A monoclonal antibody (RT97) against neurofilament protein specifically and exclusively labelled a subpopulation of rat dorsal root ganglion (DRG) neurones. For seven ganglia (L4 and T13) studied quantitatively the frequency distribution histograms of the size of labelled cells could be fitted by a single normal distribution whose parameters were extremely close to those of the normally distributed large light cell population in that ganglion. On this basis and on the basis of a statistical analysis of the results it was suggested that this antibody can be used as a much needed specific label for the large light population of neurones in rat DRGs. The small dark neurone population was not labelled by this antibody. In one ganglion the subjective analysis of whether each neurone was labelled or not was directly compared with microdensitometric measurements of reaction product intensity. This analysis supported the above conclusion, and furthermore no subdivisions of the labelled population were apparent on the basis of neuronal size plotted against intensity of the reaction product. Other neuronal cell bodies strongly labelled by this antibody were found in association with small unlabelled neurones not only in DRGs, but also in the trigeminal ganglion, the vagal ganglia, and the mesencephalic V nucleus, all of which are made up of primary afferent neurones and all of which are completely or partially derived from the neural crest. Sympathetic and central nervous system neuronal cell bodies were unlabelled or occasionally very lightly labelled although immunoreactive fibres abound in the central nervous system.

Interest in the functions of intracellular chloride expanded about twenty years ago but mostly this referred to tissues other than smooth muscle. On the other hand, accumulation of chloride above equilibrium seems to have been recognised more readily in smooth muscle. Experimental data is used to show by calculation that the Donnan equilibrium cannot account for the chloride distribution in smooth muscle but it can in skeletal muscle. The evidence that chloride is normally above equilibrium in smooth muscle is discussed and comparisons are made with skeletal and cardiac muscle. The accent is on vascular smooth muscle and the mechanisms of accumulation and dissipation. The three mechanisms by which chloride can be accumulated are described with some emphasis on calculating the driving forces, where this is possible. The mechanisms are chloride/bicarbonate exchange, (Na+K+Cl) cotransport and a novel entity, "pump III", known only from own work. Their contributions to chloride accumulation vary and appear to be characteristic of individual smooth muscles. Thus, (Na+K+Cl) always drives chloride inwards, chloride/bicarbonate exchange is always present but does not always do it and "pump III" is not universal. Three quite different biophysical approaches to assessing chloride permeability are considered and the calculations underlying them are worked out fully. Comparisons with other tissues are made to illustrate that low chloride permeability is a feature of smooth muscle. Some of the functions of the high intracellular chloride concentrations are considered. This includes calculations to illustrate its depolarising influence on the membrane potential, a concept which, experience tells us, some people find confusing. The major topic is the role of chloride in the regulation of smooth muscle contractility. Whilst there is strong evidence that the opening of the calcium-dependent chloride channel leads to depolarisation, calcium entry and contraction in some smooth muscles, it appears that chloride serves a different function in others. Thus, although activation and inhibition of (Na+K+Cl) cotransport is associated with contraction and relaxation respectively, the converse association of inhibition and contraction has been seen. Nevertheless, inhibition of chloride/bicarbonate exchange and "pump III" and stimulation of (K+Cl) cotransport can all cause relaxation and this suggests that chloride is always involved in the contraction of smooth muscle. The evidence that (Na+K+Cl) cotransport more active in experimental hypertension is discussed. This is a common but not universal observation. The information comes almost exclusively from work on cultured cells, usually from rat aorta. Nevertheless, work on smooth muscle freshly isolated from hypertensive rats confirms that (Na+K+Cl) cotransport is activated in hypertension but there are several other differences, of which the depolarisation of the membrane potential may be the most important.Finally, a simple calculation is made which indicates as much as 40% of the energy...

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SUMMARY1. A technique is described for perfusing the isolated cat pancreas with saline solutions.2. Single doses of secretin, although present in the perfusate for only a short time, caused a prolonged flow of pancreatic juice.3. In response to continuous secretin infusion, the preparation secreted for up to 6 hr a juice which was similar to that obtained in vivo, with the exception that the bicarbonate concentration decreased and the chloride concentration increased with time, even when the rate of secretion remained constant.4. The osmolalities of perfusate and secretion were identical over a range of 450 m-osmoles/kg, but the electrolyte concentration of the secretion was always slightly higher than that of the perfusate. Variations from perfusate isosmolality produced inverse changes in the secretion rate, over the range from 600 m-osmoles/kg, at which secretion ceased, to 150 m-osmoles/kg, at which the rate was highest. At perfusate osmolalities below 150 m-osmoles/kg secretion rapidly declined.5. Reduction in perfusate sodium chloride concentration, isosmolality being maintained with sucrose, caused a fall in secretion rate, but the sodium concentration of the juice remained constant until perfusate sodium concentration was reduced to about 70 m-equiv/l. Below this level it declined and sucrose was detected in the juice in quantities almost sufficient to account for the equiosmolality of juice and perfusate.6. Two hypotheses about the mechanism of water and electrolyte secretion by the pancreas are presented.

