Cholinergic False Transmitter Research Articles

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Cholinergic false transmitters: Physiological and biochemical actions in central and peripheral systems

Three N-ethyl substituted analogs of acetylcholine (ACh) were evaluated for potential use as false neurotransmitters to decrease cholinergic transmission. This evaluation included (1) the elevation of arterial blood pressure upon central administration, (2) depression of blood pressure upon intravenous injection and (3) interactions with central muscarinic and peripheral nicotinic receptors. With respect to the central presser response, ACh, acetylmonoethylcholine (AMECh) and acetyldiethylcholine (ADECh) were full agonists of decreasing potency; acetyltriethylcholine (ATECh) was a partial agonist of considerably lower potency. The duration of response paralleled potency. With respect to the peripheral depressor response, ACh and AMECh were full agonists of equal potency, and ADECh and ATECh were partial agonists of at least 100-fold lower potency. In terms of their affinity for central muscarinic receptors (brainstem and cerebral cortex), the following series was obtained: ACh > AMECh > ADECh = ATECh. All of the agents had a greater affinity for muscarinic receptors in the brainstem compared to cortex. Acetylcholine and AMECh recognized multiple receptor binding conformations; the binding of ADECh and ATECh indicated interaction with a single set of equivalent sites. The affinity for nicotinic ACh receptors from the Torpedo electric organ was ACh = AMECh > ADECh; ATECh had little affinity for these receptors. Acetylcholine, AMECh and ADECh stimulated the binding of [ 3H]phencyclidine to the ion channel of nicotinic receptor (potency series = ACh > AMECh = ADECh); ATECh was inactive. Acetylcholine, AMECh and ADECh also induced receptor conversion to a desensitized conformation; ATECh did not. These findings suggest (1) that AMECh would be ineffective as an inhibitory false transmitter because it possessed almost the same affinity and intrinsic activity as ACh and (2) that ADECh and ATECh, if released from nerve terminals in the same quantities as ACh, would produce the greatest functional hypocholinergic state.

Precursors of cholinergic false transmitters: Central effects on blood pressure and direct interactions with cholinergic receptors

The purpose of this study was to determine whether a series of analogs of choline depress central cholinergic function in a manner consistent with the activity of their acetylated derivatives. Intracerebroventricular infusion of monoethylcholine (MECh), diethylcholine (DECh) and triethylcholine (TECh) inhibited the pressor response of unanesthetized rats to the subsequent intravenous injection of physostigmine (a well-characterized muscarinic response). The order of blocking potency was TECh > DECh > MECh > choline, directly opposite to the order of potency for elicitation of a central pressor response by their associated acetylated derivative (i.e. ACh > AMECh > ADECh = ATECh; Aronstam, Marshall and Buccafusco, 1988). In contrast, there was little selectivity between the analogs of choline in terms of their affinity for muscarinic receptors in the brainstem or cortex; the Ki's for inhibition of the binding of [ 3H]quinuclidinyl benzilate ranged from 0.33 to 0.95 mM). In terms of their affinity for nicotinic receptors (from the electric organ of Torpedo californica) the following order of potency was obtained: choline > MECh = DECh > TECh. Choline and MEC stimulated the binding of [ 3H]phencyclidine to the nicotinic ion channel (EC 50's = 79 and 115 μM, respectively). At greater concentrations, all of the analogs inhibited ligand binding to the channel ( Ki's from 0.2 to 10 mM), with the following order of potency: TECh > DECh > MECh > choline. These findings suggest that the inhibitory actions of these analogs of choline are related to their synthesis and release as false cholinergic neurotransmitters.

N-Ethyl analogues of choline as precursors to cholinergic false transmitters.

