Cardiovascular effects of l-glutamate microinjection in the supraoptic nucleus of unanaesthetized rats

Chronic social defeat alters behaviors and neuronal activation in the brain of female Mongolian gerbils

Chronic social defeat has been found to be stressful and to affect many aspects of the brain and behaviors in males. However, relatively little is known about its effects on females. In the present study, we examined the effects of repeated social defeat on social approach and anxiety-like behaviors as well as the neuronal activation in the brain of sexually naïve female Mongolian gerbils (Meriones unguiculatus). Our data indicate that repeated social defeats for 20 days reduced social approach and social investigation, but increased risk assessment or vigilance to an unfamiliar conspecific. Such social defeat experience also increased anxiety-like behavior and reduced locomotor activity. Using ΔFosB-immunoreactive (ΔFosB-ir) staining as a marker of neuronal activation in the brain, we found significant elevations by social defeat experience in the density of ΔFosB-ir stained neurons in several brain regions, including the prelimbic (PL) and infralimbic (IL) subnuclei of the prefrontal cortex (PFC), CA1 subfields (CA1) of the hippocampus, central subnuclei of the amygdala (CeA), the paraventricular nucleus (PVN), dorsomedial nucleus (DMH), and ventrolateral subdivision of the ventromedial nucleus (VMHvl) of the hypothalamus. As these brain regions have been implicated in social behaviors and stress responses, our data suggest that the specific patterns of neuronal activation in the brain may relate to the altered social and anxiety-like behaviors following chronic social defeat in female Mongolian gerbils.

In the parvocellular part of paraventricular nucleus, glutamatergic and GABAergic neurons mediate cardiovascular responses to AngII

Angiotensinergic, GABAergic, and glutamatergic neurons are present in the parvocellular region of the paraventricular nucleus (PVNp). It has been shown that microinjection of AngII into the PVNp increases arterial pressure (AP) and heart rate (HR). The presence of synapses between the angiotensinergic, GABAergic, and glutamatergic neurons has been shown in the PVNp. In this study, we investigated the possible interaction between these three systems of the PVNp for control of AP and HR. All drugs were bilaterally (100 nl/side) microinjected into the PVNp of urethane-anesthetized rats, and AP and HR were recorded continuously. Microinjection of AngII into the PVNp produced pressor and tachycardia responses. Pretreatment of PVNp with AP5 or CNQX, glutamatergic NMDA and AMPA receptors antagonists, attenuated the responses to AngII. Pretreatment of PVNp with bicuculline greatly attenuated the pressor and tachycardia responses to AngII. In conclusion, this study provides the first evidence that pressor and tachycardia responses to microinjection of AngII into the PVNp are partly mediated by both NMDA and non-NMDA receptors of glutamate. Activation of glutamatergic neurons by AngII stimulates the sympathoexcitatory neurons. We also showed that the responses to AngII were strongly mediated by GABA_A receptors, probably through activation of GABAergic neurons, which in turn inhibit sympathoinhibitory neurons.

N-Methyl-D-aspartate Glutamate Receptor Modulates Cardiovascular and Neuroendocrine Responses Evoked by Hemorrhagic Shock in Rats

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.

The Supraoptic Nucleus of the Hypothalamus Modulates Autonomic, Neuroendocrine, and Behavioral Responses to Acute Restraint Stress in Rats

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.

Central mechanism of the cardiovascular responses caused by L-proline microinjected into the paraventricular nucleus of the hypothalamus in unanesthetized rats

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.

