Antisense 'knockdowns' of M1 receptors induces transient anterograde amnesia in mice

Higher sensitivity to cadmium induced cell death of basal forebrain cholinergic neurons: a cholinesterase dependent mechanism

Cadmium is an environmental pollutant, which is a cause of concern because it can be greatly concentrated in the organism causing severe damage to a variety of organs including the nervous system which is one of the most affected. Cadmium has been reported to produce learning and memory dysfunctions and Alzheimer like symptoms, though the mechanism is unknown. On the other hand, cholinergic system in central nervous system (CNS) is implicated on learning and memory regulation, and it has been reported that cadmium can affect cholinergic transmission and it can also induce selective toxicity on cholinergic system at peripheral level, producing cholinergic neurons loss, which may explain cadmium effects on learning and memory processes if produced on central level. The present study is aimed at researching the selective neurotoxicity induced by cadmium on cholinergic system in CNS. For this purpose we evaluated, in basal forebrain region, the cadmium toxic effects on neuronal viability and the cholinergic mechanisms related to it on NS56 cholinergic mourine septal cell line. This study proves that cadmium induces a more pronounced, but not selective, cell death on acetylcholinesterase (AChE) on cholinergic neurons. Moreover, MTT and LDH assays showed a dose dependent decrease of cell viability in NS56 cells. The ACh treatment of SN56 cells did not revert cell viability reduction induced by cadmium, but siRNA transfection against AChE partially reduced it. Our present results provide new understanding of the mechanisms contributing to the harmful effects of cadmium on the function and viability of neurons, and the possible relevance of cadmium in the pathogenesis of neurodegenerative diseases.

A cholinergic hypothesis of the unconscious in affective disorders

The interactions between distinct pharmacological systems are proposed as a key dynamic in the formation of unconscious memories underlying rumination and mood disorder, but also reflect the plastic capacity of neural networks that can aid recovery. An inverse and reciprocal relationship is postulated between cholinergic and monoaminergic receptor subtypes. M1-type muscarinic receptor transduction facilitates encoding of unconscious, prepotent behavioral repertoires at the core of affective disorders and ADHD. Behavioral adaptation to new contingencies is mediated by the classic prototype receptor: 5-HT1A (Gi/o) and its modulation of M1-plasticity. Reversal of learning is dependent on increased phasic activation of midbrain monoaminergic nuclei and is a function of hippocampal theta. Acquired hippocampal dysfunction due to abnormal activation of the hypothalamic-pituitary-adrenal (HPA) axis predicts deficits in hippocampal-dependent memory and executive function and further impairments to cognitive inhibition. Encoding of explicit memories is mediated by Gq/11 and Gs signaling of monoamines only. A role is proposed for the phasic activation of the basal forebrain cholinergic nucleus by cortical projections from the complex consisting of the insula and claustrum. Although controversial, recent studies suggest a common ontogenetic origin of the two structures and a functional coupling. Lesions of the region result in loss of motivational behavior and familiarity based judgements. A major hypothesis of the paper is that these lost faculties result indirectly, from reduced cholinergic tone.

Modulation of behavioral phenotypes by a muscarinic M1 antagonist in a mouse model of fragile X syndrome

RATIONALE

Muscarinic acetylcholine receptors (mAChR) are G protein-coupled receptors, widely expressed in the CNS. Electrophysiological and molecular studies have provided evidence for overactive M1 receptor signaling in the fragile X knockout (Fmr1 KO) mouse model, suggesting the involvement of the M1 receptors in fragile X syndrome. Overactive signaling through the M1 receptor has been hypothesized to contribute to the phenotypes seen in fragile X mice.

OBJECTIVE

We investigated the modulation of behavioral responses in the Fmr1 KO animals by reducing the activity through the muscarinic M1 receptor using the pharmacological agent dicyclomine, an M1 antagonist.

METHODS

The behavioral assays used to investigate the pharmacological effects include marble burying (perseverative behavior), open-field exploration (activity), passive avoidance (learning and memory), prepulse inhibition (sensorimotor gating), and audiogenic seizures.

