Noradrenaline activation of hippocampal dopamine D1 receptors promotes antidepressant effects.

Dopamine D1 receptors (D1Rs) in the hippocampal dentate gyrus (DG) are essential for antidepressant effects. However, the midbrain dopaminergic neurons, the major source of dopamine in the brain, only sparsely project to DG, suggesting possible activation of DG D1Rs by endogenous substances other than dopamine. We have examined this possibility using electrophysiological and biochemical techniques and found robust activation of D1Rs in mouse DG neurons by noradrenaline. Noradrenaline at the micromolar range potentiated synaptic transmission at the DG output and increased the phosphorylation of protein kinase A substrates in DG via activation of D1Rs and ß adrenergic receptors. Neuronal excitation preferentially enhanced noradrenaline-induced synaptic potentiation mediated by D1Rs with minor effects on ß-receptor-dependent potentiation. Increased voluntary exercise by wheel running also enhanced noradrenaline-induced, D1R-mediated synaptic potentiation, suggesting a distinct functional role of the noradrenaline-D1R signaling. We then examined the role of this signaling in antidepressant effects using mice exposed to chronic restraint stress. In the stressed mice, an antidepressant acting on the noradrenergic system induced a mature-to-immature change in the DG neuron phenotype, a previously proposed cellular substrate for antidepressant action. This effect was evident only in mice subjected to wheel running and blocked by a D1R antagonist. These results suggest a critical role of noradrenaline-induced activation of D1Rs in antidepressant effects in DG. Experience-dependent regulation of noradrenaline-D1R signaling may determine responsiveness to antidepressant drugs in depressive disorders.

[Analysis the Selection of Opioid Analgesics with Mild and Moderate Cancer Pain Patients for Opioid Naïve].

In 2018, the World Health Organization revised its cancer pain therapy, abolishing the three-step pain relief ladder and recommending the use of opioid analgesics(OA)according to the pain intensity. Of opioid naive patients who were admitted to Chibaken Saiseikai Narashino Hospital from July 2015 to June 2017, treatment with weak OA was initiated in 13 patients(WOA group)and low-dose strong OA in 12 patients(SOA group). The numerical rating scale values immediately before the start of OA and 3, 7 and 14 days later were not significantly different between the 2 groups. As for adverse events, the frequency of occurrence(p=0.01)and the prolongation of the last onset date(p=0.02)were significant in the WOA group for constipation. When the factors related to OA selection were analyzed using logistic regression analysis, there was no significance. We reported the analysis results regarding OA selection in OA naive patients.

Rapid and lasting enhancement of dopaminergic modulation at the hippocampal mossy fiber synapse by electroconvulsive treatment.

Electroconvulsive therapy (ECT) is an established effective treatment for medication-resistant depression with the rapid onset of action. However, its cellular mechanism of action has not been revealed. We have previously shown that chronic antidepressant drug treatments enhance dopamine D1-like receptor-dependent synaptic potentiation at the hippocampal mossy fiber (MF)-CA3 excitatory synapse. In this study we show that ECT-like treatments in mice also have marked effects on the dopaminergic synaptic modulation. Repeated electroconvulsive stimulation (ECS), an animal model of ECT, strongly enhanced the dopamine-induced synaptic potentiation at the MF synapse in hippocampal slices. Significant enhancement was detectable after the second ECS, and further repetition of ECS up to 11 times monotonously increased the magnitude of enhancement. After repeated ECS, the dopamine-induced synaptic potentiation remained enhanced for more than 4 wk. These synaptic effects of ECS were accompanied by increased expression of the dopamine D1 receptor gene. Our results demonstrate that robust neuronal activation by ECS induces rapid and long-lasting enhancement of dopamine-induced synaptic potentiation at the MF synapse, likely via increased expression of the D1 receptor, at least in part. This rapid enhancement of dopamine-induced potentiation at the excitatory synapse may be relevant to the fast-acting antidepressant effect of ECT. NEW & NOTEWORTHY: We show that electroconvulsive therapy (ECT)-like stimulation greatly enhances synaptic potentiation induced by dopamine at the excitatory synapse formed by the hippocampal mossy fiber in mice. The effect of ECT-like stimulation on the dopaminergic modulation was rapidly induced, maintained for more than 4 wk after repeated treatments, and most likely mediated by increased expression of the dopamine D1 receptor. These effects may be relevant to fast-acting strong antidepressant action of ECT.

