Effect of 6-OHDA on hypercapnic ventilatory response in the rat model of Parkinson's disease.

Breathing impairments, such as an alteration in breathing pattern, dyspnoea, and sleep apnoea, are common health deficits recognised in Parkinson's disease (PD). The mechanism that underlies these disturbances, however, remains unclear. We investigated the effect of the unilateral damage to the rat nigrostriatal pathway on the central ventilatory response to hypercapnia, evoked by administering 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle (MFB). The respiratory experiments were carried out in conscious animals in the plethysmography chamber. The ventilatory parameters were studied in normocapnic and hyperoxic hypercapnia before and 14 days after the neurotoxin injection. Lesion with the 6-OHDA produced an increased tidal volume during normoxia. The magnified response of tidal volume and a decrease of breathing frequency to hypercapnia were observed in comparison to the pre-lesion and sham controls. Changes in both respiratory parameters resulted in an increase of minute ventilation of the response to CO(2) by 28% in comparison to the pre-lesion state at 60 s. Our results demonstrate that rats with implemented unilateral PD model presented an altered respiratory pattern most often during a ventilatory response to hypercapnia. Preserved noradrenaline and specific changes in dopamine and serotonin characteristic for this model could be responsible for the pattern of breathing observed during hypercapnia.

Hypoxic ventilatory response after dopamine D2 receptor blockade in unilateral rat model of Parkinson's disease.

Modified non-motor brainstem ventilatory control might be involved in Parkinson's disease. Our study was designed to investigate the impact of degeneration of the nigrostriatal dopaminergic pathway on resting breathing and hypoxic ventilatory response in conscious rats. The role of central and peripheral dopamine D2 receptors in the modulation of the hypoxic ventilatory response in conditions of dopamine shortage was examined. Adult Wistar rats received a unilateral double 6-hydroxydopamine lesion of the right medial forebrain bundle. After surgery, animals were placed in whole-body plethysmographic chamber and exposed to hypoxia (8% O2). One group of animals received inraperitoneal injections of either haloperidol or domperidone before hypoxia. Levels of dopamine and its metabolite in the brainstem and striatum were assessed. Neurotoxin treatment evoked limb use asymmetry. No effect on the resting normoxic respiration was observed. An increase in tidal volume and a decrease in respiratory rate during respiratory response to hypoxia with short magnification of minute ventilation were predominant effects. Domperidone treatment in intact animals evoked a significant increase in normoxic tidal volume, while haloperidol potentiated tidal volume increase in response to hypoxia. After the lesion, the effects of both antagonists were absent. In rats with Parkinson's, the content of dopamine and its metabolite decreased substantially in the injured striatum. Augmentation of a tidal volume response to hypoxia, and the absence of stimulatory effect of intraperitoneal domperidone on normoxic and haloperidol on hypoxic tidal volume, in lesioned rats indicated altered control of breathing. This could be the result of a dopamine deficiency in the striatum and an increased turnover of DOPAC/DA in the brainstem.

Influence of temperature on survival of Escherichia coli O157:H7 in stored cattle slurry with respect to environmental biosafety.

The aim of the study was to determine the influence of temperature, i.e. 4 and 20 degrees C on the Escherichia coli O157:H7 survival time in a stored cattle slurry in a laboratory model experiment. The results of this investigation indicated that the tested microorganisms underwent a gradual elimination in the cattle slurry, whereas their inactivation rate was clearly dependent on the temperature. A higher survival rate was found in Escherichia coli O157:H7 at 4 degrees C where a theoretical survival time of these microorganisms, determined using a regression analysis, amounted to 83 days. Our study indicates that there is a necessity for the slurry to undergo hygienization processes and that a constant monitoring of liquid animal excreta in search for pathogenic microorganisms is required.

Serotoninergic modulation of cortical and respiratory responses to episodic hypoxia.

