Effects of thienorphine on synaptic structure and synaptophysin expression in the rat nucleus accumbens

Opioid-induced fragile-like regulatory T cells contribute to withdrawal

Dysregulation of the immune system is a cardinal feature of opioid addiction. Here, we characterize the landscape of peripheral immune cells from patients with opioid use disorder and from healthy controls. Opioid-associated blood exhibited an abnormal distribution of immune cells characterized by a significant expansion of fragile-like regulatory T cells (Tregs), which was positively correlated with the withdrawal score. Analogously, opioid-treated mice also showed enhanced Treg-derived interferon-γ (IFN-γ) expression. IFN-γ signaling reshaped synaptic morphology in nucleus accumbens (NAc) neurons, modulating subsequent withdrawal symptoms. We demonstrate that opioids increase the expression of neuron-derived C-C motif chemokine ligand 2 (Ccl2) and disrupted blood-brain barrier (BBB) integrity through the downregulation of astrocyte-derived fatty-acid-binding protein 7 (Fabp7), which both triggered peripheral Treg infiltration into NAc. Our study demonstrates that opioids drive the expansion of fragile-like Tregs and favor peripheral Treg diapedesis across the BBB, which leads to IFN-γ-mediated synaptic instability and subsequent withdrawal symptoms.

Sinisan alleviates depression-like behaviors by regulating mitochondrial function and synaptic plasticity in maternal separation rats

BACKGROUND

Sinisan (SNS) consists of four kinds of herbs, which is the core of antidepressant prescription widely used in traditional Chinese medicine clinic treatment for depression induced by early life stress. However, the role and precise mechanism of SNS antidepressant have not yet been elucidated.

PURPOSE

This study aimed to investigate the mechanism SNS on antidepressant of regulating mitochondrial function to improve hippocampal synaptic plasticity.

METHODS

90 Sprague-Dawley (SD) rats male pups on Post-Natal Day (PND) 0 were randomly divided into Control group (ddH₂0), Model group (ddH₂0), Fluoxetine group (5.0 mg/kg fluoxetine), and SNS-L group (2.5 g/kg SNS), SNS-M group (5.0 g/kg SNS) and SNS-H group (10.0 g/kg SNS), 15 animals per group. Maternal separation (MS) from PND1 to PND21, drug intervention from PND60 to PND90, and behavior tests including sucrose preference test, open field test and forced swimming test from PND83 to PND90 were performed. Synaptic structure and mitochondrial structure were observed by TEM. The expression levels of PSD-95 and SYN were detected by immunohistochemistry and western blot test, the adenosine triphosphate (ATP) content in the hippocampus was detected by assay kits, and the expression levels of Mfn2, Drp1 and Fis1 protein were detected by western bolt test.

RESULTS

SNS can alleviate depression-like and anxiety-like behaviors in MS rats, improve the damage of synapses and mitochondria, reduce the decrease of ATP in hippocampus, and reverse the expression levels of PSD-95, SYN, Mfn2, Drp1, and Fis1 proteins.

CONCLUSION

SNS reduced the risk of early life stress induced depression disorder via regulating mitochondrial function and synaptic plasticity. Targeting mitochondrial may be a novel prospective therapeutic avenue for antidepressant.

Effect of tramadol on apoptosis and synaptogenesis in hippocampal neurons: The possible role of µ-opioid receptor

Tramadol is a synthetic opioid with centrally acting analgesic activity that alleviates moderate to severe pain and treats withdrawal symptoms of the other opioids. Like other opioid drugs, tramadol abuse has adverse effects on central nervous system components. Chronic administration of tramadol induces maladaptive plasticity in brain structures responsible for cognitive function, such as the hippocampus. However, the mechanisms by which tramadol induces these alternations are not entirely understood. Here, we examine the effect of tramadol on apoptosis and synaptogenesis of hippocampal neuronal in vitro. First, the primary culture of hippocampal neurons from neonatal rats was established, and the purity of the neuronal cells was verified by immunofluorescent staining. To evaluate the effect of tramadol on neuronal cell viability MTT assay was carried out. The western blot analysis technique was performed for the assessment of apoptosis and synaptogenesis markers. Results show that chronic exposure to tramadol reduces cell viability of neuronal cells and naloxone reverses this effect. Also, the level of caspase-3 significantly increased in tramadol-exposed hippocampal neurons. Moreover, tramadol downregulates protein levels of synaptophysin and stathmin as synaptogenesis markers. Interestingly, the effects of tramadol were abrogated by naloxone treatment. These findings suggest that tramadol can induce neurotoxicity in hippocampal neuronal cells, and this effect was partly mediated through opioid receptors.

