Browsing by Subject "ketamine"

Currently, there is an undeniable need for more effective treatments of depression. The efficacy of traditional antidepressant drugs becomes apparent after multiple weeks of treatment. New advancements in depression treatments have been made, as glutamatergic NMDA-receptor antagonist ketamine is seen to ameliorate symptoms rapidly, even only hours after drug administration. Understanding ketamine’s mechanism of action as an antidepressant could enable the development of more effective antidepressant drugs. The critical molecular level component in ketamine’s antidepressant effect is considered to be the activation of TrkB tyrosine receptor kinase B, which subsequently leads to the initiation of signaling pathways, which regulate synaptic plasticity. So far, it has not been examined; whether there is a difference in ketamine’s antidepressant effect based on the dosing-time of day. The aim of the present study was to find out if there is a variation between ketamine’s effect on synaptic plasticity and the circadian phase in which the drug is administered. Ketamine’s (200 or 50 mg/kg, i.p.) effects were studied in C57BL/6J–mice during light phase (mouse’s inactive phase) and dark phase (mouse’s active phase) of the day. The phase of the day didn’t affect the activity of TrkB signaling in its related parts (pTrkBTyr816, pGSK3βSer9, p-p70S6KTyr421/Ser424 and p-p44/42MAPKThr202/Tyr204) in prefrontal cortex samples which were analysed in Western blot assay. Ketamine increased dose-dependently the phosphorylation of GSK3βSer9 and p70S6KTyr421/Ser424 as well as decreased p-p44/42MAPKThr202/Tyr204 at 30 minutes after drug administration in both phases of the day. Ketamine (200 mg/kg, i.p.) also lowered the glucose concentration measured from the trunk blood. To examine the effect of hypoglycemia on the activity of TrkB signaling another experiment was conducted. The hypoglycemia induced by insulin detemir (6 IU/kg, i.p.) didn’t affect any measured protein phosphorylation at 60 minutes after drug administration. The results of this study support the notion of ketamine’s rapid and dosedependent induction of neuroplasticity. The possible role of hypoglycemia in ketamine's neuropharmacology should be investigated in future studies.

Subanesthetic-dose ketamine, an N-methyl-D-aspartate receptor (NMDAR) blocker, exerts rapid antidepressant effects that sustain long after its elimination from the body. The precise mechanism remains unknown, but regulation of TrkB (tropomyosin receptor kinase B), ERK (extracellular-regulated kinase 1 and 2), GSK3β (glycogen synthase kinase 3β) and mTOR (mammalian target of rapamycin) signaling within the prefrontal cortex (PFC) have been deemed important for its antidepressant-like effects in rodents. In addition, activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) is thought to be an important step in its mechanism. Nitrous oxide (N2O), another NMDAR antagonist and a putative rapid-acting antidepressant, regulates the same molecular pathways as ketamine in the rodent PFC. The fast pharmacokinetics of N2O have been exploited to show that markers of neuronal excitation, including phosphorylation of ERK, are upregulated in the PFC during its acute pharmacological effects (NMDAR blockade), while regulation of TrkB, GSK3β and P70S6K emerges only upon N2O withdrawal. In the first part of this study, we investigated the N2O-induced biochemical changes associated with neuronal excitation and BDNF-TrkB signaling in the PFC and further, the requirement for AMPAR activation in inducing them. We focused on the effects seen after the acute pharmacological effects of N2O. N2O (65% for 20 min) was administered to adult male C57BL/6 mice with or without pretreatment with AMPAR antagonist (NBQX, 10 mg/kg) and PFC samples were collected 15 minutes after stopping N2O delivery. Within this time N2O is expected to be completely eliminated. The brain samples were analyzed using western blot, enzyme-linked immunosorbent assay and quantitative reverse transcription PCR. We observed that N2O increased levels of phosphorylated TrkB, GSK3β and P70S6K, and these effects were not attenuated by NBQX pretreatment. At the same time, we observed a decrease in the levels of phosphorylated ERK, which was attenuated in mice that received NBQX prior to N2O. Tissue levels of BDNF protein or messenger RNA (exon IV) were not different between control and experimental groups. These results indicate that the mechanism of N2O is associated with TrkB and ERK signaling that are regulated independently of each other. It appears that AMPAR activation is not required for TrkB signaling, although it might play a role in ERK signaling. Further, N2O-induced TrkB phosphorylation in the PFC is not associated with changes in total levels of BDNF. In the second part of the study, we aimed to search for new ketamine-like NMDAR blockers with antidepressant potential. Ketamine was used as a query compound for in silico substructure search to find commercial ketamine analogs. The retrieved ketamine analogs were filtered by their computed ADMET properties and then further screened virtually by docking them to the pore region of NMDAR complex (protein data bank code: 4TLM), around the predicted binding site of ketamine. Finally, we sought to study if selected ketamine analogs could elicit ketamine-like effects on TrkB and ERK signaling in mouse primary cortical neurons. However, we did not proceed to test the analogs since ketamine (positive control) did not show any effects on TrkB or ERK phosphorylation in our culture. Overall, this study advances the understanding of the mechanism of N2O, possibly giving new insight of the antidepressant mechanisms of NMDAR-blocking agents more generally. Additionally, we found promising ketamine analogs that await experimental testing.