Psychometric properties and observational data for COVID-19 Yorkshire Rehabilitation Scale (C19-YRSm) for post-COVID-19 syndrome.

BACKGROUND: The recently developed modified COVID-19 (coronavirus of 2019) Yorkshire Rehabilitation Scale (C19-YRSm) captures comprehensive biopsychosocial components of WHO's International Classification of Functioning, Disability, and Health related to the Long Covid or post-COVID syndrome. The scale response categories on C19-YRSm were done post hoc on data collected from the original version of C19-YRS. AIM: To evaluate the C19-YRSm scale using reliability and validity measures. DESIGN: Prospective, observational study. METHODS: The study includes 369 patients (clinical group) and 426 subjects of the general population (control group) and captures their post-COVID-19 symptoms. In addition, the reliability of C19-YRSm was estimated by Cronbach's alpha coefficients of internal consistency and inter-item correlations for subscales ('Symptom severity, Functional disability, and Other symptoms'). Convergent validity was established using correlations between C19-YRSm and Fatigue Severity Scale (FSS). The incremental validity of C19-YRSm was measured by introducing a hierarchical regression model using the C19-YRSm 'Overall health' subscale and FSS as criterion variables. RESULTS: C19-YRSm subscales have excellent internal consistencies (Cronbach's α value 0.81-0.96) and acceptable inter-item correlations (r value 0.23-0.79). Hereafter, the convergent validity of the C19-YRSm is good due to significant correlations between C19-YRSm subscales and FSS and C19-YRSm subscales. Finally, the hierarchical regression analysis supported consistent evidence for the incremental validity of the C19-YRSm subscales. CONCLUSION: C19-YRSm is a reliable and valid self-assessment scale for the assessment of post-COVID-19 syndrome.

Blockade of alpha2-adrenergic receptors in the caudal raphe region enhances the renal sympathetic nerve activity response to acute intermittent hypercapnia in rats.

The study investigated the role of alpha2-adrenergic receptors of the caudal raphe region in the sympathetic and cardiovascular responses to the acute intermittent hypercapnia (AIHc). Urethane-anesthetized, vagotomized, mechanically ventilated Sprague-Dawley rats (n=38) were exposed to the AIHc protocol (5×3 min, 15 % CO2+50 % O2) in hyperoxic background (50 % O2). alpha2-adrenergic receptor antagonist-yohimbine was applied intravenously (1 mg/kg, n=9) or microinjected into the caudal raphe region (2 mM, n=12) prior to exposure to AIHc. Control groups of animals received saline intravenously (n=7) or into the caudal raphe region (n=10) prior to exposure to AIHc. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were monitored before exposure to the AIHc protocol (T0), during five hypercapnic episodes (THc1-5) and at 15 min following the end of the last hypercapnic episode (T15). Following intravenous administration of yohimbine, RSNA was significantly greater during THc1-5 and at T15 than in the control group (P<0.05). When yohimbine was microinjected into the caudal raphe region, AIHc elicited greater increases in RSNA during THc1-5 when compared to the controls (THc1: 138.0+/-4.0 % vs. 123.7+/-4.8 %, P=0.032; THc2: 137.1+/-5.0 % vs. 124.1+/-4.5 %, P=0.071; THc3: 143.1+/-6.4 % vs. 122.0±4.8 %, P=0.020; THc4: 146.1+/-6.2 % vs. 120.7+/-5.7 %, P=0.007 and THc5: 143.2+/-7.7 % vs. 119.2+/-7.2 %, P=0.038). During THc1-5, significant decreases in HR from T0 were observed in all groups, while changes in MAP were observed in the group that received yohimbine intravenously. These findings suggest that blockade of the alpha2-adrenegic receptors in the caudal raphe region might have an important role in sympathetic responses to AIHc.

Hyperoxia blunts renal sympathetic nerve activity response to acute intermittent hypercapnia in rats.

