AJP - Regu Ad Instruments
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Regul Integr Comp Physiol 295: R38-R44, 2008. First published May 21, 2008; doi:10.1152/ajpregu.00172.2008
0363-6119/08 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
295/1/R38    most recent
00172.2008v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Geambasu, A.
Right arrow Articles by Krukoff, T. L.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Geambasu, A.
Right arrow Articles by Krukoff, T. L.

CALL FOR PAPERS
Physiological and Molecular Mechanisms Implicated in the Neural Control of Circulation

Adrenomedullin acts in the lateral parabrachial nucleus to increase arterial blood pressure through mechanisms mediated by glutamate and nitric oxide

Adrian Geambasu and Teresa L. Krukoff

Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada

Submitted 6 March 2008 ; accepted in final form 14 May 2008


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Adrenomedullin (ADM) acts in a site-specific manner within autonomic centers of the brain to modulate mean arterial pressure (MAP). To determine the role of ADM in the pontine autonomic center, the lateral parabrachial nucleus (LPBN), we used urethane-anesthetized adult Sprague-Dawley male rats to test the hypothesis that ADM increases MAP at this site through glutamate- and nitric oxide (NO)-dependent mechanisms. ADM microinjected into the LPBN increased MAP in a dose-dependent manner. The pressor effect of ADM (0.01 pmol) had a peak value of 11.9 ± 1.9 mmHg at 2 min and lasted for 7 min. We demonstrated that ADM's effect is receptor mediated by blocking the effect with the ADM receptor antagonist, ADM22-52. We showed that glutamate mediates ADM's pressor response, as this response was blocked using coinjections of ADM with dizolcipine hydrogen maleate or 6-cyano-7-nitroquinoxaline-2,3-dione, N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists, respectively. We tested the roles of NO with coinjections of ADM with either N5-(1-iminoethyl)-L-ornithine or 7-nitroindazole monosodium salt, nonspecific and neuronal NO synthase (NOS) inhibitors, respectively; both inhibitors blocked ADM's pressor effect. Finally, we studied the role of calcium influx in ADM's pressor effect, as intracellular calcium is important in both glutamate and NO neurotransmission. ADM's effect was blocked when nifedipine, an L-type calcium channel blocker, was coinjected with ADM into the LPBN. This study is the first to show that ADM acts in the LPBN to increase MAP through mechanisms dependent on activation of ionotropic glutamate receptors, neuronal and endothelial NOS-mediated NO synthesis, and L-type calcium channel activation.

brain autonomic centers; mean arterial pressure; glutamate receptors; nitric oxide synthase

DISCOVERED IN 1993 (20), ADRENOMEDULLIN (ADM) is a vasoactive peptide that modulates mean arterial blood pressure (MAP) through both central (36, 38, 45, 49) and peripheral (19, 32) mechanisms. Peripherally, ADM acts as a potent hypotensive agent (20). Because plasma levels of ADM are higher in human hypertensive patients, it has been suggested that ADM is involved in the physiopathology of hypertension (14, 29, 30). Hypertension affects one in four adults (44) and is highly correlated with the incidence of stroke and cardiovascular-related deaths. Therefore, it is important to understand the roles of ADM in MAP regulation.

Although ADM acts as a vasodilator in the periphery (12, 28), microinjections of ADM into various regions of the central nervous system (CNS) either decrease (49) or increase (36, 38, 45) MAP in rats, illustrating that ADM's actions in the CNS are site specific. Microinjections of ADM into the rostral ventrolateral medulla of anesthetized rats had a pressor, baroreflex-inhibiting effect (45). Similarly, microinjections of ADM into either the cerebral ventricles of conscious rats (36, 38) or into the area postrema/nucleus of the solitary tract (NTS) of anesthetized rats (1) increased MAP. Conversely, ADM induced a hypotensive effect when injected into the hypothalamic paraventricular nucleus (41, 49). These results suggest that ADM acts in a pleiotropic manner in the CNS to regulate MAP and that ADM's roles must be separately defined in individual cardiovascular centers.

The lateral parabrachial nucleus (LPBN), an important autonomic nervous center involved in MAP homeostasis, is interconnected with other autonomic cardiovascular centers, including the NTS (15), the hypothalamic paraventricular nucleus (22), and the rostral ventrolateral medulla (13), and contains neurons that express ADM (39) and ADM receptors (ADMR) (43). In vivo studies performed in rats (6, 16, 18) and cats (2, 7) suggested that the LPBN receives nervous signals related to changes in MAP, illustrated with c-fos staining or electrophysiological recordings. Glutamate plays an important role in mediating cardiovascular responses in the LPBN, as microinjections of glutamate in anesthetized rats increased both MAP and heart rate (HR) (24). Moreover, stimulation of cardiac sympathetic afferents in the anesthetized cat activated glutamatergic and neuronal nitric oxide synthase (NOS)-containing neurons in the LPBN (7). Finally, psychological stress in conscious rats activated nitric oxide (NO)-producing neurons in LPBN (23). Together, these studies show that NO and glutamate in the LPBN mediate changes in MAP and that ADM may act in the LPBN to affect MAP.

