The importance of sensory nerve endings as sites of drug action

[Hypothermic Action of Oseltamivir Not Dependent on Its Anti-influenza Virus Action]

Although the anti-influenza virus drug oseltamivir ameliorates the fever of influenza, adverse events related to its hypothermic effect have been reported. We found that oseltamivir causes dose-dependent hypothermia in normal mice, and have been studying the pharmacological mechanisms responsible for 12 years. Oseltamivir blocks nicotinic cholinergic transmission at sympathetic ganglia and reduces sympathetic modulation of brown adipose tissue (BAT), a heat generator. Oseltamivir was found to target the ion channels of nicotinic acetylcholine receptors, as demonstrated by patch clamp experiments with cells expressing the human α3β4 nicotinic receptor. Metabolized oseltamivir carboxylate, which inhibits the influenza virus neuraminidase, did not elicit hypothermia and ion channel suppression. Body temperature was decreased by intracerebroventricular administration of oseltamivir. Because this hypothermic effect was inhibited by dopamine D₂ receptor blockade, it was suggested that oseltamivir centrally stimulates the D₂ receptor. In Japan, the package inserts for oseltamivir and amantadine indicate very similar adverse neuropsychiatric reactions for the two drugs (abnormal behavior, consciousness disturbance, convulsion, delirium, delusion, hallucination). A literature search revealed that in some previous studies, oseltamivir and amantadine were shown to block the ion channel systems and activate the dopaminergic nervous system via several mechanisms. Therefore the similarity of the adverse reactions elicited by oseltamivir and amantadine was considered attributable to their similar pharmacological effects.

Critical role of peripheral sensory systems in mediating the neural effects of nicotine following its acute and repeated exposure

It is well established that the reinforcing properties of nicotine (NIC) depend on its action on nicotinic acetylcholine receptors expressed by brain neurons. However, when administered systemically, NIC first phasically activates nicotinic receptors located on the afferents of sensory nerves at the sites of drug administration before reaching the brain and directly interacting with central neurons. While this peripheral action of NIC has been known for years, it is usually neglected in any consideration of the drug's reinforcing properties and experience-dependent changes of its behavioral and physiological effects. The goal of this work was to review our recent behavioral, electrophysiological, and physiological data suggesting the critical importance of peripheral actions of NIC in mediating its neural effects following acute drug exposure and their involvement in alterations of NIC effects consistently occurring following repeated drug exposure. Because NIC, by acting peripherally, produces a rapid sensory signal to the central nervous system that is followed by slower, more prolonged direct drug actions in the brain, these two pharmacological actions interact in the central nervous system during repeated drug use with the development of Pavlovian conditioned association. This within-drug conditioning mechanism could explain the experience-dependent changes in the physiological, behavioral, and human psychoemotional effects of NIC, which, in drug-experienced individuals, always represent a combination of pharmacological and learning variables.

Intravenous nicotine injection induces rapid, experience-dependent sensitization of glutamate release in the ventral tegmental area and nucleus accumbens

Although numerous data suggest that glutamate (GLU) is involved in mediating the neural effects of nicotine, direct data on nicotine-induced changes in GLU release are still lacking. Here, we used high-speed amperometry with enzyme-based GLU and enzyme-free GLU-null biosensors to examine changes in extracellular GLU levels in the ventral tegmental area (VTA) and nucleus accumbens shell (NAcc) induced by intravenous nicotine in a low, behaviorally active dose (30 μg/kg) in freely moving rats. Using this approach, we found that the initial nicotine injection in drug-naive conditions induces rapid, transient, and relatively small GLU release (~ 90 nM; latency ~ 15 s, duration ~ 60 s) that is correlative in the VTA and NAcc. Following subsequent nicotine injections within the same session, this phasic GLU release was supplemented by stronger tonic increases in GLU levels (100-300 nM) that paralleled increases in drug-induced locomotor activation. GLU responses induced by repeated nicotine injections were more phasic and stronger in the NAcc than in VTA. Therefore, GLU is phasically released within the brain's reinforcement circuit following intravenous nicotine administration. Robust enhancement of nicotine-induced GLU responses following repeated injections suggests this change as an important mediator of sensitized behavioral and neural effects of nicotine. By using high-speed amperometry with glutamate (GLU) biosensors, we show that i.v. nicotine at a low, behaviorally relevant dose induces rapid GLU release in the NAcc and VTA that is enhanced following repeated drug injections. This is the first study reporting second-scale fluctuations in extracellular GLU levels induced by nicotine in two critical structures of the motivation-reinforcement circuit and rapid sensitization of GLU responses coupled with locomotor sensitization.

