The Hippocratic Risk: Epidemiology of Suicide in a Sample of Medical Undergraduates.

In spite of the growing awareness on medical students' mental health in recent years, epidemiologic literature about the topic is scarce, particularly for what concerns suicide. Here, we collected cases of suicides among medical students enrolled at a local University in Italy and compared it to the general population of the same age group. Our sample was collected using records of suicides in the city of Pavia, Italy between the years of 2014 and 2019. This record was cross-referenced with enrolment numbers to the Medical Faculty of the city in order to select cases that involved medical students A time-window of 6 years was chosen for the evaluation. The odds ratio of suicide in medical students in comparison to the general population was of 14.58 (p value at the exact Poisson test <0.001). We then differentiated between native Italians and students from abroad. In this case, an odds ratio of 6.81 was observed (p value at the exact Poisson test 0.011). Our estimated suicide rates exceeded what was previously reported for the general population. We call for a closer attention on mental health in medical students, and an increased effort in collecting objective data on the topic.

The roles of medical examiners in the COVID-19 era: a comparison between the United States and Italy.

Italy and the United States are two of the countries most affected by SARS-CoV-2 (COVID-19), with more than 240,760 confirmed cases in Italy and 2,699,658 in the United States (as of July 2, 2020). The current COVID-19 pandemic has led to substantial changes in many fields of medicine, specifically in the forensic discipline. Medicolegal activities related to conducting autopsies have been largely affected by the COVID-19 pandemic. Postmortem examinations are generally discouraged by government regulations due to the risk of spreading the disease further through the handling and dissection of bodies from patients who succumbed to COVID-19 infection. There is a paucity of data regarding the persistence of SARS-CoV-2 in bodies, as well as concerning the reliability of swabbing methods in human remains. On the other hand, the autopsy is an essential tool to provide necessary information about the pathophysiology of the disease that presents useful clinical and epidemiological insights. On this basis, we aim to address issues concerning general medical examiner/coroner organization, comparing the Italian and American systems. We also discuss the pivotal roles of forensic pathologists in informing infectious disease surveillance. Finally, we focus on the impact of COVID-19 emergency on medicolegal practices in Italy and the United States, as well as the responses of the forensic scientific community to the emerging concerns related to the pandemic. We believe that stronger efforts by authorities are necessary to facilitate completing postmortem examinations, as data derived from such assessments are expected to be paramount to improving patient management and disease prevention.

Determination of Antidepressants and Antipsychotics in Dried Blood Spots (DBSs) Collected from Post-Mortem Samples and Evaluation of the Stability over a Three-Month Period.

An LC-MS/MS method for the identification and quantification of antidepressants and antipsychotics was developed on dried blood spots (DBSs). Moreover, analyte stability on DBSs within a 3-month period was monitored. Aliquots of 85 µL of blood from autopsy cases were pipetted onto DBS cards, which were dried and stored at room temperature. DBSs were analyzed in triplicate immediately, within the following 3 weeks, and after 3 months. For each analysis, a whole blood stain was extracted in phosphate buffer and purified using Solid Phase Extraction (SPE) cartridges in order to avoid matrix effects and injected in the LC-MS/MS system. Thirty-nine molecules were screened. Limits of detection (LODs) ranged between 0.1 and 3.2 ng/mL (g) and 0.1 and 5.2 ng/mL (g) for antidepressants and antipsychotics, respectively. Limits of quantification (LOQs) varied from 5 to 10.0 ng/mL for both. Sixteen cases among the 60 analyzed resulted positive for 17 different analytes; for 14 of these the method was fully validated. A general good agreement between the concentrations on DBSs and those measured in conventional blood samples (collected concurrently and stored at -20 °C) was observed. The degradation/enhancement percentage for most of the substances was lower than 20% within the 3-month period. Our results, obtained from real post-mortem cases, suggest that DBSs can be used for routine sample storage.

A comparison between two different dried blood substrates in determination of psychoactive substances in postmortem samples.

