Long-lasting bradypnea induced by repeated social defeat.

Repeated social defeat in the rat induces long-lasting cardiovascular changes associated with anxiety. In this study, we investigated the effects of repeated social defeat on breathing. Respiratory rate was extracted from the respiratory sinus arrhythmia (RSA) peak frequency of the ECG in rats subjected to social defeat for 4 consecutive days. Respiratory rate was recorded under anesthesia 6 days (D+10) or 26 days (D+30) after social defeat. At D+10, defeated (D) rats spent less time in the open arms of the elevated plus maze test, had heavier adrenal glands, and displayed bradypnea, unlike nondefeated animals. At D+30, all signs of anxiety had disappeared. However, one-half of the rats still displayed bradypnea (DL rats, for low respiratory rate indicated by a lower RSA frequency), whereas those with higher respiratory rate (DH rats) had recovered. Acute blockade of the dorsomedial hypothalamus (DMH) or nucleus tractus solitarii (NTS) 5-HT3 receptors reversed bradypnea in all D rats at D+10 and in DL rats at D+30. Respiratory rate was also recorded in conscious animals implanted with radiotelemetric ECG probes. DH rats recovered between D+10 and D+18, whereas DL rats remained bradypneic until D+30. In conclusion, social stress induces sustained chronic bradypnea mediated by DMH neurons and NTS 5-HT3 receptors. These changes are associated with an anxiety-like state that persists until D+10, followed by recovery. However, bradypnea may persist in one-half of the population up until D+30, despite apparent recovery of the anxiety-like state.

Predicting and treating stress-induced vulnerability to epilepsy and depression.

Accumulation of stressful events can render individuals susceptible to develop epilepsy and comorbidities. Whether such vulnerability can be predicted and reversed is not known. Here we show that social defeat, although not producing depression by itself, produced in 50% of rats reduced threshold for status epilepticus (SE), accelerated epileptogenesis, and once epilepsy was induced, depression-like profile and cognitive deficits. Low serum brain-derived neurotrophic factor (BDNF) levels measured before SE identified this vulnerable population. Treatment with a BDNF analog before SE prevented the occurrence of comorbidities. Thus, vulnerability to comorbidities after epilepsy onset due to unresolved past stressful events may be predicted and reversed.

Involvement of the dorsomedial hypothalamus and the nucleus tractus solitarii in chronic cardiovascular changes associated with anxiety in rats.

Anxiety disorders in humans reduce both the heart rate variability (HRV) and the sensitivity of the cardiac baroreflex (BRS). Both may contribute to sudden death. To elucidate the mechanisms underlying these alterations, male rats were subjected to social defeat sessions on four consecutive days. Five days later, the rats were found to be in an anxiety-like state. At this time point, we analysed HRV and BRS in the defeated rats, with or without treatment with the anxiolytic chlordiazepoxide (CDZ). HRV was reduced after social defeat, due to changes in the autonomic balance favouring the sympathetic over the parasympathetic component. Spontaneous and pharmacological baroreflex gains were also reduced. CDZ abolished anxiety-like symptoms as well as HRV and BRS alterations. Inhibition of the dorsomedial hypothalamus (DMH) with muscimol reversed all cardiovascular alterations, whereas blockade of the nucleus tractus solitarii (NTS) 5-HT3 receptor by the local or systemic administration of granisetron restored only baroreflex gains and the parasympathetic component of HRV. In conclusion, repeated social defeat in the rat lead to an anxiety-like state that was associated with lasting reduction in HRV and baroreflex gains. The DMH and the NTS were responsible for these chronic cardiovascular alterations. These regions may therefore constitute new therapeutic targets for reducing cardiac dysfunction and fibrillation in anxiety disorders.

Brain circuits mediating baroreflex bradycardia inhibition in rats: an anatomical and functional link between the cuneiform nucleus and the periaqueductal grey.