ADM acts through two specific metabotropic receptors that are widely distributed in the brain (42, 43). These receptors are formed by the calcitonin-receptor-like-receptor and receptor activity-modifying proteins 2 or 3 (10, 25). ADM binds to its receptors and activates intracellular signaling pathways (27, 31, 40, 48), which further increase the intracellular calcium concentration (46–48) to stimulate NO production (21). Our findings support the role of NO and glutamate in mediating at least some of ADM's central effects on MAP in the rostral ventrolateral medulla and paraventricular nucleus of anesthetized rats, as inhibition of NO synthesis or blockade of glutamate ionotropic receptors in these centers abolished ADM's effects (45, 49). Furthermore, our in vitro studies confirm that ADM stimulates NO production in SK-N-SH human neuroblastoma cells (48) and in primary rat hypothalamic neuron cultures (47). ADM also regulates the activity of L-type calcium channels to facilitate calcium entry into the cell (48) to potentially contribute to a greater activation of glutamate NMDA receptors (4, 35) and to stimulation of NO synthesis (21). Although these findings address the cellular effects of ADM in other autonomic centers of the brain, the interactions among these elements in mediating the effects of ADM in the LPBN remain to be elucidated.

We used urethane-anesthetized male rats to test the hypothesis that ADM acts in the LPBN to increase MAP and HR through glutamate- and/or NO-mediated mechanisms. To determine whether these effects are ADMR mediated, we attempted to block them with the ADMR-specific antagonist, ADM22-52. Finally, to define the roles of glutamate, NO, and calcium-mediated mechanisms in ADM's effect on MAP, we coinjected ADM with glutamate receptor antagonists, NOS inhibitors, or an L-type calcium channel blocker into the LPBN.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals. Adult male Sprague-Dawley rats (350–400 g) were purchased from the Biological Animal Center, University of Alberta, housed in a 12:12-h light-dark cycle at 22°C, and given food and water ad libitum. All surgical and handling protocols were approved by the local Animal Welfare Committee.

Preparation of animals. Rats were anesthetized with urethane (1.75 g/kg ip; Sigma Chemical, St. Louis, MO); additional anesthetic was given as needed during each experiment. Body temperature was monitored with a rectal thermometer and maintained at 37°C with a heating pad.

The left femoral artery was cannulated using polyethylene (PE)-50 tubing (Becton Dickinson, Sparks, MD), and mean arterial blood pressure (MAP) and heart rate (HR) were measured using a pressure transducer connected to the computer-based acquisition system DI-150 RS (DATAQ Instruments, Akron, OH).

Rats were secured into a stereotaxic device (David Kopf Instruments, Tujunga, CA), and a guide cannula (C315G; Plastics One, Wallingford, CT) was lowered into the left LPBN according to the coordinates: –0.7–1.3 mm posterior, 2.0–2.4 mm lateral, and 2.7–3.3 mm dorsal to the interaural zero (34). An internal cannula (C315I; Plastics One) was connected to a syringe filled with pharmacological agents via PE-50 tubing and was inserted into the guide cannula. Drugs were injected into the LPBN using an electronic infusion pump (Harvard Apparatus, Holliston, MA). All injections were made in a volume of 100 nl over 1 min.

Pharmacological agents. The pharmacological agents used in this study were ADM (0.001–0.1 pmol; American Peptide, Sunnyvale, CA), ADM22-52 (0.01 pmol; American Peptide) (45), dizolcipine hydrogen maleate (MK-801, 500 pmol; Sigma Chemical) (9, 45), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50 pmol; Sigma Chemical) (37), 7-nitroindazole monosodium salt (7-NiNa, 0.05 pmol; AG Scientific, San Diego, CA) (2), N5-(1-iminoethyl)-L-ornithine (L-NIO, 200 pmol; Tocris Cookson, Ellisville, MO) and nifedipine (1 pmol and 0.1 pmol, Sigma Chemical). The doses of the pharmacological agents were chosen on the basis of our previous studies (45) and were tested alone in separate groups of control experiments to determine the concentration that would not significantly change MAP and HR (Table 1).


