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The paraventricular nucleus of the hypothalamus (PVN) regulates physiological and behavioural responses evoked by stressful stimuli, but the local neurochemical and signalling mechanisms involved are not completely understood. The soluble guanylate cyclase (sGC) within the PVN is implicated in autonomic and cardiovascular control in rodents under resting conditions. However, the involvement of PVN sGC-mediated signalling in stress responses is unknown. Therefore, we investigated the role of sGC within the PVN in cardiovascular, autonomic, neuroendocrine, and local neuronal responses to acute restraint stress in rats. Bilateral microinjection of the selective sGC inhibitor ODQ (1 nmol/100 nl) into the PVN reduced both the increased arterial pressure and the drop in cutaneous tail temperature evoked by restraint stress, while the tachycardia was enhanced. Intra-PVN injection of ODQ did not alter the number of Fos-immunoreactive neurons in either the dorsal cap parvocellular (PaDC), ventromedial (PaV), medial parvocellular (PaMP), or lateral magnocelllular (PaLM) portions of the PVN following acute restraint stress. Local microinjection of ODQ into the PVN did not affect the restraint-induced increases in plasma corticosterone concentration. Taken together, these findings suggest that sGC-mediated signalling in the PVN plays a key role in acute stress-induced pressor responses and sympathetically mediated cutaneous vasoconstriction, whereas the tachycardiac response is inhibited. Absence of an effect of ODQ on corticosterone and PVN neuronal activation in and the PaV and PaMP suggests that PVN sGC is not involved in restraint-evoked hypothalamus-pituitary-adrenal (HPA) axis activation and further indicates that autonomic and neuroendocrine responses are dissociable at the level of the PVN., (© 2024 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

A functional lateralization has been reported in control of emotional responses by the medial prefrontal cortex (mPFC). However, a hemisphere asymmetry in involvement of the mPFC in expression of fear conditioning responses has never been reported. Therefore, we investigated whether control by mPFC of freezing and cardiovascular responses during re-exposure to an aversively conditioned context is lateralized. For this, rats had guide cannulas directed to the mPFC implanted bilaterally or unilaterally in the right or left hemispheres. Vehicle or the non-selective synaptic inhibitor CoCl 2 was microinjected into the mPFC 10 min before re-exposure to a chamber where the animals had previously received footshocks. A catheter was implanted into the femoral artery before the fear retrieval test for cardiovascular recordings. We observed that bilateral microinjection of CoCl 2 into the mPFC reduced both the freezing behavior (enhancing locomotion and rearing) and arterial pressure and heart rate increases during re-exposure to the aversively conditioned context. Unilateral microinjection of CoCl 2 into the right hemisphere of the mPFC also decreased the freezing behavior (enhancing locomotion and rearing), but without affecting the cardiovascular changes. Conversely, unilateral synaptic inhibition in the left mPFC did not affect either behavioral or cardiovascular responses during fear retrieval test. Taken together, these results suggest that the right hemisphere of the mPFC is necessary and sufficient for expression of freezing behavior to contextual fear conditioning. However, the control of cardiovascular responses and freezing behavior during fear retrieval test is somehow dissociated in the mPFC, being the former bilaterally processed., Competing Interests: Declaration of competing interest None., (Copyright © 2023. Published by Elsevier Inc.)

Despite the importance of physiological responses to stress in a short-term, chronically these adjustments may be harmful and lead to diseases, including cardiovascular diseases. The lateral hypothalamus (LH) has been reported to be involved in expression of physiological and behavioral responses to stress, but the local neurochemical mechanisms involved are not completely described. The corticotropin-releasing factor (CRF) neurotransmission is a prominent brain neurochemical system implicated in the physiological and behavioral changes induced by aversive threats. Furthermore, chronic exposure to aversive situations affects the CRF neurotransmission in brain regions involved in stress responses. Therefore, in this study, we evaluated the influence of CRF neurotransmission in the LH on changes in cardiovascular function and baroreflex activity induced by chronic variable stress (CVS). We identified that CVS enhanced baseline arterial pressure and impaired baroreflex function, which were followed by increased expression of CRF 2 , but not CRF 1 , receptor expression within the LH. Local microinjection of either CRF 1 or CRF 2 receptor antagonist within the LH inhibited the baroreflex impairment caused by CVS, but without affecting the mild hypertension. Taken together, the findings documented in this study suggest that LH CRF neurotransmission participates in the baroreflex impairment related to chronic stress exposure., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Abstract: We evaluated the participation of the endocannabinoid system in the paraventricular nucleus of the hypothalamus (PVN) on the cardiovascular, autonomic, and plasma vasopressin (AVP) responses evoked by hemorrhagic shock in rats. For this, the PVN was bilaterally treated with either vehicle, the selective cannabinoid receptor type 1 antagonist AM251, the selective fatty acid amide hydrolase amide enzyme inhibitor URB597, the selective monoacylglycerol-lipase enzyme inhibitor JZL184, or the selective transient receptor potential vanilloid type 1 antagonist capsazepine. We evaluated changes on arterial pressure, heart rate, tail skin temperature (ST), and plasma AVP responses induced by bleeding, which started 10 min after PVN treatment. We observed that bilateral microinjection of AM251 into the PVN reduced the hypotension during the hemorrhage and prevented the return of blood pressure to baseline values in the posthemorrhagic period. Inhibition of local 2-arachidonoylglycerol metabolism by PVN treatment with JZL184 induced similar effects in relation to those observed in AM251-treated animals. Inhibition of local anandamide metabolism via PVN treatment with URB597 decreased the depressor effect and ST drop induced by the hemorrhagic stimulus. Bilateral microinjection of capsazepine mitigated the fall in blood pressure and ST. None of the PVN treatments altered the increased plasma concentration of AVP and tachycardia induced by hemorrhage. Taken together, present results suggest that endocannabinoid neurotransmission within the PVN plays a prominent role in cardiovascular and autonomic, but not neuroendocrine, responses evoked by hemorrhage., Competing Interests: The authors report no conflict of interests., (Copyright © 2023 by the Shock Society.)