Defence responses triggered experimentally in rats by stimulation of the dorsomedial nucleus of the hypothalamus (DMH) and the dorsolateral periaqueductal grey matter (PAG) inhibit the cardiac baroreflex response (i.e. bradycardia). It has also been proposed that the midbrain cuneiform nucleus (CnF) is involved in active responses. Our aim was to identify the neurocircuitry involved in defence-induced baroreflex inhibition, with a particular focus on the link between DMH, CnF and dorsolateral PAG. Microinjection of the anterograde tracer Phaseolus vulgaris leucoaggutinin into the CnF revealed a dense projection to the dorsolateral PAG. Moreover, activation of neurons in the CnF induced increased expression of Fos protein in the dorsolateral PAG. Inhibition of neurons of the CnF or dorsolateral PAG prevented the inhibition of baroreflex bradycardia induced by DMH or CnF stimulation, respectively. These results provide a detailed description of the brain circuitry underlying acute baroreflex modulation by neurons of the DMH. Our data have shown for the first time that the CnF plays a key role in defence reaction-associated cardiovascular changes; its stimulation, from the DMH, activates the dorsolateral PAG, which, in turn, inhibits baroreflex bradycardia.

Daily profiles of salivary and urinary melatonin and steroids in healthy prepubertal boys.

The aim of this study was to assess the circadian hormonal profile of two circadian markers, melatonin and cortisol, as well as other steroids in prepubertal boys (Tanner stage I). Nine volunteer healthy prepubertal boys aged 10.8 +/- 0.11 years participated in this study. Concentrations of daily salivary and urinary hormones were quantified around 24-hours, every 3 hours, in daytime samples (collected between 07.00 h +/- 30 min and 21.00 h +/- 30 min) and night-time samples (collected between 21.00 h +/- 30 min and 07.00 h +/- 30 min). Significant differences (p < 0.01) were found between day- and nighttime secretion of salivary melatonin and urinary 6-sulphatoxymelatonin, whereas no significant differences were found between day- and nighttime secretion of salivary and urinary cortisol nor between day- and nighttime secretion of 17-hydroxycorticosteroids (17-OHCS). The circadian profiles of salivary melatonin and cortisol showed large amplitude with a peak occurring at night (approximately 03.00 h) for melatonin and in the early morning (between 06.00 and 09.00 h) for cortisol. The curve patterns of the urinary 6-sulphatoxymelatonin and steroids (free cortisol and 17-OHCS) were coherent with data on saliva. The pattern of salivary androstenedione and testosterone were undetectable due to the very low concentrations of these steroids in the saliva of the prepubertal children. A strong significant positive correlation was observed between the daily salivary melatonin levels and the daily urinary 6-sulphatoxymelatonin excretion (R = 0.968, p < 0.001), and between free urinary cortisol and urinary 17-OHCS (R = 0.733, p = 0.025). The salivary and urinary hormones studied were independent of body mass index. This study shows the relevance of salivary cortisol and melatonin, although lower than in plasma, in testing adrenal and pineal function as markers of circadian rhythms. The data are of interest for the diagnosis and treatment of chronobiological disorders in prepubertal children.

Vulnerability to stress consequences induced by repeated social defeat in rats: Contribution of the angiotensin II type 1 receptor in cardiovascular alterations associated to low brain derived neurotrophic factor.

After social stress, rats become vulnerable to depression, and this state is characterized by persistent low blood levels of brain-derived neurotrophic factor (BDNF). The aim of this study was to determine whether low BDNF levels are associated with long term autonomic changes. Defeated animals were subjected to four daily episodes of social defeats. Twenty five days later, defeated rats with low BDNF levels (Dlow) still displayed elevated sympathetic tone (as indicated by an elevated low frequency to high frequency ratio (LF/HF) in heart rate) and elevated blood pressure, as well as reduced baroreflex sensitivity (BRS). In contrast, those with higher BDNF levels (Dhigh) similar to controls, did not. Dlow animals persistent cardiovascular changes were abolished by acute inhibition of the dorsomedial nucleus of the hypothalamus (DMH). These cardiovascular changes were also prevented by chronic sub-cutaneous osmotic infusion of losartan, an angiotensin II type 1 receptor (AT1) receptor antagonist, started immediately after social defeat. In conclusion, the results show that greater vulnerability to stress consequences following a traumatic event is associated with an elevated LF/HF ratio, a persistent high blood pressure and a low BRS, all due to an AT1 receptor activation.

Low ß2 Main Peak Frequency in the Electroencephalogram Signs Vulnerability to Depression.