Rapid sensitization of physiological, neuronal, and locomotor effects of nicotine: critical role of peripheral drug actions

Repeated exposure to nicotine and other psychostimulant drugs produces persistent increases in their psychomotor and physiological effects (sensitization), a phenomenon related to the drugs' reinforcing properties and abuse potential. Here we examined the role of peripheral actions of nicotine in nicotine-induced sensitization of centrally mediated physiological parameters (brain, muscle, and skin temperatures), cortical and VTA EEG, neck EMG activity, and locomotion in freely moving rats. Repeated injections of intravenous nicotine (30 μg/kg) induced sensitization of the drug's effects on all these measures. In contrast, repeated injections of the peripherally acting analog of nicotine, nicotine pyrrolidine methiodide (nicotine(PM), 30 μg/kg, i.v.) resulted in habituation (tolerance) of the same physiological, neuronal, and behavioral measures. However, after repeated nicotine exposure, acute nicotine(PM) injections induced nicotine-like physiological responses: powerful cortical and VTA EEG desynchronization, EMG activation, a large brain temperature increase, but weaker hyperlocomotion. Additionally, both the acute locomotor response to nicotine and nicotine-induced locomotor sensitization were attenuated by blockade of peripheral nicotinic receptors by hexamethonium (3 mg/kg, i.v.). These data suggest that the peripheral actions of nicotine, which precede its direct central actions, serve as a conditioned interoceptive cue capable of eliciting nicotine-like physiological and neural responses after repeated nicotine exposure. Thus, by providing a neural signal to the CNS that is repeatedly paired with the direct central effects of nicotine, the drug's peripheral actions play a critical role in the development of nicotine-induced physiological, neural, and behavioral sensitization.

Reduction in sympathetic nerve activity as a possible mechanism for the hypothermic effect of oseltamivir, an anti-influenza virus drug, in normal mice

Oseltamivir, an anti-influenza virus drug, has strong antipyretic effects in mice (Biological and Pharmaceutical Bulletin, 31, 2008, 638) and patients with influenza. In addition, hypothermia has been reported as an adverse event. The prodrug oseltamivir is converted to oseltamivir carboxylate (OC), an active metabolite of influenza virus neuraminidase. In this study, core body temperature was measured in mice, and oseltamivir and OC were administered intracerebroventricularly (i.c.v.) or intraperitoneally (i.p). Low i.c.v. doses of oseltamivir and OC dose-dependently produced hypothermia. Zanamivir (i.c.v.), another neuraminidase inhibitor, did not produce hypothermia. These results suggested that the hypothermic effects of oseltamivir (i.p. and i.c.v.) and OC (i.c.v.) are not due to neuraminidase inhibition. OC (i.p.) did not lower body temperature. Although mecamylamine (i.c.v.) blocked the hypothermic effect of nicotine-administered i.c.v., the hypothermic effects of oseltamivir and OC (i.c.v.) were not blocked by mecamylamine (i.c.v.). The effect of oseltamivir (i.p.) was markedly increased by s.c.-pre-administered mecamylamine and also hexamethonium, a peripherally acting ganglionic blocker, suggesting their potentiating interaction at peripheral sites. The hypothermic effect of nicotine (i.c.v.) was decreased by lower doses of oseltamivir (i.c.v.), suggesting the anti-nicotinic action of oseltamivir. These results suggest that oseltamivir (i.p.) causes hypothermia through depression of sympathetic temperature regulatory mechanisms via inhibition of nicotinic receptor function and through unknown central mechanisms.

Sweet taste and menthol increase cough reflex thresholds

Cough is a vital protective reflex that is triggered by both mechanical and chemical stimuli. The current experiments explored how chemosensory stimuli modulate this important reflex. Cough thresholds were measured using a single-inhalation capsaicin challenge. Experiment 1 examined the impact of sweet taste: Cough thresholds were measured after rinsing the mouth with a sucrose solution (sweet) or with water (control). Experiment 2 examined the impact of menthol: Cough thresholds were measured after inhaling headspace above a menthol solution (menthol vapor) or headspace above the mineral oil solvent (control). Experiment 3 examined the impact of rinsing the mouth with a (bitter) sucrose octaacetate solution. Rinsing with sucrose and inhaling menthol vapor significantly increased measured cough thresholds. Rinsing with sucrose octaacete caused a non-significant decrease in cough thresholds, an important demonstration of specificity. Decreases in cough reflex sensitivity from sucrose or menthol could help explain why cough syrups without pharmacologically active ingredients are often almost as effective as formulations with an added drug. Further, the results support the idea that adding menthol to cigarettes might make tobacco smoke more tolerable for beginning smokers, at least in part, by reducing the sensitivity of an important airway defense mechanism.

