Muscarinic Cholinergic Receptor Antagonist Research Articles

The effects and mechanisms of the action of galangin on spatial memory in rats.

Galangin, a flavonoid compound with acetylcholinesterase inhibitory activity, may improve cognitive functions by enhancing cholinergic transmission. We aimed to investigate the effects of galangin on spatial memory impairment in rats. The effects of galangin (50 and 100 mg/kg) and reference anti-dementia drug donepezil (1mg/kg) administrations were examined on memory impairment induced by the muscarinic cholinergic receptor antagonist scopolamine or the nicotinic cholinergic receptor antagonist mecamylamine in the Morris water maze (MWM) test. Hippocampal acetylcholine concentrations were also determined. Galangin 50 and 100 mg/kg significantly decreased the mean distance to platform and increased the time spent in the escape platform quadrant in scopolamine-treated rats. Galangin 100 mg/kg significantly decreased the mean distance to platform and increased the time spent in the escape platform quadrant in mecamylamine-treated rats. The effects of galangin in the MWM were comparable with donepezil. Scopolamine and mecamylamine decreased acetylcholine concentrations, whereas galangin both alone and with mecamylamine or scopolamine administration increased acetylcholine concentrations. Galangin improved memory impairment comparable to donepezil and nicotinic and muscarinic receptors may be involved in this effect. Galangin may be considered as a promising flavonoid in the prevention and treatment of memory impairment in Alzheimer's disease and other dementias (Fig. 7,Ref. 37).

Overnight transdermal scopolamine patch administration has no clear effect on cognition and emotional processing in healthy volunteers.

There has been increasing interest in the antidepressant effects of the muscarinic cholinergic receptor antagonist scopolamine. Here we assess, for the first time, whether a transdermal scopolamine patch is sufficient to induce changes in cognition that are consistent with the reported cognitive and antidepressant effects of scopolamine. A scopolamine or placebo patch was administered to healthy volunteers ( n=33) for 17 h in a double-blind, between-subject procedure. There was no clear effect of scopolamine patch on emotional cognition, verbal or working memory, suggesting that the effective dose of scopolamine available through the patch is too low to represent a viable antidepressant mechanism.

EEG dissociation induced by muscarinic receptor antagonists: Coherent 40 Hz oscillations in a background of slow waves and spindles

Mesopontine and basal forebrain cholinergic neurons are involved in the control of behavioral states and cognitive functions. Animals treated with cholinergic muscarinic receptor antagonists display a dissociated state characterized by behavioral wakefulness (W) associated with high amplitude slow oscillations and spindles in the electroencephalogram (EEG), similar to those that occur during non-REM (NREM) sleep.Oscillations in the gamma frequency band (≈ 40 Hz) of the EEG also play a critical role during W and cognition. Hence, the present study was conducted to determine the effect of muscarinic antagonists on the EEG gamma band power and coherence.Five cats were implanted with electrodes in different cortices to monitor the EEG. The effects of atropine and scopolamine on power and coherence within the low gamma frequency band (30–45 Hz) from pairs of EEG recordings were analyzed and compared to gamma activity during sleep and W.Muscarinic antagonists induced a NREM sleep-like EEG profile that was accompanied by a large increase in gamma power and coherence. The values of gamma coherence were similar to that occurring during alert W (AW), and greater than in quiet W, NREM and REM sleep.We conclude that under atropine or scopolamine, functional interactions between cortical areas in the gamma frequency band remain high, as they are during AW. This significant functional connectivity at high frequency may explain why the animals remain awake in spite of the presence of slow waves and spindles.

Diosmin is neuroprotective in a rat model of scopolamine-induced cognitive impairment.

