Distribution and morphological characteristics of acetylcholinesterase-containing neurons in the basal forebrain of the cat.

The topographical distribution and morphological characteristics of neurons containing acetylcholinesterase (AChE, EC 3.1.1.7) in the basal forebrain of the cat were studied by means of the Butcher's pharmaco-histochemical technique involving staining for AChE at various times after the administration of di-isopropylfluorophosphate (DFP). This method allows a clear visualization of numerous AChE-producing neurons in olfactory tubercle, medial septal-diagonal band area, hypothalamus and basal ganglia. In olfactory tubercle the AChE neurons abound in the deep polymorph layer where they form several types of cell clusters topographically related to the islands of Calleja. The AChE neurons in medial septal nucleus appear morphologically similar to those in nucleus of the diagonal band. As a whole, the medial septal-diagonal band area stands out as one of the major AChE cell collections in basal forebrain. In hypothalamus, neurons staining intensely for AChE occur particularly in supraoptic and paraventricular nuclei and in supramammillary nucleus. The neurons in lateral hypothalamic area stain only moderately for the enzyme. On the other hand, numerous large-sized AChE cells are scattered throughout the neostriatum. However, the AChE cells in putamen appear morphologically different, more numerous per mm2, and larger than those in caudate nucleus suggesting that the feline neostriatum is not a homogeneous structure. The globus pallidus contains both small and large cells that stain lightly and intensely for AChE, respectively. The small pallidal cells are similar to entopeduncular cells and it is proposed that they form the typical pallidal elements. In contrast, the large pallidal AChE cells appear similar to AChE neurons lying in adjacent substantia innominata, and are continuous with the AChE cells in medial septal-diagonal band area. It is suggested that these magnocellular AChE neurons form a population of "limbic" elements within the feline basal ganglia.