RESULTS

Data from the marble-burying assay suggests that treatment with dicyclomine results in a decrease in the number of marbles buried in the wild-type and in the KO animals. To examine the possibility of drug-induced sedation, overall activity was measured in an open-field chamber. Dicyclomine only increases activity at a dose of 20 mg/kg in the wild-type mice but did not affect exploration in the KO animals. Lastly, we observed that dicyclomine causes a significant decrease in the percentage of audiogenic seizures in the Fmr1 KO animals.

CONCLUSION

Our findings suggest that pharmacologically reducing the activity through the mAChR M1 alters select behavioral responses in the Fmr1 KO mice.

Antiamnesic and neuroprotective effects of the aminotetrahydrofuran derivative ANAVEX1-41 against amyloid beta(25-35)-induced toxicity in mice

The antiamnesic and neuroprotective activities of the new aminotetrahydrofuran derivative tetrahydro-N,N-dimethyl-5,5-diphenyl-3-furanmethanamine hydrochloride (ANAVEX1-41), a nonselective muscarinic receptor ligand and sigma1 protein activator, were examined in mice injected intracerebroventricularly with amyloid beta(25-35) (Abeta(25-35)) peptide (9 nmol). Abeta(25-35) impaired significantly spontaneous alternation performance, a spatial working memory, and passive avoidance response. When ANAVEX1-41 (1-1000 microg/kg i.p.) was administered 7 days after Abeta(25-35), ie, 20 min before the behavioral tests, it significantly reversed the Abeta(25-35)-induced deficits, the most active doses being in the 3-100 microg/kg range. When the compound was preadministered 20 min before Abeta(25-35), ie, 7 days before the tests, it prevented the learning impairments at 30-100 microg/kg. Morphological analysis of corticolimbic structures showed that Abeta(25-35) induced a significant cell loss in the CA1 pyramidal cell layer of the hippocampus that was prevented by ANAVEX1-41 (100 microg/kg). Increased number of glial fibrillary acidic protein immunopositive cells in the retrosplenial cortex or throughout the hippocampus revealed an Abeta(25-35)-induced inflammation that was prevented by ANAVEX1-41. The drug also prevented the parameters of Abeta(25-35)-induced oxidative stress measured in hippocampus extracts, ie, the increases in lipid peroxidation and protein nitration. ANAVEX1-41, however, failed to prevent Abeta(25-35)-induced caspase-9 expression. The compound also blocked the Abeta(25-35)-induced caspase-3 expression, a marker of apoptosis. Both the muscarinic antagonist scopolamine and the sigma1 protein inactivator BD1047 prevented the beneficial effects of ANAVEX1-41 (30 or 100 microg/kg) against Abeta(25-35)-induced learning impairments, suggesting that muscarinic and sigma1 targets are involved in the drug effect. A synergic effect could indeed account for the very low active doses measured in vivo. These data outline the therapeutic potential of ANAVEX1-41 as a neuroprotective agent in Alzheimer's disease.

Muscarinic receptor dependent long-term depression in rat visual cortex is PKC independent but requires ERK1/2 activation and protein synthesis

Intact cholinergic innervation of visual cortex is critical for normal processing of visual information and for spatial memory acquisition and retention. However, a complete description of the mechanisms by which the cholinergic system modifies synaptic function in visual cortex is lacking. Previously it was shown that activation of the m1 subtype of muscarinic receptor induces an activity-dependent and partially N-methyl-d-aspartate receptor (NMDAR)-dependent long-term depression (LTD) at layer 4-layer 2/3 synapses in rat visual cortex slices in vitro. The cellular mechanisms downstream of the Galphaq coupled m1 receptor required for induction of this LTD (which we term mLTD) are currently unknown. Here, we confirm a role for m1 receptors in mLTD induction and use a series of pharmacological tools to study the signaling molecules downstream of m1 receptor activation in mLTD induction. We found that mLTD is prevented by inhibitors of L-type Ca(2+) channels, the Src kinase family, and the mitogen-activated kinase/extracellular kinase. mLTD is also partially dependent on phospholipase C but is unaffected by blocking protein kinase C. mLTD expression can be long-lasting (>2 h) and its long-term maintenance requires translation. Thus we report the signaling mechanisms underlying induction of an m1 receptor-dependent LTD in visual cortex and the requirement of protein synthesis for long-term expression. This plasticity could be a mechanism by which the cholinergic system modifies glutamatergic synapse function to permit normal visual system processing required for cognition.