Scopolamine, a muscarinic cholinergic receptor antagonist, is used as a standard pharmaceutical model for inducing cognitive impairment in animals. Several cognitive behaviors, such as motor function, anxiety, short-term memory, attention are affected by injections of scopolamine. In this study, we have assessed the effects of administration of the diosmin (DM, 50 and 100 mg/kg), before injection of 0.4 mg/kg of scopolamine on memory and motor function, the hippocampal dentate gyrus (DG) electrophysiological activity as well as brain inflammation. Eighty male rats were randomly divided into five groups (Control, Veh + scopolamine, DM (50) + scopolamine and DM (100) + scopolamine, donepezil (DP) + scopolamine, n = 16). Scopolamine (0.4 mg/kg, i.p.) is used, in order to induce an animal model of cognitive impairment. Rats pretreated with doses of 50 and 100 mg/kg of DM, 3 mg/kg of DP and/or normal saline for 7 days, before injection of scopolamine. Long-term potentiation (LTP) recording was done for electrophysiological activity assessment. Passive avoidance task (PAT), rotarod and spatial memory tests were evaluated, using a shuttle box, rotarod apparatus and Morris water maze (MWM), respectively. Results indicated that DM at doses of 50 and 100 mg/kg, significantly reversed the LTP (amplitude and slope) impairment of the hippocampal DG neurons, induced by scopolamine. Also, DM at doses of 50 and 100 mg/kg increased the percent of the total time that animals spent in goal quarter, the step-through latency (s) and bar latency time in an animal model of cognitive impairment (p < 0.01 and p < 0.001), respectively. The concentrations of TNF-α in hippocampus of the DM and donepezil groups was significantly lower than the Veh + scopolamine group (p < 0.01). This study revealed that the DM is effective in preventing the disruption of synaptic plasticity and cognitive impairments, induced by scopolamine. The positive effects of DM may be mediated through a decline in the TNF- α concentrations in hippocampus as a pro-inflammatory cytokine. Thus, the acquired results suggested that the DM can be used, as a useful and suitable agent for memory restoration, in the treatment of dementia, seen in elderlies.

The potential antidepressant action and adverse effects profile of scopolamine co-administered with the mGlu7 receptor allosteric agonist AMN082 in mice

Scopolamine, a muscarinic cholinergic receptor antagonist, exerts fast and prolonged antidepressant effects in the clinic. In contrast, the current treatments for major depressive disorder (MDD) require long-term drug administration. On the other hand, the sole use of scopolamine might be related to the high risk of adverse effects. Therefore, it may be preferable to reduce its therapeutic dose. A new approach might include the co-administration of low-dose scopolamine with selected ligands of metabotropic glutamate (mGlu) receptors, which are known to possess antidepressant-like activity in several rodent tests and models of depression. The aim of the present study was to evaluate the potential antidepressant activity of low-dose scopolamine combined with an allosteric agonist of mGlu7 receptors, AMN082 in C57BL/6 mice. It was found that the combination of scopolamine (0.1 mg/kg) and AMN082 (1 mg/kg) exerted significant antidepressant-like effects in the tail suspension test (TST), but these effects were not observed in the mGlu7−/− mice. Furthermore, low-dose AMN082 co-administered with low-doses scopolamine (0.03 and 0.1 mg/kg) induced antidepressant-like activity in the forced swim test (FST) in mice. The tested compounds did not affect locomotor activity and did not impair spatial memory in the Morris water maze (MWM) test or motor coordination in the rotarod test. The results strongly indicated that there is an enhanced antidepressant-like action of scopolamine by AMN082. Co-administration of scopolamine with AMN082 might be a new strategy with better efficacy and a lower risk of adverse effects compared with the sole use of scopolamine or AMN082.

Murine genetic variance in muscarinic cholinergic receptor antagonism of acquisition and expression of sucrose-conditioned flavor preferences in three inbred mouse strains

Conditioned flavor preferences (CFP) are elicited by sucrose relative to saccharin in inbred mice with both the robustness of the preferences and sensitivity to pharmacological receptor antagonists sensitive to genetic variance. Dopamine, opioid and N-methyl-d-aspartate receptor antagonists differentially interfere with the acquisition (learning) and expression (maintenance) of sucrose-CFP in BALB/c and SWR inbred mice. Further, the muscarinic cholinergic receptor antagonist, scopolamine (SCOP) more potently reduces both sucrose and saccharin intake in BALB/c and C57BL/6 relative to SWR inbred mice. The present study examined whether SCOP altered the expression and acquisition of sucrose-CFP in BALB/c, C57BL/6 and SWR mice. In expression experiments, food-restricted mice alternately consumed a flavored (CS+, e.g., cherry, 5 sessions) 16% sucrose solution and a differently-flavored (CS−, e.g., grape, 5 sessions) 0.05% saccharin solution. Two-bottle CS choice tests with the two flavors mixed in 0.2% saccharin solutions occurred following vehicle or SCOP at doses of 1 or 5 mg/kg. SCOP significantly reduced the magnitude of the expression of sucrose-CFP in BALB/c, but not either C57BL/6 or SWR mice. In acquisition experiments, separate groups of BALB/c, C57BL/6 and SWR mice were treated prior to acquisition training sessions with vehicle or 2.5 or 5 mg/kg SCOP doses that was followed by six two-bottle CS choice tests without injections. SCOP dose-dependently reduced (1 mg/kg) and eliminated (2.5 mg/kg) the acquisition of sucrose-CFP in BALB/c mice, and reduced the magnitude of acquisition of sucrose-CFP in SWR mice. In contrast, neither SCOP dose affected the acquisition of sucrose-CFP in C57BL/6 mice. Thus, muscarinic cholinergic receptor signaling is essential for the learning of sucrose-CFP in BALB/c mice, to a lesser degree in SWR mice, but not in C57BL/6 mice. Murine genetic variance differentially modulates muscarinic cholinergic receptor control of sweet intake per se relative to learned conditioned flavor preferences of sweets.

