Behavioral effects of arecoline in rats

Pharmaceutical Assessment Suggests Locomotion Hyperactivity in Zebrafish Triggered by Arecoline Might Be Associated with Multiple Muscarinic Acetylcholine Receptors Activation

Arecoline is one of the nicotinic acid-based alkaloids, which is found in the betel nut. In addition to its function as a muscarinic agonist, arecoline exhibits several adverse effects, such as inducing growth retardation and causing developmental defects in animal embryos, including zebrafish, chicken, and mice. In this study, we aimed to study the potential adverse effects of waterborne arecoline exposure on zebrafish larvae locomotor activity and investigate the possible mechanism of the arecoline effects in zebrafish behavior. The zebrafish behavior analysis, together with molecular docking and the antagonist co-exposure experiment using muscarinic acetylcholine receptor antagonists were conducted. Zebrafish larvae aged 96 h post-fertilization (hpf) were exposed to different concentrations (0.001, 0.01, 0.1, and 1 ppm) of arecoline for 30 min and 24 h, respectively, to find out the effect of arecoline in different time exposures. Locomotor activities were measured and quantified at 120 hpf. The results showed that arecoline caused zebrafish larvae locomotor hyperactivities, even at a very low concentration. For the mechanistic study, we conducted a structure-based molecular docking simulation and antagonist co-exposure experiment to explore the potential interactions between arecoline and eight subtypes, namely, M1a, M2a, M2b, M3a, M3b, M4a, M5a, and M5b, of zebrafish endogenous muscarinic acetylcholine receptors (mAChRs). Arecoline was predicted to show a strong binding affinity to most of the subtypes. We also discovered that the locomotion hyperactivity phenotypes triggered by arecoline could be rescued by co-incubating it with M1 to M4 mAChR antagonists. Taken together, by a pharmacological approach, we demonstrated that arecoline functions as a highly potent hyperactivity-stimulating compound in zebrafish that is mediated by multiple muscarinic acetylcholine receptors.

DARK Classics in Chemical Neuroscience: Arecoline

Arecoline is a naturally occurring psychoactive alkaloid from areca (betel) nuts of the areca palm ( Areca catechu) endemic to South and Southeast Asia. A partial agonist of nicotinic and muscarinic acetylcholine receptors, arecoline evokes multiple effects on the central nervous system (CNS), including stimulation, alertness, elation, and anxiolysis. Like nicotine, arecoline also evokes addiction and withdrawal symptoms (upon discontinuation). The abuse of areca nuts is widespread, with over 600 million users globally. The importance of arecoline is further supported by its being the world's fourth most commonly used human psychoactive substance (after alcohol, nicotine, and caffeine). Here, we discuss neuropharmacology, pharmacokinetics, and metabolism of arecoline, as well as social and historical aspects of its use and abuse. Paralleling clinical findings, we also evaluate its effects in animal models and outline future clinical and preclinical CNS research in this field.

Systemic administration of arecoline reduces ethanol-induced sleeping through activation of central muscarinic receptor in mice

BACKGROUND

Epidemiological evidence of co-use of alcohol and areca nuts suggests a potential central interaction between arecoline, a major alkaloid of areca and a muscarinic receptor agonist, and ethanol. Moreover, the central cholinergic system plays an important role in the depressant action of ethanol and barbiturates. The purpose of this study was to investigate the effects of arecoline on pentobarbital- and ethanol-induced hypnosis in mice.

METHODS

Male ICR mice were tested for locomotor activity following acute systemic administration of ethanol alone, arecoline alone, or ethanol plus arecoline. For the loss of the righting reflex (LORR) induced by pentobarbital and ethanol, sleep latency and sleeping duration were evaluated in mice treated with arecoline alone or the combination of arecoline and scopolamine or methscopolamine.