View this table:
[in this window]
[in a new window]

  		Table 1. Maximal changes for MAP and HR induced by different pharmacological agents

 
Experimental protocol. MAP and HR were measured for 20–30 min to obtain baseline values. Increasing doses of ADM (0.001–0.1 pmol) were unilaterally microinjected in separate groups of experiments to determine the dose-dependent effects of ADM on MAP and HR. ADM at 0.01 pmol was used in subsequent experiments, as it was the lowest dose to elicit consistent increases in MAP compared with the controls. Saline, various drugs alone, or a combination of ADM (0.01 pmol) with these drugs (in saline) were unilaterally injected into the left LPBN (n ≥ 6 for each group). MAP was recorded for at least 1 h after the microinjections. Bilateral microinjections were used for experiments that employed both nifedipine and ADM, according to the following sequence: injection of nifedipine (0.1 pmol), followed 15 min later by ADM (0.01 pmol) into the ipsilateral LPBN; after a further 15 min, ADM (0.01 pmol) was injected into the contralateral LPBN. At the end of each experiment, 300 nl of 1% Evans blue were injected for the histological verification of the injection site.

Brain histology. At the end of experiments, rats were killed by decapitation. The brains were removed and fixed in 4% paraformaldehyde for 2 or 3 days, then frozen at –80°C. Coronal brain stem sections of 60 µm were cut using a cryostat (–20°C), thaw-mounted onto slides, and stained with neutral red (Allied Chemical, New York, NY). Slides were examined under a microscope, and accurate microinjections were confirmed by the presence of Evans blue within the LPBN.

Statistical analyses. All results are expressed as means ± SE. The temporal effects of various treatments on AP and HR were assessed at 1-min intervals and compared among groups using the two-way ANOVA with repeated measures followed by the Student-Newman-Keuls test for post hoc comparison of individual means. P < 0.05 indicated statistical significance.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Microinjections of ADM into the LPBN increase MAP through an ADM receptor-mediated mechanism. ADM (0.001, 0.01, and 0.1 pmol) microinjected into the LPBN (Fig. 1) increased MAP in a dose-dependent manner (Fig. 2). Microinjections of ADM placed adjacent to the LPBN did not elicit statistically significant changes in MAP, showing that ADM's effects are specific to the LPBN. ADM (0.01 pmol) in the LPBN elicited a significant increase in MAP beginning in the first minute after microinjection. The pressor effect of ADM lasted for ~7 min with the maximal increase in MAP occurring at 2 min postinjection (11.9 ± 1.9 mmHg, Fig. 2). HR was not significantly influenced by any of the ADM microinjections.


Figure 1
View larger version (62K):
[in this window]
[in a new window]

  		Fig. 1. A: Light-field photomicrograph of a brain section through the parabrachial nucleus showing a microinjection site within the lateral parabrachial nucleus (LPBN; arrow); boundaries of the LPBN, superior cerebellar peduncle (scp), and medial parabrachial nucleus (MPBN) are indicated with dotted lines. Scale bar = 0.1 mm. B: schematic representation of a coronal section through the LPBN region, showing the histologically verified adrenomedullin (ADM; 0.01 pmol) microinjection sites inside (open circles; 6 rats) and outside (solid squares; 6 rats) the LPBN. Each symbol represents one microinjection experiment. KF, Kölliker-Fuse nucleus; Su5, supratrigeminal nucleus. Modified after Paxinos and Watson (34). C: representative MAP traces showing the increase in MAP elicited with 0.01 pmol ADM (upper trace) and lack of effect on MAP with saline injections (lower trace). Times of microinjection are indicated with arrows; scale bar = 1 min.

 

Figure 2
View larger version (32K):
[in this window]
[in a new window]

  		Fig. 2. ADM (0.1 pmol–0.001 pmol) microinjected in LPBN increased MAP in a dose-dependent manner compared with saline injections. Average values of MAP are represented for each 1-min interval for each experimental group. The beginning of microinjections corresponds to time 0; n ≥ 6 for each group. ADM (*0.1 pmol or #0.01 pmol)-induced increases in MAP were significantly different (P < 0.05) from saline controls.

 
The ADM receptor antagonist, ADM22-52 (0.01 pmol), coinjected with ADM (0.01 pmol), blocked the ADM-induced increase in MAP, showing that ADM acts through its receptors in the LPBN to increase MAP (Fig. 3). ADM22-52 alone (0.01 pmol) did not affect the MAP when microinjected into the LPBN (Fig. 3 and Table 1).


Figure 3
View larger version (27K):
[in this window]
[in a new window]

  		Fig. 3. ADM receptor antagonist, ADM22-52 (0.01 pmol), coinjected with ADM (0.01 pmol) blocked the ADM-induced MAP increase. ADM22-52 alone (0.01 pmol) did not significantly change the MAP compared with saline injections. Average values of MAP are represented for each 1-min interval for each experimental group. The beginning of microinjections corresponds to time 0; n ≥ 6 for each group. The ADM (0.01 pmol)-induced increase in MAP was significantly different (P < 0.05) from +saline controls, *ADM (0.01 pmol)+ADM22-52 (0.01 pmol) or #ADM22-52 alone (0.01 pmol).

