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

BACKGROUND: Galangin, a flavonoid compound with acetylcholinesterase inhibitory activity, may improve cognitive functions by enhancing cholinergic transmission. OBJECTIVES: We aimed to investigate the effects of galangin on spatial memory impairment in rats. METHODS: 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. RESULTS: 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. CONCLUSION: 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).

Beneficial effects of resveratrol on scopolamine but not mecamylamine induced memory impairment in the passive avoidance and Morris water maze tests in rats.

Resveratrol (3,5,4-trihydroxy-trans-stilbene), which is found in grapes and red wine has been shown to protect neuronal cells with its antioxidant activity, improve memory function in dementia and reverse acetylcholine esterase (AChE) activity. The aim of this study was to investigate the effect of resveratrol on emotional and spatial memory in naive rats, as well as on scopolamine- and mecamylamine-induced memory impairment in the passive avoidance and Morris water maze (MWM) tests. Resveratrol (12.5, 25 and 50 mg/kg), scopolamine (0.6 mg/kg) and mecamylamine (10mg/kg) were administered to male Wistar rats. In the passive avoidance test, there was no significant difference in the first day latency between all groups, whereas scopolamine and mecamylamine significantly shortened the second day latency compared to the control group. Resveratrol reversed the effect of scopolamine at all doses used, but it had no effect on mecamylamine-induced memory impairment in the passive avoidance test. Both scopolamine and mecamylamine significantly decreased the time spent in the escape platform quadrant during the probe trial of the MWM test compared to the control group. Resveratrol reversed the effect of scopolamine at all doses, but did not change the effect of mecamylamine in the MWM test. There were no significant differences in the locomotor activities of any of the groups. In conclusion, we suggested that resveratrol had improving effects on learning and memory by acting on muscarinic cholinergic receptors and at least in part, may reverse AChE activity.

A novel approach for in vivo screening of toxins using the Drosophila Giant Fiber circuit.

Finding compounds that affect neuronal or muscular function is of great interest as potential therapeutic agents for a variety of neurological disorders. Alternative applications for these compounds include their use as molecular probes as well as insecticides. We have developed a bioassay that requires small amounts of compounds and allows for unbiased screening of biological activity in vivo. For this, we paired administering compounds in a non-invasive manner with simultaneous electrophysiological recordings from a well-characterized neuronal circuit, the Giant Fiber System of Drosophila melanogaster, which mediates the escape response of the fly. The circuit encompasses a variety of neurons with cholinergic, glutamatergic, and electrical synapses as well as neuromuscular junctions. Electrophysiological recordings from this system allow for the detection of compound-related effects against any molecular target on these components. Here, we provide evidence that this novel bioassay works with small molecules such as the cholinergic receptor blocker mecamylamine hydrochloride and the potassium channel blocker tetraethylammonium hydroxide, as well as with venom from Conus brunneus and isolated conopeptides. Conopeptides have been developed into powerful drugs, such as the painkillers Prialt™ and Xen2174. However, most conopeptides have yet to be characterized, revealing the need for a rapid and straightforward screening method. Our findings show that mecamylamine hydrochloride, as well as the α-conotoxin ImI, which is known to be an antagonist of the human α7 nicotinic acetylcholine receptor, efficiently disrupted the synaptic transmission of a Drosophila α7 nicotinic acetylcholine receptor-dependent pathway in our circuit but did not affect the function of neurons with other types of synapses. This demonstrates that our bioassay is a valid tool for screening for compounds relevant to human health.

Nicotine anxiogenic and rewarding effects are decreased in mice lacking beta-endorphin.

The endogenous opioid system plays an important role in the behavioral effects of nicotine. Thus, micro-opioid receptor and the endogenous opioids derived from proenkephalin are involved in the central effects of nicotine. However, the role played by the different endogenous opioid peptides in the acute and chronic effects of nicotine remains to be fully established. Mice lacking beta-endorphin were acutely injected with nicotine at different doses to evaluate locomotor, anxiogenic and antinociceptive responses. The rewarding properties of nicotine were evaluated by using the conditioned place-preference paradigm. Mice chronically treated with nicotine were acutely injected with mecamylamine to study the behavioral expression of nicotine withdrawal. Mice lacking beta-endorphin exhibited a spontaneous hypoalgesia and hyperlocomotion and a reduction on the anxiogenic and rewarding effects induced by nicotine. Nicotine induced similar antinociception and hypolocomotion in both genotypes and no differences were found in the development of physical dependence. The dissociation between nicotine rewarding properties and physical dependence suggests a differential implication of beta-endorphin in these addictive related responses.

TC-5214 (S-(+)-mecamylamine): a neuronal nicotinic receptor modulator with antidepressant activity.

