A comparison of three single layer anastomotic techniques in the colon of the rat.

INTRODUCTION: Although intestinal anastomoses are mainly made by staplers, manual anastomoses are still in use worldwide. In previous studies, single layer anastomosis has shown better results compared to double layer techniques. PURPOSE: To test experimentally some aspects of three different single layer anastomotic techniques in order to identify advantages and disadvantages of each. MATERIAL AND METHODS: The study was done on Sprague Dawley rats. Animals were randomly divided into four groups. Three experimental groups consisted of 21 animals each, and the fourth sham group contained 10 animals. By 7 animals of each group were sacrificed on the 4th and the rest of 14 animals on the 7th postoperative day. In all groups the resected distal part of the colon was anastomosed using Halsted, Gambee and Gambee-Halsted technique. To evaluate each specific technique the following were used: postoperative complication frequency, biomechanical measurements, adhesion density, condition of intestinal lumen and histological parameters of the healing process. RESULTS: The complication frequency was not significantly different between the tested techniques. The average bursting pressure and tensile strength were higher on both the 4th and 7th postoperative days with the Gambee technique. In the colon segments removed on the 4th postoperative day 97% of pressure induced ruptures occurred in the anastomotic line, whereas on the 7th postoperative day 76% of ruptures occurred about 1cm distal to the anastomotic line. CONCLUSION: The Gambee technique had significantly better biomechanical and histological results compare to the other two anastomotic techniques. Adhesion density was significantly lower in the control group (p<0.001).

Ventilatory behavior after hypoxia in C57BL/6J and A/J mice.

Given the environmental forcing by extremes in hypoxia-reoxygenation, there might be no genetic effect on posthypoxic short-term potentiation of ventilation. Minute ventilation (VE), respiratory frequency (f), tidal volume (VT), and the airway resistance during chemical loading were assessed in unanesthetized unrestrained C57BL/6J (B6) and A/J mice using whole body plethysmography. Static pressure-volume curves were also performed. In 12 males for each strain, after 5 min of 8% O2 exposure, B6 mice had a prominent decrease in VE on reoxygenation with either air (-11%) or 100% O2 (-20%), due to the decline of f. In contrast, A/J animals had no ventilatory undershoot or f decline. After 5 min of 3% CO2-10% O2 exposure, B6 exhibited significant decrease in VE (-28.4 vs. -38.7%, air vs. 100% O2) and f (-13.8 vs. -22.3%, air vs. 100% O2) during reoxygenation with both air and 100% O2; however, A/J mice showed significant increase in VE (+116%) and f (+62.2%) during air reoxygenation and significant increase in VE (+68.2%) during 100% O2 reoxygenation. There were no strain differences in dynamic airway resistance during gas challenges or in steady-state total respiratory compliance measured postmortem. Strain differences in ventilatory responses to reoxygenation indicate that genetic mechanisms strongly influence posthypoxic ventilatory behavior.

Nitric oxide deficiency contributes to impairment of airway relaxation in cystic fibrosis mice.

The pulmonary disease of cystic fibrosis (CF) is characterized by persistent airway obstruction, which has been attributed to chronic endobronchial infection and inflammation. The levels of exhaled nitric oxide (NO) are reduced in CF patients, which could contribute to bronchial obstruction through dysregulated constriction of airway smooth muscle. Because airway epithelium from CF mice has been shown to have reduced expression of inducible NO synthase, we examined airway responsiveness and relaxation in isolated tracheas of CF mice. Airway relaxation as measured by percent relaxation of precontracted tracheal segments to electrical field stimulation (EFS) and substance P, a nonadrenergic, noncholinergic substance, was significantly impaired in CF mice. The airway relaxation in response to prostaglandin E2 was similar in CF and non-CF animals. Treatment with the NO synthase inhibitor NG-nitro-L-arginine methylester reduced tracheal relaxation induced by EFS in wild-type animals but had virtually no effect in the CF mice. Conversely, exogenous NO and L-arginine, a NO substrate, reversed the relaxation defect in CF airway. We conclude that the relative absence of NO compromises airways relaxation in CF, and may contribute to the bronchial obstruction seen in the disease.