 
Effects of ADM on MAP are mediated by L-glutamate ionotropic receptors in the LPBN. The effects of ADM on MAP in the LPBN were blocked when ADM (0.01 pmol) was coinjected with MK-801 (500 pmol), a selective NMDA receptor antagonist (50 pmol; Fig. 4). Coinjection of ADM with the selective non-NMDA receptor antagonist CNQX also blocked the ADM-induced increase in MAP (Fig. 4). MK-801 (500 pmol) or CNQX (50 pmol) microinjected alone into LPBN did not affect MAP (Table 1). These results suggest that ADM acts in the LPBN to increase MAP through a mechanism dependent on the activation of ionotropic glutamate receptors.


Figure 4
View larger version (28K):
[in this window]
[in a new window]

  		Fig. 4. The selective NMDA receptor antagonist MK-801 (500 pmol) coinjected with ADM (0.01 pmol) blocked the ADM-induced MAP increase. Coinjection of ADM with CNQX (50 pmol), a selective non-NMDA receptor antagonist, also blocked the ADM-induced increase in MAP. Average values of MAP are represented for each 1-min interval for each experimental group. The beginning of microinjections corresponds to time 0; n ≥ 6 for each group. The effect of ADM (0.01 pmol) on MAP was significantly different (P < 0.05) from +saline, *ADM (0.01 pmol)+CNQX (50 pmol) or #ADM (0.01 pmol)+MK801 (500 pmol).

 
Effects of ADM in the LPBN on MAP are mediated by NO produced by nNOS. The increase in MAP was blocked when ADM (0.01 pmol) was coinjected into the LPBN with L-NIO (200 pmol), a nonspecific NO synthase inhibitor (Fig. 5). Furthermore, the neuronal NO synthase inhibitor, 7-NiNa (0.05 pmol), coinjected with ADM (0.01 pmol) into the LPBN, blocked the ADM-induced increase in MAP (Fig. 5). Neither L-NIO (200 pmol) nor 7-NiNa (0.05 pmol), microinjected alone into LPBN, elicited a significant change in MAP compared with saline controls (Table 1). These data show that the ADM-induced increase in MAP, which occurs after microinjection into LPBN, depends on NO produced by neuronal NOS.


Figure 5
View larger version (26K):
[in this window]
[in a new window]

  		Fig. 5. ADM's pressor effect was blocked when ADM (0.01 pmol) was coinjected with N5-(1-iminoethyl)-L-ornithine (L-NIO; 200 pmol), a nonspecific NO synthase inhibitor. The neuronal NO synthase inhibitor 7-NiNa (0.05 pmol) also blocked the ADM-induced MAP increase when coinjected with ADM (0.01 pmol). Average values of MAP are represented for each 1-min interval for each experimental group. The beginning of microinjections corresponds to time 0; n ≥ 6 for each group. The ADM (0.01 pmol)-induced increase in MAP was significantly different (P < 0.05) from +saline, *ADM (0.01 pmol)+7-NiNa (0.05 pmol) or #ADM (0.01 pmol)+L-NIO (200 pmol).

 
The pressor effect of ADM in the LPBN is mediated by a mechanism dependent on activity of L-type calcium-channels. The pressor effect of ADM in the LPBN was blocked when ADM (0.01 pmol) was injected into the ipsilateral LPBN 15 min after the L-type calcium-channel blocker, nifedipine (0.1 pmol) (Fig. 6). Nifedipine at 0.1 pmol was chosen in these experiments because it did not significantly affect MAP when injected alone (Table 1). To confirm that nifedipine specifically blocked ADM's effects on MAP, ADM (0.01 pmol) was then microinjected into the contralateral LPBN, in the absence of nifedipine. These contralateral injections of ADM consistently elicited increases in MAP that were not significantly different from those described for single ADM (0.01 pmol) injections (Figs. 2 and 6). These results demonstrate that the pressor effect of ADM is mediated by intracellular calcium.


Figure 6
View larger version (28K):
[in this window]
[in a new window]

  		Fig. 6. Nifedipine (0.1 pmol) blocked the pressor effect of ADM in the LPBN. Average values of mean arterial pressure (MAP) are represented for each 1-min interval for each experimental group. The beginning of microinjections corresponds to time 0; n ≥ 6 for each group. Microinjection of ADM (0.1 pmol) into the contralateral LPBN in the absence of nifedipine elicited a statistically significant increase in MAP compared with saline and ADM (0.1 pmol)+nifedipine (*).

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
In our study, we show for the first time that ADM increases MAP in a dose-dependent manner when microinjected into the LPBN, a major cardiovascular center in the brain. The pressor effect of ADM is receptor mediated, as the specific ADMR antagonist, ADM22-52, blocked this effect. Moreover, ADM's pressor effect depends on the activation of glutamate receptors because it was blocked when ADM was coinjected with either NMDA or non-NMDA receptor antagonists. The pressor effect of ADM in the LPBN is also mediated by NO, as it was abolished when NO synthesis was blocked in the LPBN. Finally, ADM's effect is dependent on intracellular calcium as nifedipine, a specific L-type calcium channel blocker, abolished the pressor effect when microinjected into the LPBN before ADM. Together, our data show that ADM increases MAP in the LPBN through mechanisms dependent on glutamate, NO, and L-type calcium channel activity.

