Essential Role of the cVRG in the Generation of Both the Expiratory and Inspiratory Components of the Cough Reflex

As stated by Korpáš and Tomori (1979), cough is the most important airway protective reflex which provides airway defensive responses to nociceptive stimuli. They recognized that active expiratory efforts, due to the activation of caudal ventral respiratory group (cVRG) expiratory premotoneurons, are the prominent component of coughs. Here, we discuss data suggesting that neurons located in the cVRG have an essential role in the generation of both the inspiratory and expiratory components of the cough reflex. Some lines of evidence indicate that cVRG expiratory neurons, when strongly activated, may subserve the alternation of inspiratory and expiratory cough bursts, possibly owing to the presence of axon collaterals. Of note, experimental findings such as blockade or impairment of glutamatergic transmission to the cVRG neurons lead to the view that neurons located in the cVRG are crucial for the production of the complete cough motor pattern. The involvement of bulbospinal expiratory neurons seems unlikely since their activation affects differentially expiratory and inspiratory muscles, while their blockade does not affect baseline inspiratory activity. Thus, other types of cVRG neurons with their medullary projections should have a role and possibly contribute to the fine tuning of the intensity of inspiratory and expiratory efforts.

Comparison between the effects of lisinopril and losartan on the cougn reflex in anesthetized and awake rabbits

The aim of the present study was to analyze differences in cough induction between losartan and lisinopril in both anaesthetized and awake rabbits, i.e., under conditions in which the influences of higher brain areas on the cough reflex are strongly reduced or abolished. Losartan (500 μg/kg), lisinopril (100 μg/kg) and NaCl 0.9% saline solution (vehicle) were administered by intravenous injections. Animals were randomly assigned to the different experimental treatments. The cough reflex was induced by chemical (citric acid) and/or mechanical stimulation of the tracheobronchial tree. In anaesthetized rabbits, losartan and lisinopril caused similar hypotensive effects. Lisinopril, but not losartan, increased the cough response induced by both mechanical and chemical stimulation due to increases in the cough number, i.e. the number of coughs induced by each stimulation challenge. In awake animals, only lisinopril significantly increased the cough number. The results support the notion that cough potentiation induced by losartan, and possibly other sartans, is lower than that induced by most angiotensin-converting enzyme inhibitors despite the reduction or complete absence of higher brain functions. In this connection, the comparison between present results and our previous findings on ramipril and zofenopril shows that losartan and zofenopril display similar cough-inducing potency, much lower than that of lisinopril and ramipril.

Role of neurokinin receptors and ionic mechanisms within the respiratory network of the lamprey

We have suggested that in the lamprey, a medullary region called the paratrigeminal respiratory group (pTRG), is essential for respiratory rhythm generation and could correspond to the pre-Bötzinger complex (pre-BötC), the hypothesized kernel of the inspiratory rhythm-generating network in mammals. The present study was performed on in vitro brainstem preparations of adult lampreys to investigate whether some functional characteristics of the respiratory network are retained throughout evolution and to get further insights into the recent debated hypotheses on respiratory rhythmogenesis in mammals, such as for instance the "group-pacemaker" hypothesis. Thus, we tried to ascertain the presence and role of neurokinins (NKs) and burst-generating ion currents, such as the persistent Na(+) current (I(NaP)) and the Ca(2+)-activated non-specific cation current (I(CAN)), described in the pre-Bötzinger complex. Respiratory activity was monitored as vagal motor output. Substance P (SP) as well as NK1, NK2 and NK3 receptor agonists (400-800 nM) applied to the bath induced marked increases in respiratory frequency. Microinjections (0.5-1 nl) of SP as well as the other NK receptor agonists (1 microM) into the pTRG increased the frequency and amplitude of vagal bursts. Riluzole (RIL) and flufenamic acid (FFA) were used to block I(NaP) and I(CAN), respectively. Bath application of either RIL or FFA (20-50 microM) depressed, but did not suppress respiratory activity. Coapplication of RIL and FFA at 50 microM abolished the respiratory rhythm that, however, was restarted by SP microinjected into the pTRG. The results show that NKs may have a modulatory role in the lamprey respiratory network through an action on the pTRG and that I(NaP) and I(CAN) may contribute to vagal burst generation. We suggest that the "group-pacemaker" hypothesis is tenable for the lamprey respiratory rhythm generation since respiratory activity is abolished by blocking both I(NaP) and I(CAN), but is restored by enhancing network excitability.

Opioid-induced depression in the lamprey respiratory network

The role of opioid receptors in modulating respiratory activity was investigated in in vitro brainstem preparations of adult lampreys by bath application of agonists and antagonists. The vagal motor output was used to monitor respiratory activity. Neuronal recordings were also performed to characterize the rostrolateral trigeminal region that has been suggested to be critical for respiratory rhythmogenesis. Microinjections of the micro-opioid receptor agonist [d-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO) were also made into this region and at different locations within the brainstem. Bath application of DAMGO (0.5-2 microM) caused marked decreases in respiratory frequency up to complete apnea. Bath application of the delta-opioid receptor agonist [d-Pen(2,5)]-enkephalin (DPDPE) at 10-40 microM induced less pronounced depressant respiratory effects, while no changes in respiratory activity were induced by the kappa-opioid receptor agonist trans-(1S,2S)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeneacetamide (U50488) at 10-40 microM. Bath application of the opioid receptor antagonists naloxone and naltrindole did not affect baseline respiratory activity, but prevented agonist-induced effects. DAMGO microinjections (1 mM; 0.5-1 nl) at sites rostrolateral to the trigeminal motor nucleus, where respiration-related neuronal activity was recorded, abolished the respiratory rhythm. The results show that opioids may have an important role in the lamprey respiratory network and that micro-opioid receptor activation is the most effective in causing respiratory depression. They also indicate that endogenous opioids are not required for the generation of baseline respiratory activity. Apneic responses induced by DAMGO microinjections support the hypothesis that a specific opioid-sensitive region rostrolateral to the trigeminal motor nucleus, that we have termed the paratrigeminal respiratory group (pTRG), likely has a pivotal role in respiratory rhythmogenesis. Since the lamprey diverged from the main vertebrate line around 450 million years ago, our results also imply that the inhibitory role of opioids on respiration is present at an early stage of vertebrate evolution.

Central nervous mechanisms in the generation of the pattern of breathing

The role of the Bötzinger complex (BötC) and the pre-Bötzinger complex (pre-BötC) in the genesis of the breathing pattern was investigated in anesthetized, vagotomized, paralysed and artificially ventilated rabbits making use of bilateral microinjections of kainic acid (KA) and excitatory amino acid (EAA) receptor antagonists. KA microinjections into either the BötC or the pre-BötC transiently eliminated respiratory rhythmicity in the presence of tonic phrenic activity (tonic apnea). Rhythmic activity resumed as low-amplitude, high-frequency irregular oscillations, superimposed on tonic inspiratory activity and displayed a progressive, although incomplete recovery. Microinjections of kynurenic acid (KYN) and D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) into the BötC caused a pattern of breathing characterized by low-amplitude, high-frequency irregular oscillations and subsequently tonic apnea. Responses to KYN and D-AP5 in the pre-BötC were similar, although less pronounced than those elicited by these drugs in the BötC and never characterized by tonic apnea. Microinjections of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) into the BötC and the pre-BötC induced much less intense responses mainly consisting of increases in respiratory frequency. The results show that the investigated medullary regions play a prominent role in the genesis of the normal pattern of breathing through the endogenous activation of EAA receptors.

