Inhibition of Bradykinin-Induced Plasma Extravasation Produced by Noxious Cutaneous and Visceral Stimuli and Its Modulation by Vagal Activity
Frederick Jia-Pei Miao1,
Wilfrid Jänig4,
Paul G. Green1, and
Jon D. Levine1, 2
1 Department of Medicine, 2 Department of Anatomy, and 3 Department of Oral and Maxillofacial Surgery, Schools of Medicine and Dentistry, University of California at San Francisco, San Francisco, California 94143-0452; and 4 Physiologisches Institut, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
 |
ABSTRACT |
Miao, Frederick Jia-Pei, Wilfrid Jänig, Paul G. Green, and Jon D. Levine. Inhibition of bradykinin-induced plasma extravasation produced by noxious cutaneous and visceral stimuli and its modulation by vagal activity. J. Neurophysiol. 78: 1285-1292, 1997. Intrathecally applied nicotine reduces bradykinin-induced plasma extravasation (BK-induced PE) in the rat knee joint. This depression is mediated by the hypothalamo-pituitary-adrenal (HPA) axis and is enhanced by interruption of impulse traffic in afferents of the abdominal vagus nerve. Like intrathecal nicotine, electrical stimulation of unmyelinated cutaneous fibers also depresses BK-induced PE, which is also dependent on an intact HPA axis. In this study, we investigated whether the inhibitory effect of intrathecal nicotine can be mimicked by noxious stimulation of skin and of viscera. Furthermore we determined whether this depression is potentiated after subdiaphragmatic vagotomy. Stimulation of visceral afferents in the peritoneum, by intraperitoneal capsaicin injection, dose-dependently decreased BK-induced PE. The capsaicin dose-response function was shifted by 1.5-2 orders of magnitude to the left after vagotomy. Stimulation of visceral afferents in the urinary bladder by capsaicin also dose-dependently reduced BK-induced PE, which similarly was potentiated after vagotomy. Transcutaneous stimulation of unmyelinated nociceptive afferents from the plantar skin of the paw depressed BK-induced PE. This depression had a threshold of ~0.25 Hz and was maximal at a stimulation frequency of ~1 Hz. After subdiaphragmatic vagotomy, the stimulus response function shifted to the left and the inhibition was significantly larger than in control, in the range of 0.125-1 Hz stimulation. These results show that noxious stimulation of skin and viscera depressed BK-induced PE and that such depression was potentiated after subdiaphragmatic vagotomy in a manner similar to that of intrathecally applied nicotine. Based on these observations, we hypothesize that intrathecal nicotine depresses BK-induced PE by exciting spinal nociceptive neurons or the central projections of nociceptive primary afferent neurons.
 |
INTRODUCTION |
Synovial plasma extravasation induced experimentally by intra-articular infusion of bradykinin (BK-induced PE) is dose dependently decreased by nicotine injected intrathecally at the level of the lumbar spinal cord (Miao et al. 1994
). BK-induced PE is also depressed by transcutaneous electrical stimulation of unmyelinated afferent nerve fibers (Green et al. 1995
, 1997
). Both of these effects are abolished after transection of the spinal cord at the thoracic level of T1/T2, after hypophysectomy, or after blockade of synthesis of corticosterone (Green et al. 1995
; Miao et al. 1994
, 1996c
, 1997a
). However, they are not affected by acute interruption or decentralization (interruption of the preganglionic axons) of the lumbar sympathetic innervation of the knee joint nor by epinephrine or another substance released from the adrenal medulla (Green et al. 1995
; Miao et al. 1996a
,c
). Thus reduction of BK-induced PE, generated by both intrathecal nicotine as well as by transcutaneous electrical stimulation of unmyelinated afferents, appears to be mediated by ascending tracts in the spinal cord and by activation of the hypothalamo-pituitary-adrenal (HPA) axis. The depression of BK-induced PE produced by intrathecal nicotine is potentiated by several orders of magnitude after subdiaphragmatic vagotomy, which is reversed by electrical stimulation of the central stump of the cut vagus nerve (Miao et al. 1994
).
These results are compatible with the view that intrathecal nicotine activates neurons in the spinal cord associated with the nociceptive system or central projections of these nociceptive primary afferent neurons. Indeed nicotinic receptors are found in the cord at this level (Boyd et al. 1991
; Khan et al. 1994b
). Furthermore, previous experiments in which the abdominal vagal afferents were interrupted or stimulated suggest that activity in these visceral afferents regulate the suppression of BK-induced PE by central inhibitory actions (Miao et al. 1994
). To further characterize these phenomena, we tested whether graded stimulation of unmyelinated cutaneous afferents, of spinal peritoneal afferents from the abdominal cavity and of spinal visceral afferents from the urinary bladder, lead to a graded inhibition of BK-induced PE and whether this inhibition is potentiated after interruption of the subdiaphragmatic vagus. In these experiments, the cutaneous afferents were excited by transcutaneous electrical stimulation at a strength that was suprathreshold for unmyelinated fibers and at a variable frequency; the visceral afferents were stimulated with capsaicin, over a range of doses.
 |
METHODS |
The experiments were performed on male Sprague-Dawley rats except for those experiments in which the spinal afferents from the urinary bladder were stimulated. In these experiments female Sprague-Dawley rats were used (300-400 g; Bantin and Kingman, Fremont, CA). Rats were anesthetized by intraperitoneal injection of sodium pentobarbital (65 mg/kg, Anthony Products, Arcadia, CA). Animal care and use conformed to the guidelines of the National Institutes of Health for the care and use of experimental rats. Experimental protocols were approved by the University of California, San Francisco Committee on Animal Research.
