Acetylcholine synthesis in normal and denervated sympathetic ganglia of the cat

Abstract

MacIntosh (1938) was the first to relate the time of failure of conduction through a denervated sympathetic ganglion with a diminution in its acetylcholine content. From the work of Brown & Feldberg (1936) on perfused ganglia, and of Feldberg (1943) on incubated extracts of ganglia, it appeared that both events might be attributed to a failure of the preganglionic endings to synthesize acetylcholine. However, Feldberg's methods (1943) were relatively insensitive (Nachmansohn, John & Berman, 1946) and did not provide unequivocal evidence that the reduced acetylcholine synthesis obtained in denervated ganglia was due to loss of the enzyme concerned (choline acetylase) rather than to loss of some other constituent of the system such as the activator fraction. We therefore decided to repeat Feldberg's work using the more refined methods he later developed (Feldberg & Mann, 1945. These methods provide a means of aetermining the choline acetylase activity of a tissue independently of other variables, and have been adapted in our experiments so that synthesis measurements could be made on individual sympathetic ganglia of the cat. METHODSOperative and experimental procedures. Twenty-nine cats and three kittens were used for the tests. Of these, nine animals with no previous operation were treated as controls; in seventeen the superior cervical ganglion on one side was denervated (aseptically) by the removal of 1-2 cm. of the cervical sympathetic trunk from a site low in the neck. In three others the vagus nerve central to the nodose ganglion and the post-ganglionic trunk of the superior cervical ganglion were both cut on the one side. The operations were performed 1-29 days before the acute experiments. For the latter, anaesthesia was obtained either by Pentobarbitone sodium, 40 mg./kg., or by 'Dial' (Ciba), 0 7 ml./kg., injected intraperitoneally or intravenously. After tracheotomy, the two cervical sympathetic nerves were prepared for stimulation. Voltages ranging from 0*5 to 20 V., with pulse durations of 0-1 or 1 msec. were delivered from a 'Ritchie-Sneath' Square-Wave Stimulator. The nerve was stimulated for 5 sec. at approximately fifty shocks per sec. and contractions ofthe nictitating membrane were recorded to provide evidence for ganglionic transmission. In the nodose ganglion experiments, the peripheral end of the vagus was tested for stretch afferent

Physiological and structural changes at the amphibian myoneural junction, in the course of nerve degeneration

“…In spite of their complexities the observations confirmed that at the time of failure of transmission a rapid functional break-down occurs in the nerve endings, associated with a decline in frequency and ultimate disappearance of the spontaneous potentials. (MacIntosh, 1938;Lissak, Dempsey & Rosenblueth, 1939;Feldberg, 1943;Banister & Scrase, 1950), namely that failure of transmission at a degenerating synapse is associated with a stoppage of transmitter production and therefore also with disappearance of the spontaneous miniature potentials (Fatt & Katz, 1952;Liley, 1956a). On further exploration, however, we found that spontaneous subthreshold activity was resumed at the denervated end-plates during the course of the second week.…”

“…In sympathetic ganglia, it has been shown that ACh synthesis vanishes within a short time after preganglionic nerve section (Feldberg, 1943;Banister & Scrase, 1950; see also Brown & Feldberg, 1936;MacIntosh, 1938). This does not necessarily conflict with our interpretation; for it would be impossible to say whether the production of ACh is completely abolished or persists at a level of less than 1% of the initial rate, and no more than this would be required to maintain the renewed end-plate activity.…”

The margin of safety of neuromuscular transmission

“…Functional and structural changes have been described at the amphibian neuromuscular junction only after 3 days denervation (Birks, Katz & Miledi, 1960). For cat superior cervical ganglion, decline of acetylcholine content has been noted within 30 hr after preganglionic section (Banister & Scrase, 1950). Emmelin (1962) did not observe 'paralytic secretion' by the cat submaxillary gland until 14 hr or longer after post-ganglionic denervation.…”

An electrophysiological analysis of the synthesis of acetylcholine in preganglionic nerve terminals

“…As this output per minute represents the rate of synthesis of transmitter at the time when the steady level of release is reached, the rate of synthesis must also be proportional to the frequency of stimulation. The rates of ACh synthesis observed in intact nervous tissue (Banister & Scrase, 1950;Hebb, Krnjevfc & Silver, 1964) are well below the rates dictated by the activity of the enzyme or the concentration of the substrate (Potter, Glover & Saelens 1968). There is only limited inhibition of choline acetyltransferase by ACh at concentrations approaching those which probably occur in the nerve terminals (Kaita & Goldberg, 1969;Glover & Potter, 1971 A model of the storage and synthesis of ACh in preganglionic terminals, derived from the results of the electrophysiological experiments reported in this and the preceding paper (Bennett & McLachlan, 1972) impulses.…”