Fog-induced respiratory responses are attenuated by nedocromil sodium in humans

Fog inhalation induces cough and bronchoconstriction in patients with asthma, but only cough in normal subjects; whether it also influences the pattern of breathing is unclear. Nedocromil sodium (NCS) inhibits the cough response to inhalation of several pharmacological agents but its effects on fog-induced cough and changes in the pattern of breathing are unknown. We evaluated the effects of no drug, placebo, and 4- and 8-mg NCS administration on the cough threshold and changes in the pattern of breathing during fog inhalation in 14 healthy subjects. Measurements of tidal volume (VT), duration of inspiratory and expiratory times (TI and TE, respectively), total duration of the respiratory cycle (TT), mean inspiratory flow (VT/TI), duty cycle (TI/TT), respiratory frequency (f, 60/TT), and inspiratory minute ventilation (V I) were obtained by inductive plethysmography. Median cough threshold values were unaffected by placebo, but were increased (p < 0.01) by both NCS doses. In no-drug and placebo trials, inhalation of the threshold fog concentration caused increases in both VT/TI and V I (p always < 0.05) due to selective increases (p < 0.01) in VT. These changes were markedly attenuated by both NCS doses administration. Thus, fog induces coughing and increases in VT, VT/ TI, and V I in healthy subjects; NCS possesses antitussive effects and attenuates fog-induced changes in the pattern of breathing, possibly through inhibition of rapidly adapting "irritant" receptors.

Respiratory neuronal activity during apnea and poststimulatory effects of laryngeal origin in the cat

We investigated the behavior of medullary respiratory neurons in cats under pentobarbitone anesthesia, vagotomized, paralysed, and artificially ventilated to elucidate neural mechanisms underlying apnea and poststimulatory respiratory depression induced by superior laryngeal nerve (SLN) stimulation. Inspiratory neurons were completely inhibited during SLN stimulation and poststimulatory apnea. During recovery of inspiratory activity, augmenting inspiratory neurons were depressed, decrementing inspiratory neurons were excited, and late inspiratory neurons displayed unchanged bursts closely locked to the end of the inspiratory phase. Augmenting expiratory neurons were either silenced or displayed different levels of tonic activity during SLN stimulation; some of them were clearly activated. These expiratory neurons displayed activity during poststimulatory apnea, before the onset of the first recovery phrenic burst. Postinspiratory or decrementing expiratory neurons were activated during SLN stimulation; their discharge continued with a decreasing trend during poststimulatory apnea. The results support the three-phase theory of rhythm generation and the view that SLN stimulation provokes a postinspiratory apnea that could represent the inhibitory component of respiratory reflexes of laryngeal origin, such as swallowing. In addition, because a subpopulation of augmenting expiratory neurons displays activation during SLN stimulation, the hypothesis can be advanced that not only postinspiratory, or decrementing expiratory neurons, but also augmenting expiratory neurons may be involved in the genesis of apnea and poststimulatory phenomena. Finally, the increase in the activity of decrementing inspiratory neurons after the end of SLN stimulation may contribute to the generation of poststimulatory respiratory depression by providing an inhibitory input to bulbospinal augmenting inspiratory neurons.

Coughing in laryngectomized patients

Ablation of the larynx implies withdrawal of afferent information from receptors involved both in the control of expiratory flow and in the genesis of protective airway reflexes including coughing. To investigate the effects of laryngectomy on the sensory and motor component of coughing, maximal voluntary cough (MVC) efforts as well as the reflex cough (RC) responses at threshold (T) and suprathreshold (1.8 x T, ST) levels induced by inhalation of progressively increasing concentrations of ultrasonically nebulized distilled water (fog) were analyzed in 10 laryngectomized patients and 10 control subjects. Cough intensity was indexed in terms of both the peak amplitude of the integrated electromyographic activity of abdominal muscles (IEMGP) and the ratio of IEMGP to the duration of the expiratory ramp (TEC), i.e., the rate of rise of IEMG activity (IEMGP/TEC). Cough peak flow was also recorded. Cough threshold was similar in patients and controls, as were IEMGP, TEC, and IEMGP/ TEC recorded during MVC and RCST. In contrast, during RCT, patients' IEMGP was significantly reduced (p < 0.05), thus leading to a significant decrease in IEMGP/TEC (p < 0.05) even in the absence of significant differences in TEC. Cough flow closely correlated with IEMG-related variables. Cough volume acceleration, i. e., the ratio of cough peak flow to the corresponding time to cough peak flow was also significantly reduced in the patients, especially during RCT (p < 0.01). The results suggest that the lack of signals arising from the larynx may result in a reduction of cough volume acceleration as well as in the intensity of abdominal muscle contractions during RCT. These factors may contribute to facilitate the onset and/or the persistence of chest infections in laryngectomized patients.

Respiratory responses to thyrotropin-releasing hormone microinjected into the rabbit medulla oblongata

We investigated the respiratory role of thyrotropin-releasing hormone (TRH) input to medullary structures involved in the control of breathing in anesthetized, vagotomized, paralyzed, and artificially ventilated rabbits. Microinjections (10-20 nl) of 1 or 10 mM TRH were performed in different regions of the ventral respiratory group (VRG), namely the rostral expiratory portion or Bötzinger complex (Böt. c.), the inspiratory portion, the transition zone between these two neuronal pools, and the caudal expiratory component. TRH microinjections were also performed in the dorsal respiratory group (DRG) and the area postrema (AP). Injection sites were localized by using stereotaxic coordinates and extracellular recordings of neuronal activity; their locations were confirmed by subsequent histological control. TRH microinjections in the Böt. c. and the directly caudally located region where a mix of inspiratory and expiratory neurons were encountered elicited depressant respiratory responses. TRH microinjections were completely ineffective at sites within the inspiratory and the caudal expiratory components of the VRG. TRH microinjections in either the DRG or the AP induced excitatory effects on inspiratory activity. The results show for the first time that TRH may exert inhibitory influences on respiration at medullary levels by acting on rostral expiratory neurons and that not only the DRG, as previously suggested, but also the AP may mediate TRH-induced excitatory effects on respiration.