Differential effects of hypercapnia on expiratory phases of respiration in the piglet.

Hypercapnia induces prolongation of expiratory time (TE) during early development. In the present study, we determined the response to steady state hypercapnia of three neural phases of the total respiratory cycle, inspiration (TI), stage 1 or passive expiration, TE-1 and stage 2 or active expiration, TE-2. Experiments were performed in decerebrate, vagotomized, spontaneously breathing piglets aged 5-10 days. Neural phases of the respiratory cycle were based on electrical activities of the thyroarytenoid (TA, laryngeal adductor) and triangularis sternii (TS, chest wall expiratory muscle) in relation to diaphragm (D) activity. We observed that hypercapnia induced prolongation of both expiratory phases. The greater prolongation of TE-1 was associated with an increase in TA activity and an increase in laryngeal resistance, which peaked early in TE-1, and then progressively decreased. These findings demonstrate that, in early postnatal life, a hypercapnia induced increase in respiratory drive is associated with centrally mediated prolongation of both phases of expiration, a greater prolongation of TE-1, and an increase in laryngeal resistance during post-inspiration. We speculate that the latter serves to optimize gas exchange by reducing large fluctuations in functional residual capacity.

Central GABAergic mechanisms are involved in apnea induced by SLN stimulation in piglets.

Stimulation of the superior laryngeal nerve (SLN) results in apnea in animals of different species, the mechanism of which is not known. We studied the effect of the GABA(A) receptor blocker bicuculline, given intravenously and intracisternally, on apnea induced by SLN stimulation. Eighteen 5- to 10-day-old piglets were studied: bicuculline was administered intravenously to nine animals and intracisternally to nine animals. The animals were anesthetized and then decerebrated, vagotomized, ventilated, and paralyzed. The phrenic nerve responses to four levels of electrical SLN stimulation were measured before and after bicuculline. SLN stimulation caused a significant decrease in phrenic nerve amplitude, phrenic nerve frequency, minute phrenic activity, and inspiratory time (P < 0.01) that was proportional to the level of electrical stimulation. Increased levels of stimulation were more likely to induce apnea during stimulation that often persisted beyond cessation of the stimulus. Bicuculline, administered intravenously or intracisternally, decreased the SLN stimulation-induced decrease in phrenic nerve amplitude, minute phrenic activity, and phrenic nerve frequency (P < 0.05). Bicuculline also reduced SLN-induced apnea and duration of poststimulation apnea (P < 0.05). We conclude that centrally mediated GABAergic pathways are involved in laryngeal stimulation-induced apnea.

The excitatory amino acid glutamate mediates reflexly increased tracheal blood flow and airway submucosal gland secretion.

In six decerebrated and in eight alpha-chloralose anesthetized, paralyzed and mechanically ventilated beagle dogs, we have studied involvement of glutamate and glutamate receptors in transmission of excitatory inputs from the airway sensory receptors to the nucleus tractus solitarius and from this site to airway-related vagal preganglionic cells that regulate the tracheal circulation and the submucosal gland secretion. Stimulation of airway sensory fibers by lung deflation-induced reflex increase in tracheal blood flow and submucosal gland secretion. These responses were diminished by prior administration of AMPA/kainate receptor antagonist CNQX into the fourth ventricle (n=6). Furthermore, topical application or microinjection of AMPA/kainate receptor blockers, into the region of the ventrolateral medulla, where airway-related vagal preganglionic neurons are located, abolished the reflex changes in tracheal submucosal gland secretion (n=8); in these dogs mucosal blood flow was not measured). These findings indicate that reflex increase in tracheal blood flow and submucosal gland secretions are mediated mainly via release of glutamate and activation of the AMPA/kainate subtype of glutamate receptors.

