Isolation of choline esters from aqueous solutions by extraction with sodium tetraphenylboron in organic solvents

Acetylcholine synthesis, muscarinic receptor subtypes, neuropeptides and secretion of ferret salivary glands with special reference to the zygomatic gland

Studies on salivary secretion are usually focused on parotid and submandibular glands. However, the film of mucin, that protects the oral structures and is responsible for the feeling of oral comfort, is produced by the submucosal glands. The submucosal zygomatic and molar glands are particularly large in carnivores such as the ferret. Comparisons between the mucous sublingual, zygomatic and molar glands, serous parotid and sero-mucous submandibular glands showed the acetylcholine synthesis, in terms of concentration, to be three to four times higher in the mucous glands than in the parotid and submandibular glands. Bromoacetylcholine inhibited 95-99% of the synthesis of acetylcholine in the incubates of the five types of glands, showing the acetylcholine synthesis to depend on the activity of choline acetyltransferase. The high acetylcholine synthesis in the zygomatic gland was of nervous origin, since cutting the buccal nerve, aiming at parasympathetic denervation, and allowing time for nerve degeneration, reduced the acetylcholine synthesising capacity of the gland by 95%. A similar reduction (96%) in the parotid gland followed upon the avulsion of the parasympathetic auriculo-temporal nerve. Zygomatic saliva was very viscous. The salivary flow rate in response to electrical stimulation (20 Hz) of the buccal nerve (zygomatic gland), expressed per gland weight, was one-third of that to stimulation of the auriculo-temporal nerve (parotid gland) or the chorda-lingual nerve (submandibular gland). As previously shown for the parotid and submandibular gland, a certain fraction (25%) of the parasympathetic secretory response of the zygomatic gland depended on non-adrenergic, non-cholinergic transmission mechanisms, probably involving substance P and vasoactive intestinal peptide and possibly calcitonin gene-related peptide. Particularly, high concentrations of vasoactive intestinal peptide were found in the sublingual and molar glands, and of substance P in the submandibular, zygomatic and molar glands; notably, the concentration of calcitonin gene-related peptide of the sublingual gland was not detectable. All five muscarinic receptor subtypes were detected in the five glands. The receptor protein profile, as judged by immunoblotting and semi-quantitative estimations, was about the same in the glands: high level of M3, low level of M2 and levels roughly in the same range of M1, M4 and M5. Compared to the parotid and submandibular glands, the M5 receptor level was particularly low in the mucin-secreting glands. The present study points out both similarities and dissimilarities between the five types of glands investigated. The zygomatic gland, in particular, appears to be a suitable model for future studies aiming at causing relief of dry mouth by local pharmacological treatment.

The otic ganglion in rats and its parotid connection: cholinergic pathways, reflex secretion and a secretory role for the facial nerve

Otic ganglionectomy in rats was found to have affected the parotid gland more profoundly than section of the auriculotemporal nerve as assessed by reduction in gland weight (by 33 versus 20%) and total acetylcholine synthesizing capacity (by 88 versus 76%) 1 week postoperatively and, when assessed on the day of surgery under adrenoceptor blockade, by reflex secretion (by 99 versus 88%). The facial nerve contributed to the acetylcholine synthesizing capacity of the gland. Section of the nerve only, at the level of the stylomastoid foramen, reduced the acetylcholine synthesis by 15% and, combined with otic ganglionectomy, by 98% or, combined with section of the auriculotemporal nerve, by 82%. The facial nerve was secretory to the gland, and the response was of a cholinergic nature. The nerve conveyed reflex secretion of saliva and caused secretion of saliva upon stimulation. Most of the facial secretory nerve fibres originated from the otic ganglion, since after otic ganglionectomy (and allowing for nerve degeneration) the secretory response to facial nerve stimulation was markedly reduced (from 23 to 4 microl (5 min)(-1)). The persisting secretory response after otic ganglionectomy, exaggerated due to sensitization, and the residual acetylcholine synthesizing capacity (mainly depending on the facial nerve) showed that a minor proportion of pre- and postganglionic nerve fibres relay outside the otic ganglion. The great auricular nerve, which like the facial nerve penetrates the gland, caused no secretion of saliva upon stimulation. Avulsion of the auriculotemporal nerve was more effective than otic ganglionectomy in reducing the acetylcholine synthesizing capacity (by 94 versus 88%) and as effective as otic ganglionectomy in abolishing reflex secretion (by 99%). When aiming at parasympathetic denervation, avulsion may be the preferable choice, since it is technically easier to perform than otic ganglionectomy.

Pre-junctional effects of oximes on [3H]-acetylcholine release in rat hippocampal slices during soman intoxication

In this study, the non-reactivating effects of oximes in the hippocampus of the rat are investigated. The potassium (51 mM) evoked release of [(3)H]-acetylcholine and the liberation of [(3)H]-choline were determined in hippocampal slices following in vitro exposure to soman and five oximes (toxogonin, HI-6, HLö-7, P2S and 2-PAM) in separate experiments by superfusion. In the absence of soman, toxogonin and HLö-7 in particular induced a concentration dependent significant increase in the evoked release of [(3)H]-acetylcholine. There was also a significant effect of HI-6, but the effect was much smaller. Two pralidoxime salts, P2S (methanesulfonate salt) and 2-PAM (methiodide salt), had similar but lower effects that were only observed at relatively high concentrations. Experiments performed following complete inhibition of the acetylcholinesterase activity by soman (1.0 microM) showed that HI-6 and HLö-7 induced a significant decrease in the potassium-evoked release of [(3)H]-acetylcholine, while the liberation of [(3)H]-choline increased. Toxogonin, P2S and 2-PAM did not reduce significantly the evoked release of [(3)H]-acetylcholine. Only limited reactivation of the acetylcholinesterase activity was observed in superfusion experiments with toxogonin, HI-6, P2S and 2-PAM following exposure of hippocampal slices to soman. However, HLö-7 was proved to be relatively more effective in reactivating the acetylcholinesterase activity at high concentrations (50 and 200 microM). The acetylcholinesterase activity was reactivated to approximately 12% and 40% of control, respectively. It is concluded that HI-6 and HLö-7 have important non-acetylcholinesterase reactivating properties following soman poisoning, as may be seen by the significant reduction in the evoked release of [(3)H]-acetylcholine effected by these oximes. HLö-7 is of particular interest in view of its ability to additionally improve reactivation of the acetylcholinesterase activity.

Exploring the regulation of the expression of ChAT and VAChT genes in NG108-15 cells: implication of PKA and PI3K signaling pathways

Involvement of different protein kinases regulated by cAMP and implication of muscarinic receptors in the regulation of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) mRNA levels and ChAT activity has been studied in NG108-15 cells. Dibutyryl cAMP enhanced both ChAT and VAChT mRNA levels and stimulated ChAT activity. Muscarinic stimulation or inhibition did not change ChAT activity or the receptor subtype mRNA pattern. MEK1/2 did not affect the regulation of ChAT and VAChT mRNA levels. However, PKA plays a major role in regulating ChAT and VAChT mRNA levels, because H89 decreased both. Strikingly, inhibition of PI3K by LY294002 had two opposite effects: ChAT mRNA level was decreased and VAChT mRNA level was increased. Such a result consolidates the observation that ChAT and VAChT genes, despite their unusual organization in a single "cholinergic locus," can be differentially or synergistically regulated, depending on the activated signaling pathways.

