Nitric oxide and central autonomic control of blood pressure: a neuroanatomical study of nitric oxide and cGMP expression in the brain and spinal cord

摘要: Essential hypertension is defined as a chronic elevation of blood pressure unknown cause. Though definitive trigger for this change in has not been established, there strong association with an upregulation sympathetic output from the central nervous system. There are number autonomic nuclei involved maintenance pressure, including brainstem regions nucleus tractus solitarii (NTS), caudal ventrolateral medulla (CVLM), rostral (RVLM), preganglionic neurons (SPNs) within intermediolateral cell column (IML) spinal cord, well forebrain such paraventricular (PVN) hypothalamus. Within these centers, vast neurotransmitters have identified that contribute to control glutamate, angiotensin II, serotonin, neurotensin, neuropeptide Y, opioids and catecholamines. Recognition role nitric oxide (NO) its multiple influences over neural gaining increasing significance. Nitric unique modulatory molecule acts non-conventional neurotransmitter. As NO gas short half-life 4 - 6 seconds, its' synthesising enzyme, synthase (NOS) often used marker location production. Once activated, best-known 'receptor' soluble guanylate cyclase (sGC), which drives production cyclic guanosine monophosphate (cGMP). Identifying presence cGMP can therefore be determine sites receptive NO. Previous studies examining focused predominantly upon application either excitatory or inhibitory drugs into key assessing pressor depressor effects. This thesis aims instead study neuroanatomical relationship functional significance expression brain cord hypertensive normotensive rat model. In first experimental chapter (Chapter 3), comparative analysis neuronal NOS SPN mature Spontaneously Hypertensive Rats (SHR) their controls, Wistar Kyoto (WKY) was undertaken. Fluorescence immunohistochemistry confirmed nNOS majority located IML region both strains. However, strain specific anatomical arrangement clusters evident while no significant difference between total each strain, were significantly fewer positive SHR animals. All found express cGMP, novel subpopulation negative, cGMP-positive identified. These cells medial edge group. results suggest signalling SPN, reduced may associated increase tone seen essential hypertension. The second 4) aimed if numbers containing translated detectable cGMP. The two strains then examined. Based on previous work by our group, it predicted would translate intrathecal administration exogenous drive differential response animal Immunohistochemical techniques relative level when compared WKY. Intrathecal 8-bromo-cGMP, drug analogous increased had dose dependent effect, causing only small anaesthetised WKY animals, driving SHR. finding raised hypothesis SHR, driver hypertension, but protective mechanism limiting potent effects SPN. third 5) examines inducible isoforms (nNOS, iNOS) RVLM rats. Reverse transcription-polymerase chain reaction (RT-PCR) analyse mRNA further protein levels nNOS. Total RNA extracted reverse transcribed male Quantitative real-time PCR indicated WKY, higher immunohistochemically. When iNOS, expressed at overall, however iNOS demonstration raises possibilities (i) up-regulated activity order re-establish homeostatic balance alternatively (ii) alteration underlie genesis augmented vasomotor during fourth 6) extends observations Chapter 5 through examination sGC RVLM. evidence relies intracellular pathway impaired hypertension. Immunohistochemistry assess active C1 RVLM, again comparing sections double labelled phenylethylamine methyl-transferase (PNMT) failed reveal aged animals despite consistent detection immunoreactivity ambiguus same adjacent sections. demonstrated absence phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) young vs. In-vitro incubation slices donor DETA-NO NMDA did any additional staining In all studies, prominent vasculature. Soluble throughout although co-localise PNMT populations. Overall, resting state cannot elicited inhibition, receptor stimulation application. A time course degradation inhibited utilised excluded. final 7) magnocellular preautonomic parvocellular PVN. Retrograde tracing visualise functionally, neurochemically topographically PVN populations Basal readily observed PVN, vascular profiles. Cyclic GMP neurons, independent subnuclei location, innervated target neurochemical phenotype. data presented indicates highly heterogeneous distribution basal supports others indicating constitutive actions likely mediated indirectly activation interneurons. Summary Together, comprise detailed regulation pressure. Under conditions, demonstrate notable differences enzymes correlating changes downstream also demonstrated. demonstrated, could detected contrast populations. Conclusion This gives insight physiological mediators control. indicate NO-cGMP dominant responsible maintaining high model globally pattern expression, indeed mediator function vary Further, possible recruited reflex pathways times marked stress, we see result compensatory mechanisms.