Involvement of glutamatergic N-methyl-d-aspartate receptors in the expression of increased head-dipping behaviors in the hole-board tests of olfactory bulbectomized mice

Aspalathus linearis infusion affects hole-board test behaviour and amino acid concentration in the brain

Rooibos tea, brewed using Aspalathus linearis leaves, is a popular South African herbal infusion, but its everyday intake is not fully described in terms of the neuropsychopharmacological outcomes. The cell-protective activity of A. linearis is connected with the ability of reducing glycaemia, inflammation as well as oxidative stress. It was already shown that "fermented" rooibos herbal tea (FRHT), which is rich in phenolic compounds, improves the cognitive performance of rats in the water maze and impacts dopaminergic striatal transmission. The present research was taken to extend the knowledge about the feasible behavioural and neurochemical implications of sustained oral FRHT consumption. We hypothesized that it might affect brain amino acid content and thus induce behaviour and neuroprotection. FRHTs of different leaf to water ratios (1:100, 2:100 and 4:100), analysed by chromatographic methods as regards their flavonoid characteristics, were given to rats as only liquid for 3 months. Their behaviour was evaluated in the hole-board test (HBT). Brain amino acids concentration was analysed in the striatum, hippocampus and prefrontal cortex by HPLC-ECD. The rats drinking rooibos tea presented increased motor activity defined as time spent on moving in the HBT. Their exploration measured by head-dipping and rearing was enhanced. Longer time of the testing-box central zone occupation indicated to reduction in anxiety-related behaviour. Excitatory amino acids (aspartate and glutamate) content was decreased in the striatum of animals drinking the infusions whereas taurine level was increased both in the striatum and hippocampus. In conclusion we suggest that long-term FRHT intake affects exploration and anxiety-related behaviour of the rats as well as exerts biochemical outcomes in the brain that support the neuroprotective impact of rooibos tea.

Multi-omics analysis of pathological changes in the amygdala of rats subjected to chronic restraint stress

OBJECTIVE

Overwhelming stress potentially results in the occurrence of many mental diseases. The amygdala is one region in the brain targeted by stress. Recent studies have shown that changes in the amygdala of subjects under stress are related to depression, anxiety and post-traumatic stress disorder (PTSD). However, researchers have not clearly elucidated the changes in the amygdala in response to stress and the underlying mechanism. We conducted several experiments to understand this mechanism.

METHODS

In this study, we first established a rat model of chronic restraint stress (CRS) and observed the changes in behavior and neurons in the amygdala. Second, an integrated metabolomics and proteomics experiment was conducted to identify potential stress-related biomarkers. Finally, we validated two molecules of interest and detected four apoptosis-related proteins using Western blotting to further determine the related mechanisms.

RESULTS

Our study revealed the presence of anxiety-like behaviors and pathological changes in amygdalar neurons in the rat model. In the multi-omics analysis, 19 potential molecules were identified. Western blotting confirmed consistent changes in the levels of Cry1 and Brcc36 obtained in previous results. The levels of proteins in the ataxia telangiectasia mutated (ATM) pathway were increased in the CRS group.

CONCLUSIONS

CRS causes anxiety-like behaviors that are potentially related to decreased levels of GABA in the amygdala. Moreover, CRS potentially alters the levels of Cry1 and Brcc36 and results in circadian rhythm disorder and impairments in DNA repair and apoptosis in the amygdala through a mechanism mediated by the ATM pathway.

Research and development of κ opioid receptor agonists and δ opioid receptor agonists