Perfusion of the knee joint
Knee joint perfusion was performed as previously described (Coderre et al. 1989
; Miao et al. 1996b
). In brief, after incision of the skin and connective tissue overlying the anterior aspect of the knee and the saphenous vein, Evans blue dye (50 mg/kg) was administered intravenously in the saphenous vein. Ten minutes after injection of the dye, a 30-gauge needle was inserted into the cavity of the knee joint for the infusion of fluid (250 µl/min, controlled by a syringe pump from Sage Instruments, Model 351, Cambridge, MA). After infusion of an initial volume of 100-200 µl of vehicle, a second needle (25-gauge) was inserted into the knee joint, ~3 mm from the inflow needle. This second needle served as an outflow cannula. Fluid was withdrawn from the joint through the outflow cannula using a second syringe pump. The fluid was infused and withdrawn at a constant rate of 250 µl/min. Perfusate samples were collected every 5 min for periods of
185 min. Samples were analyzed for the amount of Evans blue dye by spectrophotometric measurement of absorbance at 620 nm. Absorbance at this wavelength is linearly related to the dye concentration (Carr and Wilhelm, 1964
).
After a 15-min baseline perfusion period with vehicle (normal saline), plasma extravasation into the knee joint was stimulated by adding bradykinin (BK, 160 ng/ml, i.e., 1.5 × 10
7 M) to the perfusion fluid. Both knee joints in the same rat were perfused simultaneously.
Stimulation of spinal visceral afferents by capsaicin
Spinal visceral afferents from the peritoneal cavity and from the urinary bladder were excited by capsaicin. Capsaicin was injected into the peritoneal cavity in progressively higher doses (10
6 to 1 mg/kg) at 20-min intervals.
Because of their short and relatively straight urethra, female rats were used in the experiments in which visceral afferents from the urinary bladder were stimulated; it is extremely difficult to cannulate the urethra of male rats. A PE-50 polyethylene cannula was placed into the urinary bladder through the urethra without causing trauma. Starting 30 min after beginning the bradykinin infusion into the knee joint cavity, solutions of capsaicin (1 ml) in increasing concentrations (10
10 to 10
4 M) were injected into the urinary bladder. Each solution was left in the bladder for 20 min, and the bladder then was emptied before a solution with the next higher concentration of capsaicin was injected. An age-matched group of female rats was used as controls in which neither the vagus nerve was cut nor spinal visceral afferents stimulated.
The level of basal synovial plasma extravasation as well as the maximal level of BK-induced PE were smaller in female than in male rats (see Table 1). The reason for this gender difference is probably related to the differences in sex hormones (unpublished observations).
Electrical stimulation of the hindpaw
Two stainless steel electrodes were placed transversely in the plantar surface of the hindpaw contralateral to the perfused knee joint (~10 mm apart). Afferent fibers were excited by a square wave stimulus at an intensity of 25 mA (0.25-ms pulse duration). This stimulus intensity was found to reliably excite C fibers (Green et al. 1995
). The stimulus frequencies were doubled progressively, starting with 0.0625 on up to 1 Hz. A stimulation period at a given frequency lasted for 20 min.
Subdiaphragmatic and cervical vagotomy
The vagus nerves were dissected bilaterally at the subdiaphragmatic level, as described previously (Miao et al. 1994
; Precht and Poley 1985). After lateral incision of the abdominal wall in the left upper quadrant, the esophagus at the subdiaphragmatic level was exposed fully. The vagus nerves then were dissected free from the esophagus and cut. In four animals, cervical vagotomy was performed bilaterally, with a tracheal cannula in place. After medial incision of the ventral skin of the neck, both cervical vagus nerves were exposed and cut. Experiments on vagotomized rats began ~1 h after the surgical operation. Some experiments were conducted 10 days after subdiaphragmatic vagotomy.
Dose-response relationships
Dose-response relationships for capsaicin effects on the inhibition of BK-induced PE were obtained by a cumulative dose method (Miao and Lee 1989
). The doses that produced 50% of the maximum inhibition (ED50 values) were determined for each joint. From these values, the geometric means for ED50 with 95% confidence intervals were calculated (Fleming et al. 1972
; Miao and Lee 1989
).
Materials
Bradykinin acetate, 8-methyl-N-vanillyl-6-nonenamide (capsaicin), and polyoxyethylene sorbitan mono-oleate (Tween 80) were purchased from Sigma Chemical (St. Louis, MO). Capsaicin was first dissolved in a solution mixed with ethanol and Tween 80 (1:1 ratio) and then diluted in normal saline (Travenol Laboratories, Deerfield, IL). The final concentration of ethanol was <0.1%.