Behavioral effects of morphine and cocaine in M1 muscarinic acetylcholine receptor-deficient mice

RATIONALE

Muscarinic acetylcholine receptors (M1-M5) modulate the activity of the central nervous system and an array of physiological functions. Recent evidence has also implicated muscarinic receptors in behavioral effects of drugs of abuse such as morphine and cocaine. However, the genetic similarity between muscarinic receptors and the coexpression of multiple subtypes in most cells has impeded the development of selective antagonists and the determination of the role of each muscarinic receptor subtype in morphine's and cocaine's behavioral effects.

OBJECTIVE

The present studies employ mice deficient in the M1 receptor subtype (M1 KO) to assess morphine antinociception (2.5, 5.0, 10, or 20 mg/kg) and the conditioned rewarding effects of morphine and cocaine (2.5, 5.0, or 10 mg/kg).

METHODS

M1 KO and their wild-type (WT) littermates were tested using a 56 degrees C hotplate assay and a conditioned place preference procedure. Parallel studies using the M1 receptor antagonist, pirenzepine, were also conducted in the background strain C57BL6 mice.

RESULTS

The results demonstrate that M1 KO mice display a greater antinociceptive effect of morphine in the hotplate assay; however, the effects of morphine as well as cocaine were attenuated in the conditioned place preference procedure. Comparable results were obtained with the pharmacological antagonism of the M1 receptor by pirenzepine.

CONCLUSIONS

These results suggest a modulatory role of the M1 muscarinic receptor in opioid antinociception and conditioned drug reward, and demonstrate the utility of M1 receptor knockout models for the determination of the role of the M1 subtype in the behavioral effects of morphine and cocaine.

Sympathetic sprouting drives hippocampal cholinergic reinnervation that prevents loss of a muscarinic receptor-dependent long-term depression at CA3-CA1 synapses

Degeneration of septohippocampal cholinergic neurons results in memory deficits attributable to loss of cholinergic modulation of hippocampal synaptic circuits. A remarkable consequence of cholinergic degeneration is the sprouting of noradrenergic sympathetic fibers from the superior cervical ganglia into hippocampus. The functional impact of sympathetic ingrowth on synaptic physiology has never been investigated. Here, we report that, at CA3-CA1 synapses, a Hebbian form of long-term depression (LTD) induced by muscarinic M1 receptor activation (mLTD) is lost after medial septal lesion. Unexpectedly, expression of mLTD is rescued by sympathetic sprouting. These effects are specific because LTP and other forms of LTD are unaffected. The rescue of mLTD expression is coupled temporally with the reappearance of cholinergic fibers in hippocampus, as assessed by the immunostaining of fibers for VAChT (vesicular acetylcholine transporter). Both the cholinergic reinnervation and mLTD rescue are prevented by bilateral superior cervical ganglionectomy, which also prevents the noradrenergic sympathetic sprouting. The new cholinergic fibers likely originate from the superior cervical ganglia because unilateral ganglionectomy, performed when cholinergic reinnervation is well established, removes the reinnervation on the ipsilateral side. Thus, the temporal coupling of the cholinergic reinnervation with mLTD rescue, together with the absence of reinnervation and mLTD expression after ganglionectomy, demonstrate that the autonomic-driven cholinergic reinnervation is essential for maintaining mLTD after central cholinergic cell death. We have discovered a novel phenomenon whereby the autonomic and central nervous systems experience structural rearrangement to replace lost cholinergic innervation in hippocampus, with the consequence of preserving a form of LTD that would otherwise be lost as a result of cholinergic degeneration.

