Effect of potassium ions on glucose and phospholipid metabolism in the rat's cervical sympathetic ganglia with and without axotomy

High potassium-induced activation of choline-acetyltransferase in human neocortex: implications and species differences

The role of electrical and potassium (K(+))-induced depolarisation on choline-acetyltransferase (ChAT) activity in human and mouse neocortical slices was studied. When [3H]-ACh release was evoked by two K(+) stimulations in human neocortex, the mean S(2)/S(1) ratio was significantly below unity. ChAT inhibitors, like bromo-acetylcholine and ocadaic acid, raised this ratio by 79 and 63%, respectively, suggesting that the diminished S(2)/S(1) value in the absence of ChAT inhibitors reflected an increased ChAT activity at S(2) following K(+) depolarisation at S(1). When stimulated electrically, however, the S(2)/S(1) ratio in human neocortex was near unity and ocadaic acid remained without effect. In parallel experiments on mouse neocortical slices, the S(2)/S(1) ratio was near unity in both electrically or K(+)-evoked [3H]-ACh release and was not altered by ChAT inhibition. ChAT activity following K(+) depolarisation was also determined directly. ChAT activation in human neocortical slices was highest at 10 and 20mM K(+). ChAT activity in mouse neocortical tissue was not altered by K(+) depolarisation. These results suggest that in human, but not in mouse, neocortex ChAT activity may be increased due to ongoing K(+) depolarisation. This increase of ChAT activity supports a cholinergic degeneration hypothesis which has been entitled "autocannibalism" by Wurtman [TINS 15 (1992) 177].

Effects of axotomy, deafferentation, and reinnervation on sympathetic ganglionic synapses: a comparative study

The main physiological and morphological features of the synapses in the superior cervical ganglia of mammals and the last two abdominal ganglia of the frog sympathetic chain are summarized. The effects of axotomy on structure and function of ganglionic synapses are then reviewed, as well as various changes in neuronal metabolism in mammals and in the frog, in which the parallel between electrophysiological and morphological data leads to the conclusion that a certain amount of synaptic transmission occurs at "simple contacts." The effects of deafferentation on synaptic transmission and ultrastructure in the mammalian ganglia are reviewed: most synapses disappear, but a number of postsynaptic thickenings remain unchanged. Moreover, intrinsic synapses persist after total deafferentation and their number is strongly increased if axotomy is added to deafferentation. In the frog ganglia, the physiological and morphological evolution of synaptic areas is comparable to that of mammals, but no intrinsic synapses are observed. The reinnervation of deafferented sympathetic ganglia by foreign nerves, motor or sensory, is reported in mammals, with different degrees of efficiency. In the frog, the reinnervation of sympathetic ganglia with somatic motor nerve fibers is obtained in only 20% of the operated animals. The possible reasons for the high specificity of ganglionic connections in the frog are discussed.

Effects of depolarizing agents on transglutaminase activity, Ca2+ influx, and protein synthesis in superior cervical and nodose ganglia excised from rats