Experimental procedure and statistics
Results are based on different experimental interventions, each conducted on at least eight knee joints (for data summary, see Table 1). Data are presented as means ± SE; significant differences between pairs of time-effect curves were determined by two-way (group × time) repeated measures analysis of variance (ANOVA). Significant differences between pairs of dose-response curves were determined by two-way (group × dose) repeated measuresANOVA. Differences were considered statistically significant atP < 0.05.
 |
RESULTS |
Effects of graded stimulation of spinal visceral afferents by capsaicin
STIMULATION BY INTRAPERITONEAL APPLICATION OF CAPSAICIN.
Stimulation of visceral afferents by capsaicin injected intraperitoneally dose dependently inhibited BK-induced PE in the knee joint. This inhibition started at 10
4 mg/kg and was maximal at ~10
1 mg/kg (
in Fig. 1 and
in Fig. 2). Acute subdiaphragmatic or cervical vagotomy significantly potentiated the inhibition of BK-induced PE, which was generated by intraperitoneal capsaicin (subdiaphragmatic vagotomy:
in Fig. 1 and
in Fig. 2; cervical vagotomy: × in Fig. 2). After vagotomy, inhibition is now detectable from 10
6 mg/kg capsaicin and maximal at ~10
2 mg/kg. The ED50 for inhibition in the sham surgery group was significantly larger than those of subdiaphragmatic vagotomy as well as cervical vagotomy [1.9 × 10
6 mg/kg (subdiaphragmatic vagotomy) and 1.1 × 10
6 mg/kg (cervical vagotomy) vs. 3.6 × 10
4 mg/kg (sham surgery), all P < 0.01; Table 1]. There was no significant difference in the dose-response curves of the inhibition of BK-induced PE between both types of vagotomy (Fig. 2 and Table 1).

View larger version (26K):
[in this window]
[in a new window]
| FIG. 1.
Effect of intraperitoneal capsaicin on bradykinin-induced plasma extravasation (BK-induced PE) in sham surgery control and in acute subdiaphragmatic vagotomized rats. After baseline plasma extravasation in the first 3 samples, bradykinin (BK; 160 ng/ml) was added to perfusion fluid, and for remainder of the experiment, was the only substance in the perfusion fluid. In control group, rats were with intact vagus nerves and did not receive any injection of capsaicin ( , n = 8). In sham control group, the abdomen was only opened to expose subdiaphragmatic vagus nerves, without cutting them, and then closed again ( , n = 8). Bilateral subdiaphragmatic vagus nerves of rats in vagotomy group were cut 1 h before knee joint perfusion experiment ( , n = 8). In sham and vagotomy groups, capsaicin was injected in cumulative doses into the peritoneal cavity (10 6 to 1 mg/kg). In this and subsequent figures, data are presented as means ± SE. Time-effect curve of sham control group was significantly different from that of acute vagotomy group (F = 32.619, P < 0.01). Both curves of sham and vagotomy groups were significantly different from that in control group in which no capsaicin was injected (F = 49.681 and 170.970, respectively, both P < 0.01).
|
|

View larger version (19K):
[in this window]
[in a new window]
| FIG. 2.
Stimulus-response functions for inhibition of BK-induced PE generated by intraperitoneal capsaicin in sham surgery control and in acute subdiaphragmatic and cervical vagotomized rats. Capsaicin was injected in increasing concentrations (10 6 to 1 mg/kg), cumulatively, into peritoneal cavity. Acute cervical (×, n = 8) or subdiaphragmatic vagotomy ( , n = 8) potentiated action of intraperitoneal capsaicin, shifting dose-response curve significantly to the left (× vs. , F = 22.946; vs. , F = 44.008, both P < 0.01). Dose-response curves of cervical vagotomy group and that of subdiaphragmatic vagotomy group were not significantly different (× vs. , F = 2.731, P > 0.05). Data of experiments on sham-vagotomized and acute subdiaphragmatic vagotomized rats were the same as those presented as time-effect curves in Fig. 1.
|
|
STIMULATION OF AFFERENTS OF THE URINARY BLADDER BY INTRAVESICAL INJECTION OF CAPSAICIN.
Stimulation of visceral afferents from the urinary bladder by intravesical instillation of capsaicin solution dose dependently inhibited BK-induced PE in sham-vagotomized animals. The inhibition started at ~10
8 M and was maximal at 10
4 M capsaicin. Acute subdiaphragmatic vagotomy significantly potentiated this inhibition (
vs.
in Fig. 3). The inhibition now started at
10
10 M, and the ED50 of the inhibition after vagotomy was significantly smaller than the ED50 before vagotomy (6.9 × 10
10 M vs. 1.6 × 10
7 M, P < 0.01; Table 1).

View larger version (17K):
[in this window]
[in a new window]
| FIG. 3.
