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Ventral Medulla (ventral + medulla)
Selected AbstractsPremotor sympathetic neurons of conditioned fear in the ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008Pascal Carrive Abstract Conditioned fear to context, a pure form of psychological stress, is associated with sympathetically mediated changes including a marked hypertension. To identify the possible premotor sympathetic neurons mediating these changes, we conducted double-immunolabelling experiments combining fear-induced Fos with retrograde tracing from the thoracic cord (T2-L1). Presympathetic groups showing the greatest increase in the proportion of spinally projecting cells double-labelled with Fos compared with resting controls were the perifornical area (PeF; 22.7% vs. 0.4%) and paraventricular nucleus (Pa; 10.5% vs. 0.2%) in the hypothalamus, and the A5 noradrenergic group (33.6% vs. 0.2%) in the pons. In contrast, there was only a small increase in the presympathetic groups of the rostral ventral medulla, including the lateral paragigantocellular group (LPGi; 4.3% vs. 0.5%), raphe magnus and pallidus (1.1% vs. 0.6% and 1.8% vs. 0.5%), and the vasopressor group of the rostral ventrolateral medulla (RVLM; 1.9% vs. 0.8%). PeF, Pa, A5 and LPGi accounted for 21, 15, 16 and 6% of all the double-labelled cells, respectively, and RVLM for only 1%. Double-immunolabelling of Fos and tyrosine hydroxylase confirmed that many A5 neurons were activated (19%) and that practically no C1 neurons in RVLM were (1.3%). The results suggest that the main premotor sympathetic drive of the fear response comes from hypothalamic (PeF and Pa) and A5 neurons that project directly to the thoracic cord and bypass medullary presympathetic groups, and that the vasopressor premotor sympathetic neurons of the RVLM are unlikely to mediate the hypertensive pressure response of contextual fear. [source] Synaptically released 5-HT modulates the activity of tonically discharging neuronal populations in the rostral ventral medulla (RVM)EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2000Pascale Piguet Abstract There is substantial evidence for an important modulating role of monoamines (catecholamines and serotonin, 5-HT) in the rostral ventral medulla (RVM), a region which plays an important role in cardiovascular and nociceptive functions. We investigated in slices the role of endogenous monoamines in the synaptic control of the activity of rat RVM neuronal populations using intracellular recordings in the lateral RVM plus lateral aspect of nucleus paragigantocellularis lateralis. A triple-labelling protocol allowed us to identify the location of impaled neurons and their eventual monoaminergic phenotype within the serotonergic and catecholaminergic populations of the RVM. Focal electrical stimulation revealed the existence of a functional monoaminergic input onto RVM neurons which was mediated by endogenous 5-HT acting at inhibitory 5-HT1A receptors but did not involve noradrenergic neurotransmission. The slow 5-HT-mediated inhibitory postsynaptic potential (IPSP) was only observed in the regularly discharging neurons, which were found to be neither catecholaminergic nor serotonergic. The synaptic release of 5-HT was, itself, under an inhibitory control involving GABAA (,-aminobutyric acid) receptors. Moreover, we characterized the effect of the 5-HT-releasing agent fenfluramine on this functional 5-HT-mediated synaptic transmission. Our results show that the effect of fenfluramine is biphasic consisting of an initial prolongation of the serotonergic IPSP followed by a decrease in amplitude. Our data provide a basis for the previously reported inhibitory effects of exogenously applied serotonin agonists/antagonists on the autonomic functions controlled by the RVM. This 5-HT pathway, which functionally links the serotonergic and catecholaminergic regions, might play an important role in cardiovascular and nociceptive functions. [source] To breathe or not to breathe?EXPERIMENTAL PHYSIOLOGY, Issue 1 2009That is the question Our understanding of the role of the brain in respiratory rhythm generation and regulation began the early nineteenth century. Over the next 150 years the neuronal groups in the medulla oblongata and pons that were involved in eupnoea and in gasping were identified by techniques involving the lesioning of areas of the lower brainstem, several transections across the brainstem and focal electrical stimulation. An incomplete picture emerged that stressed the importance of the ventral medulla. Subsequent electrophysiological studies in in vivo, in situ and in vitro preparations have revealed the importance of restricted groups of neurones in this area, within the Bötzinger and pre-Bötzinger nuclei, that are the essential kernel for rhythm generation. The outputs to the spinal motoneurones responsible for the patterning of inspiratory and expiratory discharge are shaped by inputs from these neurones and others within the respiratory complex that determine