Anxiety and panic: from human studies to animal research and back

The role of learning and conditioning varies across human anxiety disorders, and distinguishing between fear and panic is important to guide investigation in panic disorder. By reminding that some psychological and psychobiological theories view panic attacks as false alarms of unconditioned biological origin, we suggest that employing endophenotypes of biological and evolutionary relevance--such as the respiratory responses to suffocative stimuli--can be fruitful for both human research and animal models of panic, and can help keeping unconditioned components of the clinical picture separate from the conditioned components in the experimental setting. We present a review of a model of panic disorder by which idiosyncratic environmental adverse events can promote unconditioned and unexpected spells of physical alarm. Along the proposed causal pathway the alternative splicing expression of polymorphic genes of the cholinergic system play an important role. The overproduction of the Acetylcholinesterase readthrough splice variant after minor stress can promote passive avoidance and learning through action at the level of the corticolimbic circuitries, as well as heightened sensitivity to suffocative stimuli by action upon the cholinergic components of chemoception. When a component of anticipatory anxiety complicates the clinical picture of recurrent panic attacks, and the HPA becomes activated, the glucocorticoid response element 17 kb upstream of the Acetylcholinesterase gene transcription initiation site may sustain sensitivity to suffocative stimuli for prolonged time. Finally, we review how animal models of human panic based on unconditioned provocation of alarm reactions by the same respiratory panicogens that are employed in man are viable and promising.

The pain of antisense: in vivo application of antisense oligonucleotides for functional genomics in pain and analgesia

As the genomic revolution continues to evolve, there is an increasing demand for efficient and reliable tools for functional characterization of individual gene products. Antisense oligonucleotide-mediated knockdown has been used successfully as a functional genomics tool in animal models of pain and analgesia yet skepticism regarding the validity and utility of antisense technology remains. Contributing to this uncertainty are the lack of systematic studies exploring antisense oligonucleotide use in vivo and the many technical and methodological challenges intrinsic to the method. This article reviews the contributions of antisense oligonucleotide-based studies to the field of pain and analgesia and the general principles of antisense technology. A special emphasis is placed on technical issues surrounding the successful application of antisense oligonucleotides in vivo, including sequence selection, antisense oligonucleotide chemistry, DNA controls, route of administration, uptake, dose-dependence, time-course and adequate evaluation of knockdown.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

Multielectrode recordings: the next steps

At present, a growing number of laboratories are acquiring the capability of simultaneously monitoring the extracellular activity of over a hundred single neurons in both anaesthetized and awake animals. This paradigm, known as multielectrode recordings, is changing the face of systems neuroscience by allowing, for the first time, the visualization of the function of entire neural circuits at work. Current methods of multielectrode recording employ state of the art technologies; two potential new avenues of research will likely emerge from the further development of these experimental paradigms.

Beyond the usual suspects: a cholinergic route for panic attacks

For unknown reasons and through poorly understood mechanisms, people at risk of panic attacks are hypersensitive to suffocative stimuli and experience hyperventilation and anxiety after exposure to heightened concentrations of carbon dioxide. Similarly to the physiological reflex response to hypercapnia in animals and man, the anxious response to carbon dioxide in people with panic disorder is at least partially controlled by the central muscarinic receptors. It is suggested here that some modifications of the cholinergic functions could underlie human individual differences in carbon dioxide sensitivity and proneness to experience panic attacks. The hypothesis is based upon experimental evidence that stressful and potentially harmful stimuli prime relatively long-lasting changes in cholinergic genes expression and cholinergic receptors' regulation. The adaptive sequels of these modifications include protection of the brain from overstimulation, and, at the level of the corticolimbic circuitries, promotion of passive avoidance and learning after stress. The extension of the same modifications to the cholinergic receptors involved in chemoception, however, could lower the threshold for reaction to suffocative stimuli, including carbon dioxide. The exaggerated sensitivity to carbon dioxide observed in humans suffering from panic attacks could then be thought of as an evolutionary cost of the involvement of the cholinergic system in shaping otherwise adaptive responses to stress and threatening stimuli.

