Amelioration of experimental amnesia (passive avoidance failure) in rodents by the selective M1 agonist AF102B

Clemastine Promotes Differentiation of Oligodendrocyte Progenitor Cells Through the Activation of ERK1/2 via Muscarinic Receptors After Spinal Cord Injury

The recovery of spinal cord injury (SCI) is closely associated with the obstruction of oligodendrocyte progenitor cell (OPC) differentiation, which ultimately induces the inability to generate newly formed myelin. To address the concern, drug-based methods may be the most practical and feasible way, possibly applying to clinical therapies for patients with SCI. In our previous study, we found that clemastine treatment preserves myelin integrity, decreases the loss of axons, and improves functional recovery in the SCI model. Clemastine acts as an antagonist of the muscarinic acetylcholine receptor (muscarinic receptor, MR) identified from a string of anti-muscarinic drugs that can enhance oligodendrocyte differentiation and myelin wrapping. However, the effects of clemastine on OPC differentiation through MRs in SCI and the underlying mechanism remain unclear. To explore the possibility, a rat model of SCI was established. To investigate if clemastine could promote the differentiation of OPCs in SCI via MR, the expressions of OPC and mature OL were detected at 7 days post injury (dpi) or at 14 dpi. The significant effect of clemastine on encouraging OPC differentiation was revealed at 14 dpi rather than 7 dpi. Under pre-treatment with the MR agonist cevimeline, the positive role of clemastine on OPC differentiation was partially disrupted. Further studies indicated that clemastine increased the phosphorylation level of extracellular signal–regulated kinase 1/2 (p-ERK1/2) and the expressions of transcription factors, Myrf and Olig2. To determine the relationship among clemastine, ERK1/2 signaling, specified transcription factors, and OPC differentiation, the ERK1/2 signaling was disturbed by U0126. The inhibition of ERK1/2 in SCI rats treated with clemastine decreased the expressions of p-ERK 1/2, Myrf, Olig2, and mature OLs, suggesting that ERK1/2 is required for clemastine on promoting OPC differentiation and that specified transcription factors may be affected by the activity of ERK1/2. Moreover, the impact of clemastine on modulating the level of p-ERK 1/2 was restricted following cevimeline pre-injecting, which provides further evidence that the role of clemastine was mediated by MRs. Altogether, our data demonstrated that clemastine, mediated by MRs, promotes OPC differentiation under the enhancement of Myrf and Olig2 by activating ERK1/2 signaling and suggests a novel therapeutic prospect for SCI recovery.

Neuropharmacology of Cevimeline and Muscarinic Drugs-Focus on Cognition and Neurodegeneration

At present, Alzheimer’s disease (AD) and related dementias cannot be cured. Therefore, scientists all over the world are trying to find a new approach to prolong an active life of patients with initial dementia. Both pharmacological and non-pharmacological pathways are investigated to improve the key symptom of the disease, memory loss. In this respect, influencing the neuromodulator acetylcholine via muscarinic receptors, such as cevimeline, might be one of the therapeutic alternatives. The purpose of this study is to explore the potential of cevimeline on the cognitive functions of AD patients. The methodology is based on a systematic literature review of available studies found in Web of Science, PubMed, Springer, and Scopus on the research topic. The findings indicate that cevimeline has shown an improvement in experimentally induced cognitive deficits in animal models. Furthermore, it has demonstrated to positively influence tau pathology and reduce the levels of amyloid-β (Aβ) peptide in the cerebral spinal fluid of Alzheimer’s patients. Although this drug has not been approved by the FDA for its use among AD patients and there is a lack of clinical studies confirming and extending this finding, cevimeline might represent a breakthrough in the treatment of AD.