Antidepressant-like effect of ginsenoside Rb1 on potentiating synaptic plasticity via the miR-134–mediated BDNF signaling pathway in a mouse model of chronic stress-induced depression

Background

Brain-derived neurotrophic factor (BDNF)–tropomyosin-related kinase B (TrkB) plays a critical role in the pathogenesis of depression by modulating synaptic structural remodeling and functional transmission. Previously, we have demonstrated that the ginsenoside Rb1 (Rb1) presents a novel antidepressant-like effect via BDNF–TrkB signaling in the hippocampus of chronic unpredictable mild stress (CUMS)-exposed mice. However, the underlying mechanism through which Rb1 counteracts stress-induced aberrant hippocampal synaptic plasticity via BDNF–TrkB signaling remains elusive.

Methods

We focused on hippocampal microRNAs (miRNAs) that could directly bind to BDNF and are regulated by Rb1 to explore the possible synaptic plasticity-dependent mechanism of Rb1, which affords protection against CUMS-induced depression-like effects.

Results

Herein, we observed that brain-specific miRNA-134 (miR-134) could directly bind to BDNF 3′UTR and was markedly downregulated by Rb1 in the hippocampus of CUMS-exposed mice. Furthermore, the hippocampus–targeted miR-134 overexpression substantially blocked the antidepressant-like effects of Rb1 during behavioral tests, attenuating the effects on neuronal nuclei-immunoreactive neurons, the density of dendritic spines, synaptic ultrastructure, long-term potentiation, and expression of synapse-associated proteins and BDNF–TrkB signaling proteins in the hippocampus of CUMS-exposed mice.

Conclusion

These data provide strong evidence that Rb1 rescued CUMS-induced depression-like effects by modulating hippocampal synaptic plasticity via the miR-134-mediated BDNF signaling pathway.

•

mmu-miR-134-5p could directly bind to BDNF 3’UTR, and was downregulated by Rb1 in the hippocampus of CUMS–exposed mice.

•

miR-134 overexpression blocked the effects of Rb1 on the behavioral tests in CUMS-exposed mice.

•

miR-134 overexpression blocked the effects of Rb1 on synaptic structural changes in the hippocampus of CUMS–exposed mice.

•

miR-134 overexpression blocked the effects of Rb1 on synaptic functional changes in the hippocampus of CUMS–exposed mice.

•

miR-134–mediated BDNF signaling was involved in the antidepressant-like effects of Rb1 in the CUMS–exposed mice.

Activation of 5-HT1A postsynaptic receptors by NLX-101 results in functional recovery and an increase in neuroplasticity in mice with brain ischemia

Pharmacological interventions that selectively activate serotonin 5-hydroxytryptramine-1A (5-HT_1A) heteroreceptors may prevent or attenuate the consequences of brain ischemic episodes. The present study investigated whether the preferential 5-HT_1A postsynaptic receptor agonist NLX-101 (a.k.a. F15599) mitigates cognitive and emotional impairments and affects neuroplasticity in mice that are subjected to the bilateral common carotid artery occlusion (BCCAO) model of brain ischemia. The selective serotonin reuptake inhibitor escitalopram (Esc) was used for comparative purposes because it is able to decrease morbidity and improve recovery in stroke patients and ischemic rodents. Sham and BCCAO mice received daily doses of NLX-101 (0.32 mg/kg, i.p) or Esc (20 mg/kg, i.p) for 28 days. During this period, they were evaluated for locomotor activity, anxiety- and despair-related behaviors and hippocampus-dependent cognitive function, using the open field, elevated zero maze, forced swim test and object location test, respectivelly. The mice's brains were processed for biochemical and histological analyses. BCCAO mice exhibited high anxiety and despair-like behaviors and performed worse than controls in the cognitive assessment. BCCAO induced neuronal and dendritic spine loss and decreases in the protein levels of neuronal plasticity markers, including brain-derived neurotrophic factor (BDNF), synaptophysin (SYN), and postsynaptic density protein-95 (PSD-95), in prefrontal cortex (PFC) and hippocampus. NLX-101 and Esc attenuated cognitive impairments and despair-like behaviors in BCCAO mice. Only Esc decreased anxiety-like behaviors due to brain ischemia. Both NLX-101 and Esc blocked the increase in plasma corticosterone levels and, restored BDNF, SYN and PSD-95 protein levels in the hippocampus. Moreover, both compounds impacted positively dentritic remodeling in the hippocampus and PFC of ischemic mice. In the PFC, NLX-101 increased the BDNF protein levels, while Esc in turn, attenuated the decrease in the PSD-95 protein levels induced by BCCAO. The present results suggest that activation of post-synaptic 5-HT_1A receptors is the molecular mechanism for serotonergic protective effects in BCCAO. Moreover, post-synaptic biased agonists such as NLX-101 might constitute promising therapeutics for treatment of functional and neurodegenerative outcomes of brain ischemia.

