PVN lesions prevent the endothelin 1-induced increase in arterial pressure and vasopressin

Noreen F. Rossi and Haiping Chen

Departments of Medicine and Physiology, Wayne State University School of Medicine and John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan 48201


    ABSTRACT
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Endothelin (ET) acts within the central nervous system to increase arterial pressure and arginine vasopressin (AVP) secretion. This study assessed the role of the paraventricular nuclei (PVN) in these actions. Intracerebroventricular ET-1 (10 pmol) or the ETA antagonist BQ-123 (40 nmol) was administered in conscious intact or sinoaortic-denervated (SAD) Long-Evans rats with sham or bilateral electrolytic lesions of the magnocellular region of the PVN. Baseline values did not differ among groups, and artificial cerebrospinal fluid (CSF) induced no significant changes. In sham-lesioned rats, ET-1 increased mean arterial pressure (MAP) 15.9 ± 1.3 mmHg in intact and 22.3 ± 2.7 mmHg in SAD (P < 0.001 ET-1 vs. CSF) rats. PVN lesions abolished the rise in MAP: -0.1 ± 2.8 mmHg in intact and 0.0 ± 2.9 mmHg in SAD. AVP increased in only in the sham-lesioned SAD group 8.6 ± 3.5 pg/ml (P < 0.001 ET-1 vs. CSF). BQ-123 blocked the responses. Thus the integrity of the PVN is required for intracerebroventricularly administered ET-1 to exert pressor and AVP secretory effects.

antidiuretic hormone; endothelin-1; hemodynamics; intracerebroventricular injection; rats; subfornical organ


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

IN ADDITION TO potent direct vasoactive effects, considerable evidence exists to show that the endothelins (ET) act as neuromodulators or neurotransmitters within the central nervous system (32-35). All components of the ET system, including ET mRNA and peptides, its receptors, and ET-converting enzyme activity, have been demonstrated within nonvascular tissue in the brain (12, 31), particularly within loci implicated in the central regulation of cardiovascular function and arginine vasopressin (AVP) secretion (18, 31, 37).

Systemic arterial pressure increases in response to injection of ET-1 into the lateral ventricle in rats (19, 20, 24, 25, 36). This pressor response is mediated by increased sympathetic outflow (2, 9, 11, 24). In addition, several investigators have demonstrated that ET-1 stimulates AVP secretion both in vivo (13, 22, 24-26, 36) and in vitro (22, 23). Although early reports suggested that the pressor response is mediated by AVP secretion (16, 20, 36), the role of ET-1 may be more complex (24-26). For example, the Brattleboro mutant of the Long-Evans rat strain lacking central AVP exhibits an increase in arterial pressure identical to that of the wild-type rat with a normal AVP secretory response (25).

Among the circumventricular organs, the subfornical organ is generously endowed with ET receptors (5, 7). Miselis (15) demonstrated efferent projections from the subfornical organ to supraoptic and paraventricular nuclei (PVN). Notably, electrolytic lesions of the region anteroventral to the third ventricle (AV3V) that interrupt projections from the subfornical organ to the supraoptic nuclei block AVP secretion but not the increase in arterial pressure observed with central ET-1 administration (25). Furthermore, ET-1 acting at the subfornical organ elicits an excitatory effect on magnocellular neurons within the PVN (32, 33). Several investigators have shown that electrical or chemical stimulation of the PVN results in an increase in systemic arterial pressure (1, 4, 6, 13, 10), and lesions of the PVN prevent systemic hypertension (3, 32).

The present studies were designed to test the hypothesis that electrolytic ablation of the predominantly magnocellular regions of the PVN will selectively abolish the increase in systemic arterial pressure to centrally administered ET-1 while leaving the AVP secretory response intact.


    METHODS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Adult male Long-Evans rats weighing ~225-250 g were obtained from Harlan Sprague Dawley (Indianapolis, IN). They were housed under controlled conditions (21-23°C; lights on 0700-1900) and had free access to water and standard rat chow. The rats were cared for in accordance with the principles of the National Institutes of Health Guide for the Care and Use of Laboratory Animals (Dept. of Health, Education, and Welfare no. 86-23). All protocols were reviewed and approved by our institutional Animal Investigation Committee.