The concentration of ADM (0.01 pmol) used in our study is similar to the concentrations found to exert a pressor effect in the rostral ventrolateral medulla (45) and a depressor effect in the hypothalamic paraventricular nucleus (49). We demonstrated that ADM's effects are specific to the LPBN, as no pressor effects were obtained when ADM was injected outside the LPBN. In addition, our data show that ADM's actions in the LPBN are mediated by ADMR, as ADM22-52, an ADMR-specific antagonist, blocked ADM's effect when both agents were injected together.

In the present study, we show that ADM acts in the LPBN through a glutamate receptor-dependent mechanism, as we were able to block ADM's effect by coinjecting ADM with either NMDA (MK-801) or non-NMDA (CNQX) glutamate receptor antagonists. Other studies support a role for glutamate receptors in the LPBN-generated MAP changes. For example, extracellular recordings from LPBN neurons following electrical stimulation of the NTS showed excitatory responses, mediated through both NMDA and non-NMDA glutamate receptors (17). In addition, the increase in MAP initiated by electrical stimulation of the dorsal periaqueductal gray of anesthetized rats was blocked by bilateral injections of kynurenic acid, an NMDA receptor antagonist, into the LPBN (11). Studies in anesthetized rats suggest that glutamate receptors also mediate the effects of ADM in the rostral ventrolateral medulla and paraventricular nucleus (45, 49). Thus, our data show that ADM in the LPBN increases MAP by activating glutamate receptors and suggest that the mechanisms for ADM's effects on MAP are similar in several central autonomic nuclei.

Other studies have also demonstrated roles for glutamate in mediating pressor responses in the LPBN. In anesthetized rats, injections of glutamate into the LPBN generated pressor responses (5). In other studies using anesthetized cats, glutamate microinjections in the LPBN elicited pressor responses but had no effects on HR (8), and epicardial application of bradykinin to the left ventricle of the heart activated glutamatergic neurons in LPBN, shown with immunohistochemical localization of c-fos and vesicular glutamate transporter 3 (7). In decerebrate rabbits, glutamate injected into the LPBN-induced consistent increases in MAP and HR (33). Together, these data confirm a role for glutamate in mediating pressor responses in the LPBN.

Our results establish that ADM's pressor effect in the LPBN is also dependent on NO produced by nNOS, as inhibition of NO synthesis with either L-NIO or 7-NiNa (nonspecific NOS and nNOS inhibitors, respectively) effectively blocked this effect. ADM's role in potentiating NO synthesis is also suggested by our in vitro studies showing that ADM stimulates both NO release from human neuroblastoma cells and NO production from primary rat hypothalamic neurons (47, 48). These data are further supported by studies suggesting that NO mediates the ADM-induced cardiovascular changes in the hypothalamic paraventricular nucleus and rostral ventrolateral medulla (45, 49). In addition, as discussed above, ventricular stimulation with bradykinin activated nNOS-containing neurons in the LPBN of anesthetized cats (7). Moreover, in conscious rats, stress led to c-fos activation in NO-producing neurons of the LPBN (23). Therefore, central NO appears to be involved in regulation of autonomic functions, including the blood pressure in a number of central sites, including the LPBN. Currently, the sequence of NO-dependent events, mediating ADM's pressor effect in the LPBN, downstream of NO synthesis, is not clear. Future studies using guanylate cyclase inhibitors would establish whether NO itself, rather than other proteins posttranslationally modified through NO-induced S-nitrosylation, is the primary mediator.

At the present time, the sequence of interactions among ADM, glutamate, and NO in neurons of the LPBN remains unclear. Others have shown that NMDA receptors and nNOS are functionally linked at the postsynaptic level, in a complex dependent on the protein, PSD-95 (3). It has also been shown that glutamate stimulates NO synthesis in a calcium-dependent manner and that NO then acts through a feedback mechanism to modulate the activity of presynaptic neurons; in this way, NO is thought to stimulate the release of neurotransmitters, including glutamate (26). We have shown that L-type calcium channels are required for the stimulation of NO production by ADM in neuroblastoma cells (48), and we show here that ADM's pressor effect in the LPBN is dependent on L-type calcium channels.

Perspectives and Significance

Our study provides data important for understanding ADM's central actions in MAP regulation. We have used site-specific microinjections of ADM in anesthetized rats to show that ADM acts in the LPBN to increase MAP through complex mechanisms dependent on glutamate receptor activation, NO synthesis, and L-type calcium channel activation. Additional studies in conscious animals will be needed to fully establish the physiological significance of ADM signaling in the LPBN. Future research is also required, not only to define the nature of ADM-induced cellular interactions between glutamate and NO, but to explore the possibility that dysfunctions in ADM signaling in the LPBN contribute to the development of hypertension.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by the Heart and Stroke Foundation of Alberta/Northwest Territories/Nunavut.


