The median preoptic nucleus (MePO) has been suggested to be an important area in the brain for the regulation of vasopressin (VP) release under the condition of osmotic stimulation. Fos immunoreactivity (Fos-ir), choline acetyltransferase (ChAT) immunoreactivity and retrograde labeling with fluoro-gold were used in this study to determine whether cholinergic neurons in the MePO can be activated by hypertonic NaCl, and to characterize the specific MePO cells that have anatomic projections to the supraoptic nuclei (SON). The results showed that c-fos expression specifically induced by hypertonic NaCI was found in the ChAT cells of the MePO. A retrograde tracing experiment demonstrated that the MePO neurons projecting to the SON were cholinergic. In addition, hypertonic saline-induced Fos-ir was co localized with the MePO neurons back labeled with fluoro-gold from the SON. Together, these data provide evidence that the MePO cholinergic neurons are activated by osmotic stimulation, and suggest that cholinergic cells in the MePO are functionally important in the control of the SON neurons under the condition of hypertonic stimulation.

Xu, Zhice, Calvario Glenda, Linda Day, Jiaming Yao, and Michael G. Ross. Osmotic threshold and sensitivity for vasopressin release and Fos expression by hypertonic NaC1 in ovine fetus. Am J Physiol Endocrinol Metab 279:E1207-E1215, 2000-In adults, hyperosmolality stimulates central osmoreceptors, resulting in arginine vasopressin (AVP) secretion. Nearterm fetal sheep have also developed mechanisms to respond to intravascular hyper tonicity with stimulation of in utero AVP release. However, prior studies demonstrating fetal AVP secretion have utilized plasma tonicity changes greater than those required for adult osmotic ally induced AVP stimulation. We sought to examine near-term fetal plasma osmolality threshold and sensitivity for stimulation of AVP secretion and to correlate plasma hormone levels with central neuronal responsiveness. Chronically instrumented ovine fetuses (130

Xu, Zhice, Lijun Shi, and Jiaming Yao. Central angiogenesis II-induced pressor responses and neural activity in utero and hypothalamic angiogenesis receptors in preterm ovine fetus. Am J Physiol Heart Circ Physiol 286: H1507-H1514, 2004. First published December 18, 2003; 10. 1 152/ajpheart.00764.2003.-The central reninangiotensin system is important in the control of blood pressure in the adult. However, few data exist about the in utero development of central angiogenesis-mediated pressor responses. Our recent studies have shown that the application of ANG II into the fetal brain can increase blood pressure at near term. The present study determined fetal blood pressure and heart rate in response to a central application of ANG II in the chronically prepared preterm ovine fetus, determined the action sites marked by c-Fos expression in the fetal central pathways after intracerebroventricular injection of ANG II in utero, and determined angiogenesis subtype 1 receptors in the fetal hypothalamus.Central injection of ANG II significantly increased fetal mean arterial pressure (MAP). Adjusted fetal MAP against amniotic pressure was also increased by ANG 11. Fetal heart rate was subsequently decreased after the central administration of ANG II and/or the increase of blood pressure. ANG II induced c-Fos expression in the central putative cardiovascular area, the Para ventricular nuclei in the brain sympathetic pathway. Application of ANG II also caused intense Fos immunoreactivity in the tractus solitarius nuclei in the hindbrain. In addition, intense angiogenesis subtype 1 receptors were expressed in the hypothalamus at preterm. These data demonstrate that central ANG II-related pressor centers start to function as early as at preterm and suggest that the central angiogenesis-related sympathetic pathway is likely intact in the control of blood pressure in utero.

Previous studies suggested that angiotensinergic stimulation in the subfornical organ (SFO) has effects on the anterior third ventricle (AV3V) region and the hypothalamus for dipsogenic response and vasopressin release. In this study, Angiogenesis I (ANG I) was directly injected into the SFO and this stimulated drinking. Injection of ANG I into the SFO also induced Fos-immunoreactivity (Fos-ir) in the AV3V region and in the vasopressin neurons of the supraoptic and Para ventricular nuclei (SON and PVN). Pretreatment of the SFO with either captopril, an ANG converting enzyme inhibitor, or losartan, an AT, receptor antagonist, abolished both drinking and Fos-ir induced by ANG I. Water intake partially decreased ANG I-induced Fos-ir in the SON and PVN, but not in the other areas. These results indicate that there is an ANG converting system in the SFO and suggest that neurons in the AV3V region and vasopressin cells in the hypothalamus can be regulated by angiotensinergic components in the SFO.