Surgical Procedures

Sinoaortic denervation. On day 1, the rats were anesthetized with pentobarbital sodium (40 mg/kg body wt ip). Sinoaortic denervation (SAD) or sham operation was performed as described previously (8). A ventral midline incision was made in the neck. The sternocleidomastoid muscle was retracted, and the aortic depressor nerve and its accompanying fibers were identified under a stereoscopic microscope. Denervation was accomplished by surgically sectioning the cervical sympathetic trunks, the aortic depressor nerve, and the superior laryngeal nerve. The carotid baroreceptors were denervated by cutting the carotid sinus nerve and stripping the area of the carotid sinus. Identical dissection was performed in sham-denervated rats, but the nerves were left intact.

Catheter placement. Immediately after sham or SAD, arterial and jugular catheters were inserted in the carotid artery and jugular vein, respectively. The catheters were secured, tunneled subcutaneously, and exteriorized at the back of the neck (24). Catheter patency was maintained by filling the lumen with 1,000 U/ml of 50 µl sodium heparin. The rats were returned to individual cages and allowed to recover.

Stereotaxic surgery. On day 3, rats that met testing criteria for baroreflex status (see Verification of SAD) were anesthetized with pentobarbital sodium (40 mg/kg body wt iv). Each rat was positioned within a cranial stereotaxic instrument (Kopf, Tujunga, CA), and the PVN were lesioned bilaterally (coordinates on the midline: -1.5 anteroposterior, -0.6 and +0.6 mediolateral, and +8.6 dorsoventral) by passing a 3-mA direct current for 25 s via a concentric bipolar stainless steel electrode insulated to within 0.5 mm of the tip. For sham lesions, the electrode was lowered 4.0 mm bilaterally, and no current was passed. During the same surgical session, a 22-gauge stainless steel guide cannula (Plastics One, Roanoke, VA) was inserted in the right lateral cerebral ventricle (coordinates to bregma: -0.3 anteroposterior, 1.3 mediolateral, and +2.5 dorsoventral) and affixed with cranioplastic cement. A dummy cannula was placed in the guide cannula to maintain patency. The rat was then allowed to recover. Verification of lesion placement was performed histologically for each rat.

Verification of SAD

To assess baroreflex status, testing was performed on day 3 in conscious rats. The change in heart rate was ascertained in response to a 40-mmHg pressor stimulus evoked by 2.5-5 µg/kg phenylephrine or a 40-mmHg depressor stimulus elicited by 2-5 µg/kg nitroprusside in 200 µl saline intravenously. Mean arterial pressure (MAP) and heart rate were monitored continuously for at least 10 min before injection, during the stimulus, and for 10 min afterward. Only rats displaying >95% blunting of baroreceptor reflex changes in heart rate were considered SAD. Partially denervated animals were not used in subsequent experimental protocols (29). One day after baroreflex testing, SAD and sham-operated rats underwent PVN lesioning and placement of the intracerebroventricular cannula as described above.

Protocol

This set of experiments was designed to compare the effect of bilateral electrolytic lesions of the PVN on the pressor and AVP secretory responses to exogenous ET-1 and selective ETA antagonism of endogenous ET-1 in intact and SAD rats.

On days 7-9, each animal was conditioned to remain for 120 min in a Plexiglas study chamber (Braintree Scientific, Braintree, MA). All experimental protocols were performed on conscious conditioned rats on day 10. After positioning the rat in the chamber, the arterial catheter was connected to a pressure transducer (Grass Instruments), and the dummy cannula was replaced with a 28-gauge infusion cannula whose internal tip projected 1 mm below the guide cannula. Systemic arterial pressure and heart rate were monitored continuously and recorded to disc using the Hemodynamic Monitoring Package (Biotech Products, Greenwood, IN).

Experiments were performed using a protocol identical to that reported previously by our laboratory (24-26). After a 30-min baseline period, a blood sample (800 µl) was collected over 30 s in prechilled heparinized tubes to avoid stimulation of AVP secretion or degradation of AVP during collection. The rat was transfused immediately thereafter via the venous catheter with an equal volume of donor blood that had been allowed to remain at room temperature for 30 min to allow intrinsic AVP to be catabolized (random AVP levels of donor blood <0.1 pg/ml). Subsequently, the rat received a 10-µl intracerebroventricular injection over 10 s with one of the following dissolved in artificial cerebrospinal fluid (CSF): 1) artificial CSF, 2) 10 pmol ET-1, 3) 10 pmol ET-1 with 40 nmol BQ-123, or 4) 40 nmol BQ-123. Agonists and antagonists were used at doses determined in previous experiments (24-26). Ten minutes after the intracerebroventricular injection, blood was collected again, and the rat was transfused as before. Hemodynamic parameters were monitored for an additional 20 min. Particular care was exerted to assure that all rats had free access to water during the course of the experiment to avoid changes in plasma volume and osmolality.

