Xiaobai Li

Effect of chronic administration of flesinoxan and fluvoxamine on freezing behavior induced by conditioned fear

The present study investigated the acute effects of flesinoxan (a selective 5-HT(1A) receptor agonist), fluvoxamine (a selective serotonin reuptake inhibitor) and their co-administration on the expression of conditioned freezing, and index of anxiety in rats. This study also examined the acute effects of fluvoxamine and flesinoxan following chronic flesinoxan or chronic fluvoxamine on the expression of conditioned freezing. Acute administration of flesinoxan (s.c.; 0.1-3 mg/kg) reduced freezing dose dependently, and fluvoxamine (i.p.) at a high dose (60 mg/kg) reduced freezing significantly. Acute co-administration of fluvoxamine (30 mg/kg) and flesinoxan (0.3 mg/kg) showed an additive inhibitory effect on freezing. Chronic flesinoxan treatment (0.3 mg/kg, for 13 days) did not affect the inhibitory effect of acute flesinoxan treatment, but enhanced that of acute fluvoxamine (30 mg/kg) on conditioned freezing. Chronic fluvoxamine treatment (30 mg/kg, for 13 days) enhanced the inhibitory effect of acute fluvoxamine (30 mg/kg) and the inhibitory effect of acute flesinoxan (0.3 mg/kg) on conditioned freezing. These results suggest that co-administration of a selective serotonin reuptake inhibitor and a 5-HT(1A) receptor agonist is useful for the treatment of anxiety disorders.

Monoamine oxidase inhibitors reduce conditioned fear stress-induced freezing behavior in rats

The present study examined the acute anxiolytic effects of monoamine oxidase inhibitors on freezing behavior, a putative index of anxiety induced by conditioned fear stress. The selective serotonin 1A receptor agonist tandospirone (0.1-10 mg/kg) inhibited freezing dose dependently. The irreversible, non-selective monoamine oxidase inhibitors tranylcypromine (3 and 15 mg/kg) and phenelzine (30 and 80 mg/kg) reduced freezing significantly. Clorgyline (10 mg/kg, irreversible selective monoamine oxidase A inhibitor), N-(2-aminoethyl)-5-(m-fluorophenyl)-4-thiazole carboxamide (Ro 41-1049) (30 mg/kg, reversible selective monoamine oxidase A inhibitor), selegiline (3 mg/kg, irreversible selective monoamine oxidase B inhibitor) and lazabemide (10 mg/kg, reversible selective monoamine oxidase B inhibitor) had no effect on freezing behavior. However, combined administration of clorgyline (10 mg/kg) and selegiline (3 mg/kg) reduced freezing significantly, as well as combined administration of clorgyline (10 mg/kg) and lazabemide (10 mg/kg), Ro 41-1049 (30 mg/kg) and selegiline (3 mg/kg), or Ro 41-1049 (30 mg/kg) and lazabemide (10 mg/kg). These effects of monoamine oxidase inhibitors on freezing were not due to non-specific motor effects. These results suggest that acute inhibition of both monoamine oxidase A and B reduced anxiety or fear, while inhibition of monoamine oxidase A or B alone failed to reduce anxiety or fear.

Long-lasting change in 5-HT2A receptor-mediated behavior in rats after a single footshock

To investigate the long-term functional change in the 5-HT(2A) receptor after acute stress, we examined the effect of single footshock on head shake behavior induced by the 5-HT(2A) receptor agent (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) in rats. Head shakes were evoked in a dose-dependent manner by 0.1-10 mg/kg of DOI, and the maximal response was attenuated by a single footshock given 24 h before. This suggests that there is a decrease in the number of functionally effective 5-HT(2A) receptors. The single footshock-induced reduction in head shakes evoked by DOI was observed immediately and 24 h after footshock, and lasted until 1 and 2 weeks after footshock. Because there were no changes in the [3H]ketanserin binding of the frontal cortex 1 week after footshock, decreases in head shakes were not due to the down-regulation of 5-HT(2A) receptors evoked by footshock.

Effect of chronic treatment with the protein kinase C inhibitor staurosporine on the acquisition and expression of contextual fear conditioning

The present study investigated the effects of acute and chronic administration of the protein kinase C inhibitor, staurosporine, on the acquisition and expression of conditioned freezing behavior, an index of anxiety induced by conditioned fear stress. Results revealed that acute staurosporine (0.01 and 0.1 mg/kg, i.p.) did not affect either acquisition or expression of conditioned freezing. Chronic staurosporine administration (0.01 or 0.1 mg/kg, i.p., for 14 days) significantly reduced the acquisition of conditioned freezing at a dose of 0.1 mg/kg, but failed to affect the expression of conditioned freezing at any dose. These results suggest the involvement of protein kinase C in synaptic and cellular plasticity underlying emotional learning and memory.