Purpose: Whatman™ 903 cards represent a valid type of support for collection, storage, and analysis of dried blood spots (DBS). Whatman™ FTA (Flinders Technology Associates) are a type of cards soaked in chemicals that cause denaturation of proteins, while preserving DNA and ensuring the safe handling of DBS; to date, these cards are still rarely employed in forensic toxicology. The aim of this study was to analyze several psychoactive substances on not-dried blood on the two different cards and to compare the qualitative and quantitative results. Methods: Twenty cardiac postmortem blood samples were collected and deposed on Whatman™ 903 and Whatman™ FTA cards. Spots and not-dried blood were analyzed following our validated and previously published liquid chromatography-mass spectrometry methods. Results: We were able to identify: eight drugs of abuse and their metabolites (15 cases), five benzodiazepines and their metabolites (3 cases), six antidepressants (6 cases) and two antipsychotics (3 cases). We observed a perfect qualitative correspondence and a general good quantitative correlation between data obtained from not-dried blood and the two different DBS cards, except for alprazolam, diazepam, desmethyldiazepam, fluoxetine and sertraline, that showed a lower concentration on FTA. Additional experiments suggest that the chemicals, adsorbed on FTA, are not the cause of the loss of signal observed for the substances previously mentioned and that methanol should be preferred as extraction solvent. Conclusions: This study proved that FTA cards are a good and a hazard-free alternative sample storage method for analysis of several psychoactive substances in postmortem blood. Supplementary Information: The online version contains supplementary material available at 10.1007/s11419-020-00567-2.

Distribution of Fluvoxamine and Identification of the Main Metabolite in a Fatal Intoxication.

Fluvoxamine is a selective serotonin reuptake inhibitor, with a half-life of about 30 hours, that is commonly prescribed in the treatment of depression and obsessive and compulsive disorders. Though its more favorable adverse effect profile in comparison to tricyclic antidepressants, overdosages could lead to severe central nervous system depression. We hereby report the case of a 48-year-old woman with psychiatric disorders, who died in the Protected Community where she lived. An autopsy, during which multiorgan congestion and aspiration of gastric content were found, was performed 9 days after the death. Femoral and cardiac blood, urine and bile were collected for toxicological analysis. GC-MS, LC-MS-MS and LC-HRMS screenings were performed on blood samples. The analysis allowed to identify the following drugs: fluvoxamine, clotiapine, 7-aminoclonazepam, propranolol, gabapentin and haloperidol. Quantification of the detected drugs in blood was performed by means of a validated LC-MS-MS analytical procedure, and the following results were achieved: fluvoxamine (2.20 mg/L), gabapentin (41.00 mg/L), 7-aminoclonazepam (0.24 mg/L), clotiapine (0.07 mg/L), haloperidol (<0.01 mg/L) and propranolol (0.24 mg/L). Fluvoxamine concentration in blood exceeded ~10 times the upper limit of therapeutic blood levels (0.23 mg/L). Contributory causes of death, such as due to multiple drug use, however, cannot be excluded. The distribution of fluvoxamine in all biological fluids was evaluated and a postmortem redistribution effect was observed (C/P blood ratio: 1.86). Fluvoxamine acid metabolite was identified in urine, bile and in cardiac blood, through an LC-QTOF analytical procedure.

Determination of fentanyl and 19 derivatives in hair: Application to an Italian population.

Nowadays fentanyl and its analogs represent the most numerous group among synthetic opioid and, due to their higher potency in comparison to traditionl opioids, the main cause of the critical increase of fatal intoxications opioids-intake related in the USA. We developed an LC-MS/MS method for the detection and quantification of fentanyl and its analogs in hair, then applied to 117 real samples, 97 collected from drugs users and 20 from postmortem cases of drugs addicts. The ionization and MRM parameters have been optimized for 27 molecules: 20 reached the acceptance criteria for identification and quantification. LODs and LOQs of 0.2 and 0.5 pg/mg, respectively, were reached for most of the substances, except for five compounds for which were set at 0.5 and 1.0 pg/mg. 2 out of the 97 samples collected from drug users tested positive; one for carfentanil, butyryl fentanyl, THFF and ocfentanil; the other one for 3-methyl norfentanyl. 2 out of the 20 postmortem samples show positive results: one only for fentanyl, the other for furanyl fentanyl, acetyl fentanyl, methoxyacetyl fentanyl, methoxyacetyl norfentanyl, ocfentanil and 4-ANPP. Despite the relatively small number of samples, the results suggest that the method should be included in routine hair analyses for monitoring the new synthetic opioids potential intake by drug users.

Fatal poisoning of four workers in a farm: Distribution of hydrogen sulfide and thiosulfate in 10 different biological matrices.

