Comparación de Algoritmos Lineales y no Lineales para la Detección del Desacoplamiento Cardiorrespiratorio en Ratas Endotoxémicas / Comparison of Linear and Nonlinear Algorithms for Detection of Cardiorespiratory Uncoupling in Endotoxemic Rats

Resumen En estudios previos se ha demostrado que la endotoxemia inducida por lipopolisacárido (LPS) produce un desacoplamiento cardiorrespiratorio (CRP) debido a los efectos fisiológicos de la inflamación sistémica. Adicionalmente se sabe que la oxitocina tiene efectos antiinflamatorios y propiedades cardioprotectoras; sin embargo, se desconoce si ésta modifica el acoplamiento CRP. El objetivo del presente estudio fue comparar diferentes métodos matemáticos lineales y no lineales para la detección del desacoplamiento cardiorrespiratorio entre series de tiempo cardiacas y respiratorias. Se estudiaron series de tiempo R-R obtenidas de electrocardiogramas de grupos de roedores macho a los cuales se les administró solución salina o vehículo (V); lipopolisacárido (LPS); oxitocina (O) y LPS + oxitocina (LPS+Ox). Las series R-R y respiratorias derivadas del electrocardiograma (EDR) se analizaron en conjunto para cuantificar su grado de acoplamiento a través de las técnicas de correlación cruzada; entropía muestral cruzada; entropía condicional; información mutua; e información mutua de Rényi para los cuatro grupos. Se observó que la oxitocina no parece favorecer el acoplamiento CRP durante la endotoxemia inducida por LPS. Finalmente, se encontró que la entropía muestral cruzada y la entropía condicional presentaron las mayores diferencias estadísticas para identificar el desacoplamiento CRP producido por el LPS.

Abstract Previous studies have shown that LPS-induced endotoxemia causes a cardiorespiratory (CRP) uncoupling owing to the physiological effects of systemic inflammation. Also, it is known that oxytocin has anti-inflammatory effects and cardioprotective properties; however, it is unknown whether it can modify the CRP coupling. This study aimed to compare different linear and nonlinear mathematics methods for the detection of cardiorespiratory uncoupling between cardiac and respiratory time series. The R-R time series of electrocardiograms of male rodents that were administered with saline solution (V); lipopolysaccharide (LPS); oxytocin (O) and LPS + oxytocin (LPS + Ox) were studied. We tested the R-R and respiratory series derived from the electrocardiogram (EDR) for the four groups to quantify the degree of coupling with cross-correlation; cross sample entropy; conditional entropy; mutual information; and Rényi's mutual information. We found that oxytocin does not seem to favor the CRP coupling during endotoxemia induced by LPS. Finally, we observed that the cross-sample entropy and the conditional entropy presented the highest statistical differences to identify the CRP uncoupling produced by LPS.

Vagal afferents mediate early satiation and prevent flavour avoidance learning in response to intraperitoneally infused exendin-4.

Glucagon-like peptide-1 receptor (GLP-1R) agonists such as exendin-4 (Ex-4) affect eating and metabolism and are potential candidates for treating obesity and type II diabetes. In the present study, we tested whether vagal afferents mediate the eating-inhibitory and avoidance-inducing effects of Ex-4. Subdiaphragmatic vagal deafferentation (SDA) blunted the short-term (< 1 h) but not long-term eating-inhibitory effect of i.p.-infused Ex-4 (0.1 µg/kg) in rats. A dose of 1 µg/kg Ex-4 reduced 0.5, 1, 2 and 4 h cumulative food intake in SDA and sham-operated rats to a similar extent. Paradoxically, SDA but not sham rats developed a conditioned flavour avoidance (CFA) after i.p. Ex-4 (0.1 µg/kg). SDA completely blunted the induction of c-Fos expression by Ex-4 in the hypothalamic paraventricular nucleus. Ex-4, however, increased the number of c-Fos expressing cells, independent of intact vagal afferents, in the nucleus accumbens and in the central nucleus of the amygdala, the lateral external parabrachial nucleus, the caudal ventrolateral medulla and the dorsal vagal complex. These data suggest that intact vagal afferents are only necessary for the full expression of the early satiating effect of Ex-4 but not for later eating-inhibitory actions, when circulating Ex-4 might reach the brain via the circulation. Our data also dissociate the satiating and avoidance-inducing effects of the low Ex-4 dose tested under our conditions and suggest that vagal afferent signalling may protect against the development of CFA. Taken together, these findings reveal a complex role of vagal afferents in mediating the effects of GLP-1R activation on ingestive behaviour.

