Posterior hypothalamic control of rabbit tracheal tension and involvement of central histaminergic neurons

Paradoxical conducting airway responses and heterogeneous regional ventilation after histamine inhalation in rabbit studied by synchrotron radiation CT

We studied both central conducting airway response and changes in the distribution of regional ventilation induced by inhaled histamine in healthy anesthetized and mechanically ventilated rabbit using a novel xenon-enhanced synchrotron radiation computed tomography (CT) imaging technique, K-edge subtraction imaging (KES). Images of specific ventilation were obtained using serial KES during xenon washin, in three axial lung slices, at baseline and twice after inhalation of histamine aerosol (50 or 125 mg/ml) in two groups of animals (n = 6 each). Histamine inhalation caused large clustered areas of poor ventilation, characterized by a drop in average specific ventilation (sV(m)), but an increase in sV(m) in the remaining lung zones indicating ventilation redistribution. Ventilation heterogeneity, estimated as coefficient of variation (CV) of sV(m) significantly increased following histamine inhalation. The area of ventilation defects and CV were significantly larger with the higher histamine dose. In conducting airways, histamine inhalation caused a heterogeneous airway response combining narrowing and dilatation in individual airways of different generations, with the probability for constriction increasing peripherally. This finding provides further in vivo evidence that airway reactivity in response to inhaled histamine is complex and that airway response may vary substantially with location within the bronchial tree.

Involvement of guanylate cyclase in the cardiovascular response induced by adenosine A2B receptor stimulation in the posterior hypothalamus of the anesthetized rats

Cardiovascular inhibitory effects induced by the posterior hypothalamic adenosine A(2) receptors were suggested by our previous reports. In this experiment, we examined the influence of the posterior hypothalamic adenosine A(2B) receptors on central cardiovascular regulation of blood pressure (BP) and heart rate (HR). Posterior hypothalamic injection of drugs was performed in anesthetized, artificially ventilated male Sprague-Dawley rats. Injection of 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA; 2 nmol), an adenosine A(2) receptor agonist, showed the decrease of arterial blood pressure and heart rate, and the alloxazine, an adenosine A(2B) receptor antagonist, partially blocked the depressor and bradycardiac effects of CPCA (2 nmol). To examine the role of adenosine A(2B) receptors among the adenosine A(2) subtypes, we applied the 5'-N-Ethylcarboxamidoadenosine (NECA), an adenosine A(2B) receptor agonist, to the posterior hypothalamus. Injection of NECA (1, 4 and 8 nmol) produced a dose-dependent decrease of arterial blood pressure and HR. Pretreatment with alloxazine (5 nmol) partially blocked the depressor and bradycardiac effects of NECA (4 nmol). Also, pretreatment with LY-83,583 (5 nmol), a soluble guanylate cyclase inhibitor, attenuated the depressor and bradycardiac effects of NECA (4 nmol). However, pretreatment with MDL-12,330 (10 nmol), an adenylate cyclase inhibitor, did not affect these effects of NECA (4 nmol). These results suggest that adenosine A(2B) receptor in the posterior hypothalamus plays an inhibitory role in central cardiovascular regulation, and that guanylate cyclase mediates the depressor and bradycardiac actions of adenosine A(2B) receptors.

CNS determinants of sleep-related worsening of airway functions: implications for nocturnal asthma

This review summarizes the recent neuroanatomical and physiological studies that form the neural basis for the state-dependent changes in airway resistance. Here, we review only the interactions between the brain regions generating quiet (non-rapid eye movement, NREM) and active (rapid eye movement, REM) sleep stages and CNS pathways controlling cholinergic outflow to the airways. During NREM and REM sleep, bronchoconstrictive responses are heightened and conductivity of the airways is lower as compared to the waking state. The decrease in conductivity of the lower airways parallels the sleep-induced decline in the discharge of brainstem monoaminergic cell groups and GABAergic neurons of the ventrolateral periaqueductal midbrain region, all of which provide inhibitory inputs to airway-related vagal preganglionic neurons (AVPNs). Withdrawal of central inhibitory influences to AVPNs results in a shift from inhibitory to excitatory transmission that leads to an increase in airway responsiveness, cholinergic outflow to the lower airways and consequently, bronchoconstriction. In healthy subjects, these changes are clinically unnoticed. However, in patients with bronchial asthma, sleep-related alterations in lung functions are troublesome, causing intensified bronchopulmonary symptoms (nocturnal asthma), frequent arousals, decreased quality of life, and increased mortality. Unquestionably, the studies revealing neural mechanisms that underlie sleep-related alterations of airway function will provide new directions in the treatment and prevention of sleep-induced worsening of airway diseases.