RESULTS

Ethanol (1.0 to 3.0 g/kg, i.p.) reduced locomotor activity significantly and a declining trend was observed after treatment with arecoline (0.25 to 1.0 mg/kg, i.p.), but there were no synergistic effects of ethanol and arecoline on locomotor activity. The experiments on LORR demonstrated that arecoline (0.125 to 1.0 mg/kg, s.c.) shortened the duration of sleeping induced by ethanol (4.0 g/kg, i.p.), but not pentobarbital (45 mg/kg, i.p.). In addition, alterations of sleep latency were not obvious in both pentobarbital- and ethanol-induced LORR. Statistical analyses revealed that scopolamine (centrally acting), but not methscopolamine (peripherally acting), could antagonize the effect of arecoline on the duration of ethanol-induced LORR in mice.

CONCLUSIONS

These results suggest that central muscarinic receptor is a pharmacological target for the action of arecoline to modulate ethanol-induced hypnosis.

Anthropological perspectives on use of the areca nut

This paper first reviews the identity of historical and contemporary users of the areca nut. It then considers the reasons given by users for indulging in areca consumption, drawing upon historical, ethnographic and experimental sources of evidence for the effects which users have sought to derive from it. Particularly important is the social context in which consumption occurs, and the social meanings attached to areca use and exchange. Finally, a possible evolutionary hypothesis is postulated to explain the origins of areca use as a form of behaviour indicating reproductive availability. However, diverse culturally explicit reasons underlie usage and what may once have been a sufficient rationale for consumption may no longer justify this pattern of behaviour.

Effects of combinations of arecoline and atropine on mouse motor activity

1. Effects on motor activity were studied after acute administration of arecoline, atropine alone and in combination in the mouse. 2. Atropine from 15 to 45 mg/kg increased motor activity. 3. A reduction in activity was observed at doses of arecoline above 0.2 mg/kg. 4. An antagonism between arecoline and atropine was observed only at low doses of arecoline, while higher doses of arecoline in association with atropine increased activity.

Differential responsivity of mood, behavior, and cognition to cholinergic agents in elderly neuropsychiatric populations

To evaluate the possible differential responsivity of Alzheimer patients to cholinergic agents, a series of pharmacologic challenge studies in 83 neuropsychiatric patients and controls were performed contrasting a cholinergic antagonist (scopolamine) with two cholinergic agonists (arecoline and nicotine). Alzheimer patients displayed significantly greater behavioral and cognitive responses to central cholinergic blockade at lower scopolamine doses than age-matched controls or elderly depressives. These differential changes could not be explained by group differences in the sedative, physiologic, or pharmacokinetic effects of the drug. In addition, the elderly, age-matched control subjects did reveal a profile of cognitive deficits at the highest dose (0.5 mg), which temporarily mimicked the baseline impairments found in early Alzheimer's disease. Together, these findings with scopolamine suggest an increased sensitivity to cholinergic blockade in Alzheimer's disease and demonstrate the first direct evidence of anticholinergic modelling of dementia in normal elderly subjects. To investigate further the postsynaptic cholinergic responsivity in Alzheimer's disease, patients were studied with arecoline and nicotine. While the cognitive effects of both agents were modest at best, there were significant differences in mood and behavioral responses between arecoline and nicotine in Alzheimer subjects. These behavioral changes occurred at much lower doses in the Alzheimer patients than those required in normal controls, once more supporting the notion of increased behavioral sensitivity to cholinergic agents in Alzheimer's disease. In addition, the differential mood effects between these two cholinergic agonists raise new questions about receptor selectivity in the cholinergic regulation of mood.

Action of a chronic arecoline administration on mouse motility and on acetylcholine concentrations in the CNS

The modifications of mouse motility and of the levels of acetylcholine (ACh) in two sections of the CNS caused by a chronic administration of 4.5; 9.5; 28.5 and 60 mg kg-1 day-1 of arecoline for 20 days have been studied. At low doses (4.5 and 9.5 mg kg-1 day-1), arecoline caused no modification of the ACh levels and of the motility. The higher doses (28.5 and 60 mg kg-1 day-1) caused a reduction of the mouse motility and an increase of the ACh levels in the subcortical structures of the CNS of the mouse.

