Ketamine: the best partner for isoflurane in neonatal anesthesia?

Characterization of intracellular calcium mobilization induced by remimazolam, a newly approved intravenous anesthetic

Many anesthetics, including Propofol, have been reported to induce elevation of intracellular calcium, and we were interested to investigate the possible contribution of calcium elevation to the mechanism of the newly approved remimazolam actions. Remimazolam is an intravenous anesthetic first approved in Japan in July 2020, and is thought to exert its anesthetic actions via γ-aminobutyric acid A (GABAA) receptors; however, the precise mechanisms of how remimazolam elevates intracellular calcium levels remains unclear. We examined the remimazolam-induced elevation of intracellular calcium using SHSY-5Y neuroblastoma cells, COS-7 cells, HEK293 cells, HeLa cells, and human umbilical vein endothelial cells (HUVECs) loaded with fluorescent dyes for live imaging. We confirmed that high concentrations of remimazolam (greater than 300 μM) elevated intracellular calcium in a dose-dependent manner in these cells tested. This phenomenon was not influenced by elimination of extracellular calcium. The calcium elevation was abolished when intracellular or intraendoplasmic reticulum (ER) calcium was depleted by BAPTA-AM or thapsigargin, respectively, suggesting that calcium was mobilized from the ER. Inhibitors of G-protein coupled receptors (GPCRs)-mediated signals, including U-73122, a phospholipase C (PLC) inhibitor and xestospongin C, an inositol 1,4,5-triphosphate receptors (IP3R) antagonist, significantly suppressed remimazolam-induced calcium elevation, whereas dantrolene, a ryanodine receptor antagonist, did not influence remimazolam-induced calcium elevation. Meanwhile, live imaging of ER during remimazolam stimulation using ER-tracker showed no morphological changes. These results suggest that high doses of remimazolam increased intracellular calcium concentration in a dose-dependent manner in each cell tested, which was predicted to be caused by calcium mobilization from the ER. In addition, our studies using various inhibitors revealed that this calcium elevation might be mediated by the GPCRs-IP3 pathway. However, further studies are required to identify which type of GPCRs is involved.

Crocins, the Bioactive Components of Crocus sativus L., Counteract the Disrupting Effects of Anesthetic Ketamine on Memory in Rats

Consistent experimental evidence suggests that anesthetic doses of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine cause severe memory impairments in rodents. Crocins are among the various bioactive ingredients of the plant Crocus sativus L., and their implication in memory is well-documented. It has not yet been elucidated if crocins are able to attenuate the memory deficits produced by anesthetic ketamine. The present study was undertaken aiming to clarify this issue in the rat. For this aim, the object recognition, the object location and the habituation tests, reflecting non-spatial recognition memory, spatial recognition memory and associative memory, respectively, were utilized. A post-training challenge with crocins (15–30 mg/kg, intraperitoneally (i.p.), acutely) counteracted anesthetic ketamine (100 mg/kg, i.p.)-induced performance impairments in all the above-mentioned behavioral memory paradigms. The current findings suggest that crocins modulate anesthetic ketamine’s amnestic effects.

Suberoylanilide hydroxamic acid (SAHA) alleviates the learning and memory impairment in rat offspring caused by maternal sevoflurane exposure during late gestation

Recent studies have shown that sevoflurane can cause long-term neurotoxicity and learning and memory impairment in developing and progressively neurodegenerative brains. Sevoflurane is a widely used volatile anesthetic in clinical practice. Late gestation is a rapidly developing period in the fetal brain, but whether sevoflurane anesthesia during late gestation affects learning and memory of offspring is not fully elucidated. Histone deacetylase 2 (HDAC2) plays an important regulatory role in learning and memory. This study examined the effect of maternal sevoflurane exposure on learning and memory in offspring and the underlying role of HDAC2. The Morris water maze (MWM) test was used to evaluate learning and memory function. Q-PCR and immunofluorescence staining were used to measure the expression levels of genes related to learning and memory. The results showed that sevoflurane anesthesia during late gestation impaired learning and memory in offspring rats (e.g., showing increase of the escape latency and decrease of the platform-crossing times and target quadrant traveling time in behavior tests) and upregulated the expression of HDAC2, while downregulating the expression of the cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) and the N-methyl-D-aspartate receptor 2 subunit B (NR2B) mRNA and protein in the hippocampus of offspring in a time-dependent manner. HDAC2 inhibitor suberoylanilide hydroxamic acid (SAHA) treatment alleviated all of these changes in offspring rats. Therefore, the present study indicates that sevoflurane exposure during late gestation impairs offspring rat's learning and memory via upregulation of the expression of HDAC2 and downregulation of the expression of CREB and NR2B. SAHA can alleviate these impairments.