Objective: After an intense and repeated stress some rats become vulnerable to depression. This state is characterized by persistent low serum BDNF concentration. Our objective was to determine whether electrophysiological markers can sign vulnerability to depression. Methods: Forty-three Sprague Dawley rats were recorded with supradural electrodes above hippocampus and connected to wireless EEG transmitters. Twenty-nine animals experienced four daily social defeats (SD) followed by 1 month recovery. After SD, 14 rats had persistent low serum BDNF level and were considered as vulnerable (V) while the 15 others were considered as non-vulnerable (NV). EEG signals were analyzed during active waking before SD (Baseline), just after SD (Post-Stress) and 1 month after SD (Recovery). Results: We found that V animals are characterized by higher high θ and α spectral relative powers and lower ß2 main peak frequency before SD. These differences are maintained at Post-Stress and Recovery for α spectral relative powers and ß2 main peak frequency. Using ROC analysis, we show that low ß2 main peak frequency assessed during Baseline is a good predictor of the future state of vulnerability to depression. Conclusion: Given the straightforwardness of EEG recordings, these results open the way to prospective studies in humans aiming to identify population at-risk for depression.

Normal pulmonary capillary blood volume in patients with chronic infiltrative lung disease and high pulmonary artery pressure.

STUDY OBJECTIVES: Pulmonary capillary blood volume (Qc), a component of diffusing capacity of the lung for carbon monoxide (Dlco), is increased in postcapillary pulmonary hypertension due to valve disease, but is decreased in primitive and thromboembolic pulmonary hypertension. This study was performed to evaluate which way pulmonary Qc is affected in patients with chronic infiltrative lung disease according to the value of systolic pulmonary artery pressure (SPAP). PATIENTS AND METHODS: Twenty-four patients who were nonsmokers and had chronic infiltrative lung disease secondary to connective tissue disease (12 patients), asbestosis (1 patient), sarcoidosis (5 patients), or of unknown origin (6 patients), and 8 control subjects underwent pulmonary function tests and Doppler echocardiography. MEASUREMENTS AND RESULTS: Total lung capacity, alveolar-arterial oxygen pressure difference, Dlco, and conductance of the alveolar-capillary membrane (Dm) did not differ between patients with low SPAP (LPAP) [ie, < 30 mm Hg] or high SPAP (HPAP). Patients with LPAP, but not HPAP, experienced significant decreases in pulmonary Qc, whatever the cause of the disease. There was a strong positive correlation between SPAP and Qc scaled by Dm to account for infiltrative disease severity (r = 0.68; p < 0.001). CONCLUSIONS: We thus conclude that pulmonary Qc is not decreased as expected in patients with chronic infiltrative lung disease and high pulmonary artery pressure. A high Qc/Dm ratio should encourage the physician to look for HPAP compatible with pulmonary hypertension, whatever the etiology of lung infiltrative disease.

Altered circadian patterns of salivary cortisol in low-functioning children and adolescents with autism.

BACKGROUND: Reports of higher stress responsivity, altered sleep-wake cycle and a melatonin deficit in autism have stimulated interest in the cortisol circadian rhythm in individuals with autism. METHODS: The study was conducted on 55 low-functioning children and adolescents with autism (11.3 ± 4.1 years-old) and 32 typically developing controls (11.7 ± 4.9 years-old) matched for age, sex and puberty. Behavioral assessment was performed using the Autism Diagnostic Observation Schedule (ADOS). Salivary samples for measurement of cortisol were collected during a 24-h period (at least 0800 h-Day 1, 1600 h, 0800 h-Day 2 for 46 individuals with autism and 27 controls, and 0800 h-Day 1, 1100 h, 1600 h, 2400 h, 0800 h-Day 2 for 13 individuals with autism and 20 controls). Overnight (2000 h-0800 h) urinary cortisol excretion was also measured. RESULTS: The autism group displayed significantly higher levels of salivary cortisol at all time-points, flatter daytime and nighttime slopes, higher 0800 h cortisol levels on Day 2 compared to Day 1, and greater variances of salivary and urinary cortisol. There was a significant relationship between salivary cortisol levels and impairments in social interaction and verbal language. Overnight urinary cortisol excretion was similar in the autism and control groups. CONCLUSION: Anticipation of the stressful collection procedure appears to contribute to the higher 0800 h-Day 2 versus 0800 h-Day 1 salivary cortisol levels in autism. This sensitization to stressors might be as, or even more, important clinically than exposure to novelty in autism. The similar group means for overnight urinary cortisol excretion indicate that basal HPA axis functioning is unaltered in low-functioning autism. The elevated salivary cortisol levels observed in autism over the 24-h period in a repeated stressful condition, flattened diurnal cortisol patterns and the apparent effect of anticipation are consistent with prior findings in high trait anxiety.

