Cell-type specific neuromodulation of excitatory and inhibitory neurons via muscarinic acetylcholine receptors in layer 4 of rat barrel cortex

The neuromodulator acetylcholine (ACh) plays an important role in arousal, attention, vigilance, learning and memory. ACh is released during different behavioural states and affects the brain microcircuit by regulating neuronal and synaptic properties. Here, we investigated how a low concentration of ACh (30 μM) affects the intrinsic properties of electrophysiologically and morphologically identified excitatory and inhibitory neurons in layer 4 (L4) of rat barrel cortex. ACh altered the membrane potential of L4 neurons in a heterogeneous manner. Nearly all L4 regular spiking (RS) neurons responded to bath-application of ACh with a M4 muscarinic ACh receptor-mediated hyperpolarisation. In contrast, in the majority of L4 fast spiking (FS) and non-fast spiking (nFS) interneurons 30 μM ACh induced a depolarisation while the remainder showed a hyperpolarisation or no response. The ACh-induced depolarisation of L4 FS interneurons was much weaker than that in L4 nFS interneurons. There was no clear difference in the response to ACh for three morphological subtypes of L4 FS interneurons. However, in four morpho-electrophysiological subtypes of L4 nFS interneurons, VIP+-like interneurons showed the strongest ACh-induced depolarisation; occasionally, even action potential (AP) firing was elicited. The ACh-induced depolarisation in L4 FS interneurons was exclusively mediated by M1 muscarinic ACh receptors; in L4 nFS interneurons it was mainly mediated by M1 and/or M3/5 muscarinic ACh receptors. In a subset of L4 nFS interneurons, a co-operative activation of nicotinic ACh receptors was also observed. The present study demonstrates that low-concentrations of ACh affect the different L4 neurons types in a cell-type specific way. These effects result from a specific expression of different muscarinic and/or nicotinic ACh receptors on the somatodendritic compartments of L4 neurons. This suggests that even at low concentrations ACh may tune the excitability of L4 excitatory and inhibitory neurons and their synaptic microcircuits differentially depending on the behavioural state during which ACh is released.

The Regulation Effect of α7nAChRs and M1AChRs on Inflammation and Immunity in Sepsis

The inflammatory storm in the early stage and immunosuppression in the late stage are responsible for the high mortality rates and multiple organ dysfunction in sepsis. In recent years, studies have found that the body’s cholinergic system can spontaneously and dynamically regulate inflammation and immunity in sepsis according to the needs of the body. Firstly, the vagus nerve senses and regulates local or systemic inflammation by means of the Cholinergic Anti-inflammatory Pathway (CAP) and activation of α7-nicotinic acetylcholine receptors (α7nAChRs); thus, α7nAChRs play important roles for the central nervous system (CNS) to modulate peripheral inflammation; secondly, the activation of muscarinic acetylcholine receptors 1 (M1AChRs) in the forebrain can affect the neurons of the Medullary Visceral Zone (MVZ), the core of CAP, to regulate systemic inflammation and immunity. Based on the critical role of these two cholinergic receptor systems in sepsis, it is necessary to collect and analyze the related findings in recent years to provide ideas for further research studies and clinical applications. By consulting the related literature, we draw some conclusions: MVZ is the primary center for the nervous system to regulate inflammation and immunity. It coordinates not only the sympathetic system and vagus system but also the autonomic nervous system and neuroendocrine system to regulate inflammation and immunity; α7nAChRs are widely expressed in immune cells, neurons, and muscle cells; the activation of α7nAChRs can suppress local and systemic inflammation; the expression of α7nAChRs represents the acute or chronic inflammatory state to a certain extent; M1AChRs are mainly expressed in the advanced centers of the brain and regulate systemic inflammation; neuroinflammation of the MVZ, hypothalamus, and forebrain induced by sepsis not only leads to their dysfunctions but also underlies the regulatory dysfunction on systemic inflammation and immunity. Correcting the neuroinflammation of these regulatory centers and adjusting the function of α7nAChRs and M1AChRs may be two key strategies for the treatment of sepsis in the future.