More than one way to toy with ChAT and VAChT

Expression of choline acetyltransferase (ChAT) and of the vesicular acetylcholine transporter (VAChT) is required for the acquisition and the maintenance of the cholinergic phenotype. The ChAT and VAChT genes have been demonstrated to share a common gene locus and this suggests a coordinate regulation of their expression. In the present work, we examined the effects of several differentiating treatments on the modulation of ChAT and VAChT expression at the mRNA and protein levels in growing and differentiating NG108-15 cells. In cells grown in the presence of serum, all the agents tested-retinoic acid, dexamethasone and dibutyrylcyclicAMP (dbcAMP)-induced an increase of ChAT and VAChT mRNA levels but with different efficacy. Treatment with dbcAMP plus dexamethasone resulted in the largest increase of VAChT mRNA amount while retinoic acid mostly enhanced ChAT mRNA level. However, while ChAT activity was increased by all agents, no change in the VAChT protein level was detected. In cells differentiated by serum deprivation, only retinoic acid was effective in inducing an increase of VAChT and ChAT mRNA and ChAT activity, while we observed a downregulation by dbcAMP and dexamethasone. Treatment with the antimitotic agent cytosine arabinoside led to an increase of ChAT activity which was further largely enhanced by the addition of dbcAMP plus dexamethasone, but to only a slight change in VAChT activity. We further showed that complex glycosylation processes which might play a role in targeting and/or stability of the membrane protein VAChT are deficient in these cells. Indeed, in transient transfection assays with the reporter soluble enzyme luciferase placed under regulatory and promoter regions of the VAChT gene, we observed a modulation of luciferase expression by differentiating agents. These data illustrate the complexity of the processes which participate to the expression of the ChAT and VAChT genes, both at the transcriptional and posttranslational levels.

Stimuli that induce a cholinergic neuronal phenotype of NG108-15 cells upregulate ChAT and VAChT mRNAs but fail to increase VAChT protein

The vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) are encoded by genes organized in a single gene locus, and coregulation of the transcription of the two genes has been repeatedly reported in cholinergic tissues. In the present study, different stimuli were used to induce the differentiation of the hybridoma cells NG108-15 and we examined their effects on the modulation of VAChT and ChAT expression at the mRNA and protein levels. All agents upregulated the VAChT and ChAT mRNA levels, but to a different extent. ChAT activity was increased by retinoic acid, dexamethasone, and dibutyrylcyclic AMP (dbcAMP), and a synergistic effect was observed with a combined dexamethasone and dbcAMP treatment. Nonetheless, no changes in the VAChT protein level could be observed, as judged from ligand binding studies as well as from immunochemical detection. Hemicholinium-3-sensitive choline uptake, hemicholinium-3 binding, and acetylcholine content were increased by differentiating agents, with a rank order of potency comparable to their effects on ChAT activity. Prominent changes were observed in the expression of vesicular protein markers, particularly with the associated treatment dexamethasone and dbcAMP. Thus, it appears that although the different stimuli we have been using are able to stimulate neuronal features and activate the transcription of cholinergic genes, they did not contrive to increase the level of VAChT protein in these cells.

Nicotinic agonists stimulate acetylcholine release from mouse interpeduncular nucleus: a function mediated by a different nAChR than dopamine release from striatum

Acetylcholine release stimulated by nicotinic agonists was measured as radioactivity released from perfused synaptosomes prepared from mouse interpeduncular nucleus (IPN) that had been loaded with [(3)H]choline. Agonist-stimulated release was dependent upon external calcium and over 90% of released radioactivity was acetylcholine. The release process was characterized by dose response curves for 13 agonists and inhibition curves for six antagonists. alpha-Conotoxin MII did not inhibit this release, while alpha-conotoxin AuIB inhibited 50% of agonist-stimulated release. Comparison of this process with [(3)H]dopamine release from mouse striatal synaptosomes indicated that different forms of nicotinic acetylcholine receptors (nAChRs) may mediate these processes. This was confirmed by assays using mice homozygous for the beta 2 subunit null mutation. The deletion of the beta 2 subunit had no effect on agonist-stimulated acetylcholine release, but abolished agonist-stimulated release of dopamine from striatal synaptosomes. Mice heterozygous for the beta 2 subunit null mutation showed decreased dopamine release evoked by L-nicotine with no apparent change in EC(50) value, as well as similar decreases in both transient and persistent phases of release with no changes in desensitization rates.

Cholinergic innervation and function in the mammalian pineal gland

Besides the noradrenergic sympathetic system originating from the superior cervical ganglion, a cholinergic innervation of the mammalian pineal gland has been studied over the past three decades. In 1961, it was shown that lesion of the parasympathetic greater superficial petrosal nerve of the monkey resulted in degeneration of nerve fibers in the pineal gland. This was supported by ultrastructural studies of nerve terminals within the pineal gland, demonstrating the presence of cholinergic terminals containing small clear transmitter vesicles. Biochemical studies further showed the presence of the enzyme acetylcholinesterase in several mammalian species. During the last decade, several advanced and more elaborate technologies have been developed, allowing pinealogists to establish the presence of cholinergic fibers and their receptors. Thus, choline acetyltransferase was shown in bovine pineal by immunohistochemistry. Muscarinic and nicotinic receptors were identified, characterized, and localized. Gene expression of receptors was visualized, and the receptor-mediated effector systems and functions were elucidated. Taken together, the present data suggest the presence of a cholinergic innervation of the mammalian pineal gland originating in peripheral parasympathetic ganglia. However, some of the neuronal projections to the pineal gland with origin in the brain (the central innervation) might also be cholinergic. The cholinergic nerve fibers enter the gland, where they are located both in the perivascular spaces and between the pinealocytes. Some of the terminals make synapses on pinealocytes or intrapineal neurons. The released acetylcholine from the terminals interacts with the receptors, then alters the cascade of receptor-mediated events, which results in decreased N-acetyltransferase enzyme activity, thus leading to decreased melatonin synthesis. This counterbalance mechanism between the sympathetic noradrenergic and the cholinergic systems maintains the homeostasis of pineal functions.

The effects of brucine and alcuronium on the inhibition of [3H]acetylcholine release from rat striatum by muscarinic receptor agonists

1. Radioligand binding experiments indicate that the affinity of muscarinic receptors for their agonists may be enhanced by allosteric modulators. We have now investigated if brucine can enhance the inhibitory effects of muscarinic receptor agonists on the electrically evoked release of [3H]acetylcholine ([3H]ACh) from superfused slices of rat striatum. 2. The evoked release of [3H]ACh was inhibited by all agonists tested (i.e., furmethide, oxotremorine-M, bethanechol and oxotremorine). 3. Brucine enhanced the inhibitory effects of furmethide, oxotremorine-M and bethanechol on the evoked [3H]ACh release without altering the inhibitory effect of oxotremorine. 4. Alcuronium was applied for comparison and found to diminish the inhibitory effect of furmethide on the evoked [3H]ACh release. 5. The results demonstrate that it is possible both to enhance and diminish the functional effects of muscarinic receptor agonists by allosteric modulators. 6. The direction of the observed effects of brucine and alcuronium on [3H]ACh release fully agrees with the effects of these modulators on the affinities of human M4 receptors for furmethide, oxotremorine-M, bethanechol and oxotremorine, as described by Jakubik et al. (1997). This supports the view that the presynaptic muscarinic receptors responsible for the autoinhibition of ACh release in rat striatum belong to the M4 muscarinic receptor subtype.

Nitric oxide and peroxynitrite affect differently acetylcholine release, choline acetyltransferase activity, synthesis, and compartmentation of newly formed acetylcholine in Torpedo marmorata synaptosomes

Recent reports proposed that nitric oxide was a modulator of cholinergic transmission. Here, we examined the role of NO on cholinergic metabolism in a model of the peripheral cholinergic nervous synapse: synaptosomes from Torpedo electric organ. The presence of NO synthase was immunodetected in the cell bodies, in the nerve ending area of nerve-electroplate tissue and in the electroplates. Exogenous source of NO was provided from SIN1, a donor of NO and O2-., and an end-derivative peroxynitrite (ONOO-). SIN1 increased calcium-dependent acetylcholine (ACh) release induced by KCl depolarization or a calcium ionophore A23187. The formation of ONOO- was continuously followed by a new chemiluminescent assay. The addition of superoxide dismutase, that decreases the formation of ONOO-, did not impair the stimulation of ACh release, suggesting that NO itself was the main stimulating agent. When the endogenous source of NO was blocked by proadifen, an inhibitor of cytochrome P450 activity of NO synthase, both KCl- and A23187-induced ACh release were abolished; nevertheless, the inhibitor Ng-monomethyl-L-arginine did not modify ACh release when applied in a short time duration of action. Both NO synthase inhibitors reduced the synthesis of ACh from the radioactive precursor acetate and its incorporation into synaptic vesicles as did ONOO- chemically synthesized or formed from SIN1. In addition, choline acetyltransferase activity was strongly inhibited by ONOO- and SIN1 but not by the NO donors SNAP and SNP or, by NO synthase inhibitors. Altogether these results indicate that NO and ONOO modulate presynaptic cholinergic metabolism in the micromolar range, NO (up to 100 microM) being a stimulating agent of ACh release and ONOO- being an inhibitor of ACh synthesis and choline acetyltransferase activity.

