Retaining or excising the supraspinatus tendon in complex proximal humeral fractures treated with reverse prosthesis: a biomechanical analysis in two different designs.

PURPOSE: We aimed to biomechanically evaluate the effect of the supraspinatus tendon on tuberosity stability using two different reverse shoulder arthroplasty (RSA) models for complex proximal humeral fractures (PHFs). METHODS: Four-part proximal humeral fractures were simulated in 20 cadaveric shoulders. Two different RSA designs were implemented: a glenosphere-medialized model and a glenosphere-lateralized model. Tuberosities were reconstructed, and displacement of bony fragments was measured (mm) by placing three sensors: in the humeral diaphysis (D), in the greater tuberosity (GT), and in the lesser tuberosity (LT). Axial forces were induced and measured in Newton (N). The test was performed twice in each specimen, with and without the supraspinatus tendon. The regression line (RL) was measured in mm/N. RESULTS: In the medialized model, the GT-D displacement was greater in the supraspinatus preserving model than that in the tendon excision model (p < 0.001), as well as for the LT-D displacement (p < 0.001). In the lateralized model, GT-D displacement and GT-LT distance were greater in the preserving model than that in the excision model (p < 0.001, p = 0.04). CONCLUSION: The supraspinatus tendon resection leads to a more biomechanically stable tuberosity construct when performing RSA for PHFs, while the rest of the rotator cuff tendons (infraspinatus and teres minor) are retained in the greater tuberosity. LEVEL OF EVIDENCE: Basic science study. Cadaveric study.

Glucocorticoid Receptors, Brain-Derived Neurotrophic Factor, Serotonin and Dopamine Neurotransmission are Associated with Interferon-Induced Depression.

BACKGROUND: The role of inflammation in mood disorders has received increased attention. There is substantial evidence that cytokine therapies, such as interferon alpha (IFN-alpha), can induce depressive symptoms. Indeed, proinflammatory cytokines change brain function in several ways, such as altering neurotransmitters, the glucocorticoid axis, and apoptotic mechanisms. This study aimed to evaluate the impact on mood of initiating IFN-alpha and ribavirin treatment in a cohort of patients with chronic hepatitis C. We investigated clinical, personality, and functional genetic variants associated with cytokine-induced depression. METHODS: We recruited 344 Caucasian outpatients with chronic hepatitis C, initiating IFN-alpha and ribavirin therapy. All patients were euthymic at baseline according to DSM-IV-R criteria. Patients were assessed at baseline and 4, 12, 24, and 48 weeks after treatment initiation using the Patient Health Questionnaire (PHQ), the Hospital Anxiety and Depression Scale (HADS), and the Temperament and Character Inventory (TCI). We genotyped several functional polymorphisms of interleukin-28 (IL28B), indoleamine 2,3-dioxygenase (IDO-1), serotonin receptor-1A (HTR1A), catechol-O-methyl transferase (COMT), glucocorticoid receptors (GCR1 and GCR2), brain-derived neurotrophic factor (BDNF), and FK506 binding protein 5 (FKBP5) genes. A survival analysis was performed, and the Cox proportional hazards model was used for the multivariate analysis. RESULTS: The cumulative incidence of depression was 0.35 at week 24 and 0.46 at week 48. The genotypic distributions were in Hardy-Weinberg equilibrium. Older age (p = 0.018, hazard ratio [HR] per 5 years = 1.21), presence of depression history (p = 0.0001, HR = 2.38), and subthreshold depressive symptoms at baseline (p = 0.005, HR = 1.13) increased the risk of IFN-induced depression. So too did TCI personality traits, with high scores on fatigability (p = 0.0037, HR = 1.17), impulsiveness (p = 0.0200 HR = 1.14), disorderliness (p = 0.0339, HR = 1.11), and low scores on extravagance (p = 0.0040, HR = 0.85). An interaction between HTR1A and COMT genes was found. Patients carrying the G allele of HTR1A plus the Met substitution of the COMT polymorphism had a greater risk for depression during antiviral treatment (HR = 3.83) than patients with the CC (HTR1A) and Met allele (COMT) genotypes. Patients carrying the HTR1A CC genotype and the COMT Val/Val genotype (HR = 3.25) had a higher risk of depression than patients with the G allele (HTR1A) and the Val/Val genotype. Moreover, functional variants of the GCR1 (GG genotype: p = 0.0436, HR = 1.88) and BDNF genes (Val/Val genotype: p = 0.0453, HR = 0.55) were associated with depression. CONCLUSIONS: The results of the study support the theory that IFN-induced depression is associated with a complex pathophysiological background, including serotonergic and dopaminergic neurotransmission as well as glucocorticoid and neurotrophic factors. These findings may help to improve the management of patients on antiviral treatment and broaden our understanding of the pathogenesis of mood disorders.