Cat superior cervical ganglia perfused with the choline analogue, diethylcholine, acetylated the analogue and acetyldiethylcholine was subsequently released from the ganglia in response to preganglionic nerve stimulation by a Ca2+-dependent mechanism. Rat cerebral cortical slices incubated with monoethylcholine or diethylcholine acetylated the choline analogues, and both acetylmonoethylcholine and acetyldiethylcholine were released from the slices in response to stimulation by a high K+ concentration. In brain slices pre-incubated with monoethylcholine, diethylcholine, or triethylcholine, acetylated derivatives of the choline analogues were found in both free and bound nerve-ending stores, similar to the subcellular localization of [3H]acetylcholine (ACh) in brain slices pre-incubated with [3H]choline; the relative distribution of each of the acetylated choline analogues between the two nerve-ending stores differed only slightly from that of [3H]ACh. Nerve-ending free and bound stores of acetyldiethylcholine were equally depleted when brain slices were stimulated under conditions that cause depletion of releasable acetyldiethylcholine stores; similar results were obtained with acetyltriethylcholine. It is concluded that the three acetylated ethyl analogues of choline fulfill the necessary criteria for identification as cholinergic false transmitters, and that, under the conditions of the present experiments with brain, the false transmitters are able to distribute similarly to ACh between nerve-ending stores.

Spontaneous and evoked release of acetylcholine and a cholinergic false transmitter from brain slices: Comparison to true and false transmitter in subcellular stores

Rat cerebral cortex slices were incubated with [ 14Ccholine and [ 3Hhomocholine to allow synthesis of [ 14Cacetylcholine and [ 3Hacetylhomocholine; release of the acetylated compounds was tested in the presence of eserine and hemicholinium-3. Both [ 14Cacetylcholine and [ 3Hacetylhomocholine were released spontaneously by a Ca 2+-independent mechanism; exposure of the tissue to a high K + medium resulted in a Ca 2+-dependent increase in [ 14Cacetylcholine release (30-fold) and in [ 3Hacetylhomocholine release (5 to 7-fold). Thus, spontaneous and K +-evoked transmitter release could be distinguished on the basis of their molar ratios of true to false transmitters and these ratios were compared to the molar ratios of the transmitters in subcellular fractions prepared from the incubated tissue. The molar ratio of acetylcholine to acetylhomocholine released from the tissue spontaneously differed from the ratio in subcellular fractions containing occluded transmitters. The molar ratio of acetylcholine to acetylhomocholine released by K + differed from the ratio in a fraction (H) containing occluded transmitters but was similar to the ratio in the fraction (D) containing monodisperse synaptic vesicles and the fraction (0) containing the majority of a soluble cytoplasmic marker. Comparison of the transmitter contents of subcellular fractions from unstimulated and K +-stimulated tissue showed that the three fractions (D, H and O) lost equal proportions of both transmitters as a result of K + stimulation. It is concluded that acetylhomocholine may be released from brain slices both spontaneously and in response to stimulation via mechanism similar to those that release acetylcholine, but that there must be some differences in specificity of the acetylcholine storage and/or release processes. The results also indicate that spontaneous transmitter release originates from extravesicular stores; the results are consistent with a vesicular site of origin of evoked transmitter release but do not distinguish between nerve terminal vesicles and cytoplasm as the immediate source of evoked transmitter release.

Homocholine and acetylhomocholine: False transmitters in the cholinergic electromotor system of Torpedo

The subcellular distribution and acetylation of the choline analogue, N, N,N-trimethyl- N-3-hydroxypropylamine (homocholine) was studied using the electromotor system of Torpedo marmorata. Both choline and homocholine were transported into nerve terminals by the same high-affinity uptake mechanism (K T 2.0 and 3.5 μ m respectively), and became at least partly acetylated when blocks of electric tissue were perfused with [ 14C]choline and [ 3H]homocholine. Uptake of newly synthesized acetylcholine and acetylhomocholine into synaptic vesicles was enhanced by low-frequency stimulation of the block, and occurred into a metabolically active sub-fraction. Subsequent high frequency stimulation elicited the release of both 14C and 3H, in the same ratio as the two labels were isolated from the vesicle fraction. In other experiments it was shown that unacetylated homocholine was also released by stimulation, and found to be incorporated into vesicles in the same ratio to acetylhomocholine as it appeared in the perfusate. We conclude (a) that homocholine is not only a precursor to a cholinergic false transmitter (acetylhomocholine), but also qualifies as such, itself; (b) that uptake into vesicles under these conditions is not absolutely specific for acetylcholine and that prior acetylation is not an essential pre-requisite; and (c) that both acetylcholine and the two false transmitters are released from a vesicular compartment upon stimulation.