Effects of acute subdiaphragmatic vagotomy on inhibition of BK-induced PE by capsaicin injected into the urinary bladder. One milliliter of capsaicin solution in increasing molar concentrations (10 10 to 10 4 M) was injected successively into the urinary bladder through a catheter in the urethra in female rats. Before the next higher concentration of capsaicin was injected, the urinary bladder was emptied. Maximal BK-induced PE in females is ~70% of maximal value in males (unpublished observations). Acute subdiaphragmatic vagotomy (n = 10) potentiated the action of intrabladder capsaicin, shifting dose-response curve significantly to the left (F = 27.005, P < 0.01).
|
|
Effects of graded stimulation of cutaneous afferents by transcutaneous electrical stimulation of the plantar skin
BK-induced PE was depressed powerfully by transcutaneous electrical stimulation of C fibers as described previously (Green et al. 1995
, 1997
). The depression of BK-induced PE was graded when the frequency of the electrical stimulus at C-fiber strength (25 mA) was varied from 0.0625 to 1 Hz being maximal at 1 Hz stimulation (
in Fig. 4 and
in Fig. 5). After acute subdiaphragmatic vagotomy, low frequency stimulation at 0.0625 Hz, which did not affect BK-induced PE in sham control rats, already produced a depression of BK-induced PE (
in Fig. 4 and
in Fig. 5). The dose-response curve for the depression of BK-induced PE was significantly shifted to the left after vagotomy (P < 0.01,
vs.
in Fig. 5). For example, at a stimulation frequency of 0.125 Hz, the BK-induced PE was little changed in control animals but depressed by ~50% in the vagotomized animals. Similar results were obtained from animals that were vagotomized 10 days before the experiment (data not shown).

View larger version (26K):
[in this window]
[in a new window]
| FIG. 4.
Effect of subdiaphragmatic vagotomy on depression of BK-induced PE into knee joint generated by continuous transcutaneous electrical stimulation of unmyelinated afferents (25 mA, 0.0625-1 Hz, of 0.5 ms duration). After establishment of baseline PE in first 3 samples, BK (160 ng/ml) was added to perfusion fluid and, for remainder of the experiment, was the only substance in perfusion fluid ( , n = 8). In a second group of rats with intact vagus nerves ( , n = 8), C fibers were stimulated electrically, via electrodes in 1 hindpaw, starting 40 min after onset of perfusion of BK, whereas in a third group of animals ( , n = 8) cutaneous C fibers also were stimulated, but these animals were vagotomized subdiaphragmatically immediately before the experiments. Frequency of stimuli varied from 0.0625 to 1 Hz. Time-effect curve in acute vagotomy group was significantly different from that in sham surgery group ( vs. , F = 20.085, P < 0.01). Curves of both the acute vagotomy and sham surgery groups were significantly different from that of no-stimulation control group ( vs. , F = 349.166, vs. , F = 25.756, both P < 0.01).
|
|

View larger version (15K):
[in this window]
[in a new window]
| FIG. 5.
Stimulus-response functions of the depression of BK-induced PE generated by increasing frequency of the electrical C-fiber stimulation (abscissa scale) in sham surgery control rats ( ) and in vagotomized rats ( ). Data taken from 2 last samples of each stimulation period. Same experiments as in Fig. 4A. Acute subdiaphragmatic vagotomy potentiated the action of transcutaneous C-fiber stimulation, shifting dose-response curve significantly to the left (F = 9.539, P < 0.01).
|
|
 |
DISCUSSION |
Previously we have shown that BK-induced PE in the rat knee joint is inhibited dose dependently by intrathecally applied nicotine and by electrical stimulation of cutaneous C but not A fibers. It furthermore was shown that both depressions were mediated by the HPA axis but not by the sympathetic outflow to the knee joint or by the sympathoadrenal system (Green et al. 1995
; Miao et al. 1996c
). In the present study, we have shown first that graded stimulation of peritoneal afferents and visceral afferents from the urinary bladder by capsaicin and of cutaneous C-fiber afferents by transcutaneous electrical stimulation led to a graded depression of BK-induced PE and, second, that vagotomy potentiated depression produced by both stimuli. Based on these results, we hypothesize that intrathecal nicotine does excite neurons of the nociceptive pathway. The arguments in favor of this hypothesis are as follows: 1) the nicotinic action was mimicked by stimulation of somatic and visceral nociceptive afferents; 2) vagotomy potentiated the inhibition elicited by both stimulation of nociceptive afferents and intrathecal nicotine (Miao et al. 1994
, 1997b
); 3) hypophysectomy attenuated both (Green et al. 1995
; Miao et al. 1996c
); and 4) blockade of glucocorticoid receptors attenuated both (Green et al. 1995
; Miao et al. 1996c
). These observations suggest a common modulatory mechanism shared by functionally different types of somatic and visceral nociceptive afferent input systems and that a nociceptive-neuroendocrine negative feedback loop, which controls neurogenic inflammatory processes in the synovia of the rat knee joint, is inhibited continuously by activity in vagal afferents and released after vagotomy.
We also found that acute vagotomy does not influence basal synovial plasma extravasation but increases maximal BK-induced PE (see Table 1). At present we have no explanation for this latter change. If ongoing activity in abdominal vagal afferents continuously activates the HPA axis leading to some depression of BK-induced PE, one would expect an enhancement of BK-induced PE after acute vagotomy.