Evidence for direct and indirect mechanisms in the potent modulatory action of interleukin-2 on the release of acetylcholine in rat hippocampal slices

1. The biphasic nature of the potent modulatory action of interleukin-2 (IL-2) on hippocampal acetylcholine (ACh) release was investigated by use of brain slice superfusion. 2. Both the potentiating (10(-13) M) and inhibitory (10(-9) M) effects of IL-2 on hippocampal ACh release were stimulation-dependent and were blocked by a neutralizing IL-2 receptor antibody, suggesting the activation of typical IL-2 receptors in both cases. 3. Tetrodotoxin (TTX: 10 microM) failed to block the potentiation of ACh release induced by a very low concentration of IL-2 (10(-13) M) suggesting a direct effect on cholinergic nerve terminals. 4. In contrast, the inhibitory effect seen at a higher concentration (10(-9) M) was TTX-sensitive, and hence indicative of an indirect action. 5. To establish the nature of this intermediate mediator, blockers of nitric oxide synthesis, and of opioid and gamma-aminobutyric acid (GABA) receptors were used. Only GABAA and GABAB receptor antagonists altered the inhibitory action of IL-2, suggesting the participation of GABA as mediator. 6. Taken together, these results provide further evidence for the potent role of IL-2 in the modulation of cholinergic function in the rat hippocampus.

Effects of tri-, di- and monobutyltin on synaptic parameters of the cholinergic system in the cerebral cortex of mice

Triorganotin compounds like tributyltin have been reported to be biodegraded to diorganotin, monoorganotin and then inorganic tin in animals after they have been ingested. Effects of tributyltin, dibutyltin and monobutyltin on various cholinergic parameters that are involved in synaptic transmission in the mouse cerebral cortex were investigated in vitro. Tributyltin and dibutyltin, but not monobutyltin, inhibited the activity of choline acetyltransferase, both the high-affinity and low-affinity uptakes of choline into synaptosomes, and the binding of [3H]quinuclidinyl benzilate to muscarinic acetylcholine receptors. Tributyltin and dibutyltin, but not monobutyltin, had a slightly suppressive effect on the K(+)-induced release and synthesis of acetylcholine in slices of the cortex. All three butyltins at concentrations from 10(-6) to 10(-4) M had no effect on the activity of acetylcholinesterase. The extent of the inhibitory effects on the cholinergic parameters, apart from the activity of acetylcholinesterase, was slightly greater in the case of tributyltin than dibutyltin, in particularly at the highest concentration (10(-4) M) tested. Therefore, it is concluded that tributyltin metabolites inhibit various parameters of cholinergic activity with a potency ranking of tributyltin > dibutyltin > monobutyltin.

The effect of trimethyltin on acetylcholine release in the guinea-pig trachea

The purpose of the present work was to characterise the effects of trimethyltin on the release of acetylcholine from parasympathetic nerves and its effect on the postjunctional cholinergic stimulation of a smooth muscle. The guinea-pig trachea has been used as a model. Prejunctionally, trimethyltin (3.0 × 10(-3) M) significantly enhanced in a reversible manner the high K(+) (75 mM) evoked release of endogenous acetylcholine and [(3)H]acetylcholine. The evoked release of endogenous acetylcholine and [(3)H]acetylcholine was released from a pool of acetylcholine being independent of extraneuronal Ca(2+) in the presence, but not in the absence of trimethyltin. The effect of trimethyltin on the release was not inhibited by low Ca(2+) (0 mM and 1.0 × 10(-4) M) or by Ca(2+) channel blockers (verapamil, 1.0 × 10(-4) M, flunarizine, 1.0 × 10(-4) M, ω-conotoxin GVIA, 2.0 × 10(-7) M and ω-agatoxin, 2.0 × 10(-7) M). The present results also demonstrate that trimethyltin induce emptying of a non-vesicular, probably a cytoplasmic storage pool of acetylcholine, since AH5183 (2.0 × 10(-5) M), an inhibitor of the translocation of acetylcholine into synaptic vesicles, and α-latrotoxin (1.0 × 10(-8) M), a toxin from black widow spider venom inducing vesicle depletion, had no inhibitory effects on the release of [(3)H]acetylcholine evoked by trimethyltin (3.0 × 10(-3) M). The release of [(3)H]acetylcholine was moreover enhanced by trimethyltin when the vesicular uptake of [(3)H]acetylcholine was inhibited by AH5183, probably as a result of a higher cytoplasmic concentration of [(3)H]acetylcholine. Trimethyltin also reduced the neuronal uptake of [(3)H]choline and this was probably due to a depolarising effect of trimethyltin on the cholinergic nerve terminals. A similar depolarisation induced by trimethyltin was observed during patch clamping of GH(4) C(1) neuronal cells. Postjunctionally, trimethyltin had no effect by itself or on the carbachol-induced smooth muscle contraction, indicating that trimethyltin did not have a general depolarising effect on smooth muscle cells or an effect on muscarinic receptors. Furthermore, the reduced electrical field-induced contraction and the subsequent increase in the basal smooth muscle tension that was observed by addition of trimethyltin was activity-dependent, and was most probably due to emptying of a nervous non-vesicular storage pool of acetylcholine, followed by rapid hydrolysis of acetylcholine by acetyl- and pseudocholinesterases.

Biphasic changes in the density of muscarinic and beta-adrenergic receptors in cardiac atria of rats treated with diisopropylfluorophosphate

Chronic treatment with organophosphate inhibitors of cholinesterases is known to bring about down-regulation of muscarinic acetylcholine receptors in the heart while its effect on the functionally antagonistic beta-adrenergic receptors is not known. We describe experiments in which rats were exposed to daily injections of diisopropylflurophosphate (DFP) and the density of muscarinic and beta-adrenergic binding sites in their cardiac atria was measured according to the binding of (3H)quinuclidinyl benzilate ((3H)QNB) and (-)-4-(3-tert-butylamino-2-hydroxy)-propoxy-(5,7-3H) benzimidazol-2-one ((3H)CGP 12177) as subtype non-specific muscarinic and beta-adrenergic ligands, respectively. Biphasic course of changes was discovered with both ligands. With the dosage scheme applied, the density of beta-adrenoceptors was augmented 24 h after the first dose of DFP and decreased to about one half of control values after 5 days of treatment with DFP. The density of muscarinic receptors was augmented after two days of treatment with DFP and decreased to about one half of control values after 5 days of treatment. Comparatively small changes in the heart rate were observed during the treatment, they reflected changes in the muscarinic and beta-adrenergic receptor density. The finding of DFP-induced changes in the binding of (3H)CGP 12177 suggests that the mechanisms responsible for the control of the density of muscarinic and beta-adrenergic receptors in the heart cells are interconnected but potential roles of other factors involved in in vivo experiments deserve further analysis. The transient increase in the density of muscarinic receptors after two days of DFP treatment appears related to published data on transient stimulation by cholinergic agonists of the transcription of mRNAs for muscarinic receptors.

Inhibition of potassium-stimulated acetylcholine release from rat brain cortical slices by two high-affinity analogs of vesamicol

In this work, we investigated the effects of two structural analogs of the drug vesamicol, which inhibits the vesicular acetylcholine (ACh) transport, on the potassium-stimulated release of ACh from rat brain cortical slices. These vesamicol analogs, 4-aminobenzovesamicol (ABV) and (trans)-cyclohexovesamicol (transDec), were almost as potent as vesamicol in inhibiting the evoked release of ACh from cortex slices. Similar to vesamicol, the presence of these analogues inhibited the ability of ACh newly-synthesized from [3H]choline to become releasable. However, vesamicol's action was reversible, while ABV and transDec caused a persistent block of this [3H]ACh release. In addition, vesamicol did not affect the release of pre-stored [3H]ACh, but ABV and transDec partially inhibited the release of [3H]ACh in this condition, suggesting that the two latter drugs may alter some of the steps posterior to the entry of [3H]ACh into synaptic vesicles. The rank order of potency for these drugs to reduce ACh release (vesamicol = transDec > ABV) is close to the rank order for inhibition of ACh vesicular transport (transDec > vesamicol > ABV), but is completely different from the order of affinities of these drugs for the vesamicol receptor (ABV > transDec > > vesamicol). These results suggest that although these two vesamicol analogs are able to block ACh release due to their effects on the vesicular transport system, they may have other unexpected actions not shared by vesamicol.