   FOOTNOTES
 

Address for reprint requests and other correspondence: T. L. Krukoff, Dept. of Cell Biology, 5-31 Medical Sciences Bldg., Univ. of Alberta, Edmonton, AB, Canada, T6G 2H7 (e-mail: teresa.krukoff{at}ualberta.ca)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Allen MA, Smith PM, Ferguson AV. Adrenomedullin microinjection into the area postrema increases blood pressure. Am J Physiol Regul Integr Comp Physiol 272: R1698–R1703, 1997.[Abstract/Free Full Text]
  2. Cechetto DF, Calaresu FR. Parabrachial units responding to stimulation of buffer nerves and forebrain in the cat. Am J Physiol Regul Integr Comp Physiol 245: R811–R819, 1983.[Abstract/Free Full Text]
  3. Christopherson KS, Hillier BJ, Lim WA, Bredt DS. PSD-95 assembles a ternary complex with the N-methyl-D-aspartic acid receptor and a bivalent neuronal NO synthase PDZ domain. J Biol Chem 274: 27467–27473, 1999.[Abstract/Free Full Text]
  4. Cooper DC, White FJ. L-type calcium channels modulate glutamate-driven bursting activity in the nucleus accumbens in vivo. Brain Res 880: 212–218, 2000.[CrossRef][Web of Science][Medline]
  5. Dawid Milner MS, Lara JP, Lopez de Miguel MP, Lopez-Gonzalez MV, Spyer KM, Gonzalez-Baron S. A5 region modulation of the cardiorespiratory responses evoked from parabrachial cell bodies in the anaesthetised rat. Brain Res 982: 108–118, 2003.[CrossRef][Web of Science][Medline]
  6. Erickson JT, Millhorn DE. Hypoxia and electrical stimulation of the carotid sinus nerve induce Fos-like immunoreactivity within catecholaminergic and serotoninergic neurons of the rat brainstem. J Comp Neurol 348: 161–182, 1994.[CrossRef][Web of Science][Medline]
  7. Guo ZL, Moazzami AR, Longhurst JC. Stimulation of cardiac sympathetic afferents activates glutamatergic neurons in the parabrachial nucleus: relation to neurons containing nNOS. Brain Res 1053: 97–107, 2005.[CrossRef][Web of Science][Medline]
  8. Hade JS, Mifflin SW, Donta TS, Felder RB. Stimulation of parabrachial neurons elicits a sympathetically mediated pressor response in cats. Am J Physiol Heart Circ Physiol 255: H1349–H1358, 1988.[Abstract/Free Full Text]
  9. Harris MB, Milsom WK. Apneusis follows disruption of NMDA-type glutamate receptors in vagotomized ground squirrels. Respir Physiol Neurobiol 134: 191–207, 2003.[CrossRef][Web of Science][Medline]
  10. Hay DL, Conner AC, Howitt SG, Smith DM, Poyner DR. The pharmacology of adrenomedullin receptors and their relationship to CGRP receptors. J Mol Neurosci 22: 105–113, 2004.[CrossRef][Web of Science][Medline]
  11. Hayward LF. Midbrain modulation of the cardiac baroreflex involves excitation of lateral parabrachial neurons in the rat. Brain Res 1145: 117–127, 2007.[CrossRef][Web of Science][Medline]
  12. Hinson JP, Kapas S, Smith DM. Adrenomedullin, a multifunctional regulatory peptide. Endocr Rev 21: 138–167, 2000.[Abstract/Free Full Text]
  13. Horiuchi J, Potts PD, Polson JW, Dampney RA. Distribution of neurons projecting to the rostral ventrolateral medullary pressor region that are activated by sustained hypotension. Neuroscience 89: 1319–1329, 1999.[CrossRef][Web of Science][Medline]
  14. Ishimitsu T, Nishikimi T, Saito Y, Kitamura K, Eto T, Kangawa K, Matsuo H, Omae T, Matsuoka H. Plasma levels of adrenomedullin, a newly identified hypotensive peptide, in patients with hypertension and renal failure. J Clin Invest 94: 2158–2161, 1994.[Web of Science][Medline]
  15. Jean A. The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects. Arch Int Physiol Biochim Biophys 99: A3–A52, 1991.[Web of Science][Medline]
  16. Jhamandas JH, Aippersbach SE, Harris KH. Cardiovascular influences on rat parabrachial nucleus: an electrophysiological study. Am J Physiol Regul Integr Comp Physiol 260: R225–R231, 1991.[Abstract/Free Full Text]
  17. Jhamandas JH, Harris KH. Excitatory amino acids may mediate nucleus tractus solitarius input to rat parabrachial neurons. Am J Physiol Regul Integr Comp Physiol 263: R324–R330, 1992.[Abstract/Free Full Text]
