LOCALIZATION OF CHOLINE ESTERASE IN NERVE FIBERS

Enzymes of acetylcholine metabolism in the rat inferior colliculus

Although there is strong evidence for cholinergic projections to the rat inferior colliculus, especially from the pedunculopontine tegmental nucleus (Noftz et al., 2020), there is a lack of information about the quantitative prevalence of the enzymes of acetylcholine metabolism in its various portions. We have used microdissection of freeze-dried sections combined with radiometric assays to map the distributions in the rat inferior colliculus of the activities of choline acetyltransferase (ChAT), which catalyzes synthesis of acetylcholine, and acetylcholinesterase (AChE), which catalyzes its breakdown by hydrolysis. Both enzyme activities were present throughout the inferior colliculus. Average ChAT activity was consistently somewhat higher in the external cortex, excluding its most superficial layer, than in the dorsal cortex or central nucleus. Within the external cortex, ChAT activity was about half as high laterally in its most superficial layer as elsewhere. The distribution of AChE activity was more uniform than that of ChAT. Overall, ChAT activity in the rat inferior colliculus was relatively low, about a fifth of that in whole brain of rat and lower than in other central auditory regions, whereas AChE activity was about two-thirds that of rat whole brain and about average for central auditory regions. The results are compared to previous measurements for cat and hamster inferior colliculus. They are consistent with a modest role for cholinergic neurotransmission in the inferior colliculus, to modulate the activity of its major neuronal types.

Amino acid and acetylcholine chemistry in mountain beaver cochlear nucleus and comparisons to pocket gopher, other rodents, and cat

The mountain beaver and pocket gopher are two rodents that live mostly underground in tunnel systems. Previous studies have suggested that their cochlear nucleus structure, particularly that of the dorsal cochlear nucleus (DCN), differs significantly from that of other mammals, that the hearing ability of the pocket gopher is deficient compared to that of other rodents, and that the DCN of the mountain beaver is more responsive to slow oscillations of air pressure than to sounds. We conducted some electrophysiological recordings from mountain beaver DCN and then used microchemical methods to map in mountain beaver cochlear nuclei the distributions of amino acids, including the major neurotransmitters of the brain, and enzyme activities related to the metabolism of the neurotransmitter acetylcholine, which functions in centrifugal pathways to the cochlear nucleus. Similar measurements were made for a pocket gopher cochlear nucleus. Responses to tonal stimuli were found in mountain beaver DCN. Distributions and magnitudes of neurotransmitter and related amino acids within mountain beaver and pocket gopher cochlear nuclei were not very different from those of other rodents and cat. However, the enzyme of synthesis for acetylcholine, choline acetyltransferase, had only low activities in the DCN of both mountain beaver and pocket gopher. The chemical distributions in the mountain beaver DCN support a conclusion that it corresponds to just the superficial DCN portion of other mammals. High correlations between the concentrations of γ-aminobutyrate (GABA) and glycine were found for both mountain beaver and pocket gopher cochlear nuclei, suggesting that their co-localization in cochlear nucleus synapses may be especially prominent in these animals. Previous evidence suggests convergence of somatosensory and auditory information in the DCN, and this may be especially true in animals spending most of their time underground. Our results suggest that the enlarged DCN of the mountain beaver and that of the pocket gopher are not very different from those of other rodents with respect to involvement of amino acid neurotransmitters, but they appear to have reduced cholinergic innervation.

Neuropathology

This review is based on neuropathological contributions which have either a direct or indirect relation to mental disease or are of major general interest. Notwithstanding these restrictions the field which had to be covered remains vast, and no claim can be made that the survey of the literature is complete, although it is hoped that it is, to some extent, representative. In order to counteract this defect, recent reviews or comprehensive papers on special problems have been recommended, whenever they were available. They will enable the reader to trace references which for lack of space had to be suppressed. For the same reason of economy, a number of quotations have been made from reviews. This does not mean that the original papers have not been consulted.