AF64A-induced cytotoxicity and changes in choline acetyltransferase activity in the LA-N-2 neuroblastoma cell line are modulated by choline and hemicholinium-3

The cholinergic neurotoxin AF64A (ethylcholine aziridinium) has been used to selectively destroy the cholinergic system. Due to its structural similarity to choline, this compound may be selectively taken up by the cholinergic terminal via the high-affinity choline transport (HAChT) system to produce persistent and selective cholinergic deficits. The mechanism by which it exerts its cholinotoxicity remains to be elucidated. We have examined the effects of AF64A in the human neuroblastoma cell line, LA-N-2, which has an intact sodium-coupled choline uptake system, and is capable of synthesizing acetylcholine (ACh). AF64A (25, 50 and 100 microM) produced dose-dependent increases in cell kill as measured by colony formation assay. The addition of increasing concentrations (10(-5), 10(-4) and 10(-3) M) of choline and hemicholinium-3 (HC-3) protected the cells from the cytotoxic effects of AF64A. At the same doses, AF64A also decreased choline acetyltransferase (ChAT) activity. In the presence of the highest concentration of choline or HC-3 (10(-3) M) which produced complete protection against AF64A's cytotoxicity in the colony formation assay, ChAT activity was restored to control values. These results demonstrate that agents that utilize (i.e., choline) or inhibit (i.e., HC-3) the choline uptake system prevented AF64A-induced cytotoxicity and decreases in ChAT activity, in a manner similar to that which has been observed in chick and rat primary cholinergic cultures in vitro. The LA-N-2 neuroblastoma cell line thus serves well as an in vitro model of the cholinergic neuron and provides a useful system to study the mode of cholinotoxicity induced by AF64A.

Membrane-bound choline-O-acetyltransferase in rat hippocampal tissue is associated with synaptic vesicles

Some of the choline-O-acetyltransferase (EC 2.3.1.6; ChAT) in rat hippocampal nerve terminals is non-ionically associated with membranes. The intent of the present report was to ascertain whether any of this membrane-bound ChAT might be associated with synaptic vesicles. To test this possibility, synaptosomal (P2) fractions were hypo-osmotically shocked in water, salt washed to remove ionically-bound ChAT, subjected to sucrose density gradient centrifugation, and the activity of ChAT compared with the amount of occluded ACh in the various subcellular fractions. A peak of ChAT and occluded ACh occurred in that fraction of the gradient (0.4 M sucrose) acknowledged to be enriched in synaptic vesicles. In other experiments, Immunobeads coated with an antibody directed against the synaptic vesicle specific SV2 protein immunoprecipitated both ChAT and occluded ACh from the 0.4 M sucrose fraction, but no other fraction. Immunobeads coated with an anti-ChAT antiserum immunoprecipitated synaptophysin from the 0.4 M sucrose fraction, an effect which was blocked by pretreatment of the anti-ChAT Immunobeads with purified ChAT. These results suggest that some of the membrane-bound ChAT in rat hippocampal nerve terminals is associated with cholinergic synaptic vesicles.

Regulation of expression of cholinergic neuronal phenotypic markers in neuroblastoma LA-N-2

Cholinergic neurons in PNS and CNS are identified by the presence of choline acetyltransferase and the accumulation of choline by a high-affinity, sodium-coupled choline transporter to be used for acetylcholine synthesis. It appears that expression of choline acetyltransferase can be altered by several physiological conditions, including hormones and trophic factors, but little is known about control of expression of the sodium-coupled choline carrier or whether these two phenotypic markers are regulated similarly. In the present study, the cholinergic human neuroblastoma LA-N-2 was used to investigate regulation of expression of choline acetyltransferase and choline uptake activity associated with differentiation and neurite extension. Cells grown in serum-containing basal medium maintained a relatively undifferentiated morphology, expressed low levels of choline acetyltransferase activity, and accumulated choline by a sodium-dependent process followed by conversion to acetylcholine. Transfer of cells to an enriched, serum-free defined medium resulted in morphological and neurochemical differentiation, with an enhancement of cholinergic phenotype. Hemicholinium-sensitive choline uptake activity was increased about sixfold over a 4-day period, with no change in choline acetyltransferase or acetylcholinesterase specific activity. Acetylcholine synthesis was increased in parallel with the changes in choline accumulation; choline metabolism in the differentiated cells differed significantly from that observed in the undifferentiated cells, with proportionally less converted to phosphorylcholine and proportionally more remaining as unmetabolized choline and converted to acetylcholine. The enhanced choline accumulation appeared to be mediated by an increased number of choline carriers, demonstrated by increased binding of the affinity ligand [3H]-choline mustard to the transporter and by an increased Vmax for the uptake process. The increased expression of the transport function appeared to be under transcriptional control, as the enhancement of uptake was blocked by the RNA polymerase II inhibitor alpha-amanitin as well as by the protein synthesis inhibitor cycloheximide. These results show that expression of sodium-coupled choline carriers and choline acetyltransferase may be regulated separately in the differentiating neuroblastoma LA-N-2 and that neurotransmitter synthesis is controlled by provision of precursor rather than at the level of the biosynthetic enzyme.

Effect of N,N'-dicyclohexylcarbodiimide on compartmentation and release of newly synthesized and preformed acetylcholine in Torpedo synaptosomes

Using isolated cholinergic synaptosomes prepared from Torpedo electric organ, we studied the effects of N,N'-dicyclohexylcarbodiimide (DCCD) on acetylcholine (ACh) synthesis, compartmentation, and release after stimulation. Whereas ACh synthesis was unchanged, ACh compartmentation inside synaptosomes was affected by the presence of DCCD. In resting conditions, the uptake into the synaptic vesicle pool of newly synthesized ACh (i.e., [14C]ACh synthesized in the presence of the drug) was progressively and markedly inhibited as the duration of DCCD preincubation was increased, whereas compartmentation of endogenous ACh was unchanged in the presence of DCCD. After stimulation, the release of endogenous ACh from DCCD-treated synaptosomes was similar to that of control, in contrast to the release of [14C]ACh, which was markedly inhibited. This inhibition was observed whatever the conditions of stimulation used (gramicidin D, calcium ionophore A23187, or KCl depolarization). The study of the compartmentation of [14C]ACh during stimulation revealed a transfer of highly labeled ACh from the free to the bound ACh compartment in the presence of DCCD, suggesting the existence of several ACh subcompartments within the free and bound ACh pools. The present results are discussed in comparison with the previously reported effects of vesamicol (AH5183) on ACh compartmentation and release.

Mobilization of a vesamicol-insensitive pool of acetylcholine from a sympathetic ganglion by ouabain

These experiments investigate the release of transmitter from the perfused superior cervical ganglia of cats induced by ouabain in the absence or presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol), a blocker of acetylcholine (ACh) uptake. Ouabain, perfused through the ganglia, released ACh in a Ca(2+)-dependent way. Vesamicol caused some inhibition of the release of ACh by ouabain; however, under this condition, the Na+,K(+)-ATPase inhibitor released five times more transmitter than did preganglionic stimulation at 5 Hz. Also, when ganglia exposed to vesamicol were depleted of the impulse-releasable pool of ACh, subsequent perfusion with ouabain released ACh, and this included ACh newly synthesized in the presence of vesamicol; this phenomenon could be inhibited by the lack of Ca2+ and presence of EGTA, and was completely abolished by perfusion with a medium containing 18 mM Mg2+. To test whether the release of this vesamicol-insensitive Ca(2+)-dependent pool by ouabain is associated with a decrease in the number of synaptic vesicles, ganglia treated with the ATPase inhibitor after the depletion of the impulse-releasable pool of ACh were fixed for electron microscopy. In the presence of Ca2+, coincident with the release of the vesamicol-insensitive pool of ACh, nerve terminals were almost depleted of synaptic vesicles; ganglia treated similarly, but with medium containing 18 mM Mg2+ instead of Ca2+, were not depleted of synaptic vesicles. These results suggest that ouabain releases a vesamicol-insensitive pool of ACh from the sympathetic ganglion and also support the notion that this compartment is vesicular and its exocytosis depends on extracellular Ca2+. It is suggested that empty-vesicle recycling in the presence of vesamicol restricts mobilization of full vesicles to release sites.