Delta opioid delta receptor (DOP) agonists were expected to be analgesics and many researchers tried to develop the SNC80 derivatives. However, the derivatives were dropped at the stage of early clinical trials because of undesirable side effects and weak analgesia. On the other hand, DOP agonists have been proposed as attractive candidates for the novel psychotropic drugs. We recently succeeded in synthesizing a novel selective DOP agonist KNT-127. KNT-127 produced neither catalepsy nor convulsive effects. We have demonstrated that KNT-127 has potent anxiolytic-like effect in rat models of innate anxiety. This anxiolytic-like effect was independent from known adverse effect of benzodiazepine, such as memory impairment, motor coordination deficits, and ethanol interactions. We have also demonstrated that KNT-127 showed potent and rapid antidepressant-like effects in rat models of depression. This antidepressant-like effect was independent from known adverse effect of selective serotonin reuptake inhibitor (SSRI), such as digestive symptoms. Therefore, we propose that DOP should be considered as an attractive target for the development of novel psychotropic drugs, without producing the adverse effects associated with benzodiazepine anxiolytics and SSRI antidepressants. Very recently, we developed another delta agonist NC-2800 with a different structure. NC-2800 is now in the preclinical stage using the CiCLE fund supported by AMED (Japanese Agency for Medical Research and Development).

Medium- and high-intensity rTMS reduces psychomotor agitation with distinct neurobiologic mechanisms

Definitive data are lacking on the mechanism of action and biomarkers of repetitive transcranial magnetic stimulation (rTMS) for the treatment of depression. Low-intensity rTMS (LI-rTMS) has demonstrated utility in preclinical models of rTMS treatments but the effects of LI-rTMS in murine models of depression are unknown. We examined the behavioral and neurobiologic changes in olfactory bulbectomy (OB) mice with medium-intensity rTMS (MI-rTMS) treatment and fluoxetine hydrochloride. We then compared 10-Hz rTMS sessions for 3 min at intensities (measured at the cortical surface) of 4 mT (LI-rTMS), 50 mT (medium-intensity rTMS [MI-rTMS]), or 1 T (high-intensity rTMS [HI-rTMS]) 5 days per week over 4 weeks in an OB model of agitated depression. Behavioral effects were assessed with forced swim test; neurobiologic effects were assessed with brain levels of 5-hydroxytryptamine, brain-derived neurotrophic factor (BDNF), and neurogenesis. Peripheral metabolomic changes induced by OB and rTMS were monitored through enzyme-linked immunosorbent assay and ultrapressure liquid chromatography-driven targeted metabolomics evaluated with ingenuity pathway analysis (IPA). MI-rTMS and HI-rTMS attenuated psychomotor agitation but only MI-rTMS increased BDNF and neurogenesis levels. HI-rTMS normalized the plasma concentration of α-amino-n-butyric acid and 3-methylhistidine. IPA revealed significant changes in glutamine processing and glutamate signaling in the OB model and following MI-rTMS and HI-rTMS treatment. The present findings suggest that MI-rTMS and HI-rTMS induce differential neurobiologic changes in a mouse model of agitated depression. Further, α-amino-n-butyric acid and 3-methylhistidine may have utility as biomarkers to objectively monitor the response to rTMS treatment of depression.

NMDA Receptors Regulate the Structural Plasticity of Spines and Axonal Boutons in Hippocampal Interneurons

N-methyl-D-aspartate receptors (NMDARs) are present in both pyramidal neurons and interneurons of the hippocampus. These receptors play an important role in the adult structural plasticity of excitatory neurons, but their impact on the remodeling of interneurons is unknown. Among hippocampal interneurons, somatostatin-expressing cells located in the stratum oriens are of special interest because of their functional importance and structural characteristics: they display dendritic spines, which change density in response to different stimuli. In order to understand the role of NMDARs on the structural plasticity of these interneurons, we have injected acutely MK-801, an NMDAR antagonist, to adult mice which constitutively express enhanced green fluorescent protein (EGFP) in these cells. We have behaviorally tested the animals, confirming effects of the drug on locomotion and anxiety-related behaviors. NMDARs were expressed in the somata and dendritic spines of somatostatin-expressing interneurons. Twenty-four hours after the injection, the density of spines did not vary, but we found a significant increase in the density of their en passant boutons (EPB). We have also used entorhino-hippocampal organotypic cultures to study these interneurons in real-time. There was a rapid decrease in the apparition rate of spines after MK-801 administration, which persisted for 24 h and returned to basal levels afterwards. A similar reversible decrease was detected in spine density. Our results show that both spines and axons of interneurons can undergo remodeling and highlight NMDARs as regulators of this plasticity. These results are specially relevant given the importance of all these players on hippocampal physiology and the etiopathology of certain psychiatric disorders.