Activation of the sympathetic nervous system plays an important role in the pathophysiology of sleep-related breathing disorders. The aim of the present study was to examine the effects of different levels of hypercapnia in the presence of various background oxygen levels on the magnitude of sympathoexcitation, measured by the renal sympathetic nerve activity (RSNA) in the acute intermittent hypercapnia (AIHc) rat model. The study was conducted on 56 urethane-anesthetized, vagotomized and mechanically ventilated Sprague-Dawley rats (n = 7/group). Each experimental group was subjected to a distinct AIHc protocol that varied in the applied levels of hypercapnia and background oxygen. Mean arterial pressure and RSNA were analyzed in 7 experimental time points: baseline, five hypercapnic episodes (each lasting 3 min) and 15 minutes following the last hypercapnic episode. Exposure to severe hypercapnia (FiCO2 = 0.15) evoked an increase in RSNA, which was preserved throughout the protocol, whereas in moderate hypercapnia (FiCO2 = 0.05) groups there was a trend of progressive diminution of RSNA magnitude following the first hypercapnic episode. Exposure to severe hypercapnia elicited significantly greater RSNA response during first hypercapnic episode and it was enhanced during subsequent episodes compared to exposure to moderate hypercapnia. Additionally, hyperoxic2 background (50% O2) blunted the RSNA response to AIHc compared to room air background, both in severe and moderate hypercapnia groups. Mean arterial blood pressure was preserved throughout the experimental protocol in all studied groups. These findings indicate that acute intermittent hypercapnia evokes increased renal sympathetic nerve activity that is dependent on the severity of hypercapnic exposures and the background oxygen level.

Periodicity during hypercapnic and hypoxic stimulus is crucial in distinct aspects of phrenic nerve plasticity.

This study was undertaken to determine pattern sensitivity of phrenic nerve plasticity in respect to different respiratory challenges. We compared long-term effects of intermittent and continuous hypercapnic and hypoxic stimuli, and combined intermittent hypercapnia and hypoxia on phrenic nerve plasticity. Adult, male, urethane-anesthetized, vagotomized, paralyzed, mechanically ventilated Sprague-Dawley rats were exposed to: acute intermittent hypercapnia (AIHc or AIHc(O2)), acute intermittent hypoxia (AIH), combined intermittent hypercapnia and hypoxia (AIHcH), continuous hypercapnia (CHc), or continuous hypoxia (CH). Peak phrenic nerve activity (pPNA) and burst frequency were analyzed during baseline (T0), hypercapnia or hypoxia exposures, at 15, 30, and 60 min (T60) after the end of the stimulus. Exposure to acute intermittent hypercapnia elicited decrease of phrenic nerve frequency from 44.25+/-4.06 at T0 to 35.29+/-5.21 at T60, (P=0.038, AIHc) and from 45.5+/-2.62 to 37.17+/-3.68 breaths/min (P=0.049, AIHc(O2)), i.e. frequency phrenic long term depression was induced. Exposure to AIH elicited increase of pPNA at T60 by 141.0+/-28.2 % compared to baseline (P=0.015), i.e. phrenic long-term facilitation was induced. Exposure to AIHcH, CHc, or CH protocols failed to induce long-term plasticity of the phrenic nerve. Thus, we conclude that intermittency of the hypercapnic or hypoxic stimuli is needed to evoke phrenic nerve plasticity.

The relationship between sleep habits and academic performance in dental students in Croatia.

INTRODUCTION: It is well accepted that sleep and lifestyle habits affect academic success in students. However, sleep patterns and sleep problems amongst dental students have been insufficiently addressed in the literature. The purpose of this study was to evaluate sleep habits of dental students and the relationship between sleep habits and academic performance. MATERIALS AND METHODS: A self-administered questionnaire on sleep habits, academic performance and lifestyle was administered. The participants were 447 dental students from Split University Dental Medicine School and Zagreb University Dental Medicine School from the six academic years. The subjects were classified into two groups based on academic success (high-performing vs. low-performing students) for comparison of sleep and lifestyle habits. RESULTS: Amongst the whole group of students, average bedtime and wake time during weekday was significantly earlier compared with weekend. Main findings indicate that students with high academic performance had earlier bedtimes during weekdays and weekends, earlier wake times during weekends and shorter sleep latency compared with low academic performing students. CONCLUSION: Self-reported academic performance of dental students in Croatia is associated with timing of sleep and wakefulness, rather than with total sleep time duration.

Remifentanil reversibly abolished phrenic long term facilitation in rats subjected to acute intermittent hypoxia.