Modulation of nesfatin-1-induced cardiovascular effects by the central cholinergic system

Nesfatin-1, a peptide whose receptor is yet to be identified, has been shown to be involved in the modulation of feeding, stress, and metabolic responses. Recently, increasing evidence has supported a modulatory role of nesfatin-1 in cardiovascular activity. We have previously reported that nesfatin-1 causes an increase in blood pressure in normotensive and hypotensive rats by increasing plasma catecholamine, vasopressin, and renin levels. Recent reports suggest that nesfatin-1 may activate the central cholinergic system. However, there is no evidence showing an interaction between central nesfatin-1 and the cholinergic system. Therefore, this study aimed to determine whether the central cholinergic system may have a functional role in the nesfatin-1-induced cardiovascular effect observed in normotensive rats.Intracerebroventricular injection of nesfatin-1 caused short-term increases in mean arterial pressure and heart rate responses including bradycardic/tachycardic phases in normotensive animals. Central injection of nesfatin-1 increased the acetylcholine and choline levels in the posterior hypothalamus, as shown in microdialysis studies. Central pretreatment with the cholinergic muscarinic receptor antagonist atropine and/or nicotinic receptor antagonist mecamylamine blocked nesfatin-1-induced cardiovascular effects. In conclusion, the results show that centrally administered nesfatin-1 produces a pressor effect on blood pressure and heart rate responses including bradycardic/tachycardic phases in normotensive rats. Moreover, according to our findings, the central cholinergic system can modulate nesfatin-1-evoked cardiovascular activity.

Pharmacological properties of revefenacin (TD-4208), a novel, nebulized long-acting, and lung selective muscarinic antagonist, at human recombinant muscarinic receptors and in rat, guinea pig, and human isolated airway tissues.

Revefenacin (TD‐4208) is a novel, long‐acting, and lung‐selective muscarinic cholinergic receptor (mAChR) antagonist in development as a nebulized inhalation solution for the treatment of chronic obstructive pulmonary disease (COPD) patients. This study evaluated the pharmacology of revefenacin at human recombinant mAChRs and in airway tissues from rats, guinea pigs, and humans. At human recombinant mAChRs, revefenacin displayed high affinity (pKI = 8.2‐9.8) and behaved as a competitive antagonist (pKI, apparent = 9.4‐10.9) at the five human recombinant mAChRs. Kinetic studies demonstrated that revefenacin dissociated significantly slower from the hM3 (t 1/2 = 82 minutes) compared to the hM 2 (t 1/2 = 6.9 minutes) mAChR at 37°C, thereby making it kinetically selective for the former subtype. Similarly, in functional studies, revefenacin‐mediated antagonism of acetylcholine (ACh)‐evoked calcium mobilization responses were reversed less rapidly at hM3 compared to the hM2 mAChR. In isolated tracheal tissues from rat and guinea pig and isolated bronchial tissues from humans, revefenacin potently antagonized mAChR‐mediated contractile responses. Furthermore, the antagonistic effects of revefenacin in rat, guinea pig, and human airway tissues were slowly reversible (t 1/2 of 13.3, >16, and >10 hours, respectively). These data demonstrate that revefenacin is a potent, high affinity, and selective functional mAChR antagonist with kinetic selectivity for the hM3 receptor and produces potent and long‐lasting antagonism of mAChR‐mediated contractile responses in rat, guinea pig, and human airway tissue. These data suggest that revefenacin has the potential to be a potent once‐daily dosed inhaled bronchodilator in COPD patients.

