An elevation in plasma osmolality elicits a complex neurohumoral response, including an activation of the sympathetic nervous system and an increase in arterial pressure. Using a combination of in vivo and in situ rat preparations, we sought to investigate whether hypothalamic vasopressinergic spinally projecting neurones are activated during increases in plasma osmolality to elicit sympathoexcitation. Hypertonic saline (HS, I.V. bolus), which produced a physiological increase in plasma osmolality to 299 ± 1 mosmol (kg water) −1 , elicited an immediate increase in mean arterial pressure (MAP) (from 101 ± 1 to 121 ± 3 mmHg) in vivo. Pre-treatment with prazosin reversed the HS-induced pressor response to a hypotensive response (from 121 ± 3 to 68 ± 2 mmHg), indicating significant activation of the sympathetic nervous system. In an in situ arterially perfused decorticate rat preparation, hyperosmotic perfusate consisted of either 135 mM NaCl, or a non-NaCl osmolyte, mannitol (0.5%); both increased lumbar sympathetic nerve activity (LSNA) by 32 ± 5% (NaCl) and 21 ± 1% (mannitol), which was attenuated after precollicular transection (7 ± 3% and 1 ± 1%, respectively). Remaining experiments used the NaCl hyperosmotic stimulus. In separate preparations the hyperosmotic-induced sympathoexcitation (21 ± 2%) was also significantly attenuated after transection of the circumventricular organs (2 ± 1%). Either isoguvacine (a GABA A receptor agonist) or kynurenic acid (a non-selective ionotropic glutamate receptor antagonist) microinjected bilaterally into the paraventricular nucleus (PVN) attenuated the increase in LSNA induced by the hyperosmotic stimulus (control: 25 ± 2%; after isoguvacine: 7 ± 2%; after kynurenic: 8 ± 3%). Intrathecal injection of a V 1a receptor antagonist also reduced the increase in LSNA elicited by the hyperosmotic stimulus (control: 29 ± 6%; after blocker: 4 ± 1%). These results suggest that a physiological hyperosmotic stimulus produces sympathetically mediated hypertension in conscious rats. These data are substantiated by the in situ decorticate preparation in which sympathoexcitation was also evoked by comparable hyperosmotic stimulation. Our findings demonstrate the importance of vasopressin acting on spinal V 1a receptors for mediating sympathoexcitatory response to acute salt loading.

The two recently isolated hypothalamic peptides orexin A and orexin B, also known as hypocretin 1 and 2, are reported to be important signaling molecules in feeding and sleep/wakefulness. Orexin-containing neurons in the lateral hypothalamus project to numerous areas of the rat brain and spinal cord including the intermediolateral cell column (IML) of the thoracolumbar spinal cord. An in vivo and in vitro study was undertaken to evaluate the hypothesis that orexins, acting on sympathetic preganglionic neurons (SPNs) in the rat spinal cord, increase sympathetic outflow. First, orexin A (0.3, 1, and 10 nmol) by intrathecal injection increased mean arterial pressure (MAP) and heart rate (HR) by an average of 5, 18, and 30 mmHg and 10, 42, and 85 beats/min in urethane-anesthetized rats. Intrathecal injection of saline had no significant effects. Orexin B (3 nmol) by intrathecal administration increased MAP and HR by an average of 11 mmHg and 40 beats/min. The pressor effects of orexin A were attenuated by prior intrathecal injection of orexin A antibodies (1:500 dilution) but not by normal serum albumin. Intravenous administration of the alpha(1)-adrenergic receptor antagonist prazosin (0.5 mg/kg) or the beta-adrenergic receptor antagonist propranolol (0.5 mg/kg) markedly diminished, respectively, the orexin A-induced increase of MAP and HR. Second, whole cell patch recordings were made from antidromically identified SPNs of spinal cord slices from 12- to 16-day-old rats. Superfusion of orexin A or orexin B (100 or 300 nM) excited 12 of 17 SPNs, as evidenced by a membrane depolarization and/or increase of neuronal discharges. Orexin A- or B-induced depolarizations persisted in TTX (0.5 microM)-containing Krebs solution, indicating that the peptide acted directly on SPNs. Results from our in vivo and in vitro studies together with the previous observation of the presence of orexin A-immunoreactive fibers in the IML suggest that orexins, when released within the IML, augment sympathetic outflow by acting directly on SPNs.