the activity of respiratory bulbospinal neurones. It is clear that the developmental stage of the preparation is often critical for the pattern of respiratory activity that is generated and that these patterns have important physiological consequences. The models that are currently considered to explain rhythmogenesis are critically evaluated. The respiratory network is subject to regulation from peripheral and central chemoreceptors, amongst other afferent inputs, which act to ensure respiratory homeostasis. The roles of peripheral chemoreceptors as primarily O2 sensors are considered, and the evolution of ideas surrounding their roles is described. New insights into the transduction mechanisms of chemoreception in the carotid body and chemosensitive areas of the ventral medullary surface, specifically in monitoring CO2 levels, are reviewed. As new experimental tools, both genetic and cellular, are emerging, it can be expected that the detailed network architecture and synaptic interactions that pattern respiratory activity in relation to behavioural activity will be revealed over the next years. [source] Androgen receptor expressing neurons that project to the paraventricular nucleus of the hypothalamus in the male ratTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 6 2007Martin Williamson Abstract Androgen receptors are distributed throughout the central nervous system and are contained by a variety of nuclei that are known to project to or regulate the paraventricular nucleus (PVN) of the hypothalamus, the final common pathway by which the brain regulates the hypothalamic,pituitary,adrenal (HPA) response to homeostatic threat. Here we characterized androgen receptor staining within cells identified as projecting to the PVN in male rats bearing iontophoretic or crystalline injections of the retrograde tracer FluoroGold aimed at the caudal two-thirds of the nucleus, where corticotropin-releasing hormone-expressing neurons are amassed. Androgen receptor (AR) and FluoroGold (FG) double labeling was revealed throughout the limbic forebrain, including scattered numbers of cells within the anterior and posterior subdivisions of the bed nuclei of the stria terminalis; the medial zone of the hypothalamus, including large numbers of AR-FG-positive cells within the anteroventral periventricular and medial preoptic cell groups. Strong and consistent colabeling was also revealed throughout the hindbrain, predominantly within the periaqueductal gray and the lateral parabrachial nucleus, and within various medullary cell groups identified as catecholaminergic, predominantly C1 and A1 neurons of the ventral medulla. These connectional data predict that androgens can act on a large assortment of multimodal inputs to the PVN, including those involved with the processing of various types of sensory and limbic information, and provide an anatomical framework for understanding how gonadal status could contribute to individual differences in HPA function. J. Comp. Neurol. 503:717,740, 2007. © 2007 Wiley-Liss, Inc. [source] ORIGINAL RESEARCH,BASIC SCIENCE: Effect of the Destruction of Cells Containing the Serotonin Reuptake Transporter on Urethrogenital ReflexesTHE JOURNAL OF SEXUAL MEDICINE, Issue 2 2007Karla Gravitt BSc ABSTRACT Introduction., The urethrogenital (UG) reflex is an autonomic and somatic response that mimics some of the physiological changes seen during ejaculation. The UG reflex is tonically inhibited by neurons in the ventral medulla, an area containing serotonin neurons. Aim., To examine the effect of lesions of brain neurons containing the serotonin reuptake transporter (SERT) on ejaculatory-like reflexes. Methods., Anti-SERT saporin (80 nL, 1 mM) or saline was injected bilaterally into the ventrolateral medulla of male Sprague,Dawley rats. Ten to 18 days later, animals were deeply anesthetized and the presence of the UG reflex was examined before and after acute spinal cord transection (T9,10). Following the experiment the presence and number of serotonin and norepinephrine containing neurons (using tryptophan hydroxylase and dopamine beta-hydroxylase, respectively) was performed. Main Outcome Measures., The UG reflex and cell counts. Results., In saline-injected controls the UG reflex was not evoked in the anesthetized, intact preparation, indicating the presence of the supraspinal inhibition, as previously reported. Injection of anti-SERT saporin into the ventrolateral medulla allowed the UG reflex to be activated in the intact preparation, thus removed the inhibition. This was associated with a decrease in the number of serotonin neurons in the ventrolateral medulla and raphe. No change in the number of noradrenergic neurons was observed. Conclusion., These studies suggest that ventral medullary neurons containing SERT are involved in the tonic inhibition of the UG reflex. Gravitt K, and Marson L. Effect of the destruction of cells containing the serotonin reuptake transporter on urethrogenital Reflexes. J Sex Med 2007;4:322,331. [source] | ||||||||||