Comparison of Memory Impairment and Oxidative Stress Following Single or Repeated Doses Administration of Scopolamine in Rat Hippocampus.

Introduction:Scopolamine, a muscarinic cholinergic receptor antagonist, is widely used to induce memory impairment in experimental animals. The present study aims to compare memory impairment and oxidative stress following single and repeated doses administration of scopolamine.Methods:A group of rats received a single shot of scopolamine in different doses (0.5, 1, or 3 mg/kg, IP) 24 hours after the passive avoidance training. Then the memory retrieval test was performed 30 minutes and 7 days after the injection. In the other experiment, rats received similar doses of scopolamine for 7 consecutive days, 24 hours after the training session. Then the memory retrieval test was performed 30 minutes and 7 days after the last injection. Acetylcholinesterase (AChE) activity and lipid peroxidation were measured in their hippocampus tissue, too.Results:Scopolamine administered in repeated doses caused more impairment in memory function compared to single dose injection based on the evaluation 30 minutes after injection. Moreover, the memory impairment persisted for 7 days only in repeated doses treated groups. Increase in acetylcholinesterase activity and lipid peroxidation in both groups was observed 30 minutes after scopolamine administration. These abnormal increases persisted for 7 days only in repeated doses treated groups. Increased AChE activity and lipid peroxidation was well correlated with behavioral deficit. Also AChE activity was well associated with lipid peroxidation.Conclusion:The results of present study showed that repeated administration of scopolamine induced results in memory impairment. This effect can be due to long-lasting oxidative stress which may damage the hippocampus tissue.

Dichotomous Effects of Mu Opioid Receptor Activation on Striatal Low-Threshold Spike Interneurons.

Striatal low-threshold spike interneurons (LTSIs) are tonically active neurons that express GABA and nitric oxide synthase and are involved in information processing as well as neurovascular coupling. While mu opioid receptors (MORs) and their ligand encephalin are prominent in the striatum, their action on LTSIs has not been investigated. We addressed this issue carrying out whole-cell recordings in transgenic mice in which the NPY-expressing neurons are marked with green fluorescent protein (GFP). The MOR agonist (D-Ala(2), N-MePhe(4), Gly-ol)-enkephalin (DAMGO) produced dual effects on subpopulations of LTSIs. DAMGO caused inhibitory effects, accompanied by decreases of spontaneous firing, in 62% of LTSIs, while depolarizing effects (accompanied by an increase in spontaneous firing) were observed in 23% of LTSIs tested. The dual effects of DAMGO persisted in the presence of tetrodotoxin (TTX), a sodium channel blocker or in the presence of the nicotinic acetylcholine receptor antagonist mecamylamine. However, in the presence of either the GABAA receptor antagonist picrotoxin or the muscarinic cholinergic receptor antagonist atropine, DAMGO only elicited inhibitory effects on LTSIs. Furthermore, we found that DAMGO decreased the amplitude and frequency of spontaneous GABAergic events. Unexpectedly, these effects of DAMGO on spontaneous GABAergic events disappeared after blocking of the muscarinic and nicotinic cholinergic blockers, showing that GABA inputs to LTSIs are not directly modulated by presynaptic MORs. These finding suggest that activation of MORs affect LTSIs both directly and indirectly, through modulation of GABAergic and cholinergic tones. The complex balance between direct and indirect effects determines the net effect of DAMGO on LTSIs.

Murine genetic variance in muscarinic cholinergic receptor antagonism of sucrose and saccharin solution intakes in three inbred mouse strains