Muscarinic agonists for the treatment of Alzheimer’s disease: progress and perspectives

Much interest has focused on the development of selective muscarinic agonists for the treatment of Alzheimer's disease (AD). Cholinergic replacement therapy is thought to be beneficial in alleviating some of the cognitive dysfunctions in this disorder. The cholinergic neuronal tracts are involved in memory and learning processes, and the extent of the degeneration of the cortical projections correlates with the severity of the dementia. An M1 selective muscarinic agonist may be effective in treating at least some of the cognitive symptoms in AD. Highly selective M1 agonists, producing cellular excitation, should be beneficial in AD, regardless of the extent of degeneration of presynaptic cholinergic projections to the frontal cortex or hippocampus. Functional abnormalities in AD may also occur along various signal transduction pathways mediated, in part, at least, by muscarinic receptors. In general, activities associated with mAChR subtypes and m1 receptors, in particular, indicate that M1 agonists may also be useful for this aspect of AD. Mismetabolism of amyloid precursor proteins (APPs) may induce AD. Recent studies indicate that the formation of the b-amyloid peptide (Abeta) and amyloid plaques is linked to the loss of cholinergic function in AD. New data on the activation of m1 mAChRs in conjunction with recent findings that the induction of such receptors stimulates neurotrophic-like activities, decreases tau phosphorylation and inhibits apoptosis indicate that restoring the cholinergic tone in AD may be useful both in improving memory function and in altering the onset and progression of AD dementia. This article focuses on the recent, promising developments in this field and assesses the value of muscarinic agonists currently under development for the treatment of AD.

The profile of sabcomeline (SB-202026), a functionally selective M1 receptor partial agonist, in the marmoset

1. Sabcomeline (SB-202026, 0.03 mg kg(-1), p.o.), a potent and functionally selective M1 receptor partial agonist, caused a statistically significant improvement in the performance of a visual object discrimination task by marmosets. No such improvement was seen after RS86 (0.1 mg kg(-1), p.o.). 2. Initial learning, which only required an association of object with reward and an appropriate response to be made, was not significantly affected. Reversal learning, which required both the extinction of the previously learned response and the acquisition of a new response strategy, was significantly improved after administration of sabcomeline (0.03 mg kg(-1), p.o.). 3. Sabcomeline (0.03 and 0.1 mg kg(-1), p.o.) had no significant effect on mean blood pressure measured for 2 h after administration in the conscious marmoset. 4. Sabcomeline (0.03 mg kg(-1), p.o.) caused none of the overt effects such as emesis or behaviours often seen after the administration of muscarinic agonists, e.g. face rubbing and licking. 5. This is the first study to demonstrate cognitive enhancement by a functionally selective M1 receptor partial agonist in a normal (i.e. non-cognitively impaired) non-human primate and this effect was seen at a dose which did not cause side effects. 6. Perseverative behaviour and deficient acquisition of new information are seen in patients with Alzheimer's disease (AD). Therefore the data suggest that sabcomeline might be of therapeutic benefit in the treatment of AD.

Modulation of rhythmical slow activity, long-term potentiation and memory by muscarinic receptor agonists

We investigated the cholinergic modulation of hippocampal rhythmical slow activity (or theta activity), long-term potentiation and a behavioral memory task. The intravenous administration of the muscarinic receptor agonists, AF102B ((+/-)-cis-2-methyl-spiro(1,3-oxathiolane-5,3') quinuclidine hydrochloride hemihidrate) and oxotremorine, induced rhythmical slow activity at doses of 1.0 mg/kg and 0.01 mg/kg, respectively. Long-term potentiation of population spike amplitude in the hippocampal CA1, which was induced by tetanic stimulation to the Schaffer collateral/commissural fiber, was increased by AF102B (1.0 mg/kg i.v.) and oxotremorine (0.01 mg/kg i.v.). Oral administration of AF102B and oxotremorine improved scopolamine-induced memory deficits in a passive avoidance task in mice at doses of 1.0 mg/kg and 0.2 mg/kg, respectively. The correspondence of the effective doses of muscarinic receptor agonists in these three experiments suggested the cholinergic correlation of rhythmical slow activity, long-term potentiation and memory.