NMDA and non-NMDA glutamate receptors in the paraventricular nucleus of the hypothalamus modulate different stages of hemorrhage-evoked cardiovascular responses in rats

Here we report the involvement of N-Methyl-d-Aspartate (NMDA) and non-NMDA glutamate receptors from the paraventricular nucleus of the hypothalamus (PVN) in the mediation of cardiovascular changes observed during hemorrhage and post-bleeding periods. In addition, the present study provides further evidence of the involvement of circulating vasopressin and cardiac sympathetic activity in cardiovascular responses to hemorrhage. Systemic treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP (50 μg/kg, i.v.) increased the latency to the onset of hypotension during hemorrhage and slowed post-bleeding recovery of blood pressure. Systemic treatment with the β1-adrenergic receptor antagonist atenolol (1 mg/kg, i.v.) also increased the latency to the onset of hypotension during hemorrhage. Moreover, atenolol reversed the hemorrhage-induced tachycardia into bradycardia. Bilateral microinjection of the selective NMDA glutamate receptor antagonist LY235959 (2 nmol/100 nL) into the PVN blocked the hypotensive response to hemorrhage and reduced the tachycardia during the post-hemorrhage period. Systemic treatment with dTyr(CH2)5(Me)AVP inhibited the effect of LY235959 on hemorrhage-induced hypotension, without affecting the post-bleeding tachycardia. PVN treatment with the selective non-NMDA receptor antagonist NBQX (2 nmol/100 nL) reduced the recovery of blood pressure to normal levels in the post-bleeding phase and reduced hemorrhage-induced tachycardia. Combined blockade of both NMDA and non-NMDA glutamate receptors in the PVN completely abolished the hypotensive response in the hemorrhage period and reduced the tachycardiac response in the post-hemorrhage period. These results indicate that local PVN glutamate neurotransmission is involved in the neural pathway mediating cardiovascular responses to hemorrhage, via an integrated control involving autonomic nervous system activity and vasopressin release into the circulation.

Cardiovascular responses to ATP microinjected into the paraventricular nucleus are mediated by nitric oxide and NMDA glutamate receptors in awake rats

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.

The ventral hippocampus NMDA receptor/nitric oxide/guanylate cyclase pathway modulates cardiovascular responses in rats

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.

Cardiovascular effects of the microinjection of L-proline into the third ventricle or the paraventricular nucleus of the hypothalamus in unanesthetized rats

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.

Amino acids that centrally influence blood pressure and regional blood flow in conscious rats

Functional roles of amino acids have increasingly become the focus of research. This paper summarizes amino acids that influence cardiovascular system via the brain of conscious rats. This paper firstly describes why amino acids are selected and outlines how the brain regulates blood pressure and regional blood flow. This section includes a concise history of amino acid neurotransmitters in cardiovascular research and summarizes brain areas where chemical stimulations produce blood pressure changes mainly in anesthetized animals. This is followed by comments about findings regarding several newly examined amino acids with intracisternal stimulation in conscious rats that produce changes in blood pressure. The same pressor or depressor response to central amino acid stimulations can be produced by distinct mechanisms at central and peripheral levels, which will be briefly explained. Thereafter, cardiovascular actions of some of amino acids at the mechanism level will be discussed based upon findings of pharmacological and regional blood flow measurements. Several examined amino acids in addition to the established neurotransmitter amino acids appear to differentially activate brain structures to produce changes in blood pressure and regional blood flows. They may have physiological roles in the healthy brain, but pathological roles in the brain with cerebral vascular diseases such as stroke where the blood-brain barrier is broken.

Ionotropic glutamate receptors in hypothalamic paraventricular and supraoptic nuclei mediate vasopressin and oxytocin release in unanesthetized rats

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.

Intracisternally injected L-proline activates hypothalamic supraoptic, but not paraventricular, vasopressin-expressing neurons in conscious rats

When injected into specific rat brain regions, the neurotransmitter candidate L-proline produces various cardiovascular changes through ionotropic excitatory amino acid receptors. The present study used an immunohistochemical double-labeling approach to determine whether intracisternally injected L-proline in freely moving rats, which increases blood pressure, activates hypothalamic vasopressin-expressing neurons and ventral medullary tyrosine-hydroxylase- (TH-) containing neurons. Following injection of L-proline, the number of activated hypothalamic neurons that coexpressed vasopressin and c-Fos was much greater in the supraoptic nucleus (SON) than in the paraventricular nucleus (PVN) of rats with increased blood pressure. The number of activated TH-containing neurons was significantly greater following L-proline treatment than following control injections of artificial cerebrospinal fluid (ACSF). These results clearly demonstrate that intracisternally injected L-proline activates hypothalamic supraoptic, but not paraventricular, vasopressin-expressing neurons and medullary TH-containing (A1/C1) neurons in freely moving rats.