Repeatability of cough-related variables during fog challenges at threshold and suprathreshold stimulus intensity in humans

Cough-related variables such as cough frequency, time to onset (i.e. the time until the first cough occurs) and the cough index (i.e. the ratio between the cough frequency and the time to onset) may be important when interpreting results of cough challenges for therapeutic interventions or for comparative research purposes. Nevertheless, repeatability (or reproducibility) for these widely used variables has been poorly studied. In thirty normal subjects, coughing was induced by inhalation of threshold (T) and suprathreshold (1.6 x T) concentrations of ultrasonically nebulized distilled water (fog). Cough threshold was taken as the lowest fog concentration that evoked at least one cough effort during two challenges separated by a 30-min interval. During challenges performed at both threshold and suprathreshold stimulus intensity, cough frequency, time to onset, and the cough index were assessed; within-subject repeatability for these variables was subsequently evaluated. Median +/- interquartile range cough threshold value was 0.9+/-0.5 mL x min(-1). During the two challenges performed to assess cough threshold, the mean +/-SD values of cough frequency, time to onset, and cough index were similar (5.0+/-2.7 and 5.3+/-3.1 coughs x min(-1), 32.4+/-13.3 and 32.9+/-13.6 s, and 0.2+/-0.2 and 0.2+/-0.2, respectively). However, none of these cough-related variables proved to be sufficiently repeatable. During the two challenges performed at suprathreshold stimulus intensity, mean values of cough frequency, time to onset, and cough index were also similar (20.0+/-9.0 and 18.2+/-10.2 coughs x min(-1), 13.5+/-5.8 and 12.0+/-4.62 s, and 1.7+/-1.0 and 1.8+/-1.2); furthermore, all considered variable of suprathreshold challenge turned out to be reproducible. In conclusion, during fog challenges at threshold stimulus intensity, cough frequency, time to onset and cough index cannot reliably be used for evaluating cough responses. However, these cough-related variables may represent useful and reliable research tools in the evaluation of suprathreshold cough responses.

Respiratory responses to chemical stimulation of the parabrachial nuclear complex in the rabbit

The respiratory role of the parabrachial nuclear complex (PNC) was investigated in alpha-chloralose-urethane anesthetized, vagotomized, paralysed and artificially ventilated rabbits by means of unilateral microinjections (10-20 nl) of 20 mM dl-homocysteic acid. Chemical stimulation elicited three main types of site-specific respiratory effects: excitatory, apneustic and inhibitory responses. The results suggest that the PNC plays a complex role in the control of breathing.

Defective motor control of coughing in Parkinson's disease

The high incidence of serious chest infections in patients with Parkinson's disease is unexplained, but an impairment in cough reflex may have a role. Maximal voluntary cough (MVC) and reflex cough (RC) to inhalation of ultrasonically nebulized distilled water were analyzed in patients with Parkinson's disease and age-matched control subjects by monitoring the integrated electromyographic activity (IEMG) of abdominal muscles. The peak amplitude of IEMG activity (IEMGP) was expressed as a fraction of the highest IEMGP value observed during MVC corrected to account for possible losses in abdominal muscle force due to reduced central muscle activation. Cough intensity was indexed in terms of both the IEMGP and the ratio of IEMGP to the duration of the expiratory ramp (TEC), i.e., the rate of rise of IEMG activity. Cough threshold was slightly higher in patients than in control subjects, but the difference failed to reach statistical significance. Compared with control subjects, patients displayed a lower IEMGP during maximal expiratory pressure maneuvers (PEmax), MVC, and RC (p always < 0.01); TEC during RC was longer (p < 0.01) than in controls. Consequently, the rate of rise of IEMG activity during cough was always lower in patients (p < 0. 01), especially during RC. Finally, PEmax, and both the peak and rate of rise of IEMG activity during RC were inversely related to the level of clinical disability (Spearman rank correlation coefficient, rs = -0.88, -0.86, and -0.85, respectively, p always < 0.01). The results indicate that the central neural mechanisms subserving the recruitment of motor units and/or the increase in their frequency of discharge during voluntary and, even more markedly, RC are impaired in patients with Parkinson's disease.

Area postrema glutamate receptors mediate respiratory and gastric responses in the rabbit

The role of NMDA and non-NMDA receptors of the area postrema (AP) in the control of respiration and gastric motility was investigated in anaesthetized rabbits using microinjections (10-20 nl) of specific agonists or antagonists. NMDA (20 mM) or AMPA (10 mM) caused excitatory effects on respiration and gastric relaxation. Selective blockade of NMDA or non-NMDA receptors, respectively with D(-)-2-amino-5-phosphonopentanoic acid (D-AP5; 10 mM) and 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (NBQX; 5 mM), decreased respiratory frequency and increased gastric tone. Both these effects were more marked following non-NMDA receptor blockade and were prevented by vagotomy. These findings show that NMDA and non-NMDA receptors are present on AP neurones and have a role in the tonic control of respiration and gastric motility.

Discharge patterns of Bötzinger complex neurons during cough in the cat

This study was carried out on pentobarbital sodium-anesthetized, spontaneously breathing cats to address the hypothesis that Bötzinger complex (BötC) neurons are involved in the production of the cough motor pattern induced by mechanical stimulation of the tracheobronchial tree. Phrenic nerve and abdominal muscle activities as well as intratracheal pressure were monitored; single-unit extracellular recordings from BötC neurons (n = 87) were performed. The majority of augmenting expiratory (E-Aug) neurons encountered (n = 47) displayed excitatory responses during the expulsive phases of coughing in parallel with the main components of the abdominal bursts and the corresponding increases in tracheal pressure. We also encountered E-Aug neurons markedly depressed up to complete inhibition during coughing (n = 14) as well as E-Aug neurons assuming a decremental pattern without any increase or even with some reduction in their peak activity (n = 15). During the expiratory thrusts, most decrementing expiratory neurons (n = 7) presented excitatory responses, whereas others were depressed (n = 3) or completely inhibited (n = 1). The results are consistent with the view that these neurons are involved in the generation of the cough motor pattern and, in particular, that some BötC E-Aug neurons convey excitatory drive to caudal expiratory neurons and, hence, to expiratory motoneurons.

A noninvasive electromyographic study on threshold and intensity of cough in humans

The assessment of cough threshold and intensity is important in respiratory medicine. We have developed a method for objectively and noninvasively assessing cough threshold and intensity of expiratory muscle efforts in response to inhalation of ultrasonically nebulized distilled water (UNDW). Thirty (83%) out of 36 volunteers studied coughed in response to UNDW inhalation. Cough threshold was taken as the lowest nebulizer output (mL x min(-1)) that induced cough in two challenges performed at a 30 min interval. At threshold level, repeatability of peak and slope of the integrated electromyographic (IEMG) activity of abdominal muscles was evaluated. Short- and long-term repeatability of cough threshold were evaluated in 15 subjects following a 3 h and a 6-9 month interval, respectively. Dose-response relationships between nebulizer outputs and IEMG-related variables were also investigated, as were the correlations between the latter and expiratory flow during voluntary coughing. The median (1st and 3rd quartile) cough threshold value was 0.89 (0.40 and 1.54) mL x min(-1). At threshold level, peak and slope of IEMG activity were highly reproducible. Cough threshold displayed a high degree of short- and long-term repeatability. Peak and slope of IEMG activity displayed a clear trend to increase (p<0.01) following inhalation of progressively higher UNDW outputs. Maximum flow during voluntary coughs of varying intensity correlated with the peak (p<0.05) and, more closely, with the slope (p<0.01) of abdominal IEMG activity. The assessment of cough threshold as well as the evaluation of the intensity of cough efforts by abdominal integrated electromyographic recordings may represent useful and reliable tools for cough research in humans.