Recurrent hypoxic exposure and reflex responses during development in the piglet.

The effects of recurrent hypoxia on cardiorespiratory reflexes were characterized in anesthetized piglets at 2-10 d (n=15), 2-3 weeks (n=11) and 8-10 weeks (n=8). Responses of phrenic and hypoglossal electroneurograms (ENG(phr) and ENG (hyp)) to hypoxia (8% 0(2), bal N(2), 5 min), hypercapnia (7% CO(2) bal O(2), 5 min) and intravenous capsaicin were tested before and after recurrent exposure to 11 episodes of hypoxia (8% O(2) bal N(2), 5 min). In piglets 2-10 d, ENG(phr) response to hypoxia declined in proportion to the number of hypoxic exposures; however, ENG (hyp) response to hypoxia was unchanged. In piglets at 2-10 d, intracisternal injection of bicuculline (GABA(A) receptor antagonist) reversed effects of recurrent hypoxia on ENG(phr) hypoxic response, eliminated apnea during hypoxia, as well as the delay in appearance of ENG(phr) after hypoxia. The ENG(phr) response to 7% CO(2) inhalation also decreased after recurrent hypoxia; however, the ENG(phr) response to C-fiber stimulation by capsaicin was unaltered. Piglets at 2-3 and 8-10 weeks were resistant to the depressive effects of recurrent hypoxia on respiratory reflex responses. We conclude that the response of the anesthetized newborn piglet to recurrent hypoxia is dominated by increasing inhibition of phrenic neuroelectrical output during successive hypoxic exposures. Central GABAergic inhibition may contribute significantly to the cumulative effects of repeated hypoxia in the newborn piglet experimental model.

Differential cardiorespiratory control elicited by activation of ventral medullary sites in mice.

We studied the respiratory and blood pressure responses to chemical stimulation of two regions of the ventral brainstem in mice: the rostral and caudal ventrolateral medulla (RVLM and CVLM, respectively). Stimulation of the RVLM by microinjections of the excitatory amino acid L-glutamate induced increases in diaphragm activity and breathing frequency, elevation of blood pressure (BP), and a slight increase in heart rate (HR). However, activation of the CVLM induced a decrease in breathing frequency, mainly due to prolongation of expiratory time (TE), and hypotension associated with a slight slowing of HR. Because adrenergic mechanisms are known to participate in the control of respiratory timing, we examined the role of alpha(2)-adrenergic receptors in the RVLM region in mediating these inhibitory effects. The findings demonstrated that blockade of the alpha(2)-adrenergic receptors within the RVLM by prior microinjection of SKF-86466 (an alpha(2)-adrenergic receptor blocker) significantly reduced changes in TE induced by CVLM stimulation but had little effect on BP responses. These results indicate that, in mice, activation of the RVLM increases respiratory drive associated with an elevation of BP, but stimulation of CVLM induces prolongation of TE via an alpha(2)-adrenergic signal transduction pathway.

Role of endogenous nitric oxide in hyperoxia-induced airway hyperreactivity in maturing rats.

We sought to define the effects of maturation and hyperoxic stress on nitric oxide (NO)-induced modulation of bronchopulmonary responses to stimulation of vagal preganglionic nerve fibers. Experiments were performed on decerebrate, paralyzed, and ventilated rat pups at 6-7 days (n = 21) and 13-15 days of age (n = 23) breathing room air and on rat pups 13-15 days of age (n = 19) after exposure to hyperoxia (>/=95% inspired O(2) fraction for 4-6 days). Total lung resistance (RL) and lung elastance (EL) were measured by body plethysmograph. Vagal stimulation and release of acetylcholine caused a frequency-dependent increase in RL and EL in all animals. The RL response was significantly potentiated in normoxic animals by prior blockade of nitric oxide synthase (NOS) (P < 0.05). Hyperoxic exposure increased responses of RL to vagal stimulation (P < 0.05); however, after hyperoxic exposure, the potentiation of contractile responses by NOS blockade was abolished. The response of EL was potentiated by NOS blockade in the 13- to 15-day-old animals after both normoxic and hyperoxic exposure (P < 0.01). Morphometry revealed no effect of hyperoxic exposure on airway smooth muscle thickness. We conclude that NO released by stimulation of vagal preganglionic fibers modulates bronchopulmonary contractile responses to endogenously released acetylcholine in rat pups. Loss of this modulatory effect of NO could contribute to airway hyperreactivity after prolonged hyperoxic exposure, as may occur in bronchopulmonary dysplasia.