Nutritive (e.g., sucrose) and non-nutritive (e.g., saccharin) sweeteners stimulate intake in inbred mouse strains. BALB/c, SWR and C57BL/6 mice differ in the ability of dopamine (DA) D1 (SCH23390) and opioid (naltrexone) receptor antagonism to alter sucrose intake. Whereas SCH23390 comparably reduced cumulative sucrose intake in all three strains, naltrexone reduced cumulative sucrose intake maximally in C57/BL/6 mice, in intermediate fashion in BALB/c mice, but not in SWR mice. Whereas cumulative saccharin intake was reduced by DA D1 receptor antagonism in BALB/c and SWR mice, naltrexone was more potent in SWR relative to BALB/c mice. The present study first examined whether SCH23390 (50–1600nmol/kg) and naltrexone (0.01–5mg/kg) altered saccharin intake in C57BL/6 mice. Given that scopolamine (SCOP), a muscarinic cholinergic receptor antagonist, reduces sweet intake in outbred rats, a second experiment examined whether SCOP (0.1–10mg/kg) altered 0.2% saccharin and 10% sucrose intakes in BALB/c, SWR and C57BL/6 mice. Cumulative saccharin intake was significantly reduced by SCH23390 (200–1600nmol/kg; ID40=175nmol/kg) and naltrexone (0.1–5mg/kg; ID40>5mg/kg) in C57BL/6 mice. Cumulative sucrose intake was significantly reduced following SCOP in C57BL/6 (0.1–10mg/kg; ID40=2.32mg/kg) and BALB/c (2.5–10mg/kg; ID40=0.52mg/kg) mice. In contrast, SWR mice (ID40=41.61mg/kg) only displayed transient (15min) reductions in sucrose intake following SCOP (2.5–10mg/kg). Cumulative saccharin intake was significantly reduced following SCOP in C57BL/6 and BALB/c mice (0.1–10mg/kg; ID40<0.1mg/kg). In contrast, SWR mice (ID40=2.28mg/kg) displayed smaller significant reductions in saccharin intake following SCOP (0.1–10mg/kg). These data indicate that although both nutritive and non-nutritive sweet intakes are governed by muscarinic cholinergic receptor signaling, this process is subject to murine genetic variance with greater sensitivity observed in C57BL/6 and BALB/c relative to SWR inbred mouse strains.

The memory ameliorating effects of DHP1402, an herbal mixture, on cholinergic blockade-induced cognitive dysfunction in mice

Ethnopharmacological relevanceThe seeds of Ziziphus jujuba var. spinosa (Bunge) Hu ex H.F Chow (Rhamnaceae) and the roots of Codonopsis lanceolata (Siedbold & Zucc.) Benth. & Hook. f ex Trautv. (Campanulaceae), contained in the DHP1402, have long been used for treating dementia or hypomnesia as folk medicine. Aim of the studyIt has been reported that Z. jujuba var. spinosa and C. lanceolata are effective in improving cognitive function, but via different mechanisms. Therefore, in the present study, we evaluated the synergistic effects of Z. jujuba var. spinosa and C. lanceolata on scopolamine-induced memory impairment. Materials and methodsScopolamine, a cholinergic muscarinic receptor antagonist, was used to induce cognitive dysfunction. We employed several behavioral tasks to estimate the synergistic effect of the seeds of Z. jujuba var. spinosa and the roots of C. lanceolata. In addition, we introduced the Western blotting, the antagonism passive avoidance task to investigate a synergistic effect of an herbal formulation. ResultsSynergistic effects of a combination of Z. jujuba var. spinosa and C. lanceolata at a 5:1 ratio [(w/w), DHP1402] were observed against cognitive dysfunction in the passive avoidance and Y-maze tasks. DHP1402 also ameliorated memory deficits in a dose-dependent manner in these behavioral tasks, as well as in the Morris water maze task. According to the Western blot results, the phosphorylation levels of protein kinase A (PKA), extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB) in the hippocampus were also increased in a synergistic manner after the administration of DHP1402. In addition, we found that the effects of DHP1402 on cognitive function were mediated by N-methyl-D-aspartate (NMDA) receptor signalling, based on the antagonism studies. Furthermore, we found that DHP1402 has inhibitory activity against acetylcholinesterase (AChE). ConclusionDHP1402 attenuates cholinergic blockade-induced cognitive dysfunction through NMDA receptor modulation, PKA-ERK-CREB pathway activation, and AChE inhibition. Therefore, DHP1402 could be a candidate for alleviating cognitive dysfunction.

