Hidenobu Zensho

Antidepressant drug treatments induce glial cell line‐derived neurotrophic factor (GDNF) synthesis and release in rat C6 glioblastoma cells

Modulation of neurotrophic factors to protect neurons from damage is proposed as a novel mechanism for the action of antidepressants. However, the effect of antidepressants on modulation of glial cell line‐derived neurotrophic factor (GDNF), which has potent and widespread effects, remains unknown. Here, we demonstrated that long‐term use of antidepressant treatment significantly increased GDNF mRNA expression and GDNF release in time‐ and concentration‐dependent manners in rat C6 glioblastoma cells. Amitriptyline treatment also increased GDNF mRNA expression in rat astrocytes. GDNF release continued for 24 h following withdrawal of amitriptyline. Furthermore, following treatment with antidepressants belonging to several different classes (amitriptyline, clomipramine, mianserin, fluoxetine and paroxetine) significantly increased GDNF release, but which did not occur after treatment with non‐antidepressant psychotropic drugs (haloperidol, diazepam and diphenhydramine). Amitriptyline‐induced GDNF release was inhibited by U0126 (10 µm), a mitogen‐activated protein kinase (MAPK)‐extracellular signal‐related kinase (ERK) kinase (MEK) inhibitor, but was not inhibited by H‐89 (1 µm), a protein kinase A inhibitor, calphostin C (100 nm), a protein kinase C inhibitor and PD 169316 (10 µm), a p38 mitogen‐activated protein kinase inhibitor. These results suggested that amitriptyline‐induced GDNF synthesis and release occurred at the transcriptional level, and may be regulated by MEK/MAPK signalling. The enhanced and prolonged induction of GDNF by antidepressants could promote neuronal survival, and protect neurons from the damaging effects of stress. This may contribute to explain therapeutic action of antidepressants and suggest new strategies of pharmacological intervention.

Down‐Regulation of 5‐Hydroxytryptamine7 Receptors by Dexamethasone in Rat Frontocortical Astrocytes

Abstract: Astrocytes derived from rat frontal cortex contain 5‐hydroxytryptamine7 (5‐HT)7 receptors positively coupled to adenylyl cyclase. In the present study, we investigated the effects of glucocorticoids on adenylyl cyclase activity and 5‐HT7 receptor gene expression in astrocytes. Addition of dexamethasone (0.01–100 nM, 12–72 h) to the culture medium decreased cyclic AMP formation induced by 5‐HT in a time‐ and concentration‐dependent manner. Dexamethasone treatment (10 nM, 48 h) reduced maximum responses of cyclic AMP formation induced by 5‐HT and 5‐carboxamidotryptamine without alterations in the EC50 value. In contrast, treatment with the mineralocorticoid aldosterone (48 h) had no significant effects on 5‐HT‐induced cyclic AMP formation with concentrations up to 10 nM. It was observed that dexamethasone treatment (1–100 nM, 3–72 h) also decreased the expression of 5‐HT7 receptor mRNA, using reverse transcription and polymerase chain reaction analysis. A significant reduction in expression of 5‐HT7 mRNA appeared at 3 h of dexamethasone treatment and reached a maximum at 6 h of treatment. On the other hand, dexamethasone treatment (10 nM, 48 h) did not affect basal levels of cyclic AMP and cyclic AMP synthesis stimulated by isoproterenol, N‐ethylcarboxamido‐adenosine, cholera toxin, and forskolin. These results suggest that dexamethasone decreases the expression of the 5‐HT7 receptor gene and, consequently, 5‐HT7 receptor‐mediated signal transduction in frontocortical astrocytes.

Antidepressant drugs and cytokines in mood disorders

This article reviews recent developments in cytokine research that pertain to pharmacological treatment of mood disorders such as antidepressants and lithium. We review the possible involvement of cytokines in mood disorders and their role in the therapeutic effects of antidepressant drugs. Growing evidence suggests that specific cytokines signal the brain to generate neurochemical, neuroimmune, neuroendocrine and behavior changes. An imbalance of cytokines within the central nervous system (CNS), or even systemically, may play a role in the pathophysiology of mood disorders. Modulation of these cytokines by chronic antidepressant treatment may result in restored balance. However, the effect of antidepressants on cytokines is still unclear both in clinical and preclinical research due to limited data. Further research is needed to clarify the involvement of cytokines in mood disorders. Understanding this relationship may lead to rational, therapeutic improvements in antidepressant and mood stabilizing drugs.