Critical role of peripheral actions of intravenous nicotine in mediating its central effects

In addition to its direct action on central neurons, nicotine (NIC) activates multiple nicotinic acetylcholine receptors localized on afferent terminals of sensory nerves at the sites of its administration. Although the activation of these receptors is important in mediating the primary sensory and cardiovascular effects of NIC, their role in triggering and maintaining the neural effects of NIC remains unclear. Using high-speed electroencephalography (EEG) and electromyography (EMG) recordings in freely moving rats, we showed that NIC at low intravenous (i.v.) doses (10-30 μg/kg) induced rapid, strong, and prolonged EEG desynchronization both in the cortex and ventral tegmental area (with decreases in α and robust increases in β and γ frequencies) and neck EMG activation that began during the injection (∼5 s). EEG and EMG effects of NIC were drastically reduced by pre-treatment with hexamethonium, a peripherally acting NIC antagonist, and the immediate EEG effects of NIC were strongly inhibited during urethane anesthesia. Although NIC pyrrolidine methiodide, a quaternary NIC analog that cannot enter the brain, also induced rapid EEG desynchronization, its effects were much shorter and weaker than those of NIC. Therefore, NIC by acting on peripheral nicotinic receptors provides a major contribution to its rapid, excitatory effects following i.v. administration. Since this action creates a sensory signal that rapidly reaches the brain via neural pathways and precedes the slower and more prolonged direct actions of NIC on brain cells, it could have a major role in associative learning and changes in the behavioral and physiological effects of NIC following its repeated use.

Fluctuations in central and peripheral temperatures induced by intravenous nicotine: central and peripheral contributions

Nicotine (NIC) is a highly addictive substance that interacts with different subtypes of nicotinic acetylcholine receptors widely distributed in the central and peripheral nervous systems. While the direct action of NIC on central neurons appears to be essential for its reinforcing properties, the role of peripheral actions of this drug remains a matter of controversy. In this study, we examined changes in locomotor activity and temperature fluctuations in the brain (nucleus accumbens and ventral tegmental area), temporal muscle, and skin induced by intravenous (iv) NIC at low human-relevant doses (10 and 30μg/kg) in freely moving rats. These effects were compared to those induced by social interaction, an arousing procedure that induces behavioral activation and temperature responses via pure neural mechanisms, and iv injections of a peripherally acting NIC analog, NIC pyrrolidine methiodide (NIC-PM) used at equimolar doses. We found that NIC at 30μg/kg induces a modest locomotor activation, rapid and strong decrease in skin temperature, and weak increases in brain and muscle temperature. While these effects were qualitatively similar to those induced by social interaction, they were much weaker and showed a tendency to increase with repeated drug administrations. In contrast, NIC-PM did not affect locomotion and induced much weaker than NIC increases in brain and muscle temperatures and decreases in skin temperature; these effects showed a tendency to be weaker with repeated drug administrations. Our data indicate that NIC's actions in the brain are essential to induce locomotor activation and brain and body hyperthermic responses. However, rapid peripheral action of NIC on sensory afferents could be an important factor in triggering its central effects, contributing to neural and physiological activation following repeated drug use.

The airway sensory impact of nicotine contributes to the conditioned reinforcing effects of individual puffs from cigarettes

Puffs from cigarettes are the fundamental unit of smoking reward. Here, we examined the extent to which reward from puffs can be derived from the airway sensory effect of nicotine, in the absence of a direct central nervous system effect of nicotine. We did this by assessing the self-reported reward obtained from individual puffs from nicotinized, denicotinized and unlit cigarettes within 7 s of inhalation, which is before nicotine had an opportunity to reach the brain. We also assessed the self-reported strength of airway sensations elicited by the puffs. We found that nicotinized puffs were rated as both stronger and more rewarding than denicotinized and unlit puffs. We also found that the extent to which nicotine elicited reward was directly correlated with the extent to which nicotine elicited airway sensations. This indicates that the airway sensory effects of nicotine contribute to the reward from puffs, above and beyond the reward derived from the airway sensory effects of non-nicotine constituents. These findings have implications for the interpretation of studies that use puffs as experimental units to examine nicotine reward. They also have implications for the use of denicotinized and low nicotine cigarettes as aids to smoking cessation.