Depressant effects on inspiratory and expiratory activity produced by chemical activation of Bötzinger complex neurons in the rabbit

The respiratory role of the Bötzinger complex (Böt. c.) was investigated in alpha-chloralose-urethane or pentobarbitone anesthetized rabbits by means of microinjections of DL-homocysteic acid (DLH). The animals were either spontaneously breathing or vagotomized, paralysed and artificially ventilated. Both phrenic and abdominal activities were monitored; extracellular recordings from medullary respiration-related neurons were performed. Unilateral microinjections (5-30 nl) of DLH (160 mM) into the Böt. c., at sites where intense expiratory activity with an augmenting discharge pattern was encountered, provoked mild or moderate depressant effects on inspiratory activity characterized by decreases in frequency as well as in peak amplitude and rate of rise of phrenic nerve discharge. Stronger depressant effects up to complete apnea were consistently obtained in response to bilateral microinjections. Concomitant depressant effects on the activity of both expiratory motoneurons and expiration-related (ER) neurons of the caudal ventral respiratory group (cVRG) were observed. At variance with previous findings in the cat, the results indicate that chemical activation of Böt. c. augmenting ER neurons may exert inhibitory influences not only on inspiratory activity, but also on cVRG ER neurons and, hence, on expiratory motoneurons. The functional role of the Böt. c. in the control of respiration deserves further investigations; present findings suggest that the rabbit may profitably be used for such a purpose.

Effects of central chemical drive on poststimulatory respiratory depression of laryngeal origin in the adult cat

We investigated the influences of central CO2-related chemosensory drive on poststimulatory respiratory phenomena induced by superior laryngeal nerve (SLN) stimulation in pentobarbitone-anesthetized, vagotomized, carotid sinus-denervated, paralyzed, and artificially ventilated adult cats. Respiratory output was monitored as integrated phrenic nerve activity. Under eucapnic conditions, apnea-producing SLN stimulations of both short (10 s) and long (30 s) duration were followed by persistent apnea and depression in phrenic motor output; the latter showed a gradual recovery that followed an exponential time course. Hypocapnia increased the duration of poststimulatory apnea and the intensity of poststimulatory depression in phrenic minute output owing to changes in peak phrenic activity. Hypercapnia did not affect the duration of poststimulatory apnea, but markedly attenuated poststimulatory depression in respiratory activity, mainly due to changes in respiratory frequency. The rate of respiratory recovery was similar under eucapnic and hypocapnic conditions, but it was slower during hypercapnia. The results provide evidence that central chemosensitivity plays a prominent role in counteracting poststimulatory depressant effects on respiration induced by SLN stimulation.

[Highlights in the subject of low frequency-high intensity TENS (review)]

Transcutaneous electrical neural stimulation (l.f.-h.i. TENS), employed in dentistry, allows masticatory muscles relaxation, temporary clearance of muscular and periodontal proprioceptive input and even oro-facial pain relief. The mechanisms involved in this type of stimulation are not entirely clarified. According to the most recent neurophysiological researches, the authors describe several l.f.-h.i. TENS. action modalities. Some of them are well known such as the gate control theory, the endogenous antinociceptive system activation, the metabolic recovery of the muscular tissue and the unloading reflex. Other mechanisms, instead, are less known such as hypnosis and stress analgesia, exteroceptive suppression and counterirritation (DNIC). Some hypothetical mechanisms are also considered such as endogenous inhibition and sympathetic activity reduction.

Naloxone attenuates poststimulatory respiratory depression of laryngeal origin in the adult cat

Poststimulatory depression in respiratory activity induced by superior laryngeal nerve (SLN) stimulation was quantitatively investigated in 20 adult cats. The role played in this phenomenon by endogenous opioids was studied using the opiate antagonist naloxone. The effects of hypercapnia on the same phenomenon were also investigated for comparison. Experiments were performed on cats anesthetized with pentobarbitone or alpha-chloralose, vagotomized, paralyzed, and artificially ventilated with 100% O2. Some animals were also carotid sinus denervated. Respiratory output was monitored as integrated phrenic nerve activity. SLN stimulation produced apnea, which outlasted the stimulation period; when respiration resumed, it was markedly depressed as revealed mainly by a decrease in phrenic minute output, respiratory frequency, and rate of rise of inspiratory activity. Phrenic output recovered gradually to control levels following an exponential time course. These effects varied as a function of the duration of SLN stimulation. Naloxone administration (0.8 mg/kg iv) significantly reduced the duration of poststimulatory apnea and attenuated the depression of phrenic minute output of the first recovery breath as a result of changes in peak phrenic activity; it also accelerated the time course of recovery. Hypercapnia did not affect the duration of poststimulatory apnea, but attenuated the initial poststimulatory depression because of changes in respiratory frequency; the rate of recovery was reduced. The results provide characterization of poststimulatory respiratory depression of laryngeal origin in the adult cat and suggest a role of endogenous opioids in its genesis or modulation.

Prostaglandin synthesis blockade by ketoprofen attenuates respiratory and cardiovascular responses to static handgrip

We investigated the effects of prostaglandin synthesis blockade on the changes in breathing pattern, mean blood pressure (MBP), and heart rate (HR) elicited by 3 min of static handgrip at 30% of the maximum voluntary contraction in 12 healthy volunteers. Before each handgrip trial, subjects were treated with intravenous administration of either saline placebo (control) or 1 mg/kg of ketoprofen. Muscle tension and integrated electromyographic activity of exercising muscles remained fairly constant during each trial. In agreement with our earlier findings, during control handgrip minute ventilation progressively increased (P < 0.01) due to a rise in tidal volume and, to a lesser extent, in respiratory frequency. Mean inspiratory flow, MBP, and HR also increased (P < 0.01). End-tidal PCO2 decreased (P < 0.05) during the late phases of control handgrip bouts. Ketoprofen administration reduced serum thromboxane B2 levels (from 57.5 +/- 7.0 to 1.6 +/- 0.4 pg/ml; P < 0.01) and significantly attenuated mean increases in minute ventilation (40.25 +/- 0.60%), tidal volume (37.78 +/- 7.48%), respiratory frequency (55.94 +/- 17.92%), inspiratory flow (42.66 +/- 5.11%), MBP (22.33 +/- 6.82%), and HR (11.04 +/- 2.75%) during the 3rd min of handgrip. End-tidal PCO2 remained close to normocapnic levels. In agreement with previous animal investigations, the present results show that arachidonic acid metabolites are involved in the regulation of the cardiovascular responses to static efforts in humans, possibly through a stimulatory action on muscle receptors. Furthermore, they provide the first experimental evidence that products of the cyclooxygenase metabolic pathway play a role in the mediation of the respiratory adjustments elicited by this form of exercise.

Gastric relaxation in response to chemical stimulation of the area postrema in the rabbit

Microinjections of DL-homocysteic acid into the area postrema (AP) of anesthetized rabbits provoked gastric relaxations associated with small changes in blood pressure and marked excitatory effects on respiration. Both gastric and cardiovascular effects failed to occur after bilateral vagotomy. Comparable gastric relaxations were induced before and after treatment with atropine or atropine and guanethidine. The AP appears to play a role in gastric motility via vagus nerves and nonadrenergic noncholinergic intramural inhibitory neurons.