Long-term (up to 20 years) effects of 50-Hz magnetic field exposure on immune system and hematological parameters in healthy men.

OBJECTIVES: The relationship between exposure to 50-Hz magnetic fields and human health is of increasing interest since associations have been found in brain cancer in adults and childhood leukemia. In this study we investigate the possible chronic (up to 20 years) effects of exposure to magnetic fields in humans. DESIGN AND METHODS: We examined the nocturnal profiles of red blood cells, hemoglobin, hematocrit, platelets, mean platelet volume, total white blood cells, lymphocytes, monocytes, eosinophils, basophils, neutrophils, Ig (Immunoglobulin) A, IgM, IgG, CD (cluster of differentiation) 3, CD4, CD8, natural killer cells, B cells, total CD28, CD8+ CD28+, activated T cells, interleukin (IL)-2, IL-6, and IL-2 receptor, in 15 men exposed chronically and daily for a period of 1-20 years, in the workplace and at home, to a 50-Hz magnetic field. The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 µT. The results are compared to those of 15 unexposed men age-matched, with the same synchronization and physical activity that served as controls (individual exposures ranged from 0.004 to 0.092 µT). Blood samples were taken hourly from 20:00 h to 08:00 h. RESULTS: Exposure over a long period and on a daily basis to magnetic fields resulted in no changes in the levels or patterns of hematological and immune system variables. CONCLUSIONS: Our data show that a long-term exposure to 50-Hz magnetic fields does not affect the hematological and immune system functions or their profile in healthy men, at least for the variables studied, and suggest that magnetic fields have no cumulative effects on these functions.

Long-term (up to 20 years) effects of 50-Hz magnetic field exposure on blood chemistry parameters in healthy men.

OBJECTIVES: The potential effects of a chronic exposure to magnetic fields on blood chemistry in humanswere tested. DESIGN: We examined the nocturnal profiles and levels of the following blood parameters: electrolytes (sodium, potassium, chloride, calcium, magnesium, phosphorus), nonprotein nitrogenous compounds (uric acid, urea, creatinine), and glucose, in 15 men (38.0 ± 0.9 years) exposed chronically and daily for a period of 1-20 years, in the workplace and at home, to a 50-Hz magnetic field in search of any cumulative effect from those chronic conditions of exposure. The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 µT. The results are compared to those obtained in our control group: 15 unexposed men of similar age (39.4 ± 1.2 years), with the same synchronization and physical activity that served as controls (individual exposures ranged from 0.004 to 0.092 µT). Blood samples were taken hourly from 20:00 h to 08:00 h. RESULTS: This work shows that subjects exposed over a long period (up to 20 years) and on a daily basis to magnetic fields experienced significant changes in serum sodium, chloride, phosphorus and glucose where an effect for field-hour interaction was noted for exposures greater than 0.3 µT. CONCLUSION: Our data suggest that long-term exposure to 50-Hzmagnetic fields (exposure>0.3 µT) in healthy men could induce some biological modifications of certain blood parameters, though their clinical relevance needs further investigation.

Day and nighttime excretion of 6-sulphatoxymelatonin in adolescents and young adults with autistic disorder.