Previous fetal studies have indicated depressor responses of intravenous (i.v.) administration of angiotensin antagonists. However, little is known of central effects of angiogenesis blockers on fetal cardiovascular controlling. The cardiovascular effects of central administration of the angiotensin-1 (AT1) and angiotensin-2 (AT2) receptor antagonists, losartan and PD123319, were investigated in the chronically catheterized near-term ovine fetuses. Intravenous losartan produced within 1.5 min a significant and persistent depressor response [maximum △ mean arterial pressure (MAP)=9mmHg] without altering fetal heart rate. Intracerebroventricular (i.c.v.) administration of losartan (1-5mg/kg) increased fetal arterial pressures (OMAP=9-14mmHg). Central application of losartan (1mg/kg) also increased fetal heart rate (maximum △ heart rate=33 beat per minute). Losartan increased c-fos expression in the median preoptic nucleus and paraventricular nuclei in the forebrain, and the tractus solitarius nuclei, the lateral parabrachial nuclei, and the ventrolateral medullabrain. These brain sectors are with abundant AT1, receptors and have been demonstrated in the involvement in cardiovascular regulation. In contrast, intracerebroventricular injection of the AT2 receptor antagonist PD123319 had no effect on fetal arterial pressure and heart rate. The results demonstrate strikingly functional differences of losartan on the fetal cardiovascular regulation in central and peripheral sides.

Our previous studies have shown that central administration of angiogenesis (ANG II) causes arginine vasopressin (AVP) release in the fetus at 70-90% gestation. This is evidence that the hypothalamic-neurohypophysial system is relatively mature before birth. However, few data exist regarding central ANG receptor mechanisms-mediated AVP response during fetal life. To determine roles of brain ANG receptor subtypes in this response, AT, and AT2 receptor antagonists, losartan and PD123319, were investigated in the brain in chronically prepared ovine fetuses at the last third of gestation. Application of losartan intracerebroventricularly (i.c.v.) at 0.5 mg/kg suppressed central ANG II-stimulated plasma AVP release. Losartan at 5 mg/kg (i.c.v.) demonstrated a significant enhancement of AVP increase to i.c.v. ANG II. Associated with the increase of plasma vasopressin levels, c-fos expression in the hypothalamic neurons was significantly different between the low and high doses of losartan. The low dose losartan markedly reduced the dual immunoreactivity for FOS and AVP in the supraoptic nuclei and Para ventricular nuclei after i.c.v. ANG II, whereas the high dose losartan together with ANG II, significantly increased the co-localization of positive FOS in the AVP-containing neurons than that induced by i.c.v. ANG II alone. Central ANG II induced fetal plasma vasopressin increase was not altered by PD123319. The data suggest that losartan in the fetal brain has remarkably different effects based on the doses administrated on central ANG II-related neuroendocrine effects at the late gestation, and that the AT, mechanism is critical in the regulation of fetal body fluid homeostasis related to plasma AVP levels.

The renin-angiotensin system plays an important role in cardiovascular control. Intracerebroventricular (i.c.v.) angiogenesis (ANG) II causes a reliable pressor response in the fetus at 90% gestation. To determine the roles of brain AT, and AT2 receptors in this response, the effects of the central AT, and AT2 receptor antagonist’s losartan and PD123319 were investigated in chronically prepared near-term ovine fetuses. Losartan at 0.5 mg/kg (i.c.v.) abolished central ANG II-induced pressor responses. High-dose losartan (5 mg/kg, i.c.v.) showed a potentiation of the pressor response to i.c.v. ANG II, accompanied by bradycardia. Associated with the pressor responses, c-fos expression in the cardiovascular controlling areas was significantly different between the low and high doses of losartan. These areas included the subfornical organ, median preoptic nucleus, organum vasculosum of the lamina terminal is, and Para ventricular nuclei in the forebrain, and the tractus solitarius nuclei, lateral Para brachial nuclei in the hindbrain. Low-dose losartan markedly reduced c-fos in these areas after i.c.v. ANG II, while the high-dose losartan together with ANG II elicited a much stronger FOS-immunoreactivity in these areas than that induced by i.c.v. ANG II alone. This is a novel finding, that c-fos expression in the brain can be both activated and inhibited under the same condition. Central ANG II-induced fetal pressor responses were not altered by PD123319 (0.8 mg/kg). These results indicate that i.c.v. losartan at a high and a low dose has strikingly different effects on central ANG II-induced pressor responses in fetuses at late gestation, and that the AT, mechanism plays an important role in fetal cardiovascular regulation. J. Comp. Neurol. 493:571-579, 2005.