Phosphodiester oligonucleotides inhibit mitosis and trigger apoptosis by a non-antisense, p53-mediated mechanism

Oligodeoxyribonucleotides (ODNs) are currently employed to switch-off genes selectively routinely in the laboratory practice. The drawback of ODN application is that they have been often reported to elicit non-antisense effects by different mechanisms. Recently, it has been shown that double-stranded DNA oligonucleotides (30-mers) with protruding ends activate p53 in a cell-free system. In a previous work, we described that simple addition to the culture medium of heterogeneous DNA combined with cationic lipids culminated in inhibition of mitosis and induction of apoptosis. Here, we report that the same effects are achieved by lipotransfecting cultured cells with phosphorodiester ODNs (30-mers). Such effects of ODN were mediated by a non-antisense mechanism that required the wild-type form of the p53 oncosuppressor protein and was dependent on ODN concentration. Mitosis inhibition and apoptosis induction appeared to be determined by the 3' and 5' free ends of ODNs, which activated p53 independently from their sequence. Most probably, this mechanism is analogous to that evoked by genotoxic agent-induced DNA damage or by lipotransfecting cells with heterogeneous DNA.

Sustained unilateral blockade of rat striatal M(1) muscarinic receptors with m1-toxin1 in vivo

m1-Toxin1 is a trace component of the venom of the green mamba that antagonizes M(1) muscarinic receptors specifically and irreversibly in vitro. It was injected into the right caudatoputamen of Wistar rats to occlude M(1) receptors specifically for several days ("M(1) knockdown"), and to begin to establish the unknown effects of striatal M(1)-neurotransmission on movement. The extent and duration of M(1)-blockade were evaluated with receptor binding assays and light microscopic autoradiography, using 1-2 nM [3H]pirenzepine to assess unoccupied M(1) receptors. An injection of 27 pmol m1-toxin1 blocked almost all of the M(1) receptors in one caudatoputamen (4 pmol), followed by their slow recovery to supranormal levels (115%) during a week. During maximum M(1)-blockade, the binding of 1 nM [3H]N-methylscopolamine to striatal membranes was reduced by only half, indicating no blockade of M(4) receptors, which comprise 51% of striatal muscarinic receptors. It is concluded that m1-toxin1 can produce acute, focal, selective, unilateral and long-lasting M(1)-blockade for investigations of the effects of M(1)-neurotransmission in vivo. Rats with extensive unilateral striatal M(1)-blockade appeared normal, and did not show unilateral deficits in spontaneous forearm use, in contrast to rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. Since M(1)-blockade should decrease the activity of both striatonigral and striatopallidal projection neurons, and the relative activity of these neurons is believed to control movement, the results suggest that a balanced decrease in the activity of these neurons on one side of the brain does not produce a right/left imbalance in spontaneous movement.

Hyperactivity and intact hippocampus-dependent learning in mice lacking the M1 muscarinic acetylcholine receptor

Members of the muscarinic acetylcholine receptor family are thought to play key roles in the regulation of a large number of important functions of the CNS. However, the precise roles of the individual muscarinic receptor subtypes in modulating these processes are not well understood at present, primarily because of the lack of ligands with sufficient receptor subtype selectivity. To investigate the behavioral significance of the M(1) muscarinic receptor (M(1)R), which is abundantly expressed in the forebrain, we subjected M(1) receptor-deficient mice (M(1)R(-/-) mice) to a battery of behavioral tests. M(1)R(-/-) mice showed no significant impairments in neurological reflexes, motor coordination, pain sensitivity, and prepulse inhibition. Strikingly, however, M(1)R(-/-) mice consistently exhibited a pronounced increase in locomotor activity in various tests, including open field, elevated plus maze, and light/dark transition tests. Moreover, M(1)R(-/-) mice showed reduced immobilization in the Porsolt forced swim test and reduced levels of freezing after inescapable footshocks, suggesting that M(1)R(-/-) mice are hyperactive under stressful conditions as well. An increased number of social contacts was observed in a social interaction test. Surprisingly, M(1)R(-/-) mice displayed no significant cognitive impairments in the Morris water maze and in contextual fear conditioning. M(1)R(-/-) mice showed slight performance deficits in auditory-cued fear conditioning and in an eight-arm radial maze, most likely because of the hyperactivity phenotype displayed by the M(1)R(-/-) mice. Our results indicate that M(1) muscarinic receptors play an important role in the regulation of locomotor activity but appear to be less critical for cognitive processes, as generally assumed.