  18. Jhamandas JH, Harris KH. Influence of nucleus tractus solitarius stimulation and baroreceptor activation on rat parabrachial neurons. Brain Res Bull 28: 565–571, 1992.[CrossRef][Web of Science][Medline]
  19. Jougasaki M, Wei CM, Aarhus LL, Heublein DM, Sandberg SM, Burnett JC Jr. Renal localization and actions of adrenomedullin: a natriuretic peptide. Am J Physiol Renal Fluid Electrolyte Physiol 268: F657–F663, 1995.[Abstract/Free Full Text]
  20. Kitamura K, Kangawa K, Kawamoto M, Ichiki Y, Nakamura S, Matsuo H, Eto T. Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma. Biochem Biophys Res Commun 192: 553–560, 1993.[CrossRef][Web of Science][Medline]
  21. Krukoff TL. Central actions of nitric oxide in regulation of autonomic functions. Brain Res Brain Res Rev 30: 52–65, 1999.[CrossRef][Medline]
  22. Krukoff TL, Harris KH, Linetsky E, Jhamandas JH. Expression of c-fos protein in rat brain elicited by electrical and chemical stimulation of the hypothalamic paraventricular nucleus. Neuroendocrinology 59: 590–602, 1994.[Web of Science][Medline]
  23. Krukoff TL, Khalili P. Stress-induced activation of nitric oxide-producing neurons in the rat brain. J Comp Neurol 377: 509–519, 1997.[CrossRef][Web of Science][Medline]
  24. Lara JP, Parkes MJ, Silva-Carvhalo L, Izzo P, Dawid-Milner MS, Spyer KM. Cardiovascular and respiratory effects of stimulation of cell bodies of the parabrachial nuclei in the anaesthetized rat. J Physiol 477: 321–329, 1994.[Abstract/Free Full Text]
  25. McLatchie LM, Fraser NJ, Main MJ, Wise A, Brown J, Thompson N, Solari R, Lee MG, Foord SM. RAMPs regulate the transport and ligand specificity of the calcitonin-receptor-like receptor. Nature 393: 333–339, 1998.[CrossRef][Medline]
  26. Micheva KD, Buchanan J, Holz RW, Smith SJ. Retrograde regulation of synaptic vesicle endocytosis and recycling. Nat Neurosci 6: 925–932, 2003.[CrossRef][Web of Science][Medline]
  27. Miyashita K, Itoh H, Sawada N, Fukunaga Y, Sone M, Yamahara K, Yurugi-Kobayashi T, Park K, Nakao K. Adrenomedullin provokes endothelial Akt activation and promotes vascular regeneration both in vitro and in vivo. FEBS Lett 544: 86–92, 2003.[CrossRef][Web of Science][Medline]
  28. Nagaya N, Kyotani S, Uematsu M, Ueno K, Oya H, Nakanishi N, Shirai M, Mori H, Miyatake K, Kangawa K. Effects of adrenomedullin inhalation on hemodynamics and exercise capacity in patients with idiopathic pulmonary arterial hypertension. Circulation 109: 351–356, 2004.[Abstract/Free Full Text]
  29. Nishikimi T, Nagata S, Sasaki T, Tomimoto S, Matsuoka H, Takishita S, Kitamura K, Miyata A, Matsuo H, Kangawa K. Plasma concentrations of adrenomedullin correlate with the extent of pulmonary hypertension in patients with mitral stenosis. Heart 78: 390–395, 1997.[Abstract/Free Full Text]
  30. Nishikimi T, Saito Y, Kitamura K, Ishimitsu T, Eto T, Kangawa K, Matsuo H, Omae T, Matsuoka H. Increased plasma levels of adrenomedullin in patients with heart failure. J Am Coll Cardiol 26: 1424–1431, 1995.[Abstract]
  31. Nishimatsu H, Suzuki E, Nagata D, Moriyama N, Satonaka H, Walsh K, Sata M, Kangawa K, Matsuo H, Goto A, Kitamura T, Hirata Y. Adrenomedullin induces endothelium-dependent vasorelaxation via the phosphatidylinositol 3-kinase/Akt-dependent pathway in rat aorta. Circ Res 89: 63–70, 2001.[Abstract/Free Full Text]
  32. Parkes DG. Cardiovascular actions of adrenomedullin in conscious sheep. Am J Physiol Heart Circ Physiol 268: H2574–H2578, 1995.[Abstract/Free Full Text]
  33. Paton JF, Silva-Carvalho L, Thompson CS, Spyer KM. Nucleus tractus solitarius as mediator of evoked parabrachial cardiovascular responses in the decerebrate rabbit. J Physiol 428: 693–705, 1990.[Abstract/Free Full Text]
  34. Paxinos G. The Rat Brain in Stereotaxic Coordinates. Orlando, FL: CRC, 1986.
  35. Rajadhyaksha A, Barczak A, Macias W, Leveque JC, Lewis SE, Konradi C. L-Type Ca(2+) channels are essential for glutamate-mediated CREB phosphorylation and c-fos gene expression in striatal neurons. J Neurosci 19: 6348–6359, 1999.[Abstract/Free Full Text]
