Amnesic effects of the anticholinergic drugs, trihexyphenidyl and biperiden: differences in binding properties to the brain muscarinic receptor

Cholinergic models of memory impairment in animals and man: scopolamine vs. biperiden

Scopolamine has been used as a pharmacologic model for cognitive impairments in dementia and Alzheimer's disease. The validity of this model seems to be limited because findings in animals do not readily translate to novel treatments in humans. Biperiden is also a cholinergic deficit model for cognitive impairments but specifically blocks muscarinic M1 receptors. The effects of scopolamine and biperiden (and pirenzepine) are compared in animal studies and related to findings in humans. It is concluded that the effects on cognitive functions are different for scopolamine and biperiden, and they should be considered as different cognitive deficit models. Scopolamine may model more advanced stages of Alzheimer's disease whereas biperiden may model the early deficits in declarative memory in aging and mild cognitive impairment.

The muscarinic M1 receptor modulates associative learning and memory in psychotic disorders

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Psychosis characterised by different M₁ sensitivity in learning and memory.

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Greater limbic-temporal hyperactivity in response to biperiden in psychosis.

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Hippocampal M₁ binding predicted limbic-temporal hyperactivation underlying learning.

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M₁ agonist may normalise functional response underlying learning & memory in psychosis.

Background

Psychotic disorders are characterized by prominent deficits in associative learning and memory for which there are currently no effective treatments. Functional magnetic resonance imaging (fMRI) studies in psychotic disorders have identified deficits in fronto-temporal activation during associative learning and memory. The underlying pathology of these findings remains unclear. Postmortem data have suggested these deficits may be related to loss of muscarinic M₁ receptor mediated signaling. This is supported by an in-vivo study showing improvements in these symptoms after treatment with the experimental M_1/4 receptor agonist xanomeline. The current study tests whether reported deficits in fronto-temporal activation could be mediated by loss of M₁ receptor signaling in psychotic disorders.

Methods

Twenty-six medication-free subjects diagnosed with a psychotic disorder and 29 age-, gender-, and IQ-matched healthy controls underwent two functional magnetic resonance imaging (fMRI) sessions, one under placebo and one under selective M₁ antagonist biperiden, while performing the paired associated learning task. M₁ binding potentials (BP_ND) were measured in the dorsolateral prefrontal cortex (DLPFC) and hippocampus using ¹²³I-IDEX single photon emission computed tomography.

Results

In the subjects with psychotic disorders DLPFC hypoactivation was only found in the memory phase of the task. In both learning and memory phases of the task, M₁ antagonism by biperiden elicited significantly greater hyperactivation of the parahippocampal gyrus and superior temporal gyrus in subjects with a psychotic disorders compared to controls. Greater hyperactivation of these areas after biperiden was associated with greater hippocampal M₁ receptor binding during learning, with no association found with M₁ receptor binding in the DLPFC. M₁ receptor binding in the DLPFC was related to greater functional sensitivity to biperiden of the cingulate gyrus during the memory phase.

Conclusion

The current study is the first to show differences in M₁ receptor mediated functional sensitivity between subjects with a psychotic disorder and controls during a paired associate learning and memory task. Results point to subjects with psychotic disorders having a loss of M₁ receptor reserve in temporal-limbic areas.

Understanding Central Nervous System Effects of Deliriant Hallucinogenic Drugs through Experimental Animal Models

Hallucinogenic drugs potently alter human behavior and have a millennia-long history of use for medicinal and religious purposes. Interest is rapidly growing in their potential as CNS modulators and therapeutic agents for brain conditions. Antimuscarinic cholinergic drugs, such as atropine and scopolamine, induce characteristic hyperactivity and dream-like hallucinations and form a separate group of hallucinogens known as "deliriants". Although atropine and scopolamine are relatively well-studied drugs in cholinergic physiology, deliriants represent the least-studied class of hallucinogens in terms of their behavioral and neurological phenotypes. As such, novel approaches and new model organisms are needed to investigate the CNS effects of these compounds. Here, we comprehensively evaluate the preclinical effects of deliriant hallucinogens in various animal models, their mechanisms of action, and potential interplay with other signaling pathways. We also parallel experimental and clinical findings on deliriant agents and outline future directions of translational research in this field.

Mnemonic and behavioral effects of biperiden, an M1-selective antagonist, in the rat

RATIONALE

There is a persistent pressing need for valid animal models of cognitive and mnemonic disruptions (such as seen in Alzheimer's disease and other dementias) usable for preclinical research.

