BDNF-TRKB signaling system of the dorsal periaqueductal gray matter is implicated in the panicolytic-like effect of antidepressant drugs

A Comprehensive Review of the Genetic and Epigenetic Contributions to the Development of Fibromyalgia

This narrative review summarizes the current knowledge of the genetic and epigenetic contributions to the development of fibromyalgia (FM). Although there is no single gene that results in the development of FM, this study reveals that certain polymorphisms in genes involved in the catecholaminergic pathway, the serotonergic pathway, pain processing, oxidative stress, and inflammation may influence susceptibility to FM and the severity of its symptoms. Furthermore, epigenetic changes at the DNA level may lead to the development of FM. Likewise, microRNAs may impact the expression of certain proteins that lead to the worsening of FM-associated symptoms.

Fluoxetine acts concomitantly on dorsal and ventral hippocampus to Trk-dependently modulate the extinction of fear memory

BACKGROUND

Hippocampus can be divided along its longitudinal axis into dorsal and ventral parts, which play different roles in modulating the behavioral responses to stress. However, it is not clear whether the hippocampal subregions could also differently modulate the effect of antidepressant drugs. Since fluoxetine (FLX) effect on extinction of aversive memory is well known to depend on hippocampal BDNF levels, we hypothesized that the hippocampal subregions might play different roles in fluoxetine efficacy in decreasing fear response.

METHOD

Wistar rats were fear-cued conditioned and treated chronically with FLX to subsequently investigate their extinction memory. BDNF levels were assessed separately in the dorsal (dHC) and ventral (vHC) hippocampus in animals chronically treated with FLX. An independent group received K252a (a functional Trk blocker) infusion into the dHC or vHC to assay its interaction with FLX treatment along the fear response. Next, BDNF was directly infused into either the dHC or vHC to the behavior be compared with those induced by chronic FLX treatment. Finally, FLX effect on c-Fos expression was evaluated also considering the dHC and vHC apart, along with subareas of amygdala and medial prefrontal cortex.

RESULTS

BDNF levels were increased in the vHC after acute FLX, and in the dHC after chronic FLX treatment. FLX effect on fear response was blocked by K252a administration into either dHC or vHC, after the extinction protocol. BDNF administration into the dHC increased fear response, however its administration into the vHC induced an opposite effect. Besides, a negative correlation between the fear response and c-Fos expression in the dHC CA3/CA1 and vHC CA1/DG was observed after chronic FLX treatment.

CONCLUSION

Both dHC and vHC are essential for the Trk-dependent effect of FLX on extinction memory, although a discrepancy in the fear response was observed with the infusion of BDNF into the dHC or vHC.

Adolescent cannabinoid exposure modulates the vulnerability to cocaine-induced conditioned place preference and DNMT3a expression in the prefrontal cortex in Swiss mice

RATIONALE

Cannabis sativa is the most widely used drug by adolescents globally. The recreational use of synthetic cannabinoids by teenagers has also grown in recent years. Despite the wrong perception that exposure to these drugs does not cause harm, repeated exposure to cannabinoids at early stages of life compromises important maturation processes and brain development. Chronic early cannabinoid use has been related to a higher risk of psychiatric outcomes, including cocaine addiction. Evidence suggests that exposure to natural and synthetic cannabinoids during adolescence modifies molecular and behavioral effects of cocaine in adulthood. Responses to cocaine are regulated by epigenetic mechanisms, such as DNA methylation, in the brain's reward regions. However, the involvement of these processes in modulation of the vulnerability to the effects of cocaine induced by prior exposure to cannabinoids remains poorly understood.

OBJECTIVES

Investigate whether exposure to the synthetic cannabinoid WIN55,212-2 during adolescence modulates anxiety- and depression-like behavior, memory, and cocaine reward in adult mice. We also evaluated whether exposure to cannabinoids during adolescence modulates the expression of enzymes that are involved in DNA methylation.

RESULTS

Exposure to WIN55,212-2 during adolescence did not alter anxiety- or depressive-like behavior. However, prior exposure to cannabinoids inhibited cocaine-induced conditioned place preference without modulating cocaine-induced hyperlocomotion, accompanied by an increase in expression of the enzyme DNA methyltransferase 3a (DNMT3a) in the prefrontal cortex.

CONCLUSIONS

Our findings suggest that exposure to WIN55,212-2 during adolescence leads to changes in DNMT3a expression, and this pathway appears to be relevant to modulating the rewarding effects of cocaine.

