Hypothalamic paraventricular nucleus neurons regulate medullary catecholamine cell responses to restraint stress

Both physical and psychological stressors recruit catecholamine cells (CA) located in the ventrolateral medulla (VLM) and the nucleus of the solitary tract (NTS). In the case of physical stressors, this effect is initiated by signals that first access the central nervous system at or below the level of the medulla. For psychological stressors, however, CA cell recruitment depends on higher structures within the neuraxis. Indeed, we have recently provided evidence of a pivotal role for the medial amygdala (MeA) in this regard, although such a role must involve a relay, as MeA neurons do not project directly to the medulla. However, some of the MeA neurons that respond to psychological stress have been found to project to the hypothalamic paraventricular nucleus (PVN), a structure that provides significant input to the medulla. To determine whether the PVN might regulate medullary CA cell responses to psychological stress, animals were prepared with unilateral injections of the neurotoxin ibotenic acid into the PVN (Experiment 1), or with unilateral injections of the retrograde tracer wheat germ agglutinin-gold (WGA-Au) into the CA cell columns of the VLM or NTS (Experiment 2). Seven days later, animals were subjected to a psychological stressor (restraint; 15 minutes), and their brains were subsequently processed for Fos plus appropriate cytoplasmic markers (Experiment 1), or Fos plus WGA-Au (Experiment 2). PVN lesions significantly suppressed the stress-related induction of Fos in both VLM and NTS CA cells, whereas tracer deposits in the VLM or NTS retrogradely labeled substantial numbers of PVN cells that were also Fos-positive after stress. Considered in concert with previous results, these data suggest that the activation of medullary CA cells in response to psychological stress may involve a critical input from the PVN.

Endogenous hydrogen peroxide in the hypothalamic paraventricular nucleus regulates sympathetic nerve activity responses to L-glutamate

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Exercise training normalizes an increased neuronal excitability of NTS-projecting neurons of the hypothalamic paraventricular nucleus in hypertensive rats

Stern JE, Sonner PM, Son SJ, Silva FC, Jackson K, Michelini LC. Exercise training normalizes an increased neuronal excitability of NTS-projecting neurons of the hypothalamic paraventricular nucleus in hypertensive rats. J Neurophysiol 107: 2912-2921, 2012. First published February 22, 2012; doi:10.1152/jn.00884.2011.-Elevated sympathetic outflow and altered autonomic reflexes, including impaired baroreflex function, are common findings observed in hypertensive disorders. Although a growing body of evidence supports a contribution of preautonomic neurons in the hypothalamic paraventricular nucleus (PVN) to altered autonomic control during hypertension, the precise underlying mechanisms remain unknown. Here, we aimed to determine whether the intrinsic excitability and repetitive firing properties of preautonomic PVN neurons that innervate the nucleus tractus solitarii (PVN-NTS neurons) were altered in spontaneously hypertensive rats (SHR). Moreover, given that exercise training is known to improve and/or correct autonomic deficits in hypertensive conditions, we evaluated whether exercise is an efficient behavioral approach to correct altered neuronal excitability in hypertensive rats. Patch-clamp recordings were obtained from retrogradely labeled PVN-NTS neurons in hypothalamic slices obtained from sedentary (S) and trained (T) Wistar-Kyoto (WKY) and SHR rats. Our results indicate an increased excitability of PVN-NTS neurons in SHR-S rats, reflected by an enhanced input-output function in response to depolarizing stimuli, a hyperpolarizing shift in Na+ spike threshold, and smaller hyperpolarizing afterpotentials. Importantly, we found exercise training in SHR rats to restore all these parameters back to those levels observed in WKY-S rats. In several cases, exercise evoked opposing effects in WKY-S rats compared with SHR-S rats, suggesting that exercise effects on PVN-NTS neurons are state dependent. Taken together, our results suggest that elevated preautonomic PVN-NTS neuronal excitability may contribute to altered autonomic control in SHR rats and that exercise training efficiently corrects these abnormalities.

