Nicotine washout rates from isolated rat ganglia in relation to recovery from nicotine depolarization

1. Isolated rat superior cervical ganglia recovered more slowly from the depolarizing action of nicotine than from that of carbachol or acetylcholine. This was due to sustained high nicotine concentrations in the vicinity of the receptors, since recovery was hastened by adding hexamethonium to the washout fluid.2. Ganglia incubated for 4 min in 80 muM (3)H-nicotine accumulated nicotine to a level exceeding the extracellular space, as judged from the uptake of (3)H-mannitol.3. The subsequent efflux of (3)H-nicotine into non-radioactive solution could be largely resolved into two exponential components, with rate constants of 0.55+/-0.04 and 0.094+/-0.007 min(-1). The former was similar to that for total mannitol efflux, and so might be largely ascribed to clearance of extracellular nicotine. The slower efflux might be due to clearance from intracellular compartments. Nicotine efflux rates were not affected by hexamethonium indicating that receptor-activation did not modify the slow efflux.4. Efflux of choline compounds ((3)H-acetylcholine, (3)H-choline and (3)H-carbachol) showed an additional, very slow component (rate constant 0.001 to 0.002 min(-1)).5. It was suggested that slow efflux of intracellular nicotine might sustain depolarization on washing by maintaining high perineuronal concentrations of nicotine. With choline compounds the efflux rate from such sources may be too slow to affect perineuronal concentrations.

Origin of the after-hyperpolarization that follows removal of depolarizing agents from the isolated superior cervical ganglion of the rat

1. Potential changes in isolated rat superior cervical ganglia following addition and removal of depolarizing agents were recorded using a moving-fluid extracellular electrode system.2. Ganglionic negativity produced by carbachol was followed by a pronounced ganglionic positivity on washing. This after-positivity was attributed to hyperpolarization of the ganglion cells since it was unaffected by crushing the postganglionic trunk.3. The after-hyperpolarization was selectively depressed by (a) cooling (Q(10) 2.3), (b) metabolic inhibitors (cyanide, azide, 2,4-dinitrophenol), (c) reducing [K(+)](o) or substituting Cs(+) for K(+), (d) ouabain, and (e) substituting Li(+) for Na(+). This suggested a close dependence on active Na(+) transport.4. When K(+) was restored to K(+)-free solution, or the preparation was warmed rapidly, or when metabolic inhibitors were washed away, the hyperpolarization was rapidly regenerated. The effect of restoring K(+) indicated that the hyperpolarization was generated directly by the Na(+) pump.5. The hyperpolarization was not altered by replacing Cl(-) with isethionate, indicating that the voltage change produced by the Na(+) current was not modified by passive Cl(-) movements.6. Hexamethonium added to the washout fluid augmented the after-hyperpolarization, suggesting that there was a high (cationic) leak current due to continued receptor-activation on washing with normal Krebs solution.7. The hyperpolarization was reduced by omission of Ca(2+) and restored by addition of Mg(2+). This was considered to result from changes in passive membrane permeability.8. The time-course of post-carbachol hyperpolarization accorded with a Na(+) extrusion process whose rate was directly proportional to [Na(+)](i) with a rate constant of 0.38+/-0.02 min(-1) at 23-27 degrees C.9. With increasing concentrations of carbachol, the amplitude of the hyperpolarization increased in proportion to the preceding depolarization, but the rate constant of the hyperpolarization was unchanged.

Uptake of nicotine and extracellular space markers by isolated rat ganglia in relation to receptor activation

1. Uptake of (3)H-nicotine by isolated rat superior cervical sympathetic (SCG) and nodose (NG) ganglia was measured in vitro. Depolarization of the ganglia by nicotine was measured electrically.2. Nicotine depolarized the SCG but not the NG. The mean ED50 for depolarization was 5.3 x 10(-6)M.3. Both ganglia accumulated nicotine when incubated in 3.1 x 10(-5)M(3)H-nicotine: after 30 min incubation the ratios of tissue to medium concentrations were (mean +/- S.E. of mean): SCG, 3.49 +/- 0.13; NG, 2.50 +/- 0.09.4. Total water contents, estimated by drying to constant weight, were: SCG, 83.8 +/- 0.12%; NG, 80.1 +/- 0.21%. Extracellular spaces, measured as (3)H-mannitol space, were: SCG, 38.8 +/- 1.3; NG, 40.3 +/- 0.8% wet weight. These values were not significantly altered by nicotine.5. Correction for tissue fluid spaces indicated that the ratio of the mean intracellular fluid concentration to the extracellular fluid concentration for (3)H-nicotine at 3.1 x 10(-5)M were: SCG, 7.4; NG, 5.6. The ratios were not altered in any consistent manner on varying the nicotine concentration between 3.1 x 10(-7) and 1.6 x 10(-4)M.6. When the nicotine concentration was sufficiently great (6.2 x 10(-6)M or more) to evoke large SCG depolarizations, hexamethonium (2.5 x 10(-3)M) reduced (3)H-nicotine uptake by the SCG by up to 19% without affecting uptake by the NG, and thereby reduced the uptake difference between the two ganglia. With nicotine concentrations <6.2 x 10(-6)M, hexamethonium did not modify uptake by either ganglion.7. It was concluded that nicotine may be concentrated within neurones, and that such intracellular accumulation may be augmented during depolarization induced by nicotine.