Muscarinic cholinergic receptor antagonists in the VTA and RMTg have opposite effects on morphine-induced locomotion in mice

The ventral tegmental area (VTA) and the rostromedial tegmental nucleus (RMTg) each contribute to opiate reward and each receive inputs from the laterodorsal tegmental and pedunculopontine tegmental nuclei, the two principle brainstem cholinergic cell groups. We compared the contributions of VTA or RMTg muscarinic cholinergic receptors to locomotion induced by morphine infusions into the same sites. VTA co-infusion of atropine completely blocked VTA morphine-induced locomotion providing additional support for the important role of VTA muscarinic cholinergic receptors in the stimulant effects of opiates. By contrast, RMTg co-infusion of atropine increased RMTg morphine-induced locomotion. Furthermore, RMTg co-infusion of the M3-selective antagonist 4-DAMP, but not the M4-selective antagonist Tropicamide, strongly increased RMTg morphine-induced locomotion. RMTg infusions of 4-DAMP, but not of Tropicamide, by themselves strongly increased drug-free locomotion. Muscarinic cholinergic receptors in the RMTg thus also contribute to the stimulant effects of morphine, but in a way opposite to those in VTA. We suggest that the net effect of endogenous cholinergic input to the RMTg on drug-free and on RMTg morphine-induced locomotion is inhibitory.

The change of picrotoxin-induced epileptiform discharges to the beta oscillation by carbachol in rat hippocampal slices.

The study aimed to determine whether and how the activation of the acetylcholine receptor affects epileptiform discharges in the CA3 region in a rat hippocampus. Picrotoxin (100 μM), a GABAA receptor antagonist, was applied to a hippocampal slice to induce epileptiform discharges. The effects of the cholinergic agonist, carbachol, on the discharges were examined at the several concentrations (1–30 μM). Carbachol had different impacts on epileptiform discharges at the different concentrations. Relatively low concentrations of carbachol (<10 μM) increased the frequency but decreased the amplitude of the discharges. At 10 μM, carbachol induced the discharges, including bursts of theta frequency oscillations. At 30 μM, carbachol could induce bursts of beta frequency oscillations instead of epileptiform discharges. The amplitudes of the oscillations were smaller than those of the discharges. Carbachol suppressed the evoked population EPSPs (pEPSPs) in a dose-dependent manner. These effects were blocked by the muscarinic cholinergic receptor antagonist atropine sulfate. The high level of muscarinic receptor activation can replace epileptiform discharges with theta or beta oscillation. These results suggest that the dose-dependent alternation of the acetylcholine receptor activation may provide the three different stages the epileptiform discharges, the bursts of theta oscillation, and the bursts of the beta oscillation.

Muscarinic, nicotinic and GABAergic receptor signaling differentially mediate fat-conditioned flavor preferences in rats

Rats display conditioned flavor preferences (CFP) for fats. Previous studies demonstrated that whereas expression of an already-acquired corn oil (CO)-CFP was mildly reduced by dopamine (DA) D1, DA D2, NMDA or opioid receptor antagonists, the acquisition or learning of CO-CFP was eliminated by NMDA antagonists, and significantly reduced by DA D1 and D2, but not opioid antagonists. Previous studies of fructose-CFP demonstrated that muscarinic (scopolamine) and nicotinic (mecamylamine) cholinergic receptor antagonists and GABAB (baclofen) receptor agonism reduced the expression of this acquired response, and that scopolamine, but not mecamylamine or baclofen eliminated the acquisition or learning of this response. The present study examined scopolamine, mecamylamine or baclofen effects upon expression or acquisition of CO-CFP. For expression, rats were trained over 10 sessions with CS+ (3.5% CO) and CS− (0.9% CO) flavored solutions without drugs. Two-bottle choice tests with CS+ and CS− flavors in 0.9% CO examined preferences following vehicle, scopolamine (1–10mg/kg), mecamylamine (1–8mg/kg) and baclofen (1.5–5mg/kg). In acquisition, eight groups of rats received vehicle, scopolamine (1, 2.5mg/kg), mecamylamine (4, 6mg/kg), baclofen (3, 5mg/kg) or a limited intake vehicle control 0.5h prior to all 10 CS+ and CS− training sessions followed by six 2-bottle CS+ and CS− choice tests in 0.9% CO. CO-CFP expression (percent CS+ intake) was significantly but marginally reduced by scopolamine (70%), mecamylamine (85%) and baclofen (74%) relative to vehicle (98%). CO-CFP acquisition was eliminated (41%) by scopolamine relative to vehicle (88%) and limited control (98%) conditions. Neither mecamylamine nor baclofen altered CO-CFP acquisition. Thus, the muscarinic cholinergic receptor system is essential for acquisition (learning) of both fat-induced and sugar (fructose)-induced preferences. In contrast, muscarinic, nicotinic and GABAB receptors were minimally involved in the expression (maintenance) of fat- and fructose-CFP.