Antipanic-like effect of esketamine and buprenorphine in rats exposed to acute hypoxia

The antidepressant effect of ketamine has been widely acknowledged and the use of one of its enantiomers, S-ketamine (esketamine), has recently been approved for the clinical management of treatment-resistant depression. As with ketamine, the non-selective opioid receptor-interacting drug buprenorphine is reported to have antidepressant and anxiolytic properties in humans and rodents. Given the fact that antidepressant drugs are also first line treatment for panic disorder, it is surprising that the potential panicolytic effect of these compounds has been scarcely (ketamine), or not yet (buprenorphine) investigated. We here evaluated the effects of ketamine (the racemic mixture), esketamine, and buprenorphine in male Wistar rats submitted to a panicogenic challenge: acute exposure to hypoxia (7% O₂). We observed that esketamine (20 mg/kg), but not ketamine, decreased the number of escape attempts made during hypoxia, and this effect could be observed even 7 days after the drug administration. A panicolytic-like effect was also observed with MK801, which like esketamine, antagonizes NMDA glutamate receptors. Buprenorphine (0.3 mg/kg) also impaired hypoxia-induced escape, an effect blocked by the non-selective opioid receptor antagonist naloxone, indicating an interaction with classical ligand sites, such as µ and kappa receptors, but not with nociception/orphanin FQ receptors. Altogether, the results suggest that esketamine and buprenorphine cause rapid-onset panicolytic-like effects, and may be alternatives for treating panic disorder, particularly in patients who are refractory to standard pharmacological treatment.

Imipramine attenuates anxiety- and depressive-like effects of acute and prolonged ethanol-abstinence in male rats by modulating SERT and GR expression in the dorsal hippocampus

AIMS

Considering that serotoninergic agents attenuate symptoms of anxiety and are used to treat depression, we investigated whether subchronic treatment with imipramine, a serotonin/noradrenaline reuptake inhibitor, would prevent the anxiogenic-like behaviour induced by acute and/or chronic ethanol withdrawal. We also investigated whether those changes were related to the disfunctioning of hypothalamic-pituitary-adrenal (HPA) axis and serotonergic neurotransmission.

MAIN METHODS

264 Male Wistar rats were treated with ethanol 6% (vol./vol.) for 21 days. Acute ethanol withdrawal was induced by abrupt discontinuation of treatment and sustained for 48 h. Protracted abstinence was sustained for an additional period of 21 days. Behavioural tests included the Elevated Plus Maze (EPM) or Light/Dark Box (LDB) after acute abstinence, and the Forced Swim Test (FST) after protracted abstinence. Imipramine (15 mg/kg, i.p.) was administered 24, 19 and 1 h before EPM or LDB tests.

KEY FINDINGS

Acute abstinence decreased exploration of the open arms of the EPM, without changing exploration of LDB. Additionally, chronic abstinent rats displayed more time immobile in the FST, when compared to control animals. These effects were attenuated by imipramine treatment, without changing basal response. Imipramine prevented protracted abstinence -induced decrease in glucocorticoid receptor (GR) and serotonin transporter (SERT) expression in the dorsal hippocampus.

SIGNIFICANCE

Our findings indicate that chronic ethanol withdrawal affects the hippocampal serotonergic system by decreasing serotonin transporter expression. It also disturbs the HPA axis functioning through an imbalance on GR and mineralocorticoid (MR) expression.

Activation of the TRKB receptor mediates the panicolytic-like effect of the NOS inhibitor aminoguanidine

Nitric oxide (NO) triggers escape reactions in the dorsal periaqueductal gray matter (dPAG), a core structure mediating panic-associated response, and decreases the release of BDNF in vitro. BDNF mediates the panicolytic effect induced by antidepressant drugs and produces these effects per se when injected into the dPAG. Based on these findings, we hypothesize that nitric oxide synthase (NOS) inhibitors would have panicolytic properties associated with increased BDNF signaling in the dPAG. We observed that the repeated (7 days), but not acute (1 day), systemic administration of the NOS inhibitor aminoguanidine (AMG; 15 mg/kg/day) increased the latency to escape from the open arm of the elevated T-maze (ETM) and inhibited the number of jumps in hypoxia-induced escape reaction in rats, suggesting a panicolytic-like effect. Repeated, but not acute, AMG administration (15 mg/kg) also decreased nitrite levels and increased TRKB phosphorylation at residues Y706/7 in the dPAG. Notwithstanding the lack of AMG effect on total BDNF levels in this structure, the microinjection of the TRK antagonist K252a into the dPAG blocked the anti-escape effect of this drug in the ETM. Taken together our data suggest that the inhibition of NO production by AMG increases the levels of pTRKB, which is required for the panicolytic-like effect observed.