Cholinergic False Transmitters

Publisher Summary A false neurotransmitter is a substance that is not normally present in a nerve ending, but which can accumulate in the sites that are usually occupied by the physiological neurotransmitter, and can be released by stimuli that normally release the physiological transmitter. This chapter discusses cholinergic false transmitters. All putative cholinergic false transmitters studied so far are formed from choline analogues. The criteria of presence, subcellular localization, and release have been demonstrated for acetyldiethylcholine, acetyltriethylcholine, acetylpyrrolidinecholine, and acetylhomocholine. The criteria of presence and release have been demonstrated for acetylmonethylcholine, and the criterion of presence for acetylsulfocholine. All of these presumed false transmitters are less active than is acetylcholine (ACh) at nicotinic and muscarinic receptor sites and all can be hydrolysed by acetylcholinesterase. Studies on the uptake, acetylation, storage, release and turnover of choline analogues and the false transmitters formed therefrom are likely to be of some use in clarifying presynaptic cholinergic mechanisms.

Vesicular Storage and Release of Cholinergic False Transmitters

Several analogues of choline are known, which are taken up by cholinergic nerve terminals and released in the acetylated form on stimulation. Such compounds are thus precursors of cholinergic false transmitters. This chapter discusses two compounds, N-methyl-N-2-hydroxyethylpyrrolidiniu (mPCh) and homocholine (HCh), using guinea-pig cortex and the electric organ of Torpedo marmorata. In the experiments with cortex, the false transmitter precursors were injected into the tissue and released transmitters collected in Locke solution applied to the surface of the cortex in plastic sleeves. Free vesicles and those attached to external membranes were isolated from tissue subjacent to the cup. Blocks of electric tissue corresponding to the territory of one nerve were perfused through the accompanying venous sinus, and vesicles isolated by the technique currently employed in our laboratory. In both cases, uptake of [ 14 C] choline and the tritiated analogue were promoted by electrical stimulation. Further stimulation caused the release of true and false transmitters in the same ratio, as they were found in a metabolically active subpopulation of vesicles even when this differed greatly from that found in the cytoplasm (brain) or whole tissue of (Torpedo).

Vesicular storage and release of a false cholinergic transmitter (acetylpyrrolcholine) in the Torpedo electric organ

The choline analogue N-[Me- 3H] N-hydroxyethyl-pyrrolidinium (pyrrolcholine) was studied in the Torpedo electric organ. Pyrrolcholine is transported into isolated nerve terminal sacs by the choline high affinity uptake system ( K T = 5.7 μ m). If blocks of electric tissue are perfused in the presence of both [ 3H]pyrrolcholine and [ 14C]choline both compounds become acetylated and are taken up into synaptic vesicles. This process is enhanced by low frequency stimulation (~0.1 Hz). Upon subsequent stimulation of the nerve at 5 Hz both acetylpyrrolcholine and acetylcholine are released into the perfusate by a calcium-sensitive mechanism; their molar ratio in the perfusate is the same as that for their loss from the vesicle fraction. Acetylpyrrolcholine is a potent agonist on the frog rectus abdominis muscle although 12.7-fold less active than acetylcholine. We conclude that pyrrolcholine is a precursor of a cholinergic false transmitter in the Torpedo electric organ. Acetylpyrrolcholine has been shown to fulfil all the criteria for the definition of a false transmitter, including storage in synaptic vesicles.

Acetyltriethylcholine: a cholinergic false transmitter in cat superior cervical ganglion and rat cerebral cortex.

Abstract—The accumulation and metabolism of [14C]triethylcholine by cat superior cervical ganglia [rested or stimulated (20 Hz)] and by rat cerebral cortex minces was measured. In ganglia, preganglionic nerve stimulation increased the accumulation (2.4 fold) and the acetylation (5.7 fold) of triethylcholine; however the depletion of the ganglion's acetylcholine content was 9.5 times greater than the amount of acetyltriethylcholine synthesized. In the presence of eserine, neither stimulated nor rested ganglia synthesized any extra (surplus) acetyltriethylcholine. It is concluded that the rate‐limiting step in acetyltriethylcholine synthesis is the acetylation of triethylcholine by choline acetyltransferase. Subsequent preganglionic nerve stimulation of ganglia, which had been stimulated during the exposure to [14C]‐triethylcholine, caused the increased release of only acetyltriethylcholine; the release was frequency‐dependent, required the presence of Ca2+, and was blocked by increasing the ratio of Mg2+/Ca2+ in the perfusion fluid. All of the acetyltriethylcholine which had been accumulated was available for release. Rat cerebral cortex also accumulated triethylcholine and acetylated about 3% of the accumulated choline analogue. Subsequent stimulation by high K+ (46 mM)‐atropine (3 μM) caused the increased release of acetyltriethylcholine from the cortex and this release required the presence of Ca2+. Triethylcholine can therefore form a cholinergic false transmitter in the cat superior cervical ganglion and the rat cerebral cortex.

