Inhibitory Action Of Acetylcholine Research Articles

Activity-Dependent Modulation of Layer 1 Inhibitory Neocortical Circuits by Acetylcholine

Layer 1 neocortical GABAergic interneurons control the excitability of pyramidal neurons through cell-class-specific direct inhibitory and disynaptic disinhibitory circuitry. The engagement of layer 1 inhibitory circuits during behavior is powerfully controlled by the cholinergic neuromodulatory system. Here we report that acetylcholine (ACh) influences the excitability of layer 1 interneurons in a cell-class and activity-dependent manner. Whole-cell recordings from identified layer 1 interneurons of the rat somatosensory neocortex revealed that brief perisomatic application of ACh excited both neurogliaform cells (NGFCs) and classical-accommodating cells (c-ACs) at rest by the activation of nicotinic receptors. In contrast, under active, action potential firing states, ACh excited c-ACs, but inhibited NGFCs through muscarinic receptor-mediated, IP3 receptor-dependent elevations of intracellular calcium that gated surface-membrane calcium-activated potassium channels. These excitatory and inhibitory actions of ACh could be switched between by brief periods of NGFC action potential firing. Paired recordings demonstrated that cholinergic inhibition of NGFCs disinhibited the apical dendrites of layer 2/3 pyramidal neurons by silencing widespread, GABA(B) receptor-mediated, monosynaptic inhibition. Together, these data suggest that the cholinergic system modulates layer 1 inhibitory circuits in an activity-dependent manner to dynamically control dendritic synaptic inhibition of pyramidal neurons.

Cholinergic stimulation of the immune system protects against lethal infection by Salmonella enterica serovar Typhimurium

The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

Long-Lasting Enhancement of Glutamatergic Synaptic Transmission by Acetylcholine Contrasts with Response Adaptation after Exposure to Low-Level Nicotine

Attempts to mimic synaptic delivery of acetylcholine (ACh) with brief, repetitive pulses of high concentration ACh at synapses of medial habenula (MHN) and interpeduncular nucleus (IPN) neurons in vitro elicited temporally distinct facilitation and inhibition of glutamate secretion via nicotinic and muscarinic ACh receptor-mediated pathways, respectively. ACh-induced nicotinic facilitation was sustained for up to 2 hr, whereas muscarinic inhibition was transient. Prolonged exposure to nicotine inactivated nicotinic receptors selectively, thus decreasing the relative contribution of the facilitatory versus inhibitory influences of ACh. The net effect of ACh in modulating glutamatergic transmission at MHN-IPN synapses may be determined by pre-exposure to nicotine, because the drug appears to switch the balance between the facilitatory and inhibitory actions of ACh.

Muscarinic-cholinoceptor mediated attenuation of phospholamban phosphorylation induced by inhibition of phosphodiesterase in ventricular cardiomyocytes: evidence against a cAMP-dependent effect.

In intact guinea pig ventricles, acetylcholine (ACH) has been shown to attenuate the positive inotropic effects of isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, by reducing protein phosphorylation without altering cAMP levels. In the present study, we tested the hypothesis that the cAMP-independent inhibitory action of ACH is also evident in isolated cardiomyocytes. cAMP-dependent protein kinase (PKA) activity ratio (-cAMP/+cAMP) and phosphorylation of phospholamban (PLB) were determined in unlabeled and 32P-labeled guinea pig ventricular cardiomyocytes, respectively. IBMX increased PKA activity ratio and phosphorylation of PLB in a dose-dependent manner. When cardiomyocytes were incubated simultaneously with IBMX (0-1 mM) and ACH (2 microM), ACH attenuated PLB phosphorylation stimulated by low concentration (1O-100 microM) but not by high concentrations (> 200 microM) of IBMX. EC50 value for IBMX-induced phosphorylation of PLB was 32 +/- 6 microM and increased nearly 3-fold after addition of ACH while PKA activity ratio remained unchanged. The rank order of cyclic nucleotide derivatives to phosphorylate PLB was 8 bromo-cAMP > dibutyryl cAMP > 8 bromo-cGMP > dibutyryl cGMP. ACH reduced phosphorylation of PLB stimulated by 8 bromo-cAMP. We conclude that in isolated cardiomyocytes (1) ACH inhibits phosphorylation of PLB stimulated by either IBMX or 8 bromo-cAMP and (2) ACH does not lower IBMX-stimulated PKA activity ratio. These effects of ACH on PLB phosphorylation cannot be explained by a reduction in IBMX-stimulated cAMP levels but may involve the activation of protein phosphatases.

G protein-dependent inhibition of L-type Ca2+ currents by acetylcholine in mouse pancreatic B-cells.