We evaluate the distribution of sulfide and thiosulfate (TS) in biological samples of four dairy farmers died inside a pit connected to a manure lagoon. Autopsies were performed 4 days later. Toxicological analyses of sulfide and TS were made using an extractive alkylation technique combined with gas chromatography/mass spectrometry (GC/MS). Autopsies revealed: multiorgan congestion; pulmonary edema; manure inside distal airways of three of the four victims. Sulfide concentrations were cardiac blood: 0.5-3.0 µg/mL, femoral blood: 0.5-1.2 µg/mL, bile: <0.1-2.2 µg/mL; liver 2.8-8.3 µg/g, lung: 5.0-9.4 µg/g, brain: 2.7-13.9 µg/g, spleen: 3.3-6.3 µg/g, fat: <0.1-1.5 µg/g, muscle: 2.6-3.5 µg/g. TS concentrations were cardiac blood: 2.1-4.9 µg/mL, femoral blood: 2.1-2.3 µg/mL, bile: 2.5-4.4 µg/mL, urine: <0.5-1.8 µg/mL; liver <0.5-2.6, lung: 2.8-5.4 µg/g, brain: <0.5-1.9 µg/g, spleen: 1.2-2.9 µg/g, muscle: <0.5-5.6 µg/g. The cause of death was assessed to be acute poisoning by hydrogen sulfide (H2S) for all the victims. Manure inhalation contributed to the death of three subjects. The measurement of sulfide and TS concentrations in biological samples contributed to better understand the sequence of the events. Subjects 3 provided the highest concentration of sulfide in brain, thus, supporting the hypothesis of a rapid loss of consciousness and respiratory depression. One by one, the other farmers entered the pit in attempts to rescue the coworkers but collapsed. Despite the rapid death, subject 3 was the only one with TS detectable in urine. This could be due to differences in metabolism of H2S.

Distribution of quetiapine and metabolites in biological fluids and tissues.

Quetiapine is an atypical antipsychotic drug, frequently found in post-mortem samples. The quantitative determination of active metabolites may help in the interpretation of the potential toxic effects of the parent drug and its role in death. A fully validated LC-MS/MS method was developed for the identification and quantification of quetiapine and two main metabolites (N-desalkylquetiapine and 7-hydroxyquetiapine) in blood, biological fluids and tissues. Then, the distribution of analytes in different matrices was evaluated. LODs of 0.9, 0.3 and 0.3ng/mL were calculated for quetiapine, N-desalkylquetiapine and 7-hydroxyquetiapine respectively; while a LOQ at the concentration of 10.0ng/mL was defined for the three analytes. 13 post-mortem positive real cases have been included in the experiment. The results revealed that quetiapine and N-desalkylquetiapine might undergo a significant post-mortem redistribution, while 7-hydroxyquetiapine is less affected by this factor. N-desalkylquetiapine could be found in blood in relatively high concentrations in comparison to those of quetiapine; therefore, it should be always advisable to measure both the analytes. The analysis of tissues could provide additional data on potential intoxication with quetiapine.

Distribution of the Synthetic Cathinone α-Pyrrolidinohexiophenone in Biological Specimens.

We report the analysis of the synthetic cathinones α-pyrrolidinohexiophenone (α-PHP) and α-pyrrolidinopentiophenone (α-PVP), both pyrovalerone derivatives, in blood, urine, gastric contents, main tissues and hair of a deceased person. Qualitative and quantitative analyses were performed by LC-MS-MS. All the biological samples were collected during autopsy and extracted/purified onto a solid phase extraction cartridge before instrumental analysis. The method was validated for blood and urine and proved to be highly sensitive and specific for both the synthetic cathinones (limit of detection: 0.2 ng/mL and limit of quantification: 0.5 ng/mL). Analyses provided negative results for α-PVP in all biological samples except for the 2-cm proximal hair segment, confirming that the young man had consumed in the last 2 months this compound; instead hair analysis proved that the man was a heavy α-PHP user. α-PHP was identified and quantified in biological fluids and tissues. Interestingly, bile and urine concentrations (1.2 and 5.6 ng/mL, respectively) were fairly lower than blood collected into the thoracic cavity (15.3 ng/mL). The highest concentrations were measured for lung (71.1 ng/mL) and spleen (83.8 ng/mL). Concentrations of 3.5, 7.9, 4.7 and 23.6 ng/mL were measured in liver, kidney, brain and heart, respectively. Even if it is not possible to evaluate the presence of this drug in biological samples as a cause of death, to our knowledge, this is the first case of α-PHP finding in postmortem samples, and its potential toxic effects should be elucidated in the future.

