Oxotremorine M

Biphasic effects of oxotremorine-M on turning behavior induced by caffeine in 6-OHDA-lesioned rats.[Pubmed:15588626]

Eur J Pharmacol. 2004 Dec 3;506(1):71-4.

This work studied the interactions between cholinergic and adenosine systems in the denervated striatum. For that purpose, we evaluated the effects of an intrastriatal administration of the muscarincic receptor agonist, oxotremorine-M on turning behavior induced by systemic caffeine in unilaterally 6-hydroxydopamine-lesioned rats. Low doses of oxotremorine-M (0.1 ng/microl) enhanced, whereas high doses (100 ng/microl) attenuated contralateral turning induced by caffeine. These results support a functional link between muscarinic and adenosinergic systems in the denervated striatum and suggest opposite actions of muscarinic M2 and M1 receptors on caffeine-induced turning behavior.

A novel muscarinic receptor-independent mechanism of KCNQ2/3 potassium channel blockade by Oxotremorine-M.[Pubmed:27590358]

Eur J Pharmacol. 2016 Nov 15;791:221-228.

Inhibition of KCNQ (Kv7) potassium channels by activation of muscarinic acetylcholine receptors has been well established, and the ion currents through these channels have been long known as M-currents. We found that this cross-talk can be reconstituted in Xenopus oocytes by co-transfection of human recombinant muscarinic M1 receptors and KCNQ2/3 potassium channels. Application of the muscarinic acetylcholine receptor agonist Oxotremorine-methiodide (Oxo-M) between voltage pulses to activate KCNQ2/3 channels caused inhibition of the subsequent KCNQ2/3 responses. This effect of Oxo-M was blocked by the muscarinic acetylcholine receptor antagonist atropine. We also found that KCNQ2/3 currents were inhibited when Oxo-M was applied during an ongoing KCNQ2/3 response, an effect that was not blocked by atropine, suggesting that Oxo-M inhibits KCNQ2/3 channels directly. Indeed, also in oocytes that were transfected with only KCNQ2/3 channels, but not with muscarinic M1 receptors, Oxo-M inhibited the KCNQ2/3 response. These results show that besides the usual muscarinic acetylcholine receptor-mediated inhibition, Oxo-M also inhibits KCNQ2/3 channels by a direct mechanism. We subsequently tested xanomeline, which is a chemically distinct muscarinic acetylcholine receptor agonist, and oxotremorine, which is a close analogue of Oxo-M. Both compounds inhibited KCNQ2/3 currents via activation of M1 muscarinic acetylcholine receptors but, in contrast to Oxo-M, they did not directly inhibit KCNQ2/3 channels. Xanomeline and oxotremorine do not contain a positively charged trimethylammonium moiety that is present in Oxo-M, suggesting that such a charged moiety could be a crucial component mediating this newly described direct inhibition of KCNQ2/3 channels.

LY2033298, a positive allosteric modulator at muscarinic M(4) receptors, enhances inhibition by oxotremorine of light-induced phase shifts in hamster circadian activity rhythms.[Pubmed:22610522]

Psychopharmacology (Berl). 2012 Nov;224(2):231-40.

RATIONALE: Entrainment of circadian rhythms to the light-dark cycle is essential for restorative sleep, and abnormal sleep timing is implicated in central nervous system (CNS) disorders like depression, schizophrenia, and Alzheimer's disease. Many transmitters, including acetylcholine, that exerts its actions via muscarinic receptors modulate the suprachiasmatic nucleus, the master pacemaker. OBJECTIVES: Since positive allosteric modulators of muscarinic M(4) receptors are candidates for treatment of mood and cognitive deficits of CNS disorders, it is important to evaluate their circadian actions. MATERIALS AND METHODS: The effects of intraperitoneally applied muscarinic agents on circadian wheel-running rhythms were measured employing hamsters, a model organism for studying activity rhythms. RESULTS: Systemic administration of the muscarinic receptor agonist oxotremorine (0.01-0.04 mg/kg) inhibited light-induced phase delays and advances of hamster circadian wheel-running rhythms. The M(4) positive allosteric modulator, LY2033298 (10-40 mg/kg), had no effect on light-induced phase shifts when administered alone, yet significantly enhanced (at 20 mg/kg) the inhibitory influence of oxotremorine on light-induced phase delays. In addition, the muscarinic receptor antagonist, scopolamine, which was without effect on light-induced phase shifts when administered alone (0.001-0.1 mg/kg), antagonized (at 0.1 mg/kg) the inhibitory effect of oxotremorine and LY2033298 on light-induced phase delays. CONCLUSIONS: These results are the first to demonstrate that systemically applied muscarinic receptor agonists modulate circadian activity rhythms, and they also reveal a specific role for M(4) receptors. It will be of importance to evaluate circadian actions of psychotropic drugs acting via M(4) receptors, since they may display beneficial properties under pathological conditions.