Purinergic and glutamatergic interactions in the hypothalamic paraventricular nucleus modulate sympathetic outflow

P2X receptors are expressed on ventrolateral medulla projecting paraventricular nucleus (PVN) neurons. Here, we investigate the role of adenosine 5′-triphosphate (ATP) in modulating sympathetic nerve activity (SNA) at the level of the PVN. We used an in situ arterially perfused rat preparation to determine the effect of P2 receptor activation and the putative interaction between purinergic and glutamatergic neurotransmitter systems within the PVN on lumbar SNA (LSNA). Unilateral microinjection of ATP into the PVN induced a dose-related increase in the LSNA (1 nmol: 38 ± 6 %, 2.5 nmol: 72 ± 7 %, 5 nmol: 96 ± 13 %). This increase was significantly attenuated by blockade of P2 receptors (pyridoxalphosphate-6-azophenyl-20,40-disulphonic acid, PPADS) and glutamate receptors (kynurenic acid, KYN) or a combination of both. The increase in LSNA elicited by L-glutamate microinjection into the PVN was not affected by a previous injection of PPADS. Selective blockade of non-N-methyl-D-aspartate receptors (6-cyano-7-nitroquinoxaline-2,3-dione disodium salt, CNQX), but not N-methyl-D-aspartate receptors (NMDA) receptors (DL-2-amino-5-phosphonopentanoic acid, AP5), attenuated the ATP-induced sympathoexcitatory effects at the PVN level. Taken together, our data show that purinergic neurotransmission within the PVN is involved in the control of SNA via P2 receptor activation. Moreover, we show an interaction between P2 receptors and non-NMDA glutamate receptors in the PVN suggesting that these functional interactions might be important in the regulation of sympathetic outflow

The cardiovascular actions of fractalkine/CX3CL1 in the hypothalamic paraventricular nucleus are attenuated in rats with heart failure

The paraventricular nucleus (PVN) of the hypothalamus plays an important role in the regulation of sympathetic nerve activity, which is significantly elevated in chronic heart failure (CHF). Fractalkine (FKN) and its cognate receptor, CX3CR1, are constitutively expressed in the central nervous system, but their role and physiological significance are not well known. The aims of the present study were to determine whether FKN plays a cardiovascular role within the PVN and to investigate how the actions of FKN might be altered in CHF. We show that both FKN and CX3CR1 are expressed on neurons in the PVN of rats, suggesting that they may have a physiological function in this brain nucleus. Unilateral microinjection of FKN directly into the PVN of anaesthetized rats elicited a significant dose-related decrease in blood pressure (1.0 nmol, -5 ± 3 mmHg; 2.5 nmol, -13 ± 2 mmHg; 5.0 nmol, -22 ± 3 mmHg; and 7.5 nmol, -32 ± 3 mmHg) and a concomitant increase in heart rate (1.0 nmol, 6 ± 3 beats min(-1); 2.5 nmol, 11 ± 3 beats min(-1); 5 nmol, 18 ± 4 beats min(-1); and 7.5 nmol, 27 ± 5 beats min(-1)) compared with control saline microinjections. In order to determine whether FKN signalling is altered in rats with CHF, we first performed quantitative RT-PCR and Western blot analysis and followed these experiments with functional studies in rats with CHF and sham-operated control rats. We found a significant increase in CX3CR1 mRNA and protein expression, as determined by quantitative RT-PCR and Western blot analysis, respectively, in the PVN of rats with CHF compared with sham-operated control rats. We also found that the blood pressure effects of FKN (2.5 nmol in 50 nl) were significantly attenuated in rats with CHF (change in mean arterial pressure, -6 ± 3 mmHg) compared with sham-operated control rats (change in mean arterial pressure, -16 ± 6 mmHg). These data suggest that FKN and its receptor, CX3CR1, modulate cardiovascular function at the level of the PVN and that the actions of FKN within this nucleus are altered in heart failure

Hypothalamic paraventricular nucleus neurons regulate medullary catecholamine cell responses to restraint stress

Both physical and psychological stressors recruit catecholamine cells (CA) located in the ventrolateral medulla (VLM) and the nucleus of the solitary tract (NTS). In the case of physical stressors, this effect is initiated by signals that first access the central nervous system at or below the level of the medulla. For psychological stressors, however, CA cell recruitment depends on higher structures within the neuraxis. Indeed, we have recently provided evidence of a pivotal role for the medial amygdala (MeA) in this regard, although such a role must involve a relay, as MeA neurons do not project directly to the medulla. However, some of the MeA neurons that respond to psychological stress have been found to project to the hypothalamic paraventricular nucleus (PVN), a structure that provides significant input to the medulla. To determine whether the PVN might regulate medullary CA cell responses to psychological stress, animals were prepared with unilateral injections of the neurotoxin ibotenic acid into the PVN (Experiment 1), or with unilateral injections of the retrograde tracer wheat germ agglutinin-gold (WGA-Au) into the CA cell columns of the VLM or NTS (Experiment 2). Seven days later, animals were subjected to a psychological stressor (restraint; 15 minutes), and their brains were subsequently processed for Fos plus appropriate cytoplasmic markers (Experiment 1), or Fos plus WGA-Au (Experiment 2). PVN lesions significantly suppressed the stress-related induction of Fos in both VLM and NTS CA cells, whereas tracer deposits in the VLM or NTS retrogradely labeled substantial numbers of PVN cells that were also Fos-positive after stress. Considered in concert with previous results, these data suggest that the activation of medullary CA cells in response to psychological stress may involve a critical input from the PVN. (C) 2004 Wiley-Liss, Inc.