Rapid changes in transglutaminase (TG) activity, 45Ca(2+)-influx and [3H]leucine incorporation in superior cervical ganglia (SCG), and nodose ganglia (NG) excised from adult rats were examined following addition of membrane-depolarizing agents veratridine (Ver) or high extracellular [K+]o during aerobic incubation in vitro at 37 degrees C. Addition of KCl (50 mM) stimulated TG activity to a maximal extent (four to six-fold) in SCG and NG after 30 min. Ver (0.2 mM) also increased TG activity in both ganglia after 30 min. Kinetic studies showed that the stimulation of TG activity in both ganglia caused by each depolarization condition was associated with a decrease in Km and an increase in Vmax value. The depolarizing agents Ver and high [K+]o also caused significant increases in 45Ca2+ influx into both ganglia. The Ver-induced increases in TG activity and 45Ca2+ accumulation were antagonized by tetrodotoxin (TTX, 1 microM), a sodium channel blocker. The K(+)-induced increase in TG activity was not blocked by tetraethylammonium (TEA, 20 mM), a potassium channel antagonist, although TEA did block the K(+)-induced increase in 45Ca2+ accumulation. The membrane-perturbing, sialic acid-containing compounds, GM1-ganglioside (GM1, 5 nM) and alpha-sialyl cholesterol (alpha-SC, 20 microM), were moderate inhibitors of the K(+)-induced effects on TG activity and 45Ca2+ accumulation. The sialyl compounds had little effect on Ver-induced accumulation of 45Ca2+ but enhanced the Ver-evoked stimulation in TG activity. These results suggests that the veratridine- and K(+)-induced increases in TG activity occur via modulation of Ca2+ and Na+ channel gating mechanisms that are pharmacologically distinct for each depolarizing agent. The veratridine- and K(+)-induced decrease in [3H]leucine incorporation could be a result of stimulation of TG activity as a consequence of degenerative alterations.

The effect of axotomy and denervation on calmodulin content in the superior cervical sympathetic ganglion of the rat

Calmodulin (CaM) in the superior cervical sympathetic ganglion (SCG) of the rat and its changes after transection of the pre- or postganglionic nerves were studied biochemically and immunohistochemically. The concentration of CaM in the SCG was assayed using the extent of activation of CaM-dependent adenylate cyclase from bovine neural retina. In the SCG, CaM concentration was 4.5 micrograms/mg protein, a level similar to that in another peripheral ganglion, the nodose ganglion (4.9 micrograms/mg protein). Following denervation of the SCG, the total amount of ganglionic CaM did not change significantly within a week. On the other hand, CaM content per ganglion increased gradually 3 days after axotomy. Immunohistochemical examination revealed that CaM in unoperated SCG is present both in the neuronal fibers and in the cell soma of sympathetic neurons. But the intensity of the staining with CaM-antibody in the cytoplasmic soma varied among cells. The gross profile of the CaM immunostaining seemed to be unchanged one week after either denervation or axotomy, but the immunoelectron microscopic study showed heavy staining of the innercellular membranes of irregular shape in the axotomized SCG.

Effects of extracellular choline concentration and K+ depolarization on choline kinase and choline acetyltransferase activities in superior cervical sympathetic ganglia excised from rats

The activities of choline kinase (CK) and choline acetyltransferase (ChAT) were examined in vitro in superior cervical sympathetic ganglia (SCG) excised from rats following aerobic incubation for 1 h in a medium containing various choline concentrations, with and without application of a high KCl level (70 mM). Ganglionic CK activity was strongly inhibited (by approximately 75%) at low extracellular choline concentrations (1-5 microM) but rose as the choline concentration was raised to 10-50 microM in the incubation medium, then fell and rose again with further increases in choline concentration. A similar but moderate accelerative effect on ganglionic CK activity was also observed after addition of acetylcholine (ACh; 1 mM) without eserine. Whereas specific CK activity did not change significantly in axotomized SCG, in which the ratio of glial cells to neurons is greatly increased for a week after the operation., it was remarkably increased after denervation, in which the preganglionic cholinergic nerve terminals had degenerated. When either a high KCl level or hemicholinium-3 (HC-3; 50 microM) was added to the medium in the presence or absence of choline, ganglionic CK activity was markedly inhibited. On the other hand, ChAT activity in the SCG remained at a significantly high level during incubation with low choline concentrations (1-10 microM), but the enhanced enzyme activity became inhibited as the extracellular choline concentration was raised to 50-100 microM in the medium. Addition of HC-3 to the medium did not alter ganglionic ChAT activity at low choline concentrations. However, application of quinacrine (10 microM) considerably reduced ganglionic CK activity and also suppressed ChAT activity induced by high KCl levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that phosphoinositide response is mediated by alpha 1-adrenoceptor stimulation, but not linked with excitation-contraction coupling in cardiac muscle

