Scopolamine

Scopolamine is a high affinity (nM) muscarinic antagonist. 5-HT3 receptor-responses are reversibly inhibited by Scopolamine with an IC50 of 2.09 μM.

In Vitro:Application of Scopolamine to oocytes expressing 5-HT3 receptors does not elicit a response when applied alone, but causes a concentration-dependent inhibition of the response during a co-application of 2 μM 5-HT. The pIC50 value for Scopolamine is 5.68±0.05 (IC50=2.09 μM, n=6) with a Hill Slope of 1.06 ± 0.05. This gave a Kb of 3.23 μM. The same concentration-dependent effect is also seen when Scopolamine is applied during the 5-HT application. To further test for a competitive binding at the 5-HT3 receptor, the competition of unlabelled Scopolamine is measured with [3H]granisetron, an established high-affinity competitive antagonist at these receptors. Scopolamine displays concentration-dependent competition with 0.6 nM [3H]granisetron (~Kd), yielding an average pKi of 5.17±0.24 (Ki=6.76 μM, n=3)[1].

In Vivo:In the histopathology study, there is no significant change in the histology of the brain. However, it is observed that there is a reduction in density of cells in the hippocampus of the control mice pretreated with Scopolamine who received only distilled water[2]. Scopolamine administration alone significantly increases the activity of Acetylcholinesterase enzyme (AchE) (7.98±0.065; P<0.001) when compared to the normal group (3.06±0.296). The animals treated with Scopolamine report a significant increase (34.61±4.85; P<0.01) in levels of malondialdehyde (MDA) as compared to the normal group (12.82±2.86). The Scopolamine-treated group shows significant decrease in reduced glutathione (GSH) level (P<0.001; 0.1504±0.03) as compared to the normal group (0.3906±0.02). The Scopolamine-treated rats show a significant increase in the concentration ofβ amyloid (Aβ1-42) (P<0.001; 146.2±1.74) as compared to the normal group (43.21±3.46)[3].

References:
[1]. Lochner M, et al. The muscarinic antagonists Scopolamine and atropine are competitive antagonists at 5-HT3 receptors. Neuropharmacology. 2016 Sep;108:220-8. [2]. O ET, et al. COGNITIVE-ENHANCING PROPERTIES OF MORINDA LUCIDA (RUBIACEAE) AND PELTOPHORUM PTEROCARPUM (FABACEAE) IN SCOPOLAMINE-INDUCED AMNESIC MICE. Afr J Tradit Complement Altern Med. 2017 Mar 1;14(3):136-141. [3]. Pattanashetti LA, et al. Evaluation of neuroprotective effect of Quercetin with Donepezil in Scopolamine-induced amnesia in rats. Indian J Pharmacol. 2017 Jan-Feb;49(1):60-64.

Galantamine reverses scopolamine-induced behavioral alterations in Dugesia tigrina.[Pubmed:24402079]

Invert Neurosci. 2014 Sep;14(2):91-101.

In planaria (Dugesia tigrina), Scopolamine, a nonselective muscarinic receptor antagonist, induced distinct behaviors of attenuated motility and C-like hyperactivity. Planarian locomotor velocity (pLMV) displayed a dose-dependent negative correlation with Scopolamine concentrations from 0.001 to 1.0 mM, and a further increase in Scopolamine concentration to 2.25 mM did not further decrease pLMV. Planarian hyperactivity counts was dose-dependently increased following pretreatment with Scopolamine concentrations from 0.001 to 0.5 mM and then decreased for Scopolamine concentrations >/= 1 mM. Planarian learning and memory investigated using classical Pavlovian conditioning experiments demonstrated that Scopolamine (1 mM) negatively influenced associative learning indicated by a significant decrease in % positive behaviors from 86 % (control) to 14 % (1 mM Scopolamine) and similarly altered memory retention, which is indicated by a decrease in % positive behaviors from 69 % (control) to 27 % (1 mM Scopolamine). Galantamine demonstrated a complex behavior in planarian motility experiments since co-application of low concentrations of galantamine (0.001 and 0.01 mM) protected planaria against 1 mM Scopolamine-induced motility impairments; however, pLMV was significantly decreased when planaria were tested in the presence of 0.1 mM galantamine alone. Effects of co-treatment of Scopolamine and galantamine on memory retention in planaria via classical Pavlovian conditioning experiments showed that galantamine (0.01 mM) partially reversed Scopolamine (1 mM)-induced memory deficits in planaria as the % positive behaviors increased from 27 to 63 %. The results demonstrate, for the first time in planaria, Scopolamine's effects in causing learning and memory impairments and galantamine's ability in reversing Scopolamine-induced memory impairments.

M1 and m2 muscarinic receptor subtypes regulate antidepressant-like effects of the rapidly acting antidepressant scopolamine.[Pubmed:25187432]

J Pharmacol Exp Ther. 2014 Nov;351(2):448-56.