Biphasic respiratory response to hypoxia in anesthetized animals is accompanied by changes in the EEG mostly in the low EEG frequency bands. Serotonin is a potent modulator of cortical and respiratory activity through 5-HT(2) receptors. Present study investigated whether 5-HT(2) receptors might be involved in the EEG and respiratory relationship during normoxic and hypoxic respiration assessed from integrated phrenic (Phr) and hypoglossal (HG) nerve activities. EEG signal recorded from the frontal cortex was subjected to power spectral analysis in delta, theta, alpha, and beta frequency bands. Systemic administration of 5-HT(2) agonist DOI (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) enhanced tonic and lowered peak phasic respiratory activity, and increased frequency of bursts of Phr and HG activity. At the same time, EEG activity became desynchronized and arterial blood pressure (ABP) increased. Following DOI pretreatment, 11% hypoxia induced an augmented respiratory response in comparison with the response in the baseline condition. ABP fell less then in the control hypoxia. EEG pattern changed less than in the baseline state. Subsequent administration of ketanserin, a 5-HT(2) antagonist increased respiratory activity, elicited a synchronization of EEG activity and hypotension. The respiratory response to hypoxia was attenuated and cortical response was more potent in comparison with that after DOI injection. Arterial blood pressure decreased more then during baseline hypoxic response. The results suggest that modulation of cortical synchronization and desynchronization through 5-HT(2) receptor active agents may impact to hypoxic respiratory response.

Superoxide dismutase mimetic modulates hyperoxic augmentation of the diaphragmatic response to poikilocapnic hypoxia in non-vagotomized rats.

A period of oxygen breathing enhances the subsequent respiratory responses to episodic hypoxia. Since hyperoxia increases a formation of reactive oxygen species (ROS) in lungs, in the present study we asked a question of whether superoxide anion produced during O(2) breathing would participate in the mechanisms of posthyperoxic enhancement of the response to hypoxia and whether afferent information from the lungs would contribute to this response. To scavenge a superoxide we used Tempol (4-hydroxy-2,2,6,6-tetra-methyl piperidine-N-oxyl), a superoxide dismutase mimetic. The respiratory activity of anesthetized, spontaneously breathing rats was assessed from the integrated costal diaphragm EMG. The experiments consisted of 3 min hypoxia (11% O(2)), before and after a 15 min period of breathing with 100% oxygen, with and without Tempol (33 mg/kg) preatreatment. The same protocol was performed in non-vagotomized and vagotomized rats. The results show that a SOD mimetic abolished both hyperoxia-induced slowing of respiration and posthyperoxic respiratory augmentation of the hypoxic response. The abolishment is due likely to a remodeling of the respiratory pattern involving lung vagal reeptors, since in vagotomized animals, the effects of Tempol were marginal.

Electroencephalographic and respiratory activities during acute intermittent hypoxia in anesthetized rats.

Cortical activity and respiratory responses to intermittent hypoxia were studied in anesthetized, paralyzed, vagotomized, and artificially ventilated rats. Respiratory responses to hypoxic exposure consisted of stimulation of phrenic and hypoglossal activity and a subsequent decline of the activity up to apnea. The respiratory response to hypoxia was accompanied by a gradual decrement of the total power of EEG. Relative EEG power increased in the delta frequency range and decreased in the remaining frequency ranges. During hypoxic bradypnea or apnea, the total power of EEG strongly diminished or ceased. Each episode of hypoxia caused similar respiratory and cortical effects. However, in comparison with the baseline level, the total power of EEG decreased gradually while the power of the delta frequency range increased in subsequent hypoxic episodes. EEG activity after the last hypoxic exposure recovered within 40-60 min. We conclude that hypoxia initially induces modest changes in the cortical activity that grow with the severity of hypoxia. The persistence of changes in EEG activity following intermittent hypoxia may contribute to disorders present in the sleep apnea syndrome.

Short-term depression of inspiratory activity following tonic vagal stimulation.