Increased acetylcholine content induced by adenosine in a sympathetic ganglion and its subsequent mobilization by electrical stimulation

The present study was initiated to examine the effects of ATP on acetylcholine (ACh) synthesis. The exposure of superior cervical ganglia to ATP increased ACh stores by 25%, but this effect was also evident with ADP, AMP, and adenosine, but not with beta gamma-methylene ATP, a nonhdydrolyzable analogue of ATP, or with inosine, the deaminated product of adenosine. Thus, we attribute the enhanced ACh content caused by ATP to the presence of adenosine derived from its hydrolysis by 5'-nucleotidase. The adenosine-induced increase of tissue ACh was not the consequence of an adenosine-induced decrease of ACh release. The extra ACh remained in the tissue for more than 15 min after the removal of adenosine, but it was not apparent when ganglia were exposed to adenosine in a Ca(2+)-free medium. Incorporation of radiolabelled choline into [3H]ACh was also enhanced in the presence of adenosine, suggesting an extracellular source of precursor. Moreover, the synthesis of radiolabelled forms of phosphorylcholine and phospholipid was not reduced in adenosine's presence, suggesting that the extra ACh was not likely derived from choline destined for phospholipid synthesis. Aminophylline did not prevent the adenosine effect to increase ACh content; this effect was blocked by dipyridamole, but not by nitrobenzylthioinosine (NBTI). In addition, two benzodiazepine stereoisomers known to inhibit stereoselectively the NBTI-resistant nucleoside transporter displayed a similar stereoselective ability to block the effect of adenosine. Together, these results argue that adenosine is transported through an NBTI-resistant nucleoside transporter to exert an effect on ACh synthesis. The extra ACh accumulated as a result of adenosine's action was releasable during subsequent preganglionic nerve stimulation, but not in the presence of vesamicol, a vesicular ACh transporter inhibitor. We conclude that the mobilization of ACh is enhanced as a result of adenosine pretreatment.

Free choline and choline metabolites in rat brain and body fluids: sensitive determination and implications for choline supply to the brain

In the central nervous system, choline is an essential precursor of choline-containing phospholipids in neurons and glial cells and of acetylcholine in cholinergic neurons. In order to study choline transport and metabolism in the brain, we developed a comprehensive methodical procedure for the analysis of choline and its major metabolites which involves a separation step, selective hydrolysis and subsequent determination of free choline by HPLC and electrochemical detection. In the present paper, we report the levels of choline, acetylcholine, phosphocholine, glycerophosphocholine and choline-containing phospholipids in brain tissue, cerebrospinal fluid and blood plasma of the untreated rat. The levels of free choline in blood plasma (11.4 microM), CSF (6.7 microM) and brain intracellular space (64.0 microM) were sufficiently similar to be compatible with an exchange of choline between these compartments. In contrast, the intracellular levels of glycerophosphocholine (1.15 mM) and phosphocholine (0.59 mM) in the brain were considerably higher than their CSF concentrations of 2.83 and 1.70 microM, respectively. In blood plasma, glycerophosphocholine was present in a concentration of 4.58 microM while phosphocholine levels were very low or absent (< 0.1 microM). The levels of phosphatidylcholine and lyso-phosphatidylcholine were high in blood plasma (1267 and 268 microM) but very low in cerebrospinal fluid (< 10 microM). We concluded that the transport of free choline is the only likely mechanism which contributes to the supply of choline to the brain under physiological conditions.

Effect of N,N'-dicyclohexylcarbodiimide on acetylcholine release from Torpedo synaptosomes and proteoliposomes reconstituted with the proteolipid mediatophore

The mediatophore is a presynaptic membrane protein that has been shown to translocate acetylcholine (ACh) under calcium stimulation when reconstituted into artificial membranes. The mediatophore subunit, a 15-kDa proteolipid, presents a very high sequence homology with the N,N'-dicyclohexylcarbodiimide (DCCD)-binding proteolipid subunit of the vacuolar-type H(+)-ATPase. This prompted us to study the effect of DCCD, a potent blocker of proton translocation, on calcium-dependent ACh release. The present work shows that DCCD has no effect on ACh translocation either from Torpedo synaptosomes or from proteoliposomes reconstituted with purified mediatophore. However, using [14C]DCCD, we were able to demonstrate that the drug does bind to the 15-kDa proteolipid subunit of the mediatophore. These results suggest that although the 15-kDa proteolipid subunits of the mediatophore and the vacuolar H(+)-ATPase may be identical, different domains of these proteins are involved in proton translocation and calcium-dependent ACh release and that the two proteins have a different membrane organization.

Mobilization of the readily releasable pool of acetylcholine from a sympathetic ganglion by tityustoxin in the presence of vesamicol

The present experiments tested whether preganglionic stimulation and direct depolarization of nerve terminals by tityustoxin could mobilize similar or different pools of acetylcholine (ACh) from the cat superior cervical ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol, AH5183), an inhibitor of ACh uptake into synaptic vesicles. In the absence of vesamicol, both nerve stimulation and tityustoxin increased ACh release. In the presence of vesamicol, the release of ACh induced by tityustoxin was inhibited, and just 16% of the initial tissue content could be released, a result similar to that obtained with electrical stimulation under the same condition. When the impulse-releasable pool of ACh had been depleted, tityustoxin still could release transmitter, amounting to some 10% of the ganglion's initial content. This pool of transmitter seemed to be preformed in the synaptic vesicles, rather than synthesized in response to stimuli, as tityustoxin could not release newly synthesized [3H]ACh formed in the presence of vesamicol, and hemicholinium-3 did not prevent the toxin-induced release. In contrast to the results with tityustoxin, preganglionic stimulation could not release transmitter when impulse-releasable or toxin-releasable compartments had been depleted. Our results confirm that vesamicol inhibits the mobilization of transmitter from a reserve to a more readily releasable pool, and they also suggest that, under these experimental conditions, there might be some futile transmitter mobilization, apparently to sites other than nerve terminal active zones.

Cadmium inhibits stimulus-response coupling in skate (Raja erinacea) electric organ

1. The effects of cadmium on stimulus-response coupling in the skate (Raja erinacea) electric organ were examined. 2. Cadmium decreased the evoked electrical discharge and the evoked release of 3H-ACh in a concentration-related fashion. 3. Cadmium (100 microM) also blocked voltage-dependent 45Ca uptake. 4. Both d-tubocurarine and nifedipine blocked Ca uptake and evoked potential, but not 3H-ACh release, thus most of the 45Ca uptake measured was post-synaptic through L Ca channels. 5. Nickel, cadmium, and verapamil inhibited 3H-ACh release and evoked potential, indicating a block of pre-synaptic T Ca channels.

Simultaneous quantitation of arecoline, acetylcholine, and choline in tissue using gas chromatography/electron impact mass spectrometry

A capillary gas chromatography/mass spectrometry (GC/MS) assay for the simultaneous quantitation of arecoline (ARE), acetylcholine (ACh), and choline (Ch) in biological tissue has been developed. The method utilizes hexadeuterated ARE and nonadeuterated ACh and Ch as internal standards. The compounds were ion-pair extracted from tissue using sodium tetraphenylboron in 3-heptanone. GC/MS analysis was achieved using capillary GC and electron impact mass spectrometry. Quantitation was accomplished using selected ion monitoring at m/z 140 and 146 for non-deuterated and deuterated arecoline respectively, and m/z 58 and 64 for non-deuterated and deuterated ACh and Ch respectively. The method easily detected 25 pmol of all three compounds taken through the assay, and was linear through 50 nmol.