Scopolamine produces rapid and significant symptom improvement in patients with depression, and most notably in patients who do not respond to current antidepressant treatments. Scopolamine is a nonselective muscarinic acetylcholine receptor antagonist, and it is not known which one or more of the five receptor subtypes in the muscarinic family are mediating these therapeutic effects. We used the mouse forced-swim test, an antidepressant detecting assay, in wild-type and transgenic mice in which each muscarinic receptor subtype had been genetically deleted to define the relevant receptor subtypes. Only the M1 and M2 knockout (KO) mice had a blunted response to Scopolamine in the forced-swim assay. In contrast, the effects of the tricyclic antidepressant imipramine were not significantly altered by gene deletion of any of the five muscarinic receptors. The muscarinic antagonists biperiden, pirenzepine, and VU0255035 (N-[3-oxo-3-[4-(4-pyridinyl)-1-piper azinyl]propyl]-2,1,3-benzothiadiazole-4-sulfonamide) with selectivity for M1 over M2 receptors also demonstrated activity in the forced-swim test, which was attenuated in M1 but not M2 receptor KO mice. An antagonist with selectivity of M2 over M1 receptors (SCH226206 [(2-amino-3-methyl-phenyl)-[4-[4-[[4-(3 chlorophenyl)sulfonylphenyl]methyl]-1-piperidyl]-1-piperidyl]methanone]) was also active in the forced-swim assay, and the effects were deleted in M2 (-/-) mice. Brain exposure and locomotor activity in the KO mice demonstrated that these behavioral effects of Scopolamine are pharmacodynamic in nature. These data establish muscarinic M1 and M2 receptors as sufficient to generate behavioral effects consistent with an antidepressant phenotype and therefore as potential targets in the antidepressant effects of Scopolamine.

Rubus coreanus Miquel ameliorates scopolamine-induced memory impairments in ICR mice.[Pubmed:25121635]

J Med Food. 2014 Oct;17(10):1049-56.

The present study investigated the effect of Rubus coreanus Miquel (RCM) on Scopolamine-induced memory impairments in ICR mice. Mice were orally administrated RCM for 4 weeks and Scopolamine was intraperitoneally injected into mice to induce memory impairment. RCM improved the Scopolamine-induced memory impairment in mice. The increase of acetylcholinesterase activity caused by Scopolamine was significantly attenuated by RCM treatment. RCM increased the levels of acetylcholine in the brain and serum of mice. The expression of choline acetyltransferase, phospho-cyclic AMP response element-binding protein, and phospho-extracellular signal-regulated kinase was significantly increased within the brain of mice treated with RCM. The brain antioxidant enzyme activity decreased by Scopolamine was increased by RCM. These results demonstrate that RCM exerts a memory-enhancing effect via the improvement of cholinergic function and the potentiated antioxidant activity in memory-impaired mice. The results suggest that RCM may be a useful agent for improving memory impairment.

Antidepressant treatment history as a predictor of response to scopolamine: clinical implications.[Pubmed:24767003]

J Affect Disord. 2014 Jun;162:39-42.

BACKGROUND: The intravenous administration of Scopolamine produces rapid antidepressant effects. Generally, failing multiple previous antidepressant trials is associated with a poor prognosis for response to future medications. This study evaluated whether treatment history predicts antidepressant response to Scopolamine. METHODS: Treatment resistant patients (2 failed medication trials) (n=31) and treatment naive patients (no exposure to psychotropic medication) (n=31) with recurrent major depressive or bipolar disorder participated in a double-blind, placebo-controlled, crossover clinical trial. Following a placebo lead-in, participants randomly received P/S or S/P (P=3 placebo; S=3 Scopolamine (4ug/kg) sessions 3 to 5 days apart). The Montgomery-Asberg Depression Rating Scale (MADRS) was the primary outcome measure. A linear mixed model was used to examine the interaction between clinical response and treatment history, adjusting for baseline MADRS. RESULTS: Treatment resistant and treatment naive subjects combined responded significantly to Scopolamine compared to placebo (F=15.06, p<0.001). Reduction in depressive symptoms was significant by the first post-Scopolamine session (F=42.75, p<0.001). A treatment history by Scopolamine session interaction (F=3.37, p=0.04) indicated treatment naive subjects had lower MADRS scores than treatment resistant patients; this was significant after the second Scopolamine infusion (t=2.15, p=0.03). LIMITATIONS: Post-hoc analysis: Also, we used a single regimen to administer Scopolamine, and smokers were excluded from the sample, limiting generalizability. CONCLUSIONS: Treatment naive and treatment resistant patients showed improved clinical symptoms following Scopolamine, while those who were treatment naive showed greater improvement. Scopolamine rapidly reduces symptoms in both treatment history groups, and demonstrates sustained improvement even in treatment resistant patients.