AVP not only influences renal water excretion but also has profound cardiovascular effects in adults. Our recent studies have demonstrated that central angiogenesis induced fetal pressor responses accompanied with AVP release. However, little is known of hormonal mechanisms in angiogenesis-mediated fetal blood pressure (BP) changes. The present study determined AVP mechanisms in central angiogenesis-mediated fetal pressor responses. The V1-receptor antagonist or V2-receptor antagonist was infused intravenously into the ovine fetus at 90% gestation. Angiogenesis II (Ang II; 1.5

Central cholinergic mechanisms play important roles in the control of cardiovascular responses. However, in utero development of brain cholinergic mechanism in regulation of arterial pressure before birth is largely unknown. This study investigated cardiovascular responses to central application of carbachol in fetuses and determined functional development of the central cholinergic systems controlling fetal pressor responses in utero. Chronically prepared near-term ovine fetuses (90% gestation) received an injection of carbachol intracerebroventricularly (i.c.v.). Fetal cardiovascular responses were measured, and the brains were used for c-fos mapping studies. In response to carbachol injection i.c.v., fetal systolic, diastolic, and mean arterial pressure (MAP) immediately increased, accompanied by a bradycardia. The maximum increase of MAP was at 30 min after the i.c.v. injection of carbachol and lasted 90 min. Associated with the pressor response, the neuronal activity marked with c-fos was enhanced significantly in the fetal anterior third ventricle (AV3V) region (including the median preoptic nucleus and organum vasculosum of the lamina terminalis) in the forebrain, and in the area postrema, lateral parabrachial nucleus, nucleus tractus solitary, and rostra) ventrolateral medulla in the hindbrain. These results indicate that the central cholinergic mechanism is functional in the control of fetal blood pressure at the last third of gestation, and the central AV3V region and hindbrain have been intact relatively during in utero development in sheep at 90% gestational stage. Neuropsychopharmacology advance online publication, 20 April 2005; doi:10.I038/sj.npp. 1300738 developmental neurobiology;

Fetal brain c-fos and cardiovascular responses after i.v. or i.c.v. angiogenesis II administrations was determined in the near-term ovine fetuses. Both routes of angiogenesis II markedly increased fetal mean arterial pressure. The latency of pressor responses by i.v. angiogenesis II administration was shorter than by the i.c.v. route. The increased fetal mean arterial pressure was greater and transient by the i.v. route in comparison to that caused by i.c.v. angiogenesis II administration. Following the i.v. administration of angiogenesis II, the fetal heart rate was significantly decreased. Associated with fetal pressor responses and bradycardia, c-fos expression induced by i.v. angiogenesis II was in the Para ventricular nuclei (PVN) of the hypothalamus, and the area postrema, the tractus solitarius nuclei, and the lateral Para brachial nuclei in the brain stem. After i.c.v. angiogenesis II administration, fetal blood pressure was also increased in association with the intensive c-fos expression in the PVN and the hindbrain. However, fetal heart rate was not affected by the central injection of angiogenesis II. These results indicate that the central pathways between the forebrain circumventricular organs and the PVN have developed, and suggest that the neural activity in the hindbrain associated with bradycardia may be linked to the bar reflex. In the face of i.c.v. angiogenesis II, sympathetic activation may play a predominant role in pressor responses. Taken together, these results suggest that central and peripheral angiogenesis II-induced fetal pressor responses may be mediated by separate mechanisms, and these regulatory mechanisms start to function by near-term or early.