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

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.

Vasopressin and sympathetic systems mediate the cardiovascular effects of the GABAergic system in the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BST) is an important part of the limbic system. It has been shown that chemical stimulation of the BST elicited cardiovascular depressive and bradycardic responses. It was also demonstrated that GABA is present in the BST, though its role in cardiovascular control is not yet understood. This study was performed to find the effects of GABA receptor subtypes in the BST on cardiovascular responses and to find the possible mechanisms that mediate these responses in urethane-anesthetized rats. Microinjection of muscimol (500 pmol/100 nl), a GABA(A) agonist, into the BST produced a weak unsignificant decrease in the mean arterial pressure (MAP) and heart rate (HR). Injection of bicuculline methiodide (BMI, 100 pmol/100 nl), a GABA(A) antagonist, caused a significant increase in the MAP (41.3+/-5.1 mmHg) as well as in the HR (33.2+/-5.6 beats/min). Injection of two doses (500 and 1000 pmol/100 nl) of phaclofen, a GABA(B) antagonist, produced no significant change in either MAP or HR. Administration (i.v.) of the muscarinic receptor blocker, homatropine methyl bromide had no effect on the magnitude of mean arterial pressure or heart rate responses to BMI. This suggests that the parasympathetic system is not involved in these responses. However, administration (i.v.) of the nicotinic receptor blocker, hexamethonium bromide had no effect on the magnitude of mean arterial pressure response but abolished heart rate response to BMI. This suggests that the sympathetic system is involved in the bradycardic effect of GABA. On the other hand, administration (i.v.) of a selective vasopressin V(1) receptor antagonist abolished the pressor effect of BMI, which indicates that the GABAergic system of the BST decreases the arterial pressure via tonic inhibition of vasopressin release. In summary, we demonstrated, for the first time, that GABA exerts its influence in the BST through the activation of GABA(A), but not GABA(B), receptors that, in turn, tonically inhibit vasopressin release and sympathetic outflow to the heart.

Mechanisms involved in the pressor response to noradrenaline microinjection into the supraoptic nucleus of unanesthetized rats

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.

Paraventricular nucleus is involved in the central pathway of cardiac sympathetic afferent reflex in rats

Our previous studies have shown that angiotensin II and reactive oxygen species in the paraventricular nucleus (PVN) modulate the cardiac sympathetic afferent reflex (CSAR). The present study was designed to demonstrate more conclusively that the PVN is an important component of the central neurocircuitry of the CSAR. In anaesthetized Sprague-Dawley rats with sinoaortic denervation and cervical vagotomy, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were continuously recorded. The CSAR was evaluated by the response of the RSNA to epicardial application of bradykinin or capsaicin. Bilateral microinjection of the anaesthetic, lignocaine, into the PVN abolished the CSAR without significant effects on the baseline RSNA and MAP, while l-glutamate, which excites the neurons in the PVN, enhanced the CSAR and increased the baseline RSNA and MAP. Bilateral electrolytic lesions of the PVN irreversibly abolished the CSAR without significant effects on the baseline RSNA and MAP. Bilateral selective lesions of the neurons in the PVN with kainic acid induced rapid and great increases in both RSNA and MAP which returned to nearly normal levels in 60 min. At the 90th minute after kainic acid, epicardial application of bradykinin or capsaicin failed to induce the CSAR. These results indicate that inhibition or lesion of the PVN abolishes the CSAR, but excitation of the neurons in the PVN enhances the CSAR, suggesting that the PVN is an important component of the central neurocircuitry of the CSAR.