Rosana M Sibug

Doublecortin-like, a microtubule-associated protein expressed in radial glia, is crucial for neuronal precursor division and radial process stability

During corticogenesis, progenitors divide within the ventricular zone where they rely on radial process extensions, formed by radial glial cell (RG) scaffolds, along which they migrate to the proper layers of the cerebral cortex. Although the microtubule‐associated proteins doublecortin (DCX) and doublecortin‐like kinase (DCLK) are critically involved in dynamic rearrangement of the cytoskeletal machinery that allow migration, little is known about their role in early corticogenesis. Here we have functionally characterized a mouse splice‐variant of DCLK, doublecortin‐like (DCL), exhibiting 73% amino acid sequence identity with DCX over its entire length. Unlike DCX, DCL is expressed from embryonic day 8 onwards throughout the early neuroepithelium. It is localized in mitotic cells, RGs and radial processes. DCL knockdown using siRNA in vitro induces spindle collapse in dividing neuroblastoma cells, whereas overexpression results in elongated and asymmetrical mitotic spindles. In vivo knockdown of the DCLK gene by in utero electroporation significantly reduced cell numbers in the inner proliferative zones and dramatically disrupted most radial processes. Our data emphasize the unique role of the DCLK gene in mitotic spindle integrity during early neurogenesis. In addition, they indicate crucial involvement of DCLK in RG proliferation and their radial process stability, a finding that has thus far not been attributed to DCX or DCLK.

Effects of brain mineralocorticoid receptor blockade on blood pressure and renal functions in DOCA–salt hypertension

In normotensive rats, we have previously demonstrated a role of brain mineralocorticoid receptors in blood pressure and renal function control. In the present study, the coordinate cardiovascular and renal effects of brain mineralocorticoid receptor blockade were examined by intracerebroventricular (i.c.v.) administration of a selective mineralocorticoid receptor antagonist (RU28318; 3,3-oxo-7 propyl-17-hydroxy-androstan-4-en-17yl-propionic acid lactone) in rats with hypertension induced by deoxycorticosterone acetate (DOCA) and salt. DOCA pellets were implanted s.c. in male Wistar rats given 0.9% NaCl as drinking solution 3 or 5 weeks before assessment of the effects of i.c.v. injection of RU28318 on cardiovascular and renal functions. Changes in expression of brain angiotensinogen, atrial natriuretic peptide (ANP) and mineralocorticoid receptor mRNA in specific brain areas in 3-week DOCA-salt rats were evaluated by in situ hybridization. The rise in systolic blood pressure induced by DOCA-salt treatment was most marked during the first 3 weeks. At 3 and 5 weeks after implantation of the DOCA-pellets a single i.c.v. injection of 10 ng of RU28318 significantly decreased systolic blood pressure during 24 h as assessed at 2, 8 and 24 h, while heart rate was not altered. Increased urinary excretion of water and electrolytes was observed in 3- and 5-week DOCA-salt rats during the period 0-8 h after i.c.v. injection of RU28318 while the suppressed plasma renin activity was not affected. The expression of brain angiotensinogen, ANP and mineralocorticoid receptor mRNA was not altered by 3-week DOCA-salt treatment, but 3 h after i.c.v. injection of RU28318, mineralocorticoid receptor mRNA expression in hippocampal cell fields responded with an increase of about 40%. In conclusion, these results demonstrate that in rats with hypertension induced by DOCA-salt, brain mineralocorticoid receptor blockade affects renal function and blood pressure regulation.

Intracerebroventricular administration of a glucocorticoid receptor antagonist enhances the cardiovascular responses to brief restraint stress

Intracerebroventricular (i.c.v.) administration of the glucocorticoid receptor antagonist 17beta-hydroxy-11beta(4-dimethylamino-phenyl)17alpha-(1-propynyl)estra-4,9dien-3one (RU38486) in conscious rats slowly increased systolic blood pressure as assessed with the indirect tail cuff method. However, direct measurement of blood pressure in freely moving rats did not reveal changes in blood pressure after i.c.v. injection of this antagonist either in the light or in the dark phase. In the present study, the hypothesis is tested that aspects of the tail cuff procedure, involving heat (30 min, 32 degrees C) and brief restraint stress, are necessary conditions to detect the glucocorticoid receptor-mediated cardiovascular effect. Freely moving rats equipped with a telemetric transmitter to directly measure heart rate and blood pressure were injected i.c.v. with either the glucocorticoid receptor or the mineralocorticoid receptor antagonist and were either left undisturbed for 24 h, or were subjected to the tail cuff procedure at 1.5, 6.5 and 23.5 h after injection. Then after 30-min warming and during brief restraint, blood pressure and heart rate showed a rapid increase. The mineralocorticoid receptor antagonist administered i.c.v. did not affect these stress-induced increases in cardiovascular responses. The glucocorticoid receptor antagonist i.c.v. significantly increased the heart rate and pressor response at 24 h. In the undisturbed rats, neither basal heart rate nor blood pressure were affected by either antagonist during the circadian cycle. In conclusion, the blockade of central glucocorticoid receptor causes a long-lasting facilitation of the stress-induced pressor and heart rate response, which does not require a 2-week training to the condition of heat and stress.