Chemical activation of caudal medullary expiratory neurones alters the pattern of breathing in the cat

1. The purpose of this work was to ascertain whether the activation of caudal expiratory neurones located in the caudal part of the ventral respiratory group (VRG) may affect the pattern of breathing via medullary axon collaterals. 2. We used microinjections of DL-homocysteic acid (DLH) to activate this population of neurones in pentobarbitone-anaesthetized, vagotomized, paralysed and artificially ventilated cats. Both phrenic and abdominal nerve activities were monitored; extracellular recordings from medullary and upper cervical cord respiratory neurones were performed. 3. DLH (160 mM) microinjected (10-30 nl for a total of 1.6-4.8 nmol) into the caudal VRG, into sites where expiratory activity was encountered, provoked an intense and sustained activation of the expiratory motor output associated with a corresponding period of silence in phrenic nerve activity. During the progressive decline of the activation of abdominal motoneurones, rhythmic inspiratory activity resumed, displaying a decrease in frequency and a marked reduction or the complete suppression of postinspiratory activity as its most consistent features. 4. Medullary and upper cervical cord inspiratory neurones exhibited inhibitory responses consistent with those observed in phrenic nerve activity, while expiratory neurones in the caudal VRG on the side contralateral to the injection showed excitation patterns similar to those of abdominal motoneurones. On the other hand, in correspondence to expiratory motor output activation, expiratory neurones of the Bötzinger complex displayed tonic discharges whose intensity was markedly lower than the peak level of control breaths. 5. Bilateral lignocaine blockades of neural transmission at C2-C3 affecting the expiratory and, to a varying extent, the inspiratory bulbospinal pathways as well as spinal cord transections at C2-C3 or C1-C2, did not suppress the inhibitory effect on inspiratory neurones of either the ipsi- or contralateral VRG in response to DLH microinjections into the caudal VRG. 6. The results show that neurones within the column of caudal VRG expiratory neurones promote inhibitory effects on phrenic nerve activity and resetting of the respiratory rhythm. We suggest that these effects are mediated by medullary bulbospinal expiratory neurones, which may, therefore, have a function in the control of breathing through medullary axon collaterals.

Respiratory and cardiovascular responses to static handgrip exercise in humans

We studied the time course of respiratory and cardiovascular responses by evaluating changes in the breathing pattern, mean blood pressure (MBP), and heart rate elicited by 3 min of static handgrip at 15, 25, and 30% of the maximum voluntary contraction (MVC) in 15 healthy volunteers. Muscle tension and integrated electromyographic activity remained fairly constant during each trial. During 15% MVC bouts, initially only mean inspiratory flow increased; then, tidal volume and minute ventilation (VI) also rose progressively. No significant changes in MBP and heart rate were observed. During 25 and 30% MVC bouts, not only did mean inspiratory flow, VT, and VI increase but MBP and heart rate increased as well. A slight and delayed rise in respiratory rate was also observed. Unlike 15 and 25% MVC handgrip, 30% MVC handgrip caused a small decrease in end-tidal PCO2. Changes in the pattern of breathing occurred more promptly than those in cardiovascular variables in the majority of subjects. Furthermore, we found a positive correlation between changes in VI and those in cardiovascular variables at the end of 25 and 30% MVC trials. This study indicates that respiratory and cardiovascular responses to static handgrip exercise are controlled independently.

Excitatory and depressant respiratory responses to chemical stimulation of the rostral ventrolateral medulla in the cat

The rostral ventrolateral medulla (rVLM) is known to play an important role in cardiorespiratory control. In the rVLM an 'apnoea region', in which unilateral focal blocks induce strong depressant effects on inspiratory activity up to complete apnoea, has been described. This study was designed to systematically investigate the effects provoked by unilateral micro-injections (10-30 nl) of D,L-homocysteic acid 160 mM into this region on respiratory activity and arterial blood pressure in pentobarbitone anaesthetized, vagotomized, paralyzed and artificially ventilated cats. Micro-injections into the rostral portion of this area caused depressant respiratory responses up to complete apnoea, while micro-injections into more caudally located sites induced excitatory respiratory responses. Similar effects were observed in the activity of phrenic nerves and inspiration-related medullary neurons of both the dorsal and ventral respiratory group. The respiratory responses could be accompanied by marked increases in blood pressure (> or = 30 mmHg), especially at locations ventral to the retrofacial and facial nucleus; however, they could also occur in the absence of appreciable changes or even in association with slight decreases in blood pressure. Similar respiratory and pressor effects were observed in carotid sinus denervated cats. The results indicate that two distinct rVLM neuronal populations, one located more rostrally and the other more caudally, may have an important role in the genesis and/or maintenance of respiratory rhythm by exerting respectively inhibitory and excitatory influences on inspiratory activity. Furthermore, they support the hypothesis that different neural substrates of the rVLM are involved in the regulation of respiratory and cardiovascular functions.

Respiratory responses to electrical and chemical stimulation of the area postrema in the rabbit

1. The respiratory role of the area postrema (AP) has been investigated in pentobarbitone- or alpha-chloralose-anaesthetized, vagotomized, paralysed and artificially ventilated rabbits, by means of electrical stimulation and microinjections of DL-homocysteic acid (DLH). Phrenic nerve activity was used as an index of central respiratory drive. 2. Bipolar electrical or chemical stimulation (microinjections of DLH, 5-30 nl; 160 mM) of the caudal compact portion of the AP provoked excitatory effects on the inspiratory motor output, without apparent changes in the arterial blood pressure. 3. Depressant effects on inspiratory activity, accompanied on some occasions by changes in arterial blood pressure (as a rule, increases > or = 30 mmHg) were induced by DLH microinjections in close neighbouring areas (including the medial part of the nucleus tractus solitarii) or in the IV ventricle. 4. These results support a role for the AP in the neural control of respiration. The findings are discussed in connection with other autonomic functions to which the AP has been reported to contribute, in different animal species.

Alterations of ballistic movements in epileptic patients with phenytoin intoxication

We assessed the effects of phenytoin (PHT) overdosage on ballistic arm abduction movements in nine epileptic patients receiving long-term PHT treatment. During the overdosage period, all but one showed clinical abnormalities referable to impaired cerebellar function; one also had slowness of movement. Ballistic movements showed abnormalities in all of the patients although a great variability was present in the type and severity of abnormalities. In four patients, kinematic and EMG recordings differed least from the normal, in four they resembled those described in patients with cerebellar deficits, and in one those described in patients with Parkinson disease. The type and severity of clinical disturbances of voluntary motor control as well as alterations of ballistic movements were not related to specific PHT plasma concentrations. One month after the adjustment of PHT dosage, the patients who had clinical abnormalities completely recovered or markedly improved. Previously observed kinematic and EMG abnormalities completely disappeared or improved markedly.