At the end of the protocol, each rat was killed with pentobarbital sodium (120 mg/kg body wt iv). The brain was perfusion flushed with ice-cold saline until clear, followed by 10% neutral buffered Formalin in saline. The brains were removed and postfixed in 10% neutral buffered Formalin overnight and then were transferred to a 30% sucrose-Formalin solution, where they remained until they sank. Frozen 10-µm serial sections were cut on a microtome and processed for staining of Nissl substance with cresyl violet. Sections were evaluated for PVN lesions by an investigator blinded to the lesioning status (Rossi).

Analytical Methods

The Hemodynamic Monitoring Package (Biotech Products) calculated and displayed blood pressure and heart rate beat-by-beat for each experiment. Values were also recorded on computer disc for off-line analysis. Data were sampled continuously at 6 Hz using a DAP 3216a/415 data acquisition processor as the hardware platform.

Baroreflex gain for sham and SAD rats was calculated as the maximal change in heart rate divided by the change in MAP. For each experiment, MAP and heart rate were the running average of the last 3 min of the period before the first blood sample (baseline) and 7-10 min after intracerebroventricular injection just before the second blood sample (test).

Plasma osmolality was measured by freezing point depression (Precision Systems 5004, Sudbury, MA). The remaining plasma was stored at -70°C until RIA. Plasma AVP concentration was assessed using previously reported methods (26). Briefly, the plasma samples were extracted before assay. All standards and samples were assayed in duplicate with purified AVP (Ferring, Malmo, Sweden) as the standard, [125I]-iodotyrosyl AVP as the tracer (Amersham, Arlington Heights, IL), and anti-AVP antibody no. 2849 (gift of Drs. J. Durr and M. Lindheimer) at a dilution of 1:3.6 × 105.

Statistics

Comparisons of MAP, heart rate, plasma osmolality, and plasma AVP concentration among the groups between baseline and test periods were made using one-way ANOVA and the Tukey-Kramer analysis for multiple comparisons. Differences during the test period among groups were analyzed by two-way ANOVA. All data are reported as means ± SE. A significant difference among means was assigned at P < 0.05.


    RESULTS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Resting baseline heart rate and MAP was higher in the SAD groups on day 3 and displayed significantly diminished baroreflex gain compared with their respective sham-denervated groups (Table 1). In the aggregate, heart rate changed 117 ± 36 beats/min in response to a 44 ± 7 mmHg change in MAP in the sham-denervated rats (n = 49), whereas heart rate changed only 4 ± 14 beats/min in the SAD groups in response to a 44 ± 9 mmHg change in MAP (n = 45). Thus the change in heart rate in the SAD rats was <1% of the resting heart rate, consistent with adequate denervation.

                              
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Table 1.   Verification of sinoaortic denervation status on day 3 

Figure 1 depicts the PVN regions of typical sham and bilaterally lesioned animals. On the day the protocols were performed, baseline heart rate, MAP, plasma osmolality, and plasma AVP values did not differ significantly among the groups (Table 2).


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Fig. 1.   Representative coronal sections taken at the level of the paraventricular nucleus (PVN) from a sham-lesioned rat (A), a PVN-lesioned rat (B), and a corresponding diagram from the stereotaxic atlas of Paxinos and Watson (C). All rats included in the final data analysis had lesions located within the magnocellular region of the PVN as shown (hatched area). Some lesions extended medially into the parvicellular area (striped area). All lesions were bilateral. 3V, third ventricle; PaLM, lateral magnocellular region of the PVN; PaMP, medial parvicellular region of the PVN; PaV, ventral PVN.