1. The effect of acetylcholine (ACh) on voltage-dependent Ca2+ currents in mouse pancreatic B-cells was studied using the whole-cell configuration of the patch-clamp technique. 2. ACh (0.25-250 microM) reversibly and dose-dependently inhibited the Ca2+ current elicited by depolarizations from -80 mV to +10 mV. Maximal inhibition was observed at concentrations > 25 microM where it amounted to approximately 35%. The effect was voltage independent and prevented by atropine (10 microM) suggesting that it was mediated by muscarinic receptors. 3. The inhibitory action of ACh on the Ca2+ current was abolished when the cytoplasmic solution contained GDP beta S (2 mM) and became irreversible when the non-hydrolysable GTP analogue GTP gamma S (10 microM) was included in the pipette. This indicates the participation of G proteins in the inhibitory effect of ACh but pretreatment of the cells with either pertussis or cholera toxin failed to prevent the effect of ACh on the Ca2+ current. 4. ACh remained equally effective as an inhibitor of the whole-cell Ca2+ current in the presence of the L-type Ca2+ channel agonist (-)-Bay K 8644 and after partial inhibition of the current by nifedipine. Addition of omega-agatoxin IVA, omega-conotoxin GVIA or omega-conotoxin MVIIC neither affected the peak Ca2+ current amplitude nor the extent of inhibition produced by ACh. These pharmacological properties indicate that ACh acts by inhibiting L-type Ca2+ channels. 5. The inhibitory action of ACh on the B-cell Ca2+ current was not secondary to elevation of [Ca2+]i and ACh remained equally effective as an inhibitor when Ba2+ was used as the charge carrier, when [Ca2+]i was buffered to low concentrations using EGTA and under experimental conditions preventing the mobilization of Ca2+ from intracellular stores. 6. These results suggest that ACh reduces the whole-cell Ca2+ current in the B-cell through a G protein-regulated, voltage- and Ca(2+)-independent inhibition of L-type Ca2+ channels.

Inhibitory action of acetylcholine, baclofen and GTP- γ- S on calcium channels in adult rat sensory neurons

High- and low-voltage activated calcium channel currents (HVA and LVA) were inhibited by acetylcholine (10–100 μM) and baclofen (10 μM) in adult rat sensory neurons. This modulatory effect was present on dihydropyridine (nifedipine 1 μM) and/or ω-conotoxin (3.2 μM, 2–5 h incubation) insensitive components and was insensitive to holding potentials ( V h −50 to −90 mV). GTP- γ- S (100 μM) prolonged calcium channel current activation in a time- and voltage-dependent manner. On the other hand, the current amplitude reduction induced by muscarinic and GABA B receptor activation, was not relieved by a 50-ms conditioning prepulse to +50 mV. This suggests the possibility of an alternative voltage-independent modulation mechanism.

Adrenergic and cholinergic inhibition of Ca2+ channels mediated by different GTP-binding proteins in rat sympathetic neurones.

Effects of acetylcholine (ACh) and noradrenaline (NA) on voltage-gated ion channels of sympathetic neurones acutely dissociated from rat superior cervical ganglion (SCG) were examined using the whole-cell voltage-clamp technique. Depolarizing voltage steps elicited two types of low- and high-voltage-activated (LVA and HVA) Ca2+ currents. Pressure applications of ACh and NA produced concentration-dependent inhibition of the HVA Ca2+ current without affecting the LVA Ca2+ current. The inhibitory action of ACh on the Ca2+ current was blocked by a muscarinic antagonist, atropine. The action of NA was suppressed by an alpha 2-adrenergic antagonist, yohimbine, but not by an alpha 1-adrenergic antagonist, prazosin. Delayed rectifying outward K+ currents and inward rectifying K+ current were not affected by either ACh or NA. Tetrodotoxin-sensitive and -insensitive Na+ currents also remained unaffected under actions of ACh and NA. When recorded with electrode containing guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S), the inhibitory actions of ACh and NA on Ca2+ currents became irreversible. After treatment of SCG neurones with pertussis toxin, the inhibitory action of ACh on the Ca2+ current was almost completely abolished, whereas the action of NA was only partially reduced. The results suggest that ACh and NA differentially inhibit the HVA Ca2+ current via different G proteins coupling muscarinic and alpha 2-adrenergic receptors to Ca2+ channels in rat SCG neurones.