The insular cortex (IC) is a brain structure involved in physiological and behavioural responses during stressful events. However, the local neurochemical mechanisms involved in control of stress responses by the IC are poorly understood. Thus, this study aimed to investigate the involvement of glutamatergic neurotransmission within the IC in cardiovascular, autonomic and neuroendocrine responses to an acute session of restraint stress. For this, the selective NMDA glutamate receptor antagonist LY235959 (1 nmol/100 nL) or the selective non-NMDA glutamate receptor antagonist NBQX (1 nmol/100 nL) were microinjected into the IC 10 min before the onset of the 60 min session of restraint stress. We observed that the antagonism of NMDA receptors within the IC enhanced the restraint-evoked increase in arterial pressure and heart rate, while blockade of non-NMDA receptors did not affect these cardiovascular responses. Spontaneous baroreflex analysis demonstrated that microinjection of LY235959 into the IC decreased baroreflex activity during restraint stress. The decrease in tail skin temperature during restraint stress was shifted to an increase in animals treated with the NMDA receptor antagonist. Nevertheless, the blockade of either NMDA or non-NMDA glutamate receptors within the IC did not affect the increase in circulating corticosterone levels during restraint stress. Overall, our findings provide evidence that IC glutamatergic neurotransmission, acting via local NMDA receptors, plays a prominent role in the control of autonomic and cardiovascular responses to restraint stress, but without affecting neuroendocrine adjustments., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Previous studies showed a prominent role of the medial prefrontal cortex (mPFC), especially the prelimbic (PL) and infralimbic (IL) subregions, in behavioral and physiological responses to stressful stimuli. Nevertheless, the local neurochemical mechanisms involved are not completely understood. In this sense, previous studies identified cholinergic terminals within the mPFC, and stressful stimuli increased local acetylcholine release. Despite these pieces of evidence, the specific role of cholinergic neurotransmission in different subregions of the mPFC controlling the cardiovascular responses to stress has never been systematically evaluated. Therefore, the purpose of this study was to investigate the involvement of cholinergic neurotransmission present within PL and IL in cardiovascular responses to an acute session of restraint stress in rats. For this, rats received bilateral microinjection of the choline uptake inhibitor hemicholinium-3 before exposure to restraint stress. The arterial pressure and heart rate (HR) increases and the decrease in tail skin temperature as an indirect measurement of sympathetically-mediated cutaneous vasoconstriction were recorded throughout the restraint stress session. The results showed that the depletion of acetylcholine within the PL caused by local microinjection of hemicholinium-3 decreased the tachycardia to restraint stress, but without affecting the pressor response and the drop in tail skin temperature. Conversely, IL treatment with hemicholinium-3 decreased the restraint-evoked pressor response and the sympathetically-mediated cutaneous vasoconstriction without interfering with the HR response. Taken together, these results indicate functional differences of cholinergic neurotransmission within the PL and IL in control of cardiovascular and autonomic responses to stressful stimuli., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Here, we report the participation of N-methyl-D-aspartate (NMDA) glutamate receptor in the mediation of cardiovascular and circulating vasopressin responses evoked by a hemorrhagic stimulus. In addition, once NMDA receptor activation is a prominent mechanism involved in nitric oxide (NO) synthesis in the brain, we investigated whether control of hemorrhagic shock by NMDA glutamate receptor was followed by changes in NO synthesis in brain supramedullary structures involved in cardiovascular and neuroendocrine control. Thus, we observed that intraperitoneal administration of the selective NMDA glutamate receptor antagonist dizocilpine maleate (MK801, 0.3 mg/kg) delayed and reduced the magnitude of hemorrhage-induced hypotension. Besides, hemorrhage induced a tachycardia response in the posthemorrhage period (i.e., recovery period) in control animals, and systemic treatment with MK801 caused a bradycardia response during hemorrhagic shock. Hemorrhagic stimulus increased plasma vasopressin levels during the recovery period and NMDA receptor antagonism increased concentration of this hormone during both the hemorrhage and postbleeding periods in relation to control animals. Moreover, hemorrhagic shock caused a decrease in NOx levels in the paraventricular nucleus of the hypothalamus (PVN), amygdala, bed nucleus of the stria terminalis (BNST), and ventral periaqueductal gray matter (vPAG). Nevertheless, treatment with MK801 did not affect these effects. Taken together, these results indicate that the NMDA glutamate receptor is involved in the hemorrhagic shock by inhibiting circulating vasopressin release. Our data also suggest a role of the NMDA receptor in tachycardia, but not in the decreased NO synthesis in the brain evoked by hemorrhage., Competing Interests: The authors declare that there is no conflict of interest regarding the publication of this article., (Copyright © 2021 Cristiane Busnardo et al.)