Modulation of reflex and sleep related apnea by pedunculopontine tegmental and intertrigeminal neurons

We describe and summarize here our recent findings about the role in respiration of two pontine structures that are not classically included in the pontine respiratory group: the pedunculopontine tegmental nucleus (PPT) and the intertrigeminal region (ITR). We also discuss significant contributions of other workers in the field, especially, S. Datta [Cell. Mol. Neurobiol. 17: 341-365, 1997], R. Lydic and H. Baghdoyan [Sleep, 25: 617-622, 2002], and N. Chamberlin and C. Saper [J. Neurosci. 18: 6048-6056, 1998], who postulated a role for the ITR in modulating reflex apnea. In anesthetized and freely moving rats we have consistently documented that PPT and ITR have a role in respiration. Neurochemical manipulations of each area affected the brainstem respiratory pattern generator and respiratory pattern variability,observed as spontaneous disturbances during sleep or as induced reflex apnea. Although the exact central mechanisms of apnea cannot be determined from our studies to date, we postulate that reflex and sleep-related apneas in rats share some common brainstem pathways, which may include PPT and ITR.

Intertrigeminal region attenuates reflex apnea and stabilizes respiratory pattern in rats

The goal of the present study was to determine whether the newly described anatomical pathway involving the pontine intertrigeminal region (ITR), (Chamberlin and Saper, 1998), has a physiological role in mediating or modulating vagally-induced reflex apnea. We explored the ITR impact on vagal reflex apnea elicited by intravenuously injected 5-HT in ten anesthetized rats. The animals had a catheter inserted into the femoral vein for administration of 5-HT (0.00375 mg) and respiration was recorded by piezo-electric crystal. Multibarrel pipettes were used to pressure inject glutamate (5-10 nl, 10 mM), kynurenic acid (10 nl, 50 mM, a glutamate receptor antagonist), and red dye into the ITR, unilaterally and bilaterally. Intravenous administration of 5-HT produced an immediate 3-s apnea. Microinjections of glutamate into the ITR produced apneas, while microinjections of kynurenic acid blocked the glutamate effect. Following glutamate antagonism, subsequent administration of 5-HT produced apneas of much longer duration (8 s). Acute ponto-medullary transection in two animals yielded even greater prolongation of 5-HT-induced apnea. We conclude that a physiological role for the ITR in respiration is to attenuate vagally-induced reflex apneas. This finding is in agreement with the general modulatory role of pontine structures in autonomic activities including respiration, heart rate and regulation of blood pressure. In addition, our data indicate that medullary circuits, independent of pontine structures, are sufficient to produce 5-HT induced reflex apnea.

Sensory and physiologic effects of menthol and non-menthol cigarettes with differing nicotine delivery

Many smokers choose menthol-flavored cigarettes, however, the influence of menthol on the effects of smoke-delivered nicotine is unknown. Research and commercial cigarettes, menthol and non-menthol, that delivered a wide range of nicotine were evaluated. Menthol (n=18) and non-menthol (n=18) cigarette smokers participated in a single session during which three cigarettes were smoked 45 min apart, in random order. Federal Trade Commission (FTC) nicotine yields of the three cigarettes were: research, low yield, 0.2 mg, commercial cigarettes (average), 1.2 mg; research, high yield, 2.5 mg. Commercial and high-yield cigarettes increased heart rate (HR) and blood pressure more than low-yield cigarettes; although, no differences in exhaled carbon monoxide (CO) occurred. Participants smoked commercial cigarettes faster and with fewer puffs than either of the research cigarette indicating production differences can affect topography. There was a significant group by cigarette interaction on satisfaction, and relief from cigarette craving. High-yield non-menthol cigarettes reduced craving and were rated as more satisfying than high-yield menthol cigarettes. No differences between menthol and non-menthol cigarettes on other subjective measures (strength, psychological reward, negative effects) were observed. Our findings indicate that nicotine delivery, but not mentholation, influences cardiovascular and most subjective measures. These results illustrate the importance of threshold levels of nicotine on subjective responses to cigarette smoking.