The immature dentate gyrus represents a shared phenotype of mouse models of epilepsy and psychiatric disease.

OBJECTIVES: There is accumulating evidence to suggest psychiatric disorders, such as bipolar disorder and schizophrenia, share common etiologies, pathophysiologies, genetics, and drug responses with many of the epilepsies. Here, we explored overlaps in cellular/molecular, electrophysiological, and behavioral phenotypes between putative mouse models of bipolar disorder/schizophrenia and epilepsy. We tested the hypothesis that an immature dentate gyrus (iDG), whose association with psychosis in patients has recently been reported, represents a common phenotype of both diseases. METHODS: Behaviors of calcium/calmodulin-dependent protein kinase II alpha (α-CaMKII) heterozygous knock-out (KO) mice, which are a representative bipolar disorder/schizophrenia model displaying iDG, and pilocarpine-treated mice, which are a representative epilepsy model, were tested followed by quantitative polymerase chain reaction (qPCR)/immunohistochemistry for mRNA/protein expression associated with an iDG phenotype. In vitro electrophysiology of dentate gyrus granule cells (DG GCs) was examined in pilocarpine-treated epileptic mice. RESULTS: The two disease models demonstrated similar behavioral deficits, such as hyperactivity, poor working memory performance, and social withdrawal. Significant reductions in mRNA expression and immunoreactivity of the mature neuronal marker calbindin and concomitant increases in mRNA expression and immunoreactivity of the immature neuronal marker calretinin represent iDG signatures that are present in both mice models. Electrophysiologically, we have confirmed that DG GCs from pilocarpine-treated mice represent an immature state. A significant decrease in hippocampal α-CaMKII protein levels was also found in both models. CONCLUSIONS: Our data have shown iDG signatures from mouse models of both bipolar disorder/schizophrenia and epilepsy. The evidence suggests that the iDG may, in part, be responsible for the abnormal behavioral phenotype, and that the underlying pathophysiologies in epilepsy and bipolar disorder/schizophrenia are strikingly similar.

Reversal of hippocampal neuronal maturation by serotonergic antidepressants.

Serotonergic antidepressant drugs have been commonly used to treat mood and anxiety disorders, and increasing evidence suggests potential use of these drugs beyond current antidepressant therapeutics. Facilitation of adult neurogenesis in the hippocampal dentate gyrus has been suggested to be a candidate mechanism of action of antidepressant drugs, but this mechanism may be only one of the broad effects of antidepressants. Here we show a distinct unique action of the serotonergic antidepressant fluoxetine in transforming the phenotype of mature dentate granule cells. Chronic treatments of adult mice with fluoxetine strongly reduced expression of the mature granule cell marker calbindin. The fluoxetine treatment induced active somatic membrane properties resembling immature granule cells and markedly reduced synaptic facilitation that characterizes the mature dentate-to-CA3 signal transmission. These changes cannot be explained simply by an increase in newly generated immature neurons, but best characterized as "dematuration" of mature granule cells. This granule cell dematuration developed along with increases in the efficacy of serotonin in 5-HT(4) receptor-dependent neuromodulation and was attenuated in mice lacking the 5-HT(4) receptor. Our results suggest that serotonergic antidepressants can reverse the established state of neuronal maturation in the adult hippocampus, and up-regulation of 5-HT(4) receptor-mediated signaling may play a critical role in this distinct action of antidepressants. Such reversal of neuronal maturation could affect proper functioning of the mature hippocampal circuit, but may also cause some beneficial effects by reinstating neuronal functions that are lost during development.