Both the autonomic nervous system and the neuroendocrine system are activated by osmotic stimulation (OS) evoking cardiovascular effects. The current study investigated the mechanisms involved in the cardiovascular responses evoked by an acute osmotic stimulus with intraperitoneal (i.p.) injection of either isotonic (0.15 M NaCl) or hypertonic saline (0.6 M NaCl) in conscious rats. Hypertonic saline increased mean arterial pressure (MAP) and heart rate (HR) for 30 min, as well as plasma osmolality and sodium content. Urinary sodium and urinary volume were also increased. Pretreatment with the ganglion blocker pentolinium (i.v.) did not affect the pressor response, but significantly decreased the tachycardic response caused by OS. Pretreatment with the V 1 -vasopressin receptor antagonist dTyr(CH 2 ) 5 (Me)AVP (i.v.) reduced the pressor response, without affecting the tachycardic response evoked by the hypertonic OS. Neither the pressor nor the tachycardic response to OS was affected by pretreatment with either the oxytocin receptor antagonist atosiban or the α1-antagonist prazosin. Pretreatment with the β1-antagonist atenolol had no effect on the pressor response, but markedly decreased the tachycardic response evoked by OS. Results indicate that i.p. hypertonic OS-evoked pressor response is mediated by the release of vasopressin, with a minor influence of the vascular sympathetic input.LAY SUMMARYIncreased plasma osmolality, such as that observed during dehydration or salt intake, is a potent stimulus yielding to marked cardiovascular and neuroendocrine responses. The intraperitoneal (i.p.) injection of hypertonic saline solution is a commonly used animal model to cause a sustained increase in plasma osmolality, leading to a cardiovascular response characterized by sustained blood pressure and heart increases, whose systemic mechanisms were presently studied. Our findings indicate that the pressor response to the i.p. osmotic stimulus (OS) is mediated mainly by the release of vasopressin into the blood circulation with a minor or even the noninvolvement of the vascular sympathetic nervous system, whereas activation of the sympathetic-cardiac system mediates the tachycardic response to OS.

Aims: Acute restraint stress (RS) has been reported to cause neuronal activation in the supraoptic nucleus of the hypothalamus (SON). The aim of the study was to evaluate the role of SON on autonomic (mean arterial pressure [MAP], heart rate [HR], and tail temperature), neuroendocrine (corticosterone, oxytocin, and vasopressin plasma levels), and behavioral responses to RS., Methods: Guide cannulas were implanted bilaterally in the SON of male Wistar rats for microinjection of the unspecific synaptic blocker cobalt chloride (CoCl2, 1 mM) or vehicle (artificial cerebrospinal fluid, 100 nL). A catheter was introduced into the femoral artery for MAP and HR recording. Rats were subjected to RS, and it was studied the effect of microinjection of CoCl2 or vehicle into the SON on pressor and tachycardic responses, drop in tail temperature, plasma oxytocin, vasopressin, and corticosterone levels, and anxiogenic-like effect induced by RS., Results: SON pretreatment with CoCl2 reduced the RS-induced MAP and HR increase, without affecting the RS-evoked tail temperature decrease. Microinjection of CoCl2 into areas surrounding the SON did not affect RS-induced increase in MAP and HR, reinforcing the idea that SON influences RS-evoked cardiovascular responses. Also, SON pretreatment with CoCl2 reduced RS-induced increase in corticosterone and oxytocin, without affecting vasopressin plasma levels, suggesting its involvement in RS-induced neuroendocrine responses. Finally, the CoCl2 microinjection into SON inhibited the RS-caused delayed anxiogenic-like effect., Conclusion: The results indicate that SON is an important component of the neural pathway that controls autonomic, neuroendocrine, and behavioral responses induced by RS., (© 2019 S. Karger AG, Basel.)