The alpha3 subtype of the nicotinic acetylcholine receptor is expressed in airway-related neurons of the nucleus tractus solitarius, but is not essential for reflex bronchoconstriction in ferrets.

To assess the role of nicotinic acetylcholine receptors (nACh-R) in the transmission of afferent constricting inputs from bronchopulmonary receptors to the nucleus tractus solitarius (nTS) and in the mediation of reflex airway constriction, we performed a combined immunohistological and functional study. In ferrets, the expression of nAch-R on the nTS neurons activated by histamine stimulation of airway sensory receptors was studied using laser scanning confocal microscopy to co-immunolocalize c-fos encoded protein (cFos) and nACh-R alpha3 subunit. We observed that activation of airway sensory receptors by inhalation of aerosolized histamine, induced cFos expression in a subset of nTS neurons that also expressed the nAch-R alpha3 subtype. Furthermore, activation of nACh-R within the commissural subnucleus by nicotine, increased cholinergic outflow to the airways. These effects were diminished by prior administration of hexamethonium (nACh-R blocker) within the commissural subnucleus of the nTS. However, hexamethonium had no significant effects on airway reflex constrictions induced by lung deflation. These findings indicate that nACh-R are expressed by the nTS neurons receiving inputs from airway sensory receptors, activation of which by nicotine increases cholinergic outflow to the airways, but the nACh-R pathways are not required for reflex bronchoconstriction.

alpha(2)-adrenergic receptors are not required for central anti-hypertensive action of moxonidine in mice.

In the mouse medulla oblongata, we characterized binding properties and functional responses of two recognition sites for imidazoline compounds: I(1)-imidazoline and alpha(2)-adrenergic receptors. The mouse medulla expresses a higher density of I(1)-receptors than in the rat, whereas alpha(2)-receptor densities were similar between the two species. In anesthetized, ventilated and paralyzed mice, we tested the hypotensive actions of the I(1)/alpha(2) agonist moxonidine, determined its central site of its actions, and the relative roles of I(1) and alpha(2)-receptors. Experiments were performed in C(57)Bl(6) wild type and alpha(2A)-adrenergic receptor deficient mice. In both types of mice, neuronal activation within the rostral ventrolateral medulla (RVLM) region by glutamate microinjection elicited increases in arterial pressure. Moxonidine (0.5 nmol/site/10 nl) microinjected bilaterally into this vasopressor region decreased arterial pressure by 30% and heart rate by 11% in wild type mice. Efaroxan, the I(1)/alpha(2) antagonist (0.4 nmol) when microinjected into the RVLM elevated blood pressure itself and abolished the action of moxonidine, whereas alpha(2)-blockade with SK&F 86466 had no significant effect on blood pressure and did not attenuate moxonidine's effect. To more definitively test the role of alpha(2)-adrenergic receptors in the action of moxonidine, moxonidine was microinjected into the RVLM of alpha(2A)-adrenergic deficient mice. The decreases in arterial pressure were nearly identical to those of wild type mice, whereas bradycardia was attenuated. Thus, in the mouse moxonidine acts within the RVLM region to lower arterial pressure mainly through the I(1)-imidazoline receptor independent of alpha(2)-adrenergic receptors.

Involvement of glutamate in transmission of afferent constrictive inputs from the airways to the nucleus tractus solitarius in ferrets.

