Nitric oxide exerts important regulatory functions in various brain processes. Its synthesis in neurons has been most commonly ascribed to the neuronal nitric oxide synthase (nNOS) isoform. However, the endothelial isoform (eNOS), which is significantly associated with caveolae in different cell types, has been implicated in synaptic plasticity and is enriched in the dendrites of CA1 hippocampal neurons. Using high resolution microscopy and co-distribution analysis of eNOS with synaptic and raft proteins, we now show for the first time in primary cortical and hippocampal neuronal cultures, virtually devoid of endothelial cells, that eNOS is present in neurons and is localized in dendritic spines. Moreover, eNOS is present in a postsynaptic density-enriched biochemical fraction isolated from these neuronal cultures. In addition, qPCR analysis reveals that both the nNOS as well as the eNOS transcripts are present in neuronal cultures. Moreover, eNOS inhibition in cortical cells has a negative impact on cell survival after excitotoxic stimulation with N-methyl-D-aspartate (NMDA). Consistent with previous results that indicated nitric oxide production in response to the neurotrophin BDNF, we could detect eNOS in immunoprecipitates of the BDNF receptor TrkB while nNOS could not be detected. Taken together, our results show that eNOS is located at excitatory synapses where it could represent a source for NO production and thus, the contribution of eNOS-derived nitric oxide to the regulation of neuronal survival and function deserves further investigations.
The effects of chronic mild hypoxemia on the binding of angiotensin receptors in selected brain stem nuclei and reflex responses were studied in fetal sheep. Fetal and maternal catheters were placed at 120 days' gestation, and animals received intratracheal maternal administration of nitrogen (n ϭ 16) or compressed air in controls (n ϭ 19). Nitrogen infusion was adjusted to reduce fetal brachial artery PO2 by 25% during 5 days. Spontaneous baroreflex sensitivity and spectral analysis of the pulse interval were analyzed during the 5 days hypoxemia period using 90 min of daily recording. Brains of control and hypoxemic animals were collected, and brain stem angiotensin receptor binding was studied by in vitro autoradiography at 130 days of gestation. After 5 days of hypoxemia, some animals in each group were submitted to one complete umbilical cord occlusion during 5 min. [125 I]sarthran binding showed that chronic mild hypoxemia significantly increases angiotensin type 1 receptor, angiotensin type 2 receptor, and ANG-(1-7) angiotensin receptor binding sites in the nucleus tractus solitarius and dorsal motor nucleus of the vagus (P Ͻ 0.05). Hypoxemia induced lower baroreflex sensitivity and a higher low frequency-to-high frequency ratio in the fetus, consistent with a shift from vagal to sympathetic autonomic cardiac regulation. Cord occlusion to elicit a chemoreflex response induced a greater bradycardic response in hypoxemic fetuses (slope of the initial fall in heart rate; 11.3 Ϯ 1.9 vs. 6.4 Ϯ 1.2 beats ⅐ min Ϫ1 ⅐ s Ϫ1 , P Ͻ 0.05). In summary, chronic mild hypoxemia increased binding of angiotensin receptors in brain stem nuclei, decreased spontaneous baroreflex gain, and increased chemoreflex responses to asphyxia in the fetus. These results suggest hypoxemia-induced alterations in brain stem mechanisms for cardiovascular control.fetus; hypoxemia; baroreflex OXYGEN DEPRIVATION IMPOSES diverse challenges to fetal development, with changes in the autonomic cardiovascular control via baroreflex and chemoreflex pathways playing a major role as a survival strategy (16). In fetal sheep, acute episodes of hypoxemia induce a redistribution of cardiac output to maintain blood flow and oxygen delivery to the heart and brain (14). This response is initiated by stimulation of peripheral chemoreceptors and maintained by endocrine mechanisms involving secretion of hormones such as catecholamines, neuropeptide Y, arginine vasopressin, and cortisol (11). During acute severe hypoxia, i.e., complete occlusion of the umbilical cord, fetuses respond with a fall in heart rate (FHR) and an increase in blood pressure. This acute FHR during hypoxia represents a key fetal adaptation, believed to help reduce myocardial work and oxygen requirements (11). This initial bradycardia, which is mediated by chemoreflex vagal pathways (5, 17, 23), occurs before the increase in blood pressure and is an indication of the severity of the hypoxic insult (5). Recently, it was reported that the slope of the initial bradycardia increases during short ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.