Motor responses of autoimmune NZB/B1NJ and C57BL/6Nnia mice to arecoline and nicotine

In 11-13 month C57BL/6Nnia mice, arecoline produced a dose-dependent decrease in motor activity at doses of 0.64-2.5 mg/kg, whereas at doses of 5.0-20.0 mg/kg arecoline produced a dose-dependent increase in motor activity. In marked contrast, age-matched NZB/B1NJ (New Zealand Black) mice failed to exhibit the first phase of the response, but showed a greater dose-dependent increase in motor activity following the doses of 10 and 20 mg/kg. Nicotine, 0.64-2.5 mg/kg, produced a dose-dependent decrease in motor activity in both strains. The effects of arecoline and nicotine were antagonized by scopolamine (2.5 mg/kg) and mecamylamine (1.0 mg/kg), respectively. These findings suggest that muscarinic neurotransmission may be altered in NZB/B1NJ mice, which produce brain-reactive autoantibodies, exhibit learning/memory dysfunctions, and also exhibit a loss of neurons staining positive for choline acetyltransferase.

Action of arecoline on the levels of acetylcholine, norepinephrine and dopamine in the mouse central nervous system

Modifications caused by arecoline (2 mg/kg and 10 mg/kg injected subcutaneously) in the levels of acetylcholine (ACh), norepinephrine (NE) and dopamine (DA) in the mouse cortex and "subcortex" were studied. The animals were killed by microwave irradiation of the head 15 minutes after drug administration. Arecoline 10 mg/kg caused a reduction in levels of ACh in the cortex and "subcortex" at the limit of statistical significance (p 5-10%) and a statistically significant reduction in levels on NE. A statistically significant increase in DA was observed only in the cortex after 2 mg/kg and 10 mg/kg of arecoline.

Tolerance to the disruptive effects of arecoline on schedule-controlled behavior

The roles of dispositional, physiological, and behavioral factors in the development of tolerance to the effects of arecoline on operant behavior were assessed. In Experiment I, rats were trained to press a lever on a variable-interval 15-s schedule for milk reinforcement. Dose-effect relationships were assessed prior to and during chronic arecoline (1.74 mg/kg/day) treatment. After 21 days of arecoline administration prior to each session, the dose-effect relationship for total number of responses did not shift. However, the dose-effect relationship for total number of reinforcers shifted to the right. In Experiment II, rats were trained to respond on a fixed-ratio 20 schedule for milk reinforcement. Dose-effect relationships were assessed prior to and during chronic arecoline (0.87 mg/kg/day) administration. One group of rats received daily injections of arecoline prior to the session and a second group received arecoline injections 30 min after the session. Daily administration of arecoline resulted in a greater shift to the right of the dose-effect relationship for the presession group than it did for the postsession group. These data demonstrate the importance of behavioral factors in the development of tolerance to arecoline.

Discriminative stimulus properties of arecoline: a new approach for studying central muscarinic receptors

Rats were trained to discriminate arecoline (1.74 mg/kg) from saline in a milk-reinforced (variable interval 12s) two-lever operant paradigm. The discriminative stimulus (DS) effects of arecoline were antagonized by atropine sulfate, but not by atropine methylnitrate or mecamylamine. In contrast to the effects on discrimination, atropine did not antagonize the response rate suppressant effects of arecoline. The DS effect of arecoline completely generalized to oxotremorine, partially generalized to pilocarpine, and did not generalize to nicotine. These data demonstrate that the DS effect of arecoline depends on central muscarinic receptors.

Dose-response effects of scopolamine on activity in an open field

The frequency of the responses, i.e., squares entered (ambulation), rearing and grooming, were recorded over 30 min for saline, and 0.25, 1.0, 2.0 and 4.0 mg/kg scopolamine treated groups. Scopolamine produced an inverted U dose-response curve for ambulation, an increase in rearing but no effect on grooming. All three responses decreased over time; scopolamine did not attenuate this rate of habituation. There did appear a dose-related time effect. It was concluded that scopolamine may have different effects on various responses recorded simultaneously over a range of doses. The results when compared to other experiments emphasized the importance of environmental factors in determining drug effects on behaviour.