The thromboxane A2 mimetic U-46619 inhibits somatomotor activity via a vagal reflex from the lung

Vagal reflexes from the heart and lungs elicit autonomic as well as somatomotor responses. The purpose of the present investigation was to determine whether the inflammatory mediator thromboxane A2 inhibits the knee-jerk reflex via a vagally mediated reflex from either the heart or the lung. The thromboxane A2 mimetic U-46619 (0. 8 +/- 0.08 microg/kg) was injected through a catheter placed near the right atrium (n = 11), near the aortic arch (n = 7), or into the pericardial sac (n = 4) in 11 chloralose-anesthetized cats. The knee-jerk reflex, elicited by striking the patellar tendon with a solenoid-driven hammer, was used to evaluate somatomotor activity. The mean maximum tension produced by the knee-jerk reflex was 306 +/- 21 g (range 154-471 g). Intravenous U-46619 injection inhibited the knee-jerk reflex by 25 +/- 6% and increased peak systolic pressure 53 +/- 7 mmHg on average. Bilateral cervical vagotomy abolished the somatomotor inhibition but did not reduce the pressor response. Intra-arterial U-46619 injection inhibited the knee-jerk reflex in two of seven cats and increased peak systolic pressure by 41 +/- 11 mmHg. Vagotomy abolished the inhibition in one of the two cats but did not reduce the pressor response. Intrapericardial U-46619 injection did not affect the knee-jerk reflex nor blood pressure. The results indicate that U-46619 inhibited the knee-jerk reflex via a vagal reflex from the lung because the inhibition predominated after intravenous injection and was abolished by vagotomy. Speculation is made that the inflammatory mediator thromboxane A2 may contribute via a vagal reflex to the depression of motor activity associated with sickness behavior.

Arteriovenous differences in plasma concentration of nicotine and catecholamines and related cardiovascular effects after smoking, nicotine nasal spray, and intravenous nicotine

BACKGROUND AND OBJECTIVES

Delivery of a high concentration bolus of nicotine through the arterial circulation is believed to be an important determinant of the addictive, behavioral, and physiologic effects of nicotine. To better understand the pharmacologic features of nicotine with different routes of administration, we measured arterial and venous plasma concentrations of nicotine, cotinine, epinephrine, and norepinephrine after tobacco smoking, intravenous nicotine infusion, and use of a nicotine nasal spray.

SUBJECTS AND METHODS

Arterial and venous blood samples were drawn simultaneously from 12 male smokers. Six subjects received a single dose of 1 mg nicotine nasal spray, and six subjects smoked cigarettes, one puff per minute for 10 minutes. All 12 subjects were administered nicotine as a 30-minute infusion beginning 70 minutes after administration of the nicotine nasal spray or commencement of smoking.

RESULTS

The mean peak arterial plasma concentrations of nicotine (Cmax) after smoking or administration of nicotine nasal spray, or intravenous nicotine averaged twofold those of venous plasma. For nicotine nasal spray, the time to Cmax was much faster for arterial than for venous plasma (median, 5 versus 18 minutes, p < 0.01). Intravenous nicotine produced the greatest increase in plasma epinephrine concentration, although smoking had a greater chronotropic effect. Acute tolerance to the chronotropic effects of nicotine was suggested at pharmacodynamic analysis with venous nicotine concentrations, whereas analysis of arterial concentrations found the opposite--a time lag between plasma concentration and effect.

CONCLUSION

Nicotine is rapidly absorbed from nicotine nasal spray. The Cmax of nicotine after smoking or administration of nicotine nasal spray, or intravenous nicotine is substantially higher in arterial than venous plasma. Acute tolerance to the chronotropic effects of nicotine is not apparent if arterial plasma concentrations are measured.

Nicotine impairs reflex renal nerve and respiratory activity in deoxycorticosterone acetate-salt rats

Smoking exacerbates the increase in arterial pressure in hypertension. The effect of nicotine on the baroreceptor-mediated reflex responses of renal nerve activity (RNA), heart rate, and respiratory activity (minute diaphragmatic activity [MDA]) after bolus injections of phenylephrine was compared in deoxycorticosterone acetate (DOCA)-salt sensitive and normotensive rats. Osmotic minipumps that dispensed either nicotine (2.4 mg/kg/day) or saline were implanted in DOCA and normotensive rats for 18 days. Anesthetized DOCA-nicotine, DOCA-saline, control-nicotine, and control-saline rats had mean arterial pressures (MAP) of 117 +/- 3, 110 +/- 9, 90 +/- 3, and 89 +/- 5 mm Hg, respectively. Nicotine decreased the sensitivity (p less than 0.05) of baroreceptor reflex control of RNA (% delta RNA/delta MAP) in the DOCA-nicotine rats (-0.92 +/- 0.08) compared with the DOCA-saline (-1.44 +/- 0.16), control-nicotine (-1.45 +/- 0.08), or control-saline (-1.45 +/- 0.21) rats. The reflex decrease in respiratory activity (% delta MDA/delta MAP x 100) was impaired (p less than 0.01) in both control-nicotine (-24.5 +/- 3.3) and DOCA-nicotine (-18.2 +/- 4.6) rats compared with control-saline (-59.2 +/- 9.1) and DOCA-saline (-52.5 +/- 9.9) rats. The reflex decrease in heart rate (absolute delta HR/delta MAP) in both DOCA-nicotine (1.56 +/- 0.17) and control-nicotine (1.54 +/- 0.24) rats was augmented compared with DOCA-saline and control-saline rats (0.91 +/- 0.12 and 0.97 +/- 0.14).(ABSTRACT TRUNCATED AT 250 WORDS)