Phosphoinositide metabolism is known to be associated with neuronal or humoral stimulation of excitable cells. The present study examined whether the phosphoinositide response is involved in such events using isolated rat papillary muscles labeled with [3H]inositol. It was found that neither increase in the stimulation frequencies (0-2 Hz) nor prolongation of the pulse duration (10-70 msec) altered the labeling of phosphoinositides and the accumulation of [3H]inositol phosphates in this preparation. However, phenylephrine, a known alpha 1-agonist, was capable of provoking the breakdown of phosphoinositides associated with a positive inotropic effect in this preparation. We report the evidence that phosphoinositide response is mediated by alpha 1-adrenoceptor stimulation, but not linked with excitation-contraction coupling in cardiac muscle.

Accumulation of inositol phosphates in sympathetic ganglia. Effects of depolarization and of amine and peptide neurotransmitters

Depolarization of isolated [3H]inositol-labelled rat superior cervical sympathetic ganglia in a high-K+ medium stimulates an accumulation of labelled inositol phosphates. This accumulation occurs only when ganglia are incubated in a Ca2+-containing medium, suggesting that it represents a receptor-stimulated hydrolysis of inositol lipid(s) activated by an endogenously released neurotransmitter. A minor fraction of this accumulation appears to be activated by intraganglionically released acetylcholine, since it is slightly reduced by atropine. The accumulation of inositol phosphates is unaffected by blockade of appropriate catecholamine, histamine and 5-hydroxytryptamine receptors and also by aspirin and indomethacin. This response to depolarization is potentiated by incubation with proteinase inhibitors, suggesting that it might be caused by an endogenously released peptide neutrotransmitter. However, it is not prevented by a V1-vasopressin receptor antagonist, and none of the peptides tested so far fully reproduces the response: these include a stable substance P analogue, physalaemin, neurokinin alpha, bradykinin, angiotensin, pancreozymin, bombesin and luteinizing-hormone-releasing hormone. Stimulated inositol lipid breakdown in depolarized sympathetic ganglia seems likely to be activated by an as-yet-unidentified peptide neurotransmitter: this might serve as an intraganglionic mediator of postsynaptic excitation by employing the same signalling mechanism as muscarinic cholinergic and V1-vasopressin receptors.

Rapid accumulation of inositol phosphates in isolated rat superior cervical sympathetic ganglia exposed to V1-vasopressin and muscarinic cholinergic stimuli

An accumulation of 3H-labelled inositol phosphates is observed when prelabelled rat superior cervical sympathetic ganglia are exposed to [8-arginine]vasopressin or to muscarinic cholinergic stimuli. The response to vasopressin is much greater than the response to cholinergic stimuli. The response to vasopressin is blocked by a V1-vasopressin antagonist, and oxytocin is a much less potent agonist than vasopressin. Vasopressin causes no increase in the cyclic AMP content of ganglia. These ganglia therefore appear to have functional V1-vasopressin receptors that are capable of activating inositol lipid breakdown, but no V2-receptors coupled to adenylate cyclase. The first [3H]inositol-labelled products to accumulate in stimulated ganglia are inositol trisphosphate and inositol bisphosphate, suggesting that the initiating reaction in stimulated inositol lipid metabolism is a phosphodiesterase-catalysed hydrolysis of phosphatidylinositol 4,5-bisphosphate (and possibly also phosphatidylinositol 4-phosphate). This response to exogenous vasopressin occurs in ganglia incubated in media of reduced Ca2+ concentration. The physiological functions of the V1-vasopressin receptors of these ganglia remain unknown.