Slitrk2 deficiency causes hyperactivity with altered vestibular function and serotonergic dysregulation.

SLITRK2 encodes a transmembrane protein that modulates neurite outgrowth and synaptic activities and is implicated in bipolar disorder. Here, we addressed its physiological roles in mice. In the brain, the Slitrk2 protein was strongly detected in the hippocampus, vestibulocerebellum, and precerebellar nuclei-the vestibular-cerebellar-brainstem neural network including pontine gray and tegmental reticular nucleus. Slitrk2 knockout (KO) mice exhibited increased locomotor activity in novel environments, antidepressant-like behaviors, enhanced vestibular function, and increased plasticity at mossy fiber-CA3 synapses with reduced sensitivity to serotonin. A serotonin metabolite was increased in the hippocampus and amygdala, and serotonergic neurons in the raphe nuclei were decreased in Slitrk2 KO mice. When KO mice were treated with methylphenidate, lithium, or fluoxetine, the mood stabilizer lithium showed a genotype-dependent effect. Taken together, Slitrk2 deficiency causes aberrant neural network activity, synaptic integrity, vestibular function, and serotonergic function, providing molecular-neurophysiological insight into the brain dysregulation in bipolar disorders.

Augmentation of lenvatinib efficacy by topical treatment of miR-634 ointment in anaplastic thyroid cancer.

Anaplastic thyroid cancer (ATC) is one of the most lethal types of human tumors. Lenvatinib can improve the disease control and prognosis in patients with ATC. However, there is an unmet need to develop a therapeutically safer and non-invasive strategy that improves the efficacy of lenvatinib for advanced ATC tumors, which grow larger close to the skin. We previously demonstrated that the topical application of an ointment incorporating tumor suppressive microRNA (TS-miR), miR-634, is a useful strategy as a TS-miR therapeutics. Here, we found that the overexpression of miR-634 synergistically increased lenvatinib-induced cytotoxicity by concurrently downregulating multiple genes related to cytoprotective processes, including ASCT2, a glutamine transporter, in ATC cell lines. Furthermore, the topical application of a miR-634 ointment on subcutaneous tumors effectively augmented the anti-tumor effects of lenvatinib in an ATC xenograft mouse model. Thus, we propose topical treatment of a miR-634 ointment as a rational strategy for improving lenvatinib-based therapy for ATC.

Improving the Efficacy of EGFR Inhibitors by Topical Treatment of Cutaneous Squamous Cell Carcinoma with miR-634 Ointment.

For cutaneous squamous cell carcinoma (cSCC), topical treatment is an essential option for patients who are not candidates for, or who refuse, surgery. Epidermal growth factor receptor (EGFR) plays a key role in the development of cSCC, but EGFR tyrosine kinase inhibitors (TKIs), such as gefitinib, have shown only partial clinical benefit in this disease. Thus, there is an unmet need to develop novel strategies for improving the efficacy of TKIs in cSCC. We previously demonstrated that the tumor-suppressive microRNA (miRNA) miR-634 functions as a negative modulator of the cytoprotective cancer cell survival processes and is a useful anticancer therapeutic agent. In the present study, we found that topical application of an ointment containing miR-634 inhibited in vivo tumor growth without toxicity in a cSCC xenograft mouse model and a 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced papilloma mouse model. Functional validation revealed that miR-634 overexpression reduced glutaminolysis by directly targeting ASCT2, a glutamine transporter. Furthermore, overexpression of miR-634 synergistically enhanced TKI-induced cytotoxicity by triggering severe energetic stress in vitro and in vivo. Thus, we propose that topical treatment with miR-634 ointment is a useful strategy for improving for EGFR TKI-based therapy for cSCC.

Predominant Role of Serotonin at the Hippocampal Mossy Fiber Synapse with Redundant Monoaminergic Modulation.