Changes in respiratory activity induced by mastication in humans

We studied the influence of mastication on respiratory activity in nine healthy volunteers who were requested to masticate a 5-g chewing gum bolus at a spontaneous rate (SR) for 5 min and "at the maximum possible rate" (MPR) for 1 min. Significant increases in respiratory frequency were induced by SR mastication due to a decrease in both the inspiratory and expiratory time. Tidal volume displayed slight nonsignificant decreases, but minute ventilation and mean inspiratory flow significantly increased. The duty cycle (TI/TT) did not change significantly. Total airway resistance significantly increased. Both peak and rate of rise of the integrated electromyographic activity of inspiratory muscles presented marked increases, accompanied by the appearance of a low level of tonic muscular activity. Similar but more intense effects on respiratory activity were induced by MPR mastication; in addition, a significant decrease in tidal volume and a significant increase in TI/TT were observed. Rhythmic handgrip exercise performed at metabolic rates comparable to those attained during SR or MPR mastication induced similar changes in the drive and time components of the breathing pattern, although accompanied respectively by nonsignificant or significant increases in tidal volume. Furthermore, the frequency of SR mastication significantly entrained the respiratory rhythm. The results suggest that mastication-induced hyperpnea does not merely represent a ventilatory response to exercise but also reflects complex interactions between respiratory and nonrespiratory functions of the upper airway and chest wall muscles.

Respiratory responses induced by the activation of somatic nociceptive afferents in humans

To further investigate the role of somatic nociceptive afferents in the neural control of breathing, we studied the respiratory effects of their activation by means of either electrical stimulation or ischemic pain in 14 healthy volunteers. Painful electrical cutaneous stimulation increased respiratory frequency (f), mean inspiratory flow (VT/TI), and rate of rise (XP/TI) of integrated electromyographic activity of diaphragm (IEMGdi). Painful muscular electrical stimulation caused similar but larger changes accompanied by increases in tidal volume (VT), peak XP of IEMGdi, and ventilation (VE); it also entrained respiratory rhythm. Ischemic pain, which was characterized by a progressively increasing intensity, caused augmentation in respiratory activity that displayed an increasing trend: VE, f, VT, XP, VT/TI, and XP/TI increased. In the light of available literature, it seems conceivable to suggest that respiratory responses to painful electrical stimulation are mediated through the activation of cutaneous (A delta) and muscular (group III) fine-myelinated afferents, and responses to ischemic pain are mediated by the activation of both fine myelinated (group III) and unmyelinated (group IV) muscular afferents. The input conveyed by these afferents may constitute an effective stimulus to respiration in humans.

Reciprocal connections between rostral ventrolateral medulla and inspiration-related medullary areas in the cat

We investigated connections between the rostral ventrolateral medulla (rVLM) and the two main inspiration-related medullary areas, i.e., the dorsal respiratory group (DRG) and the rostral ventral respiratory group (rVRG) in the cat. Non respiration-related tonically firing units encountered in the rVLM displayed either antidromic or orthodromic responses to DRG or rVRG microstimulation. Some units responded to the stimulation of both regions. We suggest that at least part of rVLM neurons are components of medullary loops operating in the control of breathing.

Enhanced in vivo release of substance P in the nucleus tractus solitarii during hypoxia in the rabbit: role of peripheral input

In the adult, pentobarbitone-anaesthetized rabbit, the in vivo release of substance P-like immunoreactivity was measured in the nucleus tractus solitarii using microdialysis and radioimmunoassay. Increased 160 +/- 16%) extracellular concentrations of substance P-like immunoreactivity were observed during hypoxic provocations of 9% O2 in N2 which also resulted in an increase in phrenic nerve activity. In bilateral carotid sinus nerve-denervated animals no enhanced release of substance P was seen in response to hypoxic challenges (105 +/- 6%) and the phrenic nerve activity was not significantly affected. Perfusion of the nucleus tractus solitarii region with the dopamine agonist, apomorphine (10(-5) M) resulted in a significant decrease in the extracellular level of substance P. These results provide further evidence that substance P is involved in the mediation of the hypoxic drive inputs from the peripheral chemoreceptors. The interactions of apomorphine with substance P release might also suggest a presynaptic modulation of substance Pergic neurons by dopamine in the nucleus tractus solitarii.

Expiration-related neurons in the caudal ventral respiratory group of the cat: influences of the activation of Bötzinger complex neurons

The functional role of Bötzinger complex (Böt. c.) projections to the expiration-related (ER) area of the caudal ventral respiratory group (cVRG) was investigated in anesthetized, vagotomized, paralyzed and artificially ventilated cats. ER neurons in both the ipsi- and the contralateral cVRG displayed excitatory responses to Böt. c. electrical microstimulation. They were also activated by microinjections of D,L-homocysteic acid into the Böt. c. region. We propose that at least part of the Böt. c. projections to the cVRG have an excitatory function.

Somatostatin in the control of respiration

Somatostatin has been found to induce apnoea when applied into the brain ventricular system (Fuxe et al. 1982, Härfstrand et al. 1985). The site of action of somatostatin was suggested to be in the dorsal respiratory neurons in the medulla oblongata of the rat (Fuxe et al. 1982) where high somatostatin-like immunoreactivity has been detected (Kalia et al. 1984a). In the present study we wanted to further localize the site(s) of action of somatostatin on respiration by microinjection of somatostatin into the medulla oblongata of the cats. We could not detect any inhibitory effect of somatostatin on respiration after microinjection into the nuclear complex of the solitary tract. On the other hand microinjection of somatostatin into the region of nucleus paragigantocellularis lateralis consistently caused apnoea. This finding further supports the idea that this structure functions as an integrative area of respiratory drive inputs.

Effects of expected perturbations on the velocity control of fast arm abduction movements

A triphasic electromyographic pattern of sequential activation of agonist, antagonist, and again agonist muscles underlies rapid or ballistic limb movements in humans. The first agonist burst reflects muscular force accelerating the limb, the antagonist burst is mainly related to the braking process of movement, while the second agonist burst is considered a reactive adjustment to the deceleration. The duration of the first agonist burst has been reported to be constant for movements of different amplitudes, thus suggesting that only changes in its amplitude contribute to the velocity control of movement. The present research has been undertaken to investigate the strategy whereby the nervous system increases agonist impulsive force for ballistic performance in response to experimental conditions requiring perceptual and/or provisional processes related to expected changes in load or accuracy constraints. The effects of expected perturbations of different strengths on some kinematic and electromyographic variables of fast arm abduction movements performed in a step-tracking task and in an outer-stop terminated task were analyzed in normal subjects. All motor performances were characterized by triphasic electromyographic patterns. In the absence of expected perturbations, the mean velocity of the movements was markedly higher in the outer-stop terminated task. Correspondingly, greater amplitudes and durations of the first agonist burst were observed. In both types of motor tasks, when expected perturbations were inserted, the velocity of the movement increased as well as the amplitude and the duration of the first agonist burst. These results, in agreement with previous observations, indicate that the normal mechanism, whereby the nervous system increases agonist impulsive force in rapid movements, comprises changes not only in the amplitude but also in the duration of the first agonist burst.

Influences of superior laryngeal afferent stimulation on expiratory activity in cats

The effects of superior laryngeal nerve (SLN) stimulation on the activity of the expiratory muscles and medullary expiration-related (ER) neurons were investigated in 24 pentobarbital-anesthetized cats. In some experiments the animals were also paralyzed and artificially ventilated. Sustained tetanic stimulation of SLN consistently caused an apneic response associated with the appearance of tonic CO2-dependent activity in the expiratory muscles and in ER neurons located in the caudal ventral respiratory group (VRG) and the Bötzinger complex. Single shocks or brief tetani at the same stimulation intensities failed to evoke excitatory responses in the expiratory muscles and in the vast majority of ER neurons tested. At higher stimulation strengths, single shocks or short tetani elicited excitatory responses in the expiratory muscles (20- to 35-ms latency) and in the majority of ER neurons of the caudal VRG (7.5- to 15.5-ms latency). These responses were obtained only during the expiratory phase and proved to be CO2 independent. On the contrary, only inhibitory responses were evoked in the activity of Bötzinger complex neurons. The observed tonic expiratory activity most likely represents a disinhibition phenomenon due to the suppression of inspiratory activity; activation of expiratory muscles at higher stimulation intensities appears to be a polysynaptic reflex mediated by ER neurons of the caudal VRG but not by Bötzinger complex neurons.