Hepatic-portal vein infusions of glucagon-like peptide-1 reduce meal size and increase c-Fos expression in the nucleus tractus solitarii, area postrema and central nucleus of the amygdala in rats.

We recently reported that brief, remotely controlled intrameal hepatic-portal vein infusions of glucagon-like peptide-1 (GLP-1) reduced spontaneous meal size in rats. To investigate the neurobehavioural correlates of this effect, we equipped male Sprague-Dawley rats with hepatic-portal vein catheters and assessed (i) the effect on eating of remotely triggered infusions of GLP-1 (1 nmol/kg, 5 min) or vehicle during the first nocturnal meal after 3 h of food deprivation and (ii) the effect of identical infusions performed at dark onset on c-Fos expression in several brain areas involved in the control of eating. GLP-1 reduced (P < 0.05) the size of the first nocturnal meal and increased its satiety ratio. Also, GLP-1 increased (P < 0.05) the number of c-Fos-expressing cells in the nucleus tractus solitarii, the area postrema and the central nucleus of the amygdala, but not in the arcuate or paraventricular hypothalamic nuclei. These data suggest that the nucleus tractus solitarii, the area postrema and the central nucleus of the amygdala play a role in the eating-inhibitory actions of GLP-1 infused into the hepatic-portal vein; it remains to be established whether activation of these brain nuclei reflect satiation, aversion, or both.

Weakened [corrected] taste-LPS association during endotoxin tolerance.

In naive individuals, the administration of bacterial lipopolysaccharide (LPS) provokes a rapid systemic increase in pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6, inducing an acute phase response including sickness behavior. Strong associative learning occurs when relevant gustatory/olfactory stimuli precede the activation of the immune system, affecting long-term individual food selection and nutritional strategies. Repeated LPS administration results in the development of an endotoxin tolerance status, characterized by a drastic reduction in the LPS-induced cytokine response. Here we investigated how the postprandial categorization of a relevant taste (0.2% saccharin) changed after administration of a high dose of LPS (0.5 mg/kg i.p.) in LPS-tolerant animals. Determination of the consummatory fluid intake revealed that, in contrast to LPS-naive rats, taste-LPS association did not occur during endotoxin tolerance. Ninety minutes after the single association trial, the plasma responses of TNF-alpha, IL-1beta and IL-6 were completely blunted in LPS-tolerant animals, which also resulted in low LPS-adipsogenic and LPS-anorexic effects. These findings indicate that an identical immune challenge can result in completely different neuro-behavioral consequences depending on the immune history of the individual, thus revealing part of the complex interconnection between the immune and neuro-endocrine systems in regulating food selection and consumption during the infectious process.

Behavioural endocrine immune-conditioned response is induced by taste and superantigen pairing.

Administration of bacterial superantigen, such as staphylococcal enterotoxin B (SEB), induces in vivo stimulation of T cell proliferation and cytokine production such as interleukin-2 (IL-2). It has been previously reported that SEB administration induces fever, c-Fos expression in the brain, and hypothalamus-pituitary-adrenal axis activation, demonstrating that the brain is able to sense and respond to SEB. Previously it had been shown that immune functions can be behaviourally conditioned pairing a novel gustatory stimulus together with an immunomodulatory drug or an antigen. We designed an experimental protocol using Dark Agouti rats in which saccharin taste, as conditioned stimulus, was paired with an i.p. injection of SEB (2 mg/kg), as unconditioned stimulus. Six days later, when conditioned animals were re-exposed to the conditioned stimulus they displayed strong conditioned taste avoidance to the saccharin. More importantly, re-exposure to the conditioned stimulus significantly increased IL-2, interferon-gamma and corticosterone plasma levels, in comparison with conditioned animals which had not been re-exposed to saccharin taste. These results demonstrate a behavioural-immune-endocrine conditioned response using a superantigen as unconditioned stimulus. In addition, they illustrate the brain abilities to mimic the unconditioned effects of a superantigen by yet unknown mechanisms.