Responses of normal and denervated cat superior cervical ganglia to some stimulant compounds

1. The effect of preganglionic denervation on the sensitivity of the cat superior cervical ganglion to close-arterial injections of some stimulant compounds in vivo has been studied.2. Ganglionic responses were assessed (a) by recording simultaneously ganglion depolarization and post-ganglionic nerve action potential discharges, and (b) by measuring the contractions of the nictitating membrane and applying a correction for the change in sensitivity of the membrane to noradrenaline.3. No change could be detected in the electrical responses of the ganglion to carbachol after denervation.4. Nictitating membrane recording suggested that denervation increased the response of the ganglion to acetylcholine, but had little effect on ganglionic sensitivities to carbachol, nicotine, tetramethylammonium or potassium chloride.5. It was concluded that the neurones of the superior cervical ganglion do not, in general, show any substantial change of sensitivity to cholinesterase-resistant stimulant compounds after denervation. The supersensitivity to acetylcholine is probably the result of a reduction of ganglionic acetylcholinesterase.

3H-Nicotine in cat superior cervical and nodose ganglia after close-arterial injection in vivo

1. Concentrations of (3)H-nicotine in the superior cervical and nodose ganglia of anaesthetized cats were measured after close-arterial injection.2. Shortly after injection there was a higher concentration of (3)H-nicotine in the superior cervical ganglion than in the nodose ganglion. Mean concentration ratios, superior cervical ganglion/nodose ganglion (S/N ratios) were: 2 min after injection, 1.60 +/- 0.19; 4 min, 1.21 +/- 0.19; 8 min, 0.92 +/- 0.05. These ratios were independent of the dose of nicotine over the range 4 to 200 mug in 0.2 ml.3. There was no comparable difference in the concentrations of injected (14)C-inulin or (3)H(2)O in the two ganglia, or in total water content.4. Procedures which reduced the pharmacological action of nicotine (pre-treatment with hexamethonium, admixture of (14)C-inulin) tended to reduce the S/N ratio for nicotine.5. Autoradiographs showed that nicotine entered the neurones of both superior cervical and nodose ganglia.6. It was concluded that the higher concentration of nicotine in the superior cervical ganglion was probably related to its selective pharmacological action at this site, and may have been due to a greater intracellular retention of nicotine.

Location of Radioactively Labelled Extracellular Fluid Indicators in Nervous Tissue by Autoradiography

The location of three radioactively labelled extracellular-space indicators ([3H]methoxyinulin, [3H]-D-mannitol and sodium [35S]sulphate) in the superior cervical sympatmhetic and nodose ganglia of cats was studied using an autoradiographic technique. The technique was designed to eliminate movement of soluble, diffusible substances in tissues after excision, and to provide high autoradiographic resolution. Ganglia were rapidly excised after administration of the radioactive compounds in vivo, and frozen in liquid propane. Frozen sections were cut at -60°C at a thickness of 0.7-0. µ. The frozen sections were freeze-dried, dry-mounted on dried, photographic emulsion-coated microscope slides, and exposed at -15°C until development.

The highest densities of silver grains in the autoradiographs were associated with regions of the tissue containing the greatest amounts of connective tissue. Lowest densities occurred beneath neurons and myelinated nerve fibres. The silver grain density beneath neuron perikarya was between 10% and 15% of that associated with plasma. Attempts were made to determine the source of these subneuronal silver grains. The results suggested that they could not be ascribed to the following: background; chemographs and pressure artefacts; spread of radiation from radioactive material outside the perikarya; and in vitro translocation of radioactive material into the neurons or into the emulsion beneath the neurons. It was concluded that the subneuronal grains reflected a small amount of intraneuronal penetration of the compounds in vivo. There was very little difference between inulin, mannitol and sulphate with regard to the proportion of intracellular activity. Except for this small amount of intracellular radioactivity, the findings accord with the view that inulin, mannitol and sulphate are confined predominantly to the extracellular fluid.