The sensory-efferent function of capsaicin-sensitive sensory neurons

Capsaicin-sensitive sensory neurons convey to the central nervous system signals (chemical and physical) arising from viscera and the skin which activate a variety of visceromotor and neuroendocrine reflexes integrated at various levels (intramurally in peripheral organs, at level of prevertebral ganglia, spinal and supraspinal level). Much evidence is now available that peripheral terminals of certain sensory neurons, widely distributed in skin and viscera have the ability to release, upon adequate stimulation, their transmitter content. In addition to the well-known "axon reflex" arrangement, the capsaicin-sensitive sensory neurons have the ability to release the stored transmitter also from the same terminal which is excited by the environmental stimulus. The efferent function of these sensory neurons is realized through the direct and indirect (i.e. mediated by activation of other cells) effects of released mediators. The action of released transmitters on postjunctional elements covers a wide range of effects which may have a physiological or pathological relevance. Development of drugs capable of controlling the sensory-efferent functions of the capsaicin-sensitive sensory neurons represent a new and very promising area of research for pharmacological treatment of various human diseases.

Sensitivity of pulmonary chemo reflexes and lung inflation reflexes to repetitive stimulation and to inhibition with lidocaine and morphine

To study reflex responses caused by stimulation of pulmonary C-fibers and lung inflation, we used a preparation in which the left pulmonary artery and veins were ligated and cannulated and the right and left bronchi were cannulated separately in open-chest dogs. These experiments were performed to establish whether the reflex responses to injections of 150 micrograms of capsaicin through the left pulmonary circulation and inflations of this left lung to 30 cm H2O would be diminished if repeated frequently. Furthermore, the sensitivities of the reflex responses evoked by these capsaicin injections and by left lung inflations (LLI) to blockade with lidocaine or with morphine were studied. Both repeated injections of capsaicin into the left pulmonary circulation and repeated inflations of the left lung for up to 100 min produced a persistent triad of reflex responses: bradycardia, hypotension, and cessation of diaphragmatic contractions. Lidocaine injections (50 mg) into the pulmonary artery of the vascularly isolated lung abolished all reflex responses to subsequent injections of capsaicin, but only attenuated the triad of responses to subsequent left lung inflations by half. Morphine sulfate (60 mg) administered to the pulmonary vascular bed of the isolated lung reduced, but did not eliminate, the triad of reflex responses to subsequent capsaicin injections and lung inflations. The influences of morphine upon capsaicin and lung inflation responses were not abolished by naloxone.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary resistance and compliance changes evoked by pulmonary opiate receptor stimulation

The administration of [D-Ala2,Met5]enkephalinamide (DAME, 10-250 micrograms/kg) or morphine sulfate (MS, 2 mg/kg) into the right atrium (RA) of spontaneously breathing decerebrate rats caused an increase in lung resistance (RL) and a decrease in dynamic compliance (Cdyn). The maximal percentage increase in RL for DAME (250 micrograms/kg) and MS (2 mg/kg) was 120 +/- 21 and 160 +/- 40%, respectively, occurring during the first 30 s following an initial period of apnea, and subsiding within 1.5-2.0 min. The fall in Cdyn (DAME = -31 +/- 8%; MS = -35 +/- 4%) followed a more prolonged time course returning to control within 4-5 min. These responses were completely abolished by pretreatment with naloxone HCl (100 micrograms/kg i.v.), as well as bilateral cervical vagotomy. Pretreatment with antihistaminic, antiserotinergic, and antimuscarinic agents had no effect on the opioid induced changes in RL and Cdyn. Further studies carried out in ventilated animals showed blockade of the mechanical responses following the administration of neuromuscular blockers, C7 spinal cord transection, and ventral midline opening and retraction of the chest. Electromyograms obtained from intercostal muscles showed excitation of expiratory motor units and inhibition of inspiratory motor units following the administration of opioids. Similar results were obtained with phenyldiguanide (PDG), a known stimulant of pulmonary J-receptors. However, PDG effects were not blocked by naloxone. It was concluded that changes in RL resulted from a decrease in thoracic volume and resultant decrease in the radial traction of the airways. Changes in Cdyn were caused by spasm of expiratory muscles of the chest wall.