The aim was to investigate whether intravenous infusion of remifentanil would depress phrenic long term facilitation (pLTF) evoked by acute intermittent hypoxia (AIH) in adult, male, urethane anaesthetized Sprague-Dawley rats, bilaterally vagotomized, paralyzed and mechanically ventilated. The experimental group received a remifentanil infusion (0.5 µg/kg/min i.v., n=12), whereas the control group (n=6) received saline. Rats were exposed to AIH protocol. Phrenic nerve amplitude (PNA), burst frequency (f) and breathing rhythm parameters (Ti, Te, Ttot) were analyzed during 5 hypoxias and at 15, 30, and 60 minutes after the final hypoxia, and compared to baseline values. At the end of the experiment, the infusion of remifentanil was stopped and phrenic nerve activity was compared to baseline values prior to remifentanil infusion. In the control group, peak phrenic nerve activity (pPNA) significantly increased at 60 min (T60, increase by 138.8±28.3%, p=0.006) after the last hypoxic episode compared to baseline values, i.e. pLTF was induced. In remifentanil treated rats, there were no significant changes in peak phrenic nerve activity at T60 compared to baseline values (decrease by 5.3±16.5%, p>0.05), i.e. pLTF was abolished. Fifteen minutes following cessation of remifentanil infusion, pPNA increased by 93.2±40.2% (p<0.05) and remained increased compared to pre-remifentanil-infusion values for more than 30 minutes, i.e. pLTF could be observed after cessation of the remifentanil infusion. In conclusion, the short acting µ-opioid receptor agonist, remifentanil, reversibly abolished phrenic long term facilitation in urethane anesthetized rats.

A K(ATP) channel gene effect on sleep duration: from genome-wide association studies to function in Drosophila.

Humans sleep approximately a third of their lifetime. The observation that individuals with either long or short sleep duration show associations with metabolic syndrome and psychiatric disorders suggests that the length of sleep is adaptive. Although sleep duration can be influenced by photoperiod (season) and phase of entrainment (chronotype), human familial sleep disorders indicate that there is a strong genetic modulation of sleep. Therefore, we conducted high-density genome-wide association studies for sleep duration in seven European populations (N=4251). We identified an intronic variant (rs11046205; P=3.99 × 10(-8)) in the ABCC9 gene that explains ≈5% of the variation in sleep duration. An influence of season and chronotype on sleep duration was solely observed in the replication sample (N=5949). Meta-analysis of the associations found in a subgroup of the replication sample, chosen for season of entry and chronotype, together with the discovery results showed genome-wide significance. RNA interference knockdown experiments of the conserved ABCC9 homologue in Drosophila neurons renders flies sleepless during the first 3 h of the night. ABCC9 encodes an ATP-sensitive potassium channel subunit (SUR2), serving as a sensor of intracellular energy metabolism.

Propofol abolished the phrenic long-term facilitation in rats.

The aim was to investigate the effect of propofol anesthesia on the phrenic long-term facilitation (pLTF) in rats. We hypothesized that pLTF would be abolished during propofol-compared with urethane anesthesia. Fourteen adult, male, anesthetized, vagotomized, paralyzed, and mechanically ventilated Sprague-Dawley rats (seven per group), were exposed to the acute intermittent hypoxia (AIH) protocol. Peak phrenic nerve activity (PNA), burst frequency (f), and breathing rhythm parameters (Ti, Te, Ttot) were analyzed during the first hypoxia (TH1), as well as at 15 (T15), 30 (T30), and 60min (T60) after the final hypoxic episode, and compared to the baseline values. In propofol-anesthetized rats no significant changes of PNA were recorded after the last hypoxic episode, i.e. no pLTF was induced. There was a significant increase of PNA (59.4+/-6.6%, P<0.001) in urethane-anesthetized group at T60. AIH did not elicit significant changes in f, Ti, Te, Ttot in either group at T15, T30, and T60. The pLTF, elicited by AIH, was induced in the urethane-anesthetized rats. On the contrary, pLTF was abolished in the propofol-anesthetized rats.

The acute hypoxic ventilatory response under halothane, isoflurane, and sevoflurane anaesthesia in rats.