A multi-analyte LC-MS/MS method for screening and quantification of 16 synthetic cathinones in hair: Application to postmortem cases.

A multi-analyte method for detection and quantification of 16 synthetic cathinones (known also as "bath salts") in human hair has been developed and fully validated using liquid chromatography-tandem mass spectrometry system. About 20 mg of hair samples, previously washed and homogenized, were ultrasonicated with 1 mL HCl 0.1 M solution. Samples were then extracted using a solid phase extraction procedure (SPE), taken to dryness and reconstituted in 100 µL mobile phase. Finally, they were directly injected into a liquid chromatographic system, coupled with tandem mass spectrometer detector. The validation criteria parameters were satisfactory according with the international guidelines. A LOQ of 5 pg/mg was obtained for 4-fluoromethcathinone (4-FMC), buphedrone, ethcathinone, methcathinone, mephedrone and naphyrone, while the method proved to be more sensitive for 4-methylethcathinone (4-MEC), methedrone, alpha-pyrrolidinopentiophenone (α-PVP), alpha-pyrrolidinohexiophenone (α-PHP), methylenedioxypyrovalerone (MDPV), butylone, ethylone, 3,4-dimethylmethcathinone (3,4-DMMC), pentedrone and pentylone, reaching a LOQ of 1 pg/mg. Potential use of bath salts was investigated in postmortem cases of young subjects previously tested positive at least to one traditional drug of abuse. Two samples out of 17 cases analyzed provided positive results for synthetic cathinones. One sample has been divided in two segments of 2.5 cm length each. Both segments were positive for 8 different cathinone derivatives, namely: 3,4-DMMC, 4-FMC, 4-MEC, α-PHP, α-PVP, methcathinone, methedrone and pentedrone. The second case provided positive results for ethcathinone.

Drug Abuse-Related Neuroinflammation in Human Postmortem Brains: An Immunohistochemical Approach.

The aim of the study was to investigate blood-brain barrier alterations, neuroinflammation, and glial responses in drug abusers. Five immunohistochemical markers (CD3, zonula occludens-1 [ZO-1], intracellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule [VCAM-1], and glial fibrillary acidic protein [GFAP]) were assessed on postmortem brain samples collected from drug abusers who died from acute intoxication of cocaine, heroin, or a combination of both, compared with controls. CD3 and ICAM-1 immunopositivity were significantly stronger in drug abusers than in controls. VCAM-1 immunopositivity was similar across drug abuser and control groups. In heroin abusers, significantly lower ZO-1 immunopositivity was observed relative to controls. GFAP positivity did not show significant differences between groups, but its distribution within the brain did differ. Both cocaine and heroin abuse promoted neuroinflammation, increasing expression of ICAM-1 and recruiting CD3+ lymphocytes. Heroin affected the molecular integrity of tight junctions, as reflected by reduced ZO-1 expression. The outcomes of the present study are, overall, consistent with prior available evidence, which is almost exclusively from studies conducted in vitro or in animal models. These findings provide important information about the downstream consequences of neuroinflammation in drug abusers and may help to inform the development of potential therapeutic targets.

Determination of benzodiazepines in blood and in dried blood spots collected from post-mortem samples and evaluation of the stability over a three-month period.

We successfully developed and validated an LC-MS/MS method for the identification of 27 and quantification of 9 benzodiazepines and metabolites in whole blood and DBSs. The results provided a good qualitative and quantitative correlation between DBSs stored at room temperature and whole blood stored at -20°C. A good stability for a three-month period was observed for most of the compounds detected in real post-mortem samples.

Two Fatal Cases Involving Cardiovascular Drugs Diltiazem and Amlodipine.

A liquid chromatographic tandem mass spectrometric method for the identification and quantification of 18 cardiovascular drugs was developed in order to evaluate two cases of fatal intoxication involving diltiazem and amlodipine respectively. Samples were simply diluted and centrifuged using a three-steps procedure with methanol, acetonitrile and mobile phase. The method proved to be selective and all the validation parameters fulfilled the acceptance criteria. In particular, linearity was studied in the range limits of quantitation (LOQ)-1,000 ng/mL (LOQ ranging from 0.8 to 33.3 ng/mL for urine and from 0.7 to 41.3 ng/mL for whole blood). The method was successfully applied to two real cases involving diltiazem and amlodipine fatal intoxications, respectively. Though the subject intoxicated by diltiazem did survive several hours after drug intake, central and peripheral blood levels at autopsy were extremely high (23.4 and 13.4 mg/L, respectively); the cause could be due to the formation of a pharmacobezoar that was found in the duodenum and that could have delayed the drug absorption. Moreover, diltiazem showed postmortem redistribution. On the contrary, the amlodipine peripheral blood level in the second case was relatively low (0.17 mg/L), thus confirming that even the uncontrolled intake of a less toxic calcium channel blocker can lead to death. Furthermore, blood samples were analyzed after 2 years of storage at -20°C: both diltiazem and amlodipine showed a significant degradation (70 and 99%, respectively).