The hippocampal mossy fiber (MF) synapse has been implicated in the pathophysiology and treatment of psychiatric disorders. Alterations of dopaminergic and serotonergic modulations at this synapse are candidate mechanisms underlying antidepressant and other related treatments. However, these monoaminergic modulations share the intracellular signaling pathway at the MF synapse, which implies redundancy in their functions. We here show that endogenous monoamines can potentiate MF synaptic transmission in mouse hippocampal slices by activating the serotonin 5-HT4 receptor. Dopamine receptors were not effectively activated by endogenous agonists, suggesting that the dopaminergic modulation is latent. Electroconvulsive treatment enhanced the 5-HT4 receptor-mediated serotonergic synaptic potentiation specifically at the MF synapse, increased the hippocampal serotonin content, and produced an anxiolytic-like behavioral effect in a 5-HT4 receptor-dependent manner. These results suggest that serotonin plays a predominant role in monoaminergic modulations at the MF synapse. Augmentation of this serotonergic modulation may mediate anxiolytic effects of electroconvulsive treatment.

Chronic fluoxetine bidirectionally modulates potentiating effects of serotonin on the hippocampal mossy fiber synaptic transmission.

Selective serotonin reuptake inhibitors (SSRIs) have been used to treat various psychiatric disorders. Although the cellular mechanisms underlying amelioration of particular symptoms are mostly unknown, recent studies have shown critical importance of the dentate gyrus of the hippocampus in behavioral effects of SSRIs in rodents. Here, we show that serotonin potentiates synaptic transmission between mossy fibers, the sole output of the dentate granule cells, and CA3 pyramidal cells in mouse hippocampal slices. This potentiation is mediated by activation of 5-HT(4) receptors and intracellular cAMP elevation. A chronic treatment of mice with fluoxetine, a widely used SSRI, bidirectionally modulates the 5-HT-induced potentiation: Fluoxetine enhances the potentiation induced by lower concentrations of serotonin, while attenuates that by the higher concentration, which represents stabilization of synaptic 5-HT action. In contrast to the chronic treatment, an acute application of fluoxetine in slices induces a leftward shift in the dose-response curve of the 5-HT-induced potentiation. Thus, acute and chronic fluoxetine treatments have distinct effects on the serotonergic modulation of the mossy fiber synaptic transmission. Exposure of mice to novel environments induces increases in locomotor activity and hippocampal extracellular 5-HT levels. In mice chronically treated with fluoxetine, the novelty-induced hyperactivity is reduced without significant alterations in home cage activity and motor skills. Our results suggest that the chronic fluoxetine treatment can stabilize the serotonergic modulation of the central synaptic transmission, which may contribute to attenuation of hyperactive behaviors.

Targeting the hippocampal mossy fiber synapse for the treatment of psychiatric disorders.

It is widely known that new neurons are continuously generated in the dentate gyrus of the hippocampus in the adult mammalian brain. This neurogenesis has been implicated in depression and antidepressant treatments. Recent evidence also suggests that the dentate gyrus is involved in the neuropathology and pathophysiology of schizophrenia and other related psychiatric disorders. Especially, abnormal neuronal development in the dentate gyrus may be a plausible risk factor for the diseases. The synapse made by the mossy fiber, the output fiber of the dentate gyrus, plays a critical role in regulating neuronal activity in its target CA3 area. The mossy fiber synapse is characterized by remarkable activity-dependent short-term synaptic plasticity that is established during the postnatal development and is supposed to be central to the functional role of the mossy fiber. Any defects, including developmental abnormalities, in the dentate gyrus and drugs acting on the dentate gyrus can modulate the mossy fiber-CA3 synaptic transmission, which may eventually affect hippocampal functions. In this paper, I review recent evidence for involvement of the dentate gyrus and mossy fiber synapse in psychiatric disorders and discuss potential importance of drugs targeting the mossy fiber synapse either directly or indirectly in the therapeutic treatments of psychiatric disorders.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity.