Neuronal histamine release elicited by hyperthermia mediates tracheal dilation and pressor response

Whether brain histaminergic neurons contribute to the regulation of tracheal tone and peripheral vascular tone under hyperthermia was investigated in anesthetized rabbits. Histamine release from the rostral ventrolateral medulla (RVLM), the raphe nuclei, and the solitary nucleus of the medulla oblongata was significantly increased by hyperthermia. The increased histamine was significantly suppressed by 10−6 M tetrodotoxin microdialyzed in each area. Tracheal pressure and mean arterial pressure were significantly decreased and increased by hyperthermia, respectively. An H1-receptor antagonist, 5 × 10−6 M (+)-chlorpheniramine, bilaterally microdialyzed in the RVLM significantly enhanced histamine release in the RVLM as well as significantly suppressed tracheal dilation and pressor response caused by hyperthermia. These data indicate that histamine release in the medulla oblongata is enhanced by hyperthermia. The enhanced histamine is the neuronal origin and the cause of tracheal dilation and pressor response at least via H1 receptors in the RVLM. Brain histaminergic neurons play important roles in tracheal tone and peripheral vascular tone via H1 receptors in the RVLM and homeostasis on body temperature.

Involvement of central histaminergic neurons in polypnea induced by hyperthermia in rabbits

A role of central histamine in the preoptic area/anterior hypothalamus (POA/AH) for the regulation of hyperthermia-induced polypnea was examined in anesthetized, paralyzed, vagotomized and artificially ventilated rabbits. Phrenic nerve activities were recorded to monitor respiratory neuronal output. Hyperthermia increased respiratory frequency by reductions of inspiratory time (T(I)) and expiratory time (T(E)). Pyrilamine, an H1 receptor antagonist, which was applied to the POA/AH reduced polypnea under hyperthermia. The effect of S+alpha-fluoromethylhistidine, a specific inhibitor of histidine decarboxylase, applied in a lateral ventricle was comparable to the effect of pyrilamine on polypnea. Moreover, histamine dihydrochloride applied into the POA/AH at a normal body temperature produced polypnea by reductions of T(I) and T(E). The results suggest that central histamine in the POA/AH contributes to the generation of polypnea in hyperthermia through H1 receptors.

Histamine in the control of porcine and human sphincter of Oddi activity

Histamine decreases sphincter of Oddi (SO) contractility in vivo in opossum, but increases contractility in vitro in guinea-pig. In resistor-like SO, such as in pig and man, the histamine effect is poorly known. We investigated the effect of histamine on pig SO in vivo and in vitro and on human SO in vitro. Perfusion manometry catheter and two silver electrodes for simultaneous pressure and electromyography registration were inserted into the SO transduodenally by laparotomy in six anaesthetized pigs weighing for 25-28 kg. Histamine (5-10 microgram kg-1) was infused intra-arterially (i.a.) into the pancreaticoduodenal artery with and without diphenhydramine (75 microgram kg-1) i.a. premedication. Acetylcholine (4 microgram kg-1) i.a., a potent SO stimulator, was used as positive control. After these experiments, the SO was removed and, together with seven human SO from Whipple specimens, were cut into 1.0-1.5 mm thick transverse sections (rings). The rings were placed between two hooks in oxygenated organ bath solution at 37 degrees C. The SO contraction force was measured with isometric force-displacement transducers and registered on a polygraph. SO rings were incubated with histamine (10-100 micromol L-1) and acetylcholine (100 micromol L-1) with or without diphenhydramine (10 micromol L-1), cimetidine (10 micromol L-1), or atropine (1 micromol L-1). Acetylcholine induced huge electrical bursts, and basal SO pressure increased by 20 +/- 10 mmHg. Histamine (10 microgram kg-1) induced strong SO contraction and the SO remained oedematous for over 10 min. Histamine (5 microgram kg-1) resulted in electromyographic burst activity with phasic SO contractions and increase in basal SO pressure by 34 +/- 19 mmHg for over 15 min. Diphenhydramine did not alter acetylcholine-induced SO motility, but significantly decreased histamine-induced contractions and almost abolished electrical activity. In vitro, acetylcholine induced SO contractions in pig (335 +/- 111 mg) and in man (323 +/- 54 mg). Histamine did not change SO tone in man, but in pig it induced dose-dependent contractions in the same way as acetylcholine. These contractions could be inhibited by diphenhydramine, but not by cimetidine or atropine. We conclude that histamine has a stimulatory effect, mediated by H1-receptor, on the pig SO motility. The SO response to histamine is different in adult humans from that observed in young pigs.

Lack of temperature-induced polypnea in histamine H1 receptor-deficient mice

Breathing patterns are influenced by body temperature. However, the central mechanism for changes of breathing patterns is unknown. We previously showed that central histamine contributed to temperature-induced polypnea in mice (Izumizaki, M., Iwase, M., Homma, I., Yanai, K., Watanabe, T. and Watanabe, T., Central histamine contributed to the temperature-induced polypnea in mice, Neurosci. Res., 23 (1999) S282). In this study we examined the role of central histamine H1 receptors in temperature-induced polypnea using wild and mutant mice lacking histamine H1 receptors. Breathing patterns were characterized at two different body temperatures during hypercapnia under conscious conditions. In wild mice a raised body temperature increased respiratory frequency mainly due to a reduction in expiratory time, whereas in mutant mice respiratory frequency did not increase even though the body temperature was elevated. These results indicate that central histamine contributes to an increase in respiratory frequency due to a reduction in expiratory time through histamine H1 receptors when body temperature is raised.