Delta-9-tetrahydrocannabinolic acid A (THC-A) in urine of a 15-month-old child: A case report.

INTRODUCTION: The acidic forms of cannabinoids, THC-A and CBD-A are naturally present in cannabis plants and preparations and are generally decarboxylated to the active compounds before the use (e.g. thermally decarboxylated through smoking). Hence, the identification of the acidic compounds in urine could be an evidence of cannabis ingestion rather than a passive exposure to smoke. This case report described a 15-month-old child that suffered an acute intoxication by accidental cannabis ingestion. It is important to assess the ingestion and to discriminate it from a passive exposure to better interpret the clinical findings and to establish the correct therapeutic procedure. METHODS: Urine samples were simply diluted in deionized water and directly injected in the LC-MS/MS system. D3-THCCOOH was used as internal standard. Chromatographic separation of THCCOOH, THC-A and CBD-A was carried out in reversed phase on a c18 column. A triple quad in MRM negative mode was used to monitor the three analytes. RESULTS AND DISCUSSION: The developed LC-MS/MS method was simple and fast. A LOD of 3.0ng/mL and a LOQ of 10.0ng/mL were measured for the three compounds. The analytical procedure was validated accordingly to international guidelines. The two urine samples collected from the 15-month-old child at the hospitalization and after three days provided positive results for THCCOOH (130.0 and 10.0ng/mL respectively). THC-A was found only in the urine sample collected at the hospitalization (concentration: 70.0ng/mL). CONCLUSION: THC-A was detected and quantitated in a urine sample of a 15-month-old child.

Variability on ethyl glucuronide concentrations in hair depending on sample pretreatment, using a new developed GC-MS/MS method.

Quantitative determination of ethyl glucuronide in keratin matrix, particularly in hair samples, provides a significant contribution to the evaluation of the extent of ethanol intake. The first-choice method to carry out this analysis is LC-MS/MS, but other techniques may be used. The aim of this work is: a) to develop and validate a GC-MS/MS method for ethyl glucuronide determination in hair; b) to compare GC-MS/MS and LC-MS/MS in analysis of real samples; c) to compare EtG concentration obtained after hair cutting and pulverization. About 30 mg hair samples were washed, pulverized and soaked in 1 ml deionized water. After incubation, the solution was purified through a SPE anion exchange cartridge; the eluate was dried under nitrogen stream, derivatized with PFPA and reconstituted in n-hexane. Then, the sample was injected in the GC-MS/MS system, operating in negative chemical ionization mode and in selected reaction monitoring. The two most intense transitions were used to monitor ethyl glucuronide and deuterated internal standard. All the validation parameters fulfilled the international acceptance criteria. LOD and LOQ were set at 2.0 and 3.0 pg/mg respectively. This method was applied to 194 hair samples collected from teetotallers and alcohol consumers and represents a suitable alternative to LC-MS/MS for the determination of EtG in hair samples, in particular when scarce quantity of hair is available. This study confirmed that pulverization of hair increases the concentration of EtG, but some variability of EtG levels remains probably due to the presence of non-homogeneous material even though pulverization.

A liquid chromatography-tandem mass spectrometry method for the determination of cocaine and metabolites in blood and in dried blood spots collected from postmortem samples and evaluation of the stability over a 3-month period.