Dual effects of 5-hydroxytryptamine on the heart of a pulmonate, Achatina fulica Férussac

1. The effects of 5-hydroxytryptamine (serotonin) were examined on the isolated ventricle from the African giant snail, Achatina fulica Férussac. 2. Serotonin at concentrations above 10 −9M enhanced the frequency and amplitude of heart beat, while at high concentrations (∼10 −5M) it produced a periodic arrest of beating after potentiation. 3. Methysergide inhibited the potentiation of heart beat and cinanserin strongly antagonized the periodic arrest of beating, suggesting that the two actions of serotonin are mediated through separate receptors. 4. The inhibitory actions of acetylcholine (ACh) on heart beat were also demonstrated. Strychnine partially blocked the responses to ACh. 5. Strychnine did not significantly inhibit the periodic arrest of beating caused by serotonin. High magnesium solution was also ineffective in blocking the two serotonin actions.

Interaction between the inhibitory action of acetylcholine and the alpha-adrenoceptor autoinhibitory feedback system on release of [3H]-noradrenaline from rat atria and rabbit ear artery.

Stimulation-induced increases in the efflux of radioactivity (S-I efflux) were measured in the bathing medium following labelling of the noradrenergic transmitter pools of rat atria and rabbit artery preparations with [3H]-noradrenaline. In atria stimulated with trains of 16 or 60 pulses at 2 Hz, phentolamine enhanced, whereas acetylcholine inhibited S-I efflux. With trains of 16 pulses phentolamine had a smaller enhancing effect than with trains of 60 pulses, whereas the inhibitory effect of acetylcholine was more pronounced with 16 pulses of stimulation. The inhibitory effect of acetylcholine was markedly enhanced by phentolamine when stimulation was with 60 pulses. With 16 pulses of stimulation the effect of acetylcholine was unaltered by phentolamine and abolished by the alpha 2-adrenoceptor agonist 3,4-dihydroxyphenylimino-2-imidazolidine (DPI). Phentolamine had no effect on the negative inotropic effect of acetylcholine on driven left atrial preparations. In arterial preparations stimulated with trains of 30 pulses at 1 Hz, both acetylcholine and clonidine inhibited S-I efflux, whereas yohimbine and idazoxan enhanced S-I efflux. Combining acetylcholine with clonidine did not alter the inhibitory effect of clonidine but the combination of acetylcholine with yohimbine or idazoxan abolished the marked enhancing effects of yohimbine or idazoxan on S-I efflux. These findings indicate that there may be a reciprocal interaction between prejunctional alpha-adrenoceptors and prejunctional muscarinic cholinoceptors.

The effects of chlormethiazole on single unit activity in rat brain; interactions with inhibitory and excitatory neurotransmitters.

Extracellular recordings were made of single unit activity in the brainstem of urethane anaesthetized rats. Drugs were applied by microiontophoresis from multibarrelled micropipettes or administered intraperitoneally. Chlormethiazole (CMZ) caused a decrease in spontaneous firing rate when applied with high currents (greater than 40 nA). When applied with lower currents CMZ did not cause changes in firing rate, but enhanced the inhibitory effects of gamma-aminobutyric acid (GABA), muscimol and glycine in a dose-dependent manner. The inhibitory actions of acetylcholine were not affected. Excitatory responses to glutamate and acetylcholine were unaffected by applications of CMZ which caused potentiation of GABA, muscimol and glycine. When applied at higher currents CMZ caused a decrease in the response to glutamate. Intraperitoneal administration of CMZ (50-600 mumol kg-1) also enhanced responses to microiontophoretically applied GABA, muscimol and glycine. These results are compared with those reported for other anticonvulsant drugs and possible mechanisms of action of CMZ are discussed.

Effects of kinins on isolated blood vessels. Role of endothelium.

Bradykinin (BK) and des-Arg9-BK were used to determine whether the stimulatory and inhibitory actions of the kinins in various isolated vessels require the presence of endothelium and may be mediated by arachidonic acid metabolites. It was found that the presence of intact endothelium is required only for the relaxation of the dog common carotid artery in response to bradykinin. Stimulatory actions of both BK and des-Arg9-BK in arterial (rabbit aorta) and venous (rabbit jugular and mesenteric vein) smooth muscle do not require the presence of endothelium. Inhibition of the arachidonic acid cascade at various levels affects the relaxing action of acetylcholine (rabbit aorta and dog common carotid artery) while being inactive against both the relaxing (dog common carotid artery) and contractile actions (rabbit aorta, rabbit jugular and mesenteric veins) of bradykinin and des-Arg9-BK. Inhibitors of the arachidonic acid cascade also do not affect the inhibitory action of isopropylnoradrenaline on the rabbit aorta. The present results indicate that stimulant actions of kinins in isolated vascular smooth muscles do not require the presence of endothelium. Endothelium is required for the inhibitory actions of acetylcholine and bradykinin but not for that of isopropylnoradrenaline on the dog carotid artery. Moreover, the inhibition of arachidonic acid metabolism only affects the response of isolated vessels to acetylcholine. The present results suggest that several mechanisms may be involved in the inhibition of vascular tone by vasodilators.