PD-L2 is a ligand for the immune checkpoint receptor PD-1; however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells by topical application of small interfering RNA (siRNA) inhibits the elicitation of contact hypersensitivity (CHS). Here, we investigated the effects of topical application of PD-L2 siRNA on allergic skin disease. PD-L2 was induced in dendritic cells concurrently with the elevation of major histocompatibility complex class II and CD86 expression. Topical application of PD-L2 siRNA inhibited the elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying dendritic cells into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb inhibited CHS to the same extent. PD-L2 siRNA treatment inhibited CHS in PD-1/PD-L1 double knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and T helper type 2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous dendritic cells acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical application of siRNA represents a therapeutic approach for contact allergy.

Spike train timing-dependent associative modification of hippocampal CA3 recurrent synapses by mossy fibers.

In the CA3 region of the hippocampus, extensive recurrent associational/commissural (A/C) connections made by pyramidal cells may function as a network for associative memory storage and recall. We here report that long-term potentiation (LTP) at the A/C synapses can be induced by association of brief spike trains in mossy fibers (MFs) from the dentate gyrus and A/C fibers. This LTP not only required substantial overlap between spike trains in MFs and A/C fibers, but also depended on the temporal order of these spike trains in a manner not predicted by the well-known rule of spike timing-dependent plasticity and requiring activation of type 1 metabotropic glutamate receptors. Importantly, spike trains in a putative single MF input provided effective postsynaptic activity for the induction of LTP at A/C synapses. Thus, the timing of spike trains in individual MFs may code information that is crucial for the associative modification of CA3 recurrent synapses.

Synapse-selective rapid potentiation of hippocampal synaptic transmission by 7,8-dihydroxyflavone.

AIM: The identification of 7,8-dihydroxyflavone (DHF) as a small molecule agonist for tropomyosin-related kinase B (TrkB) facilitated understanding of the role of TrkB signaling in regulating higher brain functions. DHF can penetrate the blood-brain barrier after systemic administration and changes the performance of cognitive and emotional behavioral tasks. However, it is poorly understood how DHF modulates neuronal functions at cellular levels. Aiming to understand the cellular basis underlying DHF-induced modifications of the brain functions, we examined the effects of DHF on the hippocampal excitatory synaptic transmission. METHODS: Field excitatory postsynaptic potentials were recorded using hippocampal slices prepared from adult male mice. Effects of bath-applied DHF on the synaptic efficacy were examined. RESULTS: We found that DHF induced robust synaptic potentiation at the mossy fiber to CA3 synapse. DHF had minimal effects at other hippocampal excitatory synapses or at immature mossy fiber synapse in juvenile mice. The TrkB receptor blockers K252a and ANA-12 did not affect the DHF-induced synaptic potentiation. Drug screening revealed that relatively low concentrations of 2-aminoethoxydiphenylborane blocked the DHF-induced synaptic potentiation. CONCLUSION: Our results demonstrate that DHF selectively potentiates hippocampal mossy fiber synaptic transmission via a TrkB receptor-independent mechanism. This novel neuromodulatory effect of DHF may influence higher brain functions by itself or together with the activation of the TrkB receptor. The rapid induction of the potentiation implies its potential importance in the acute behavioral effects of DHF.

Attenuated bidirectional short-term synaptic plasticity in the dentate gyrus of Schnurri-2 knockout mice, a model of schizophrenia.