We investigated the involvement of nitrergic neurotransmission within the paraventricular nucleus of the hypothalamus (PVN) in modulation of local neuronal activation, autonomic and neuroendocrine responses and behavioral consequences of acute restraint stress in rats. Bilateral microinjections of the selective neuronal nitric oxide (NO) synthase (nNOS) inhibitor N w -Propyl-L-arginine (NPLA) or the NO scavenger carboxy-PTIO into the PVN reduced arterial pressure and heart rate increases, as well as the fall in cutaneous tail temperature induced by restraint stress. PVN injection of either NPLA or carboxy-PTIO also inhibited restraint-induced increases in anxiety-related behaviors in the elevated plus-maze 24 h later. Local microinjection of NPLA or carboxy-PTIO into the PVN reduced the number of c-fos-immunoreactive neurons in the dorsal parvocellular, ventromedial, medial parvocellular and lateral magnocelllular portions of the PVN in animals subjected to restraint stress. However, neither NPLA nor carboxy-PTIO into the PVN affected restraint-induced increases in plasma corticosterone concentration. The present results indicate that PVN nitrergic neurotransmission acting via nNOS activation has a facilitatory influence on autonomic responses to acute restraint and the delayed emotional consequences of restraint stress. Our results also provide evidence of a prominent role of local nitrergic neurotransmission in PVN neuronal activation during stress., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Previously, we reported that microinjection of L-proline (L-Pro) into the paraventricular nucleus of the hypothalamus (PVN) caused vasopressin-mediated pressor responses in unanesthetized rats. In the present study, we report on the central mechanisms involved in the mediation of the cardiovascular effects caused by the microinjection of L-Pro into the PVN. Microinjection of increasing doses of L-Pro (3-100nmol/100nL) into the PVN caused dose-related pressor and bradycardic responses. No cardiovascular responses were observed after the microinjection of equimolar doses (33nmol/100nL) of its isomer D-Proline (D-Pro) or Mannitol. The PVN pretreatment with either a selective non-NMDA (NBQX) or selective NMDA (LY235959 or DL-AP7) glutamate receptor antagonists blocked the cardiovascular response to L-Pro (33nmol/100nL). The dose-effect curve for the pretreatment with increasing doses of LY235959 was located at the left in relation to the curves for NBQX and DL-AP7, showing that LY235959 is more potent than NBQX, which is more potent than DL-AP7 in inhibiting the cardiovascular response to L-Pro. The cardiovascular response to the microinjection of L-Pro into the PVN was not affected by local pretreatment with N ω -Propyl-l-arginine (N-Propyl), a selective inhibitor of the neuronal nitric oxide synthase (nNOS), suggesting that NO does not mediate the responses to L-Pro in the PVN. In conclusion, the results suggest that ionotropic receptors in the PVN, blocked by both NMDA and non-NMDA receptor antagonists, mediate the pressor response to L-Pro that results from activation of PVN vasopressinergic magnocellular neurons and vasopressin release into the systemic circulation., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The bed nucleus of the stria terminalis (BNST) is a forebrain structure implicated in physiological and behavioral responses to emotional stress. However, the local neurochemical mechanisms mediating the BNST control of stress responses are not fully known. Here, we investigated the involvement of BNST cholinergic neurotransmission, acting via muscarinic receptors, in cardiovascular (increase in blood pressure and heart rate and fall in tail skin temperature) and neuroendocrine (increase in plasma corticosterone) responses and behavioral consequences (anxiogenic-like effect in the elevated plus-maze) evoked by acute restraint stress in rats. Bilateral microinjection into the BNST of either the choline uptake inhibitor hemicholinium-3 (3 nmol/100 nl) or the muscarinic receptor antagonist methylatropine (3 nmol/100 nl) enhanced the heart rate increase and inhibited the anxiogenic-like effect observed in the elevated plus-maze evoked by restraint. However, neither hemicholinium-3 nor methylatropine affected the increase in blood pressure and plasma corticosterone levels and the fall in tail skin temperature. Facilitation of local cholinergic signaling by microinjection of the acetylcholinesterase inhibitor neostigmine (0.1 nmol/100 nl) into the BNST reduced restraint-evoked pressor and tachycardiac responses and the fall in tail cutaneous temperature, without affecting the increase in plasma corticosterone. All effects of neostigmine were completely abolished by local BNST pretreatment with methylatropine. These findings indicate an opposite role of BNST cholinergic neurotransmission, acting via local muscarinic receptor, in control of cardiovascular responses (inhibitory influence) and emotional consequences (facilitatory influence) evoked by restraint stress. Furthermore, present findings provide evidence that BNST control of neuroendocrine responses to stress is mediated by mechanisms others than local cholinergic signaling., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The dorsal periaqueductal gray area (dPAG) is involved in cardiovascular modulation. In a previous study, we showed that noradrenaline (NA) microinjected into the dPAG caused a vasopressin-mediated pressor response, involving a relay in the hypothalamic paraventricular nucleus (PVN). In the present study, we evaluated the involvement of ionotropic glutamate receptors within the PVN in the cardiovascular response to NA microinjection into the dPAG of unanesthetized rats. Microinjection of the selective NMDA glutamate receptor antagonist LY235959 (2nmol/100nL) unilaterally into the PVN did not affect the cardiovascular response evoked by microinjection of NA (15nmol/50nL) into the dPAG. On the other hand, unilateral PVN pretreatment with the non-NMDA glutamate receptor antagonist NBQX (2nmol/100nL) significantly reduced the pressor and cardiac response caused by microinjection of NA into the dPAG. In addition, bilateral PVN pretreatment with NBQX (2nmol/100nL) blocked the cardiovascular response to NA injected into the dPAG. In conclusion, the present results suggest that bilateral PVN activation of non-NMDA glutamate receptors mediates the vasopressin-related cardiovascular response to the microinjection of NA into the dPAG., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In the present study, the involvement of paraventricular nucleus of the hypothalamus (PVN) glutamate receptors in the modulation of autonomic (arterial blood pressure, heart rate and tail skin temperature) and neuroendocrine (plasma corticosterone) responses and behavioral consequences evoked by the acute restraint stress in rats was investigated. The bilateral microinjection of the selective non-NMDA glutamate receptor antagonist NBQX (2 nmol/ 100 nL) into the PVN reduced the arterial pressure increase as well as the fall in the tail cutaneous temperature induced by the restraint stress, without affecting the stress-induced tachycardiac response. On the other hand, the pretreatment of the PVN with the selective NMDA glutamate receptor antagonist LY235959 (2 nmol/100 nL) was able to increase the stress-evoked pressor and tachycardiac response, without affecting the fall in the cutaneous tail temperature. The treatment of the PVN with LY235959 also reduced the increase in plasma corticosterone levels during stress and inhibited the anxiogenic-like effect observed in the elevated plus-maze 24h after the restraint session. The present results show that NMDA and non-NMDA receptors in the PVN differently modulate responses associated to stress. The PVN glutamate neurotransmission, via non-NMDA receptors, has a facilitatory influence on stress-evoked autonomic responses. On the other hand, the present data point to an inhibitory role of PVN NMDA receptors on the cardiovascular responses to stress. Moreover, our findings also indicate an involvement of PVN NMDA glutamate receptors in the mediation of the plasma corticosterone response as well as in the delayed emotional consequences induced by the restraint stress., (Copyright © 2012 Elsevier B.V. and ECNP. All rights reserved.)