In this study, we identified the neurons within nucleus tractus solitarius (nTS) activated by stimulation of airway sensory systems and examined the expression of AMPA receptor subtype(s) by these cells. We also investigated the possible involvement of endogenously released glutamate and AMPA receptors in the transmission of excitatory inputs from the sensory system of the respiratory tract to the neurons of the nTS. In these experiments we used: (1) immunodetection of c-fos encoded protein (cFos) expression to identify the nTS neurons activated by the stimulation of the airway sensory system; (2) receptor immunochemistry and confocal microscopy to determine the receptor(s) expressed by activated nTS neurons; (3) microdialysis to measure glutamate release, and (4) physiological measurements to examine the effects of selective receptor blockers, and thereby define the role of the glutamate and AMPA glutamatergic receptor subtype(s) in reflexly induced airway constriction. The results showed that activation of airway sensory receptors, by inhalation of aerosolized histamine or capsaicin, induced cFos expression in a subset of nTS neurons that also expressed the AMPA subtype of glutamate receptors. Furthermore, activation of sensory bronchoconstrictive receptors induced glutamate release within nTS, and blockade of the AMPA receptor subtype within nTS inhibited reflexly increased cholinergic outflow to the airways. These data indicate for the first time that glutamate and AMPA receptor signaling pathways are involved in the transmission of afferent inputs from the airways to the nTS, and in mediating reflex airway constriction.

CO2-induced c-fos expression in medullary neurons during early development.

In this study, we characterized the responses of brainstem neurons to hypercapnic loading at 5, 15, and 40 postnatal days, using c-fos gene encoded protein (Fos), as a marker of neuronal activity. At any of these studied ages exposure to 10% CO2 for 1 h produced a significant increase in the number of activated neurons within the ventral and the dorsal aspects of the brainstem. In the ventrolateral aspect of the medulla oblongata, Fos positive cells were observed within the ventrolateral medulla, extending from the pontomedullary border to the decussation of the pyramids. In the most rostral regions, within the retrotrapezoid field, the number of Fos positive cells was lower than in caudal ventral medullary regions at the levels of the area postrema and the caudal to it. No age related differences were observed in the number of neurons exhibiting CO2-induced Fos expression. Fos positive cells were additionally observed in the lateral paragigantocellular and gigantocellular reticular nuclei, in the medullary midline complex, in the raphe pallidus and in the raphe obscurus. The number of activated cells in the midline neurons was higher at 5 than at 40 days of age. In the dorsal aspect of the medulla oblongata Fos positive neurons were observed mainly within the caudal nucleus tractus solitarius (nTS). Postnatal age had no effect on the distribution and number of nTS cells activated by hypercapnic loading. These findings indicate that neurons activated by increases in CO2/H+ concentrations appear to be well developed from the first days of postnatal life in maturing rat pups.

CO2-induced prolongation of expiratory time during early development.

In these studies, we determined the contribution of central mechanisms and the role of GABA(A)-receptor signal transduction pathways in mediating hypercapnia-induced slowing of breathing frequency. Experiments were performed in decerebrate, vagotomized, paralyzed and mechanically ventilated piglets of 3-5 days and 2-3 weeks of age (n=19). Repeated exposure to progressive hyperoxic hypercapnia induced a reproducible increase in phrenic nerve activity, accompanied by a CO2 concentration-dependent increase in expiratory duration. No differences were observed in piglets with intact or cut carotid sinus nerves. Intravenous administration of bicuculline (2 mg/kg: n=7), a gamma-aminobutyric acid (GABA(A)) receptor antagonist, significantly reduced the CO2-induced prolongation of TE. These data demonstrate for the first time that in early postnatal life, hypercapnia induced increase in phrenic activity is associated with centrally mediated prolongation of expiratory duration. Furthermore. the results suggest that brainstem GABAergic mechanisms play an important role in CO2-induced prolongation of expiratory time during early development.

Changes in respiratory timing induced by hypercapnia in maturing rats.