Cholinergic modulation of distinct inhibitory domains in granule cells of the olfactory bulb

Early olfactory processing relies on a large population of inhibitory neurons in the olfactory bulb (OB), the granule cells (GCs). GCs inhibit the OB output neurons, the mitral and tufted cells (M/TCs), shaping their responses to odors both in the spatial and temporal domains, therefore, the activity of GCs is finely tuned by local and centrifugal excitatory and inhibitory inputs. While the circuit substrates underlying regulatory inputs onto GCs are well-established, how they are locally modulated remains unclear. Here, we examine the regulation of GABAergic inhibition onto GCs by acetylcholine, a main neuromodulatory transmitter released in the OB, by basal forebrain (BF) neurons. In acute brain slices from male and female mice, we show that activation of muscarinic acetylcholine receptors (mAChRs) produces opposing effects on local and centrifugal inhibition onto GCs. By using electrophysiology, laser uncaging and optogenetics we show that the kinetics of GABAergic currents in GCs could be correlated with distal and proximal spatial domains from where they originate, along the GC somatodendritic axis. Proximal inhibition from BF afferents, is suppressed by activation of M2/M4-mAChRs. In contrast, distal local inhibition from deep short axon cells (dSACs) is enhanced by activation of M3-mAChRs. Furthermore, we show that the cholinergic enhancement of distal inhibition in GCs reduces the extent of dendrodendritic inhibition in MCs. Interestingly, the excitatory cortical feedback, which also targets the proximal region of GCs, was not modulated by acetylcholine, suggesting that muscarinic activation shifts the synaptic balance towards excitation in GCs. Together, these results suggest that BF cholinergic inputs to the OB fine tune GC-mediated inhibition of M/TCs by differentially modulating the proximal and distal domains of inhibition in GCs.

Screening and Structure-Activity Relationship of Potential Compounds against Proposed Targets of COVID-19 Infection

Background: With reference to COVID-19 pandemic prevailing across the globe, chloroquine and hyrdoxycholoroquine were reported as effective against the disease to some extent. This effectiveness can be attributed to the glycosylation interruption of Angiotensin-converting enzyme 2 (ACE2) receptor which is a known target for SARS-CoV-2 entery. On the other hand, studies suggest that inhibition of ACE2 can prove to be lethal in certain cases thereby causing cardiovascular disorders, specially in patients already suffering from heart related diseases. Methods: In this study, most probable targets (other than ACE2) have been proposed for the treatment of COVID-19 infection by taking chloroquine and hydroxychloroquine as reference drugs. To achieve this objective, SwissTargetPrediction and PASSonline tools were used. Known drugs against each target possessing close relation to either viral infections or lung disorders were assessed from DrugBank database and simultaneous efficacy of these drugs towards other proposed targets were analyzed. By taking most effective drugs as reference, similar compounds were screened from ChEMBL library by using SwissSimilarity tool. Finally, molecular docking studies were performed through MOE software by using screened compounds against proposed targets. Results: Four most probable targets have been proposed including chemokine receptors (CCRs), dipeptidyl peptidase 4 (DPP4), muscarinic acetylcholine receptors (CHRMs) and histamine N-methyltransferase (HNMT). Furthermore, it has been evaluated that Quinacrine and vildagliptin are effective against most of the proposed targets. Taking vildagliptin and quinacrine as reference drugs, eight other similar compounds effective against these targets have been screened from ChEMBL library. Molecular docking studies with CCR5, DPP4 and CHRM5 suggested that quinacrine and its analogue (ChEMBL1782742) as well as vildagliptin and its analogue (ChEMBL511785) are the most suitable compounds hitting these targets. Conclusions: It has been established that quinacrine, ChEMBL1782742, vildagliptin, ChEMBL511785, mavorixafor, atropine, and N-(2-aminoethyl)-1-aziridineethanamine can be considered as effective in descending order for the treatment of COVID-19 infection.