A comparison of the effects of the novel muscarinic receptor agonists L-689,660 and AF102B in tests of reference and working memory

Four experiments compared the CNS effects of a novel M1/M3 receptor agonist L-689,660 with those of the M1/M3 muscarinic receptor agonist AF102B. In the mouse tail-flick test of antinociception (TF) the minimum effective doses to increase tail-flick latency (MED) of L-689,660 and AF102B were 0.03 mg/kg and 10.0 mg/kg, respectively. In a rat conditioned-suppression-of-drinking (CSD) test of reference memory, doses of 0.3 and 1.0 mg/kg L-689,660 and a dose of 5.0 mg/kg AF102B reversed a scopolamine-induced deficit in performance (0.6 mg/kg). Although there was a tendency for L-689,660 to reverse the scopolamine-induced (0.4 mg/kg) performance deficit in a rat delayed-matching-to-position (DMTP) test, the difference failed to reach statistical significance. In contrast, a 5.0 mg/kg dose of AF102B potentiated the scopolamine-induced deficit in choice accuracy and the number of trials completed on this task. In a response sensitivity (RS) test, chain-pulling rates were significantly decreased by L-689,660 (MED = 0.03 mg/kg) and by AF102B (MED = 5.0 mg/kg). These results suggest that L-689,660 and AF102B may ameliorate or reverse a scopolamine-induced deficit, but only at doses that also reduce chain-pulling rates on operant schedules of reinforcement.

AF102B, a novel M1 agonist, enhanced spatial learning in C57BL/10 mice with a long duration of action

Orally administered AF102B, a selective muscarinic M1 cholinergic agonist, improved spatial learning in C57BL/10 mice in the Morris water maze. In four experiments in which all drug-treated animals received only one single administration of AF102B, improvement of acquisition depended on two factors: pretreatment time (tp) and dose. When a standard tp of 1 h was used, AF102B exhibited a U-shaped dose-response curve that is characteristic of many nootropic agents: learning was significantly improved by dose levels ranging from 0.1 to 1 mg/kg p.o. When the tp was extended out to as long as 8 days, two new effects emerged: (a) 1 mg/kg, the dose that had been the peak active dose at 1 h, exhibited a biphasic time course of action, being active at 1 h or at all tp intervals from 3 h to 5 days, but not at 1.5 h; (b) 0.03 mg/kg, a dose that had been inactive at a tp of 1 h, was active at all tp intervals from 3 h to 5 days, but not at shorter (1 and 2 h) or longer (6-8 days) tp intervals. In another experiment, animals received 0.03 mg/kg for 1-5 consecutive days: this dose level was active if the tp interval between the last dose and the learning session was 24-120 h, but not if it was only 1 h. Thus AF102B enhanced cognition in mice with a longer duration of action than reported for traditional muscarinic agonists.

Dose- and delay-dependent working/episodic memory impairments following intraventricular administration of ethylcholine aziridinium ion (AF64A)

The present study examined the effects of intraventricular administration of the cholinergic neurotoxin ethylcholine aziridinium ion (AF64A) on performance of a radial arm maze task. Male Sprague-Dawley rats were trained to perform a delayed-nonmatch to sample radial arm maze task in which a 1-h delay was imposed between the fourth and fifth arm selections. Following acquisition, animals were injected bilaterally with AF64A (1.5 or 0.75 nmol/side) or artificial cerebrospinal fluid into the lateral cerebral ventricles and allowed 7 days to recover before behavioral testing resumed. Significant dose- and delay-dependent impairments in the radial maze performance were observed in AF64A-treated rats as evidenced by fewer correct choices following the delay and by more errors to complete the task. Long-term testing in this task revealed significant recovery of memory performance. These findings indicate dose-dependent impairments in memory following intraventricular administration of AF64A and spontaneous behavioral recovery following such insult.

Cholinergic strategies in the treatment of Alzheimer's disease

Since the identification of the cholinergic deficit, strategies aimed at enhancing cholinergic neurotransmission have dominated the field of pharmacology in Alzheimer's disease (AD). These strategies include increasing acetylcholine precursor availability, delaying synaptic degradation and stimulating muscarinic receptors. Although most clinical trials report mild symptomatic improvements in some patients, support for large-scale clinical use of cholinomimetics in AD is not yet available. This article presents the most representative clinical trials, discusses the limitations of the cholinergic strategies and suggests future directions in the treatment of AD.