Inhibitory action of acetylcholine on potassium uptake of the sinus node.

The effect of endogenously released and exogenously administered acetylcholine on potassium uptake was studied in the sinus node of the guinea pig under different conditions. The results suggest the following conclusions: (1) acetylcholine is released in small amounts in the sinus node perfused in vitro and more so during electrical stimulation; (2) when the muscarinic receptors are blocked, an inhibitory action of endogenously-released acetylcholine on potassium uptake is revealed; (3) the inhibition requires small concentrations of acetylcholine, for 10(-5) mol/i eserine, by preventing acetylcholine hydrolysis, turns the inhibition into a stimulation of potassium uptake; and (4) the inhibitory action of acetylcholine on potassium uptake can be reproduced by administering small amounts of exogenous acetylcholine.

Excitatory and inhibitory actions of acetylcholine on hearts of oyster and mussel.

Excitatory and inhibitory actions of acetylcholine on hearts of oyster and mussel.

The evolution of vascular smooth muscle responses to histamine and 5-hydroxytryptamine. II. Appearance of inhibitory actions of 5-hydroxytryptamine in amphibians.

AbstractSystematic studies on the vascular smooth muscle responses to histamine and 5‐hydroxytryptamine, similar to those previously accomplished in jawless vertebrates and fish, were performed in amphibians (frogs, toads and salamanders). Both intact animals and artificially perfused preparations were studied. The effects were recorded as changes in systemic arterial blood pressure after intravascular administration of drugs or as changes in vascular resistance after introduction of drugs into the perfusion fluid during perfusion at constant flow rate. Responses to adrenaline, noradrenaline and acetylcholine were studied for comparison. The direct or indirect nature of actions produced by the different drugs were evaluated by means of pharmacological blocking agents. The outcome of the studies may be summarized as follows: Marked and specific inhibitory actions of 5‐hydroxytryptamine on vascular smooth muscle, manifest as vasodilatation, are present in all studied species, displaying a feature which has not been demonstrated in jawless vertebrates and fish. In addition, the blood vessels of some amphibians occasionally show a constrictor response to 5‐hydroxytryptamine. The nature of the latter response remains uncertain. Histamine apparently has but negligible influence on amphibian vascular smooth muscle. The inhibitory and stimulatory actions of adrenaline and noradrenaline and the stimulatory action of acetylcholine, pharmacological characteristics of vascular smooth muscle also in more primitive vertebrates, are retained in the amphibians, while the inhibitory action of acetylcholine, like the inhibitory action of 5‐hydroxytryptamine, appears as a new feature.

Serum lactic dehydrogenase activity and folate deficiency in myelosclerosis and other haematological diseases.

Layer 1 neocortical GABAergic interneurons control the excitability of pyramidal neurons through cell-class-specific direct inhibitory and disynaptic disinhibitory circuitry. The engagement of layer 1 inhibitory circuits during behavior is powerfully controlled by the cholinergic neuromodulatory system. Here we report that acetylcholine (ACh) influences the excitability of layer 1 interneurons in a cell-class and activity-dependent manner. Whole-cell recordings from identified layer 1 interneurons of the rat somatosensory neocortex revealed that brief perisomatic application of ACh excited both neurogliaform cells (NGFCs) and classical-accommodating cells (c-ACs) at rest by the activation of nicotinic receptors. In contrast, under active, action potential firing states, ACh excited c-ACs, but inhibited NGFCs through muscarinic receptor-mediated, IP₃ receptor-dependent elevations of intracellular calcium that gated surface-membrane calcium-activated potassium channels. These excitatory and inhibitory actions of ACh could be switched between by brief periods of NGFC action potential firing. Paired recordings demonstrated that cholinergic inhibition of NGFCs disinhibited the apical dendrites of layer 2/3 pyramidal neurons by silencing widespread, GABA_B receptor-mediated, monosynaptic inhibition. Together, these data suggest that the cholinergic system modulates layer 1 inhibitory circuits in an activity-dependent manner to dynamically control dendritic synaptic inhibition of pyramidal neurons.

Effect of acetylcholine on the membrane resistance and threshold of atrial muscle fibres.

THERE is substantial indirect evidence that acetylcholine increases the conductance of the atrial muscle membrane probably by increasing the permeability to K+ and Cl− 1,2. In addition, acetylcholine has an effect on the sodium-carrying system3. These two actions form the basis of a hypothesis suggested by us3 for the possible explanation of the excitatory and inhibitory actions of acetylcholine on atria described by Burn4.

The inhibitory action of acetylcholine with special reference to small doses.

The inhibitory action of acetylcholine with special reference to small doses.