M1 muscarinic receptor signaling in mouse hippocampus and cortex (original) (raw)
Related papers
Agonist binding to M1 muscarinic receptors is sensitive to guanine nucleotides
European Journal of Pharmacology: Molecular Pharmacology, 1989
Putative M 1 (high-affinity pirenzepine) muscarinic receptors in rabbit hippocampal membranes, treated with 0.1 mM N-ethylmaleimide (NEM), were selectively labeled with [3H]pirenzepine. A single class of binding sites was labeled with a K d of 3.4 nM, consistent with the pharmacologically-defined M 1 subtype of muscarinic receptors. While full muscarinic agonists bound to high-and low-affinity states of [3H]pirenzepine-labeled M1 sites with a KL/K H ratio of approximately 100, the ratio for partial muscarinic agonists was approximately 10. The high-affinity binding of all agonists tested required divalent cations, and was interconverted to low-affinity binding in the presence of the non-hydrolyzable GTP analogue, guanylyl imidodiphosphate (GppNHp). Direct labeling of the high-affinity agonist state of M 1 receptors was achieved with 5 nM [3H]oxotremorine-M by selectively uncoupling the high-affinity agonist state of M 2 (low-affinity pirenzepine) receptors with NEM. The rate of dissociation of [3H]Pxotremorine-M from M 1 receptors was accelerated 6-fold by GppNHp. These results provide further evidence which suggests that putative M 1 muscarinic receptors activate second messenger systems by coupling to NEM-insensitive guanine nucleotide-binding proteins.
Neurodegeneration, 1996
THE ACETYLCHOLINE MUSCARINIC receptor family consists of five different gene products that activate different signal transduction pathways via intermediate GTP binding 'G'-proteins. The m2 and m4 receptors are coupled via pertussis toxin-sensitive G-proteins to the inhibition of adenylyl cyclase activity (Peralta et al., 1988), whereas the m1, m3 and m5 receptors act via pertussis toxin-insensitive G-proteins to stimulate phospholipases C, D and A2 (Conklin et al., 1988; Peralta et al., 1988; Sandman et al., 1991). The m1, m2 and m3 gene products correspond, respectively, to the pharmacologically defined M1, M2 and M3 receptor types. The idea that disrupted acetylcholine muscarinic receptor-mediated signal transduction could limit the success of cholinergic replacement therapies for Alzheimer's disease dementia (Fowler et al., 1990; Flynn et al., 1991) has provided the impetus for a number of studies to determine the functional integrity of muscarinic receptors in this disorder. When investigating the effects of guanylylimidodiphosphate (Gpp[NH]p) on carbachol agonist displacement of [ 3 H]pirenzepine antagonist binding, Smith et al. and Flynn and colleagues found that the ability of putative muscarinic M1 receptors to form high affinity agonistreceptor complexes with G-proteins was impaired in Alzheimer's disease parietal (Smith et al., 1987) and pre-frontal (Flynn et al., 1991) cortices. Muscarinic receptor-G-protein interactions have also been suggested to be disrupted in Alzheimer's disease thalamus (Warpman et al., 1993), whereas others have
European Journal of Pharmacology, 1989
Muscarinic acetylcholine receptors in intact, cultured explants of rat hippocampus were investigated in binding experiments with tritiated quinuclidinyl benzilate ([3H]QNB) as ligand. Dissociation constants (K j) were determined to 320-575 pM and maximal binding capacity (Bma x) to 67-87 fmol/explant. The K d s obtained in kinetic experiments were very similar. Hippocampal explants cultured alone contained more muscarinic receptors than hippocampal explants reinnervated by cholinergic fibers from co-cultured septal explants. Pretreatment of hippocampal explants with carbachol resulted in a down-regulation of receptor number which was counteracted by the simultaneous addition of atropine. Atropine added alone had no effect on receptor number in hippocampal explants cultured alone whereas it occasionally caused an up-regulation in co-cultured hippocampus. Displacement experiments with scopolamine and oxotremorine as competitors, showed that hippocampal explants cultured alone contain multiple types of muscarinic receptors. With atropine, pirenzepine and AF-DX 116, only one class of receptors could be detected.