ELECTRIC POTENTIAL AND ACTIVITY OF CHOLINE ESTERASE IN THE ELECTRIC ORGAN OF ELECTROPHORUS ELECTRICUS (LINNAEUS)

1. If the concentration of choline esterase is determined at different sections from the head to the caudal end of the electric organ of Electrophorus electricus (Linneaus) S-like curves are obtained. These curves are essentially the same as those which show the number of electric discs per centimeter and the E.M.F. per centimeter. 2. In the organ of Hunter the concentration of the enzyme does not differ from that in the adjacent parts in the main organ. This again coincides with the observations on the number of plates per centimeter in this organ. 3. The concentration of the enzyme was determined in different parts of the brain and the spinal cord and compared with that in a gold fish. The concentrations here are of the same order, but in the spinal cord of the eel the concentration is even lower than in the gold fish. As the cell bodies of the nerves innervating the electric organ in the spinal cord, these results do not lend support to the assumption of a special concentration of the enzyme in these nerves. 4. In the muscles adjacent to the electric organ an enzyme concentration has been found which is of the order of that in the electric tissue itself and much higher than in ordinary striated muscles. 5. The suitability of the organ for the preparation of enzyme solutions has been investigated and compared with that of the organ of Torpedo.

The isolation of a cell membrane fraction from rat liver

A procedure is described for isolating cell membranes from rat liver homogenates. 20 gm. of rat liver was homogenized in a Dounce homogenizer in ice cold water buffered to pH 7.5 with NaHCO₃, rupturing all of the cells and most nuclei. The diluted homogenate was filtered through cheesecloth to remove precipitated nucleoprotein and centrifuged at 1500 g, 10 minutes, to sediment a crude membrane fraction. The membrane containing sediment was recentrifuged 3 times in conical tubes (1220 g, 10 minutes), the top layer of the 2-layered sediment being retained. Flotation in a sucrose solution d = 1.22 freed the preparation from contaminating cell fragments and nuclear membranes not previously disintegrated. The floating material ∼0.4 ml. was quite homogeneous and consisted of thin amorphous membranes. Electron micrographs revealed numerous double profiles similar in shape and dimensions to apposed liver cell membranes in intact tissue.

Immunolocalization of muscarinic acetylcholine subtype 2 receptors in rat cochlear nucleus

It has been suggested that cholinergic effects in the rat cochlear nucleus (CN) are mediated by muscarinic acetylcholine receptors. In this study, immunohistochemistry for muscarinic subtype 2 (m2) receptors using a monoclonal subtype-specific antibody (Levey et al. [1995] J. Comp. Neurol. 351:339-356) revealed an m2-like system in the rat CN. A prominent lamina of m2-immunoreactive fibers and puncta was located in a subgranular layer of the caudal anteroventral cochlear nucleus (AVCN) and the posteroventral cochlear nucleus (PVCN). The superficial granular layer of the rostral AVCN and the medial sheet region also contained notable immunoreactivity for m2. Some labeled somata and their processes were found in magnocellular regions of the ventral CN. A network of neurites and puncta was located in the fusiform soma and deep layers of the dorsal CN. The olivocochlear bundle and its branches to the CN were also m2 immunoreactive and possibly contributed m2-labeled fibers and terminals to the CN. Some similarities and some differences were found between this m2 receptor distribution pattern and previous results for choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and muscarinic acetylcholine receptor immunohistochemistry and binding in the CN. The results suggest that m2 receptors that are located both pre- and postsynaptically mediate many cholinergic effects in the rat CN.

Choline acetyltransferase and acetylcholinesterase in centrifugal labyrinthine bundles of rats

Activities of choline acetyltransferase and acetylcholinesterase were measured for the acetylcholinesterase-positive fiber bundles containing axons projecting from the brainstem to the labyrinth of the rat. These activities were compared to those of a well-established cholinergic tract: the facial motor root. The choline acetyltransferase activities were roughly similar between the tracts, consistent with a conclusion that the centrifugal labyrinthine fibers are all cholinergic. The acetylcholinesterase activities were much higher in the centrifugal labyrinthine bundle than in the facial motor root, probably relating to the smaller diameters of the labyrinthine fibers. Transection of the centrifugal labyrinthine bundle led to virtually total loss of its choline acetyltransferase activity lateral to the cut, consistent with a centrifugal direction of all the fibers, but loss of only half its acetylcholinesterase activity, even after 34 days. These results agree with those for well-established cholinergic pathways, including the facial motor root in the present study, and with previous suggestions that a component of the acetylcholinesterase in cholinergic tracts might be synthesized by cells other than the neurons in the tract.

