Expression of messenger RNAs for glutamic acid decarboxylase,preprotachykinin,cholecystokinin, somatostatin, proenkephalin and neuropeptide Y in the adult rat superior colliculus

The mammalian superior colliculus is an important subcortical integrator of sensorimotor behaviours. It is multi-layered, each layer containing specif ic neuronal types and possessing distinct input/output relationships. Here we use in situ hybridisation methods to map the distribution of seven neuro transmitters/neuromodulator systems in adult rat superior colliculus. Coron al sections were probed for preprotachykinin, cholecystokinin, somatostatin , proenkephalin, neuropeptide Y and the enzymes glutamic acid decarboxylase and choline acetyltransferase, markers for GABA and acetylcholine respecti vely. Cells expressing glutamic acid decarboxylase messenger RNA were the m ost abundant, the highest density being found in the superficial layers. Ma ny cells containing proprotachykinin messenger RNA were found in stratum zo nale and the upper two-thirds of stratum griseum superficiale; cells were a lso located in deeper tectal laminae, particularly caudomedially. Most chol ecystokinin messenger RNA expressing cells were located in the superficial layers with a prominent band in the middle third of stratum griseum superfi ciale. Cells expressing moderate to high levels of somatostatin messenger R NA formed a dense band in the lower third of stratum griseum superficiale/u pper stratum opticum; two less distinct tiers of labelling were seen in dee per layers. These in situ hybridisation data reveal three distinct sublamin ae in rat stratum griseum superficiale. Cells expressing moderate to low le vels of proenkephalin messenger RNA were located in lower stratum griseum s uperficiale/upper stratum opticum and intermediate laminae. A cluster of en kephalinergic cells was located medially in the deep tectal laminae. Expres sion of neuropeptide Y messenger RNA was relatively low and mostly confined to cells in stratum griseum superficiale and stratum opticum. No choline a cetyltransferase messenger RNA was detected. This in situ analysis of seven different neurotransmitters/neuromodulator s ystems sheds new Light on the neurochemical organisation of the rat superio r colliculus. The data are related to what is known anatomically and physio logically about intrinsic and extrinsic tectal circuitry, and the potential involvement of different neuropeptides in these circuits is discussed. The work forms the basis for future developmental studies examining the effect s of transplantation and visual deprivation/ deafferentation on tectal neur ochemistry and function. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.