PATTERN-FORMATION IN THE DEVELOPING SUPERIOR COLLICULUS - ONTOGENY OFTHE PERIODIC ARCHITECTURE IN THE INTERMEDIATE LAYERS

The superior colliculus of mammals contains a striking neurochemical a rchitecture in which histochemically identifiable compartments are dis tributed in an iterative arrangement in the intermediate layers. We us ed stains for acetylcholinesterase activity as a compartment marker to trace ontogenesis of this architecture during pre- and postnatal deve lopment in the domestic cat. We found that compartmentation in the int ermediate collicular layers is virtually absent at birth, and only gra dually emerges during the first weeks of postnatal life. Over the same postnatal period, acetylcholinesterase activity shifts from a predomi nantly perikaryal expression pattern immediately postnatally to a near ly exclusive localization in the neuropil at maturity. Remarkably, a s triking compartmentation of the superior colliculus was readily appare nt with acetylcholinesterase histochemistry prenatally. The first appe arance of a periodic architecture in the superior colliculus was obser ved at embryonic day 34, a time at which the collicular plate had not yet become laminated. The compartments characterized by high levels of acetylcholinesterase activity then gained in prominence until late in the prenatal period, when they receded and disappeared. The loss of t he acetylcholinesterase-positive compartments in the perinatal period did not reflect a loss of compartmentation altogether. Neonatally, the re was a distinct compartmental architecture visible with enkephalin i mmunohistochemistry. The virtual absence of acetylcholinesterase-posit ive compartments in the superior colliculus at birth therefore reflect s developmental regulation of enzyme expression in the compartments, n ot regulation of the compartments as structural entities. We conclude that the periodic architecture, which characterizes the intermediate c ollicular layers in the adult cat, arises early in ontogenesis. These observations raise the possibility that the histochemical compartments are ontogenetic units that undergo remodelling as the superior collic ulus matures. (C) 1994 Wiley-Liss, Inc.