The aims of this study were (1) to identify and quantify cocaine (COC), benzoylecgonine (BE), ecgonine methyl ester (EME), and cocaethylene (CE) in DBS; (2) to compare dried blood spots (DBSs) analytical results with the routine blood analyses; (3) to monitor analytes stability on DBS within a 3-month period. Eighty-five µL of blood from postmortem cases were put on a card for DBS analysis and kept in the dark, at room temperature. Samples were extracted through solid-phase extraction (SPE) cartridges and injected in the liquid chromatography-tandem mass spectrometry (LC-MS/MS) system. The analytical procedure is simple, sensitive, and specific. Limits of detection (LODs) and quantification (LOQs) were calculated at 1.0 and 5.0 ng/mL(g) for COC and CE, and at 0.5 and 2 ng/mL for EME and BE, respectively. Validation parameters fulfilled all the acceptance criteria. Fifty-five postmortem cases were evaluated. Eighteen cases were positive for COC (44-2456 ng/mL) and BE (228-4700 ng/mL), 12 for EME (92-1500 ng/mL), and 11 cases for CE (11-273 ng/mL). Stability was evaluated on 8 cases collected in the period January 2017-January 2018. For each case, 5 DBSs were collected at T0. Four DBSs were analyzed within the 4 following weeks and 1 sample was analyzed after 3 months. The concentrations on DBSs, stored at room temperature, always matched the ones obtained on blood samples kept at -20°C (<20% variation, both at T0 and after 3 months). BE and COC concentrations remained stable after a 3-month storage, EME concentrations slightly increased after 3 weeks in the 2 analyzed samples, while CE provided a less homogeneous stability depending on the sample.

Death after 25C-NBOMe and 25H-NBOMe consumption.

A teenager male was found dead in a waterway after he was spotted jumping off into the water stream. The boy looked agitated and confused after a party with friends. At the gathering place, investigators seized packages of blotter papers. A complete autopsy and a histological evaluation of the main tissues were performed; although the death occurred by drowning, the prosecutor requested toxicological exams, in order to evaluate the potential role of drugs of abuse in the episode. Blood (both peripheral and central) and urine samples as well as seized blotter papers were collected and analyzed as follows. The blotter paper, analyzed through a GC-MS method, revealed the presence of 25-NBOMes. A liquid chromatography tandem mass spectrometric (LC-MS/MS) system was used to identify and quantify 5 different 25-NBOMes (namely 25B-NBOMe, 25C-NBOMe, 25D-NBOMe, 25H-NBOMe, 25I-NBOMe) in blood and urine. 25E-NBOMe was used as internal standard (IS). 1mL of urine and 1mL of blood (both peripheral and cardiac) were diluted in 2mL phosphate buffer at pH 6.0, containing IS and purified on a solid phase extraction (SPE) cartridge. LOD and LOQ for the five 25-NBOMes were calculated at 0.05 and 0.1ng/mL respectively. Linearity, accuracy, precision, ion suppression, carry over and recovery were tested and all parameters fulfilled the acceptance criteria. Blood and urine provided positive results for 25C-NBOMe and 25H-NBOMe. Eventually, the seized blotter papers were analyzed by means of LC-MS/MS and the presence of the two NBOMes was confirmed: 25C-NBOMe and 25H-NBOMe were measured at the concentration of 2.80 and 0.29ng/mL in peripheral blood, of 1.43 and 0.13ng/mL in central blood and of 0.94 and 0.14ng/mL in urine, respectively. THC and THCCOOH were also detected in biological fluids, at the concentration of 15.5 and 56.0ng/mL in peripheral blood, 9.9 and 8.5ng/mL in central blood, respectively. NBOMes can produce severe hallucination even at very low doses, and the 25C-NBOMe levels measured in the subject's blood are considered potentially toxic.

All muscarinic acetylcholine receptors (M1-M5) are expressed in murine brain microvascular endothelium.

Clinical and experimental studies indicate that muscarinic acetylcholine receptors are potential pharmacological targets for the treatment of neurological diseases. Although these receptors have been described in human, bovine and rat cerebral microvascular tissue, a subtype functional characterization in mouse brain endothelium is lacking. Here, we show that all muscarinic acetylcholine receptors (M1-M5) are expressed in mouse brain microvascular endothelial cells. The mRNA expression of M2, M3, and M5 correlates with their respective protein abundance, but a mismatch exists for M1 and M4 mRNA versus protein levels. Acetylcholine activates calcium transients in brain endothelium via muscarinic, but not nicotinic, receptors. Moreover, although M1 and M3 are the most abundant receptors, only a small fraction of M1 is present in the plasma membrane and functions in ACh-induced Ca2+ signaling. Bioinformatic analyses performed on eukaryotic muscarinic receptors demonstrate a high degree of conservation of the orthosteric binding site and a great variability of the allosteric site. In line with previous studies, this result indicates muscarinic acetylcholine receptors as potential pharmacological targets in future translational studies. We argue that research on drug development should especially focus on the allosteric binding sites of the M1 and M3 receptors.