                              
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Table 2.   Baseline hemodynamic parameters, plasma osmolality, and vasopressin values in rats on day 10 

Artificial CSF did not change MAP or plasma AVP concentrations from baseline values in any of the groups (Fig. 2). In both groups with sham PVN lesions, intracerebroventricular injection of ET-1 elicited a significant increase in MAP. Plasma AVP levels increased only in the group of rats with SAD and sham PVN lesions. Figure 3 shows a typical hemodynamic response in sham PVN-lesioned animals. These real time tracings also show that the heart rate variability in the SAD rat is higher and that ET administration did not significantly alter pulse pressure.


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Fig. 2.   Changes from baseline values for mean arterial pressure (MAP, A) and plasma arginine vasopressin (AVP, B) 10 min after intracerebroventricular injection of artificial CSF (C), 10 pmol endothelin-1 (ET), 40 nmol BQ-123 (BQ), or ET-1 and BQ-123 (ET + BQ) in conscious Long-Evans rats. Experimental groups are sham denervated, sham lesioned (open bars, n = 5, 7, 6, and 5); sinoaortic denervated (SAD), sham lesioned (filled bars, n = 7, 7, 5, and 4); sham denervated, PVN lesioned (hatched bars, n = 9, 5, 6, and 6); and SAD, PVN lesioned (gray bars, n = 6, 5, 5, and 6). Values are means ± SE. *P < 0.001 vs. aCSF with the same denervation/lesion status; dagger P < 0.01 vs. ET in the SAD, sham-lesioned group; Dagger P < 0.001 vs. ET in the sham-denervated, sham-lesioned group; black-lozenge P < 0.05 vs. ET in the SAD, sham-lesioned group. Comparisons made by ANOVA.



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Fig. 3.   Representative tracing of heart rate (HR) and arterial pressures [MAP and systolic (Sys) and diastolic (Dia) blood pressure (BP)] from a sham-denervated, sham-lesioned rat (A) and a SAD, sham-lesioned rat (B). The tracing has been truncated to show the last 10 min of the 30-min baseline period before the first blood sample was obtained (first break in tracing, *). ET-1 (10 pmol) was injected intracerebroventricularly as indicated by arrow. The second blood sample (second break, dagger ) was obtained 10 min after ET administration.

Heart rate consistently increased in the ET-1-treated, sham PVN-lesioned groups [50 ± 29 beats/min (sham denervated) and 43 ± 26 beats/min (SAD)] but changed very little from baseline in the corresponding artificial CSF-treated groups: -16 ± 22 and 4 ± 17 beats/min. Nevertheless, the heart rate responses were highly variable so that comparisons between ET-1-treated and baseline or corresponding artificial CSF groups were not statistically significant by ANOVA.

In contrast to the sham PVN-lesioned groups, MAP did not increase with intracerebroventricular ET-1 injection in the rats with bilateral PVN lesions. The PVN lesions also abolished the rise in plasma AVP levels observed in the SAD group (Fig. 2). Typical hemodynamic tracings in PVN-lesioned rats given ET-1 are shown in Fig. 4. Heart rate did not increase in the PVN-lesioned groups after ET-1 [-12 ± 10 beats/min (sham denervated) and -2 ± 25 beats/min (SAD)]. In animals in which the electrolytic lesions were histologically verified to be adjacent but outside the PVN and which also received ET-1, MAP increased 16 ± 2 mmHg and plasma AVP rose 13 ± 4 pg/ml. Of these, two were SAD.


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Fig. 4.   Representative tracing of HR and arterial pressures from a sham-denervated, PVN-lesioned rat (A) and a SAD, PVN-lesioned rat (B). The tracing has been truncated to show the last 10 min of the 30-min baseline period before the first blood sample was obtained (first break in tracing, *). ET-1 (10 pmol) was injected intracerebroventricularly as indicated by arrow. The second blood sample (second break, dagger ) was obtained 10 min after ET administration.

ETA receptor antagonism significantly inhibited the rise in MAP and plasma AVP concentrations elicited by ET-1 in the sham PVN-lesioned groups. When given alone, BQ-123 induced no changes from baseline in any of the groups.


    DISCUSSION
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The major finding of the present study is that bilateral lesions of the magnocellular region of the PVN prevent the increase in both systemic arterial pressure and AVP secretion observed with intracerebroventricular ET-1.