OBJECTIVES

We have set out to test the validity of administration of biperiden, an M1-acetylcholine receptor antagonist with central selectivity, as a potential tool for generating a fast screening model of cognitive impairment, in outbred Wistar rats.

METHODS

We used several variants of the Morris water maze task: (1) reversal learning, to assess cognitive flexibility, with probe trials testing memory retention; (2) delayed matching to position (DMP), to evaluate working memory; and (3) "counter-balanced acquisition," to test for possible anomalies in acquisition learning. We also included a visible platform paradigm to reveal possible sensorimotor and motivational deficits.

RESULTS

A significant effect of biperiden on memory acquisition and retention was found in the counter-balanced acquisition and probe trials of the counter-balanced acquisition and reversal tasks. Strikingly, a less pronounced deficit was observed in the DMP. No effects were revealed in the reversal learning task.

CONCLUSIONS

Based on our results, we do not recommend biperiden as a reliable tool for modeling cognitive impairment.

Scopolamine-induced passive avoidance memory retrieval deficit is accompanied with hippocampal MMP2, MMP-9 and MAPKs alteration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive loss of memory and cognitive deficit. The observed amnesia in the early stages of AD is suggested to be a retrieval problem, rather than encoding and consolidation deficit. According to the cholinergic hypothesis of AD, scopolamine is used to induce an animal model of amnesia. Howbeit the effect of scopolamine on memory retrieval is contradictory. This study aimed to assess the effect of scopolamine on passive avoidance memory retrieval. Additionally according to the reported changes of MMP-2, MMP-9 and MAPKs (ERK, P38 and JNK) in AD pathology the hippocampal contents of these proteins were determined. Male NMRI mice weighing 20-25g were trained in passive avoidance apparatus. The drug or its vehicle was injected 24h after training (30min before retention test). The hippocampal tissue was isolated and western blot analysis was done for MMP-2, MMP-9 and MAPKs (ERK, P38 and JNK). The results indicated that scopolamine (1mg/kg) disrupts passive avoidance memory retrieval. This scopolamine treatment resulted in hippocampal MMP-2 and MMP-9 decline while increased MAPKs in the hippocampus. These results suggest that cholinergic system has an important role in learnt memory retrieval. It might also suggest the positive role of MMP-2 and MMP-9 in this phase of memory while propose that MAPKs affect negatively the reactivation of memory which is compatible with MAPKs activation in AD.

Comparison of pro-amnesic efficacy of scopolamine, biperiden, and phencyclidine by using passive avoidance task in CD-1 mice

INTRODUCTION

Memory disorders accompany numerous diseases and therapies, and this is becoming a growing medical issue worldwide. Currently, various animal models of memory impairments are available; however, many of them require high financial outlay and/or are time-consuming. A simple way to achieve an efficient behavioral model of cognitive disorders is to inject defined drug that has pro-amnesic properties. Since the involvement of cholinergic and glutamatergic neurotransmission in cognition is well established, the utilization of a nonselective muscarinic receptor antagonist, scopolamine (SCOP), a selective M1 muscarinic receptor antagonist, biperiden (BIP), and a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, phencyclidine (PCP) seems to be reliable tools to induce amnesia. As the determination of their effective doses remains vague and the active doses vary significantly in laboratory settings and in mouse species being tested, the aim of this study was to compare these three models of amnesia in CD-1 mice.

METHODS

Male Swiss Albino mice were used in passive avoidance (PA) test. All the compounds were administered intraperitoneally (ip) at doses 1mg/kg, 5mg/kg, and 10mg/kg (SCOP and BIP), and 1mg/kg, 3mg/kg, and 6mg/kg (PCP).

RESULTS

In the retention trial of the PA task, SCOP and PCP led to the reduction of step-through latency at all the tested doses as compared to control, but BIP was effective only at the dose of 10mg/kg.

CONCLUSION

This study revealed the effectiveness of SCOP, PCP, and BIP as tools to induce amnesia, with the PCP model being the most efficacious and SCOP being the only model that demonstrates a clear dose-response relationship.