Epidural vs. intravenous fentanyl during colorectal surgery using a double-blind, double-dummy design.

BACKGROUND: The overall therapeutic effectiveness of epidural fentanyl vs. the intravenous route is controversial. The present work describes a randomized, controlled, double-blind, double-dummy study of the intraoperative requirements of fentanyl administered by the intravenous or epidural routes during open colon surgery. METHODS: Thirty patients were randomized to receive intraoperative analgesia with boluses of fentanyl administered by either the epidural or intravenous route (2 µg/kg). The first fentanyl bolus was administered 10 min before incision, and repeated boluses were given when mean arterial pressure or heart rate increased more than 20% over basal values. General anaesthesia was maintained with a propofol infusion. Intraoperative fentanyl and propofol requirements, time to awakening, time to analgesia request, and incidence of adverse effects were recorded. RESULTS: Median [interquartile range (range)] fentanyl requirements in the epidural and intravenous groups were 0.81 [0.65 (0.47-2.61)] and 2.5 [1.08 (1.07-4.85)] µg/kg/h, respectively (P < 0.001). The epidural group had a shorter time to awakening, with a median of 8 min [4.5 (3-18)] compared with 20 min [12.5 (7-34)] for the intravenous group (P < 0.001). There were no significant differences in propofol requirements. The time to analgesia request was also delayed in the epidural group, with a median of 5 h [5.5 (1-16)] vs. 2 h [1 (1-5)] when fentanyl was administered intravenously (P < 0.001). The incidence of adverse effects was similar in both groups. CONCLUSION: During major abdominal surgery, epidural administration requires lower doses of intraoperative fentanyl when compared with the intravenous route. Epidural fentanyl also facilitates early awakening and residual analgesia without increasing adverse events.

Psychosocial and biological predictors of resident physician burnout.

BACKGROUND: A high proportion of health professionals in training suffer from work-related stress and may develop a burnout syndrome. OBJECTIVES: To study the incidence of burnout after the first year of residency in a teaching hospital and to identify baseline psychological, psychosocial work conditions, and biological risk factors. METHODOLOGY: We assessed the following in a prospective cohort of residents at baseline (first month residence) and after 1 year: background factors (socio-demographics, psychiatric history), perceived stress score (Perceived Stress Scale), Maslach Burnout Inventory score, and psychosocial factors (Job Content Questionnaire). Blood samples were obtained to study serum cortisol, IL-6, and TNF-α concentrations. The cumulative incidence was modelled by multivariate log-binomial regression analysis. RESULTS: We included 71 participants with a female majority (64.8%), age 26.4 (2.65) years, psychiatric history in 20%, and burnout in 13%. Among those without burnout initially (N = 59), it had developed by 1 year in 22% of residents. Increased job demand (RR = 1.259, 95%CI = 1.019-1.556, p = 0.033) and decreased cortisol levels (RR = 0.877, 95%CI = 0.778-0.989, p = 0.032) predicted burnout after 1 year of residency among medical trainees. CONCLUSION: Burnout syndrome develops in 22% of residents by 1 year of training and can be predicted by increased work demands and decreased cortisol levels.

Cognitive performance in recreational ecstasy polydrug users: a two-year follow-up study.