The relative order of potency of anaesthetic agents on the hypoxic ventilatory response has been tested in humans, but animal data are sparse. We examined the effects of 1.4, 1.6, 1.8, and 2.0 MAC halothane, isoflurane, and sevoflurane on phrenic nerve activity in euoxia (baseline) and during acute normocapnic hypoxia (inspired oxygen fraction 0.09) in adult male Sprague-Dawley rats. With halothane, all animals became apnoeic even in euoxia, and the hypoxic response was completely abolished at all anaesthetic levels. With isoflurane, 5 of 14 animals exhibited phrenic nerve activity in euoxia at 1.4 MAC and demonstrated a hypoxic response (302% of baseline activity), but all became apnoeic and lost the hypoxic response at higher doses. With sevoflurane, phrenic nerve activity and a hypoxic response was preserved in at least some animals at all doses (i.e. even the highest dose of 2.0 MAC). Similar to the rank order of potency previously observed in humans, the relative order of potency of depression of the hypoxic ventilatory response in rats was halothane (most depressive) > isoflurane > sevoflurane (p = 0.01 for differences between agents).

Blockade of 5-HT(1A) receptors in the phrenic nucleus of the rat attenuated raphe induced activation of the phrenic nerve activity.

Stimulation of the raphe pallidus nucleus produces facilitatory effects on respiratory activity. Numerous serotonergic projections from the raphe pallidus have been shown to terminate in the phrenic nucleus. This study was undertaken to examine the role of 5-hydroxytryptamine 1A (5-HT(1A)) receptors in the phrenic nucleus on the excitatory response of the phrenic nerve activity elicited from the raphe pallidus. We hypothesized that blockade of 5-HT(1A) receptors in the phrenic nucleus will attenuate raphe-induced facilitation of the phrenic nerve. Chemical stimulation of the raphe pallidus by synaptic excitant D,L-homocysteic acid produced increase in the amplitude of the phrenic nerve activity. After microinjection of the specific 5-HT(1A) receptor antagonist WAY, N-(2-(4,2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridinyl-cyclohexane-carboxamide maleate into the phrenic nucleus, the raphe-induced facilitation of the phrenic nerve was attenuated. These data suggest that excitation of the phrenic nerve activity elicited by activation of the neurons in the raphe pallidus is mediated by 5-HT(1A) receptors in the phrenic nucleus.

Phrenic nerve activity is enhanced by 5-HT1A receptor agonist 8-OH-DPAT in spontaneously breathing anesthetized rats.

Activation of serotonin 1A (5-HT(1A)) receptors has been shown to have diverse effects on respiration. The purpose of this study was to determine changes in respiratory motor pattern of phrenic nerve activity and respiratory rhythm after systemic application of specific 5-HT(1A) receptor agonist 8-hydroxy-2-di-npropylamino-tetralin (8-OH-DPAT). We hypothesized that systemic application of specific 5-HT(1A) receptor agonist 8-OH-DPAT in spontaneously breathing anaesthetized rats will enhance phrenic motor output and phrenic respiratory rate. The study was performed in spontaneously breathing urethane anesthetized rats. Intravenous application of 8-OH-DPAT produced dose dependent increase in the amplitude of integrated phrenic nerve activity and disturbances in respiratory rhythm. Stimulating effect of 8-OH-DPAT on phrenic nerve activity was abolished by intravenous application of the selective 5-HT(1A) receptor antagonist WAY, N-(2-(4,2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridinyl-cyclohexane-carboxamide maleate (WAY-100635). These results show that stimulation of 5-HT(1A) receptors by intravenous application of 8-OH-DPAT enhances phrenic nerve activity in spontaneously breathing rats.

Influence of meteorological conditions on post-tonsillectomy haemorrhage.

AIM: To evaluate the relationship between the incidence of primary post-tonsillectomy haemorrhage and the daily weather condition, over a five-year period. STUDY DESIGN AND SETTING: This was a retrospective study carried out in the ENT department of the Split University Hospital between January 2000 and December 2004. RESULTS: Out of 3377 patients undergoing tonsillectomy, primary post-operative haemorrhage occurred in 83 (2.5 per cent). The season, daily atmospheric pressure and daily change in atmospheric pressure did not have any significant influence on post-tonsillectomy haemorrhage incidence. However, there was a statistically significant increase in the incidence of primary post-operative haemorrhage when cyclonic conditions prevailed (p = 0.035). CONCLUSION: The incidence of primary post-tonsillectomy haemorrhage in our study population was 2.5 per cent. Avoiding tonsillectomy during cyclonic weather conditions may reduce the incidence of primary post-tonsillectomy haemorrhage.

