retinorecip ient layers and the numbers of PECs in this band gradually increased, reaching adultlike values by PCD 44 and PCD 50 in the rat and rabbit, respectively. In the rat, monocular eye enucleations on PCD 23 resulte d in similar to 55% reduction in the number of PECs in the retinorecip ient layers of the contralateral colliculi examined on PCD 44 or PCD 5 0. Unilateral ablations of the entire visual cortex on PCD 23 (before the first corticotectal fibers from visual cortices reach the SC) or o n PCD 28 (when about half of the corticotectal fibers have reached col liculus) resulted in, respectively, similar to 55% and similar to 25% relative reduction in the number of PECs in the retinorecipient layers of the ipsilateral colliculi examined on PCD 44 or PCD 50. We conclud e that the ontogenetic expression of parvalbumin in most of PECs in th e retinorecipient collicular layers is induced by the activity of the contralateral retinotectal and/or the activity of the ipsilateral cort icotectal afferents. (C) 1998 Wiley-Liss, Inc.