Figure 6 outlines the putative central neuronal and neuroendocrine circuits that might mediate the vagal modulation of the depression of BK-induced PE generated by noxious stimulation of skin as well as by stimulation of spinal visceral afferents. Afferent activity from skin, viscera, and probably the deep somatic domain is proposed to converge on the same spinal ascending tract neurons that project via the brain stem to the hypothalamus. The nature of this ascending tract is unknown. However, it is clear from our data that this central neural pathway is under powerful inhibitory control from abdominal vagal afferents acting via the nucleus of the solitary tract (NTS) either at the level of the spinal cord, the brain stem and/or the hypothalamus. The final efferent signal derives from the adrenal cortex and is possibly a glucocorticoid (Green et al. 1995
, 1997
). The target cells mediating the inflammatory process upon which this endocrine signal acts, leading to depression of BK-induced PE, are unclear. They generally are assumed to be cells belonging to the immune system (e.g., macrophages, lymphocytes, and polymorphonuclear leukocytes) or the microvascular endothelium. However, this signal from the adrenal cortex also could act primarily on sympathetic postganglionic terminals because these are necessary to mediate a large part of the BK-induced PE (Green et al. 1997
; Miao et al. 1996b
,d
).

View larger version (33K):
[in this window]
[in a new window]
| FIG. 6.
Schematic diagram showing hypothetical peripheral and central pathways that modulate bradykinin-induced synovial plasma extravasation (BK-induced PE). BK-induced PE is largely dependent on the presence, but not activity, of the terminals of sympathetic postganglionic neurons in synovia (Miao et al. 1996a ,b ). Stimulation of spinal nociceptive primary afferents from skin and abdominal and pelvic viscera excites ascending systems in spinal cord and brain stem, which, in turn, activate hypothalamo-pituitary adrenal axis, resulting in depression of BK-induced PE, probably via glucocorticoid released from adrenal cortex (Green et al. 1995 , 1997 ; Miao et al. 1996c ). Activity in vagal abdominal afferents inhibits ascending pathway. Site of this inhibition is unknown. NTS, nucleus of solitary tract.
|
|
Although the spinal mechanism by which intrathecal nicotine inhibits BK-induced PE is not known, several lines of evidence suggest that it is through spinal nociceptive neurons because there are nicotinic receptors on nociceptive sensory neurons (Boyd et al. 1991
; Khan et al. 1994b
). Given that the nociceptive neurons can be activated by nicotine via these nicotinic cholinergic receptors (Renshaw et al. 1993
; Steen and Reeh 1993
), nicotine also should stimulate the central terminals of these afferent neurons. Although some investigators have shown that intrathecal nicotine generates nociceptive behavior in rats (Khan et al. 1994a
-c
) others have elicited antinociceptive effects by these nicotinic stimuli (Gillberg et al. 1990
; Rogers and Iwamoto 1993
). The reason for these differences are unknown but may be related to the fact that nicotinic receptors are not only on the central terminals of nociceptive afferent neurons but also on other neurons in the spinal cord (Hösli and Hösli 1994
; Khan et al. 1994d
).
Intraperitoneal capsaicin probably produces depression of BK-induced PE through stimulation of two sets of afferents. First, it may stimulate spinal afferents from the visceral peritoneal lining covering abdominal and pelvic organs that project through different splanchnic nerves to the thoracic and upper lumbar spinal cord (Jänig and Morrison 1986
). Most of these afferents are mechanosensitive and chemosensitive (i.e., responding to inflammatory agents, ischemia, etc.) (for review, see Jänig 1996
). They are involved in visceral nociception and visceral pain (see Cervero and Morrison 1986
; Gebhart 1995
), visceral protective reflexes (Jänig 1996
; Jänig and Häbler 1995) and possibly regulations of visceral organs. Second, it also may excite afferents innervating the parietal peritoneum. Little is know about the functional properties of these afferents, but they also may respond to local mechanical and chemical stimuli (Bahns et al. 1986
), these afferents may belong to the so-called "silent afferents", which are only activated under special extreme conditions (Michaelis et al. 1996
). They are not visceral in the true sense but deep somatic afferents (see Lewis 1942
). Finally, intraperitoneal capsaicin may stimulate vagal afferents that project to the nucleus of the solitary tract (Ritter and Dinh 1988
). The functional types of vagal afferents excited in this way are unknown.
Capsaicin injected into the urinary bladder excites sacral as well as lumbar visceral afferents (vagal visceral afferents should not be involved because there is no vagal innervation to the urinary bladder) (Jänig 1996
; Jänig and Morrison 1986
). Both sets of afferents are involved in visceral nociception of the urinary bladder (Jänig and Koltzenburg 1993
); both also may be involved in inhibitory control of BK-induced PE. The magnitude of the vagotomy-induced leftward shift for the dose-response curve and the maximal depression of BK-induced PE generated by the three stimulus paradigms were similar in degree (Table 1).
The hypothesis of vagal afferent modulation of inflammatory responses via the HPA axis is in agreement with reports that indicate that activity in the vagus nerve inhibits this axis (Bueno et al. 1989
; Gonzalez-Fernandez and Gonzalo-Sanz 1987
) and, therefore, the effects of stimuli that activate the HPA axis. Because activation of the HPA axis produces a potent anti-inflammatory effect, an enhanced activity of the HPA axis after removal of the vagal afferent activity would be expected to potentiate the anti-inflammatory effect of intrathecal nicotine, noxious visceral stimuli, or noxious cutaneous stimuli in reducing synovial plasma extravasation. An interesting corollary of the present study is that spinal visceral afferents and vagal visceral afferents have functionally opposite reflex effects on the neurogenic inflammatory process via the HPA axis.
