Acetylcholinesterase-containing neurons in the striatum, septum and hippocampus of the rat in embryonic culture and adult in situ.

Neurons of the rat brain, of either adult in situ or embryonic culture, have been studied by using a sensitive method for acetylcholinesterase (AChE) histochemistry. In the culture system, incubated for 6-18 days, AChE-positive neurons were found in tissues originating from the striatum and septum, but not in those from the hippocampus. These positive somata were morphometrically analyzed in terms of the cell size, i.e. the lengths of the major axis (Lmax) and the minor axis (Lmin) in cultured dishes of the striatum and septum; the mean Lmax was 20 and 22 microns, respectively. In in situ adult brain sections, a similar morphometric examination of AChE-positive neurons gave comparable results to those obtained in the culture system. An evaluation of both in vitro and in vivo through the histogramatical analysis revealed that the striatum contained more than two populations of AChE-positive cells differing in cell size. In contrast, a major single peak of Lmax was detected in the histogram of the septum. In both cases of striatum and septum in in situ adult brain, sagittal sections show larger size of Lmax, indicating that AChE-positive neurons are arranged in the sagittal direction. In studies on electrophysiological properties of large striatal cells in culture, both acetylcholine and glutamate induced changes in the membrane potential and/or the frequency of excitatory postsynaptic potential, while dopamine induced much smaller responses.