The hippocampus is a limbic structure that is involved in the expression of defensive reactions and autonomic changes in rats. The injection of L-glutamate (L-glu) into the ventral hippocampus (VH) decreases blood pressure and heart rate in anesthetized rats. Activation of NMDA receptors in the VH increases the production of nitric oxide (NO), leading to guanylate cyclase activation. The hypothesis of the present study was that a local NMDA receptor-NO-guanylate cyclase interaction mediates the cardiovascular effects of microinjection of L-glu into the VH. Microinjection of increasing doses of L-glu (30, 60 and 200 nmol/200 nL) into the VH of conscious rats caused dose-related pressor and tachycardiac responses. The cardiovascular effects of L-glu were abolished by local pretreatment with: the glutamate receptor antagonist AP-7 (0.4 nmol); the selective neuronal NO synthase (nNOS) inhibitor N(ω)-Propyl-L-arginine (0.04 nmol); the NO scavenger C-PTIO (2 nmol) or the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (2 nmol). Moreover, these cardiovascular responses were blocked by intravenous pretreatment with: the ganglionic blocker mecamylamine (2mg/Kg); the nonselective β-adrenergic receptor antagonist propranolol (2mg/Kg); the β1-adrenergic receptor selective antagonist atenolol (1mg/kg). However, pretreatment with the selective α1-adrenergic receptor antagonist prazosin (0,5mg/kg) caused only a small reduction in the pressor response, without affecting the L-glu evoked tachycardia. In conclusion, our results suggest that cardiovascular responses caused by L-glu microinjection into the VH are mediated by NMDA glutamate receptors and involve local nNOS and guanylate cyclase activation. Moreover, these cardiovascular responses are mainly mediated by cardiac sympathetic nervous system activation, with a small involvement of the vascular sympathetic nervous system., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In the present study, we report on the cardiovascular effects caused by the microinjection of L-proline (L-Pro) into the supraoptic nucleus (SON) in unanesthetized rats: the possible involvement of ionotropic glutamate receptors in the SON, as well as the peripheral mechanisms involved in the mediation of its cardiovascular effects. We compared the L-Pro effects with those caused by the injection of L-glutamate (L-Glu) into the SON. Microinjection of increasing doses of L-Pro into the SON caused dose-related cardiovascular responses in unanesthetized rats that were similar to those observed after the injection of L-Glu. Pretreatment of the SON with either a selective non-NMDA (NBQX) or a selective NMDA (LY235959) glutamate receptor antagonist blocked the cardiovascular response to L-Pro. The dose-effect curve for the pretreatment with increasing doses of LY235959 was shifted to the left in relation to the curve for NBQX, showing that LY235959 is more potent than NBQX in inhibiting the cardiovascular response to L-Pro. On the other hand, the cardiovascular response to L-Glu was only significantly reduced by pretreatment with NBQX (2 nmol/100 nL), but not affected by LY235959 (2 nmol/100 nL). The pressor response to L-Pro was not affected by intravenous pretreatment with the ganglion blocker pentolinium, but it was blocked by intravenous pretreatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP. In conclusion, these results suggest that L-Pro has a selective receptor that is sensitive to ionotropic glutamate receptor antagonists. Its activation in the SON results in vasopressin release into the systemic circulation, causing pressor and bradycardiac responses.

We hypothesize that a local ATP-NO-NMDA glutamate receptor interaction in the paraventricular nucleus (PVN) modulates the baseline mean arterial pressure and heart rate in unanaesthetized rats. The microinjection of α,β-methylene ATP [methyl ATP; 0.06, 0.12 and 1.2 nmol (100 nl)(-1)] into the PVN caused pressor and tachycardiac responses. Cardiovascular responses evoked by methyl ATP [0.12 nmol (100 nl)(-1)] in the PVN were blocked by pretreatment with the ganglion blocker pentolinium (5 mg kg(-1) i.v.). Also, responses to the injection of methyl ATP [0.12 nmol (100 nl)(-1)] into the PVN were reduced by pretreatment with the selective P2 purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid [0.5 nmol (100 nl)(-1)], the neuronal NO synthase inhibitor N(ω)-propyl-l-arginine [0.04 nmol (100 nl)(-1)] or the selective NMDA glutamate receptor antagonist LY235959 [2 nmol (100 nl)(-1)]. In addition, an injection of the NO donor sodium nitroprusside [27 nmol (100 nl)(-1)] into the PVN caused similar cardiovascular responses to those observed after methyl ATP, which were blocked by local pretreatment with LY235959. Therefore, the present results suggest that cardiovascular responses evoked by methyl ATP in the PVN involve a local production of NO, which promotes local glutamate release and activation of NMDA receptors that are probably located in pre-autonomic parvocellular neurons, leading to sympathetic nervous system stimulation.

We investigated the cardiovascular effects of the microinjection of L-proline (L-Pro) into the third ventricle (3V) and its peripheral mechanisms. Different doses of L-Pro into the 3V caused dose-related pressor and bradycardiac responses. The pressor response to L-Pro injected into the 3V was potentiated by intravenous pretreatment with the ganglion blocker pentolinium (5 mg/kg), thus excluding any significant involvement of the sympathetic nervous system. Because the response to the microinjection of L-Pro into the 3V was blocked by intravenous pretreatment with the V1-vasopressin receptor antagonist dTyr(CH(2) )(5) (Me)AVP (50μg/kg), it is suggested that these cardiovascular responses are mediated by a vasopressin release. The pressor response to the microinjection of L-Pro into the 3V was found to be mediated by circulating vasopressin, so, given that the paraventricular nucleus of the hypothalamus (PVN) is readily accessible from the 3V, we investigated whether the PVN could be a site of action for the L-Pro microinjected in the 3V. The microinjection of L-Pro (0.033 μmoles/0.1 μl) into the PVN caused cardiovascular responses similar to those of injection of the 3V and were also shown to be mediated by vasopressin release. In conclusion, these results show that the microinjection of L-Pro into the 3V causes pressor and bradycardiac responses that could involve stimulation of the magnocellular cells of the PVN and release of vasopressin into the systemic circulation. Also, because the microinjection of L-Pro into the PVN caused a pressor response, this is the first evidence of cardiovascular effects caused by its injection in a supramedullary structure., (Copyright © 2012 Wiley Periodicals, Inc.)

The periaqueductal gray area (PAG) is a mesencephalic area involved in cardiovascular modulation. Glutamate (L-Glu) is an abundant excitatory amino acid in the central nervous system (CNS) and is present in the rat PAG. Moreover, data in the literature indicate its involvement in central blood pressure control. Here we report on the cardiovascular effects caused by microinjection of L-Glu into the dorsomedial PAG (dmPAG) of rats and the glutamatergic receptors as well as the peripheral mechanism involved in their mediation. The microinjection of L-Glu into the dmPAG of unanesthetized rats evoked dose-related pressor and bradycardiac responses. The cardiovascular response was significantly reduced by pretreatment of the dmPAG with a glutamatergic M-methyl-D-aspartate (NMDA) receptor antagonist (LY235959) and was not affected by pretreatment with a non-NMDA receptor antagonist (NBQX), suggesting a mediation of that response by the activation of NMDA receptors. Furthermore, the pressor response was blocked by pretreatment with the ganglion blocker pentolinium (5 mg/kg, intravenously), suggesting an involvement of the sympathetic nervous system in this response. Our results indicate that the microinjection of L-Glu into the dmPAG causes sympathetic-mediated pressor responses in unanesthetized rats, which are mediated by glutamatergic NMDA receptors in the dmPAG., (Copyright © 2012 Wiley Periodicals, Inc.)