Central histaminergic neurons regulate rabbit tracheal tension through the cervical sympathetic nerve

We previously showed that stimulation of the posterior hypothalamus decreases tracheal tension and involves central histaminergic neurons. In the present study, we reveal that central histaminergic neurons project to the rostral ventrolateral medulla and affect cervical sympathetic nervous activity in rabbits. Administration of histamine into the fourth ventricle increased cervical sympathetic nervous activity and decreased tracheal tension. These effects were inhibited by administration of a histamine H receptor antagonist, pyrilamine, into the fourth ventricle. Unilateral injection of DL-homocysteic acid into the tuberomammillary nucleus increased cervical sympathetic nervous activity, an effect was antagonized by bilateral injection of pyrilamine into the rostral ventrolateral medulla. The pulse correlogram between the stimulation pulse applied to the tuberomammillary nucleus and the cervical sympathetic nerve activity showed a mode at 150 to 200 ms, which was reduced by pyrilamine administration into the fourth ventricle. Fibers anterogradely labeled by Phaseolus vulgaris leucoagglutinin (PHA-L) injected into the tuberomammillary nucleus were distributed in the A1, A2, C1, and C2 areas which are determined by tyrosine hydroxylase-immunohistochemistry. PHA-L positive neurons were in close contact with tyrosine hydroxylase-immunoreactive neurons in these four areas. Cell bodies in the tuberomammillary nucleus retrogradely labeled with fluorogold from the rostral ventrolateral medulla were immunoreactive with histamine. These results suggest that an excitatory efferent pathway projects from the tuberomammillary nucleus to the cervical sympathetic nerve and that the histaminergic neurons of this pathway influence tracheal tension through the rostral ventrolateral medulla.

Autoregulation of histamine release in medulla oblongata via H3-receptors in rabbits

The release of histamine (HA) from the rostral ventrolateral medulla (RVL), the raphe nuclei (nR), and the solitary nucleus (nTS) was investigated in anesthetized rabbits using microdialysis and high-performance liquid chromatography. HA release upon electrical stimulation of the posterior hypothalamus (PH), where histaminergic cell bodies are located, was increased to 168% of the baseline level in the RVL (n = 6), 139% of the baseline level in the nR (n = 5), and 166% of the baseline level in the nTS (n = 4). Upon perfusion of thioperamide, an H3-receptor antagonist, via a microdialysis probe, HA release from the RVL, nR and nTS increased. The increase in HA release from the RVL, nR and nTS following thioperamide perfusion was suppressed by co-perfusion of thioperamide and an H3-receptor agonist, imetit. We found that HA is released from the RVL, nR and nTS, that the HA release from all three areas is increased upon stimulation of the PH, and that the HA release is locally influenced in opposite directions by thioperamide and imetit. These results suggest that HA release in the medulla oblongata is controlled by the PH and that H3-receptors participate in the autoregulation of HA release by providing negative feedback locally. Autoregulation of HA release via H3-receptors may be important for maintaining tonic output to the sympathetic nervous system.

Nonadrenergic relaxation of the cat cervical trachea evoked by stimulation in the lateral hypothalamic area

The purpose of this study was to evaluate hypothalamic contributions to control of tracheal tone. We found hypothalamic sites where electrical stimulation (60-90 microA: 1 ms pulse duration: 50 Hz: 5-10 s) and microinjection of L-glutamate (5-50 nmol) produced tracheal relaxation responses along with decreased blood pressure and heart rate in anesthetized, spontaneously breathing cats. Responsive sites were located in anterior (LHAa) and tuberal (LHAt) regions of the lateral hypothalamic area indicating that neuronal cells in those regions are responsible for development of tracheal relaxation. In a second experiment, we evaluated possible pathways mediating the tracheal relaxation response elicited by LHA stimulation. Tracheal relaxation was not attenuated by beta-adrenergic blockade (propranolol i.v., 0.2-0.5 mg/kg); the response is mediated by nonadrenergic mechanisms Muscarinic blockade (atropine i.v.) at doses of 0.05-0.1 mg/kg almost abolished tracheal tone during spontaneous breathing, and LHA stimulation evoked a small, insignificant reduction of tracheal tone. Cervical vagotomy completely abolished the trachea tone, and LHA stimulation no longer evoked the tracheal relaxation. These results indicate the existence of a nonadrenergic descending pathway within the vagal efferents, which is linked with behavioral control arising from LHA, and causes trachea relaxation.