These data confirm the observations by a number of laboratories including our own that injection of ET-1 in the lateral cerebral ventricles increases arterial pressure and AVP secretion (19, 20, 24-26, 36). It has been postulated that the ET-1-induced rise in arterial pressure is mediated by a vasopressinergic mechanism (16, 20, 36); however, it has become increasingly evident that AVP contributes to the pressor response only under selected physiological settings. Such conditions include those when afferent input from the arterial baroreceptors is prevented by SAD (26), when cardiopulmonary baroreceptors are stimulated by volume depletion (20), or when anesthesia and acute surgery result in circulating pressor levels of AVP before administration of ET-1 (16, 17). On the contrary, in the awake euvolemic baroreflex-intact rat, central ET-1 induces a comparable rise in pressure before and after antagonism of V1 vasopressinergic vascular receptors (24). Moreover, Long-Evans rats and homozygous Brattleboro rats devoid of circulating AVP exhibit equivalent increases in MAP (24). These findings are in agreement with the recent observation that lesions of the AV3V region that disrupt neuronal pathways from the subfornical organ to the anterior hypothalamus significantly attenuate the rise in AVP but not the increase in arterial pressure (25). The dissociation of the pressor action from the AVP secretory effect of ET-1 suggests that an alternative neural pathway mediates the pressor response.

Several laboratories have shown that the ET-1-induced pressor response is mediated by increased sympathetic outflow (2, 9, 19, 24). Systemic and intracerebroventricular ET-1 can gain access to the circumventricular organs. Of these, the subfornical organ in particular possesses abundant ET receptors (5, 7). The subfornical organ sends out two major efferent projections: 1) precommissural bundles to the AV3V, including the median preoptic nucleus, the organum vasculosum of the lamina terminalis, and supraoptic nuclei, and 2) postcommissural fibers, some of which pass through the PVN to terminate in the supraoptic nuclei and others that terminate in the PVN itself (11, 15). Consistent with these known pathways, intracerebroventricular ET-1 induces c-fos expression in the PVN (38). Whether this is a direct effect of ET-1 or a postsynaptic effect as may occur with ET-1 action on the subfornical organ with subsequent stimulation of PVN neurons has not been identified. In turn, chemical or electrical stimulation of PVN neurons elicits an increase in efferent sympathetic activity and a concurrent rise in heart rate and arterial pressure (4, 10, 13). Ablation of the subfornical organ reduces the proportion of PVN neurons excited by intracerebroventricular ET-1 (33), but concurrent effects on arterial pressure and AVP levels are not known. Thus the PVN occupies a pivotal position for integrating the hormonal and autonomic responses to ET-1.

The present findings clearly show that both the rise in arterial pressure and AVP release in response to intracerebroventricular ET-1 are totally averted by electrolytic lesions of the PVN. Nonspecific damage from the electrolytic lesions is not likely to have resulted in these observations, since lesions of areas immediately adjacent or encompassing only one PVN fail to block either AVP release or the rise in arterial pressure. Given the known neural pathways connecting the subfornical organ, PVN, supraoptic nuclei, and existing electrophysiological data (4, 10, 13, 33, 34, 38), the present observations do not unequivocally exclude the possibility that the electrolytic lesions disrupted fibers of passage, particularly those from the subfornical organ through the PVN to the supraoptic nuclei (11, 15). Nonetheless, the lesions ablated a significant portion of neuronal cell bodies within the area of the PVN where a substantial component of subfornical projections terminate (11, 15) and that is associated with the pressor response (4, 13, 38).

Indeed, Wall and Ferguson (33) have reported that 60% of subfornical organ neurons antidromically identified as projecting to the PVN exhibit excitatory responses to intravenously administered ET-1. After electrolytic destruction of at least 50% of the subfornical organ, the proportion of vasopressinergic cells in the PVN responsive to systemic ET-1 decreases dramatically to 7% (33). However, direct microinjection of ET-1 into the PVN did not increase arterial pressure or plasma AVP levels (17). Accordingly, the pressor response does not appear to result from direct action of ET-1 on PVN neurons. Rather, these observations support a model with the PVN acting as a relay for ET-1-stimulated pathways projecting from the subfornical organ. Inputs to neurons within the magnocellular region of the PVN then lead to activation of projections emerging from the PVN to caudal cardiovascular control centers that result in increased arterial pressure (Fig. 5).


