ABSTRACT
The appearance and changes of Acetylcholinesterase (ACHE) in the brains of 62 rats from early embryos to adults were studied by histochemical method and the brains of 19 rats of corresponding stages were examined with Nissl stain. The main results are as follows:1. AChE appeared in the following sequence: spinal cord, myelencephalon, metencephalon, mesencephalon, diencephalon and finally in telencephalon. In telencephaIon, AChE appeared earlier in paleocortex than in neocortex. The sequence described above showed that the appearance of AChE reflects cephalization of the nervous system in the rat.2. AChE-positive neurons of the rat brain consisted of cholinergic neurons and cholinoceptive ceils, both of which are related to the neurotransmitter ACh.3. The following nuclei of adult rat brain were shown to be AchE-positive in our specimens, but had not been reported in available literature: n. tractus mesencephali, n. anterior dorsalis thalami, n. anterior ventralis thalami, n. lateralis thalami, n. habenulae lateralis, n. reticularis thalami, n. supraopticus, n. paraventricularis, n. parafascicularis and n. ruber. In the cerebral cortex very few positive cells have been noticed.