Recently it was shown in experiments in monkeys and rats that vagal afferents are involved in control of nociception and pain. In rats, cervical vagotomy reduces stress-induced analgesia generated by intermittent foot shocks (Maixner and Randich 1984
; Maixner et al. 1982
). Furthermore, stimulation of volume receptors from the right atrium produces inhibition of tail flick reflex to noxious radiant heat (Maixner and Randich 1984
). In monkeys, electrical stimulation of cervical vagal afferents suppresses transmission of impulse activity in spino-thalamic relay neurons with nociceptive function at all levels of the spinal cord. Electrical stimulation of subdiaphragmatic vagal afferents has no effect on the spino-thalamic relay neurons in this species. These observations are in favor of the notion that particularly cardio-pulmonary afferents are involved in this inhibitory control. The central pathways that mediate this effect are neurons in the subceruleus-parabrachial complex (noradrenergic) and neurons in the nucleus raphe magnus of the rostro-ventral medulla (serotonergic) that project to the dorsal horn (for review, see Foreman 1989
). Similar results were obtained in the rat by Gebhart and coworkers. Here transmission of nociceptive impulses from skin and colon in the dorsal horn and the tail-flick-reflex elicited by noxious heat stimulation of the tail were enhanced by electrical stimulation of myelinated vagal afferents and depressed by electrical stimulation of unmyelinated vagal afferents. The subdiaphragmatic vagal afferents were particularly powerful in eliciting these modulatory effects. As in the monkey, the inhibitory effects were generated via descending systems from the subceruleo-parabrachial complex and from the rostroventral medulla. The facilitatory effect was mediated by suprapontine pathways (see Gebhart and Randich 1992
; Randich and Gebhart 1992
).
The present study, together with our previous reports (Green et al. 1995
; Miao et al. 1994
, 1996c
), has demonstrated a novel nociceptive-neuroendocrine negative feedback mechanism that regulates microvascular permeability in the knee joint of the rat. It is hypothesized that excitation of the spinal ascending neurons, generated by intrathecal nicotine, cutaneous, or visceral noxious stimuli, decreases synovial plasma extravasation via activating the HPA axis and that activity of vagal afferents from abdominal visceral organs modulates this negative-feedback circuit, leading to its attenuation when the level of activity in vagal afferents increases and to its potentiation when the level of vagal activity decreases. Vagal afferents from the abdominal organs project organotopically to the NTS (Ritter et al. 1992
). The second-order neurons in the nucleus of the solitary tract interact with neurons of the ascending system to the hypothalamus; the hypothalamic neurons are activated by the nociceptive visceral and cutaneous inputs. It is unclear at which site this interaction occurs, but central pathways mediating these inhibitory vagal effects may be the same as those that are involved in inhibitory control of nociceptive and pain from the visceral domain (Foreman 1989
; Gebhart and Randich 1992
; Randich and Gebhart 1992
) (Fig. 6). This feedback system may play an important role in modulating somatic inflammatory responses under physiological (e.g., by changes of motility and chemical content of the duodenum and small intestine after a meal) and pathophysiological conditions (e.g., by intoxication and inflammation of the small intestine).
The functional type(s) of the vagal afferents involved in this modulation of the negative feedback neuroendocrine mechanism that controls BK-induced PE are unknown. The subdiaphragmatic vagus nerves in the rat are composed of five major branches projecting to the stomach, to the liver, and, via the coeliac ganglion, particularly to the small intestine (Precht and Powley 1985
; Ritter et al. 1992
). Recent studies in our laboratory suggests that afferents in the coeliac and accessory coeliac branches are important in this inhibitory modulation but not afferents in the hepatic and gastric branches (Miao et al. 1997b
).
In summary, noxious stimulation of skin and viscera produces depression of BK-induced PE, and this depression is potentiated after subdiaphragmatic vagotomy as is the suppression of BK-induced PE by intrathecal nicotine. The results imply that intrathecal nicotine may excite spinal nociceptive neurons and/or axons. Further elucidation of the underlying mechanisms should provide details on important intrinsic neural pathways for modulation of the inflammatory response.
 |
ACKNOWLEDGEMENTS |
This work was supported by National Institute of Neurological Disorders and Stroke Grant NS-21647.
 |
FOOTNOTES |
Address for reprint requests: J. D. Levine, Department of Medicine, School of Medicine, Box 0452, University of California at San Francisco, San Francisco, CA 94143-0452.
Received 21 February 1997; accepted in final form 3 June 1997.
 |
REFERENCES |
-
BAHNS, E.,
ERNSBERGER, U.,
JÄNIG, W.,
NELKE, A.
Discharge properties of mechanosensitive afferents supplying the retroperitoneal space.
Pflügers Arch.
407: 519-523, 1986.[Medline]
-
BOYD, R. T.,
JACOB, M. H.,
MCEACHERN, A. E.,
CARON, S.,
BERG, D. K.
Nicotinic acetylcholine receptor mRNA in dorsal root ganglion neurons.
J. Neurophysiol.
22: 1-14, 1991.
-
BUENO, G.,
GUE, M.,
FARGEAS, M. J.,
ALVINERIE, M.,
JUNIEN, J. L.,
FIORAMONTI, J.
Vagally mediated inhibition of acoustic stress-induced cortisol release by orally administered kappa-opioid substances in dog.