This study tested the role of inhibitory neurotransmission in the glutaminergic control of short-term depression (STD) of the inspiratory activity initiated by sustained stimulation of the vagus nerve in anesthetized and vagotomized cats. STD, calculated from the integrated phrenic nerve signal, lasted longer when glutaminergic neurotransmission was inhibited by ketamine, a NMDA receptor antagonist. Application of picrotoxin, a GABAA receptor antagonist, reversed the effect of ketamine and shortened the STD duration below that present in the control condition. The results showed that alternation of the neural excitability by antagonists of excitatory and inhibitory neurotransmission modulates the STD of inspiratory activity, evoked by vagal stimulation. The STD depends on the state of neural excitability and is easier accomplished when the excitability is on the high side.

Neurotransmitter mechanisms in the enhancement of the hypoxic ventilatory response by antecedent hyperoxia in the anesthetized rat.

A brief period of antecedent oxygen breathing enhances the ventilatory response to hypoxia. The mechanisms of this phenomenon are uncertain and have been variably linked to the central glutamatergic or nitrergic pathways. In the present study we put a question of how blockade of either neurotransmitter pathway would compare with the concurrent blockade of them both in terms of the enhancement of posthyperoxic hypoxic ventilation. The study was performed on the anesthetized, vagotomized, spontaneously breathing rats divided into the following experimental groups: control NaCl-treated, glutamate blocker 2-amino-5-phosphonopentanoic acid (AP5)-treated, nitric oxide synthase blocker 7-nitroindazol (7NI)-treated, and AP5+7NI-treated. The protocol consisted of measuring the ventilatory response to 12% O2, a steady- state poikilocapnic hypoxia, undertaken in three consecutive conditions in each animal: the initial control, 25 min after injection of a given chemical agent, and then after a 15-min period of oxygen breathing. Respiration was evaluated from the diaphragmatic EMG signal. We found that the posthyperoxic hypoxic ventilatory enhancement was but partially dampened by either AP5 or 7NI. Concurrent administration of the two blockers further diminished, but did not abolish, the hypoxic ventilatory enhancement. We conclude that although the glutamate-NO system accounts for an appreciable part of the posthyperoxic hypoxic ventilatory enhancement, other, as yet unclear, mechanisms contribute as well. These mechanisms may be worth exploring given the substantial enhancing effect the antecedent oxygen has on hypoxic hyperventilation.

Biphasic effect of ethyl alcohol on short-term potentiation of the respiratory activity in the rabbit.

This study investigated the effects of systemic alcohol injections on respiratory activity and short-term potentiation (STP) of the phrenic nerve and hypoglossal nerve activities, evoked by electrical stimulation of the superior laryngeal nerve (SLN), in anesthetized, paralyzed, and artificially ventilated rabbits. Alcohol, in a dose of 500 mg/kg, given singly or in cumulative fractions of 100mg/kg, depressed hypoglossal activity with little or no effect on phrenic activity. SLN stimulation inhibited both phrenic and hypoglossal activities and this effect remained unchanged by either way of alcohol administration. After cessation of stimulation, hypoglossal activity increased above the control level and slowly declined to the baseline, showing signs of STP. The amplitude and duration of the hypoglossal STP decreased following a single dose of alcohol. Cumulative fractions of the alcohol dose evoked a biphasic effect on the respiratory STP. In a lower range, alcohol enhanced the hypoglossal STP and tended to increase the duration of the phrenic STP. This effect gradually declined with increasing cumulative dose of alcohol and finally reversed to the inhibition of the STP of both nerves. The results demonstrate a dose-dependent biphasic effect of alcohol on the induction and maintaining of the hypoglossal STP. A reduction in STP, together with hypoglossal activity depression following alcohol accumulation, may contribute to the facilitation of upper airway obstruction by alcohol.

Divergent effects of bicuculline and picrotoxin on ketamine-induced apneustic breathing.

