Search results for "Muscarine"

Acetylcholine At Motor Nerves: Storage, Release, and Presynaptic Modulati On By Autoreceptors and Adrenoceptors

1992

Publisher Summary This chapter focuses on the modulation of acetylcholine release from the motor endplate by presynaptic receptors. An individual neuron can regulate its function, the release of transmitters or modulators, through the activation of local feedback loops. After escaping the neuronal membrane and entering the synaptic cleft (or extracellular space), the transmitter activates both the receptors localized at the endorgan (postsynaptic receptors) and the receptors localized at the nerve terminal within its diffusion radius (so-called presynaptic or neuronal receptors). Stimulation of presynaptic receptors triggers the generation of intracellular signals that modify ion channels o…

SUBTYPES OF MUSCARINE RECEPTORS IN THE GUINEA-PIG ILEUM

1986

Regulation of serotonin release from the intestinal mucosa.

1991

Summary In the mammalian intestine serotonin (5-hydroxytryptamine, 5-HT) is present in high concentrations in the enterochromaffin cells. The release of 5-HT from the intestinal mucosa is regulated by a complex pattern of neuronal and humoral inputs to the enterochromaffin cells. The enterochromaffin cells appear to be endowed with different inhibitory ( α 2 -adrenoceptors, GABA A - and GABA B -receptors, histamine H 3 -receptors, receptors for vasoactive intestinal polypeptide and somatostatin) as well as stimulatory receptors ( β -adrenoceptors, muscarine and nicotine receptors). The physiological significance of this complex system of receptors is suggested by experiments which demonstra…

Synthese und pharmakologische Wirkung von carbocyclischen Muskarinanalogen

1974

Als carbocyclische Muskarinanaloga wurden das (3-Hydroxycyclopentylmethyl)trimethyl-ammonium-jodid und dessen Acetat dargestellt und am isolierten Ileum des Meerschweinchens untersucht. Synthesis and Pharmacological Activity of Carbocyclic Analogs of Muscarine As carbocyclic analogs of muscarine (3-hydroxycyclopentylmethyl)trimethylammonium iodide and (3-acetoxycyclopentylmethyl)trimethylammonium iodide were synthesized and tested on the isolated guinea pig ileum.

Pre- and postsynaptic effects of muscarinic agonists in the guinea-pig ileum

1980

The effects of several muscarinic agonists on smooth muscle (postsynaptic effect) and on acetylcholine release (presynaptic effect) were compared in the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum. 1. For release experiments the acetylcholine stores of the preparation were labelled with 3H-choline. Electrical field stimulation in the absence of a cholinesterase inhibitor caused an outflow of tritium that reflected release of 3H-acetylcholine. The agonists oxotremorine, arecaidinepropargylester, methylfurmethide, muscarine, carbachol, arecoline and pilocarpine inhibited the stimulation-induced outflow in a concentration-dependent manner. At the highest concentrat…

Different muscarine receptors mediate the prejunctional inhibition of [3H]-noradrenaline release in rat or guinea-pig iris and the contraction of the…

1989

To investigate the muscarine receptor type mediating inhibition of [3H]-noradrenaline release from the isolated rat and guinea-pig iris we have determined the potency of antimuscarinic drugs to antagonize the methacholine-induced inhibition of [3H]-noradrenaline overflow evoked by field stimulation (3 Hz, 2 min). The prejunctional apparent affinities were compared with those obtained for postjunctional muscarine receptors mediating the methacholine-induced contraction of the isolated rabbit iris sphincter muscle. Prejunctional apparent affinity constants of pirenzepine (6.67), himbacine (8.51), methoctramine (7.92), 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, 8.00), hexahydro-d…

Facilitatory and inhibitory muscarine receptors on the rat phrenic nerve: effects of pirenzepine and dicyclomine

1988

Neuronal transmitter stores of the rat phrenic nerve were labelled by an incubation with [3H]choline. Release of [3H]acetylcholine was elicited either by a short (100 pulses, 5 Hz) or by a long (1500 pulses, 5 or 25 Hz) period of electrical nerve stimulation. Pirenzepine and dicyclomine enhanced transmitter release evoked by the short stimulation period. Both antagonists reduced transmitter release evoked by the long stimulation period. Pirenzepine reduced transmitter release at low concentrations (1 nmol/l) whereas a higher concentration was necessary for the enhancing effect; the opposite pattern was found for dicyclomine. A low concentration of oxotremorine (10 nmol/l) enhanced and a hig…

Choline inhibits acetylcholine release via presynaptic muscarine receptors

1981

The effect of exogenous choline on the outflow of 3H-acetylcholine evoked by field stimulation was studied on the myenteric plexus-longitudinal muscle preparation of the guinea pig. Choline at concentrations of 100 microM and higher depressed the evoked outflow of 3H-acetylcholine in a concentration-dependent manner. The EC50 for the inhibitory action was 300 microM. Scopolamine (10 nM) antagonized the effect of choline which indicates that the inhibition of 3H-acetylcholine outflow is mediated by muscarine receptors. The findings imply that choline at high concentrations does not improve cholinergic synaptic neurotransmission in tissues that are endowed with presynaptic muscarine receptors…

Two types of neuronal muscarine receptors modulating acetylcholine release from guinea-pig myenteric plexus

1985

Longitudinal muscle strips of the guinea-pig ileum were incubated with [3H]choline and the effects of muscarinic agonists on smooth muscle contraction and on spontaneous and electrically-evoked outflow of tritium were studied. Muscarine and pilocarpine concentration-dependently increased both muscle contraction and spontaneous outflow of [3H]ACh, and inhibited the electrically-evoked outflow of [3H]ACh. The increase in spontaneous outflow was prevented by tetrodotoxin and scopolamine, but not by hexamethonium. Oxotremorine (1-100 microM) did not increase the spontaneous outflow of tritium. Pirenzepine in concentrations of 10 and 100 nM hardly affected the muscle contractions induced by pilo…

Control of Acetylcholine Release and of Intestinal Motility by Subtypes of Muscarine Receptors

1988

Two types of neuronal muscarine receptors have been investigated in the myenteric plexus preparation of the guinea-pig small intestine: 1. Presynaptic receptors activation of which inhibits the depolarization-evoked release of acetylcholine. Pirenzepine and dicyclomine have low affinities to the release-inhibitory receptors (pA2 values 6.9 and 7.6) which suggests that the presynaptic receptors (similar to the smooth muscle receptors) belong to the M2 subtype. The inhibition of the electrically-evoked acetylcholine release by muscarine (0.01 - 1 μmol/1) was not affected by forskolin (1μmol/l). This indicates that cyclic AMP is not crucially involved in the muscarinic inhibition of acetylchol…