Endocrinology
124: 1788-1793, 1989.[Abstract]
-
CARR, J.,
WILHELM, D. L.
The evaluation of increased vascular permeability in the skin of guinea pigs.
Aust. J. Exp. Biol. Med. Sci.
42: 511-522, 1964.[Medline]
-
CERVERO, F.,
MORRISON, J.F.B.
(Editor) Visceral sensation.
In: Progress in Brain Research.,
. Amsterdam: Elsevier, 1986, vol. 67, p. 1-342
-
CHRISTENSEN, M. K.,
SMITH, D. F.
Anticociceptive effects of the stereoisomers of nicotine given intrathecally in spinal rats.
J. Neural Transm.
80: 189-194, 1990.[Medline]
-
CODERRE, T. J.,
BASBAUM, A. I.,
LEVINE, J. D.
Neural control of vascular permeability: interactions between primary afferents, mast cells, and sympathetic efferents.
J. Neurophysiol.
62: 48-58, 1989.[Abstract/Free Full Text]
-
FLEMING, W. W.,
WESTFALL, D. P.,
DE LA LANE, I. S.,
JELLETT, L. B.
Log-normal distribution of equieffective doses of norepinephrine and acetylcholine in several tissues.
J. Pharmacol. Exp. Ther.
181: 339-345, 1972.[Medline]
-
FOREMAN, R. D.
Organization of the spinothalamic tract as a relay for cardiopulmonary sympathetic afferent fiber activity.
Prog. Sensory Physiol.
9: 1-51, 1989.
-
GEBHART, G. F.
(Editor). Visceral pain.
In: Progress in Pain Research and Management.,
. Seattle: IASP Press, 1995, vol. 5, p. 1-516
-
GEBHART, G. F.,
RANDICH, A.
Vagal modulation of nociception.
Am. Pain Soc. J.
1: 26-32, 1992.
-
GILLBERG, P. G.,
HARTVIG, P.,
GORDH, T.,
SOTTILE, A.,
JANSSON, I.,
ARCHER, T.,
POST, C.
Behavioral effects after intrathecal administration of cholinergic receptor agonists in the rat.
Psychopharmacology
100: 464-469, 1990.[Medline]
-
GONZALEZ-FERNANDEZ, I.,
GONZALO-SANZ, L. M.
Vagal influence on the adrenocortical function of the rat.
Rev. Espan. Fisiol.
43: 203-207, 1987.[Medline]
-
GREEN, P. G.,
JÄNIG, W.,
LEVINE, J. D.
Sympathetic terminal: target for negative feedback neuroendocrine control of inflammatory response in the rat.
J. Neurosci.
17: 3234-3238, 1997.[Abstract/Free Full Text]
-
GREEN, P. G.,
MIAO, F. J.-P.,
JÄNIG, W.,
LEVINE, J. D.
Negative feedback neuroendocrine control of the inflammatory response in rats.
J. Neurosci.
15: 4678-4685, 1995.[Abstract]
-
HÖSLI, E.,
HÖSLI, L.
Colocalization of binding sites for somatostatin, muscarine and nicotine on cultured neurons of rat neocortex, cerebellum, brain stem and spinal cord: combined autoradiographic and immunohistochemical studies.
Neurosci. Lett.
173: 71-74, 1994.[Medline]
-
JÄNIG, W.
Neurobiology of visceral afferent neurons: neuroanatomy, functions, organ regulations and sensations.
Biol. Psychol.
42: 29-51, 1996.[Medline]
-
JÄNIG, W. AND HÄBLER, H. J. Visceral-autonomic integration. In: Visceral pain. Progress in Pain Research and Management, edited by G. F. Gebhart. Seattle: IASP Press., 1995. vol. 5, p. 311-348.
-
JÄNIG, W.,
KOLTZENBURG, M.
Pain arising from the urogenital tract.
In: The Autonomic Nervous System, Nervous Control of the Urogenital System,
edited by
and C. A. Maggi
. Chur, Switzerland: Harwood Academic Publishers, 1993, vol. 2, p. 523-576
-
JÄNIG, W.,
MORRISON, J.F.B.
Functional properties of spinal visceral afferents supplying abdominal and pelvic organs with special emphasis on visceral nociception.
In: Visceral Sensation. Progress in Brain Research. Visceral Sensation,
edited by
F. Cervero,
and J.F.B. Morrison
. Amsterdam: Elsevier, 1986, vol. 67, p. 87-114
-
KHAN, I. M.,
PRINTZ, M. P.,
YAKSH, T. L.,
TAYLOR, P.
Augmented responses to intrathecal nicotinic agonists in spontaneous hypertension.
Hypertension
24: 611-619, 1994a.[Abstract]
-
KHAN, I. M.,
TAYLOR, P.,
YAKSH, T. L.
Cardiovascular and behavioral responses to nicotinic agents administered intrathecally.
J. Pharmacol. Exp. Ther.
270: 150-158, 1994b.[Abstract]
-
KHAN, I. M.,
TAYLOR, P.,
YAKSH, T. L.
Stimulatory pathways and sites of action of intrathecally administered nicotinic agents J.
Pharmacol. Exp. Ther.
271: 1550-1557, 1994c.[Abstract]
-
KHAN, I. M.,
YAKSH, T. L.,
TAYLOR, P.