Both clinical and preclinical data support a potential therapeutic benefit of modulating the activity of CNS neuronal nicotinic receptors (NNRs) to treat depression and anxiety disorders. Based on the notion that the depressive states involve hypercholinergic tone, we have examined the potential palliative role of NNR antagonism in these disorders, using TC-5214 (S-(+) enantiomer of mecamylamine), a noncompetitive NNR antagonist. TC-5214 demonstrated positive effects in a number of animal models of depression and anxiety. TC-5214 was active in the forced swim test in rats (minimum effective dose (MED)=3 mg/kg i.p.), a classical depression model. It was also active in the behavioral despair test in mice (0.1-3.0 mg/kg i.p.), another model of depression. In the social interaction paradigm in rats, a model of generalized anxiety disorder (GAD), TC-5214 was active at a dose of 0.05 mg/kg s.c. In the light/dark chamber paradigm in rats, a model of GAD and phobia, TC-5214 was also active at a dose of 0.05 mg/kg s.c. Although TC-5214 shows modest selectivity among NNR subtypes, the antidepressant and anxiolytic effects seen in these studies are likely attributable to antagonist effects at the alpha4beta2 NNRs. This is supported by the observation of similar effects with alpha4beta2-selective partial agonists such as cytisine and with alpha4beta2-selective antagonists such as TC-2216. TC-5214 was well tolerated in acute and chronic toxicity studies in mice, rats, and dogs, showed no mutagenicity and displayed safety pharmacology, pharmacokinetic and metabolic profiles appropriate for therapeutic development. Overall, the results support a novel nicotinic cholinergic antagonist mechanism for antidepressant and anxiolytic effects and highlight the potential of NNR antagonists such as TC-5214 as therapeutics for the treatment of anxiety and depression.

Nicotine-induced antinociception, rewarding effects, and physical dependence are decreased in mice lacking the preproenkephalin gene.

It has been shown previously that the endogenous opioid system may be involved in the behavioral effects of nicotine. In the present study, the participation of endogenous enkephalins on nicotine responses has been investigated by using preproenkephalin knock-out mice. Acute nicotine-induced hypolocomotion remained unaffected in these mice. In contrast, antinociception elicited in the tail-immersion and hot-plate tests by acute nicotine administration was reduced in mutant animals. The rewarding properties of nicotine were then investigated using the place-conditioning paradigm. Nicotine induced a conditioned place preference in wild-type animals, but this effect was absent in knock-out mice. Accordingly, in vivo microdialysis studies revealed that the enhancement in dopamine extracellular levels in the nucleus accumbens induced by nicotine was also reduced in preproenkephalin-deficient mice. Finally, the somatic expression of the nicotine withdrawal syndrome precipitated in nicotine-dependent mice by mecamylamine was significantly attenuated in mutant animals. In summary, the present results indicate that endogenous opioid peptides derived from preproenkephalin are involved in the antinociceptive and rewarding properties of nicotine and participate in the expression of physical nicotine dependence.

Decreased signs of nicotine withdrawal in mice null for the beta4 nicotinic acetylcholine receptor subunit.

Withdrawal from chronic exposure to nicotine, the main addictive component of tobacco, produces distinctive symptoms in humans. The appearance of these symptoms is a major deterrent when people try to quit smoking. To study which type of nicotine receptor is relevant for the onset of the withdrawal syndrome, we used a mouse model of nicotine withdrawal. Wild-type mice and mice null for the beta4 (beta4-/-) or the beta2 (beta2-/-) nicotinic acetylcholine receptor subunits were implanted with osmotic minipumps delivering 24 mg x kg(-1) x d(-1) nicotine for 13 d. Subsequently, a single intraperitoneal injection of the nicotinic receptor antagonist mecamylamine induced behavioral symptoms of withdrawal measured as increased grooming, chewing, scratching, and shaking, plus the appearance of some unique behaviors such as jumping, leg tremors, and cage scratching. Mecamylamine injection triggered comparable withdrawal signs in wild-type and in beta2-/- mice, whereas the beta4-/- mice displayed significantly milder somatic symptoms. In addition, nicotine withdrawal produced hyperalgesia in wild-type but not beta4-/- mice. Finally, chronic nicotine produced an increase in epibatidine binding in several areas of the brain in both wild-type and in beta4-/- mice, but such receptor upregulation did not correlate with the severity of withdrawal signs. Our results demonstrate a major role for beta4-containing nicotinic acetylcholine receptors in the appearance of nicotine withdrawal symptoms. In contrast, the beta2 subunit does not seem to greatly influence this phenomenon. We also show that the upregulation of epibatidine binding sites attributable to chronic nicotine, an effect associated with beta2-containing receptors, is probably not related to the mechanisms underlying withdrawal.

Castration in rats impairs performance during acquisition of a working memory task and exacerbates deficits in working memory produced by scopolamine and mecamylamine.