We report changes in plasma arginine vasopressin (AVP) and oxytocin (OT) concentrations evoked by the microinjection of l-glutamate (l-glu) into the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus (PVN) of unanesthetized rats, as well as which local mechanisms are involved in their mediation. l-Glu microinjection (10 nmol/100 nl) into the SON increased the circulating levels of both AVP and OT. The AVP increases were blocked by local pretreatment with the selective non-N-methyl-d-aspartate (NMDA) receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX) (2 nmol/100 nl), but it was not affected by pretreatment with the NMDA-receptor antagonist LY235959 (2 nmol/100 nl). The OT response to l-glu microinjection into the SON was blocked by local pretreatment with either NBQX or LY235959. Furthermore, the administration of either the non-NMDA receptor agonist (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) (5 nmol/100 nl) or NMDA receptor agonist NMDA (5 nmol/100 nl) into the SON had no effect on OT baseline plasma levels, but when both agonists were microinjected together these levels were increased. l-Glu microinjection into the PVN did not change circulating levels of either AVP or OT. However, after local pretreatment with LY235959, the l-glu microinjection increased plasma levels of the hormones. The l-glu microinjection into the PVN after the local treatment with NBQX did not affect the circulating AVP and OT levels. Therefore, results suggest the AVP release from the SON is mediated by activation of non-NMDA glutamate receptors, whereas the OT release from this nucleus is mediated by an interaction of NMDA and non-NMDA receptors. The present study also suggests an inhibitory role for NMDA receptors in the PVN on the release of AVP and OT.

Microinjection of the cholinergic agonist carbachol into the bed nucleus of the stria terminalis (BST) has been reported to cause pressor response in unanesthetized rats, which was shown to be mediated by an acute release of vasopressin into the systemic circulation and followed by baroreflex-mediated bradycardia. In the present study, we tested the possible involvement of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei in the pressor response evoked by carbachol microinjection into the BST of unanesthetized rats. For this, cardiovascular responses following carbachol (1 nmol/100 nL) microinjection into the BST were studied before and after PVN or SON pretreatment, either ipsilateral or contralateral in relation to BST microinjection site, with the nonselective neurotransmission blocker cobalt chloride (CoCl₂, 1 mM/100 nL). Carbachol microinjection into the BST evoked pressor response. Moreover, BST treatment with carbachol significantly increased plasma vasopressin levels, thus confirming previous evidences that carbachol microinjection into the BST evokes pressor response due to vasopressin release into the circulation. SON pretreatment with CoCl₂, either ipsilateral or contralateral in relation to BST microinjection site, inhibited the pressor response to carbachol microinjection into the BST. However, CoCl₂ microinjection into the ipsilateral or contralateral PVN did not affect carbachol-evoked pressor response. In conclusion, our results suggest that pressor response to carbachol microinjection into the BST is mediated by SON magnocellular neurons, without significant involvement of those in the PVN. The results also indicate that responses to carbachol microinjection into the BST are mediated by a neural pathway that depends on the activation of both ipsilateral and contralateral SON., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In the present study, we describe the cardiovascular effects of local acetylcholine (Ach) microinjection into both the ventrolateral (vlPAG) and dorsal (dPAG) periaqueductal gray areas of anesthetized rats and the possible local receptors involved with these responses. Microinjection of Ach (9, 27, 45 or 81 nmol/50 nL) into the vlPAG caused dose-related depressor responses. These hypotensive responses were blocked by local pretreatment with increasing doses of the nonselective muscarinic antagonist atropine (1, 3 or 9 nmol/50 nL)(.) The microinjection of Ach into the dPAG caused no significant cardiovascular responses in anesthetized rats. In conclusion, the present findings suggest that a cholinergic system present in the vlPAG, but not in the dPAG, is involved with cardiovascular system control. Moreover, these cardiovascular responses evoked by Ach are mediated by muscarinic receptors., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Objective: The objective of this study was to evaluate the involvement of peripheral nitric oxide (NO) in vagotomy-induced pulmonary edema by verifying whether the nitric oxide synthases (NOS), constitutive (cNOS) and inducible (iNOS), participate in this mechanism., Introduction: It has been proposed that vagotomy induces neurogenic pulmonary edema or intensifies the edema of other etiologies., Methods: Control and vagotomized rats were pretreated with 0.3 mg/kg, 3.0 mg/kg or 39.0 mg/kg of L-NAME, or with 5.0 mg/kg, 10.0 mg/kg or 20.0 mg/kg of aminoguanidine. All animals were observed for 120 minutes. After the animals' death, the trachea was catheterized in order to observe tracheal fluid and to classify the severity of pulmonary edema. The lungs were removed and weighed to evaluate pulmonary weight gain and edema index., Results: Vagotomy promoted pulmonary edema as edema was significantly higher than in the control. This effect was modified by treatment with L-NAME. The highest dose, 39.0 mg/kg, reduced the edema and prolonged the survival of the animals, while at the lowest dose, 0.3 mg/kg, the edema and reduced survival rates were maintained. Aminoguanidine, regardless of the dose inhibited the development of the edema. Its effect was similar to that observed when the highest dose of L-NAME was administered. It may be that the non-selective blockade of cNOS by the highest dose of L-NAME also inhibited the iNOS pathway., Conclusion: Our data suggest that iNOS could be directly involved in pulmonary edema induced by vagotomy and cNOS appears to participate as a protector mechanism.