Rocuronium attenuates oculocardiac reflex during squint surgery in children anesthetized with halothane and nitrous oxide.

BACKGROUND: The oculocardiac reflex (OCR) may be activated during squint surgery. The aim of this study was to test whether rocuronium 0.4 mg kg(-1) could reduce the frequency of OCR, and also whether a single dose of succinylcholine 1 mg kg(-1) could affect the frequency of OCR during anesthesia with halothane in a nitrous oxide/oxygen mixture. METHODS: A total of 161 ASA I children, 3-10 years old, undergoing elective surgery of the medial rectus muscle (MRM) were randomly assigned to three groups. Group R (n = 51), received 0.4 mg kg(-1) of rocuronium intravenously before endotracheal intubation. Group S (n = 58) received 1 mg kg(-1) of succinylcholine. Group C (controls, n = 52) received no relaxant. Oculocardiac reflex was defined as a reduction in heart rate (HR) > or = 15% and/or the appearance of any other arrhythmias, during manipulation of the MRM. Analysis of variance (anova), chi-squared, Kruskal-Wallis, and Student's t-tests were used for statistical analysis; P< 0.05 was considered statistically significant. RESULTS: In group R, OCR occurred in 15/51 (29%) of children, in group S in 31/58 (53%), and in group C in 23/52 (44%) (chi2 = 6.46, P = 0.049). In group R, the incidence of arrhythmias such as nodal rhythms, supraventricular and ventricular premature beats was 6%, compared with 22% in group S and 19% in group C (chi2 = 6.01, P = 0.040). However, there was no reduction in the occurrence of bradycardia (chi2 = 0.16, P = 0.924). CONCLUSION: Rocuronium reduced the frequency of OCR, mainly by reducing the incidence of supraventricular and ventricular premature beats.

Children war casualties during the 1991-1995 wars in Croatia and Bosnia and Herzegovina.

AIM: To analyze clinical course of war-related injuries in children treated at the Split University Hospital during the wars in Croatia (1991-1995) and Bosnia and Herzegovina (1992-1995). METHODS: Medical records of 94 treated children were analyzed. The severity of wounds was scored according to the Abbreviated Injury Scale (AIS) and Injury Severity Score (ISS) evaluation systems. RESULTS: Most children were wounded during shelling/bombing (n = 28, 10 boys and 18 girls) and by left over explosive devices (n = 26). Children injured by left over explosive devices were predominantly boys (23/26 children), aged 10 to 16 years (19/26 children). Extremities were the most frequently wounded body regions (43% of all wounded regions). The wounds to the head/neck (median AIS = 5.0, range 1-6) and abdomen (median AIS = 4.5, range 3-5) were the most severe. Abdominal wounds required surgical procedures (p < 0.001) and antibiotic treatment (p < 0.05) most frequently, as well as patients with greater AIS and ISS scores (p < 0.05). According to the treatment outcome, more patients wounded to the abdomen and extremities showed improvement than no change or complete recovery (p < .05). Permanent disability remained in 37 (39.4%) children and three (3.3%) children died. CONCLUSION: Boys in upper elementary grades and high school were at greater risk of being wounded by fragments of left over explosive devices than younger boys or girls. The most severe wounds were to the head/neck and the abdomen and inflicted during the shelling or bombing. This should be taken into account in organization of surgical care for the children with war-related injuries.

Increased incidence of colorectal cancer in the split-dalmatia county: epidemiological study.