RATIONALE: Although much research has focused on the effects of ovarian hormones on learning and memory in females, less information is available regarding the effects of testicular hormones on learning and memory in males. Additionally, despite evidence of an interaction of testicular hormones and the cholinergic system in areas of the brain implicated in learning and memory, no information is available regarding the behavioral consequences of that interaction. OBJECTIVES: We assessed the effect of castration in male rats on working memory during acquisition of a radial maze. We also assessed the interactive effects of castration and scopolamine, a muscarinic receptor antagonist, as well as mecamylamine, a nicotinic receptor antagonist, on behavior. METHODS: Young adult male rats were castrated or underwent sham surgeries. Beginning 10 days after surgeries, performance on a task of working memory was assessed across 24 days of acquisition in an eight-arm radial maze. Following acquisition, scopolamine and mecamylamine dose-effect curves were established. RESULTS: Castration of male rats significantly decreased arm-choice accuracy during acquisition. Castration significantly exacerbated impairments in arm-choice accuracy produced by scopolamine as well as mecamylamine, without altering the disruptive effects of the drugs on the rate at which rats entered the arms of the maze. CONCLUSIONS: These results indicate that castration in male rats impairs working memory during acquisition of a spatial maze task. Additionally, these results suggest that the absence of testicular hormones increases the sensitivity of male rats to the impairing effects of scopolamine as well as mecamylamine on working memory.

Mecamylamine: new therapeutic uses and toxicity/risk profile.

BACKGROUND: Mecamylamine hydrochloride was initially developed for its ganglion-blocking activity and has been marketed as an antihypertensive agent in the United States for >40 years. Several other potential therapeutic applications are being investigated, most of them focusing on the drug's ability to cross the blood-brain barrier and selectively antagonize neuronal nicotinic acetylcholine receptors. This central activity of mecamylamine is demonstrable at much lower doses than the effective antihypertensive dose, thus avoiding many of the bothersome side effects associated with the drug's inhibition of parasympathetic activity. OBJECTIVE: Because investigations are being conducted in new patient populations, including pediatric patients, an update of the toxicity/risk profile of mecamylamine is timely. This review describes nonclinical and clinical data pertaining to the pharmacology, toxicity, and tolerability of mecamylamine, including some previously unpublished toxicology and clinical pharmacokinetics data. Potential new therapeutic applications are discussed, including the use of mecamylamine in treating autonomic dysreflexia; dependencies on nicotine, cocaine, and other substances of abuse; Tourette's syndrome; and other neuropsychiatric disorders. METHODS: Information for this review of mecamylamine was identified through a search of MEDLINE from 1966 to the present, as well as from the master files of Merck & Co, Inc, the drug's original manufacturer, and Layton BioScience, Inc, its present manufacturer. CONCLUSIONS: The available data concerning potential new applications of mecamylamine, although sparse, suggest that the drug's toxicity/risk profile may be much improved at lower doses.

The role of brain acetylcholine in phenol-induced tremor in mice.

The relation between phenol-induced tremor and brain acetylcholine levels, and the effects of cholinergic drugs on the tremor were investigated, using male ddY mice weighing 28-35 g. The magnitude of phenol-induced tremor was graded on a 4-point scale: 0, normal; 1, slight; 2, moderate; 3, severe, and acetylcholine levels were measured by high-performance liquid chromatography with electrochemical detection. The magnitude of tremor and the decrease in acetylcholine levels in the striatum and cerebral cortex induced by s.c. injection of phenol (50, 100, 200 mg/kg) were dose-dependent, and both showed parallel time courses. Intracerebroventricular (i.c.v.) injection of phenol (100 micrograms/mouse) caused a decrease in acetylcholine levels in the striatum but did not induce tremor. Intraperitoneal injection of pentobarbital (10 mg/kg), which inhibits the release of acetylcholine, weakened both the magnitude of the tremor and the decrease in acetylcholine levels induced by phenol (200 mg/kg), whereas i.c.v. injection of pentobarbital (120 micrograms/mouse) attenuated the decrease in acetylcholine levels induced by phenol, but did not affect the magnitude of the tremor. Intraperitoneal (20 mg/kg) or i.c.v. (60 micrograms/mouse) injection of mecamylamine further strengthened the tremor. Intraperitoneal (0.3 mg/kg) injection of physostigmine strengthened the tremor, while i.c.v. injection (1 microgram/mouse) caused a reduction in its magnitude. These results suggest that the tremor is caused directly by the phenol-induced increase in acetylcholine release in the peripheral nervous system (motor nerve endings), that the decrease in brain acetylcholine levels may be due to phenol-induced increases in acetylcholine release within the central nervous system, and that the resultant reduction in brain acetylcholine levels indirectly suppresses the tremor.