Bi-phasic change in BDNF gene expression following antidepressant drug treatment.

The gene for brain derived neurotrophic factor (BDNF) has recently received attention in relation to the therapeutic action of antidepressant treatment. This study aimed to clarify the influence of post drug interval on the effect of acute and repeated treatment with antidepressant drugs on BDNF gene expression in the rat brain. It was found that repeated administration of either the monoamine oxidase inhibitor tranylcypromine (TCP) or 5-hydroxytryptamine (5-HT) re-uptake inhibitors (fluoxetine, paroxetine and sertraline), evoke a bi-phasic and time-dependent effect on BDNF gene expression in the rat hippocampus (especially dentate gyrus). A down-regulation of the BDNF gene was detected at 4 h (TCP and fluoxetine) and an up-regulation at 24 h (TCP, paroxetine, fluoxetine, sertraline) after the last of twice daily injections for 14 days. After a single injection the down-regulation was detected at 4 h (TCP, fluoxetine, paroxetine and sertraline) but BDNF mRNA levels were not altered at 24 h post drug (TCP, fluoxetine and paroxetine). Administration of inhibitors of noradrenaline re-uptake (desipramine and maprotiline) or the atypical antidepressant mianserin had no effect on BDNF mRNA levels at either single (4 h post drug, desipramine) or repeated (24 h post drug, desipramine, maprotiline, mianserin) treatment. The gene expression for NT-3, which is distributed in a high density in the dentate gyrus, was not affected by single or repeated injections of antidepressant drugs (TCP, fluoxetine, paroxetine, sertraline, desipramine, maprotiline or mianserin) at 4 or 24 h post drug. In conclusion, these data show that the effect of antidepressant drugs on BDNF gene expression may be more complex and less widespread across treatments than previously thought. Thus, in this study drugs interacting with the central 5-HT system altered BDNF expression but the effect was bi-phasic over the 24 h post drug period.

Manipulations of brain 5-HT levels affect gene expression for BDNF in rat brain.

The aim of the present study was to investigate whether changes in brain 5-HT concentrations affect the expression of BDNF mRNA in rat brain. Brain 5-HT concentration in the rat was elevated by combined treatment with tranylcypromine and L-tryptophan, tranylcypromine alone, by a single dose of the 5-HT releasing agent p-chloroamphetamine (PCA) or by the selective 5-HT reuptake inhibitor paroxetine. 5-HT was depleted by either multiple p-chlorophenylalanine (pCPA) or PCA injections. The extent of 5-HT depletion following pCPA or PCA was monitored using 5-HT immunocytochemistry. BDNF mRNA abundance in treated rats and the corresponding vehicle injected control rats was studied by in situ hybridization histochemistry (ISHH). Two hours after the combined administration of tranylcypromine and L-tryptophan BDNF mRNA abundance in the dentate gyrus was significantly decreased but increased in the frontal cortex. Tranylcypromine alone or a single injection of PCA had similar effects on BDNF mRNA expression to the combination of tranylcypromine and L-tryptophan, i.e. they caused significant reductions of BDNF mRNA expression in dentate gyrus and increased it in frontal cortex. Paroxetine also reduced BDNF mRNA in DG but was without effect in frontal cortex. Multiple injections of both pCPA or PCA resulted in marked reductions of 5-HT immunoreactive axons in the hippocampus, pCPA being more effective. Both drugs significantly increased BDNF mRNA abundances in the dentate gyrus. Multiple PCA injections also increased BDNF mRNA expression in parietal cortex, while pCPA induced 5-HT depletion was ineffective. These results suggests that 5-HT modulates BDNF mRNA levels in rat brain.

In vitro enzymatic processing of radiolabelled big ET-1 in human kidney.

We have investigated enzymatic processing of big ET-1 in sections of human renal cortex by examining selected binding characteristics of the radiolabelled precursor and cleaved peptide. Sections of histologically normal human kidney obtained from patients undergoing nephrectomy for hypernephroma (50-74 years, N = 10, male or female) were incubated with 0.1 nM [125I]-ET-1, [125I]-Tyr13 big ET-1 or [125I]-Tyr31 big ET-1 in culture media at 37 degrees to facilitate enzymatic activity. Specific binding measured from sections incubated with [125I]-Try13 big ET-1 (which would yield [125I]-ET-1 on enzymatic cleavage) was 39.7 +/- 2.5%. This was significantly reduced to 19.0 +/- 2.0% following co-incubation with 10 microM thiorphan, an inhibitor of neutral endopeptidase (NEP) but not the putative endothelin converting enzymes (ECE). No further reduction in specific binding was obtained with 100 microM thiorphan, indicating that this is a maximal effect. However phosphoramidon (100 microM), an inhibitor of ECE and NEP, almost abolished specific binding, indicating that both NEP and ECE cleave big ET-1 in the kidney. No specific binding was detected when sections were labelled with [125I]-Tyr31 big ET-1 (which would be expected to yield [125I] labelled C-terminal fragment). Binding of the product of processed [125I]-Tyr13 big ET-1 was inhibited mainly by the ET(B) selective antagonist (BQ788 = 75.1 +/- 2.1% inhibition; FR139317 = 9.7 +/- 7.3% inhibition), consistent with the predominance of this subtype in human kidney. We conclude that big ET-1 is processed by NEP and ECE in human kidney and that the cleaved product binds predominantly to the ET(B) receptor subtype. ECE may be a therapeutic target in the attenuation of renal diseases in which ET-1 has been implicated.