There is important preclinical evidence of long lasting neurotoxic and selective effects of ecstasy MDMA on serotonin systems in non-human primates. In humans long-term recreational use of ecstasy has been mainly associated with learning and memory impairments. The aim of the present study was to investigate the neuropsychological profile associated with ecstasy use within recreational polydrug users, and describe the cognitive changes related to maintained or variable ecstasy use along a two years period. We administered cognitive measures of attention, executive functions, memory and learning to three groups of participants: 37 current polydrug users with regular consumption of ecstasy and cannabis, 23 current cannabis users and 34 non-users free of illicit drugs. Four cognitive assessments were conducted during two years. At baseline, ecstasy polydrug users showed significantly poorer performance than cannabis users and non-drug using controls in a measure of semantic word fluency. When ecstasy users were classified according to lifetime use of ecstasy, the more severe users (more than 100 tablets) showed additional deficits on episodic memory. After two years ecstasy users showed persistent deficits on verbal fluency, working memory and processing speed. These findings should be interpreted with caution, since the possibility of premorbid group differences cannot be entirely excluded. Our findings support that ecstasy use, or ecstasy/cannabis synergic effects, are responsible for the sub-clinical deficits observed in ecstasy polydrug users, and provides additional evidence for long-term cognitive impairment owing to ecstasy consumption in the context of polydrug use.

Mechanisms of Na+ and Ca2+ influx into respiratory neurons during hypoxia.

Changes in intracellular Na+ and Ca2+ in inspiratory neurons of neonatal mice were examined by using ion-selective fluorescent indicator dyes SBFI and fura-2, respectively. Both [Na+]i and [Ca2+]i signals showed rhythmic elevations, correlating with the inspiratory motor output. Brief (2-3 min) hypoxia, induced initial potentiation of rhythmic transients followed by their depression. During hypoxia, the basal [Na+]i and [Ca2+]i levels slowly increased, reflecting development of an inward current (Im). By antagonizing specific mechanisms of Na+ and Ca2+ transport we found that increases in [Na+]i, [Ca2+]i and Im due to hypoxia are suppressed by CNQX, nifedipine, riluzole and flufenamic acid, indicating contribution of AMPA/kainate receptors, persistent Na+ channels, L-type Ca2+ channels and Ca2+-sensitive non-selective cationic channels, respectively. The blockers decreased also the amplitude of the inspiratory bursts. Modification of mitochondrial properties with FCCP and cyclosporine A decreased [Ca2+]i elevations due to hypoxia by about 25%. After depletion of internal Ca2+ stores with thapsigargin, the blockade of NMDA receptors, Na+/K+ pump, Na+/H+ and Na+/Ca2+ exchange, the hypoxic response was not changed. We conclude that slow [Na+]i and [Ca2+]i increases in inspiratory neurons during hypoxia are caused by Na+ and Ca2+ entry due to combined activation of persistent Na+ and L-type Ca2+ channels and AMPA/kainate receptors.

[Survival of patients with HIV-related tuberculosis. Study of mortality during the first 9 months of treatment]. / Supervivencia en pacientes con tuberculosis infectados por VIH. Estudio de los fallecimientos en los primeros nueve meses de tratamiento.

BACKGROUND: Among the individuals with tuberculosis who are infected with HIV a high degree of lethality has been found to exist during the first few weeks following the start of tuberculosis treatment. In this study, the survival of these individuals is studied within the framework of a retrospective cohort study. METHODS: This study included 1135 subjects infected by HIV over age fifteen and residents of Barcelona who were registered by the Barcelona Tuberculosis Prevention and Control Program and were diagnoses within the 1988-1993 period. The variables analyzed were age, gender, former imprisonment, municipal district, risk group, percentage of T CD4+ lymphocytes, tuberculin test, AIDS diagnosis (as per CDC-1987), X-ray pattern, bacteriology and part of the body affected by the tuberculosis. The Cox semiparametric method, the Kaplan-Meir curves and the log-rank test were employed. RESULTS: A 77% probability of survival during the first nine months was found to exist, with wide-ranging variations among the different subgroups. The only significant variables in the Cos multivariate model were AIDS, the percentage of T CD4+ lymphocytes and their interaction. The risk of death for an individual not having AIDS and a T CD4+ lymphocyte percentage of 14% or lower was 7.69 times higher than the risk of dying for an individual not having AIDS who had a T CD4+ lymphocyte percentage of above 14%. CONCLUSIONS: The survival of those individuals having tuberculosis who are infected with HIV varies greatly. Those who died in the short term were diagnosed as having AIDS on starting the tuberculosis treatment and who also had a T CD4+ lymphocyte percentage of 14% or lower.

