Molecular interactions between general anesthetics and the 5HT2B receptor

Assessment of the molecular mechanism in fish using eugenol as anesthesia based on network pharmacology

Eugenol is a commonly used fish anesthetic, but its mechanism of action is not fully understood. This study employed network pharmacology, molecular docking, and molecular dynamics simulation to explore the anesthetic targets of eugenol in fish. Initially, 63 potential targets for eugenol anesthesia were identified using databases such as SwissTarget, TargetNet, GeneCards, OMIM, and TTD. The DAVID database was utilized to analyze the GO functions and KEGG pathways of these targets, revealing 384 GO enrichment terms and 43 KEGG pathways. These terms involved neuroactive ligand-receptor interaction, calcium signaling pathway, and synaptic transmission. Subsequently, AutodockTools software facilitated molecular docking with targets in the KEGG pathway for "neuroactive ligand-receptor interaction." The results showed that eugenol had a strong affinity with these proteins. Concurrently, molecular dynamics simulations were conducted on the proteins with the top four lowest binding energies (Cnr1, Oprk1, Nr3c1, and Chrm5a) in the presence of eugenol. The eugenol-protein complexes remained stable and equilibrated within the dynamic environment. The results indicated that eugenol-anesthesia might affect membrane receptors, neurotransmitters, and ion signaling. This study elucidates the anesthetic mechanism of eugenol, enriches the primary data on fish anesthesia, and offers new analytical tools for understanding the action mechanisms of fishery drugs.

Optogenetic activation of dorsal raphe serotonin neurons induces brain-wide activation

Serotonin is a neuromodulator that affects multiple behavioral and cognitive functions. Nonetheless, how serotonin causes such a variety of effects via brain-wide projections and various receptors remains unclear. Here we measured brain-wide responses to optogenetic stimulation of serotonin neurons in the dorsal raphe nucleus (DRN) of the male mouse brain using functional MRI with an 11.7 T scanner and a cryoprobe. Transient activation of DRN serotonin neurons caused brain-wide activation, including the medial prefrontal cortex, the striatum, and the ventral tegmental area. The same stimulation under anesthesia with isoflurane decreased brain-wide activation, including the hippocampal complex. These brain-wide response patterns can be explained by DRN serotonergic projection topography and serotonin receptor expression profiles, with enhanced weights on 5-HT1 receptors. Together, these results provide insight into the DR serotonergic system, which is consistent with recent discoveries of its functions in adaptive behaviors.

Investigation of the Role of Stimulation and Blockade of 5-HT7 Receptors in Ketamine Anesthesia

Although several pieces of evidence have indicated the ability of the serotonin-7 receptor (5-HTR₇) to modulate N-methyl-_D-aspartate receptor (NMDAR) activation, the possible impact on ketamine anesthesia has not been examined directly. The purpose of the present study is thus to investigate the possible role of the 5-HTR₇ in ketamine anesthesia using a 5-HTR₇ agonist and/or antagonist. The influence of a 5-HTR₇ agonist/antagonist on ketamine anesthesia for behavioral impact was assessed by testing potential anesthetic parameters. Its functional impact was assessed by mRNA expression with real-time PCR and immunostaining in the hippocampus and prefrontal cortex of mice. Two different doses of ketamine-high and low-were administered to induce anesthesia. In the high-dose ketamine-applied group in particular, the administration of both the 5-HTR₇ agonist and antagonist intensified the anesthetic effect of ketamine. The reflection of the change in anesthesia parameters to 5-HTR₇ expression was observed as an increase in the hippocampus and a decrease in the prefrontal cortex in the anesthetized groups by stimulation of 5-HTR₇. It is noteworthy that the results of NMDAR expressions are parallel to the results of the 5-HTR₇ expressions of both the hippocampus and the prefrontal cortex. The 5-HTR₇ may play a role in ketamine anesthesia. It may act through NMDAR in ketamine anesthesia, depending on the parallelism between both receptors.

Computational Methods for the Identification of Molecular Targets of Toxic Food Additives. Butylated Hydroxytoluene as a Case Study

Butylated hydroxytoluene (BHT) is one of the most commonly used synthetic antioxidants in food, cosmetic, pharmaceutical and petrochemical products. BHT is considered safe for human health; however, its widespread use together with the potential toxicological effects have increased consumers concern about the use of this synthetic food additive. In addition, the estimated daily intake of BHT has been demonstrated to exceed the recommended acceptable threshold. In the present work, using BHT as a case study, the usefulness of computational techniques, such as reverse screening and molecular docking, in identifying protein-ligand interactions of food additives at the bases of their toxicological effects has been probed. The computational methods here employed have been useful for the identification of several potential unknown targets of BHT, suggesting a possible explanation for its toxic effects. In silico analyses can be employed to identify new macromolecular targets of synthetic food additives and to explore their functional mechanisms or side effects. Noteworthy, this could be important for the cases in which there is an evident lack of experimental studies, as is the case for BHT.

