C. C. D. Shute

Journal Article THE ASCENDING CHOLINERGIC RETICULAR SYSTEM: NEOCORTICAL, OLFACTORY AND SUBCORTICAL PROJECTIONS Get access C. C. D. SHUTE, C. C. D. SHUTE From the Anatomy School, University of Cambridge Search for other works by this author on: Oxford Academic PubMed Google Scholar P. R. LEWIS P. R. LEWIS From the Anatomy School, University of Cambridge Search for other works by this author on: Oxford Academic PubMed Google Scholar Brain, Volume 90, Issue 3, September 1967, Pages 497–520, https://doi.org/10.1093/brain/90.3.497 Published: 01 September 1967

EVIDENCE has accumulated for a close functional relationship between the brain-stem reticular formation and the hippocampal formation (hippo-campus and dentate gyrus) of the fore-brain. On the one hand, it has been shown that stimulation of the mid-brain reticular formation not only causes

1. Unilateral lesions were made in the fimbria of adult rats with a stereotaxically-applied, radio-frequency current. After 3-23 days survival, fresh, unfixed, transverse sections were cut of the forebrain. Half the sections were stained histochemically to show the distribution of acetylcholinesterase (AChE) activity. From the other sections, small, anatomically defined areas were dissected out and assayed for choline acetylase (ChAc) activity (acetyl-CoA: choline-O-acetyltransferase EC2.3.1.6).2. In the fimbria, anterior to the lesion, ChAc activity rises sharply and is still approximately twice the normal after 7 days. In the hippocampus, ChAc activity falls: in most experiments activity on the operated side was 20-40% of that on the control side, but in some experiments values below 10% were obtained. These changes closely parallel those observed in the staining for AChE.3. The results go far towards proving that the hippocampus receives a massive cholinergic innervation via the fimbria. The fibres concerned appear to be those which stain characteristically for AChE and it seems likely that other pathways showing the same histochemical behaviour are also cholinergic.

Abstract The thiocholine technique for cholinesterase has been successfully adapted for the demonstration of enzyme distribution with the electron microscope. After fixation in buffered glutaraldehyde, thin slices of tissue were taken through a histochemical procedure designed to minimize diffusion artifacts and cytological damage; appropriate areas were dissected out, fixed with osmium tetroxide and embedded in Araldite. This technique has been used to study the distribution of enzyme in and around known cholinergic neurons in the rat. In diaphragm muscle the intense staining of the motor end plates is confined to the actual synaptic clefts. The distribution of cytoplasmic staining was similar in all three types of cholinergic neurons studied (ventral horn cells from the cervical cord, cells from the dorsal motor nucleus of the vagus, and cells from the hypoglossal nucleus). There was intense staining of the space contained within the individual bilaminar sheets of the rough endoplasmic reticulum and occasionally in areas of the nuclear envelope. Mitochondria, lysosomes, the smooth endoplasmic reticulum and most of the plasma membrane were unstained. In cholinergic nerve fibres staining was particularly intense at the axonal membrane and absent from the myelin sheath. In several regions of the brain known to receive an afferent cholinergic innervation many of the identifiable synaptic areas were heavily stained. Staining here was usually present round most of the presynaptic process, spreading over part of the postsynaptic process and often penetrating into the actual synaptic space. The mitochondria, microvesicles and the general cytoplasm of the synaptic processes were all unstained. In some areas, such as the hippocampus, there was intense membrane staining of fine cholinergic neuropil. The enzyme specificity of the technique is not in doubt and evidence is adduced for the view that diffusion artifacts are small. The close correlation between the electron-microscopic results and evidence from physiological and biochemical investigations is discussed.