Diagnostic and pharmacological approaches in Alzheimer's disease

Alzheimer's disease is a chronic progressive disease affecting higher intellectual functioning. The clinical diagnosis is made when the onset of illness is insidious, the course slowly progressive and all the treatable causes of dementia have been ruled out. The use of more stringent criteria has improved clinical diagnosis, but at best only 80% of patients are accurately diagnosed. Ultimately the diagnosis depends upon pathological confirmation. The neuritic plaques and neurofibrillary tangles described by Alzheimer, although not pathognomonic for the disease, continue to be the basis for pathological diagnosis. The aetiology and pathophysiology of Alzheimer's disease are presently unknown. Epidemiological studies have suggested a genetic basis for the disorder, and many biochemical studies have linked it to degeneration of central cholinergic neurons, and possibly to abnormalities of other neurotransmitter systems. A marker which would permit accurate diagnosis early in the course of disease would be of major importance to researchers and clinicians alike. No marker has been found to date, although recent research results are promising. Various pharmacological strategies have been employed in the treatment of Alzheimer's disease. More recently attempts have focused on enhancing central cholinergic transmission. Despite the well-founded rationale for these studies, results have been modest.

Cholinergic drugs reverse AF64A-induced impairment of passive avoidance learning in rats

The cholinergic neurotoxin AF64A was administered to rats in order to produce learning impairment to test the effect of cholinergic drugs. Seven days after receiving an intracerebroventricular injection of AF64A (2.5-7.5 nmol), rats were subjected to one-trial passive avoidance acquisition and tested 24 h later. Learning was significantly impaired at 3.75 nmol AF64A, a dose at which significant reduction in acetylcholine level and choline acetyltransferase and acetylcholinesterase activity in the hippocampus was observed but changes in monoamine levels in the hippocampus, general behavior, or sensory sensitivity were not observed. Arecoline (4 mg/kg, IP) and physostigmine (0.1 mg/kg, IP) significantly decreased the learning impairment produced by AF64A (3.75 nmol) when given before the acquisition of passive avoidance learning but not when given after the acquisition or before the 24 h retention test. These drugs and oxotremorine (0.1 mg/kg, IP) given immediately after the acquisition, however, improved passive avoidance retention when the interval between the acquisition and the test was shortened to 1 h. These results indicate that the impairment of learning in AF64A-treated rats is caused by a memory retention deficit and suggest that such impairment can be effectively ameliorated by cholinergic drugs.

Sympathoexcitatory action of a novel muscarinic receptor agonist, AF102B, and its blockade by pirenzepine

The pharmacological effects of a novel, selective muscarinic (M1) receptor agonist, AF102B (cis-2-methyl-spiro-(1,3-oxathiolane-5,3')-quinuclidine hydrochloride hemihydrate), on sympathetic nerve activity are described. Intravenous administration of AF102B (1 and 10 mg/kg) produced a dose-dependent increase in cardiac sympathetic nerve activity accompanied by tachycardia in spinal-intact rats. In addition, AF102B (10 mg/kg) caused a marked increase in cardiac sympathetic nerve activity and heart rate in pithed rats. Pirenzepine (50 micrograms/kg) inhibited these sympathoexcitatory effects of AF102B (10 mg/kg) in pithed rats. These findings suggest that AF102B possesses a sympathoexcitatory action which is mediated by M1-receptors.

Effects of a M1 muscarinic receptor agonist on the central cholinergic system, evaluated by brain microdialysis

The effects of a novel M1-receptor agonist, AF102B (FKS-508; cis-2-methylspiro(1,3-oxathiolane-5,3')quinuclidine), on the central cholinergic system in vivo were evaluated by determination of acetylcholine (ACh) content in the rat brain after microwave irradiation and by measurement of ACh release with microdialysis perfusion in freely moving rats. Intraperitoneal administration of AF102B resulted in a significant decrease of ACh content in the brain, while AF102B produced an increase of in vivo ACh release. The present results suggest that ACh content in the brain after treatment with muscarinic agents may be related to the changes of ACh release, in which both M1 and M2 muscarinic receptors may be involved.

Central muscarinic activities of an M1-selective agonist: preferential effect on reversal of amnesia

Effects of FKS-508 (AF102B; cis-2-methylspiro (1,3-oxathiolane-5,3')-quinuclidine), a novel M1-selective agonist, on central muscarinic responses in mice were examined in comparison with oxotremorine. FKS-508 was slightly less potent (6 times) in reversal of scopolamine-induced amnesia (passive avoidance failure), but far less potent (260 and 55 times) in producing hypothermia and tremor than oxotremorine. These results show that the selective M1 agonist FKS-508 differentiates highly between the central muscarinic effects.