Butyrylcholinesterase-rich neurons in rat brain demonstrated by a sensitive histochemical method

Butyrylcholinesterase (BChE) is a highly active enzyme in brain, but little is known about its physiological functions. One obstacle has been the lack of a sensitive and specific method for determining its cellular localization. We report here on a histochemical technique that has permitted BChE to be detected in neuronal, glial, and vascular structures. The method, which utilizes butyrylthiocholine iodide as the substrate, is a modification of our previously described method for acetylcholinesterase (AChE) histochemistry. BChE-rich neuronal somata stained much more intensely than capillaries or glia. Prominent neuronal groups were located in the anterodorsal, laterodorsal, anteroventral, reuniens, centrolateral, paratenial, and periventricular thalamic nuclei, the laterodorsal tegmental nucleus, the pedunculopontine tegmental nucleus, and the dorsal motor nucleus of vagus. Several other areas of the forebrain and brainstem showed modest numbers of positive cells. No positive cells were detected in the striatum, hippocampus, and most parts of the hypothalamus, which are regions containing numerous AChE-rich neurons. Although the distribution pattern of BChE-rich neurons differed from that of AChE-rich neurons, some neuronal groups contained both esterases. The results suggest that BChE may play a unique role in neuronal function, particularly since many BChE-rich neurons have not been identified as to neurotransmitter type.