Ligand specificity of nicotinic acetylcholine receptors in rat spinal cord: studies with nicotine and cytisine.
J. Pharmacol. Exp. Ther.
270: 159-166, 1994d.[Abstract]
-
LEWIS, T. Pain. Macmillan: Basingstoke, 1942.
-
MAIXNER, W.,
RANDICH, A.
Role of the right vagal nerve trunk in antinociception.
Brain Res.
298: 374-377, 1984.[Medline]
-
MAIXNER, W.,
TOUW, K. B.,
BRODY, M. J.,
GEBHART, G. F.,
LONG, J. P.
Factors regulating the altered pain perception in the spontaneously hypertensive rat.
Brain Res.
237: 137-145, 1982.[Medline]
-
MIAO, F.J.-P.,
BENOWITZ, N. L.,
HELLER, P. H.,
LEVINE, J. D.
Contribution of adrenal hormones to nicotine-induced inhibition of synovial plasma extravasation in the rat.
Br. J. Pharmacol.
120: 298-304, 1997a.[Abstract]
-
MIAO, F.J.-P.,
BENOWITZ, N. L.,
LEVINE, J. D.
Neural and endocrine circuits mediating inhibition of bradykinin-induced plasma extravasation by subcutaneous and spinal-intrathecal nicotine J.
Pharmacol. Exp. Ther.
277: 1510-1516, 1996a.[Abstract]
-
MIAO, F.J.-P.,
GREEN, P.,
CODERRE, T. J.,
JÄNIG, W.,
LEVINE, J. D.
Sympathetic-dependent and -independent mechanisms for synovial plasma extravasation induced by bradykinin is dose-dependent.
Neurosci. Lett.
205: 165-168, 1996b.[Medline]
-
MIAO, F.J.-P.,
JÄNIG, W.,
DALLMAN, M. F.,
BENOWITZ, N. L.,
HELLER, P. H.,
BASBAUM, A. I.,
LEVINE, J. D.
Role of vagal afferents and spinal pathways in modulating inhibition of bradykinin-induced plasma extravasation by intrathecal nicotine.
J. Neurophysiol.
72: 1199-1207, 1994.[Abstract/Free Full Text]
-
MIAO, F.J.-P.,
JÄNIG, W.,
GREEN, P.,
LEVINE, J. D.
Inhibition of bradykinin-induced synovial plasma extravasation produced by intrathecal nicotine is mediated by the hypothalmo-pituitary adrenal axis.
J. Neurophysiol.
76: 2813-2821, 1996c.[Abstract/Free Full Text]
-
MIAO, F.J.-P.,
JÄNIG, W.,
LEVINE, J. D.
Contribution of sympathetic postganglionic nerve terminals to bradykinin-induced synovial plasma extravasation.
J. Neurophysiol.
75: 715-724, 1996d.[Abstract/Free Full Text]
-
MIAO, F.J.-P.,
JÄNIG, W.,
LEVINE, J. D.
Vagal branches involved in inhibiton of bradykinin-induced synovial plasma extravasation produced by intrathecal nicotine and noxious stimulation in the rat.
J. Physiol. Lond.
498: 473-484, 1997b.[Abstract]
-
MIAO, F.J.-P.,
LEE, T.J.-F.
Effects of bilirubin on cerebral arterial tone in vitro.
J. Cereb. Blood Flow Metab.
9: 666-674, 1989.[Medline]
-
MICHAELIS, M.,
HÄBLER, H.-J.,
JÄNIG, W.
Silent afferents: a further class of nociceptors?
Clin. Exp. Pharmacol. Physiol.
23: 14-20, 1996.
-
PRECHT, J. C.,
POWLEY, T. L.
Organization and distribution of the rat subdiaphragmatic vagus and associated paraganglia.
J. Comp. Neurol.
235: 182-195, 1985.[Medline]
-
RANDICH, A.,
GEBHART, G. F.
Vagal afferent modulation of nociception.
Brain Res. Rev.
17: 77-99, 1992.[Medline]
-
RENSHAW, G.,
RIGBY, P.,
SELF, G.,
LAMB, A.,
GOLDIE, R.
Exogenously administered alpha-bungarotoxin binds to embryonic chick spinal cord: implications for the toxin-induced arrest of natural motoneuron death.
Neuroscience
53: 1163-1172, 1993.[Medline]
-
RITTER, S.,
DINH, T. T.
Capsaicin-induced neuronal degeneration: silver impregnation of cell bodies, axons and terminals in the central nervous system of the adult rat.
J. Comp. Neurol.
271: 79-90, 1988.[Medline]
-
RITTER, S.,
RITTER, R. C.,
BARNES, C. D
In: . Neuroanatomy and Physiology of Abdominal Afferents.,
. Boca Raton: CRC Press, 1992
-
ROGERS, D. T.,
IWAMOTO, E. T.
Multiple spinal mediators in parenteral nicotine-induced antinociception.
J. Pharmacol. Exp. Ther.
267: 341-349, 1993.[Abstract]
-
STEEN, K. H.,
REEH, P. W.
Actions of cholinergic agonists and antagonists on sensory nerve endings in rat skin, in vitro.
J. Neurophysiol.
70: 397-405, 1993.[Abstract/Free Full Text]