Prelimbic neuronal nitric oxide synthase inhibition exerts antidepressant-like effects independently of BDNF signalling cascades

OBJECTIVES

NMDA antagonists and nitric oxide synthase (NOS) inhibitors induce antidepressant-like effects and may represent treatment options for depression. The behavioural effects of NMDA antagonists seem to depend on Tyrosine kinase B receptor (TrkB) activation by BDNF and on mechanistic target of rapamycin (mTOR), in the medial prefrontal cortex (mPFC). However, it is unknown whether similar mechanisms are involved in the behavioural effects of NOS inhibitors. Therefore, this work aimed at determining the role of TrkB and mTOR signalling in the prelimbic area of the ventral mPFC (vmPFC-PL) in the antidepressant-like effect of NOS inhibitors.

METHODS

Pharmacological treatment with LY235959 or ketamine (NMDA antagonists), NPA or 7-NI (NOS inhibitors), BDNF, K252a (Trk antagonist) and rapamycin (mTOR inhibitor) injected systemically or into vmPFC-PL followed by behavioural assessment.

RESULTS

We found that bilateral injection of BDNF into the vmPFC-PL induced an antidepressant-like effect, which was blocked by pretreatment with K252a and rapamycin. Microinjection of LY 235959 into the vmPFC-PL induced antidepressant-like effect that was suppressed by local rapamycin but not by K252a pretreatment. Microinjection of NPA induced an antidepressant-like effect insensitive to both K252a and rapamycin. Similarly, the antidepressant-like effects of a systemic injection of ketamine or 7-NI were not affected by blockade of mTOR or Trk receptors in the vmPFC-PL.

CONCLUSION

Our data support the hypothesis that NMDA blockade induces an antidepressant-like effect that requires mTOR but not Trk signalling into the vmPFC-PL. The antidepressant-like effect induced by local NOS inhibition is independent on both Trk and mTOR signalling in the vmPFC-PL.

Multimodal early-life stress induces biological changes associated to psychopathologies

Evidences suggest the contributive role of early-life stress (ELS) to affective and anxiety disorders. Chronic exposure to the same stressor may generate habituation, while the exposure to different and repeated stressors gradually promotes maladaptive plasticity. Therefore, to further understand the effects of heterotypic stressors during early life period, male Wistar rat pups (P1-P21) were exposed to Multimodal ELS paradigm. Results indicate pups did not habituate to multimodal ELS and neonates respond to both physical and psychogenic stressors. Adult rats that underwent ELS protocol showed significant lower sucrose intake, decreased latency to immobility in the forced swim test and increased latency to light compartment in the light-dark test when compared to control group. Although it has been shown that ELS-induced changes in hippocampus can be used as biomarkers, multimodal ELS did not significantly alter BDNF, Tyrosine Kinase B (TrkB) receptor expression or neurogenesis in the hippocampus. Taken together, these findings indicate that multimodal ELS protocol can be an interesting experimental model for understanding long-term psychiatric disorders associated with stress. Indeed, our data with neurogenesis, BDNF and TrkB, and conflicting data from the literature, suggest that additional studies on synaptic plasticity/intracellular cascades would help to detect the underlying mechanisms.

Activation of brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling in the pedunculopontine tegmental nucleus: a novel mechanism for the homeostatic regulation of rapid eye movement sleep

Rapid eye movement (REM) sleep dysregulation is a symptom of many neuropsychiatric disorders, yet the mechanisms of REM sleep homeostatic regulation are not fully understood. We have shown that, after REM sleep deprivation, the pedunculopontine tegmental nucleus (PPT) plays a critical role in the generation of recovery REM sleep. In this study, we used multidisciplinary techniques to show a causal relationship between brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (TrkB) signaling in the PPT and the development of REM sleep homeostatic drive. Rats were randomly assigned to conditions of unrestricted sleep or selective REM sleep deprivation (RSD) with PPT microinjections of vehicle control or a dose of a TrkB receptor inhibitor (2, 3, or 4 nmol K252a or 4 nmol ANA-12). On experimental days, rats received PPT microinjections and their sleep-wake physiological signals were recorded for 3 or 6 h, during which selective RSD was performed in the first 3 h. At the end of all 3 h recordings, rats were killed and the PPT was dissected out for BDNF quantification. Our results show that K252a and ANA-12 dose-dependently reduced the homeostatic responses to selective RSD. Specifically, TrkB receptor inhibition reduced REM sleep homeostatic drive and limited REM sleep rebound. There was also a dose-dependent suppression of PPT BDNF up-regulation, and regression analysis revealed a significant positive relationship between REM sleep homeostatic drive and the level of PPT BDNF expression. These data provide the first direct evidence that activation of BDNF-TrkB signaling in the PPT is a critical step for the development of REM sleep homeostatic drive.