Pancreozymin in man as in animals appears to act as a specific enzyme stimulant. The preparations of pancreozymin used in these experiments also contain cholecystokinin, which causes the gall bladder to contract, and a smooth muscle stimulant, possibly substance P.The (Lagerlof, 1939(Lagerlof, , 1942 Diamond, Siegel, Gall, and Karlen, 1939;Diamond andSiegel, 1940, 1941;Comfort and Osterberg, 1940;Pratt, Brugsch, and Rostler, 1940;Pollard, Miller, and Brewer, 1942;Lake, 1947;Dornberger, Comfort, Wollaeger, and Power, 1948;Dreiling and Hollander, 1948, 1950;Friedman and Snape, 1950;Dreiling, 1950Dreiling, , 1951Dreiling, , 1953Dreiling, , 1955 Dreiling and Janowitz, 1957;Wenger and Raskin, 1958).In anaesthetized animals secretin produced a large volume of pancreatic juice of constant alkalinity and low enzyme content. Harper and Raper (1943) isolated from the small intestine a second material, other than secretin, which increased the enzyme output by the pancreas without affecting the volume of juice. This material they named pancreozymin. Crick, Harper, and Raper (1949) later published a revised method of preparing secretin and pancreozymin and preliminary experiments showed that pancreozymin had the same effect on man as in animals

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1. In fasted anaesthetized cats which were secreting pancreatic juice at a steady slow rate in response to continuous intravenous infusion of secretin, stimulation of the dorsal vagus trunk increased the rate of secretion, the rate of output of amylase and the concentration of bicarbonate in the juice.2. The increase in rate of secretion and in concentration of bicarbonate was reduced but not abolished by atropine. It was unaffected by adrenergic blocking agents, but abolished by hexamethonium.3. No increase in rate of secretion of secretin-stimulated juice was observed on cervical stimulation of vagus nerves in which the efferent fibres had degenerated after supra-nodose section of the nerves. It is concluded that the increase in secretion rate is mediated by ;atropine-resistant' efferent vagal fibres.4. Pancreozymin, antral extracts and histamine increased the rate of secretion of secretin-stimulated juice. Pancreozymin and antral extracts also increased the rate of amylase output. These effects of pancreozymin and antral extracts were not abolished by atropine or hexamethonium.5. As vagal stimulation pancreozymin, antral extracts and histamine have little or no effect on the resting pancreas of the anaesthetized cat, it is concluded that they exert a potentiating effect on secretin. It is suggested that the mechanism of this potentiation is an increase in pancreatic blood flow, which facilitates the supply of secretin to the gland.

1. The bicarbonate concentration in cat pancreatic juice falls and the chloride concentration increases at slow secretory rates. The concentration of sodium and potassium remain constant at all secretory rates.2. Acetazolamide reduces the maximal rate of secretion markedly, and the maximal bicarbonate concentration slightly, but does not alter the reciprocal relationship between bicarbonate and chloride at slow rates of flow.3. By perfusion of the main duct it has been shown that there is a loss of bicarbonate and a gain of chloride across the duct wall due to a passive process of exchange diffusion. It is suggested that this may account for a substantial part of the flow-dependent changes in bicarbonate and chloride concentrations in the intact gland.4. The enzyme content of pancreatic juice is made up of a small continuous basal output, to which may be added a much larger secretion in response to hormonal stimulation.5. From analysis of successive small samples of juice it has been found that the response to single injections of pancreozymin lasts a very short time, during which the secretory cells release enzymes in a small volume of chloride-containing fluid.6. It is concluded that in the cat pancreatic secretion consists of an isosmolar primary secretion mostly of sodium bicarbonate, to which is added small amounts of a chloride-containing enzyme secretion. This fluid is modified, particularly at slow flow rates, by transductal exchange of chloride and bicarbonate which, at least in the main duct, is passive in nature.