Flunarizine-induced parkinsonism in the elderly

Twenty-seven patients (19 women and 8 men, ages 63 to 88 years; mean, 74 years) displayed mild to moderate parkinsonism and altered ballistic motor performances during long-term flunarizine treatment. One month after, flunarizine withdrawal, 20 patients showed clear-cut improvements in both clinical features and ballistic motor performances; a complete recovery within 6 months was observed in all these patients but one, who still showed very mild slowness of movement. On the other hand, seven patients showed little clinical improvement and still maintained markedly altered ballistic motor performances 1 month after drug withdrawal. At the 2-month follow-up assessments, either they did not improve further or they deteriorated; they were successfully treated with L-dopa and, despite the ameliorations, after 12 to 24 months they still have definite parkinsonian syndrome. The authors conclude that (1) flunarizine, even at the recommended dose (10 mg daily), can induce reversible parkinsonism, at least in subjects older than 60; (2) the persistence of a marked symptomatology 2 months after flunarizine withdrawal should lead to starting treatment with antiparkinsonism drugs; (3) the study of ballistic movements is proposed as a useful tool for objective quantification and early detection of bradykinesia.

Increase in muscular pain threshold following low frequency-high intensity peripheral conditioning stimulation in humans

The effects of low frequency-high intensity transcutaneous and intramuscular electrical nerve stimulation (TENS and IENS, respectively) on ipsilateral muscular pain threshold were studied in healthy volunteers. The combined effects of TENS (or IENS) and vibration as well as the effects of TENS applied to contralateral regions were also investigated. Muscular pain threshold was evaluated by the subjects' verbal reports in response to electrical stimulation (wire electrodes) of the vastus medialis muscle and by the appearance of blink response (startle reaction) without habituation. TENS was generally applied to the skin overlying the same muscle, and in some instances to the skin overlying the contralateral vastus medialis or triceps muscle. IENS was performed through the same electrodes used for inducing muscular pain. Vibration was applied to the tendon of ipsilateral quadriceps femoris muscle. TENS consistently induced marked and long-lasting elevations of ipsilateral muscular pain threshold. Comparable results were obtained by IENS. TENS and vibration performed simultaneously induced increases in muscular pain threshold, which were greater than those obtained with each individual conditioning stimulation. TENS proved to be capable of enhancing muscular pain threshold even when applied to contralateral regions; however, these effects were smaller and of shorter duration. The results provide evidence that low frequency-high intensity TENS (or IENS) are effective in raising muscular pain threshold and support the hypothesis that this type of stimulation brings supraspinal control systems into action through the activation of group III afferent fibres.

Effects of electrical and chemical stimulation of the Bötzinger complex on respiratory activity in the cat

The effects of electrical and chemical stimulation of the expiratory neuronal population in the region of the retrofacial nucleus, the so called 'Bötzinger complex' (Böt. c.), on respiratory activity were investigated in vagotomized cats under pentobarbitone anaesthesia. Some of the experiments were performed on paralyzed or bilaterally thoracotomized, artificially ventilated animals. Sustained tetanic electrical stimulation (20 to 100-Hz, 0.5-ms current pulses at intensities of 5-60 microA) induced strong depressant effects on the inspiratory motor output which could lead to complete apnoea. The apnoeic response was accompanied by tonic activation of expiratory muscles; the appearance and the strength of tonic expiratory activity were dependent upon the frequency of stimulation. Brief tetani (40 to 100 ms trains of 0.5-ms rectangular pulses at 100-300 Hz) timed either during the inspiratory or the expiratory phase caused depression of inspiratory activity and prolongation of expiratory time, respectively. These effects increased gradually as the onset of stimulation was progressively delayed during each respiratory phase. The effects of sustained tetanic stimulation were mimicked by microinjections (25-100 nl) of 0.5 M L-glutamate or 0.16 M DL-homocysteic acid in the same region, thus indicating that they were the result of the stimulation of cell bodies and not of axons of passage. The present results support the hypothesis that Böt. c. neurons play an important role in the control of the breathing pattern by exerting inhibitory influences on inspiratory activity and, possibly, by contributing to the off-switch mechanisms. Furthermore, they suggest that these neurons are involved in the central control of expiratory activity.

Effects of heterotopic ischemic pain on muscular pain threshold and blink reflex in humans

Ischemic pain was induced in the left arm of 6 healthy volunteers using a modification of the submaximal effort tourniquet test. Its effects on both muscular pain threshold (determined in the vastus medialis muscle by means of electrical stimulation) and on the 2nd component of the blink reflex (R2) were investigated in the contralateral body side. Muscular pain threshold increased (peak value during ischemic pain) and maintained significantly higher values for 60 min. R2 response decreased while its latency increased; these variations appeared during ischemic pain and reached a maximum soon after the end of ischemia, still remaining significant for 15 min. The results support the suggestion that the analgesic effects of heterotopic noxious stimulation in humans are subserved by supraspinal inhibitory mechanisms.

In vivo release of substance P in the nucleus tractus solitarii increases during hypoxia

In vivo release of substance P (SP) was measured by microdialysis in the nucleus tractus solitarii (nTS) in adult cats. Small perfused semipermeable tubules (microdialysis probes) were implanted stereotaxically in the nTS, at the position of respiration-related neurons and perfused with artificial CSF. SP was determined by radioimmunoassay of the perfusate. Increased extracellular concentrations of SP-like immunoreactivity (SP-LI) were measured during hypoxia induced in artificially ventilated cats. In addition, a prolonged increase in the extracellular SP-LI concentration was encountered after cervical vagotomy. The results corroborate the suggestion that SP is a mediator of the central response to hypoxia.

Respiration-related neurons in the medial nuclear complex of the solitary tract of the cat

Respiration-related (RR) neuronal activity was systematically searched for in the nuclear complex of the solitary tract (nTS) with special interest focused on regions located medially to the ventrolateral subnucleus (vlnTS) which is widely considered to be the anatomical location of the dorsal respiratory group (DRG). The experiments were carried out on cats under pentobarbitone anaesthesia, paralyzed and artificially ventilated. RR activity was recorded consistently not only in the vlnTS, but also in more medial regions. R alpha-type neurons were often encountered in ventral and medial aspects of the nTS. R beta-type neurons and expiration-related neurons were found also in ventral regions of the nTS. A small number of 'late onset' and 'early burst' inspiration-related neurons was found respectively in ventral and ventromedial regions of the nTS. The activity of neurons presenting a rhythmic pattern completely determined by lung volume changes due to the respirator was consistently recorded both in ventral and medial areas of the nTS. Most of these neurons were excited by lung inflation and displayed a discharge pattern characteristic of P-neurons. A few neurons, designated as 'inverse' P-neurons displayed an opposite behaviour, being inhibited by lung inflation. The results are consistent with both histological and neurophysiological studies showing that pulmonary stretch receptor afferents terminate also on the medial side of the solitary tract. It is suggested that the DRG is not restricted to the vlnTS, but comprises also neurons located in more medial regions of the nTS.