Peripheral versus central cardiorespiratory effects of morphine

The administration of morphine sulfate (MS, 2 mg/kg) into the right atrium in decerebrate rats, produced a dramatic bradycardia, apnea, and a slight transient biphasic blood pressure response within 1 sec. The bradycardia was slowly restored to control levels within 8-10 min and was prevented by pretreatment with atropine. Apnea (7.3 +/- 2.2 sec) was followed by a period of rapid shallow breathing. Acute tolerance to these effects developed to subsequent doses of morphine. In paralyzed artificially ventilated animals, morphine produced: (1) cessation of phrenic nerve (PN) activity which was followed by bursts of shortened duration; and (2) concomitant excitation of the recurrent laryngeal nerve (RLN), this activity exhibited a continuous discharge which was asynchronous with that of phrenic nerve. These actions of morphine were qualitatively similar to those observed with phenyldiguanide (PDG) and were found to be reflexogenic, i.e. emanating from the lungs via stimulation of pulmonary C-fibers. Bilaterally vagotomized animals only responded to morphine with respiratory depression, characterized by a severe decrease in respiratory rate and minute ventilation. On the other hand, animals with intact vagi showed stimulation of rate and minute ventilation following a brief period of apnea. They were less sensitive than vagotomized animals to the depressant action during the first 8 min after administration of morphine. All the effects of morphine were blocked by pretreatment with naloxone (50-400 micrograms/kg, i.v.). These results indicate that the initial cardiorespiratory effects of morphine are due to a peripheral reflex action arising from the stimulation of opiate receptors associated with pulmonary C-fibers, e.g. J-fibers.

Pulmonary vagal afferent stimulants in the conscious rat: opioids and phenyldiguanide

Phenyldiguanide (PDG, 40 microgram/kg), D-ala2-met5-enkephalinamide (D-AME, 250 microgram/kg) and morphine sulfate (MS, 2 mg/kg) injected into the right atrium (RA) of conscious freely moving rats produced a profound bradycardia and hypotension 1-2 sec subsequent to administration. Concomitant with the cardiovascular effects apnea occurred and lasted approximately 5 sec. Atropine methyl nitrate (2 mg/kg, RA) significantly attenuated the bradycardia and hypotension produced by all three agents. Naloxone blocked only the opioid responses. Coordinated motor activity was impaired following the administration of PDG (40 microgram/kg, RA). Fifty percent of the animals receiving PDG failed to remain on a rotor rod for a 2 min period. Only 8 percent of the saline treated group fell off during this period. It was concluded that the cardiovascular, respiratory, and motor effects caused by PDG, in the conscious freely moving rat, were the result of stimulation of pulmonary vagal afferents (J-receptors). The cardiovascular effects of opioids are also believed to arise from the stimulation of J-receptors. However, unlike PDG, these effects are mediated by pulmonary opiate receptors.

Greater splanchnic nerve activity in the rat

The greater splanchnic nerve trunks in the rat, unlike in other experimental animals, do not join celiac plexus directly. These nerve trunks join small ganglia, the cardiac ganglia, on either side. The cardiac ganglia are located about 1 cm rostro-lateral to unpaired celiac ganglion. The greater splanchnic nerve activity immediately proximal to celiac ganglion is predominantly post-ganglionic in the rat. On the other hand, the activity of the greater splanchnic nerve proximal to the celiac ganglion is predominantly preganglionic in other experimental animals, (e.g., cat), In the rat, preganglionic sympathetic nerve activity is predominant in the segment of the greater splanchnic nerve proximal to the cardiac ganglion.

Nicotinic nociceptors on perivascular sensory nerve endings

Intra-arterial injection of increasing doses of acetylcholine, nicotine, carbachol and pilocarpine into the pain reflex ear of the rabbit dose-dependently caused a reflex fall in mean arterial blood pressure. The order of potency of the algesic substances was: nicotine greater than acetylcholine much greater than carbachol much greater than pilocarpine, whereas the purely muscarinic agonist bethanechol was inactive up to 3 mg. Atropine at 1 microgram/ml did not influence the effect of acetylcholine. At 30 micrograms/ml it reduced the effect of acetylcholine but also that of bradykinin suggesting an unspecific action. Hexamethonium (1 microgram/ml) blocked the algesic effect of acetylcholine and nicotine without influencing that of bradykinin. Morphine, given systemically, blocked the algesic effect of acetylcholine and nicotine. Since nicotine showed the highest algesic potency (whereas bethanechol was inactive) and hexamethonium blocked the effect of acetylcholine and nicotine, the cholinergic "pain receptor" on sensory nerve endings is assumed to be of the nicotinic type.