The paraventricular nucleus of the hypothalamus (PVN) has been implicated in several aspects of neuroendocrine and cardiovascular control. The PVN contains parvocellular neurons that release the corticotrophin release hormone (CRH) under stress situations. In addition, this brain area is connected to several limbic structures implicated in defensive behavioral control, as well to forebrain and brainstem structures involved in cardiovascular control. Acute restraint is an unavoidable stress situation that evokes corticosterone release as well as marked autonomic changes, the latter characterized by elevated mean arterial pressure (MAP), intense heart rate (HR) increases and decrease in the tail temperature. We report the effect of PVN inhibition on MAP and HR responses, corticosterone plasma levels and tail temperature response during acute restraint in rats. Bilateral microinjection of the nonspecific synaptic blocker CoCl(2) (1 mM/100 nL) into the PVN reduced the pressor response; it inhibited the increase in plasma corticosterone concentration as well as the fall in tail temperature associated with acute restraint stress. Moreover, bilateral microinjection of CoCl(2) into areas surrounding the PVN did not affect the blood pressure, hormonal and tail vasoconstriction responses to restraint stress. The present results show that a local PVN neurotransmission is involved in the neural pathway that controls autonomic and neuroendocrine responses, which are associated with the exposure to acute restraint stress., (Copyright © 2010 Elsevier B.V. All rights reserved.)

In the present study, we investigated the role played by the hypothalamic paraventricular nucleus (PVN) in the modulation of cardiac baroreflex activity in unanesthetized rats. Bilateral microinjections of the nonselective neurotransmission blocker CoCl(2) into the PVN decreased the reflex bradycardic response evoked by blood pressure increases, but had no effect on reflex tachycardia evoked by blood pressure decreases. Bilateral microinjections of the selective NMDA glutamate receptor antagonist LY235959 into the PVN caused effects that were similar to those observed after microinjections of CoCl(2), decreasing reflex bradycardia without affecting tachycardic response. The microinjection of the selective non-NMDA glutamate receptor antagonist NBQX into the PVN did not affect the baroreflex activity. Also, the microinjection of L-glutamate into the PVN increased the reflex bradycardia, an effect opposed to that observed after PVN treatment with CoCl(2) or LY235959, and this effect of L-glutamate was blocked by PVN pretreatment with LY235959. LY235959 injected into the PVN after i.v. treatment with the selective beta(1)-adrenoceptor antagonist atenolol still decreased the reflex bradycardia. Taken together, our results suggest a facilitatory influence of the PVN on the bradycardic response of the baroreflex through activation of local NMDA glutamate receptors and a modulation of the cardiac parasympathetic activity., (Copyright 2010 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

It has been reported that L-glutamate (L-glu) microinjection into the hypothalamic paraventricular nucleus (PVN) evokes pressor and tachycardiac responses in unanesthetized rats. In the present study the hypothesis was tested that a local nitric oxide (NO)-guanylate cyclase interaction mediates cardiovascular effects of L-glu microinjection into the PVN of rats. The cardiovascular responses evoked by 10 nmol/100 nL of L-glu microinjected into the PVN were measured before and 10 min after PVN treatment with vehicle, the selective neuronal NO-synthase (nNOS) inhibitor N(omega)-Propyl-L-arginine (N-Propyl, 0.04 nmol or 4 nmol/100 nL), the NO scavenger carboxy-PTIO (C-PTIO, 1 nmol/100 nL) or the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL). In a final experiment, different doses of the NO donor sodium nitroprusside (SNP; 9, 27 or 45 nmol/100 nL) were microinjected into the PVN. Cardiovascular responses evoked by L-glu microinjection into the PVN were abolished by local pretreatment with N-Propyl in both anesthetized and unanesthetized rats. PVN treatment with either C-PTIO or ODQ also reduced L-glu cardiovascular responses. The microinjection of SNP into the PVN caused pressor and tachycardiac responses in unanesthetized rats, whereas depressor and bradycardiac responses were observed in anesthetized rats. The present results suggest that cardiovascular responses evoked by L-glu microinjection into the PVN involve a local production of NO and activation of guanylate cyclase., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

The dorsal periaqueductal gray area (dPAG) is involved in cardiovascular modulation. In a previous study, we reported that noradrenaline (NA) microinjection into the dPAG of rats caused pressor response that was mediated by vasopressin release. Vasopressin is synthesized by magnocellular neurons in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. In the present study, we verified which nuclei mediated the cardiovascular response to NA as well as the existence of direct neural projection from the dPAG to hypothalamic nuclei. Then, we studied the effect of treating either PVN or SON with the nonselective synaptic blocker cobalt chloride (1mM) on the cardiovascular response to NA (15 nmol) microinjection into dPAG. Attempting to identify neural projections from dPAG to hypothalamic nuclei, we microinjected the neuronal tracer biotinylated-dextran-amine (BDA) into the dPAG and searched varicosity-containing nerve terminals in the PVN and SON. Unilateral cobalt-induced inhibition of synapses in the SON did not affect the cardiovascular response to NA. However, unilateral inhibition of PVN significantly reduced the pressor response to NA. Moreover, cobalt-induced inhibition of synapses in both PVN blocked the pressor response caused by NA microinjected into the dPAG. Microinjection of BDA into the dPAG evidenced presence of varicosity-containing neuronal fibers in PVN but not in SON. The results from cobalt treatment indicated that synapses in PVN mediate the vasopressin-induced pressor response caused by NA microinjection into the dPAG. In addition, the neuroanatomical results from BDA microinjection into the dPAG pointed out the existence of direct neural projections from the dPAG site to the PVN.