Molecular Psychiatry, 2003
Among the five different muscarinic receptors that have been cloned and characterized, M2 and M4 receptors are localized both post-and presynaptically and are believed to have a pronounced autoreceptor role. The functional importance of these receptors in the regulation of acetylcholine release in the hippocampus and in cognitive processes was investigated by using M2 and M4 receptor single knockout (KO) as well as M2/M4 receptor double KO mice. We found profound alterations in acetylcholine homeostasis in the hippocampus of both M2-and M4-KO mice as well as of the combined M2/M4-KOs, as assessed by in vivo microdialysis. Basal acetylcholine efflux in the hippocampus was significantly increased in M4-KO and was elevated further in M2/M4-KOs. The increase in hippocampal acetylcholine induced by local administration of scopolamine was markedly reduced in M2-KO and completely abolished in M2/M4-KOs. In M2-KO and much more in M2/M4-KOs, the increase in hippocampal acetylcholine triggered by exposure to a novel environment was more pronounced both in amplitude and duration, with a similar trend observed for M4-KOs. Dysregulation of cholinergic function in the hippocampus, as it could result from perturbed autoreceptor function, may be associated with cognitive deficits. Importantly, M2-and M2/M4-KO, but not M4-KO, animals showed an impaired performance in the passive avoidance test. Together these results suggest a crucial role for muscarinic M2 and M4 receptors in the tonic and phasic regulation of acetylcholine efflux in the hippocampus as well as in cognitive processes.
Muscarinic receptors involved in hippocampal plasticity
Life Sciences, 1997
The cholinergic septohippocampal system has been associated with learning and memory, as evidenced by the severe loss of these functions in lesioned animals as well as in senile demented patients. In an attempt to comprehend the physiological basis of the cholinergic innervation for hippocampal functions, numerous studies employed the in-vitro hippocampal slice preparation and analyzed the consequences of exposing the cells to cholinergic ligands. Many effects of activating a cholinergic receptor in the hippocampus were thus described, including blockade of several types of potassium conductances, yet few of these effects are intuitively related to the involvement of the cholinergic system in hippocampal plasticity. An alternative approach involves focusing on the possible effect of low concentration of cholinergic ligands on reactivity of the hippocampus to afferent stimulation. We found two new actions of acetylcholine (ACh); The first one is a fast onset, short lived increase in cellular responses to activation of the N-methyl-D-aspartate (NMDA) receptor, and the second one is a slow onset, long lasting increase in reactivity to afferent stimulation, resembling that produced by a tetanic stimulation, which we called muscarinic long term potentiation (LTPm). The latter effect is mediated by a postsynaptic M2 receptor, and it shares several properties with the more familiar tetanic LTP. In addition, LTPm involves a rise of intracellular calcium concentration and an activation of both a tyrosine kinase and a serinelthreonine kinase. Intuitively, LTPm is better related to hippocampal plasticity than the other reported effects of ACh in the hippocampus. Indeed, aged rats, which are cognitively impaired, lack LTPm while they do express other muscarinic actions. It is proposed that LTPm is an important link between the cholinergic action and function in the hippocampus.
Preservation of acetylcholine muscarinic M2 receptor G-protein interactions 1995
The efficacy of acetylcholine muscarinic M2 receptor-G-protein coupling was investigated in Alzheimer's disease and control neocortical membranes by measuring the effects of MgC12 and 5'-guanylylimidodiphosphate Gpp[NH]p) on high-affinity [3H]oxotremorine-M ([3H]OXO-M) binding. MgC12 gave similar enhancements of [3H]OXO-M binding in Alzheimer's disease and control occipital cortex. In contrast, MgC12 enhanced [3H]OXO-M binding was significantly higher in Alzheimer's disease superior temporal cortex, compared to controls. MgCl* enhanced [3H]OXO-M binding in both the occipital and temporal cortices of the Alzheimer's disease cases was reversed to control levels by Gpp[NH]p. It is concluded that the number of high-affinity muscarinic M2 sites is increased in Alzheimer's disease superior temporal, but not occipital, cortex and that M2 sites in both regions maintain an efficient Gprotein coupling. Despite convincing evidence that the early degenera-0304-3940/95/$09.50 0 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3940(95)11281-W
Selective cognitive dysfunction in acetylcholine M1 muscarinic receptor mutant mice
Nature Neuroscience, 2002
Muscarinic, cholinergic receptor blockade produces an array of profound deficits in attentional processing, memory acquisition and memory consolidation. Five muscarinic receptor subtypes and their corresponding genes, termed M 1 -M 5 , have been identified and cloned, but their high degree of sequence similarity has hindered the development of highly selective ligands 1 . Therefore, the broad array of deficits produced by antagonists such as scopolamine or atropine and more selective ligands (for example, pirenzepine or dicyclomine for M 1 ) could result from action at multiple receptor subtypes 1-3 .