Agonist-induced desensitization of adenylyl cyclase activity mediated by 5-hydroxytryptamine7 receptors in rat frontocortical astrocytes

Our previous study has demonstrated that astrocytes derived from the rat frontal cortex contain 5-hydroxytryptamine (5-HT)7 receptors positively coupled to adenylyl cyclase. In this study, we observed a desensitization of 5-HT7 receptors induced by a treatment with agonists (0.1, 1, and 10 muM, 0.5 to 3.5 h). Maximum responses, but not the EC50 values, in the concentration-response curve of 5-HT-induced cyclic AMP formation were decreased after pretreatment with 5-HT. Pretreatment with 5-carboxamidotryptamine (5-CT) elicited a potent desensitization of 5-HT-induced cyclic AMP formation. Neither 2-methyl-5-HT nor alpha-methyl-5-HT caused the desensitization. When the astrocytes were treated with isoproterenol, N-ethylcarboxamidoadenosine, and dibutyryl cyclic AMP (all of which increase intracellular cyclic AMP levels), 5-HT-induced cyclic AMP responses were not affected. Conversely, adenylyl cyclase activity mediated by either isoproterenol or N-ethylcarboxamidoadenosine was attenuated by pretreatment with each of these agonists, but not 5-HT. In addition, our study showed that the administration of 5-HT, 5-CT, and 8-hydroxy-2-(di-n-propylamino)tetralin to the astrocytes stimulated cyclic AMP formation both in the presence and absence of forskolin, whereas in neuron-rich cultures of the frontal cortex, these agonists did not change basal cyclic AMP levels and decreased forskolin-stimulated cyclic AMP formation. Neurons may predominantly contain 5-HT1A receptors that are negatively coupled to adenylyl cyclase. These results suggest that 5-HT7 receptors are highly expressed in astrocytes but not in neuronal cells, and that pretreatment with their agonists results in a homologous desensitization of the receptors.

Plasma Levels of Cyclic GMP, Immune Parameters and Depressive Status during Interferon Therapy

In this report, we investigated the relationship between depressive symptoms and plasma interferon (IFN)-alpha-like immunoreactivity, cyclic GMP (cGMP) and soluble interleukin-2 receptor (sIL-2R) levels during IFN therapy. An altered mood state was observed in 5 of 26 patients. IFN-alpha-like immunoreactivity in the depressed group tended to be elevated. cGMP levels of depressed patients were significantly greater than those of control subjects before and 6 weeks after IFN therapy. However, sIL-2R levels were not different between the two groups. These results suggest that a number of patients suffered from depression during IFN therapy and that patients had greater concentrations of cGMP levels.

Phosphatidylethanol inhibits phosphatidylinositol-phospholipase C activity in a competitive manner with phosphatidylinositol-4,5-bisphosphate

The effect of phosphatidylethanol (PEth) on phosphatidylinositol-phospholipase C (PLC) activity was investigated in rat cerebral cortex. PEth decreased PLC activity in both the membrane and the cytosol of the cortex in a concentration-dependent manner, varying from 6 to 400 microM, and PLC activity was almost entirely inhibited at concentrations of PEth over 200 microM (90% inhibition). The IC50 of PEth in the cytosol was 25.2 microM and was 22.1 microM in the membrane. Preincubation of the cytosol with anti-PLC-beta 1, anti-PLC-gamma 1 or anti-PLC-delta 1 antibodies did not prevent the decrease in PLC activity. These results suggest that PEth caused the decrease in PLC activity without isozyme specificity. The sensitivity of PLC to Ca2+ in the cytosol and membrane was not changed by PEth, suggesting that PEth may act on PLC at a site different from that of Ca2+ activation. In higher concentrations of the PLC substrate, PEth did not inhibit PLC activity, indicating that PEth inhibited PLC activity in a substrate competitive manner. Neomycin, which binds to negatively charged phospholipids such as phosphatidylinositol-4,5-bisphosphate (PIP2) and thus causes inhibition of PLC activity, attenuated the PEth-induced decrease in PLC activity. This result suggests that the inhibitory action of PEth on PLC may be related to the fact that PEth is a negatively charged phospholipid similar to PIP2.

Positive influence of a liaison program on the rate of psychiatric consultation referrals for cancer patients

To improve access to psychiatric consultation for cancer patients as well as non‐cancer patients with psychiatric disorders, a psychiatric liaison programme to communicate closely with physicians and ward staff regarding anticipated psychiatric morbidity in patients, was introduced in each ward of a general hospital. The rate of psychiatric consultation referrals for cancer patients was significantly higher after the psychiatric liaison programme was established. The programme had a greater impact on the rate of psychiatric consultation in a unit with cancer patients who were informed of their diagnoses. The greater consultation rates in cancer patients after the liaison programme might be, in part, associated with the physicians’ attitude toward the more open disclosure of the cancer diagnosis.