We report on the cardiovascular effects of L-glutamate (L-glu) microinjection into the hypothalamic paraventricular nucleus (PVN) as well as the mechanisms involved in their mediation. L-glu microinjection into the PVN caused dose-related pressor and tachycardiac responses in unanesthetized rats. These responses were blocked by intravenous (i.v.) pretreatment with the ganglion blocker pentolinium (PE; 5 mg/kg), suggesting sympathetic mediation. Responses to L-glu were not affected by local microinjection of the selective non-NMDA receptor antagonist NBQX (2 nmol) or by local microinjection of the selective NMDA receptor antagonist LY235959 (LY; 2 nmol). However, the tachycardiac response was changed to a bradycardiac response after treatment with LY235959, suggesting that NMDA receptors are involved in the L-glu heart rate response. Local pretreatment with LY235959 associated with systemic PE or dTyr(CH(2))(5)(Me)AVP (50 microg/kg) respectively potentiated or blocked the response to L-glu, suggesting that L-glu responses observed after LY235959 are vasopressin mediated. The increased pressor and bradycardiac responses observed after LY + PE was blocked by subsequent i.v. treatment with the V(1)-vasopressin receptor antagonist dTyr(CH(2))(5)(Me)AVP, suggesting vasopressin mediation. The pressor and bradycardiac response to L-glu microinjection into the PVN observed in animals pretreated with LY + PE was progressively inhibited and even blocked by additional pretreatment with increasing doses of NBQX (2, 10, and 20 nmol) microinjected into the PVN, suggesting its mediation by local non-NMDA receptors. In conclusion, results suggest the existence of two glutamatergic pressor pathways in the PVN: one sympathetic pathway that is mediated by NMDA receptors and a vasopressinergic pathway that is mediated by non-NMDA receptors., ((c) 2009 Wiley-Liss, Inc.)

Microinjection of noradrenaline into the bed nucleus of the stria terminalis (BST) has been reported to cause a pressor response in unanesthetized rats, which was shown to be mediated by acute vasopressin release into the systemic circulation. In the present study we verified the involvement of magnocellular neurons of the hypothalamic paraventricular (PVN) or supraoptic (SON) nuclei and the local neurotransmitter involved in the pressor response to noradrenaline microinjection into the BST. The PVN pretreatment with the non-selective neurotransmission blocker CoCl2 (1 nmol/100 nL) inhibited the noradrenaline-evoked pressor response. However, responses were not affected by SON treatment with CoCl2. Further experiments were carried out to test if glutamatergic neurotransmission in the PVN mediates the pressor response evoked by noradrenaline microinjection into the BST. Pretreatment of the PVN with the selective N-methyl-d-aspartate (NMDA) receptor antagonist LY235959 (2 nmol/100 nL) did not affect the noradrenaline-evoked pressor response. However, PVN pretreatment with the selective non-NMDA receptor antagonist NBQX (2 nmol/100 nL) significantly reduced the pressor response to noradrenaline microinjection into the BST. In conclusion, our results suggest that pressor responses to noradrenaline microinjection into the BST are mediated by PVN magnocellular neurons without involvement of SON neurons. They also suggest that a glutamatergic neurotransmission through non-NMDA glutamate receptors in the PVN mediates the response.

We report on the cardiovascular effects of noradrenaline (NA) microinjection into the hypothalamic supraoptic nucleus (SON) as well as the central and peripheral mechanisms involved in their mediation. Microinjections of NA 1, 3, 10, 30 or 45 nmol/100 nL into the SON caused dose-related pressor and bradycardiac response in unanesthetized rats. The response to NA 10 nmol was blocked by SON pretreatment with 15 nmol of the alpha(2)-adrenoceptor antagonist RX821002 and not affected by pretreatment with equimolar dose of the selective alpha(1)-adrenoceptor antagonist WB4101, suggesting that local alpha(2)-adrenoceptors mediate these responses. Pretreatment of the SON with the nonselective beta-adrenoceptor antagonist propranolol 15 nmol did not affect the pressor response to NA microinjection of into the SON. Moreover, the microinjection of the 100 nmol of the selective alpha(1)-adrenoceptor agonist methoxamine (MET) into the SON did not cause cardiovascular response while the microinjection of the selective alpha(2)-adrenoceptor agonists BHT920 (BHT, 100 nmol) or clonidine (CLO, 5 nmol) caused pressor and bradycardiac responses, similar to that observed after the microinjection of NA. The pressor response to NA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium and was blocked by intravenous pretreatment with the V(1)-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP, suggesting an involvement of circulating vasopressin in this response. In conclusion, our results suggest that pressor responses caused by microinjections of NA into the SON involve activation of local alpha(2)-adrenoceptor receptors and are mediated by vasopressin release into circulation.

The lateral septal area (LSA) is a part of the limbic system and is involved in cardiovascular modulation. We previously reported that microinjection of noradrenaline (NA) into the LSA of unanesthetized rats caused pressor responses that are mediated by acute vasopressin release. Magnocellular neurons of the paraventricular (PVN) and supraoptic (SON) of the hypothalamus synthesize vasopressin. In the present work, we studied which of these nuclei is involved in the pressor pathway activated by unilateral NA injection into the LSA as well as the local neurotransmitter involved. Chemical ablation of the SON by unilateral injection of the nonspecific synapses blocker cobalt chloride (1 mM/100 nl) did not affect the pressor response evoked by NA (21 nmol/200 nl) microinjection into the LSA. However, the response to NA was blocked when cobalt chloride (1 mM/100 nl) was microinjected into the PVN, indicating that this hypothalamic nucleus is responsible for the mediation of the pressor response. There is evidence in the literature pointing to glutamate as a putative neurotransmitter activating magnocellular neurons. Pretreatment of the PVN with the selective non-N-methyl-D-asparate (NMDA) antagonist NBQX (2 nmol/100 nl) blocked the pressor response to NA microinjected into the LSA, whereas pretreatment with the selective NMDA antagonist LY235959 (2 nmol/100 nl) did not affect the response to NA. Our results implicate the PVN as the final structure in the pressor pathway activated by the microinjection of NA into the LSA. They also indicate that local glutamatergic synapses and non-NMDA glutamatergic receptors mediate the response in the PVN., ((c) 2008 Wiley-Liss, Inc.)