The dentate gyrus of the hippocampus has been implicated in the pathophysiological basis of neuropsychiatric disorders including schizophrenia. We have identified several mouse models of neuropsychiatric disorders with robust molecular and functional defects in the dentate gyrus. Among them, mice lacking Schnurri-2 (Shn2 or HIVEP2) have been proposed as a model of schizophrenia and intellectual disability. Shn2 knockout mice exhibit behavioral abnormalities resembling symptoms of schizophrenia and HIVEP2-related intellectual disability as well as marked functional alterations in the soma and output synapse of the dentate granule cells (GCs). Although robust abnormalities were also observed in the dendritic spine morphology in the GCs, their functional correlates remain unknown. In the present study, we performed electrophysiological analyses of synaptic transmission at the medial perforant path (MPP) input onto the GCs in Shn2 knockout mice. While the basal synaptic efficacy was preserved, short-term synaptic depression induced by paired-pulse or low-frequency stimulation was reduced in the mutant mice. High-frequency tetanic stimulation induced lasting synaptic potentiation in both wild-type and mutant mice. However, the decaying synaptic potentiation shortly after the tetanic stimulation was significantly reduced in the mutant mice. These results indicate that the Shn2 deficiency attenuates bidirectional short-term synaptic plasticity at the MPP-GC synapse, thereby rendering the synapse more static. Our finding further supports a possible role of the dentate gyrus dysfunction in pathophysiology of schizophrenia and may also provide important information in interpreting morphology changes of the brain synapses in neuropsychiatric disorders.

Dopamine selectively potentiates hippocampal mossy fiber to CA3 synaptic transmission.

Dopamine has been implicated in various brain functions and the pathology of neurological diseases. In the hippocampus, dopamine has been shown to induce acute depression of synaptic transmission in the CA1 region, but it remains largely unknown how it works in the CA3 region. We here report that dopamine induces acute synaptic potentiation at the synapse formed by mossy fibers (MFs) on mouse hippocampal CA3 pyramidal cells, but not at converging associational/commissural synapses. Dopamine potentiated both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) components of MF synaptic responses similarly in respect of the magnitude and time course. The dopamine-induced potentiation was intact in the presence of picrotoxin, required activation of D(1)-like receptors and was apparently occluded by an activator of adenylate cyclase. The potentiation was accompanied by a decrease in magnitude of synaptic facilitation, suggesting the presynaptic site for the expression of the potentiation. The present study is the first demonstration of acute potentiation of hippocampal excitatory synaptic transmission by dopamine, which is most probably mediated by presynaptic D(1)-like receptor-cAMP cascades.

Rapid and stable changes in maturation-related phenotypes of the adult hippocampal neurons by electroconvulsive treatment.

Electroconvulsive therapy (ECT) is a highly effective and fast-acting treatment for depression. Despite a long history of clinical use, its mechanism of action remains poorly understood. Recently, a novel cellular mechanism of antidepressant action has been proposed: the phenotype of mature brain neurons is transformed to immature-like one by antidepressant drug treatments. We show here that electroconvulsive stimulation (ECS), an animal model of ECT, causes profound changes in maturation-related phenotypes of neurons in the hippocampal dentate gyrus of adult mice. Single ECS immediately reduced expression of mature neuronal markers in almost entire population of dentate granule cells. After ECS treatments, granule cells showed some of physiological properties characteristic of immature granule cells such as higher somatic intrinsic excitability and smaller frequency facilitation at the detate-to-CA3 synapse. The rapid downregulation of maturation markers was suppressed by antagonizing glutamate NMDA receptors, but not by perturbing the serotonergic system. While single ECS caused short-lasting effects, repeated ECS induced stable changes in the maturation-related phenotypes lasting more than 2 weeks along with enhancement of synaptic excitation of granule cells. Augmentation of synaptic inhibition or blockade of NMDA receptors after repeated ECS facilitated regaining the initial mature phenotype, suggesting a role for endogenous neuronal excitation in maintaining the altered maturation-related phenotype probably via NMDA receptor activation. These results suggest that brief neuronal activation by ECS induces "dematuration" of the mature granule cells and that enhanced endogenous excitability is likely to support maintenance of such a demature state. The global increase in neuronal excitability accompanying this process may be relevant to the high efficacy of ECT.