Effect of axotomy on the cyclic GMP increase induced by preganglionic stimulation and high extracellular K+ concentration in superior cervical sympathetic ganglion of the rat

Cyclic GMP generation, induced by preganglionic nerve stimulation or by high extracellular potassium ion concentration (70 mM) in the medium, was studied during aerobic incubation of the excised superior cervical sympathetic ganglion of the rat with and without axotomy, and the results were compared with that of preganglionic denervation. Both axotomy and denervation of the ganglion for a week caused complete loss of increase of cyclic GMP content in the ganglion in response to the preganglionic nerve stimulation. However, the increase of the ganglionic cyclic GMP content evoked by raising the extracellular potassium ion concentration was maintained at a level about two-thirds of the control after axotomy for 1-4 days, while it was abolished within a day after denervation. Ganglionic choline acetyltransferase activity was maintained for several days after axotomy, but it was decreased rapidly by denervation. Acetylcholinesterase, dopamine-beta-hydroxylase and muscarinic cholinergic receptor sites had been lost almost completely a week after axotomy. These results suggest that the increase of ganglionic cyclic GMP content caused by depolarization with high extracellular K+ is associated with the preganglionic nerve terminals rather than with postganglionic receptor.

Synthesis of acetylcholine from acetate in a sympathetic ganglion

The present experiments tested whether acetate plays a role in the provision of acetyl-CoA for acetylcholine synthesis in the cat's superior cervical ganglion. Labeled acetylcholine was identified in extracts of ganglia that had been perfused for 20 min with Krebs solution containing choline (10(-5) M) and [3H], [1-14C], or [2-14C]acetate (10(-3) M); perfusion for 60 min or with [3H]acetate (10(-2) M) increased the labeling. The acetylcholine synthesized from acetate was available for release by a Ca2+-dependent mechanism during subsequent periods of preganglionic nerve stimulation. When ganglia were stimulated via their preganglionic nerves or by exposure to 46 mM K+, the labeling of acetylcholine from [3H]acetate was reduced when compared with resting ganglia. The reduced synthesis of acetylcholine from acetate during stimulation was not due to acetate recapture, shunting of acetate into lipid synthesis, or the transmitter release process itself. In ganglia perfused with [2-14C]glucose, the amount of labeled acetylcholine formed was clearly enhanced during stimulation. An increase in acetylcholine labeling from [3H]acetate was shown during a 15-min resting period following a 60-min period of preganglionic nerve stimulation (20 Hz). It is concluded that acetate is not the main physiological acetyl precursor for acetylcholine synthesis in this sympathetic ganglion, and that during preganglionic nerve stimulation there is enhanced delivery of acetyl-CoA to choline acetyltransferase from a source other than acetate.

Glucose utilization in sympathetic ganglia of male Fischer-344 rats at different ages

The relation of glucose utilization to age was studied with the [14C]2-deoxy-D-glucose method in 3 peripheral sympathetic ganglia of conscious male Fischer-344 rats. The hypogastric ganglion, coeliac-mesenteric ganglion complex and superior cervical ganglion were examined in 3-, 12-, 24- and 30-33-month-old animals. Glucose utilization increased significantly between 12 and 30-33 months in the superior cervical ganglion and between 3 and 24 months in the coeliac-mesenteric ganglion complex. No significant, age-related changes were observed in the hypogastric ganglion. In addition, neuron density decreased significantly between 3 and 12 months in the hypogastric ganglion and between 3 and 30-33 months in the coeliac-mesenteric ganglion complex, but no changes were observed in the superior cervical ganglion. Despite the increased glucose utilization in the superior cervical ganglion, heart rate decreased between 12 and 24 months, and mean arterial blood pressure decreased between 24 and 30-33 months. The results suggest that functional activity of some sympathetic ganglia increases in older rats, although end organ effects may be reduced.