An ultrasound biomicroscopy study after deep sclerectomy with supraciliary implant.

OBJECTIVE: To evaluate patients 24 months after deep sclerectomy (DE) with supraciliary implant, and identify any predictive success factors by examination with ultrasound biomicroscopy (UBM) MATERIAL AND METHODS: This study included 26 eyes of 23 patients evaluated by UBM 24 months after a deep sclerectomy with a supraciliary hema implant. RESULTS: There was a significant reduction in intraocular pressure (IOP), changing from a preoperative mean of 25.6 ± 6.4 mmHg to a postoperative mean of 16.2 ± 3.4 mmHg (P<.001). The number of preoperative glaucoma medications also decreased from 2.5 ± 0.6 drugs per patient to 0.5 ± 0.5 (P<.001). No change was observed in the best-corrected visual acuity. The anatomical characteristics of the surgical area, and its relationship with IOP were examined using UBM. There was no correlation between the level of IOP at the time of UBM and the horizontal (r=-.05: P=.71) and vertical diameter (r=-.1; P=.63), the height (r=.28; P=.25) and the volume of intrascleral space (r=-.08; P=.79), the thickness (r=-.07; P=.73) and the length (r=.39; P=.13) of trabeculo-Descemet's membrane (TDM), the presence of filtering bleb (P=.30) and the hypoechoic area in the supraciliary space (P=.24). CONCLUSIONS: The insertion of a hema implant in the supraciliary space is an effective and safe surgery for patients with open angle glaucoma (OAG). No predictive success factors for supraciliary implant were found using the UBM study.

Investigation of decision-making under uncertainty in healthy subjects: a multi-centric fMRI study.

Decision-making is an everyday routine that entails several subprocesses. Decisions under uncertainty occur when either prior information is incomplete or the outcomes of the decision are unclear. The aim of the present study was to disentangle the neural correlates of information gathering as well as reaching a decision and to explore effects of uncertainty acceptance or avoidance in a large sample of healthy subjects. Sixty-four healthy volunteers performed a decision-making under uncertainty task in a multi-center approach while BOLD signal was measured with fMRI. Subjects either had to indicate via button press from which of two bottles red or blue balls were drawn (decision-making under uncertainty condition), or they had to indicate whether 8 red balls had been presented (baseline condition). During the information gathering phase (contrasted against the counting phase) a widespread network was found encompassing (pre-)frontal, inferior temporal and inferior parietal cortices. Reaching a decision was correlated with activations in the medial frontal cortex as well as the posterior cingulate and the precuneus. Effects of uncertainty acceptance were found within a network comprising of the superior frontal cortex as well as the insula and precuneus while uncertainty avoidance was correlated with activations in the right middle frontal cortex. The results depict two distinct networks for information gathering and the indication of having made a decision. While information-gathering networks are modulated by uncertainty avoidance and - acceptance, underlying networks of the decision itself are independent of these factors.

Acute effects of a single, oral dose of d9-tetrahydrocannabinol (THC) and cannabidiol (CBD) administration in healthy volunteers.