In vitro sensitivity of cholinesterases and [3H]oxotremorine-M binding in heart and brain of adult and aging rats to organophosphorus anticholinesterases.[Pubmed:18761328]

Biochem Pharmacol. 2008 Oct 15;76(8):1047-58.

Organophosphorus (OP) insecticides elicit toxicity via acetylcholinesterase inhibition, allowing acetylcholine accumulation and excessive stimulation of cholinergic receptors. Some OP insecticides bind to additional macromolecules including butyrylcholinesterase and cholinergic receptors. While neurotoxicity from OP anticholinesterases has been extensively studied, effects on cardiac function have received less attention. We compared the in vitro sensitivity of acetylcholinesterase, butyrylcholinesterase and [(3)H]oxotremorine-M binding to muscarinic receptors in the cortex and heart of adult (3 months) and aging (18 months) rats to chlorpyrifos, methyl parathion and their active metabolites chlorpyrifos oxon and methyl paraoxon. Using selective inhibitors, the great majority of cholinesterase in brain was defined as acetylcholinesterase, while butyrylcholinesterase was the major cholinesterase in heart, regardless of age. In the heart, butyrylcholinesterase was markedly more sensitive than acetylcholinesterase to inhibition by chlorpyrifos oxon, and butyrylcholinesterase in tissues from aging rats was more sensitive than enzyme from adults, possibly due to differences in A-esterase mediated detoxification. Relatively similar differences were noted in brain. In contrast, acetylcholinesterase was more sensitive than butyrylcholinesterase to methyl paraoxon in both heart and brain, but no age-related differences were noted. Both oxons displaced [(3)H]oxotremorine-M binding in heart and brain of both age groups in a concentration-dependent manner. Chlorpyrifos had no effect but methyl parathion was a potent displacer of binding in heart and brain of both age groups. Such OP and age-related differences in interactions with cholinergic macromolecules may be important because of potential for environmental exposures to insecticides as well as the use of anticholinesterases in age-related neurological disorders.

Functional properties of muscarinic receptor subtypes Hm1, Hm3 and Hm5 expressed in Sf9 cells using the baculovirus expression system.[Pubmed:8930161]

J Pharmacol Exp Ther. 1996 Nov;279(2):593-601.

The human muscarinic ACh receptor subtypes m1, m3 and m5 have been expressed in Sf9 cells using the baculovirus expression system. Stimulation of all three subtypes with CCh caused an increase in inositol-1,4,5-trisphosphate and intracellular Ca++. The increase in cytosolic free Ca++ was to a large extent due to influx. The levels of receptors (< 0.1-1 pmol/mg protein) increased with infection time in a narrow time span (24-36 h). The changes in the receptor densities did not significantly affect the EC50 values of CCh-mediated Ca++ mobilization with the m3 or the m5 subtype. The EC50 value was higher with the m1 receptor at low expression levels (approximately 100 fmol/mg protein), and it decreased with an increase in receptor density. The receptor subtypes displayed no gross differences in their response to oxotremorine-M, which behaved as a full agonist, or to oxotremorine and pilocarpine, which were less active. With the m3 subtype, there was an increase in the maximal response to oxotremorine with longer infection times. The results demonstrate that the recombinant muscarinic receptors, expressed in Sf9 cells, show many of the characteristics of endogenously expressed receptors when studied at low expression levels and that the receptor density may significantly affect the receptor pharmacology.

Oxotremorine M iodide is a potent and non-selective muscarinic acetylcholine receptor (mAChR) agonist. Oxotremorine M iodide potentiates NMDA receptors by muscarinic receptor dependent and independent mechanisms.

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