BACKGROUND: Several reports indicate that nocturnal production of melatonin is reduced in autism. Our objective was to examine whether melatonin production is decreased during the whole 24-h cycle, whether the melatonin circadian rhythm is inverted, and whether the reduction in melatonin production is related to the severity of autistic behavioral impairments. METHOD: Day and nighttime urinary excretion of 6-sulphatoxymelatonin (6-SM) was examined during a 24-h period in post-pubertal individuals with autism (N=43) and typically developing controls (N=26) matched for age, sex and pubertal stage. RESULTS: Low 6-SM excretion (mean ± SEM) was observed in autism, both at daytime (0.16 ± 0.03 vs. 0.36 ± 0.05 µg/h, p<0.01), nighttime (0.52 ± 0.07 vs. 1.14 ± 0.23 µg/h, p<0.05), and during 24h (8.26 ± 1.27 vs. 18.00 ± 3.43 µg/24-h collection, p<0.001). Intra-individual nighttime-daytime differences (delta values) in 6-SM excretion were smaller in individuals with autism than in controls (0.36 ± 0.07 vs. 0.79 ± 0.23 µg/h, p<0.05). Nocturnal excretion of 6-SM was negatively correlated with autism severity in the overall level of verbal language (Spearman ρ=-0.30, p<0.05), imitative social play (Spearman ρ=-0.42, p<0.05), and repetitive use of objects (Spearman ρ=-0.36, p<0.05). CONCLUSION: A deficit in melatonin production is present both at daytime and at nighttime in individuals with autism, particularly in the most severely affected individuals. These results highlight interest in potential therapeutic uses of melatonin in autistic disorder, especially in individuals with severe autistic impairment and/or low urinary 6-SM excretion.

Twenty-four-hour profiles of urinary excretion of calcium, magnesium, phosphorus, urea, and creatinine in healthy prepubertal boys.

OBJECTIVES: Available data on 24-h urinary solute excretion in healthy children are sparse. We thus documented the daily and overnight variations of urinary electrolytes (calcium, magnesium, and phosphorus), urea, and creatinine in prepubertal (Tanner stage I) boys. DESIGN AND METHODS: Nine voluntary healthy prepubertal boys aged 10.8+/-0.11 years participated in this study. Concentrations of variables were quantified in daytime samples (collected between 07:00 h+/-30 min and 21:00 h+/-30 min) and nighttime samples (collected between 21:00 h+/-30 min and 07:00 h+/-30 min) in spring, during a period of 24-h every 3 h. RESULTS: Significant differences were found between daytime and nighttime excretion of calcium (p<0.05), magnesium (p<0.001), phosphorus (p<0.01), and urea (p<0.05), with high concentrations during the night. The 24-h solute/creatinine ratio was 0.072+/-0.008 mg/mg for calcium, 0.069+/-0.008 mg/mg for magnesium, 0.698+/-0.070 mg/mg for phosphorus, and 0.017+/-0.001 g/mg for urea. Statistically significant correlation analyses showed that urea and creatinine were positively associated with body mass index (BMI) (R=0.790, p=0.0113 for urea; R=0.889, p=<0.0013 for creatinine) and weight (R=0.717, p=0.0297 for urea; R=0.978, p=<0.001 for creatinine). The other urinary variables were independent of BMI and body mass. CONCLUSION: These data are of interest for the diagnosis of certain renal disease in prepubertal children.

Magnetic fields and the melatonin hypothesis: a study of workers chronically exposed to 50-Hz magnetic fields.

Because epidemiological studies report clinical disorders (mainly neurobehavioral alterations and/or cancer) that may be related to diminished melatonin secretion or to changes in its circadian rhythm in subjects living or working in environments exposed to magnetic fields, research on the effects of these fields in humans is particularly important. In this study, we examine the circadian rhythm of melatonin in 15 men exposed chronically and daily for a period of 1-20 yr, in the workplace and at home, to a 50-Hz magnetic field in search of any cumulative effect from those chronic conditions of exposure. The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 microT. The results are compared with those for 15 unexposed men who served as controls (individual exposures ranged from 0.004 to 0.092 microT). Blood samples were taken hourly from 2000 to 0800. Nighttime urine was also collected and analyzed. This work shows that subjects exposed over a long period (up to 20 yr) and on a daily basis to magnetic fields experienced no changes in their plasma melatonin level, their urinary 6-sulfatoxymelatonin level, or the circadian rhythm of melatonin. Our data strongly suggest that magnetic fields do not have cumulative effects on melatonin secretion in humans and thus clearly rebut the "melatonin hypothesis" that a decrease in plasma melatonin concentration (or a disruption in its secretion) explains the occurrence of clinical disorders or cancers possibly related to magnetic fields.