RATIONALE: Animal and humans studies suggest that the two main constituents of cannabis sativa, delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) have quite different acute effects. However, to date the two compounds have largely been studied separately. OBJECTIVE: To evaluate and compare the acute pharmacological effects of both THC and CBD in the same human volunteers. METHODS: A randomised, double-blind, cross-over, placebo controlled trial was conducted in 16 healthy male subjects. Oral THC 10 mg or CBD 600 mg or placebo was administered in three consecutive sessions, at one-month interval. Physiological measures and symptom ratings were assessed before, and at 1, 2 and 3 hours post drug administration. The area under the curve (AUC) between baseline and 3 hours, and the maximum absolute change from baseline at 2 hours were analysed by one-way repeated measures analysis of variance, with drug condition (THC or CBD or placebo) as the factor. RESULTS: Relative to both placebo and CBD, administration of THC was associated with anxiety, dysphoria, positive psychotic symptoms, physical and mental sedation, subjective intoxication (AUC and effect at 2 hours: p < 0.01), an increase in heart rate (p < 0.05). There were no differences between CBD and placebo on any symptomatic, physiological variable. CONCLUSIONS: In healthy volunteers, THC has marked acute behavioural and physiological effects, whereas CBD has proven to be safe and well tolerated.

[Poor premorbid adjustment linked to deterioration in theory of mind skills: a study in stabilised schizophrenic patients]. / Ajuste premórbido pobre vinculado al deterioro en habilidades de teoría de la mente: estudio en pacientes esquizofrénicos estabilizados.

INTRODUCTION: Previous studies suggest that there is a deficit in theory of mind (ToM) in stabilised schizophrenic patients. More specifically, it has been claimed that poor premorbid adjustment covaries with the abnormalities in ToM skills detected in such patients. It has also been suggested that this deficit could be a trait marker for schizophrenic disorders. PATIENTS AND METHODS: The aim of this study was to examine the performance in mentalistic skills in 36 stabilised schizophrenic patients in comparison to a standard control group. We also sought to examine the relation between ToM skills and premorbid adjustment in our target sample. Premorbid adjustment was evaluated using the modified Cannon-Spoor premorbid adjustment scale, and ToM measurements were obtained by means of first- and second-order verbal experimental tasks. RESULTS: Schizophrenic patients presented statistically significant poorer performances in first- and second-order ToM tasks, although no differences were observed between these patients and the control sample as regards overall cognitive acuity. Poor premorbid adjustment in areas of social functioning in the patients was also associated with statistically significant poorer performance in both ToM tasks. CONCLUSIONS: Deficient premorbid adjustment in schizophrenia may be linked to a ToM deficit that can be assessed with simple tasks.

ORALVEQ: external quality assessment scheme of drugs of abuse in oral fluid: results obtained in the first round performed in 2007.

The Institut Municipal d'Investigació Mèdica IMIM-Hospital del Mar (Barcelona, Spain) in cooperation with the Istituto Superiore di Sanità (Rome, Italy) organized an external quality assessment scheme to assess the reliability of analytical laboratories when analyzing drugs of abuse in oral fluid (ORALVEQ). For the first round of ORALVEQ, performed in February 2007, three different samples (S1, S2 and S3) were sent to 21 participating international laboratories. S1 was a blank sample and S2 and S3 were prepared by addition of drugs at known concentrations to pre-screened drug-free oral fluid (containing sodium azide) and diluted up to 50% with acidic buffer. S2 contained 6-monoacetyl morphine, morphine, cocaine and benzoylecgonine and S3 contained 3,4-methylendioxymethamphetamine and 3,4-methylendioxyamphetamine. Results were evaluated from a qualitative and quantitative point of view. Whereas only half laboratories performed screening analysis, all of them reported a quantitative result for almost all analytes. Eighteen false-positive and 3 false-negative results were reported by 8 (from a total of 21) laboratories. The quantitative evaluation was performed measuring dispersion (% coefficient of variation, CV%) and accuracy (% error, ERR%) of results and calculating the z-score values (using robust statistics). ERR% between 2% and 20% and CVs% around 40% were obtained for all analytes. In terms of z-score, a high percentage of adequate results (between 85 and 95%) was obtained. In general, the participating laboratories had a satisfactory performance. The number of false-negatives reported was very low, the false-positives were reported by a reduced number of laboratories and the scatter in the quantitative results was principally due to a few outlying values; since applying robust statistics, there was no rejection of outliers.

HAIRVEQ 2006: evolution of laboratories' performance after different educational actions.