Vasomotor control by the sympathetic nervous system presents substantial heterogeneity within different tissues, providing appropriate homeostatic responses to maintain basal/stimulated cardiovascular function both at normal and pathological conditions. The availability of a reproducible technique for simultaneous measurement of sympathetic drive to different tissues is of great interest to uncover regional patterns of sympathetic nerve activity (SNA). We propose the association of tyrosine hydroxylase immunoreactivity (THir) with image analysis to quantify norepinephrine (NE) content within nerve terminals in arteries/arterioles as a good index for regional sympathetic outflow. THir was measured in fixed arterioles of kidney, heart, and skeletal muscle of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (123 ± 2 and 181 ± 4 mmHg, 300 ± 8 and 352 ± 8 beats/min, respectively). There was a differential THir distribution in both groups: higher THir was observed in the kidney and skeletal muscle (∼3-4-fold vs. heart arterioles) of WKY; in SHR, THir was increased in the kidney and heart (2.4- and 5.3-fold vs. WKY, respectively) with no change in the skeletal muscle arterioles. Observed THir changes were confirmed by either: 1) determination of NE content (high-performance liquid chromatography) in fresh tissues (SHR vs. WKY): +34% and +17% in kidney and heart, respectively, with no change in the skeletal muscle; 2) direct recording of renal (RSNA) and lumbar SNA (LSNA) in anesthetized rats, showing increased RSNA but unchanged LSNA in SHR vs. WKY. THir in skeletal muscle arterioles, NE content in femoral artery, and LSNA were simultaneously reduced by exercise training in the WKY group. Results indicate that THir is a valuable technique to simultaneously evaluate regional patterns of sympathetic activity.

The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamo-neurohypophyseal system (HNS) undergo a dramatic function-related plasticity during dehydration. We hypothesize that alterations in steady-state transcript levels might be partially responsible for this remodeling. In turn, regulation of transcript abundance might be mediated by transcription factors. We used microarrays to identify changes in the expression of mRNAs encoding transcription factors in response to water deprivation in the SON. We observed downregulation of 10 and upregulation of 28 transcription factor transcripts. For five of the upregulated mRNAs, namely gonadotropin inducible ovarian transcription factor 1 (Giot1), Giot2, cAMP-responsive element binding protein 3-like 1, CCAAT/enhancer binding protein ␤, and activating transcription factor 4, in situ hybridization was used to confirm the array results, demonstrating a significant increase in expression in SON and PVN magnocellular neurons (MCNs) after 3 d of water deprivation and, in some cases, upregulation in parvocellular PVN neurons. Using a viral vector expressing a potent inhibitor of cAMP-dependent protein kinase A (PKA), we show that the osmotically induced increase in the abundance of transcripts encoding Giot1 is mediated in vivo by the PKA pathway. We thus suggest that signaling pathways activated by dehydration in MCNs mediate transcription factor gene activation, which, in turn, regulate target genes that mediate HNS remodeling.

The present data provide evidence that T3 treatment reduces glycaemia and improves insulin sensitivity in diabetic rats, and that at least part of this effect could result from its negative modulation of inflammatory cytokine expression.

ATP (0.31, 0.62, 1.25, and 2.5 nmol/50 nl) into the nucleus tractus solitarii (NTS) produced a dose-dependent pressor response. Prazosin abolished the pressor response and produced no change in the bradycardic response to ATP. Microinjection of pyridoxal phosphate-6-azophenyl-2Ј,4Ј-disulfonic acid (0.25 nmol/50 nl), a nonselective P2 receptor antagonist into the NTS, reduced the bradycardic response but had no effect on the pressor response to microinjection of ATP (1.25 nmol/50 nl) into the NTS. Microinjection of suramin (2 nmol/50 nl), another nonselective P2 receptor antagonist, had no effect on the pressor and bradycardic responses to microinjection of ATP (1.25 nmol/50 nl) into the NTS. Antagonism of A1 receptors of adenosine with 1,3-dipropyl-8-cyclopentylxanthine also produced no changes in the cardiovascular responses to microinjection of ATP into the NTS. The involvement of excitatory amino acid (EAA) receptors in the pressor and bradycardic responses to microinjection of ATP into the NTS was also evaluated. Microinjection of kynurenic acid, a nonselective EAA receptor antagonist (10 nmol/50 nl), into the NTS reduced the bradycardic response and had no effect on the pressor response to microinjection of ATP into the NTS. The data show that 1) microinjection of ATP into the NTS of awake rats produced pressor and bradycardic responses by independent mechanisms, 2) the activation of parasympathetic component may involve an interaction of P2 and EAA receptors in the NTS, and 3) the sympathoexcitatory response to microinjection of ATP into the NTS was not affected by the blockade of P2, A1, or EAA receptors. adenosine 5Ј-triphosphate; P2 purinergic receptors; kynurenic acid; suramin; pyridoxalphosphate-6-azophenyl-2Ј,4Ј-disulfonic acid; 8-cyclopentyl-1,3-dipropylxanthine THE CONCEPT THAT ATP may act as a nonadrenergic noncholinergic neurotransmitter on peripheral nerves was established by Burnstock (4), and several recent studies indicate that ATP and adenosine can act as neurotransmitters or neuromodulators in the central nervous system, including areas involved in cardiovascular regulation, such as the nucleus tractus solitarii (NTS) (1-3, 7, 8, 13, 19, 20, 24, 26 -28, 33). Immunohistochemical studies documented the presence of different subtypes of P2 receptors in the NTS of rats (11,15,34,35). ATP interacts with two distinct families of receptors, P2X and P2Y, which differ in structure and signal transduction mechanism (9, 21). There is evidence indicating that the available P2 receptor antagonists such as pyridoxal phosphate-6-azophenyl-2Ј,4Ј-disulfonic acid (PPADS) and suramin produced no blockade of P2X4 and P2X6 receptor subtypes (25).Studies performed in anesthetized rats documented that microinjection of ATP into the NTS produced a fall in arterial pressure and bradycardia, which were altered in different manner by suramin (8). These cardiovascular responses to ATP in anesthetized rats exhibited a typical pattern of fast transmitter similar to the responses to microinjection of L-glutamate into th...