This study tested the potential role of inhibitory neurotransmission in the mechanism of apneustic respiration evoked by ketamine, an NMDA receptors antagonist. In the experiments performed in anesthetized, paralyzed, and ventilated cats, ketamine, in a dose of 0.5 mg/kg, was administered before and after GABA(A) receptor blockade with picrotoxin or bicuculline; all agents were given intravenously. Ketamine elicited a transient, hourlong apneustic respiration consisting of an increase in inspiratory duration and a decrease in inspiratory neural amplitude. After prior administration of picrotoxin, but not bicuculline, the maximum apneustic-like prolongation of inspiration evoked by ketamine was considerably reduced. The results suggest that the GABA receptor subunits specifically sensitive to picrotoxin play a role in shaping the ketamine-induced apneustic breathing.

Hypoglossal and phrenic nerve responses to changes in oxygen tension during picrotoxin-induced seizures in the rat.

The aim of this study was to examine the response of phrenic and hypoglossal motor outputs to hyperoxia and 11% hypoxia during picrotoxin-induced seizures. Adult rats were anesthetized with a mixture of urethane with alpha-chloralose. The animals were bilaterally vagotomized, paralyzed, and artificially ventilated. Picrotoxin was administered intravenously in a cumulative dose until seizures occurred. The response to changes in oxygen tension was studied after the convulsive dose of picrotoxin and compared with the baseline level. The results show that the picrotoxin-induced seizures evoked a complex respiratory response that consisted of an augmentation of phrenic and hypoglossal nerve activities and irregular disturbances in phasic respiratory discharges. The excitation of the hypoglossal activity appeared earlier and showed a more irregular pattern than that of the phrenic activity. Hyperoxia elicited a similar decrease in neural respiratory outputs during the control and seizure conditions, suggesting the unaltered peripheral chemoreceptor mechanism. In the pre-seizure condition, hypoxia caused an initial excitation of the phrenic and hypoglossal outputs followed by some decline of the effect. During seizures, the striking effect of hypoxia was a decrease of the respiratory rate. A biphasic response to hypoxia was maintained in the hypoglossal activity due to stimulation of the hypoglossal amplitude. In contrast, in the phrenic activity the excitatory phase of hypoxia was absent and depression ensued. The mechanism underlying the facilitation of hypoxic respiratory depression during seizures is discussed.

Changes in short-term potentiation of hypoglossal activity by modulators of nitric oxide production in the rabbit.

Stimulation of the superior laryngeal nerve (SLN) causes a potentiation of hypoglossal nerve activity persisting after cessation of stimulation. The mechanism of this phenomenon is uncertain. We investigated a potential role of the nitric oxide (NO) pathway in modulation of the after-effects of SLN stimulation on phrenic and hypoglossal activity in rabbits. L-Arginine, a substrate for NO synthesis and NG-Nitro-L-Arginine (L-NNA) an inhibitor of NO synthase (NOS), were administered systemically. L-Arginine and L-NNA alone caused small changes in respiratory activity. During pre-treatment with NO precursor the amplitude and duration of hypoglossal potentiation evoked by SLN stimulation were reduced. Systemic NO synthase inhibition partially reversed these effects of L-Arginine. The results showed that interference with NO production by NO substrate and NOS inhibitor modulates the effects of SLN stimulation on hypoglossal activity. Nitric oxide might be a negative modulator of the transmission of short-term potentiation (STP) in hypoglossal activity.

[Diaphragmatic electromyogram and respiratory pattern after unilateral and bilateral partial denervation of the diaphragm in the cat]. / Elektromiogram przepony i wxorzec oddechowy po jednostronnym i obustronnym czesciowym odnerwieniu przepony u kota.

In the present study we investigated the mechanism of early respiratory compensation of partial paralysis of the sternal and lateral diaphragm due to an unilateral or bilateral section of the C5 rootlet of the phrenic nerves in anesthetized cats. Compensatory effects were evaluated from the recordings of the bilateral diaphragmatic EMGs, neural respiratory pattern and ventilation. The results of the study demonstrate that successive C5 denervation of the diaphragm caused a decrease in the ipsilateral diaphragmatic EMG. Bilateral C5 section evoked an up to 10 percent decrease in minute ventilation. The compensation of the unilateral and then bilateral partial impairment of the muscle function was achieved always by an increase in the neuromuscular projection to the currently contralateral diaphragm. Neural mechanisms of compensation involve a general increase in the respiratory drive, expressed mostly as an increase in the frequency of breathing. The contribution of afferent respiratory muscles to these mechanisms is likely.