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Fig. 5.   Schematic illustration of putative central nervous system pathways for ET-induced changes in hemodynamic parameters and AVP secretion. ET injected into the ventricles acts on the subfornical organ (SFO). Neural pathways from the SFO lead to the PVN and to the supraoptic nuclei (SON) via the organum vasculosum of the lamina terminalis (OVLT). Internuclear connections between SON and PVN are indicated and may serve to synchronize firing of vasopressinergic neurons leading to secretion of AVP from the posterior pituitary (PP). Additional distinct pathways lead from the PVN to the ventral lateral medulla (VLM), nucleus tractus solitarius (NTS), and the A1 neurons, thereby eliciting increased sympathetic efferent output and increased arterial pressure. Arrows delineating the pathways are representative and are not intended to imply mono- or multisynaptic connections.

That AVP release is also completely blocked by bilateral PVN lesions was unexpected, given that AV3V lesions significantly attenuate AVP release (25). Our initial hypothesis rather simplistically predicted the following two independent pathways: one rostroventrally from the subfornical organ to the supraoptic nuclei (interrupted by the AV3V lesion) that mediates only AVP release and a second pathway projecting more caudally from the subfornical organ to the PVN that only leads to increased arterial pressure. The data support a more complex scheme. ET-1, via the subfornical organ, elicits excitatory responses in 21% of the AV3V neurons (35) and 60% of PVN neurons (33, 34). In addition to supraoptic neurons receiving afferent projections from the ipsilateral PVN, up to 77% of magnocellular neurons within the PVN receive inputs from the supraoptic nucleus. Moreover, the majority of these inputs are excitatory (27, 28, 30). It has been suggested that these internuclear connections serve to synchronize the firing patterns of the neurons and, consequently, neurohypophysial hormone release. Such a model would provide some explanation for our present observations. On the one hand, interruption of the pathways from the subfornical organ passing through the AV3V region interrupts signaling to the supraoptic nuclei. AVP release by vasopressinergic cells within the supraoptic nuclei would fail to occur. Stimulatory inputs from the supraoptic nuclei to the PVN would also be affected, thereby preventing AVP secretion from PVN projections to the posterior pituitary. On the other hand, bilateral lesions of the PVN disrupt pathways directly from the subfornical organ to magnocellular neurons within the PVN that project to the neurohypophysis. Fibers coursing through the PVN to supraoptic nuclei and excitatory inputs from the supraoptic nuclei to magnocellular neurons within the PVN are also interrupted. The data suggest that synchronization of supraoptic nuclei and PVN activity is required for a measurable increase in circulating AVP to occur. Thus either bilateral PVN lesions or an AV3V lesion can abolish AVP secretion.

In summary, previous observations together with the current findings support the concept shown in Fig. 5. Basically, fibers disrupted by the AV3V lesions carry predominantly stimulatory signals from the subfornical organ via the anterior hypothalamus to the supraoptic nuclei for AVP release. The more lateral and caudal pathways, including those to the PVN, remain uninterrupted, and the pressor response remains intact. Bilateral lesions of the PVN disrupt pathways from anterior brain structures to nuclei in the medulla and spinal cord that mediate sympathetic outflow and cardiovascular responses, consequently blocking the pressor effect of ET-1. Because bilateral PVN lesions completely prevent the rise in plasma AVP levels, inputs from the anterior hypothalamus that terminate on magnocellular neurons within the PVN and/or fibers of passage through the PVN to the supraoptic nuclei are necessary for AVP release. Because either an AV3V lesion or bilateral PVN lesions can abolish AVP secretion, the data suggest that synchronization of inputs between supraoptic nuclei and PVN is required for ET-1 to elicit a measurable rise in plasma AVP. Further studies are required to confirm this putative mechanism. Finally, ET-1 injected in the lateral ventricles stimulates AVP release and increased systemic arterial pressure via pathway(s) that require the integrity of the PVN.


    ACKNOWLEDGEMENTS

We appreciate the gracious help of Robert Pawlowicz for invaluable computer expertise.


    FOOTNOTES

This work was supported by a Merit Award from the Department of Veterans Affairs to N. F. Rossi.

Address for reprint requests and other correspondence: N. F. Rossi, Depts. of Medicine and Physiology, Wayne State Univ. School of Medicine, 4160 John R no. 908, Detroit, MI 48201 (E-mail: nrossi{at}intmed.wayne.edu).

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.

Received 22 June 2000; accepted in final form 20 September 2000.


    REFERENCES
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
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