In this study, we investigated some mechanisms involved in sodium-dependent hypertension of rats exposed to chronic salt (NaCl) intake from weaning until adult age. Weaned male Wistar rats were placed under high (0.90% w/w, HS) or regular (0.27% w/w, Cont) sodium diets for 12 weeks. Water consumption, urine output and sodium excretion were higher in HS rats compared to control. Blood pressure (BP) was directly measured by the arterial catheter and found 13.8% higher in HS vs Cont rats. Ganglionic blockade with hexamethonium caused greater fall in the BP of HS rats (33%), and central antagonism of AT1 receptors (losartan) microinjected into the lateral ventricle reduced BP level of HS, but not of Cont group. Heart rate variability analysis revealed sympathetic prevalence on modulation of the systolic interval. HS diet did not affect creatinine clearance. Kidney histological analysis revealed no significant change in renal corpuscle structure. Sodium and potassium concentrations in CSF were found higher in HS rats despite no change in plasma concentration of these ions. Taken together, data suggest that animals exposed to chronic salt intake to a level close to that reported for human’ diet since weaning lead to hypertension, which appears to rely on sodium-driven neurogenic mechanisms.

-A high-salt diet can lead to hydromineral imbalance and increases in plasma sodium and osmolality. It is recognized as one of the major contributing factors for cardiovascular diseases such as hypertension. The paraventricular nucleus (PVN) plays a pivotal role in osmotically driven sympathoexcitation and high blood pressure, the precise mechanisms of which are not fully understood. Recent evidence indicates that AVP released from magnocellular neurons might be involved in this process. Using a combination of in vivo and in situ studies, we sought to investigate whether AVP, acting on PVN neurons, can change mean arterial pressure (MAP) and sympathetic nerve activity (SNA) in euhydrated male rats. Furthermore, we wanted to determine whether V 1a receptors on PVN neurons would be involved in saltinduced sympathoexcitation and hypertension. In rats, 4 days of salt loading (NaCl 2%) elicited a significant increase in plasma osmolality (39 Ϯ 7 mosmol/kgH 2O), an increase in MAP (26 Ϯ 2 mmHg, P Ͻ 0.001), and sympathoexcitation compared with euhydrated rats. Microinjection of AVP into the PVN of conscious euhydrated animals (100 nl, 3 M) elicited a pressor response (14 Ϯ 2 mmHg) and a significant increase in lumbar SNA (100 nl, 1 mM) (19 Ϯ 5%). Pretreatment with a V 1a receptor antagonist, microinjected bilaterally into the PVN of salt-loaded animals, elicited a decrease in lumbar SNA (Ϫ14 Ϯ 5%) and MAP (Ϫ19 Ϯ 5 mmHg), when compared with the euhydrated group. Our findings show that AVP plays an important role in modulating the salt-induced sympathoexcitation and high blood pressure, via V 1a receptors, within the PVN of male rats. As such, V 1a receptors in the PVN might contribute to neurogenic hypertension in individuals consuming a high-salt diet.vasopressin; paraventricular nucleus of the hypothalamus; salt loading; sympathoexcitation; hypertension A HIGH DIETARY INTAKE OF SALT is one of the major contributing factors to cardiovascular diseases, such as hypertension (11,12,32). High-salt diets can lead to a hydromineral imbalance and increases the plasma sodium concentrations and osmolality. This, in turn, can activate central hypothalamic nuclei that elevate sympathetic outflow and arterial blood pressure (BP), leading to a disorder referred to as salt-sensitive neurogenic hypertension (33).Osmotic perturbations are primarily sensed by osmosensing neurons located in brain regions that lack a blood-brain barrier termed circumventricular organs (CVOs). Under systemic hyperosmotic conditions, the CVOs are activated and send excitatory inputs to the paraventricular nucleus of the hypothalamus (PVN), an important integrative center involved in the autonomic and neuroendocrine functions to maintain body fluids and cardiovascular homeostasis (14,19,28). The PVN lies adjacent to the third ventricle in the anterior hypothalamus, and it is composed of magnocellular neurons (MCNs) and parvocellular neurons (PCN). The PCN send projections to autonomic nuclei, such as the rostral ventrolateral medulla (RVLM) and intermediola...