Activation of paraventricular nucleus of hypothalamus 5-HT1A receptor on sodium intake

Hypothalamic paraventricular nucleus (PVN) has an important role in the regulation of water and sodium intake. Several researches described the presence of 5-HT1 receptors in the central nervous system. 5-HTIA was one of the prime receptors identified and it is found in the somatodendritic and post-synaptic forms. Therefore, the aim of this study was to investigate the participation of serotonergic 5-HT1A receptors in the PVN on the sodium intake induced by sodium depletion followed by 24 h of deprivation (injection of the diuretic furosemide plus 24 h of sodium-deficient diet). Rats (280-320 g) were submitted to the implant of cannulas bilaterally in the PVN. 5-HT injections (10 and 20 mu g/0.2 mu l) in the PVN reduced NaCl 1.8% intake. 8-OH-DPAT injections (2.5 and 5.0 fig/0.2 mu l) in the PVN also reduced NaCl 1.8% intake. pMPPF bilateral injections (5-HT1A antagonist) previously to 8-OH-DPAT injections have completely blocked the inhibitory effect over NaCl 1.8% intake. 5-HT1A antagonists partially reduced the inhibitory effect of 5-HT on NaCl 1.8% intake induced by sodium depletion. In contrast, the intake of palatable solution (2% sucrose) under body fluid-replete conditions was not changed after bilateral PVN 8-OH-DPTA injections. The results show that 5HT(1A) serotonergic mechanisms in the PVN modulate sodium intake induced by sodium loss. The finding that sucrose intake was not affected by PVN 5-HT1A activation suggests that the effects of the 5-HT1A treatments on the intake of NaCl are not due to mechanisms producing a nonspecific decrease of all ingestive behaviors. (c) 2006 Elsevier B.V. All rights reserved.

Macrophage Migration Inhibitory Factor in the Paraventricular Nucleus Plays a Major Role in the Sympathoexcitatory Response to Salt

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Hypothalamic supraoptic but not paraventricular nucleus is involved in cardiovascular responses to carbachol microinjected into the bed nucleus of stria terminalis of unanesthetized rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hypothalamic disconnection caudal to paraventricular nucleus affects cardiovascular and drinking responses to central angiotensin II and carbachol

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Glycemic State Regulates Brain-Derived Neurotrophic Factor Responsiveness of Neurons in the Paraventricular Nucleus of the Hypothalamus

Brain derived neurotrophic factor (BDNF) is a member of the family of neurotrophins and binds to the tropomyosin-related kinase B (TrkB) receptor. Like other neurotrophic factors, BDNF is involved in the development and differentiation of neurons. Recently, studies have suggested important roles for BDNF in the regulation of energy homeostasis. The paraventricular nucleus (PVN) is critical for normal energy balance contains high levels of both BDNF and TrkB mRNA. Studies have shown that microinjections of BDNF into the PVN increase energy expenditure, suggesting BDNF plays a role in energy homeostasis through direct actions in this hypothalamic nucleus. We used male Sprague-Dawley rats to perform whole-cell current-clamp experiments from PVN neurons in slice preparation. BDNF was bath applied at a concentration of 2nM and caused depolarizations in 54% of neurons (n = 25; mean change in membrane potential: 8.9 ± 1.2 mV), hyperpolarizations in 23% (n = 11; mean change in membrane potential: -6.7 ± 1.4 mV), while the remaining cells tested were unaffected. Previous studies showing effects of BDNF on γ-aminobutyric acid type A (GABAA) mediated neurotransmission in PVN led us to examine if these BDNF-mediated changes in membrane potential were maintained in the presence of tetrodotoxin (TTX) sodium channel blocker (N = 9; 56% depolarized, 22% hyperpolarized, 22% non-responders) and bicuculline (GABAA antagonist) (N = 12; 42% depolarized, 17% hyperpolarized, 41% non-responders), supporting the conclusion that these effects on membrane potential were postsynaptic. We also evaluated the effects of BDNF on these neurons across varying physiologically relevant extracellular glucose concentrations. At 10 mM 23% (n = 11; mean: -6.7 ± 1.4 mV) of PVN neurons hyperpolarized in response to BDNF treatment, whereas at 0.2 mM glucose, 71% showed hyperpolarizing effects (n = 12; mean: -6.3 ± 2.8 mV). Our findings reveal that BDNF has direct impacts on PVN neurons and that these neurons are capable of integrating multiple sources of metabolically relevant input. Our analysis regarding glucose concentrations and their effects on these neurons’ response to other metabolic signals emphasizes the importance of using physiologically relevant conditions for study of central pathways involved in the regulation of energy homeostasis.