The uptake, metabolism and release of homocholine: studies with rat brain synaptosomes and cat superior cervical ganglion.

Abstract—The accumulation of [3H]homocholine (3‐trimethylamino‐propan‐1‐01) by isolated synaptosomes prepared from rat brain was resolved kinetically into a high (KT= 3.0 μM) and a low (KT= 14.5 μM) affinity system. Although homocholine was not acetylated by solubilized choline acetyltransferase, 64% of the homocholine accumulated by intact synaptosomes via the high affinity uptake process was acetylated. Homocholine was also acetylated in the superior cervical ganglion of the cat, and the amount of acetylhomocholine formed was increased (12‐fold) by preganglionic nerve stimulation. In ganglia, acetylhomocholine was available for release by preganglionic nerve impulses, and its release was Ca2+‐dependent, It is concluded that homocholine can form a cholinergic false transmitter, and that the substrate specificity of choline acetyltransferase in vitro might be different from that in situ.

Effects of N-hydroxyethyl-pyrrolidinium methiodide, a choline analogue, on passive avoidance behaviour in mice

N-Hydroxyethyl-pyrrolidinium methiodide (pyrrolcholine) administered intraventricularly impaired passive avoidance learning in mice. This effect of pyrrolcholine was antagonized by choline and hemicholinium-3, potentiated by scopolamine, and depending upon the time of injection, either potentiated or antagonized by physostigmine. The results are consistent with the hypothesis that pyrrolcholine disrupts central cholinergic pathways by a presynaptic mechanism. Based on metabolism studies, both in vitro and in vivo, it is postulated that the action of pyrrolcholine is mediated via acetylpyrrolcholine, a putative cholinergic false transmitter

Triethylcholine as a precursor to a cholinergic false transmitter

A FALSE transmitter is a substance that is stored and released by a nerve terminal instead of its normal transmitter. Several false transmitters have been demonstrated at adrenergic synapses1, but there has been no report of the synthesis, storage and release of a false transmitter at cholinergic synapses. It has been suggested that the triethyl analogue of choline (2-hydroxyethyl-triethylammonium iodide, TEC) might form a cholinergic false transmitter; in vitro studies have shown that it can be accumulated by tissues that take up choline2, and that choline acetyltransferase can acetylate TEC (refs 3 and 4). Nothing is known, however, about the specificity of the processes associated with storage and release of acetylcholine in intact tissue. The possibility that TEC can form a false transmitter was studied in the present experiments. The results demonstrate the uptake of TEC, its acetylation, and the release of acetyl-TEC by the superior cervical ganglion of the cat.

Quantum aspects of central and ganglionic synaptic transmission in vertebrates.