AIM: To investigate the incidence of colorectal cancer in the Split-Dalmatia County in the 1981-1998 period, and compare it with the incidence in the Republic of Croatia. METHODS: The data were obtained using case records and registries of all hospitals and Public Health Institute in the County and the Croatian Cancer Registry. Age-standardized incidence per 100,000 was calculated from the number of patients with colorectal cancer and the number of inhabitants. RESULTS: There were 2,454 new cases of colorectal cancer (1,383 men and 1,071 women) in the Split-Dalmatia County in 1981-1998. Colon cancer was diagnosed in 55% of the cases. Age-standardized incidence rates for colorectal carcinoma per 100,000 population were 11.4 (men 14.8, women 9.0) in 1981, and 63.5 (men 93.1, women 42.5) in 1998. The total incidence increased from 16.1 (colon cancer 7.9, rectal cancer 8.2) in 1981-1985 period to 52.8 (colon cancer 30.5, rectal cancer 22.3) in 1994-1998 period, or approximately 3.3 times. The colorectal cancer incidence rate in the Split-Dalmatia County increased from 16.2 in 1985 to 46.4 in 1995, and in whole Croatia from 32.4 in 1985 to 37.8 in 1995. CONCLUSION: There was a great increase in the reported incidence of colorectal cancer in the Split-Dalmatia County in the 1981-1998 period. The relative increase of incidence in the colorectal cancer was much greater in the Split-Dalmatia County than in Croatia as a whole. These changes call for preventive and screening measures for colorectal carcinoma.

Hypertensive retinopathy and pre-eclampsia.

The aim of the study was to determine the relationship between hypertensive retinopathy and the severity of pre-eclampsia. Forty women with pre-eclampsia, mean age 29.1 (+/- 7.4; range, 19-44) years, were retrospectively analyzed. They were treated at the Department of Obstetrics and Gynecology of the Clinical Hospital Split, from January 1997 to December 1999. The mean age of gestation was 36.0 +/- 2.8 weeks (range, 28-39). Pre-eclampsia was classified according to Goecke. Based on the ophthalmoscopic fundus examinations the patients were divided into four groups, according to Keith-Wagner classification system of grading retinal changes. Of 40 analyzed women, 18 (45%) had ophthalmologically verified hypertensive retinopathy. Ten of them were classified as grade I, six as grade II and two as grade III. Twenty-two patients had mild pre-eclampsia, ten patients had moderate pre-eclampsia, and eight patients had severe pre-eclampsia. A statistically significant correlation (t-test) was found between the degree of hypertensive retinopathy and patient age, Apgar score, trophism, Goecke's index, proteinuria, systolic and diastolic pressure (P < 0.001) and edema (P = 0.01). The degree of hypertensive retinopathy was directly proportional with the severity of pre-eclampsia and significant correlation was found between them (r = 0.338, p = 0.033). These findings showed that the degree of hypertensive retinopathy in women with pre-eclampsia is a valid and reliable prognostic factor in determining the severity of the pre-eclampsia. Therefore, it can be concluded that the examination of the fundus is a valuable and necessary diagnostic procedure in pregnant women with pre-eclampsia.

Effect of central CO(2) drive on lung inflation responses of expiratory bulbospinal neurons in dogs.

The purpose of these studies is to better understand the nature of the reflex interactions that control the discharge patterns of caudal medullary, expiratory (E) bulbospinal neurons. We examined the effect of central chemodrive inputs measured as arterial CO(2) tension (Pa(CO(2))) during hyperoxia on the excitatory and inhibitory components of the lung inflation responses of these neurons in thiopental sodium-anesthetized, paralyzed dogs. Data from slow ramp inflation and deflation test patterns, which were separated by several control inflation cycles, were used to produce plots of neuronal discharge frequency (F(n)) versus transpulmonary pressure (P(t)). P(t) was used as an index of the activity arising from the slowly adapting pulmonary stretch receptors (PSRs). Changes in inspired CO(2) concentrations were used to produce Pa(CO(2)) levels that ranged from 20 to 80 mmHg. The data obtained from 41 E neurons were used to derive an empirical model that quantifies the average relationship for F(n) versus both P(t) and Pa(CO(2)). This model can be used to predict the time course and magnitude of E neuronal responses to these inputs. These data suggest that the interaction between Pa(CO(2)) and PSR-mediated excitation and inhibition of F(n) is mainly additive, but synergism between Pa(CO(2)) and excitatory inputs is also present. The implications of these findings are discussed.

Differential roles of ionotropic glutamate receptors in canine medullary inspiratory neurons of the ventral respiratory group.