Dexmedetomidine mitigates isoflurane-induced neurodegeneration in fetal rats during the second trimester of pregnancy

Dexmedetomidine has significant neuroprotective effects. However, whether its protective effects can reduce neurotoxicity caused by isoflurane in fetal brain during the second trimester of pregnancy remains unclear. In this study, timed-pregnancy rats at gestational day 14 spontaneously inhaled 1.5% isoflurane for 4 hours, and were intraperitoneally injected with dexmedetomidine at dosages of 5, 10, 20, and 20 μg/kg 15 minutes before inhalation and after inhalation for 2 hours. Our results demonstrate that 4 hours after inhaling isoflurane, 20 μg/kg dexmedetomidine visibly mitigated isoflurane-induced neuronal apoptosis, reversed downregulation of brain-derived neurotrophic factor expression, and lessened decreased spatial learning and memory ability in adulthood in the fetal rats. Altogether, these findings indicate that dexmedetomidine can reduce neurodegeneration induced by isoflurane in fetal rats during the second trimester of pregnancy. Further, brain-derived neurotrophic factor participates in this process.

Regional brain dysregulation of Ca(2+)-handling systems in ketamine-induced rat model of experimental psychosis

Chronic N-methyl-D-aspartate receptor (NMDAR) antagonist treatment can provide valuable neurochemical and neuroanatomical models of experimental psychosis. One such antagonist, ketamine, with its short half-time and well-documented psychotomimetic action, has cognitive effects resembling various aspects of schizophrenia-like symptoms. In order to obtain insights into possible relationships between Ca(2+) homeostasis and schizophrenia-related symptoms, we investigate the effects of chronic ketamine administration on intracellular Ca(2+) levels in various brain regions and on the expression level of key members of the neuronal Ca(2+)-handling system in rats. We show increased intracellular [Ca(2+)] in all of the examined brain regions following ketamine treatment but an altered cytosolic Ca(2+) level correlated with hyperlocomotor activity was only established for the cortex and striatum. Our findings also suggest that an imbalance in the expression between the calcium "on" and "off" systems contributes to the deregulation of brain Ca(2+) homeostasis in our ketamine-induced model of experimental psychosis. Identification of the genes whose expression is affected by ketamine treatment indicates their involvement as putative etiological factors in schizophrenia.

Lifetime behavioural changes after exposure to anaesthetics in infant rats

The aim of this study was to assess the effect of acute use of general anaesthetic with or without a surgical procedure, at post-natal day 14 (P14), on behavioural responses in the short-, medium- and long-term, evaluated in open field (OF) and elevated plus-maze (EPM) tests. Fourteen-day-old male Wistar rats were divided into two experimental designs (ED): inhalation and intravenous anaesthetic, and these groups were subdivided into: 1st ED - control (C), isoflurane (ISO), isoflurane/surgery (ISO-SUR); 2nd ED - control (C), fentanyl/S(+)-ketamine (FK) and fentanyl+ketamine-s/surgery (FK-SUR). In the OF the following were found: (a) in the 1st ED: an increase in the locomotor activity in the ISO group at P14, and ISO and ISO-SUR groups at P30; the ISO-SUR group showed a reduced latency to leave the first quadrant at P30 and P60; (b) in the 2nd ED: FK and FK-SUR groups presented increased locomotor activity at P30, and the FK group showed a reduction in the number of faecal boluses. In the EPM the following were found: FK and FK-SUR groups presented an increase in the number of non-protected head-dipping (NPHD) movements and in the number of entries and time spent in open arms at P30; the FK group showed an increased number of protected head-dipping movements, NPHD and entries and time spent in the open arms at P60. The behavioural changes observed may be related to locomotor activity (1st ED) and anxiety level (2nd ED) and they may result from changes in neurotransmitters/hormones (DA, 5HT, CRH) and glutamate/NMDA receptors, respectively.