Acetylcarnitine, carnitine and glucose diminish the effect of muscarinic antagonist quinuclidinyl benzilate on striatal acetylcholine content

The content of acetylcholine (ACh) in the striatum, brain cortex and hippocampus of rats was lowered 20-180 min after intraperitoneal injection of the muscarinic antagonist quinuclidinyl benzilate (QNB). The depletion of ACh content in the striatum was diminished in animals treated with a single dose of acetyl-L-carnitine, L- or D,L-carnitine, or D-glucose. It is likely that QNB stimulates ACh release by blocking presynaptic muscarinic autoreceptors and that acetylcarnitine, carnitine and glucose support the resynthesis of ACh by increasing the availability of acetylcoenzyme A. They do not have the same consistent effect in the brain cortex and hippocampus; this difference may be related to the lower turnover rate of ACh and to the difference in the anatomical arrangement of cholinergic structures in these parts of the brain.

Regulation of diacylglycerol levels in carbachol-stimulated pancreatic acinar cells: relationship to the breakdown of phosphatidylcholine and metabolism to phosphatidic acid

Rat pancreatic acinar cells prelabeled with [14C]palmitic acid and then exposed to carbachol (CCh) exhibited a time-dependent increase in 1,2-[14C]diacylglycerol ([14C]DAG) levels, which was first detected at 2 min and then continued to rise in a linear manner. There was a concomitant increase in [14C]phosphatidic acid, which plateaued after 2 min and then remained at steady-state levels. CCh also promoted the release of phosphocholine, but not choline, within 60 s and caused a decrease in [14C]phosphatidylcholine in cells prelabeled with [14C]glycerol after 15 min. The inability to detect a rise in [14C]phosphatidylethanol accumulation and a fall in [14C]phosphatidate levels in [14C]palmitate prelabeled cells after exposure to CCh plus ethanol documented the absence of a phospholipase D-mediated pathway. The rapid phosphorylation of diglyceride in homogenates from unstimulated and carbachol-treated cells increased with increasing concentrations of exogenous substrate, thereby affirming that carbachol stimulates the phosphorylation of DAG by promoting the accumulation of the diglyceride. These collective findings provide evidence for the existence of an integrative control mechanism for regulating endogenous DAG levels during pancreatic acinar cell activation involving phosphatidylcholine-specific phospholipase C and DAG kinase.

The synthesis and release of acetylcholine by depolarized hippocampal slices is increased by increased choline available in vitro prior to stimulation

The objective of these experiments was to determine whether preincubating hippocampal slices with choline provides precursor that can be used during a subsequent incubation to support or enhance the synthesis of acetylcholine (ACh). Slices were preincubated for 60 min with 0, 10, 25, or 50 microM choline, washed, resuspended, and then incubated for 10 min in choline-free buffer containing 4.74 (Krebs-Ringer bicarbonate, KRB) or 25 mM KCl. The tissue contents of ACh and choline were determined prior to and after the preincubation, as well as after the incubation; the amounts of ACh and choline released were measured, and ACh synthesis was calculated. Preincubation in the absence of choline increased the tissue content of ACh to 242% of original levels; preincubation with 10 microM choline did not lead to a further increase, but preincubation with 25 or 50 microM choline increased the ACh content to 272% of original levels, significantly greater than that of slices preincubated with either 0 or 10 microM choline. When tissues were subsequently incubated for 10 min with either KRB or 25 mM KCl, ACh release from slices preincubated with 50 microM choline was greater than from slices preincubated with 0, 10, or 25 microM choline. Incubation of slices with KRB did not alter the tissue content of ACh, but when tissues were incubated with 25 mM KCl, the ACh content of slices preincubated with 0 or 10 microM choline decreased significantly, whereas that of slices preincubated with 25 or 50 microM choline did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine synthesis in a primary culture of porcine intermediate lobe cells

Abstract Previous pharmacological studies with the pituitary gland have suggested that acetylcholine (ACh) might be involved in the regulation of intermediate lobe (IL) function. Whether ACh is endogenous to the IL cells or provided from an extrinsic source is unclear. The present experiments tested the possibility that the endocrine cells of the IL may be a source of ACh by measuring certain cholinergic markers in a primary culture of dissociated porcine cells. The endogenous ACh content was readily measurable in both the freshly dissociated IL cells and in 2- or 4-day primary cultures. Choline acetyltransferase activity was also measurable in the freshly dissociated and cultured IL cells and was reduced by 53% in the presence of a specific inhibitor, napthylvinylpyridine (50 muM). IL cells incubated in the presence of [(14)C]choline (1 muM) were able to synthesize [(14)C]ACh and the accumulation of the new ACh was inhibited by hemicholinium-3 (30 muM), a competitive inhibitor of high affinity choline uptake at cholinergic nerve terminals. In conclusion, these results demonstrate that the endocrine cells of the IL are capable of synthesizing and storing ACh.

Characterisation and properties of a small cell lung cancer cell line and xenograft WX322 with marked sensitivity to alpha-interferon

Controversy exists as to whether interferons usefully influence the growth of epithelial carcinomas. A small cell lung carcinoma (SCLC) cell line, WX322, has been derived which is greater than 1000-fold more sensitive to alpha-interferon (IFN) when grown in agar than other reported SCLC cell lines. The WX322 line has been characterised to prove its epithelial origin and its chemosensitivity compared with that of the NCI-H69 small cell line. The WX322 cell line expresses neuroendocrine and epithelial markers and possesses a morphology consistent with SCLC origin. A concentration of 5 IU ml-1 of IFN produced 50% inhibition of colony formation in agar in the WX322 line, whereas a concentration of greater than 10(5) IU ml-1 was required to produce a comparable effect with the NCI-H69 cell line. In contrast, WX322, possessed similar sensitivity to NCI-H69 cells when exposed to a range of cytotoxic agents. Analysis of the cell cycle indicated that IFN increased the percentage of cells in the G0/G1 phase for the WX322 cell line but increased the percentage in S phase for the NCI-H69 line. Growth of the xenograft, from which the cell line was derived, was also inhibited by IFN at doses greater than 10(5) IU/mouse/day. The WX322 cell line whether grown in agar or as a xenograft shows an unusually high sensitivity to IFN and provides an interesting model for studying mechanisms of IFN cytotoxicity to epithelial cells.

Positive and negative effects of tacrine (tetrahydroaminoacridine) and methoxytacrine on the metabolism of acetylcholine in brain cortical prisms incubated under "resting" conditions

The effects of tacrine (1,2,3,4-tetrahydro-9-aminoacridine) and 7-methoxytacrine on the metabolism of acetylcholine were investigated in experiments on prisms of rat cerebral cortex incubated in vitro in low-potassium (3 mmol/L K+) media; cholinesterases were inactivated by paraoxon to avoid any action of tacrine and methoxytacrine via their inhibition. Under "resting" conditions, tacrine and methoxytacrine increased the synthesis of unlabeled acetylcholine in the prisms; at the same time, they inhibited the uptake of [14C]choline from the medium and the synthesis of [14C]acetylcholine. The concentration of free choline was not increased by tacrine or methoxytacrine in either the tissue or the medium. The contradiction between the increased synthesis of unlabeled and the diminished synthesis of labeled acetylcholine indicates that the utilization of intracellular choline (which is presumably mobilized from intracellular choline esters) for the synthesis of acetylcholine is increased by tacrine and methoxytacrine. This conclusion is supported by the observation that the inhibition of acetylcholine synthesis during incubation with hemicholinium-3 (an inhibitor of choline transport into cholinergic nerve terminals) was overcome when tacrine was present simultaneously with hemicholinium-3. When the prisms were preincubated with [14C]choline and incubated with tacrine or methoxytacrine only after this, the amount of [14C]acetylcholine recovered in the tissue plus the medium was higher at the end of incubation with tacrine or methoxytacrine than without them, again suggesting that the drugs were able to increase the utilization of intracellular [14C]choline or its esters for acetylcholine synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of streptozotocin-induced diabetes on acetylcholine metabolism in rat brain