Serotonin derivatives, major safflower (Carthamus tinctorius L.) seed antioxidants, inhibit low-density lipoprotein (LDL) oxidation and atherosclerosis in apolipoprotein E-deficient mice.

The effects of defatted safflower seed extract and its phenolic constituents, serotonin derivatives, on atherosclerosis were studied. Ethanol-ethyl acetate extract of safflower seeds (SSE) inhibited low-density lipoprotein (LDL) oxidation induced in vitro by an azo-containing free-radical initiator V70 or copper ions. Two serotonin derivatives [N-(p-coumaroyl)serotonin, CS; N-feruloylserotonin, FS] and their glucosides were identified as the major phenolic constituents of the extract. The study with chemically synthesized materials revealed that a majority of the antioxidative activity of SSE was attributable to the aglycones of these two serotonin derivatives. Orally administered CS and FS suppressed CuSO(4)-induced plasma oxidation ex vivo. Long-term (15 week) dietary supplementation of SSE (1.0 wt %/wt) and synthetic serotonin derivatives (0.2-0.4%) significantly reduced the atherosclerotic lesion area in the aortic sinus of apolipoprotein E-deficient mice (29.2-79.7% reduction). The plasma level of both lipid peroxides and anti-oxidized LDL autoantibody titers decreased concomitantly with the reduction of lesion formation. Serotonin derivatives were detected as both intact and conjugated metabolites in the plasma of C57BL/6J mice fed on 1.0% SSE diet. These findings demonstrate that serotonin derivatives of SSE are absorbed into circulation and attenuate atherosclerotic lesion development possibly because of the inhibition of oxidized LDL formation through their strong antioxidative activity.

Role of the 5-HT4 receptor in chronic fluoxetine treatment-induced neurogenic activity and granule cell dematuration in the dentate gyrus.

BACKGROUND: Chronic treatment with selective serotonin (5-HT) reuptake inhibitors (SSRIs) facilitates adult neurogenesis and reverses the state of maturation in mature granule cells (GCs) in the dentate gyrus (DG) of the hippocampus. Recent studies have suggested that the 5-HT4 receptor is involved in both effects. However, it is largely unknown how the 5-HT4 receptor mediates neurogenic effects in the DG and, how the neurogenic and dematuration effects of SSRIs interact with each other. RESULTS: We addressed these issues using 5-HT4 receptor knockout (5-HT4R KO) mice. Expression of the 5-HT4 receptor was detected in mature GCs but not in neuronal progenitors of the DG. We found that chronic treatment with the SSRI fluoxetine significantly increased cell proliferation and the number of doublecortin-positive cells in the DG of wild-type mice, but not in 5-HT4R KO mice. We then examined the correlation between the increased neurogenesis and the dematuration of GCs. As reported previously, reduced expression of calbindin in the DG, as an index of dematuration, by chronic fluoxetine treatment was observed in wild-type mice but not in 5-HT4R KO mice. The proliferative effect of fluoxetine was inversely correlated with the expression level of calbindin in the DG. The expression of neurogenic factors in the DG, such as brain derived neurotrophic factor (Bdnf), was also associated with the progression of dematuration. These results indicate that the neurogenic effects of fluoxetine in the DG are closely associated with the progression of dematuration of GCs. In contrast, the DG in which neurogenesis was impaired by irradiation still showed significant reduction of calbindin expression by chronic fluoxetine treatment, suggesting that dematuration of GCs by fluoxetine does not require adult neurogenesis in the DG. CONCLUSIONS: We demonstrated that the 5-HT4 receptor plays an important role in fluoxetine-induced adult neurogenesis in the DG in addition to GC dematuration, and that these phenomena are closely associated. Our results suggest that 5-HT4 receptor-mediated phenotypic changes, including dematuration in mature GCs, underlie the neurogenic effect of SSRIs in the DG, providing new insight into the cellular mechanisms of the neurogenic actions of SSRIs in the hippocampus.