Descending pathways from the paraventricular nucleus contribute to the recruitment of brainstem nuclei following a systemic immune challenge

Hypothalamic nuclei, particularly the paraventricular nuclei (PVN), are important brain sites responsible for central nervous system responses during an immune challenge. The brainstem catecholamine cells of the nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM) have been shown to play critical roles in relaying systemic immune signals to the PVN. However, whilst it is well recognised that PVN divisions also innervate the NTS and VLM, it is not known whether descending PVN pathways can modulate the recruitment of brainstem cells during an immune challenge. Using systemic administration of the proinflammatory cytokine interleukin-1β, in combination with Fos immunolabelling, we firstly investigated the effect of PVN lesions on NTS and VLM catecholamine and non-catecholamine cell responses. We found that ibotenic acid lesions of the PVN significantly reduced numbers of Fos-positive non-catecholamine, noradrenergic and adrenergic cells observable in the VLM and NTS after interleukin-1β administration. We then investigated the origins of descending inputs to the VLM and NTS, activated by systemic interleukin-1β, by mapping the distribution of Fos-positive retrogradely-labelled cells in divisions of the PVN after iontophoretically depositing choleratoxin-b subunit into the NTS or VLM one week prior to interleukin-1β administration. We found that, after either NTS or VLM deposits, the majority of retrogradely-labelled Fos-positive cells activated by interleukin-1β were localised in the medial and lateral parvocellular PVN divisions. Retrogradely-labelled Fos-positive cells were also observed in the NTS after VLM deposits, and in the VLM after NTS tracer deposits, suggesting reciprocal communication between these two nuclei after systemic interleukin-1β. Thus the present study shows that the PVN has the capacity to modulate NTS and VLM responses after an immune challenge and that these may result from descending projections arising in the medial and lateral PVN divisions. These findings suggest that central nervous system responses to an immune challenge are likely to involve complex reciprocal connections between the PVN and the brainstem as well as between brainstem nuclei themselves.

Ionotropic Glutamate Receptors in Hypothalamic Paraventricular and Supraoptic Nuclei Mediate Vasopressin and Oxytocin Release in Unanesthetized Rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Renal effects of angiotensin II receptor subtype 1 and 2-selective ligands injected into the paraventricular nucleus of conscious rats

We determined the effects of losartan and CGP42112A (selective ligands of the AT1 and AT2 angiotensin receptors, respectively) and salarasin (a relatively nonselective angiotensin receptor antagonist) on urinary volume and urinary sodium and potassium excretion induced by administration of angiotensin II (ANG II) into the paraventricular nucleus (PVN) of conscious rats. Both the AT1 and AT2 ligands and salarasin administered in the presence of ANG II elicited a concentration-dependent inhibition of urine excretion, but losartan inhibited only 75% of this response. The IC50 for salarasin, CGP42112A, and losartan was 0.01, 0.05, and 6 nM, respectively. Previous treatment with saralasin, CGP42112A and losartan competitively antagonized the natriuretic responses to PVN administration of ANG II, and the IC50 values were 0.09, 0.48, and 10 nM, respectively. The maximum response to losartan was 65% of that obtained with saralasin. Pretreatment with saralasin, losartan, and CGP42112A injected into the PVN caused shifts to the right of the concentration-response curves, but the losartan concentrations were disproportionately greater compared with salarasin or CGP42112A. The IC50 values were 0.06, 0.5, and 7.0 for salarasin, CGP42112A, and losartan, respectively. These results suggest that both AT1 and AT2 receptor subtypes in the PVN are involved in ANG II-related urine, sodium, and potassium excretion, and that the inhibitory responses to AT2 blockade are predominant. Copyright (C) 1999 Elsevier Science B.V.