The main objective of this study was to determine whether uncontrolled hyperglycemia, as a consequence of diabetes, altered the metabolism of acetylcholine (ACh) in rat brain. To accomplish this, rats received injections of streptozotocin (STZ, 60 mg/kg, i.v.) or vehicle, and were maintained for up to 7 weeks after the injections. Various indices of ACh metabolism were determined in striatum and hippocampus, two brain regions densely innervated by cholinergic neurons. STZ induced diabetes in 96% of the rats injected, as evidenced by glucose spillage into the urine within 48 hours. Serum glucose levels increased to 326% of control values by 1 week and remained at this level for the duration of the study. The steady-state concentrations of ACh and choline, determined in brain tissue from animals killed by head-focused microwave irradiation, did not differ between the control and STZ-injected groups. However, the synthesis and release of neurotransmitter by striatal slices, measured in vitro, decreased in a time-dependent manner. Although the basal release of ACh was unaltered at 1 week, neurotransmitter release decreased significantly by 21% at 5 weeks and by 26% at 7 weeks. The release of ACh evoked by incubation with 35 mM KCl was inhibited significantly by 20% at all time points studied. ACh synthesis by slices incubated under basal conditions decreased by 13% and 27% at 5- and 7-weeks, respectively, the latter significantly less than controls. Synthesis by striatal slices incubated with 35 mM KCl was inhibited by 17% at 7 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Choline uptake in cholinergic nodose cell bodies

Isolated living cell bodies were obtained by mechanical and enzymatic dissociation from adult rabbit nodose ganglion followed by separation of fibres and cells using a Percoll gradient. A purification yield of 45% was measured. Based on previous results obtained in whole ganglion and showing the presence of cholinergic cell bodies among the afferent fibres of the vagus nerve, this preparation was used to study choline uptake by neuron cell somata. Cholinergic cells counted after choline acetyltransferase immunohistological staining showed a stained population of 2.9% among the isolated population. Two [3H]choline uptake mechanisms were detected at the cell body level. The first, with Km1 = 7 microM and Vm1 = 200 pmol/h per ganglion is sodium dependent, related to acetylcholine synthesis (43%) and has an IC50 with hemicholinium-3 equal to 50 microM. The second, with Km2 = 54 microM and Vm2 = 2235 pmol/h per ganglion is sodium independent, poorly associated to acetylcholine synthesis (12%) and exhibits an IC50 of 2 microM with hemicholinium-3. Except for their sensitivity to hemicholinium-3, the high and low affinity choline uptake mechanisms observed at the somatic level have, respectively, the same characteristics as the high and low affinity mechanisms described at the synaptic level. Their physiological role, their opposed sensitivity to hemicholinium-3 compared to the synaptic uptake systems and the relation between the somatic high affinity choline transport and an acetylcholine somatic release are discussed.

Immunomodulatory Effect and Acetylcholine Receptor Binding of a Thymopeptide (Tp4) on Human Peripheral Blood Lymphocytes

The effect of a synthetic thymopeptide, Tp4 (RGH 0206) on nAChR binding capacity and stimulatory responses of normal human peripheral lymphocytes were studied. The present study is the first to demostrate that Tp4 binds to the nAChR on PBLs and this binding is resulted in rapid modulatory effect on the activation signal and affects also the proliferative response. The inhibitory effect of Tp4 on 125Iα-Btx or 3H-nicotine binding was in correlation with a rapid increase of cGMP-level. Another activation parameter; AChE activity, showing the same concentration dependency, was declined reaching the maximal effect in the same, 6–60 nM, range. After a 72h incubation with suboptimal dose of PHA, both proliferation rate and AChE activity were inhibited. The results are in good agreement with earlier observations on the suppressive nature of nAChR on PBLs and on binding of thymopeptides to nAChR from electric tissue, as well as with the reported inhibiting effect of thymus hormones on IL-2 production. The present data might have relevance to the pathogenesis and diagnostics of myasthenia gravis, because the binding of overproduced thymopeptides to nAChRs in various organs could lead to different effects, i.e. to altered cholinergic transmission at the neuromuscular junctions and to the alteration of lymphocyte functions on PBLs and on thymocytes too.

Evidence that somatostatin enhances endogenous acetylcholine release in the rat hippocampus

The present experiments show that somatostatin (SS)-like immunoreactive material is present in the hippocampus and that its release can be increased by K+ stimulation of rat hippocampal slices, suggesting that SS-like peptides may be of significance to neurotransmission in the hippocampus. Exogenous SS-28 and SS-14 enhanced the K(+)-evoked release of endogenous acetylcholine (ACh) from rat hippocampal slices, whereas amino-terminal fragments of SS-28 did not. The increased ACh release in the presence of either peptide appeared to be mediated by an interaction with SS receptors because cyclo-SS, a putative SS antagonist, abolished the effects of both SS-28 and SS-14. In addition, the increase in ACh release induced by SS-14 or SS-28 was antagonized by the calcium channel antagonists omega-conotoxin GVIA, nifedipine, and cinnarizine, implicating voltage-sensitive calcium channels in this effect. Moreover, the effect was sensitive to tetrodotoxin, suggesting an indirect action of the peptides at a site distal to cholinergic nerve terminals. Cysteamine, which has been reported to deplete SS content and to increase SS release in brain, augmented the basal and evoked release of ACh from hippocampal slices, without affecting SS-like content and release. Finally, neuropeptide Y, which is colocalized with SS in many neurons of the hippocampal formation, did not alter ACh release, nor did it facilitate the SS-induced increase. The results suggest that in the rat hippocampus, both SS-28 and SS-14 interact with SS receptors to regulate ACh release indirectly by a mechanism that involves alterations of calcium influx during depolarization.

Neurotensin regulation of endogenous acetylcholine release from rat cerebral cortex: effect of quinolinic acid lesions of the basal forebrain

The effects of neurotensin (NT) on endogenous acetylcholine (ACh) release from basal forebrain, frontal cortex, and parietal cortex slices were tested. The results show that NT differentially regulates evoked ACh release from frontal and parietal cortex slices without altering either spontaneous or evoked ACh release from basal forebrain slices. In the frontal cortex, NT significantly inhibited evoked ACh release by a tetrodotoxin (TTX)-insensitive mechanism, suggesting an action directly on cholinergic terminals. In the parietal cortex, NT enhanced evoked ACh release by a TTX-sensitive mechanism, suggesting an action of NT on the cholinergic neuron or in close proximity to the cholinergic neuron. The effects of NT on ACh release were confined to evoked ACh release; that is, spontaneous ACh release was not affected. NT did not affect spontaneous or potassium-evoked ACh release from occipital cortex slices. The second set of experiments tested the effects of quinolinic acid (QUIN) lesions of the basal forebrain cell bodies on the NT-induced regulation of evoked ACh release in the cerebral cortex. QUIN lesions of basal forebrain cell bodies caused decreases in choline acetyltransferase activity (27 and 28%), spontaneous ACh release (14 and 21%), and evoked ACh release (38 and 44%) in frontal and parietal cortex, respectively. In addition, 11 days following QUIN lesions of basal forebrain cell bodies, the action of NT to regulate evoked ACh release in frontal cortex or parietal cortex was no longer observed. The results suggest that in the rat frontal and parietal cortex, NT differentially regulates the activity of cholinergic neurons by decreasing and increasing evoked ACh release, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic estradiol treatment alters central cholinergic function in the female rat: effect on choline acetyltransferase activity, acetylcholine content, and nicotinic autoreceptor function

The purpose of the present study was to determine the effects of chronic (2-month) estradiol (E2) treatment on cholinergic function in the frontal cortex, hippocampus and hypothalamus of the female rat. Chronic E2 treatment selectively increased choline acetyltransferase (ChAT) activity in the frontal cortex and decreased ChAT activity in the hypothalamus: hippocampal ChAT activity was not significantly changed. The decrease of ChAT activity in the hypothalamus was paralleled by a significant reduction in the content and release (basal and evoked) of acetylcholine (ACh) in this structure. Neither the content nor the release of ACh was altered in the frontal cortex. In the hippocampus, there was a significant increase in spontaneous ACh release; however, hippocampal ACh content and evoked ACh release were not changed. Chronic E2 treatment also altered nicotinic binding sites in these same regions as determined by saturation analysis of [3H]methylcarbamylcholine (MCC) to membranes. There was a decrease in the affinity and an increase in the density of [3H]MCC binding sites in hippocampal membranes and an increase in the density of [3H]MCC binding sites was observed in hypothalamic membranes. These alterations were paralleled by changes in nicotinic autoreceptor function within these two structures. In the hippocampus, the increase in spontaneous ACh release induced by MCC in control animals was no longer apparent after chronic treatment with E2. In hypothalamus, higher concentrations of the nicotinic agonist were required to increase spontaneous ACh release in slices from E2-treated rats as compared to control rats. Taken together, these results suggest that chronic E2 treatment decreases presynaptic cholinergic function in the female rat hippocampus and hypothalamus.