Effects of the selective M1 muscarinic receptor antagonist dicyclomine on emotional memory

The nonselective muscarinic antagonist scopolamine is known to impair the acquisition of some learning tasks such as inhibitory avoidance. There has been recent research into the effects of this drug in contextual fear conditioning and tone fear conditioning paradigms. The purpose of the present study was to assess the role of the selective M1 muscarinic antagonist dicyclomine in these paradigms and in the inhibitory avoidance test. Rats were administered different doses of dicyclomine or saline 30 min before acquisition training. The animals were tested 24 hr later, and it was observed that 16 mg/kg of dicyclomine impaired both contextual fear conditioning and inhibitory avoidance. However, dicyclomine (up to 64 mg/kg) did not affect tone fear conditioning. These results suggest that the selective M1 muscarinic antagonist dicyclomine differentially affects aversively motivated tasks known to be dependent on hippocampal integrity (such as contextual fear conditioning and inhibitory avoidance) but does not affect similar hippocampus-independent tasks.

Loss of muscarinic antinociception by antisense inhibition of M(1) receptors

The effect on cholinergic analgesia of inactivation of the M(1) gene by an antisense oligodeoxyribonucleotide (aODN) was investigated in the mouse hot plate test. Mice received a single intracerebroventricular (i.c.v.) injection of anti-M(1) aODN (0.3, 1. 0 or 2.0 nmol per injection), degenerate ODN (dODN) or vehicle on days 1, 4 and 7. A dose-dependent inhibition of the antinociception induced by the muscarinic agonists oxotremorine (0.1 mg kg(-1) s.c.) and McN-A-343 (30 microg per mouse i.c.v.) and the cholinesterase inhibitor physostigmine (0.2 mg kg(-1) s.c.) was observed 24 h after the last i.c.v. injection of aODN. Time-course experiments revealed that, after the end of the aODN treatment, sensitivity to analgesic drugs progressively appeared reaching the normal range at 96 h. The anti-M(1) aODN was selective against muscarinic antinociception since the enhancement of pain threshold produced by morphine and baclofen were not affected by the above-mentioned treatment. dODN, used as control, did not affect muscarinic antinociception. Binding studies evidenced a selective reduction of M(1) receptor levels in the hippocampus of aODN-treated mice. Neither aODN, dODN nor vehicle produced any behavioural impairment of mice as revealed by the rota-rod and Animex experiments. These results indicate that activation of M(1) muscarinic receptor subtype is fundamental to induce central cholinergic analgesia in mice.

Role of metabotropic glutamate receptor subclasses in modulation of adenylyl cyclase activity by a nootropic NS-105

The involvement of metabotropic glutamate (mGlu) receptors in the modulatory actions of a novel cognition enhancer, (+)-5-oxo-D-prolinepiperidinamide monohydrate (NS-105), on adenylyl cyclase activity in rat cerebrocortical membranes and primary neuronal cultures was investigated using selective antagonists and antisense oligodeoxynucleotides for mGlu receptor subclasses. In rat cerebrocortical membranes, the inhibitory action of NS-105 (0.1 microM) on forskolin-stimulated cAMP formation was blocked by a group II mGlu receptor antagonist, (+/-)-alpha-ethylglutamic acid, and by a group III antagonist, (+)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP-4), but not by a group I antagonist, (+/-)-1-aminoindan-1,5-dicarboxylic acid (AIDA), whereas the facilitation of cAMP formation by NS-105 (1 microM) in pertussis toxin-pretreated membranes was abolished by AIDA but not by (+/-)-alpha-ethylglutamic acid or MAP-4. In primary cultured neurons of mouse cerebral cortex, the inhibitory action of NS-105 on adenylyl cyclase activity disappeared after treatment with antisense oligodeoxynucleotides for group II (mGlu(2) and mGlu(3) receptors) and group III (mGlu(4) and mGlu(7) receptors) but not group I (mGlu(5) receptor) mGlu receptor subclasses. These findings suggest that the inhibitory action of NS-105 on adenylyl cyclase activity is mediated through group II and group III mGlu receptor subclasses while the facilitatory action is dependent on the group I mGlu receptor subclass.