Flesinoxan treatment reduces 5-HT1A receptor mRNA in the dentate gyrus independently of high plasma corticosterone levels

Flesinoxan acts as a full 5-HT1A receptor agonist and displays anxiolytic and anti-depressant properties. 5-HT1A receptor agonists, including flesinoxan, increase corticosterone (B) levels in the blood and reduces 5-HT1A receptor mRNA expression in the hippocampus. In this study, we examined whether the 5-HT1A receptor downregulation induced by flesinoxan involves corticosterone control of 5-HT1A receptor gene transcription. In experiment I, intact male Wistar rats (180-200 g) were treated with flesinoxan (1.0, 3.0 and 10 mg/kg bw, sc) or vehicle and decapitated 3 h later. Flesinoxan administration resulted in a significant, dose-dependent downregulation of 5-HT1A receptor mRNA in the dentate gyrus and dorsal raphe nucleus. In experiment II, rats were sham-operated and implanted with a cholesterol pellet (100 mg) or were adrenalectomized and implanted with a corticosterone pellet (20 mg corticosterone + 80 mg cholesterol). Flesinoxan injection also caused a dose-dependent decrease of 5-HT1A mRNA in the dentate gyrus of adrenalectomized animals with corticosterone replacement. There was no effect in the dorsal raphe nucleus. In experiment III, adrenalectomized and adrenalectomized + corticosterone rats were sc injected with flesinoxan (10 mg/kg bw) or vehicle, and flesinoxan appeared to downregulate 5-HT1A receptor expression in the dentate gyrus independently of corticosterone as well. No significant effects were observed in the dorsal raphe nucleus. It is concluded that flesinoxan reduces 5-HT1A receptor expression in the dentate gyrus both through homologous downregulation and a corticosterone-mediated effect on the serotonergic (5-HT) system.

Maternal deprivation increases 5-HT1A receptor expression in the CA1 and CA3 areas of senescent Brown Norway rats

Maternally-deprived male Brown Norway rats were classified as non-impaired or impaired according to their performance in the water maze when 3 and 30-32 months old. Age and spatial learning ability did not affect the pattern and density of hippocampal 5-HT(1A)-receptor mRNA in mother-reared control rats. However, senescent maternally-deprived rats with impaired spatial learning ability showed increased expression of 5-HT(1A)-receptor mRNA in the hippocampal CA1 (14%) and CA3 (13%) areas but not in the dentate gyrus.

Estrogen reduces vascular endothelial growth factor164 expression in the mouse nucleus paraventricularis of the hypothalamus

The aim of the present study was to establish whether estrogen and corticosteroids exert effects on vascular endothelial growth factor (VEGF)(164) expression in the hippocampus and nucleus paraventricularis of the hypothalamus by in situ hybridization. Female mice were ovariectomized and treated either with estradiol benzoate or vehicle and male mice were either adrenalectomized or sham-operated. Ovariectomy plus estrogen reduced VEGF(164) expression in the nucleus paraventricularis but not in the hippocampus. Adrenalectomy did not influence VEGF(164) mRNA levels in the hippocampus and nucleus paraventricularis. Our results show for the first time an inhibitory effect of estrogen on VEGF(164) expression in the nucleus paraventricularis and suggest a role for estrogen in the regulation of VEGF(164) expression and function in the central nervous system.

Effects of flesinoxan on corticosteroid receptor expression in the rat hippocampus

Many agents that influence serotonergic neurotransmission modulate expression of hippocampal corticosteroid receptors. We have studied the effect of the specific 5-hydroxytryptamine, 5-HT(1A), receptor agonist flesinoxan on mRNA for glucocorticoid and mineralocorticoid receptors in the hippocampus and dorsal raphe nucleus. Since some responses to 5-HT(1A) receptor stimulation show a strong desensitization, we studied the effect of a single and repeated injections of flesinoxan. Because of the close interrelationship between the serotonergic system and the hypothalamo-pituitary-adrenal axis, we also studied the possible involvement of corticosterone as a mediator of the effects of flesinoxan. We found that a single injection of flesinoxan (3 and 10 mg/kg subcutaneously, s.c.) after 3 h leads to a downregulation of glucocorticoid receptor mRNA in the hippocampus (dentate gyrus and CA1 areas) and dorsal raphe nucleus. This effect does not desensitize after a second treatment over 2 days. Mineralocorticoid receptor mRNA expression remained unaltered. The decrease in hippocampal glucocorticoid receptor mRNA expression occurs independently of circulating corticosterone since flesinoxan reduced glucocorticoid receptor mRNA in the hippocampus of adrenalectomized rats with or without corticosterone replacement. These data indicate that the 5-HT(1A) receptor agonist flesinoxan alters glucocorticoid receptor expression via a direct pathway independently of corticosterone and argues for an intrinsic effect selective for hippocampal glucocorticoid receptor mRNA.

Stress Effect of Assisted Reproduction

The goal of the classic Selye alarm reaction is to survive, and it is facilitated by the blockage of all processes and systems that may harm the survival attempt. Severe stress in women may inhibit gonadotropin-releasing hormone (GnRH) production and thus lead to anovulation. A more subtle example of stress in reproduction might be the adverse effects of urinary (rather than recombinant) gonadotropins on the implantation process, resulting in a protracted gestation period in mice. The mouse model might explain the observation that singleton pregnancies from assisted reproduction have a significantly worse perinatal outcome than nonassisted singleton pregnancies. Very preterm birth is associated with later neuromotor and cognitive impairment, reduced school performance, and psychiatric morbidity. Young adults who are born very prematurely have different personality types from their term-born peers. This may be associated with an increased risk of psychiatric difficulties.