  36. Saita M, Shimokawa A, Kunitake T, Kato K, Hanamori T, Kitamura K, Eto T, Kannan H. Central actions of adrenomedullin on cardiovascular parameters and sympathetic outflow in conscious rats. Am J Physiol Regul Integr Comp Physiol 274: R979–R984, 1998.[Abstract/Free Full Text]
  37. Saleh TM, Connell BJ, McQuaid T, Cribb AE. Estrogen-induced neurochemical and electrophysiological changes in the parabrachial nucleus of the male rat. Brain Res 990: 58–65, 2003.[CrossRef][Web of Science][Medline]
  38. Samson WK, Murphy TC, Resch ZT. Central mechanisms for the hypertensive effects of preproadrenomedullin-derived peptides in conscious rats. Am J Physiol Regul Integr Comp Physiol 274: R1505–R1509, 1998.[Abstract/Free Full Text]
  39. Serrano J, Uttenthal LO, Martinez A, Fernandez AP, Martinez de Velasco J, Alonso D, Bentura ML, Santacana M, Gallardo JR, Martinez-Murillo R, Cuttitta F, Rodrigo J. Distribution of adrenomedullin-like immunoreactivity in the rat central nervous system by light and electron microscopy. Brain Res 853: 245–268, 2000.[CrossRef][Web of Science][Medline]
  40. Shimekake Y, Nagata K, Ohta S, Kambayashi Y, Teraoka H, Kitamura K, Eto T, Kangawa K, Matsuo H. Adrenomedullin stimulates two signal transduction pathways, cAMP accumulation and Ca2+ mobilization, in bovine aortic endothelial cells. J Biol Chem 270: 4412–4417, 1995.[Abstract/Free Full Text]
  41. Smith PM, Ferguson AV. Adrenomedullin acts in the rat paraventricular nucleus to decrease blood pressure. J Neuroendocrinol 13: 467–471, 2001.[CrossRef][Web of Science][Medline]
  42. Sone M, Takahashi K, Satoh F, Murakami O, Totsune K, Ohneda M, Sasano H, Ito H, Mouri T. Specific adrenomedullin binding sites in the human brain. Peptides 18: 1125–1129, 1997.[CrossRef][Web of Science][Medline]
  43. Stachniak TJ, Krukoff TL. Receptor activity modifying protein 2 distribution in the rat central nervous system and regulation by changes in blood pressure. J Neuroendocrinol 15: 840–850, 2003.[CrossRef][Web of Science][Medline]
  44. Wolf-Maier K, Cooper RS, Banegas JR, Giampaoli S, Hense HW, Joffres M, Kastarinen M, Poulter N, Primatesta P, Rodriguez-Artalejo F, Stegmayr B, Thamm M, Tuomilehto J, Vanuzzo D, Vescio F. Hypertension prevalence and blood pressure levels in 6 European countries, Canada, and the United States. JAMA 289: 2363–2369, 2003.[Abstract/Free Full Text]
  45. Xu Y, Krukoff TL. Adrenomedullin in the rostral ventrolateral medulla increases arterial pressure and heart rate: roles of glutamate and nitric oxide. Am J Physiol Regul Integr Comp Physiol 287: R729–R734, 2004.[Abstract/Free Full Text]
  46. Xu Y, Krukoff TL. Adrenomedullin in the rostral ventrolateral medulla inhibits baroreflex control of heart rate: a role for protein kinase A. Br J Pharmacol 148: 70–77, 2006.[CrossRef][Web of Science][Medline]
  47. Xu Y, Krukoff TL. Adrenomedullin stimulates nitric oxide production from primary rat hypothalamic neurons: roles of calcium and phosphatases. Mol Pharmacol 72: 112–120, 2007.[Abstract/Free Full Text]
  48. Xu Y, Krukoff TL. Adrenomedullin stimulates nitric oxide release from SK-N-SH human neuroblastoma cells by modulating intracellular calcium mobilization. Endocrinology 146: 2295–2305, 2005.[Abstract/Free Full Text]
  49. Xu Y, Krukoff TL. Decrease in arterial pressure induced by adrenomedullin in the hypothalamic paraventricular nucleus is mediated by nitric oxide and GABA. Regul Pept 119: 21–30, 2004.[CrossRef][Web of Science][Medline]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
295/1/R38    most recent
00172.2008v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Geambasu, A.
Right arrow Articles by Krukoff, T. L.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Geambasu, A.
Right arrow Articles by Krukoff, T. L.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2008 by the American Physiological Society.