Browsing by study line "Farmakologi"

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.

Rodent studies indicate that the effects of pharmacological antidepressant treatments depend on the TrkB (tropomyosin-related kinase B) receptor of the neurotrophic factor BDNF (brain-derived neurotrophic factor). However, the mechanism by which TrkB signaling becomes active remains disputed. Our group proposes that the activation of TrkB signaling is a result of an indirect physiological adaptation to the drug treatment, which is supported by observations made with rapid-acting antidepressants ketamine and nitrous oxide. Previous studies indicate that the immediate effects of the drugs are followed by a sedative state resembling deep sleep, during which TrkB signaling becomes active. The sedative state is accompanied with a drop in core body temperature, and preliminary findings indicate that preventing the drug-induced hypothermia blocks TrkB signaling in the cortex.    The purpose of this study was to investigate the effect of ambient temperature on TrkB signaling in the hippocampus following nitrous oxide administration. Nitrous oxide (65 % ad 100 % O2) was administered to adult male mice for 20 minutes. After the drug treatment the animals were kept in different recovery conditions: room temperature or a heightened ambient temperature of approximately 36 °C for 15 minutes. Following the recovery, the animals were euthanised, and hippocampus samples were collected from the animals. Levels of BDNF and TrkB signaling were analysed with ELISA and western blot, respectively.    Nitrous oxide caused a significant drop in core body temperature, but this was not accompanied with increased BDNF levels or TrkB signaling. Evidence suggests that hippocampal atrophy contributes to depression, but the acute effects of antidepressant treatments on TrkB signaling in this brain area appear to be less pronounced than those seen in the prefrontal cortex. The findings indicate that nitrous oxide has a replicable hypothermic effect, but this is not associated with increased TrkB signaling in the hippocampus.