M1 muscarinic receptors are necessary for retrieval of remote context fear memory

Several studies have investigated the transition of consolidation of recent memory to remote memory in aversively motivated tasks, such as contextual fear conditioning (CFC) and inhibitory avoidance (IA). However, the mechanisms that serve the retrieval of remote memories, has not yet been fully understood. Some evidences suggest that the central cholinergic system appears be involved in the modulation of these processes. Therefore, the present study aimed to investigate the effects of a pre-test administration of dicyclomine, a high-affinity M1 muscarinic receptor antagonist, on the retrieval of remote memories in fear conditioning and IA tasks. Male Wistar rats were trained, and after 1 or 28days, the rats received dicyclomine (16 or 32mg/kg, intraperitoneally, i.p.) and were tested in CFC, tone fear conditioning (TFC) and IA tasks. At both time intervals, 32mg/kg dicyclomine induced impairment of CFC. In TFC task only the performance of the rats 28days after training was impaired. The IA task was not affected in any of the studied intervals. These findings suggest a differential contribution of muscarinic receptors on recent and remote memories retrieval revealing a more generalized role in remote memory.

Modelling Alzheimer-like cognitive deficits in rats using biperiden as putative cognition impairer

To enable the development of effective treatments for dementias such as Alzheimer's disease (AD), it is important to establish valid animal models of cognitive impairments. Scopolamine is widely used to induce cognitive deficits in animal models of AD, but also causes non-cognitive side effects. We assessed whether biperiden, a selective antagonist of M1 muscarinic receptors, which are predominantly expressed in brain areas involved in cognitive processes, causes cognitive deficits without inducing peripheral side-effects. Two different doses of biperiden (3 or 10mgkg(-1)) on the acquisition of a spatial cone field task were assessed in male Lister Hooded rats. This task measures, among others, spatial working (WM) - and reference memory (RM) simultaneously. Biperiden did not impair learning of the task. The animals reached asymptotic levels for all variables except reference memory and the number of rewards collected. However, the 10mgkg(-1) dose decreased the tendency of rats to use searching strategies to solve the task and made them slower to start searching and completing the task. In conclusion, though no effects on WM and RM performance were seen, the present study cannot conclude that biperiden acts as a more selective cognition impairer than scopolamine in other rats strains and/or other doses than those tested.

Performance of conventional pigs and Göttingen miniature pigs in a spatial holeboard task: effects of the putative muscarinic cognition impairer Biperiden

Background

The pig is emerging as a model species that bridges the gap between rodents and humans in research. In particular, the miniature pig (referred to hereafter as the minipig) is increasingly being used as non-rodent species in pharmacological and toxicological studies. However, there is as yet a lack of validated behavioral tests for pigs, although there is evidence that the spatial holeboard task can be used to assess the working and reference memory of pigs. In the present study, we compared the learning performance of commercial pigs and Göttingen minipigs in a holeboard task.

Methods

Biperiden, a muscarinic M1 receptor blocker, is used to induce impairments in cognitive function in animal research. The two groups of pigs were treated orally with increasing doses of biperiden (0.05 – 20 mg.kg^-1) after they had reached asymptotic performance in the holeboard task.

Results

Both the conventional pigs and the Göttingen minipigs learned the holeboard task, reaching nearly errorless asymptotic working and reference memory performance within approximately 100 acquisition trials. Biperiden treatment affected reference, but not working, memory, increasing trial duration and the latency to first hole visit at doses ≥ 5 mg.kg^-1.

Conclusion

Both pig breeds learned the holeboard task and had a comparable performance. Biperiden had only a minor effect on holeboard performance overall, and mainly on reference memory performance. The effectiveness needs to be evaluated further before definitive conclusions can be drawn about the ability of this potential cognition impairer in pigs.

Biperiden (M₁ antagonist) impairs the expression of cocaine conditioned place preference but potentiates the expression of cocaine-induced behavioral sensitization

Cocaine addiction is a public health issue in many countries, stressing the need for more effective treatments. As all drugs of abuse, cocaine acts on the brain reward system, increasing dopamine (DA) levels. Other neurotransmitters such as acetylcholine (ACh) are involved in the mechanisms underlying the development and the maintenance of cocaine addiction. ACh plays an important role in learning and memory processes and also regulates DA in some specific regions of the central nervous system. The present study investigated the effects of biperiden, a muscarinic cholinergic (mACh) antagonist in two animal models: conditioned place preference (CPP) and behavioral sensitization. Male C57BL/6J mice were used in both studies. The CPP protocol was unbiased and carried out in three phases: habituation, conditioning and testing. For conditioning, cocaine was injected at a dose of 10mg/kg in eight 15 min-sessions. The treatment with biperiden (doses of 0.1, 1 and 10 mg/kg) was made 30 min prior to the testing session. For behavioral sensitization development, cocaine was administered at the dose of 10 mg/kg for 10 days. After sensitization, two challenges were performed: saline and cocaine (5 mg/kg). Biperiden (10 mg/kg) was administered 30 min before the cocaine challenge. At the dose of 10 mg/kg, biperiden blocked the cocaine-CPP expression, suggesting an effect on conditioned memory retrieval. However, the same dose potentiated the expression of behavioral sensitization, suggesting an increase in DA release, probably in the NAc. Biperiden, as other mACh antagonists, may be a promising drug for the pharmacologic treatment of cocaine addiction.

