Only extra-high dose of ketamine affects l-glutamate-induced intracellular Ca2+ elevation and neurotoxicity

“K-Powder” Exposure during Adolescence Elicits Psychiatric Disturbances Associated with Oxidative Stress in Female Rats

Ketamine, also called ‘K-powder’ by abusers, an analog of phencyclidine, primarily acts as an antagonist of N-methyl-D-aspartic acid (NMDA) receptors, therapeutically used as an anesthetic agent. Ketamine also stimulates the limbic system, inducing hallucinations and dissociative effects. At sub-anesthetic doses, ketamine also displays hallucinatory and dissociative properties, but not loss of consciousness. These behavioral consequences have elicited its recreational use worldwide, mainly at rave parties. Ketamine is generally a drug of choice among teenagers and young adults; however, the harmful consequences of its recreational use on adolescent central nervous systems are poorly explored. Thus, the aim of the present study was to characterize the behavioral and biochemical consequences induced by one binge-like cycle of ketamine during the early withdrawal period in adolescent female rats. Adolescent female Wistar rats (n = 20) received intraperitoneally administered ketamine (10 mg/kg/day) for 3 consecutive days. Twenty-four hours after the last administration of ketamine, animals were submitted to behavioral tests in an open field, elevated plus-maze, and forced swimming test. Then, animals were intranasally anesthetized with 2% isoflurane and euthanized to collect prefrontal cortex and hippocampus to assess lipid peroxidation, antioxidant capacity against peroxyl radicals, reactive oxygen species, reduced glutathione, and brain-derived neurotrophic factor (BDNF) levels. Our results found that 24 h after recreational ketamine use, emotional behavior disabilities, such as anxiety- and depression-like profiles, were detected. In addition, spontaneous ambulation was reduced. These negative behavioral phenotypes were associated with evidence of oxidative stress on the prefrontal cortex and hippocampus.

Effect of preconditioning on propofol-induced neurotoxicity during the developmental period

At therapeutic concentrations, propofol (PPF), an anesthetic agent, significantly elevates intracellular calcium concentration ([Ca2 +]i) and induces neural death during the developmental period. Preconditioning enables specialized tissues to tolerate major insults better compared with tissues that have already been exposed to sublethal insults. Here, we investigated whether the neurotoxicity induced by clinical concentrations of PPF could be alleviated by prior exposure to sublethal amounts of PPF. Cortical neurons from embryonic day (E) 17 Wistar rat fetuses were cultured in vitro, and on day in vitro (DIV) 2, the cells were preconditioned by exposure to PPF (PPF-PC) at either 100 nM or 1 μM for 24 h. For morphological observations, cells were exposed to clinical concentrations of PPF (10 μM or 100 μM) for 24 h and the survival ratio (SR) was calculated. Calcium imaging revealed significant PPF-induced [Ca2+]i elevation in cells on DIV 4 regardless of PPF-PC. Additionally, PPF-PC did not alleviate neural cell death induced by PPF under any condition. Our findings indicate that PPF-PC does not alleviate PPF-induced neurotoxicity during the developmental period.

Antidepressant Actions of Ketamine: Potential Role of L-Type Calcium Channels

Recently, the United States Food and Drug Administration approved esketamine, the S-enantiomer of ketamine, as a fast-acting therapeutic drug for treatment-resistant depression. Although ketamine is known as an N-methyl-d-aspartate (NMDA) receptor antagonist, the underlying mechanisms of how it elicits an antidepressant effect, specifically at subanesthetic doses, are not clear and remain an advancing field of research interest. On the other hand, high-dose (more than the anesthetic dose) ketamine-induced neurotoxicity in animal models has been reported. There has been progress in understanding the potential pathways involved in ketamine-induced antidepressant effects, some of which include NMDA-receptor antagonism, modulation of voltage-gated calcium channels, and brain-derived neurotrophic factor (BDNF) signaling. Often these pathways have been shown to be linked. Voltage-gated L-type calcium channels have been shown to mediate the rapid-acting antidepressant effects of ketamine, especially involving induction of BDNF synthesis downstream, while BDNF deficiency decreases the expression of L-type calcium channels. This review focuses on the reported studies linking ketamine's rapid-acting antidepressant actions to L-type calcium channels with an objective to present a perspective on the importance of the modulation of intracellular calcium in mediating the effects of subanesthetic (antidepressant) versus high-dose ketamine (anesthetic and potential neurotoxicant), the latter having the ability to reduce intracellular calcium by blocking the calcium-permeable NMDA receptors, which is implicated in potential neurotoxicity.

