Fluoxetine-induced change in rat brain expression of brain-derived neurotrophic factor varies depending on length of treatment.

Recent studies indicate that brain-derived neurotrophic factor (BDNF) may be implicated in the clinical action of antidepressant drugs. Repeated (2-3 weeks) administration of antidepressant drugs increases BDNF gene expression. The onset of this response as well as concomitant effects on the corresponding BDNF protein is however, unclear. The present study investigated the effects of acute and chronic administration of the selective serotonin reuptake inhibitor, fluoxetine (10mg/kg p.o.), upon regional rat brain levels of BDNF mRNA and protein expression. To improve the clinical significance of the study, fluoxetine was administered orally and mRNA and protein levels were determined ex vivo using the techniques of in situ hybridisation histochemistry and immunocytochemistry respectively. Direct measurement of BDNF protein was also carried out using enzyme-linked immunosorbent assay (ELISA). Four days of once daily oral administration of fluoxetine induced decreases in BDNF mRNA (hippocampus, medial habenular and paraventricular thalamic nuclei). Whilst 7 days of treatment showed a non-significant increase in BDNF mRNA, there were marked and region-specific increases following 14 days of treatment. BDNF protein levels remained unaltered until 21 days of fluoxetine treatment, when the numbers of BDNF immunoreactive cells were increased, reaching significance in the pyramidal cell layer of CA1 and CA3 regions of Ammon's horn (CA1 and CA3) but not in the other sub-regions of the hippocampus. Indicative of the highly regional change within the hippocampus, the ELISA method failed to demonstrate significant up-regulation at 21 days, measuring levels of BDNF protein in the whole hippocampus. In contrast to the detected time dependent and biphasic response of the BDNF gene, activity-regulated, cytoskeletal-associated protein (Arc) mRNA showed a gradual increase during the 14-day course of treatment. The results presented here show that BDNF is expressed differentially depending on length of fluoxetine administration, which could contribute in explaining the slow onset of antidepressant activity observed with selective serotonin reuptake inhibitors.

Evidence for co-ordinated changes between vascular endothelial growth factor and nitric oxide synthase III immunoreactivity, the functional status of the thyroid follicles, and the microvascular bed during chronic stimulation by low iodine and propylthiouracyl in old mice.

Vasoactive and angiogenic factors are involved in the autocrine/paracrine thyroid regulation of microvascular bed during goiter development. In the thyroid of old mice, the presence of slowly functioning ('cold') follicles allowed us to study the microvascular regulation of each follicle in correlation with the immunohistochemical expression of vascular endothelial growth factor (VEGF) and nitric oxide synthase III (NOSIII). Mice aged 20 months did or did not receive a goitrogenic treatment (low iodine diet and propylthiouracyl), and their thyroids were processed for light and electron microscopy, and for autoradiography. The relative volumes (Vv) of the capillaries, the number of vessels per follicular area, the mean capillary area and the number of [(3)H]thymidine labeled nuclei were measured separately for 'hot' and 'cold' follicles. Already in control mice, the capillary bed surrounding 'hot' follicles was significantly larger than that seen around 'cold' follicles, because of larger diameters and twice the number of capillaries. This difference persisted whatever the length of the stimulatory treatment. During this treatment, the Vv of the capillaries increased to a larger extent around 'hot' follicles than around 'cold' ones. All vascular changes around 'cold' follicles were less extended and the increase in the capillary diameter was delayed. In control mice, the 'cold' follicles were negative for NOSIII and positive for VEGF while 'hot' follicles were positive for both. During stimulation, all follicles became progressively NOSIII positive. These data support the concept of 'angio-follicular units' in the thyroid and demonstrate their differential regulation in chronic stimulation during which local secretion of VEGF and NO is clearly involved.