ATP11B deficiency leads to impairment of hippocampal synaptic plasticity

Synaptic plasticity is known to regulate and support signal transduction between neurons, while synaptic dysfunction contributes to multiple neurological and other brain disorders; however, the specific mechanism underlying this process remains unclear. In the present study, abnormal neural and dendritic morphology was observed in the hippocampus following knockout of Atp11b both in vitro and in vivo. Moreover, ATP11B modified synaptic ultrastructure and promoted spine remodeling via the asymmetrical distribution of phosphatidylserine and enhancement of glutamate release, glutamate receptor expression, and intracellular Ca2+ concentration. Furthermore, experimental results also indicate that ATP11B regulated synaptic plasticity in hippocampal neurons through the MAPK14 signaling pathway. In conclusion, our data shed light on the possible mechanisms underlying the regulation of synaptic plasticity and lay the foundation for the exploration of proteins involved in signal transduction during this process.

Intranasal cerebrolysin improves cognitive function and structural synaptic plasticity in photothrombotic mouse model of medial prefrontal cortex ischemia

Medial prefrontal cortex (mPFC) ischemia affects post-stroke cognitive outcomes. We aimed to investigate the effects of different doses and routes of cerebrolysin (CBL) on the structural synaptic plasticity and cognitive function after mPFC ischemia in mice. Thence, CBL (1, 2.5 ml/kg/i.p./daily) or (1 ml/kg/i.n./daily), were administrated in photothrombotic mouse model of mPFC ischemia for two weeks. Episodic and spatial memories were assessed by the What-Where-Which (WWWhich) and Barnes tasks. Growth-associated protein 43 (GAP-43), postsynaptic density-95 (PSD-95), and synaptophysin (SYN) levels were measured in the lesioned area using western blot analysis. Dendritic arbors, spine densities, and morphology were assessed via Golgi-Cox staining. Treatment with 2.5 ml/kg/i.p. and 1 ml/kg/i.n. doses attenuated mPFC ischemia-induced episodic and spatial memories impairment. Results showed an obvious increase in the GAP-43, PSD-95 and SYN levels and improvement in the structural synaptic indexes in lesioned area induced by the same doses and routes of CBL. In conclusion, we found that specific doses/routes of CBL have positive effects on the structural synaptic plasticity and cognitive outcomes after mPFC ischemia.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

RACK1 promotes maintenance of morphine-associated memory via activation of an ERK-CREB dependent pathway in hippocampus

Existence of long-term drug-associated memories may be a crucial factor in drug cravings and relapse. RACK1 plays a critical role in morphine-induced reward. In the present study, we used conditioned place preference (CPP) to assess the acquisition and maintenance of morphine conditioned place preference memory. The hippocampal protein level of RACK1 and synaptic quantitation were evaluated by Western blotting, immunohistochemistry and electron microscopy, respectively. Additionally, shRACK1 (shGnb2l1) was used to silence RACK1 in vivo to evaluate the role and the underlying mechanism of RACK1 in maintenance of morphine CPP memory. We found that morphine induced CPP was maintained for at least 7 days after the last morphine treatment, which indicated a positive correlation with hippocampal RACK1 level, and was accompanied simultaneously by increases in the synapse density and hippocampal expression of synaptophysin (SYP), phosphorylation of extracellular signal-regulated kinase1/2 (pERK1/2) and the phosphorylation of cyclic adenosine monophosphate response element-binding (pCREB). ShGnb2l1 icv injection significantly suppressed the expression of all above proteins, decreased the synapse density in the hippocampus and attenuated the acquisition and maintenance of morphine CPP. Our present study highlights that RACK1 plays an important role in the maintenance of morphine CPP, likely via activation of ERK-CREB pathway in hippocampus.

Changed Synaptic Plasticity in Neural Circuits of Depressive-Like and Escitalopram-Treated Rats

BACKGROUND

Although progress has been made in the detection and characterization of neural plasticity in depression, it has not been fully understood in individual synaptic changes in the neural circuits under chronic stress and antidepressant treatment.

METHODS

Using electron microscopy and Western-blot analyses, the present study quantitatively examined the changes in the Gray's Type I synaptic ultrastructures and the expression of synapse-associated proteins in the key brain regions of rats' depressive-related neural circuit after chronic unpredicted mild stress and/or escitalopram administration. Meanwhile, their depressive behaviors were also determined by several tests.

RESULTS

The Type I synapses underwent considerable remodeling after chronic unpredicted mild stress, which resulted in the changed width of the synaptic cleft, length of the active zone, postsynaptic density thickness, and/or synaptic curvature in the subregions of medial prefrontal cortex and hippocampus, as well as the basolateral amygdaloid nucleus of the amygdala, accompanied by changed expression of several synapse-associated proteins. Chronic escitalopram administration significantly changed the above alternations in the chronic unpredicted mild stress rats but had little effect on normal controls. Also, there was a positive correlation between the locomotor activity and the maximal synaptic postsynaptic density thickness in the stratum radiatum of the Cornu Ammonis 1 region and a negative correlation between the sucrose preference and the length of the active zone in the basolateral amygdaloid nucleus region in chronic unpredicted mild stress rats.

CONCLUSION

These findings strongly indicate that chronic stress and escitalopram can alter synaptic plasticity in the neural circuits, and the remodeled synaptic ultrastructure was correlated with the rats' depressive behaviors, suggesting a therapeutic target for further exploration.