Venlafaxine increases cell proliferation and regulates DISC1, PDE4B and NMDA receptor 2B expression in the hippocampus in chronic mild stress mice.

Recent evidence has identified disrupted in schizophrenia-1 (DISC1) as an important genetic risk factor for the development of many psychiatric disorders, including major depressive disorders. In addition, studies using animal models have demonstrated that chronic stress affects hippocampal structure and function. However, the functional effects of chronic stress on DISC1 remain unknown. Using a chronic mild stress (CMS) paradigm, we investigated the effects of CMS on depressive-like behaviors, hippocampal cell proliferation, and hippocampal protein expression of DISC1, phosphodiesterase 4B (PDE4B) and N-methyl-d-aspartate receptor 2B subunit (NMDA receptor 2B), which may be involved in the regulation of DISC1 and neurogenesis. We also examined the effects and possible mechanisms of the antidepressant venlafaxine in CMS mice. CMS increased the expression of DISC1 and PDE4B. Chronic treatment with venlafaxine blocked the increases in these proteins, and also reversed the CMS-induced decrease in neurogenesis and NMDA receptor 2B protein in the hippocampus. These results suggest that DISC1 may play an important role in the etiology of depression and in the action of antidepressants.

Duloxetine prevents the effects of prenatal stress on depressive-like and anxiety-like behavior and hippocampal expression of pro-inflammatory cytokines in adult male offspring rats

Stress during pregnancy may cause neurodevelopmental and psychiatric disorders. However, the mechanisms are largely unknown. Currently, pro‐inflammatory cytokines have been identified as a risk factor for depression and anxiety disorder. Unfortunately, there is very little research on the long‐term effects of prenatal stress on the neuroinflammatory system of offspring. Moreover, the relationship between antidepressant treatment and cytokines in the central nervous system, especially in the hippocampus, an important emotion modulation center, is unclear. Therefore, the aim of this study was to determine the effects of prenatal chronic mild stress during development on affective‐like behaviors and hippocampal cytokines in adult offspring, and to verify whether antidepressant (duloxetine) administration from early adulthood could prevent the harmful consequences. To do so, prenatally stressed and non‐stressed Sprague‐Dawley rats were treated with either duloxetine (10 mg/kg/day) or vehicle from postnatal day 60 for 21 days. Adult offspring were divided into four groups: 1) prenatal stress + duloxetine treatment, 2) prenatal stress + vehicle, 3) duloxetine treatment alone, and 4) vehicle alone. Adult offspring were assessed for anxiety‐like behavior using the open field test and depression‐like behavior using the forced swim test. Brains were analyzed for pro‐inflammatory cytokine markers in the hippocampus via real‐time PCR. Results demonstrate that prenatal stress‐induced anxiety‐ and depression‐like behaviors are associated with an increase in hippocampal inflammatory mediators, and duloxetine administration prevents the increased hippocampal pro‐inflammatory cytokine interleukin‐6 and anxiety‐ and depression‐like behavior in prenatally stressed adult offspring. This research provides important evidence on the long‐term effect of PNS exposure during development in a model of maternal adversity to study the pathogenesis of depression and its therapeutic interventions.

Involvement of CaMKIV in neurogenic effect with chronic fluoxetine treatment.

Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that has been suggested to participate in fluoxetine (FLX)-induced phosphorylation of cyclic AMP-response element binding protein (CREB). CREB is a key transcription factor in adult neurogenesis. The present study aimed at evaluating whether CaMKIV is involved in adult hippocampal neurogenesis with FLX treatment. Effects of chronic FLX on hippocampal cell proliferation, survival and phenotypes were assessed using bromodeoxyuridine (BrdU) immunohistochemistry or BrdU/neuronal nuclei (NeuN)/S100β immunofluorescence staining in wild-type (WT) and CaMKIV knockout (KO) mice. Expression and phosphorylation of CaMKIV and CREB were assessed using RT-PCR and Western blotting. The behavioural action with FLX was assessed in the novelty suppressed feeding test (NSF), which is considered neurogenesis-dependent. CaMKIV KO mice have reduced cell proliferation, but not survival in the dentate gyrus of hippocampus with chronic treatment of FLX when compared to wild littermates. Phenotype analysis showed that most newborn cells matured into neurons. Phosphorylation of CaMKIV was up-regulated in WT mice and phosphorylation of CREB was impaired in CaMKIV KO mice after FLX treatment. The behavioural effects of FLX in NSF were similar in both types. These data suggest that CaMKIV is involved in some aspects of FLX-promoting hippocampal neurogenesis.