articleQuantum aspects of central and ganglionic synaptic transmission in vertebratesM. KunoM. KunoPublished Online:01 Oct 1971https://doi.org/10.1152/physrev.1971.51.4.647MoreSectionsPDF (5 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByReliable evaluation of the quantal determinants of synaptic efficacy using Bayesian analysisG. S. Bhumbra, and M. Beato15 January 2013 | Journal of Neurophysiology, Vol. 109, No. 2EditorialJournal of Neuroscience Methods, Vol. 130, No. 2Long-term potentiation of nicotinic synaptic transmission in rat superior cervical ganglia produced by phorbol ester and tetanic stimulationAutonomic Neuroscience, Vol. 105, No. 1Primary Afferent Depolarizations of Sensory Origin Within Contact-Sensitive Mechanoreceptive Afferents of a Crayfish LegA. R. Marchand, W.J.P. Barnes, and D. Cattaert1 June 1997 | Journal of Neurophysiology, Vol. 77, No. 6On the quantal analysis of hippocampal long-term potentiation and related phenomena of synaptic plasticityNeuroscience, Vol. 56, No. 2Perpetual inhibitory activity in mammalian brain slices generated by spontaneous GABA releaseBrain Research, Vol. 545, No. 1-2Applicability of Pascal distribution to quantal analysis for non-stationary release of neurotransmitterNeuroscience Letters, Vol. 115, No. 2-3Stochastic approaches to the study of synaptic functionProgress in Neurobiology, Vol. 35, No. 2Enhancement of Ia synaptic transmission following muscle nerve section: dependence upon protein synthesisNeuroscience Research, Vol. 5, No. 4Quantal analysis of paired-pulse facilitation in guinea pig hippocampal slicesNeuroscience Letters, Vol. 77, No. 2A comparison of the effects of climbing fiber deafferentiation in adult and weanling ratsBrain Research, Vol. 383, No. 1-2Postsynaptic action of kynurenic acid in the rat dentate gyrusNeuroscience Letters, Vol. 66, No. 1Frequency-to-voltage conversion in the pyramidal tract neuron: An important role of the inhibitory postsynaptic potentialNeuroscience Letters, Vol. 57, No. 2Regulation of endogenous calcium-dependent synaptic membrane phospholipase A2Brain Research, Vol. 290, No. 2Long-term potentiation in the hippocampusNeuroscience, Vol. 10, No. 4Ethanol alters synaptic activity in cultured spinal cord neuronsBrain Research, Vol. 243, No. 1Binary mode of transmitter release at central synapsesTrends in Neurosciences, Vol. 5Neural fuzzy point processesFuzzy Sets and Systems, Vol. 5, No. 2Spontaneous inhibitory post-synaptic potentials in hippocampus: Mechanism for tonic inhibitionBrain Research, Vol. 200, No. 1Spontaneous and evoked release of acetylcholine and a cholinergic false transmitter from brain slices: Comparison to true and false transmitter in subcellular storesNeuroscience, Vol. 5, No. 9The recovery of a random variable from a noisy record with application to the study of fluctuations in synaptic potentialsJournal of Neuroscience Methods, Vol. 2, No. 4Vesicle recycling and transmitter releaseNeuroscience, Vol. 4, No. 12Spontaneous miniature synaptic potentials in hippocampal neuronsBrain Research, Vol. 177, No. 1Ultrastructural plasticity in stimulated nerve terminals: Pseudopodial invasions of abutted terminals in Torpedine ray electric organNeuroscience, Vol. 4, No. 5Junctional mechanisms at group Ia synapsesProgress in Neurobiology, Vol. 12, No. 1The present status of the vesicular hypothesisProgress in Neurobiology, Vol. 13, No. 3Impaired synaptic potentiation processes in the hippocampus of aged, memory-deficient ratsBrain Research, Vol. 150, No. 1Post-synaptic potentials recorded from afferent nerve fibres of the posterior semicircular canal in the frogBrain Research, Vol. 135, No. 1Frequency of firing of Stein's model neuron with application to cells of the dorsal spinocerebellar tractBrain Research, Vol. 116, No. 2Frequency facilitation and post-tetanic potentiation of a unitary synaptic potential inAplysia californica are limited by different processesBrain Research, Vol. 109, No. 1Frequency and the brainLife Sciences, Vol. 18, No. 1Generation of spike trains in CNS neuronsBrain Research, Vol. 84, No. 1Linear models for biological transducers and impulse train spectra: general formulation and reviewKybernetik, Vol. 13, No. 1Miniature end-plate potentials: evidence that the intervals are not fit by a Poisson distributionBrain Research, Vol. 54 More from this issue > Volume 51Issue 4October 1971Pages 647-678 Copyright & PermissionsCopyright © 1971 the American Physiological Societyhttps://doi.org/10.1152/physrev.1971.51.4.647PubMed4331079History Published online 1 October 1971 Published in print 1 October 1971 Metrics

Quantal Nature of Synaptic Transmission

Quantal Nature of Synaptic Transmission