The stimulation of inositol lipid metabolism that accompanies calcium mobilization in stimulated cells: defined characteristics and unanswered questions

It now appears to be generally agreed that the 'phosphatidylinositol response', discovered in 1953 by Hokin & Hokin, occurs universally when cells are stimulated by ligands that cause an elevation of the ionized calcium concentration of the cytosol. The initiating reaction is almost certainly hydrolysis of an inositol lipid by a phosphodiesterase. Phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate all break down rapidly under such circumstances. However, we do not yet know which of these individual reactions is most closely coupled to receptor stimulation, nor do we know where in the cell it occurs. With many stimuli, inositol phospholipid breakdown is closely coupled to occupation of receptors and appears not to be a response to changes in cytosol [Ca2+]: this provoked the suggestion that it may be a reaction essential to the coupling between activation of receptors and the mobilization of Ca2+ within the cell. In a few situations, however, it appears probable that inositol lipid breakdown can occur as a result of the rise in cytosol [Ca2+] that follows receptor activation: such observations gave rise to the alternative opinion that inositol lipid breakdown cannot be related to stimulus-response coupling at calcium-mobilizing receptors. It now seems likely that these two views are too rigidly polarized and that some cells probably display both receptor-linked and Ca2+-controlled breakdown of inositol lipids. Both may sometimes occur simultaneously or sequentially in the same cell.

Studies on neurotransmitter-stimulated phospholipid metabolism with cerebral tissue suspensions: a possible biochemical correlate of synaptogenesis in normal and undernourished rats

The phenomenon of neurotransmitter-stimulated incorporation of 32Pi into phosphatidic acid and inositol phosphatides (neurotransmitter effect) in developing brain was studied in vitro as a possible measure of synaptogenesis. While the neurotransmitter effect was not observed with brain homogenates, highly consistent and significant effects were noted with brain tissue suspensions obtained by passing the tissue through nylon bolting cloth. The magnitude of the effect decreased with the increase in mesh number. Maximum stimulations obtained with the 33 mesh adult brain cortex preparations (mean +/- S.E.M. of 6 experiments) were 203 +/- 8%, 316 +/- 17% and 150 +/- 8% with 10(-3) M acetylcholine (ACh) + 10(-3) M eserine; 10(-2) M norepinephrine (NE) and 10(-2) M serotonin (5-HT), respectively. Experiments with developing rat brain at 7, 14 and 21 days of age showed that the neurotransmitter effects due to ACh, NE and 5-HT increase progressively in different regions of the brain but that there are marked regional differences. It is suggested that the neurotransmitter effect is a valid biochemical correlate of synaptogenesis. In rats undernourished from birth to 21 days of age, by increasing the litter size, the neurotransmitter effect with ACh, NE or 5-HT was not altered in the cortex but was significantly reduced in the brain stem. In cerebellum the effects due to ACh and NE were significantly altered, while that with 5-HT was unaffected. It is concluded that cholinergic, adrenergic and serotonergic synapses are relatively unaffected in the cortex but are significantly affected in the brain stem by undernutrition. In the cerebellum of undernourished rats the adrenergic and cholinergic, but not serotonergic systems, are altered.

Investigation of the relationship between cell-surface calcium-ion gating and phosphatidylinositol turnover by comparison of the effects of elevated extracellular potassium ion concentration on ileium smooth muscle and pancreas

Incubation of fragments of guinea-pig ileum smooth muscle in the presence of an elevated extracellular K+ concentration, which causes an increase in cell-surface Ca2+ permeability and thus leads to contraction, caused a marked increase in phosphatidylinositol turnover, as assessed by incorporation of 32Pi. This response was not diminished by atropine or propylbenzilycholine mustard, two muscarinic cholinergic antagonists, and was therefore not caused by the release of endogenous acetylcholine within the tissue. In contrast, exposure of guinea-pig pancreas fragments to high extracellular [K+], which does not increase cell-surface Ca2+ permeability or evoke secretion, did not cause an increase in phosphatidylinositol turnover, even though such an increase was triggered by carbamoylcholine, which is a secretagogue. These observations are consistent with a suggested function for phosphatidylinositol breakdown in the mechanisms of cell-surface Ca2+ gates.