Ketamine promotes the neural differentiation of mouse embryonic stem cells by activating mTOR

Ketamine is a widely used general anesthetic and has been reported to demonstrate neurotoxicity and neuroprotection. Investigation into the regulatory mechanism of ketamine on influencing neural development is of importance for a better and safer way of relieving pain. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the critical neural associated gene expression, and flow cytometry to detect the neural differentiation effect. Hence, in the present study the underlying mechanism of ketamine (50 nM) on neural differentiation of the mouse embryonic stem cell (mESC) line 46C was investigated. The results demonstrated that a low dose of ketamine (50 nM) promoted the differentiation of mESCs to neural stem cells (NSCs) and activated mammalian target of rapamycin (mTOR) by upregulating the expression levels of phosphorylated (p)‑mTOR. Furthermore, inhibition of the mTOR signaling pathway by rapamycin or knockdown of mTOR suppressed neural differentiation. A rescue experiment further confirmed that downregulation of mTOR inhibited the promotion of neural differentiation induced by ketamine. Taken together, the present study indicated that a low level of ketamine upregulated p‑mTOR expression levels, promoting neural differentiation.

"Special K" Drug on Adolescent Rats: Oxidative Damage and Neurobehavioral Impairments

Ketamine is used in clinical practice as an anesthetic that pharmacologically modulates neurotransmission in postsynaptic receptors, such as NMDA receptors. However, widespread recreational use of ketamine in "party drug" worldwide since the 1990s quickly spread to the Asian orient region. Thus, this study aimed at investigating the behavioral and oxidative effects after immediate withdrawal of intermittent administration of ketamine in adolescent female rats. For this, twenty female Wistar rats were randomly divided into two groups: control and ketamine group (n = 10/group). Animals received ketamine (10 mg/kg/day) or saline intraperitoneally for three consecutive days. Three hours after the last administration, animals were submitted to open field, elevated plus-maze, forced swim tests, and inhibitory avoidance paradigm. Twenty-four hours after behavioral tests, the blood and hippocampus were collected for the biochemical analyses. Superoxide dismutase, catalase, nitrite, and lipid peroxidation (LPO) were measured in the blood samples. Nitrite and LPO were measured in the hippocampus. The present findings demonstrate that the early hours of ketamine withdrawal induced oxidative biochemistry unbalance in the blood samples, with elevated levels of nitrite and LPO. In addition, we showed for the first time that ketamine withdrawal induced depressive- and anxiety-like profile, as well as short-term memory impairment in adolescent rodents. The neurobehavioral deficits were accompanied by the hippocampal nitrite and LPO-elevated levels.

Intravenous anesthetic-induced calcium dysregulation and neurotoxic shift with age during development in primary cultured neurons

Anesthetic-induced neurotoxicity in the developing brain is a concern. This neurotoxicity is closely related to anesthetic exposure time, dose, and developmental stages. Using calcium imaging and morphological examinations in vitro, we sought to determine whether intravenous anesthetic-induced direct neurotoxicity varies according to different stages of the days in vitro (DIV) of neurons in primary culture. Cortical neurons from E17 Wistar rats were prepared. On DIV 3, 7, and 13, cells were exposed to the intravenous anesthetics thiopental sodium (TPS), midazolam (MDZ), or propofol (PPF), to investigate direct neurotoxicity using morphological experiments. Furthermore, using calcium imaging, the anesthetic-induced intracellular calcium concentration ([Ca²⁺]i) elevation was monitored in cells on DIV 4, 8, and 13. All anesthetics elicited significant [Ca²⁺]i increases on DIV 4. While TPS (100 μM) and MDZ (10 μM) did not alter neuronal death, PPF (10 μM and 100 μM) decreased the survival ratio (SR) significantly. On DIV 8, TPS and MDZ did not elicit [Ca²⁺]i elevation or SR decrease, while PPF still induced [Ca²⁺]i elevation (both at 10 μM and 100 μM) and significant SR decrease at 100 μM (0.76 ± 0.03; P < 0.05), but not at 10 μM (0.91 ± 0.03). Such anesthetic-induced [Ca²⁺]i elevation and SR decrease were not observed on DIV 13-14 for any of the anesthetic drugs. Our study indicates that more caution may be exercised when using PPF compared to TPS or MDZ during development.