The role of raphe and tractus solitarius neuronal structures in the modulation of respiratory pattern in rabbits.

We studied the effects of MNR stimulation on phrenic (Phr) electroneurogram and external intercostal muscles (EI) electromiogram in spontaneously breathing rabbits. Additionally, experiments were performed before and after lignocaine blockade of nucleus tractus solitarii (NTS) to determine whether the information from MNR is transmitted via NTS neurones. The completeness of the blockade of NTS region was checked by studying the Hering-Breuer reflex. MNR was stimulated at the level 2-7 mm rostral to the obex. Stimulation at the rostral part of this region produced inhibition of phasic inspiratory activity, whereas stimulation in the caudal part elicited tonic activity throughout the respiratory cycle. These effects were more pronounced on EI than Phr. Responses to MNR stimulation were attenuated after lignocaine blockade, suggesting that the neurons located in NTS take part in the transmission of the modulatory information from the MNR to respiratory motoneurones.

The respiratory response to magnetic stimulation of the cortex in the unanaesthetized baboon.

Transcranial magnetic stimulation has been used to study cortical input to the respiratory system in unanaesthetized baboons. Single magnetic pulse caused usually a short-latency excitation with subsequent inhibition in stimulated inspiratory phase and change in the amplitude and timing of the respiratory cycle. The results suggest that cortical information is processed by the medullary pattern generator.

Inspiratory action of separate external and parasternal intercostal muscle contraction.

We have previously shown that electrical stimulation of the thoracic spinal cord produces near maximal activation of the inspiratory intercostal muscles. In the present investigation, we used this technique to evaluate the relative capacity of separate external (EI) and parasternal intercostal (PA) muscle contraction to produce changes in airway pressure and inspired volume. Studies were performed in 23 anesthetized phrenicotomized dogs. Electrical stimuli were applied to the spinal cord after hyperventilation-induced apnea, before and after sequentially severing either the PA or EI muscles from the first through sixth intercostal spaces. During spinal cord stimulation (SCS), measurements were made of inspired volume (delta V) with the airway open and negative airway pressure (delta P) during tracheal occlusion. Compared with control values, sectioning of the PA muscles resulted in a 40.9% reduction in delta P and 35.7% reduction in delta V during SCS. In other animals, initial sectioning of the EI muscles produced reductions in delta P and delta V of 67.4 and 63.0, respectively, during SCS. After subsequent section of the PA muscles, SCS produced only negligible inspired volumes and changes in airway pressure. We conclude that 1) the EI and PA muscles are each capable of generating substantial changes in airway pressure and large inspired volumes and 2) the ventilatory capacity of the EI muscles exceeds that of the PA muscles.

Inspiratory muscle interaction in the generation of changes in airway pressure.

The mechanical interaction of the inspiratory muscles in the generation of changes in airway pressure is unclear. Using upper thoracic spinal cord stimulation to activate the intercostal muscles (IC) and bilateral supramaximal phrenic nerve stimulation to activate the diaphragm (D), we measured the changes in airway pressure produced by separate and combined IC and D activation over a wide range of lung volumes. Changes in parasternal IC and D length were assessed by sonomicrometry. With increasing lung volume, activation of the IC and D resulted in progressive decrements in generated airway pressure. Combined IC and D contraction produced greater negative swings in airway pressure than the arithmetic sum of separate IC and D contraction alone, indicating a synergistic effect. Moreover, synergism increased progressively with increasing lung volume. During combined muscle contraction, both the IC and D shortened less than during contraction of either muscle group alone. The tendency for the parasternal muscle to lengthen for a given change in airway pressure during D contraction alone increased with increasing lung volume, suggesting that the tendency for the rib cage to recoil inward increased progressively with increasing lung volume. Likewise, the tendency of the D to lengthen for a given change in airway pressure during IC contraction alone also increased progressively with increasing lung volume, suggesting that the tendency for the abdomen-D compartment to recoil inward also increased with increasing lung volume. We conclude that the IC and D interact synergistically to produce changes in airway pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Artificial ventilation by means of electrical activation of the intercostal/accessory muscles alone in anesthetized dogs.