Expiration-related neurons in the region of the retrofacial nucleus: vagal and laryngeal inhibitory influences

The influences of vagal and laryngeal afferent inputs on expiration-related neurons of Bötzinger complex were studied in anesthetized, paralyzed and artificially ventilated cats. Unilateral electrical stimulation (single shocks or short trains of stimuli at 200 Hz) applied to the cervical vagus nerve or to the superior laryngeal nerve induced inhibitory effects on the activity of these neurons. During apnoea due to hyperventilatory hypocapnia, expiration-related units displayed a low level of tonic activity which was rhythmically inhibited by pump-induced lung inflations. The functional significance of these findings is briefly discussed.

Electromyographic observations in patients with foot pain syndromes

Abductor hallucis muscle EMGs were performed in control subjects and in patients with chronic foot pain (9 affected by the disease of the metatarsophalangeal joint of the big toe, 6 affected by chronic foot strain) to investigate pathophysiological mechanisms of muscle pain syndromes. Unlike control subjects, patients showed an abnormal involuntary activity when standing. All patients presented a decrease of abnormal EMG activity when postural changes were induced either by variations in body weight distribution on the feet, or by changes of position in the weight-bearing foot achieved by arch supports or by boards of variable thickness applied under the forefeet or the heels. Anaesthesia of the metatarsophalangeal joint of the hallux (injection into the joint cavity of 2-3 ml 0.50% bupivacaine) reduced the abnormal EMG activity only in patients with hallux valgus, whereas it did not affect muscular activity in the other patients. Present results support the idea of the role of abnormal muscular activity in causing and maintaining chronic pain and suggest that alterations of postural mechanisms and of afferent input, in particular that arising from joint receptors, are involved in the genesis of this abnormal muscular activity.

Auditory and somatosensory evoked potentials (AEPs and SEPs) and ballistic movements in Parkinson disease

In five patients with initial idiopathic Parkinson disease AEPs (early and late components of auditory evoked potentials), SEPs (somatosensory evoked potentials) and arm ballistic movements (abduction of the humerus) were studied. Experimental sessions were conducted before starting treatment (L-Dopa plus Carbidopa) and at two and six month intervals. Before treatment evoked potential abnormalities were found in four out of five patients; EMG patterns underlying ballistic arm abduction movements were altered in all patients; corresponding prolonged duration of initial movements and low mean velocities were found. After treatment AEP and SEP showed a reduction of previously observed abnormalities and both EMG patterns and kinematic variables consistently improved. It is suggested that the electrophysiological investigations employed in this preliminary study may be a useful tool in clinical and pharmacological researches on Parkinson disease.

Effects of graded focal cold block in rostral areas of the medulla

Unilateral focal cold blocks (20 degrees C) in structures located ventrolaterally in rostral medulla consistently caused apnoea or deep depression of inspiratory motor output. The inhibitory effect could be correlated with the cooling temperature. Apnoeic response occurred either with complete absence of any inspiratory activity or combined with low level tonic inspiratory motor activity ('tonic apnoea'). The appearance of apnoea was CO2-independent, whereas the tonic component of the latter increased with increasing levels of PCO2. The results suggest that the structures in the deep, ventro-lateral aspect of rostral medulla, from which apnoea can be induced, correspond partly to the nucleus paragigantocellularis lateralis (nPGL) and the nucleus preolivaris. These structures appear to be relevant for the drive inputs necessary for respiratory rhythmogenesis. Unilateral focal cooling in the rostral medulla, including the 'Bötzinger Complex', caused increments in respiratory rate both in vagotomized and non-vagotomized animals. The increase in respiratory rate in response to cooling in the region of the 'Bötzinger Complex' was combined with either an enhancement or some depression of respiratory motor output. This area in the rostral part of the ventral respiratory group (VRG) seems not to be crucial for respiratory rhythmogenesis, but to play a role in determining both the intensity and timing of the respiratory activity. All effects of unilateral cold block were bilaterally symmetrical.

Effects of graded focal cold block in the solitary and para-ambigual regions of the medulla in the cat

Unilateral focal cold blocks in the region of the nucleus tractus solitarius and the dorsal respiratory group of neurons, DRG, of anaesthetized cats consistently caused apneustic-type breathing. There was no concomitant change in the initial rate of rise of inspiratory activity. The apneustic prolongation of inspiratory duration, TI, was most pronounced in, but was not confined to, the DRG. The apneustic effects were more marked after vagotomy. In cats with intact vagus nerves being given artificial ventilation, focal cooling at certain sites of the DRG region could produce 'unlocking' of the respiratory rhythm from that of the respiratory pump. At other sites in this region, focal cooling could selectively block the effects of the inspiration-facilitating reflex induced by deflation without blocking the inspiration-inhibiting Hering-Breuer reflex. Unilateral focal cold blocks in the region of the intermediate part of the ventral respiratory group of neurons, VRG, generally caused depression of the rate of rise of inspiratory activity, but almost never apneustic effects. All effects of unilateral focal cooling both in the DRG and VRG were bilaterally symmetrical. No systematic differences between the effects on phrenic and external intercostal inspiratory activity were found in response to focal cooling either of the DRG or VRG suggesting that differential control of phrenic and external intercostal motoneurons is not exerted mainly at the level of these medullary structures. The results suggest that the DRG and VRG areas exert somewhat different effects on the respiratory pattern: DRG appears to be more concerned with integration of vagal and other inputs contributing to the inspiratory off-switch mechanisms which, however, are not confined only to the DRG. The VRG inspiratory mechanisms, on the other hand, appear to be more involved in the gain control of the inspiratory output intensity.

Release of expiratory muscle activity by graded focal cold block in the medulla

Disinhibition or 'release' of expiratory muscle activity in response to focal cooling of various medullary structures was of two kinds: (1) release of rhythmic expiratory activity even when no such activity was recruited in the control situation and (2) release of tonic activity in the 'expiratory' muscles. Release of rhythmic expiratory activity was mainly elicited by focal cooling of structures in the intermediate part of the medulla and release of tonic activity was preferentially induced by cooling rostroventral structures, although a considerable overlap did occur. Release of rhythmic expiratory activity was not related to any changes in expiratory time (TE) or to any associated variations in the pattern of inspiratory activity. It showed a marked increase with increasing levels of PCO2. The release of tonic activity was not CO2-dependent. Both types of effects could be mimicked by focal microinjections of lignocaine and were reflected by corresponding changes in activity of a majority of the expiration-related neurons. These results suggest that complex and widespread neural substrates subserve the control of the intensity of rhythmic expiratory activity and of the tonic activity of the abdominal and intercostal muscles. These neural mechanisms can apparently operate independently from those controlling the inspiratory activity. The release of the tonic activity observed in the 'expiratory' muscles might reflect a disinhibition of mechanisms involved in non-respiratory functions of expiratory muscles.