Premature infants respond to hypercapnia by an attenuated ventilatory response that is characterized by a decrease in respiratory frequency. We hypothesized that this impaired hypercapnic ventilatory response is of central origin and is mediated via gamma-aminobutyric acid-ergic (GABAergic) pathways. We therefore studied two groups of maturing Sprague-Dawley rats: unrestrained rats in a whole body plethysmograph at four postnatal ages (5, 16-17, 22-23, and 41-42 days); and ventilated, decerebrate, vagotomized, paralyzed rats in which phrenic nerve responses to hypercapnia were measured at 4-6 and 37-39 days of age. In the unrestrained group, the increase in minute ventilation induced by hypercapnia was significantly lower at 5 days vs. beyond 16 days. Although there was an increase in tidal volume at all ages, frequency decreased significantly from baseline at 5 days, whereas it increased significantly at 16-17, 22-23, and 41-42 days. The decrease in frequency at 5 days of age was mainly due to a significant prolongation in expiratory duration (TE). In the ventilated group, hypercapnia also caused prolongation in TE at 4-6 days but not at 37-39 days of age. Intravenous administration of bicuculline (GABA(A)-receptor blocker) abolished the prolongation of TE in response to hypercapnia in the newborn rats. We conclude that newborn rat pups exhibit a characteristic ventilatory response to CO(2) expressed as a centrally mediated prolongation of TE that appears to be mediated by GABAergic mechanisms.

Moxonidine acting centrally inhibits airway reflex responses.

We examined the role of I1-imidazoline (I1-IR) receptors in control of airway function, by testing the effects of systemic administration of the I1-IR agonist moxonidine on reflex responses of tracheal smooth muscle (TSM) tone to either lung deflation or mechanical stimulation of intrapulmonary rapidly adapting receptors. Experiments were performed in either alpha-chloralose anesthetized or decorticate, paralyzed, and mechanically ventilated beagle dogs. Moxonidine (10-100 micrograms/kg) administered via three different routes (femoral vein, muscular branch of superior thyroid artery, and vertebral artery) attenuated TSM responses to stimulation of airway sensory nerve fibers by two different ways and caused a decrease in arterial pressure and heart rate. These effects were dose dependent and were significantly reversed by efaroxan (an I1-IR and alpha 2-adrenergic blocker) administered via the vertebral artery. Intravertebral efaroxan abolished the hemodynamic effects of moxonidine. Intravenous moxonidine (10-100 micrograms/kg) did not alter airway smooth muscle responses to electrical stimulation of the peripheral vagus nerve. In addition, in vitro moxonidine (1-100 micrograms/ml) had no effect on contractile responses to increasing doses of acetylcholine. These findings indicate that moxonidine may act at a central site to suppress reflex airway constriction, even when given into the systemic circulation. Given the presence of I1-IR sites and alpha 2-adrenergic receptors in brain regions participating in airway reflexes, these receptor classes may be involved in brainstem control of the cholinergic outflow to the airways.

Mechanism for substance P-induced relaxation of precontracted airway smooth muscle during development.

Release of substance P (SP) from sensory nerve endings of the tracheobronchial system modulates airway smooth muscle contraction and may cause relaxation of precontracted airways. We sought to elucidate the effect of postnatal maturation on SP-induced relaxation of precontracted airways and determine the roles of endogenously generated nitric oxide (NO) and prostaglandins (PGs). Cylindrical airway segments were isolated from the midtrachea of rats at four different ages, 1, 2, and 4 wk and 3 mo, and contracted to 50-75% of the maximum response induced by bethanechol. SP was then administered in the absence and presence of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), the PG inhibitor indomethacin, or both. Relaxation of airways with SP decreased significantly with advancing postnatal age. SP-induced tracheal relaxation was consistently attenuated by pretreatment with L-NAME, indomethacin, or both. In a different group of animals, L-NAME significantly attenuated the relaxant response of airways to PGE2 exposure, but indomethacin had no significant effect on the relaxant response to exogenous NO. We conclude that SP induces a relaxant effect on precontracted airway smooth muscle, which decreases with advancing age and is mediated via SP-induced release of NO and/or PG.