Nicotinic and muscarinic cholinergic receptors are recruited by acetylcholine-mediated neurotransmission within the locus coeruleus during the organisation of post-ictal antinociception.

Post-ictal antinociception is characterised by an increase in the nociceptive threshold that accompanies tonic and tonic-clonic seizures (TCS). The locus coeruleus (LC) receives profuse cholinergic inputs from the pedunculopontine tegmental nucleus. Different concentrations (1μg, 3μg and 5μg/0.2μL) of the muscarinic cholinergic receptor antagonist atropine and the nicotinic cholinergic receptor antagonist mecamylamine were microinjected into the LC of Wistar rats to investigate the role of cholinergic mechanisms in the severity of TCS and the post-ictal antinociceptive response. Five minutes later, TCS were induced by systemic administration of pentylenetetrazole (PTZ) (64mg/kg). Seizures were recorded inside the open field apparatus for an average of 10min. Immediately after seizures, the nociceptive threshold was recorded for 130min using the tail-flick test. Pre-treatment of the LC with 1μg, 3μg and 5μg/0.2μL concentrations of both atropine and mecamylamine did not cause a significant effect on seizure severity. However, the same treatments decreased the post-ictal antinociceptive phenomenon. In addition, mecamylamine caused an earlier decrease in the post-ictal antinociception compared to atropine. These results suggest that muscarinic and mainly nicotinic cholinergic receptors of the LC are recruited to organise tonic-clonic seizure-induced antinociception.

The electroacupuncture-induced analgesic effect mediated by 5-HT1, 5-HT3 receptor and muscarinic cholinergic receptors in rat model of collagenase-induced osteoarthritis.

BackgroundOsteoarthritis (OA) is an degenerative disease characterized by chronic joint pain. Complementary and alternative treatment such as acupuncture have been utilized to alleviate pain. The objective of this study was to investigate the analgesic mechanisms of electroacupuncture (EA) in the collagenase-induced osteoarthritis (CIOA) rat model.MethodsFour weeks after inducing CIOA by injecting collagenase solution into the left knee of 5-week-old male Sprague-Dawley rats, 2 Hz and 100 Hz EA on Zusanli (ST 36) was performed. The analgesic effect of EA was evaluated by the tail flick latency (TFL) and paw pressure threshold (PPT) tests. To investigate the analgesic mechanism, serotonergic and muscarinic cholinergic receptor agonists and antagonists were injected 20 min prior to EA and the resultant changes were evaluated by the TFL and PPT tests.ResultsEA on Zusanli (ST 36) demonstrated an analgesic effect in the CIOA rat model. The 2 Hz EA treatment showed a significantly greater analgesic effect than the 100 Hz treatment. The analgesic effect of 2 Hz EA was not strengthened by 5-HT1, 5-HT2, 5-HT3, and muscarinic cholinergic receptor agonist pretreatment, was blocked by 5-HT1, 5-HT3, and muscarinic cholinergic receptor antagonist pretreatment, but not blocked by 5-HT2 receptor antagonist pretreatment.ConclusionsIn the CIOA rat model, EA on Zusanli (ST 36) exhibited analgesic effects, and 2 Hz EA resulted in a significantly greater analgesic effect than 100 Hz EA. The analgesic effect of 2 Hz EA was reduced by pretreatment of 5-HT1 receptor, 5-HT3 receptor and muscarinic cholinergic receptor antagonists.

The ethanolic extract of the Eclipta prostrata L. ameliorates the cognitive impairment in mice induced by scopolamine