We have previously shown that large inspired volumes can be achieved in phrenicotomized animals by intercostal/accessory muscle activation via spinal cord stimulation. In the present study, we evaluated the utility of this technique to provide complete ventilatory support for prolonged time periods (6 to 8 h, selected arbitrarily). In 10 deeply anesthetized dogs, a single electrode was introduced onto the epidural surface of the spinal cord and positioned at the T2-T3 spinal level. Bilateral phrenicotomy was performed in all animals to prevent possible diaphragm activation. The spinal cord was rhythmically stimulated approximately 13 times/min with trains of 15- to 20-Hz impulses of sufficient amplitude to achieve inspired volumes of 13 to 15 ml/kg and pressure-time index (product of duty cycle and delta P/Pmax) of less than 0.15 with each contraction. Level of alveolar ventilation was monitored by end-tidal PCO2 and intermittent arterial blood gas measurements. Mean inspired volume and minute ventilation were 236 +/- 7.84 (SE) ml and 3.12 +/- 0.13 (SE) L/min, respectively, and not significantly different between the first and sixth hours of continuous stimulation. Mean duty cycle (Ti/Ttot) was 0.26 +/- 0.01. Mean airway pressure (delta P) during prolonged electrical stimulation under conditions of airway occlusion was 8.05 +/- 0.61 (SE) cm H2O. Mean ratio of delta P/Pmax was 0.47 +/- 0.03 (SE) cm H2O; mean pressure-time index was 0.12 +/- 0.01 (SE). There was no evidence of system fatigue, as evidenced by the lack of any significant shift in the pressure frequency curve over a 6-h time period.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-latency phrenic response to vagal stimulation after midsagittal lesion of the medulla in rabbit.

The effect of midsagittal lesions of the medulla on the phrenic nerve output and the central transmission of the vagal input were studied. The rabbits were anaesthetized with a mixture of chloralose with urethane, paralysed and artificially ventilated. Both vagi were sectioned in the neck and one of them was prepared for electrical stimulation of its proximal end. Lesions of the medulla were performed in steps and at each stage the short-latency phrenic response to a single electrical shock applied to the vagus was studied. The results indicate that, at the levels 1 to 5 mm rostra1 to the obex and 3 mm in depth from the dorsal medullary surface, there is a maximal density of crossing connections important for transmission of the descending respiratory activity, synchronization of the respiratory activity generated by left and right part of the medulla and transmission of the vagal signal.

Phrenic reflexes in the decerebrate and spinal rabbit.

Investigations were undertaken to study the characteristics of phrenic reflexes with partial or total elimination of the descending neuronal pathways. Experiments were performed on 17 decerebrate, vagotomized, paralysed and artificially ventilated rabbits. The experimental procedure included a midsagittal section of the medulla or a hemisection followed by a total transection of the spinal cord at C1. The effects of compression of the rostral or caudal parts of the thorax, pressure on the muscles at the lumbar level and passive movements of the hindlimb were studied on the efferent vagal and phrenic neurograms. Partial elimination of the descending pathways evoked an increase in the intensity of the spinal reflexes. Characteristics of the reflexes which we have obtained after lesions of the medulla or spinal cord enable us to search for their central path. After transection of the spinal cord, no sustained phasic phrenic nerve activities were observed. The results suggest that after high cordotomy the phrenic motoneuronal pool has a potential capability for generating phasic bursts and additional inputs are required for their development.