HAIRVEQ is a proficiency testing program for hair analysis of illicit drugs organized by the Istituto Superiore di Sanità (Rome, Italy) and the Institut Municipal d'Investigació Mèdica (Barcelona, Spain). The aim of the three exercises performed in 2006 was the evaluation of 32 laboratories' performance when analyzing the same hair sample containing opiates, cocaine and methadone, after carrying out some specific educational interventions. In the first round, the sample was sent to be analyzed following laboratory routine methodology. In the second round, standard operating procedures (SOP) for hair testing including sample preparation, method validation and qualitative and quantitative data evaluation, and an open hair sample for SOP training were also sent together with other hair samples including the one used for performance evaluation. After the second round, a workshop was held with participant laboratories to discuss methodological issues and interpretation of obtained results. An additional amount of open samples was distributed to the laboratories for implementing the SOPs. In the third round, the same unknown sample containing opiates, cocaine and methadone was resent for the final evaluation of laboratory performance. In the first round, 11 incorrect qualitative results (10 false negative and 1 false positive) were reported by seven laboratories (22%), in the second round, a reduction in the number of incorrect results was observed (4 false negatives and 1 false positive were reported by four laboratories, 13%) and in the third round, 5 false positives and 5 false negatives were reported by seven laboratories (22%). Concerning quantitative results, the scatter was similar between the three rounds and similar to the ones reported by other proficiency tests in hair analysis. More educational actions should be addressed to a group of laboratories, which did not yet show satisfying qualitative and quantitative results.

Four years' experience in external proficiency testing programs for hair testing of drugs of abuse in Italy (HAIRVEQ) and comparison with the Society of Hair Testing program in 2005.

Since 2002, the Istituto Superiore di Sanità, Rome, Italy, in cooperation with Institut Municipal d'Investigaciò Mèdica, Barcelona, Spain, has set up an external proficiency testing program (HAIRVEQ) to evaluate reliability in hair testing for drug abuse by laboratories from the Italian National Health Service. The results obtained in the last 2 rounds (2004-2005) by 26 laboratories and the evolution of the performance in hair testing for drugs of abuse by laboratories that have participated during the whole external proficiency testing program are presented. The 3 hair samples from the last exercise (2005) were also included in the proficiency test organized by the Society of Hair Testing (SoHT) and 17 international laboratories reported results. Samples analyzed in both exercises were real hair samples from drug consumers. In 2004, 2 identical samples were sent containing cocaine and opiates. One sample was a pulverized specimen and the second one was cut in short segments. In 2005, 2 samples, one containing MDMA and another containing cocaine, were included together with one blank sample. In 2004, approximately 42% of HAIRVEQ laboratories reported an erroneous qualitative result. The scatter of quantitative results was high, although no statistical differences, except for codeine, were found between results reported for the hair specimen if pulverized or reduced in short cuts. In 2005, 47 incorrect qualitative results were reported by HAIRVEQ laboratories, whereas only 5 were informed by SoHT laboratories. Concerning quantitative results, the ones from HAIRVEQ laboratories were comparable, although more dispersed, than those reported by SoHT laboratories. The scatter in quantitative results remained quite high and similar to those of the previous years; nonetheless, an improvement in the qualitative performance was observed. Considering the few number of laboratories showing a satisfying performance, guidelines have to be provided focused on method validation and qualitative and quantitative data evaluation.

Hyperpolarization-activated current, Ih, in inspiratory brainstem neurons and its inhibition by hypoxia.

A hyperpolarization-activated current, Ih, is often implied in pacemaker-like depolarizations during rhythmic oscillatory activity. We describe Ih in the isolated respiratory centre of immature mice (P6-P11). Ih was recorded in 15% (22/146) of all inspiratory neurons examined. The mean half-maximal Ih activation occurred at -78 mV and the reversal potential was -40 mV. Ih was inhibited by Cs+ (1-5 mM) and by organic blockers N-ethyl-1,6-dihydro-1, 2-dimethyl-6-(methylimino)-N-phenyl-4-pyrimidinamine (ZD 7288; 0.3-3 microM) and N,N'-bis-(3,4-dimethylphenylethyl)-N-methylamine (YS 035, 3-30 microM), but not by Ba2+ (0.5 mM). The organic Ih blockers did not change the inspiratory bursts recorded from the XIIth nerve and synaptic drives in inspiratory neurons. Hypoxia reversibly inhibited Ih but, in the presence of organic blockers, the hypoxic reaction remained unchanged. We conclude that although Ih channels are functional in a minority of inspiratory neurons, Ih does not contribute to respiratory rhythm generation or its modulation by hypoxia.