Pulmonary opiate receptor activation evokes a cardiorespiratory reflex

The administration of [D-Ala2,Met5]enkephalinamide (D-AME) and [D-Ala2,Leu5]enkephalinamide (D-ALE) into the right atrium of decerebrate rats caused bradycardia, a slight transient biphasic blood pressure response and apnea within 1-2 sec. Apnea was followed by rapid shallow breathing. These effects were dose related (1-1000 micrograms/kg) and blocked by pretreatment with naloxone. Atropine blocked the bradycardia. Sectioning the vagi at the level of the diaphragm did not affect the responses, whereas bivagotomy below the cardiac branches abolished all responses. The triad of responses was attributed to a reflex action arising from vagal afferents within the lung. These results were confirmed in paralyzed , artificially ventilated animals. In these animals, the enkephalin analogues produced a cessation of phrenic nerve (PN) activity followed by a decrease in the duration of bursts. The recurrent laryngeal nerve (RLN) was concomitantly excited in a continuous decremental fashion. This excitation was independent of PN inhibition. Recordings of single and near single pulmonary vagal afferents demonstrated no effect of D-AME or D-ALE on stretch and irritant receptors. However, type J-receptors were stimulated.

Vasopressin release by nicotine in the cat

Our goal in this study was to examine where nicotine acted on the neurohypophysial release of arginine vasopressin (AVP). In the chamber-isolated, unanesthetized cat, an IV infusion of nicotine (25--50 micrograms/kg/min for 10 min) produced a 54-fold rise in plasma AVP (65 +/- 12.5 microU/ml) and a behavioral sequence of restlessness, ear twitching, salivation, chewing and retching. Chloralose anesthesia and acute surgical preparation increased plasma AVP (9.4 +/- 3.8 microU/ml) 4-times the control level in the unanesthetized state (2.4 +/- 0.1 microU/ml). In the anesthetized cat, an IV infusion of nicotine produced a 140-fold rise in plasma AVP (802.7 +/- 289.0 microU/ml) and a biphasic response in mean arterial blood pressure (MABP) which rose to 32% above control in the first 5 min and fell to 25% below control during the last 5 min. Bilateral surgical section of the carotid sinus and vagus nerves increased plasma AVP (47.6 +/- 25.8 microU/ml) to 5-times the control level in the anesthetized state (9.4 +/- 3.8 microU/ml). In the anesthetized, baroreceptor-denervated cat, an IV infusion of nicotine produced a 3-fold rise in plasma AVP (141.5 +/- 31.3 microU/ml) and a biphasic MABP response. Hypophysectomy abolished the nicotine-induced rise in AVP but did not modify the biphasic MABP response. These data suggest that in the cat nicotine releases AVP from the neurohypophysis by multiple sites of action within the receptive fields of te carotid sinus and vagus nerves and at unknown loci within the central nervous system.

The effects of sodium cromoglycate on lung irritant receptors and left ventricular cardiac receptors in the anaesthetized dog

1 The time from the injection of sodium cromoglycate 10 to 50 mug/kg into a saphenous vein, the cervical carotid arteries, the left ventricle and the aortic arch, to the onset of reflex hypotension has been measured in anaesthetized dogs. The shortest latency was 16.9 s on injection of sodium cromoglycate into the left ventricle.2 Instillation of 2% lignocaine into the pericardium of an anaesthetized dog blocked the reflex hypotensive response to sodium cromoglycate (10 to 50 mug/kg i.v.), and also prevented sodium cromoglycate (100 mug/kg) from reversing reflex bronchoconstriction induced by inhalation of an aerosol of histamine.3 The effect of sodium cromoglycate (100 mug/kg i.v.) on resting discharge and histamine-induced discharge (20 mug/kg i.v.) of five lung irritant receptors in five anaesthetized dogs has been studied. Sodium cromoglycate (100 mug/kg i.v.) did not affect the resting discharge of these receptors or their ability to respond to histamine.4 Sodium cromoglycate (100 mug/kg i.v.) increased the rate of discharge of three receptors found in the endocardium of the left ventricle of the canine heart. A solution of sodium cromoglycate (0.1%) was applied topically to one receptor and its rate of discharge was increased.5 It is suggested that in the dog, sodium cromoglycate produces reflex hypotension and reverses histamine-induced reflex bronchoconstriction by activating receptors in the left ventricle of the heart.