Ketamine-induced neurotoxicity blocked by N-Methyl-d-aspartate is mediated through activation of PKC/ERK pathway in developing hippocampal neurons

Ketamine, a non-competitive N-methyl d-aspartate (NMDA) receptor antagonist, is widely used in pediatric clinical practice. However, prolonged exposure to ketamine results in widespread anesthetic neurotoxicity and long-term neurocognitive deficits. The molecular mechanisms that underlie this important event are poorly understood. We investigated effects of anesthetic ketamine on neuroapoptosis and further explored role of NMDA receptors in ketamine-induced neurotoxicity. Here we demonstrate that ketamine induces activation of cell cycle entry, resulting in cycle-related neuronal apoptosis. On the other hand, ketamine administration alters early and late apoptosis of cultured hippocampus neurons by inhibiting PKC/ERK pathway, whereas excitatory NMDA receptor activation reverses these effects. Ketamine-induced neurotoxicity blocked by NMDA is mediated through activation of PKC/ERK pathway in developing hippocampal neurons.

Ketamine attenuates the glutamatergic neurotransmission in the ventral posteromedial nucleus slices of rats

Background

Ketamine is a frequently used intravenous anesthetic, which can reversibly induce loss of consciousness (LOC). Previous studies have demonstrated that thalamocortical system is critical for information transmission and integration in the brain. The ventral posteromedial nucleus (VPM) is a critical component of thalamocortical system. Glutamate is an important excitatory neurotransmitter in the brain and may be involved in ketamine-induced LOC.

Methods

The study used whole-cell patch-clamp to observe the effect of ketamine (30 μM–1000 μM) on glutamatergic neurotransmission in VPM slices.

Results

Ketamine significantly decreased the amplitude of glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs), but only higher concentration of ketamine (300 μM and 1000 μM) suppressed the frequency of sEPSCs. Ketamine (100 μM–1000 μM) also decreased the amplitude of glutamatergic miniature excitatory postsynaptic currents (mEPSCs), without altering the frequency.

Conclusions

In VPM neurons, ketamine attenuates the glutamatergic neurotransmission mainly through postsynaptic mechanism and action potential may be involved in the process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-017-0404-5) contains supplementary material, which is available to authorized users.

Thiopental sodium preserves the responsiveness to glutamate but not acetylcholine in rat primary cultured neurons exposed to hypoxia

Although many in vitro studies demonstrated that thiopental sodium (TPS) is a promising neuroprotective agent, clinical attempts to use TPS showed mainly unsatisfactory results. We investigated the neuroprotective effects of TPS against hypoxic insults (HI), and the responses of the neurons to l-glutamate and acetylcholine application. Neurons prepared from E17 Wistar rats were used after 2weeks in culture. The neurons were exposed to 12-h HI with or without TPS. HI-induced neurotoxicity was evaluated morphologically. Moreover, we investigated the dynamics of the free intracellular calcium ([Ca(2+)]i) in the surviving neurons after HI with or without TPS pretreatment following the application of neurotransmitters. TPS was neuroprotective against HI according to the morphological examinations (0.73±0.06 vs. 0.52±0.07, P=0.04). While the response to l-glutamate was maintained (0.89±0.08 vs. 1.02±0.09, P=0.60), the [Ca(2+)]i response to acetylcholine was notably impaired (0.59±0.02 vs. 0.94±0.04, P<0.01). Though TPS to cortical cultures was neuroprotective against HI morphologically, the [Ca(2+)]i response not to l-glutamate but to acetylcholine was impaired. This may partially explain the inconsistent results regarding the neuroprotective effects of TPS between experimental studies and clinical settings.