Serotonin (5-HT) Shapes the Macrophage Gene Profile through the 5-HT2B-Dependent Activation of the Aryl Hydrocarbon Receptor

Macrophages can either promote or resolve inflammatory responses, and their polarization state is modulated by peripheral serotonin (5-hydroxytryptamine [5-HT]). In fact, pro- and anti-inflammatory macrophages differ in the expression of serotonin receptors, with 5-HT_2B and 5-HT₇ expression restricted to M-CSF-primed monocyte-derived macrophages (M-MØ). 5-HT₇ drives the acquisition of profibrotic and anti-inflammatory functions in M-MØ, whereas 5-HT_2B prevents the degeneration of spinal cord mononuclear phagocytes and modulates motility of murine microglial processes. Because 5-HT_2B mediates clinically relevant 5-HT-related pathologies (valvular heart disease, pulmonary arterial hypertension) and is an off target of anesthetics, antiparkinsonian drugs, and selective serotonin reuptake inhibitors, we sought to determine the transcriptional consequences of 5-HT_2B engagement in human macrophages, for which 5-HT_2B signaling remains unknown. Assessment of the effects of specific agonists and antagonist revealed that 5-HT_2B engagement modifies the cytokine and gene signature of anti-inflammatory M-MØ, upregulates the expression of aryl hydrocarbon receptor (AhR) target genes, and stimulates the transcriptional activation of AhR. Moreover, we found that 5-HT dose dependently upregulates the expression of AhR target genes in M-MØ and that the 5-HT-mediated activation of AhR is 5-HT_2B dependent because it is abrogated by the 5-HT_2B-specific antagonist SB204741. Altogether, our results demonstrate the existence of a functional 5-HT/5-HT_2B/AhR axis in human macrophages and indicate that 5-HT potentiates the activity of a transcription factor (AhR) that regulates immune responses and the biological responses to xenobiotics.

Zebrafish behavioural profiling identifies GABA and serotonin receptor ligands related to sedation and paradoxical excitation

Anesthetics are generally associated with sedation, but some anesthetics can also increase brain and motor activity—a phenomenon known as paradoxical excitation. Previous studies have identified GABA_A receptors as the primary targets of most anesthetic drugs, but how these compounds produce paradoxical excitation is poorly understood. To identify and understand such compounds, we applied a behavior-based drug profiling approach. Here, we show that a subset of central nervous system depressants cause paradoxical excitation in zebrafish. Using this behavior as a readout, we screened thousands of compounds and identified dozens of hits that caused paradoxical excitation. Many hit compounds modulated human GABA_A receptors, while others appeared to modulate different neuronal targets, including the human serotonin-6 receptor. Ligands at these receptors generally decreased neuronal activity, but paradoxically increased activity in the caudal hindbrain. Together, these studies identify ligands, targets, and neurons affecting sedation and paradoxical excitation in vivo in zebrafish.

Some anesthetics despite being generally associated with sedation, can also increase brain activity—a phenomenon called paradoxical excitation. The authors identified dozens of compounds that generally decrease neuronal activity, but increase activity in the caudal hindbrain of zebrafish.

Synergistic action of CB1 and 5-HT2B receptors in preventing pilocarpine-induced status epilepticus in rats

Endocannabinoids (eCBs) and serotonin (5-HT) play a neuromodulatory role in the central nervous system. Both eCBs and 5-HT regulate neuronal excitability and their pharmacological potentiation has been shown to control seizures in pre-clinical and human studies. Compelling evidence indicates that eCB and 5-HT systems interact to modulate several physiological and pathological brain functions, such as food intake, pain, drug addiction, depression, and anxiety. Nevertheless, there is no evidence of an eCB/5-HT interaction in experimental and human epilepsies, including status epilepticus (SE). Here, we performed video-EEG recording in behaving rats treated with the pro-convulsant agent pilocarpine (PILO), in order to study the effect of the activation of CB₁/5-HT₂ receptors and their interaction on SE. Synthetic cannabinoid agonist WIN55,212-2 (WIN) decreased behavioral seizure severity of PILO-induced SE at 2 mg/kg (but not at 1 and 5 mg/kg, i.p.), while 5-HT_2B/2C receptor agonist RO60-0175 (RO; 1, 3, 10 mg/kg, i.p.) was devoid of any effect. RO 3 mg/kg was instead capable of potentiating the effect of WIN 2 mg/kg on the Racine scale score. Surprisingly, neither WIN 2 mg/kg nor RO 3 mg/kg had any effect on the incidence and the intensity of EEG seizures when administered alone. However, WIN+RO co-administration reduced the incidence and the severity of EEG SE and increased the latency to SE onset after PILO injection. WIN+RO effects were blocked by the selective CB₁R antagonist AM251 and the 5-HT_2BR antagonist RS127445, but not by the 5-HT_2CR antagonist SB242084 or the 5-HT_2AR antagonist MDL11,939. These data revealed a synergistic interaction between CB₁R/5-HT_2BR in the expression of PILO-induced SE.

Mechanisms of the Immunological Effects of Volatile Anesthetics: A Review

Volatile anesthetics (VAs) have been in clinical use for a very long time. Their mechanism of action is yet to be fully delineated, but multiple ion channels have been reported as targets for VAs (canonical VA targets). It is increasingly recognized that VAs also manifest effects outside the central nervous system, including on immune cells. However, the literature related to how VAs affect the behavior of immune cells is very limited, but it is of interest that some canonical VA targets are reportedly expressed in immune cells. Here, we review the current literature and describe canonical VA targets expressed in leukocytes and their known roles. In addition, we introduce adhesion molecules called β2 integrins as noncanonical VA targets in leukocytes. Finally, we propose a model for how VAs affect the function of neutrophils, macrophages, and natural killer cells via concerted effects on multiple targets as examples.