Anxiolytic-like effect of mirtazapine mediates its effect in the median raphe nucleus

Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA), blocks the α2-adrenergic autoreceptors and heteroreceptors, which are responsible for controlling noradrenaline and 5-hydroxytryptamine (5-HT) release. Though preclinical and clinical studies have shown that mirtazapine exerts an anxiolytic action, its precise brain target sites remain unclear. In the present study, we investigated the brain area(s) in which mirtazapine exerts its anxiolytic-like effects on the expression of contextual conditioned freezing in rats. Mirtazapine (3μg/site) was directly injected into three brain structures, the median raphe nucleus (MRN), hippocampus and amygdala. Freezing behavior tests were carried out 10min after injections. Our results showed that the intra-MRN injection of mirtazapine reduced freezing significantly, whereas injections into the hippocampus or the amygdala did not. In addition, the intra-MRN injection of mirtazapine did not affect locomotor activity. These results suggest that the anxiolytic-like effect of mirtazapine might be mediated by its action on the MRN.

Sex-specific effects of prenatal chronic mild stress on adult spatial learning capacity and regional glutamate receptor expression profiles

Both animal experiments and clinical studies have demonstrated that prenatal stress can cause cognitive disorders in offspring. To explore the scope of these deficits and identify potential underlying mechanisms, we examined the spatial learning and memory performance and glutamate receptor (GluR) expression patterns of adult rats exposed to prenatal chronic mild stress (PCMS). Principal component analysis (PCA) was employed to reveal the interrelationships among spatial learning indices and GluR expression changes. Female PCMS-exposed offspring exhibited markedly impaired spatial learning and memory in the Morris water maze (MWM) task compared to control females, while PCMS-exposed males showed better initial spatial learning in the MWM compared to control males. PCMS also altered basal and post-MWM glutamate receptor expression patterns, but these effects differed markedly between sexes. Male PCMS-exposed offspring exhibited elevated basal expression of NR1, mGluR5, and mGluR2/3 in the prefrontal cortex (PFC), whereas females showed no basal expression changes. Following MWM training, PCMS-exposed males expressed higher NR1 in the PFC and mammillary body (MB), higher mGluR2/3 in PFC, and lower NR2B in the hippocampus (HIP), PFC, and MB compared to unstressed MWM-trained males. Female PCMS-exposed offspring showed strongly reduced NR1 in MB and NR2B in the HIP, PFC, and MB, and increased mGluR2/3 in PFC compared to unstressed MWM-trained females. This is the first report suggesting that NMDA subunits in the MB are involved in spatial learning. Additionally, PCA further suggests that the NR1-NR2B form is the most important for spatial memory formation. These results reveal long-term sex-specific effects of PCMS on spatial learning and memory performance in adulthood and implicate GluR expression changes within HIP, PFC, and MB as possible molecular mechanisms underlying cognitive dysfunction in offspring exposed to prenatal stress.

Adolescent escitalopram prevents the effects of maternal separation on depression- and anxiety-like behaviours and regulates the levels of inflammatory cytokines in adult male mice

There is little research on the effects of adolescent administration of antidepressants on behavioural function and inflammation in early‐life stressed adult mice. Using maternal separation (MS), a paradigm of early adversity, we investigated the effects of adolescent (PND 33‐54) escitalopram (ES; 10 mg/kg) exposure on depression‐ and anxiety‐like behaviours and the levels of inflammatory cytokines (interleukin [IL]‐1β, tumor necrosis factor [TNF]‐α, and IL‐10) in the ventral hippocampus (HPV), prefrontal cortex (PFC), and serum in adult (PND 61) male offspring mice. The results showed that MS has no effect on locomotor activity, but increased depression‐like behaviours in the saccharin preference test and increased anxiety‐like behaviours in the social preference and elevated plus maze tests. MS increased the levels of IL‐1β in the HPV, PFC, and serum, while decreasing the level of IL‐10 in the HPV. Furthermore, adolescent ES treatment inhibited these depression‐ and anxiety‐like behaviours, decreased the levels of IL‐1β, and increased the level of IL‐10 in the HPV. The results also showed that there are no effects of chronic escitalopram administration on normal behaviour in control mice. Taken together, the current data provide experimental evidence that MS increases depression and anxiety levels in adult male offspring. Additionally, the findings support the idea that early pharmacological intervention with ES may be an effective treatment for reducing the behavioral abnormalities induced by early adversity and regulating the underlying inflammatory mechanisms involved.