Balanced modulation of neuromuscular synaptic transmission via M1 and M2 muscarinic receptors during inhibition of cholinesterases

Organophosphorus (OP) compounds that inhibit acetylcholinesterase are a common cause of poisoning worldwide, resulting in several hundred thousand deaths each year. The pathways activated during OP compound poisoning via overstimulation of muscarinic acetylcholine receptors (mAChRs) play a decisive role in toxidrome. The antidotal therapy includes atropine, which is a nonspecific blocker of all mAChR subtypes. Atropine is efficient for mitigating depression in respiratory control centers but does not benefit patients with OP-induced skeletal muscle weakness. By using an ex vivo model of OP-induced muscle weakness, we studied the effects of the M1/M4 mAChR antagonist pirenzepine and the M2/M4 mAChR antagonist methoctramine on the force of mouse diaphragm muscle contraction. It was shown that weakness caused by the application of paraoxon can be significantly prevented by methoctramine (1 µM). However, neither pirenzepine (0.1 µM) nor atropine (1 µM) was able to prevent muscle weakness. Moreover, the application of pirenzepine significantly reduced the positive effect of methoctramine. Thus, balanced modulation of neuromuscular synaptic transmission via M1 and M2 mAChRs contributes to paraoxon-induced muscle weakness. It was shown that methoctramine (10 µM/kg, i.p.) and atropine (50 µM/kg, i.p.) were equieffective toward increasing the survival of mice poisoned with a 2xLD50 dose of paraoxon.

Effects of acute and repeated administration of the selective M4 PAM VU0152099 on cocaine vs. food choice in male rats

Ligands that stimulate muscarinic acetylcholine receptors 1 and 4 (M1, M4) have shown promising effects as putative pharmacotherapy for cocaine use disorder in rodent assays. We have previously shown reductions in cocaine effects with acute M4 stimulation, as well as long-lasting, delayed, reductions in cocaine taking and cocaine seeking with combined M1/M4 receptor stimulation or with M1 stimulation alone. M4 stimulation opposes dopaminergic signaling acutely, but direct dopamine receptor antagonists have proved unhelpful in managing cocaine use disorder because they lose efficacy with long-term administration. It is therefore critical to determine whether M4 approaches themselves can remain effective with repeated or chronic dosing. We assessed the effects of repeated administration of the M4 positive allosteric modulator (PAM) VU0152099 in rats trained to choose between intravenous cocaine and a liquid food reinforcer, to obtain quantitative measurement of whether M4 stimulation could produce delayed and lasting reduction in cocaine taking. VU0152099 produced progressively augmenting suppression of cocaine choice and cocaine intake, but produced neither rebound nor lasting effects after treatment ended. To compare and contrast effects of M1 vs. M4 stimulation, we tested whether the M4 PAM VU0152100 suppressed cocaine self-administration in mice lacking CalDAG-GEFI signaling factor, required for M1- mediated suppression of cocaine self-administration. CalDAG-GEFI ablation had no effect on M4- mediated suppression of cocaine self-administration. These findings support the potential usefulness of M4 PAMs as pharmacotherapy to manage cocaine use disorder, alone or in combination with M1-selective ligands, and show that M1 and M4 stimulation modulate cocaine-taking behavior by distinct mechanisms.

Acetylcholine receptors (muscarinic) in GtoPdb v.2021.3

Muscarinic acetylcholine receptors (mAChRs) (nomenclature as agreed by the NC-IUPHAR Subcommittee on Muscarinic Acetylcholine Receptors [50]) are activated by the endogenous agonist acetylcholine. All five (M1-M5) mAChRs are ubiquitously expressed in the human body and are therefore attractive targets for many disorders. Functionally, M1, M3, and M5 mAChRs preferentially couple to Gq/11 proteins, whilst M2 and M4 mAChRs predominantly couple to Gi/o proteins. Both agonists and antagonists of mAChRs are clinically approved drugs, including pilocarpine for the treatment of elevated intra-ocular pressure and glaucoma, and atropine for the treatment of bradycardia and poisoning by muscarinic agents such as organophosphates.