Ethnopharmacological relevanceEclipta prostrata L. (Asteraceae) has been prescribed for whole body nourishment and nervine tonic in Asia. However, the effects of E. prostrata in learning and memory have not been fully explored. Aim of the studyTo scientifically elucidate the effects of E. prostrata on cognitive functions, we examined whether E. prostrata could ameliorate a cholinergic blockade-induced memory impairment, and we also investigated the effects of E. prostrata on the synaptic plasticity in the hippocampus. Materials and methodsMemory impairment was induced by scopolamine, a cholinergic muscarinic receptor antagonist. The anti-amnesic effects of the ethanolic extract of Eclipta prostrata L. (EEEP) were measured in mice by the passive avoidance, Y-maze and Morris water maze tasks. To test the effects of EEEP on synaptic plasticity, we measured long-term potentiation (LTP) in the hippocampus. We also studied several signaling molecules related to learning and memory, such as phosphorylated protein kinase B (Akt) or phosphorylated glycogen synthase kinase-3β (GSK-3β). ResultsIn the passive avoidance task, EEEP (50 or 100mg/kg, p.o.) significantly ameliorated the shortened step-through latency induced by scopolamine. EEEP (100mg/kg, p.o.) also showed significant increase in alternation behavior during the Y-maze task. In the Morris water maze task, scopolamine-induced a decrease in both the swimming time within the target zone and the number of crossings where the platform had been placed were significantly reversed by EEEP (50 or 100mg/kg, p.o.). Moreover, EEEP (100μg/ml) significantly enhanced hippocampal LTP without affecting basal synaptic transmission. The administration of EEEP (100mg/kg) increased the phosphorylation levels of Akt and GSK-3β in the hippocampal region. ConclusionThese results suggest that EEEP has memory-ameliorating activity against scopolamine-induced cognitive impairment and facilitates LTP in the hippocampus. This could be, at least in part, mediated by the activation of the Akt-GSK-3β signaling pathway.

Dorsal raphe nucleus acetylcholine-mediated neurotransmission modulates post-ictal antinociception: The role of muscarinic and nicotinic cholinergic receptors

The dorsal raphe nucleus (DRN) is a key structure of the endogenous pain inhibitory system. Although the DRN is rich in serotoninergic neurons, cholinergic neurons are also found in that nucleus. Both ictal and inter-ictal states are followed by post-ictal analgesia. The present study investigated the role of cholinergic mechanisms in postictal antinociceptive processes using microinjections of atropine and mecamylamine, muscarinic and nicotinic cholinergic receptor antagonists, respectively, in the DRN of rats. Intraperitoneal injection of pentylenetetrazole (PTZ) (at 64mg/kg) caused tonic and tonic-clonic seizures. The convulsive motor reactions were followed by an increase in pain thresholds, a phenomenon known as post-ictal analgesia. Pre-treatment of the DRN with atropine or mecamylamine at 1µg, 3µg and 5µg/0.2µL decreased the post-ictal antinociceptive phenomenon. The present results showed that the post-ictal analgesia was mediated by muscarinic and nicotinic cholinergic receptors in the DRN, a structure crucially involved in the neural network that organises post-ictal hypoalgesia.

Neuropeptide S ameliorates olfactory spatial memory impairment induced by scopolamine and MK801 through activation of cognate receptor-expressing neurons in the subiculum complex.

Our previous studies have demonstrated that neuropeptide S (NPS), via selective activation of the neurons bearing NPS receptor (NPSR) in the olfactory cortex, facilitates olfactory function. High level expression of NPSR mRNA in the subiculum complex of hippocampal formation suggests that NPS-NPSR system might be involved in the regulation of olfactory spatial memory. The present study was undertaken to investigate effects of NPS on the scopolamine- or MK801-induced impairment of olfactory spatial memory using computer-assisted 4-hole-board spatial memory test, and by monitoring Fos expression in the subiculum complex in mice. In addition, dual-immunofluorescence microscopy was employed to identify NPS-induced Fos-immunereactive (-ir) neurons that also bear NPSR. Intracerebroventricular administration of NPS (0.5nmol) significantly increased the number of visits to switched odorants in recall trial in mice suffering from odor-discriminating inability induced by scopolamine, a selective muscarinic cholinergic receptor antagonist, or MK801, a N-methyl-D-aspartate receptor antagonist, after training trials. The improvement of olfactory spatial memory by NPS was abolished by the NPSR antagonist [D-Val(5)]NPS (40nmol). Ex vivo c-Fos and NPSR immunohistochemistry revealed that, as compared with vehicle-treated mice, NPS markedly enhanced Fos expression in the subiculum complex encompassing the subiculum (S), presubiculum (PrS) and parasubiculum (PaS). The percentages of Fos-ir neurons that also express NPSR were 91.3, 86.5 and 90.0% in the S, PrS and PaS, respectively. The present findings demonstrate that NPS, via selective activation of the neurons bearing NPSR in the subiculum complex, ameliorates olfactory spatial memory impairment induced by scopolamine and MK801 in mice.