A1 adenosine receptors modulate respiratory activity of the neonatal mouse via the cAMP-mediated signaling pathway.

The effects of adenosine and its analogs on the function of the respiratory center were studied in the spontaneously active rhythmic slice of neonatal and juvenile mice (4-14 days old). Whole cell, spontaneous postsynaptic currents (sPSCs) and single channel KATP currents were recorded in inspiratory neurons of the pre-Bötzinger complex. Adenosine (50-600 microM) inhibited the respiratory rhythm. This was accompanied by increase in the activity of KATP channels in cell-attached patches. The A1 adenosine receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA, 0.3-2 microM), inhibited the respiratory rhythm, sPSCs, and enhanced activity of KATP channels. The A1 adenosine receptor antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 1-3 microM), showed opposite effects and occluded the CCPA actions. Agents specific for A2 adenosine receptors (CGS 21860 and NECA, both applied at 1-10 microM) were without effect. Elevation of intracellular cAMP concentration ([cAMP]i) by 8-Br-cAMP (200-500 microM), forskolin (0.5-2 microM), or isobutylmethylxantine (IBMX, 30-90 microM) reinforced the rhythm, whereas NaF (100-800 microM) depressed it. The open probability of single KATP channels in cell-attached patches decreased after application of forskolin and increased in the presence of NaF. [cAMP]i elevation reversed the effects of A1 receptors both on the respiratory rhythm and KATP channels. A1 receptors and [cAMP]i modified the hypoxic respiratory response. In the presence of A1 agonists the duration of hypoxic augmentation shortened, and depression of the respiratory rhythm occurred earlier. Elevation of [cAMP]i prolonged augmentation and delayed the development of the depression. We conclude that A1 adenosine receptors modulate the respiratory rhythm via inhibition of intracellular cAMP production and concomitant activation of KATP channels.

Hypoxia activates ATP-dependent potassium channels in inspiratory neurones of neonatal mice.

1. The respiratory centre of neonatal mice (4 to 12 days old) was isolated in 700 micro(m) thick brainstem slices. Whole-cell K+ currents and single ATP-dependent potassium (KATP) channels were analysed in inspiratory neurones. 2. In cell-attached patches, KATP channels had a conductance of 75 pS and showed inward rectification. Their gating was voltage dependent and channel activity decreased with membrane hyperpolarization. Using Ca2+-containing pipette solutions the measured conductance was lower (50 pS at 1.5 mM Ca2+), indicating tonic inhibition by extracellular Ca2+. 3. KATP channel activity was reversibly potentiated during hypoxia. Maximal effects were attained 3-4 min after oxygen removal from the bath. Hypoxic potentiation of open probability was due to an increase in channel open times and a decrease in channel closed times. 4. In inside-out patches and symmetrical K+ concentrations, channel currents reversed at about 0 mV. Channel activity was blocked by ATP (300-600 microM), glibenclamide (10-70 microM) and tolbutamide (100-300 microM). 5. In the presence of diazoxide (10-60 microM), the activity of KATP channels was increased both in inside-out, outside-out and cell-attached patches. In outside-out patches, that remained within the slice after excision, the activity of KATP channels was enhanced by hypoxia, an effect that could be mediated by a release of endogenous neuromodulators. 6. The whole-cell K+ current (IK) was inactivated at negative membrane potentials, which resembled the voltage dependence of KATP channel gating. After 3-4 min of hypoxia, K+ currents at both hyperpolarizing and depolarizing membrane potentials increased. IK was partially blocked by tolbutamide (100-300 microM) and in its presence, hypoxic potentiation of IK was abolished. 7. We conclude that KATP channels are involved in the hypoxic depression of medullary respiratory activity.