Interleukin-12 suppresses filaria-induced pulmonary eosinophilia, deposition of major basic protein and airway hyperresponsiveness.

Tropical Pulmonary Eosinophilia (TPE) is a severe form of allergic asthma caused by the host inflammatory response to filarial helminths in the lung microvasculature, and is characterized by pulmonary eosinophilia, increased filarial-specific IgG and IgE antibodies, and airway hyperresponsiveness. The current study examined the effect of IL-12 on pulmonary eosinophilia, deposition of eosinophil major basic protein and airway hyperresponsiveness in mice inoculated i.v. with Brugia malayi microfilariae. Injection of recombinant murine IL-12 modulated the T helper (Th) response in the lungs from Th2- to Th1-like, with elevated IFN-gamma, and decreased IL-4 and IL-5 production. Consistent with this shift in cytokine response, antigen-specific IgG2a was elevated, and IgG1 and total serum IgE were decreased. In addition, eosinophils in BAL fluid from IL-12 treated mice were reduced from 56% to 11%, and there was no detectable MBP on respiratory epithelial cells. Importantly, IL-12 suppressed airway hyperresponsiveness compared with saline-injected control animals. Taken together, these data clearly demonstrate that by modulating Th associated cytokine production, IL-12 down-regulates filaria-induced lung immunopathology.

I1-imidazoline receptors and cholinergic outflow to the airways.

We examined the role of I1-imidazoline receptors in the control of airway function, by testing the effects of systemic administration of the I1-imidazoline agonist moxonidine on reflex responses of tracheal smooth muscle (TSM) tone to either lung deflation or mechanical stimulation of intrapulmonary rapidly adapting receptors. Experiments were performed in either alpha-chloralose anaesthetized or decorticate, paralyzed and mechanically ventilated beagle dogs. Moxonidine (10-100 microg/kg) administered via three different routes (the femoral vein, muscular branch of superior thyroid artery, and vertebral artery) attenuated TSM responses to stimulation of airway sensory nerve fibers by two different ways, and caused a decrease in arterial pressure and heart rate. These effects were dose-dependent, and were significantly reversed by efaroxan (an I1-imidazoline and alpha2-adrenergic blocker) administered via the vertebral artery. Intravertebral efaroxan abolished the hemodynamic effects of moxonidine. Intravenous moxonidine (10-100 microg/kg) did not alter airway smooth muscle responses to electrical stimulation of the peripheral vagus nerve. In addition, in vitro moxonidine (1-100 microg/ml) had no effect on contractile responses to increasing doses of acetylcholine. These findings indicate that moxonidine may act at a central site to suppress reflex airway constriction, even when given into the systemic circulation. Given the presence of I1-imidazoline sites and alpha2-adrenergic receptors in brain regions participating in airway reflexes, these receptor classes may be involved in brainstem control of the cholinergic outflow to the airways.

The role of the medullary raphe nuclei in regulation of cholinergic outflow to the airways.

In these studies we determined the role of the medullary midline nuclei on a cholinergic outflow to the airways by examining the response of tracheal tone and lung resistance to pharmacological stimulation. Studies were performed on alpha-chloralose-anesthesized, paralyzed and mechanically ventilated cats, and ferrets. L-glutamate microinjection into the medullary midline neurons significantly decreased tracheal tension, and reduced lung resistance. These effects were abolished by prior topical application of methysergide, a broad spectrum serotonin receptor antagonist. Stimulation of the medullary raphe nuclei was also associated with a significant increase in the phrenic nerve output, and a decrease in arterial blood pressure. The results indicate that the medullary midline neurons are involved in regulation of cholinergic outflow to the airways, and raise the possibility that alterations in the serotonergic pathways may cause airway dysfunction.