Heat shock protein 72 restores cyclic AMP accumulation after heat shock in N18TG2 cells.

Although there are several reports on the alteration of intracellular signal transduction during heat shock in somatic cells, the long term effects of heat shock on neuronal cells remain unknown. In this report, we investigated cyclic AMP (cAMP) accumulation and the expression of heat shock proteins following heat shock in mouse neuroblastoma N18TG2 cells. Basal cAMP accumulation, or that stimulated by serotonin (10 microM), cholera toxin (1 microg/ml), and forskolin (1 microM) was suppressed at 0, 3, and 6 h following heat shock (45 degrees C for 30 min). The cAMP levels were restored at 15 and 24 h after heat shock, corresponding with the expression of stress-induced heat shock protein 72 (HSP72). Quercetin, an inhibitor of HSP expression, decreased the expression of HSP72 and inhibited the recovery of cAMP levels 24 h after heat shock. Quercetin also decreased the basal expression of the constitutive heat shock cognate protein 70 (HSC70) and suppressed cAMP accumulation in non-heat shocked cells. These results suggest that stress-induced HSP72 restores cAMP accumulation to control levels following heat shock and that constitutive HSC70 is related to cAMP levels in non-stress conditions.

Modulation of endothelin-induced intracellular Ca2+ mobilization by interleukin-1β and lipopolysaccharide in C6 rat glioma cells

We have investigated the effects of interleukin (IL)-1 beta and lipopolysaccharide (LPS) on endothelin (ET)-induced intracellular Ca2+ rise in C6 rat glioma cells in order to study the mechanisms of their effects on Ca2+ signaling systems. Pretreatment with IL-1 beta (10(3) U/mL) and LPS (1 microgram/mL) for 24 h significantly inhibited 100 nM ET-1-induced increase in intracellular Ca2+ either in the presence or absence of external Ca2+. Their inhibitory effects were in dosedependent (IL-1 beta; 50-1000 U/mL, LPS; 10-1000 ng/mL) and time-dependent (12-24 h) manners. A tyrosine kinase antagonist genistein (50 microM) but not a protein kinase C inhibitor H7 (30 microM) prevented the inhibition of the ET response by IL-1 beta and LPS. These results suggest that activation of tyrosine kinase may be essential for the inhibition of the ET receptor-mediated Ca2+ signaling systems by IL-1 beta and LPS.

Chronic amitriptyline exposure reduces 5-HT3 receptor-mediated cyclic GMP formation in NG 108-15 cells

In the present study, we investigated the effects of chronic in vitro administration of amitriptyline, a tricyclic antidepressant, on cyclic GMP formation stimulated by 5-hydroxytryptamine (5-HT) in the neuroblastoma x glioma hybrid cell line, NG 108-15, 5-HT (0.01-100 microM)-stimulated cyclic GMP formation was concentration-dependent and was sensitive to ICS 205-930, a 5-HT3 receptor antagonist. Exposure of NG 108-15 cells to 5 microM amitriptyline for 3 days significantly reduced 5-HT-stimulated cyclic GMP formation. Acute treatment with amitriptyline had no effect on 5-HT-stimulated cyclic GMP formation. The reduction by chronic amitriptyline exposure of 10 microM 5-HT-stimulated cyclic GMP formation was concentration-dependent over the concentration range examined (0.5 to 10 microM). The IC50 of amitriptyline was 1.9 microM. In contrast, amitriptyline exposure, even at a concentration of 8 microM, failed to modify cyclic GMP formation stimulated by bradykinin, sodium nitroprusside, or atrial natriuretic peptide. Increases in intracellular Ca2+ concentration ([Ca2+]i) evoked by 10 microM 5-HT were attenuated in amitriptyline-exposed cells, while 100 nM bradykinin-induced [Ca2+]i increases were not affected. In addition, chronic exposure to 5 microM amitriptyline caused a decrease in affinity (Kd) of [3H]zacopride specific binding to 5-HT3 recognition sites. The Bmax for the labelled ligand remained unchanged. These results suggest that chronic amitriptyline exposure reduces 5-HT-stimulated cyclic GMP formation and [Ca2+]i increases, and this may reflect the functional changes of 5-HT3 receptors.