Isolation and enzymic assay of choline and phosphocholine present in cell extracts with picomole sensitivity

Increasing interest in receptor-regulated phospholipase C and phospholipase D hydrolysis of cellular phosphatidylcholine motivates the development of a sensitive and simple assay for the water-soluble hydrolytic products of these reactions, phosphocholine and choline respectively. Choline was partially purified from the methanol/water upper phase of a Bligh & Dyer extract by ion-pair extraction using sodium tetraphenylboron, and the mass of choline was determined by a radioenzymic assay using choline kinase and [32P]ATP. After removal of choline from the upper phase, the mass of residual phosphocholine was determined by converting it into choline by using alkaline phosphatase, followed by radioactive phosphorylation. In addition to excellent sensitivity (5 pmol for choline and 10 pmol for phosphocholine), these assays demonstrated little mutual interference (phosphocholine----choline = 0%; choline----phosphocholine = 5%), were extremely reproducible (average S.E.M. of 3.5% for choline and 2.9% for phosphocholine), and were simple to perform with instrumentation typically available in most laboratories. In addition, the ability to apply the extraction technique to the upper phase of Bligh & Dyer extracts permitted simple analysis not only of choline and phosphocholine, but also of phosphatidylcholine and lipid products of phospholipase C and phospholipase D activity (1,2-diacylglycerol and phosphatidic acid respectively) from the same cell or tissue sample.

Acetylcholine and ATP are coreleased from the electromotor nerve terminals of Narcine brasiliensis by an exocytotic mechanism

Although the exocytotic mechanism for quantal acetylcholine (ACh) release has been widely accepted for many years, it has repeatedly been challenged by reports that ACh released upon stimulation originates from the cytosol rather than synaptic vesicles. In this report, two independent experimental approaches were taken to establish the source of ACh released from the electromotor system of Narcine brasiliensis. Since ATP is colocalized with ACh in the cholinergic vesicle, the exocytotic theory predicts the corelease of these two components with a stoichiometry identical to that of the vesicle contents. The stimulated release of ATP from isolated synaptosomes could be accurately quantitated in the presence of the ATPase inhibitor adenosine 5'-[alpha, beta-methylene]triphosphate (500 microM), which prevented degradation of the released ATP. Various concentrations of elevated extracellular potassium (25-75 mM), veratridine (100 microM), and the calcium ionophore ionomycin (5 microM) all induced the corelease of ACh and ATP in a constant molar ratio of 5-6:1 (ACh/ATP), a stoichiometry consistent with that established for the vesicle content. In parallel to these stoichiometry studies, the compound 2-(4-phenylpiperidino)cyclohexanol (AH5183) was used to inhibit specifically the vesicular accumulation of newly synthesized (radiolabeled) ACh without affecting cytosolic levels of newly synthesized ACh in cholinergic nerve terminals. Treatment with AH5183 (10 microM) was shown to inhibit the release of newly synthesized ACh without markedly affecting total ACh release; thus, the entry of newly synthesized ACh into the synaptic vesicle is essential for its release. We conclude that ACh released upon stimulation originates exclusively from the vesicular pool and is coreleased stoichiometrically with other soluble vesicle contents.

Choline acetyltransferase in bovine pineal gland

Recent studies from our laboratories have shown that the bovine pineal gland contains a muscarinic cholinergic receptor with a Kd value of 0.423 +/- 0.010 nM and a Bmax value of 69.75 +/- 20.91 fmol/mg protein. In order to substantiate further the possible existence of a pineal cholinergic transmission, we have measured the activity of choline acetyltransferase and delineated its kinetic properties in the bovine pineal gland. This enzyme exhibited an activity of 0.0339 +/- 0.0042 nmol/mg protein/min. Furthermore, the bovine pineal choline acetyltransferase possessed a Km value of 124.86 +/- 24.06 microM and a Vmax value of 0.0598 +/- 0.0034 nmol/mg protein/min for acetyl CoA, and a Km value of 3.11 +/- 0.94 mM and a Vmax value of 0.0155 +/- 0.0016 nmol/mg protein/min for choline. The presence of muscarinic cholinergic receptors along with a specific choline acetyltransferase are supportive evidences that the bovine pineal gland may receive cholinergic innervation.

Localization of interleukin-2 immunoreactivity and interleukin-2 receptors in the rat brain: interaction with the cholinergic system

The present work characterizes the presence of interleukin-2 (IL-2)-like immunoreactive material and IL-2 binding sites in the adult rat brain. The results show that there are detectable levels of IL-2-like material in extracts of rat hippocampus, striatum, and frontal cortex. However, specific [125I]IL-2 binding sites were observed only in the hippocampus, using both homogenate-binding and autoradiographic techniques. In this region of the rat brain, specific [125I]IL-2 binding was inhibited by 100 nM non-radioactive recombinant human IL-2. In kainate-lesioned hippocampi, the density of [125I]IL-2 sites was apparently increased, suggesting their localization to extrinsic innervation and/or glial cells. In slices of hippocampus, which contain both IL-2-like immunoreactive material and specific IL-2 sites, exogenous IL-2 significantly decreased the potassium (25 mM)-evoked, but not the basal, release of acetylcholine. This IL-2-induced effect was concentration-dependent, and was apparent at a relatively low concentration (1 nM). This IL-2 effect was also region-specific, such that acetylcholine release from other tissue slices (striatal, frontal cortical) was not affected. In slices from kainate-lesioned hippocampi, the IL-2-induced reduction of acetylcholine release was only modestly enhanced, suggesting that the extra IL-2 sites that appear post-lesion may not be localized to cholinergic terminals.

Binding sites for [3H]AF-DX 116 and effect of AF-DX 116 on endogenous acetylcholine release from rat brain slices

The present study shows that the putative M2 ligand, [3H]AF-DX 116, binds to two classes of muscarinic sites in homogenates of rat hippocampus, striatum and cerebral cortex: one with a high affinity (Kd less than 5 nM)/low capacity (Bmax = 30-63 fmol/mg protein), and a second of lower affinity (Kd greater than 65 nM) and higher capacity (Bmax greater than 190 fmol/mg protein). In experiments which tested the effects of the muscarinic antagonists on acetylcholine (ACh) release from brain slices, the non-selective antagonist (-)-quinuclidinyl benzylate and atropine significantly enhanced the potassium (25 mM)-evoked release of ACh. This effect was mimicked by the M2 ligand AF-DX 116, but neither the M1-selective antagonist pirenzepine, nor the putative M3-muscarinic antagonist, 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), altered ACh release. Also, the muscarinic agonist, oxotremorine, significantly depressed evoked ACh release from brain slices, an effect that was completely antagonized by atropine or by AF-DX 116, but not by pirenzepine or 4-DAMP. Thus, it appears that presynaptic muscarinic autoreceptors in the rat hippocampus, striatum and cerebral cortex belong to the M2 subtype of muscarinic receptors.

Physostigmine, tacrine and metrifonate: the effect of multiple doses on acetylcholine metabolism in rat brain

The effects of two consecutive intramuscular doses of three cholinesterase inhibitors (physostigmine, tetrahydroaminoacridine and metrifonate) were compared in rats. The results revealed major differences in biochemical effects on the brain of the rat including the extent and duration of inhibition of cholinesterase, inhibition of release of acetylcholine and increase in levels of acetylcholine. Side effects were also markedly different in the time of appearance, duration and severity. These results suggest that there are significant differences in the mechanisms of action of various cholinesterase inhibitors. Since all three cholinesterase inhibitors are currently used in the experimental treatment of Alzheimer's disease, these findings have potential implications for the symptomatic therapy of these patients.