The relative roles of ionotropic N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in supplying excitatory drive to inspiratory (I) augmenting pattern neurons of the ventral respiratory group were studied in anesthetized, ventilated, paralyzed, and vagotomized dogs. Multibarrel micropipettes were used to record simultaneously single-unit neuronal activity and pressure microeject the NMDA antagonist, 2-amino-5-phosphonovalerate (AP5; 2 mM), the non-NMDA antagonist 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 0.25 mM), and an artificial cerebrospinal fluid vehicle. Ejected volume-rates were measured directly via meniscus level changes. The moving time average of phrenic nerve activity was used to determine respiratory phase durations and to synchronize cycle-triggered histograms of the discharge patterns. Both AP5 and NBQX produced dose-dependent reductions in peak spontaneous I neuronal discharge frequency (Fn). The average (+/- SE) maximum reduction in peak Fn produced by AP5 was 69.1 +/- 4.2% and by NBQX was 47.1 +/- 3.3%. Blockade of both glutamate receptor subtypes nearly silenced these neurons, suggesting that their activity is highly dependent on excitatory synaptic drive mediated by ionotropic glutamate receptors. Differential effects were found for the two glutamatergic antagonists. AP5 produced downward, parallel shifts in the augmenting pattern of discharge, whereas NBQX reduced the slope of the augmenting discharge pattern. These results suggest that time-varying excitatory input patterns to the canine I bulbospinal neurons are mediated by non-NMDA glutamate receptors and that constant or tonic input patterns to these neurons are mediated by NMDA receptors.

Differential effects of GABAA receptor antagonists in the control of respiratory neuronal discharge patterns.

To ascertain the role of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in shaping and controlling the phasic discharge patterns of medullary respiratory premotor neurons, localized pressure applications of the competitive GABAA receptor antagonist bicuculline (BIC) and the noncompetitive GABAA receptor antagonist picrotoxin (PIC) were studied. Multibarrel micropipettes were used in halothane anesthetized, paralyzed, ventilated, vagotomized dogs to record single unit activity from inspiratory and expiratory neurons in the caudal ventral respiratory group and to picoeject GABAA receptor antagonists. The moving time average of phrenic nerve activity was used to determine respiratory phase durations and to synchronize cycle-triggered histograms of discharge patterns. Picoejection of BIC and PIC had qualitatively different effects on the discharge patterns of respiratory neurons. BIC caused an increase in the discharge rate during the neuron's active phase without inducing activity during the neuron's normally silent phase. The resulting discharge patterns were amplified replicas (x2-3) of the underlying preejection phasic patterns. In contrast, picoejection of PIC did not increase the peak discharge rate during the neuron's active phase but induced a tonic level of activity during the neuron's normally silent phase. The maximum effective BIC dose (15 +/- 1.8 pmol/min) was considerably smaller than that for PIC (280 +/- 53 pmol/min). These findings suggest that GABAA receptors with differential pharmacology mediate distinct functions within the same neuron, 1) gain modulation that is BIC sensitive but PIC insensitive and 2) silent-phase inhibition blocked by PIC. These studies also suggest that the choice of an antagonist is an important consideration in the determination of GABA receptor function within the respiratory motor control system.

Modulation of the synaptic drive to respiratory premotor and motor neurons.

The characteristics of GABAergic inhibitory modulation of respiratory bulbospinal neuronal activity and short-term potentiation (STP) of phrenic motoneuronal activity were studied. Extracellular unit recording and picoejection techniques in anesthetized dogs showed that both the spontaneous rhythmic and reflexly induced discharge patterns of inspiratory (I) and expiratory (E) premotor neurons were proportionately amplified by the localized application of picomole amounts of bicuculline (Bic), a competitive GABAA antagonist. Intracellular recording and paired-pulse stimulation techniques in anesthetized rats demonstrated an STP of phrenic motor output that appears to be mediated by NMDA receptors and is associated with facilitation of EPSPs and prolonged depolarization of individual phrenic motoneurons. We speculate that both GABAergic gain modulation of premotor neuronal activity and NMDA-mediated STP of phrenic activity may be neural substrates which are involved with the optimization of respiratory and non-respiratory behaviors, via adaptive and/or differential control of breathing.