Scopolamine administration modulates muscarinic, nicotinic and NMDA receptor systems

Studies on the effect of scopolamine on memory are abundant but so far only regulation of the muscarinic receptor (M1) has been reported. We hypothesized that levels of other cholinergic brain receptors as the nicotinic receptors and the N-methyl-D-aspartate (NMDA) receptor, known to be involved in memory formation, would be modified by scopolamine administration.

C57BL/6J mice were used for the experiments and divided into four groups. Two groups were given scopolamine 1 mg/kg i.p. (the first group was trained and the second group untrained) in the multiple T-maze (MTM), a paradigm for evaluation of spatial memory. Likewise, vehicle-treated mice were trained or untrained thus serving as controls. Hippocampal levels of M1, nicotinic receptor alpha 4 (Nic4) and 7 (Nic7) and subunit NR1containing complexes were determined by immunoblotting on blue native gel electrophoresis.

Vehicle-treated trained mice learned the task and showed memory retrieval on day 8, while scopolamine-treatment led to significant impairment of performance in the MTM. At the day of retrieval, hippocampal levels for M1, Nic7 and NR1 were higher in the scopolamine treated groups than in vehicle-treated groups.

The concerted action, i.e. the pattern of four brain receptor complexes regulated by the anticholinergic compound scopolamine, is shown. Insight into probable action mechanisms of scopolamine at the brain receptor complex level in the hippocampus is provided. Scopolamine treatment is a standard approach to test cognitive enhancers and other psychoactive compounds in pharmacological studies and therefore knowledge on mechanisms is of pivotal interest.

A comparison of scopolamine and biperiden as a rodent model for cholinergic cognitive impairment

RATIONALE

The nonselective muscarinic antagonist scopolamine hydrobromide (SCOP) is employed as the gold standard for inducing memory impairments in healthy humans and animals. However, its use remains controversial due to the wide spectrum of behavioral effects of this drug.

OBJECTIVE

The present study investigated whether biperiden (BIP), a muscarinic m1 receptor antagonist, is to be preferred over SCOP as a pharmacological model for cholinergic memory deficits in rats. This was done by comparing the effects of SCOP and BIP using a battery of operant tasks: fixed ratio (FR5) and progressive ratio (PR10) schedules of reinforcement, an attention paradigm and delayed nonmatching to position task.

RESULTS

SCOP induced diffuse behavioral disruption, which included sensorimotor responding (FR5, 0.3 and 1 mg/kg), food motivation (PR10, 1 mg/kg), attention (0.3 mg/kg, independent of stimulus duration), and short-term memory (delayed nonmatching to position (DNMTP), 0.1 and 0.3 mg/kg, delay-dependent but also impairment at the zero second delay). BIP induced relatively more selective deficits, as it slowed sensorimotor responding (FR5, 10 mg/kg) and disrupted short-term memory (DNMTP, 3 mg/kg, delay-dependent but no impairment at the zero second delay). BIP had no effect on food motivation (PR10) or attention.

CONCLUSION

Muscarinic m1 antagonists should be considered an interesting alternative for SCOP as a pharmacological model for cholinergic mnemonic deficits in animals.

Prose memory in patients with idiopathic Parkinson's disease

BACKGROUND

The findings of previous studies have suggested that verbal memory impairments were observed in people suffering from Parkinson's disease (PD). Very few studies have examined the comprehensive profile of prose memory deficits that challenges people with PD.

METHODS

Prose memory of 19 patients with PD was examined. Their performance in three constructs, namely recall accuracy, temporal sequence, and distortions, during immediate, delayed and recognition trials was studied.

RESULTS

The patients with PD performed significantly worse in recall accuracy and temporal sequencing of information in the immediate recall trial. During the recognition trial, they made more false alarms than their healthy counterparts.

CONCLUSIONS

Our findings confirm that the performance of people with PD in immediate recall of a prose was impaired. However, the level of performance in subsequent learning and delayed recall trials became comparable to that of the normal controls. The deficit remaining after multiple learning trials was the significantly high false alarms committed in the recognition trial. Our findings highlight the importance of qualitative analysis, in addition to quantitative evaluation, of prose memory in PD.