Isoenzymes of soluble and membrane-bound acetylcholinesterase in boine splanchnic nerve and adrenal medulla

Centrifugation of homogenates of bovine splanchnic nerve trunks and adrenal medulla showed that 47% and 31%, respectively, of the acetylcholinesterase activity was not sedimentable. The possibility that the soluble acetylcholinesterase activity was derived artefactually from the membrane-bound form was excluded. Gel electrophoresis revealed that the soluble acetylcholinesterase activity in adrenal medulla was distributed between five isoenzymes, only one of which was found in the supernatant fraction of splanchnic nerve homogenates. Solubilization of the membranes of both tissues with Triton X-100 gave a single isoenzyme of acetylcholinesterase, common to both tissues, whose electrophoretic mobility was less than that of any of the soluble isoenzymes. Some of the properties of the soluble and membrane-bound isoenzymes of acetylcholinesterase of splanchnic nerve were compared: the Michaelis constants were identical, both isoenzymes sedimented to the same position as catalase (molecular mass 240 000) in a density gradient, their mobilities varied in a parallel fashion upon electrophoresis in gels of different concentration. It was concluded that the higher electrophoretic mobility of the soluble isoenzyme was because it carried a greater charge than, but had a similar molecular mass to, the membrane-bound isoenzyme.

Investigation of the spasmogenic effect of manganese on the guineapig isolated ileum preparation

1. The mechanism of the manganese-induced spasm of the guinea-pig ileum was investigated using agents known to modify nerve function. The spasm was reduced by cooling, tetrodotoxin, procaine, Botulinus toxin (Type A), hyoscine and pempidine. It was potentiated by mipafox.2. In the presence of manganese, the release of acetylcholine from the ileum was greatly increased.3. Tetrodotoxin prevented the manganese-induced increase in acetylcholine output from the ileum but had no significant effect on the spontaneous acetylcholine output.4. It is suggested that the manganese-induced spasm of the ileum results from an action on intramural cholinergic nerves.

Cholinesterase activity per unit surface area of conducting membranes

According to theory, the action of acetylcholine (ACh) and ACh-esterase is essential for the permeability changes of excitable membranes during activity. It is, therefore, pertinent to know the activity of ACh-esterase per unit axonal surface area instead of per gram nerve, as it has been measured in the past. Such information has now been obtained with the newly developed microgasometric technique using a magnetic diver. (1) The cholinesterase (Ch-esterase) activity per mm(2) surface of sensory axons of the walking leg of lobster is 1.2 x 10(-3) microM/hr. (sigma = +/- 0.3 x 10(-3); SE = 0.17 x 10(-3)); the corresponding value for the motor axons isslightly higher: 1.93 x 10(-3) microM/hr. (sigma = +/- 0.41 x 10(-3); SE = +/- 0.14 x 10(-3)). Referred to gram nerve, the Ch-esterase activity of the sensory axons is much higher than that of the motor axons: 741 microM/hr. (sigma = +/- 73.5; SE = +/- 32.6) versus 111.6 microM/hr. (sigma = +/- 28.3; SE = +/- 10). (2) The enzyme activity in the small fibers of the stellar nerve of squid is 3.2 x 10(-4) microM/mm(2)/hr. (sigma = +/- 0.96 x 10(-4); SE = +/- 0.4 x 10(-4)). (3) The Ch-esterase activity per mm(2) surface of squid giant axon is 9.5 x 10(-5) microM/hr. (sigma = +/- 1.55 x 10(-5); SE = +/- 0.38 x 10(-5)). The value was obtained with small pieces of carefully cleaned axons after removal of the axoplasm and exposure to sonic disintegration. Without the latter treatment the figurewas 3.85 x 10(-5) microM/mm(2)/hr. (sigma = +/- 3.24 x 10(-5); SE = +/- 0.93 x 10(-5)). The experiments indicate the existence of permeability barriers in the cell wall surrounding part of the enzyme, since the substrate cannot reach all the enzyme even when small fragments of the cell wall are used without disintegration. (4) On the basis of the data obtained, some tentative approximations are made of the ratio of ACh released to Na ions entering the squid giant axon per cm(2) per impulse.