The adult corpus striatum in mammals is divided into distinct histochemical compartments1. If the cat caudate nucleus is stained for acetylcholinesterase a number of macroscopically visible zones appear that have lower acetylcholinesterase activity than the surrounding tissue2. These patches, called 'striosomes'1, correspond to regions of high [Met]-enkephalin-like immunoreactivity3 and dense opiate receptor binding4 and are related to the uneven distribution of striatal efferent neurones and cortical afferent terminations5,6. One of the highest concentrations of neurotensin-like immunoreactivity is in the striatum and the immunoreactive material co-elutes with synthetic neurotensin on gel chromatography7. Recently, we have found that neurotensin-like immunoreactivity in the cat caudate nucleus coincides with the striosomes 8. We have now localized neurotensin receptors in the cat caudate nucleus by autoradiography9 and found low density in the neurotensin-rich striosomes and a high density in the neurotensin-poor surrounding tissue.
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