ENKEPHALIN-POSITIVE AND ACETYLCHOLINESTERASE-POSITIVE PATCH SYSTEMS IN THE SUPERIOR COLLICULUS HAVE MATCHING DISTRIBUTIONS BUT DISTINCT DEVELOPMENTAL HISTORIES

Histochemical stains for acetylcholinesterase activity and enkephalin- like immunoreactivity both demonstrate a high degree of patterning in the superior colliculus, particularly in the intermediate and deep lay ers. Both markers occur predominantly in the neuropil of these layers, and both are principally distributed in distinct macroscopic compartm ents. We report here that patches of heightened acetylcholinesterase a ctivity correspond to patches of high enkephalin-like immunoreactivity . The two markers thus delineate largely the same domain in the interm ediate and deep layers. The most prominent zones of staining for enkep halin-like peptide and for acetylcholinesterase also coincided in the dorsolateral periaqueductal gray matter. These findings suggest a clos e interlocking of one or more acetylcholinesterase-containing systems with one or more pathways related to endogenous opioids in the superio r colliculus. As the acetylcholinesterase expression in the patches is known to match in detail choline acetyltransferase expression, our re sults also suggest the possibility of local cholinergic-opiatergic int eractions. In some sections, blood vessels associated with enkephalin- rich and acetylcholinesterase-rich patches extended beyond the collicu lus into the periaqueductal gray matter, where they again became surro unded by dense fibrous labelling. This pattern suggests that neurohumo ral signal exchange might occur through blood vessels even in a sensor y-motor structure such as the colliculus. In a postnatal developmental series of kitten brains we found that enkephalin-like immunoreactivit y was already distinctly compartmental in the intermediate layers at b irth and continued to show this distribution throughout postnatal deve lopment. By contrast, acetylcholinesterase staining was nearly homogen eous at birth and became compartmental gradually during the first post natal weeks. Thus, despite the eventual near coincidence of the enkeph alin-rich and acetylcholinesterase-rich compartments of the superior c olliculus, they mark systems that follow distinct programs of neuroche mical development. (C) 1994 Wiley-Liss, Inc.