GluN2A-selective positive allosteric modulator-nalmefene-flumazenil reverses ketamine-fentanyl-dexmedetomidine-induced anesthesia and analgesia in rats

NMDA receptors as therapeutic targets for depression treatment: Evidence from clinical to basic research

Ketamine, functioning as a channel blocker of the excitatory glutamate-gated N-methyl-d-aspartate (NMDA) receptors, displays compelling fast-acting and sustained antidepressant effects for treatment-resistant depression. Over the past decades, clinical and preclinical studies have implied that the pathology of depression is associated with dysfunction of glutamatergic transmission. In particular, the discovery of antidepressant agents modulating NMDA receptor function has prompted breakthroughs for depression treatment compared with conventional antidepressants targeting the monoaminergic system. In this review, we first summarized the signalling pathway of the ketamine-mediated antidepressant effects, based on the glutamate hypothesis of depression. Second, we reviewed the hypotheses of the synaptic mechanism and network of ketamine antidepressant effects within different brain areas and distinct subcellular localizations, including NMDA receptor antagonism on GABAergic interneurons, extrasynaptic and synaptic NMDA receptor-mediated antagonism, and ketamine blocking bursting activities in the lateral habenula. Third, we reviewed the different roles of NMDA receptor subunits in ketamine-mediated cognitive and psychiatric behaviours in genetically-manipulated rodent models. Finally, we summarized the structural basis of NMDA receptor channel blockers and discussed NMDA receptor modulators that have been reported to exert potential antidepressant effects in animal models or in clinical trials. Integrating the cutting-edge technologies of cryo-EM and artificial intelligence-based drug design (AIDD), we expect that the next generation of first-in-class rapid antidepressants targeting NMDA receptors would be an emerging direction for depression therapeutics. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Endogenous opiates and behavior: 2020

This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Safety and Efficacy of Ketamine-Fentanyl-Dexmedetomidine-Induced Anesthesia and Analgesia in Neonatal and Aged Rats

The efficiency of many anesthetic regimens is controversial, with side effects especially in the vulnerable children and old population. The study aimed to evaluate the safety and efficacy of low-dose combination of ketamine, fentanyl, and dexmedetomidine (KFD) for anesthesia and analgesia in the neonatal and elderly rats. KFD rapidly induced anesthesia and analgesia in either postnatal days 6 (P6) or 13 months (13M) old rats. Meanwhile, KFD administration had no adverse effects on the cardiovascular and respiratory systems. Compared with control group, there were no distinct morphologic changes in kidney, liver, and brain in KFD group. Moreover, administration of KFD had no influence on hepatic and renal function in rats of both ages. Furthermore, there was no obvious difference in cognitive function between control and KFD groups. These results indicated that the administration of KFD combination offered safe and efficient anesthesia. Collectively, our results suggest the potential implication of the KFD combination in anesthesia management.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Pharmacodynamic elucidation of glutamate & dopamine in ketamine-induced anaesthesia

General anaesthetics are some of the most widely used and essential therapeutic agents. However, despite over a century of research, the molecular mechanisms of general anaesthesia in the central nervous system remain elusive. Ketamine (ketamine hydrochloride) has been approved for use in general anaesthesia either alone or in combination with other medications. It is a superb drug for use in short-term medical procedures that do not require skeletal muscle relaxation, and it has approval for the induction of general anaesthesia as a pre-anaesthetic to other general anaesthetic agents. However, Several questions remain unsolved, including the exact identification of the neural substrate of consciousness and its components, the pharmacodynamic interactions between anaesthetic agents, the mechanisms of cognitive alterations that follow an anaesthetic procedure, the identification of an eventual unitary mechanism of anaesthesia-induced alteration of consciousness, the relationship between network effects and the biochemical targets of anaesthetic agents, leading to difficulties in between-studies comparisons. Thus, the glutamate and dopamine systems play distinct roles in terms of neuronal signalling, yet both have proposed to contribute significantly to the pathophysiology of neuropsychiatric diseases. Imaging of the glutamate system and other aspects of research on the dopamine system have produced less consistent findings, potentially due to methodological limitations and the heterogeneity of the disorder. In this review, we discuss the neural circuits through which the two systems interact and how their disruption may cause psychotic symptoms. We also summarize from a molecular perspective of mechanisms of action of ketamine as general anaesthetics on ligand-gated ion channels mediated modulation of dopamine in the brain region.