Cholinergic Signaling Exerts Protective Effects in Models of Sympathetic Hyperactivity-Induced Cardiac Dysfunction

Cholinergic control of the heart is exerted by two distinct branches; the autonomic component represented by the parasympathetic nervous system, and the recently described non-neuronal cardiomyocyte cholinergic machinery. Previous evidence has shown that reduced cholinergic function leads to deleterious effects on the myocardium. Yet, whether conditions of increased cholinergic signaling can offset the pathological remodeling induced by sympathetic hyperactivity, and its consequences for these two cholinergic axes are unknown. Here, we investigated two models of sympathetic hyperactivity: i) the chronic beta-adrenergic receptor stimulation evoked by isoproterenol (ISO), and ii) the alpha(2A)/alpha(2C)-drenergic receptor knockout (KO) mice that lack pre-synaptic adrenergic receptors. In both models, cholinergic signaling was increased by administration of the cholinesterase inhibitor, pyridostigmine. First, we observed that isoproterenol produces an autonomic imbalance characterized by increased sympathetic and reduced parasympathetic tone. Under this condition transcripts for cholinergic proteins were upregulated in ventricular myocytes, indicating that non-neuronal cholinergic machinery is activated during adrenergic overdrive. Pyridostigmine treatment prevented the effects of ISO on autonomic function and on the ventricular cholinergic machinery, and inhibited cardiac remodeling. alpha(2A)/alpha(2C)-KO mice presented reduced ventricular contraction when compared to wild-type mice, and this dysfunction was also reversed by cholinesterase inhibition. Thus, the cardiac parasympathetic system and non-neuronal cardiomyocyte cholinergic machinery are modulated in opposite directions under conditions of increased sympathetic drive or ACh availability. Moreover, our data support the idea that pyridostigmine by restoring ACh availability is beneficial in heart disease

Murine model to study brain, behavior and immunity during hepatic encephalopathy

AIM: To propose an alternative model of hepatic encephalopathy (HE) in mice, resembling the human features of the disease. METHODS: Mice received two consecutive intraperitoneal injections of thioacetamide (TAA) at low dosage (300 mg/kg). Liver injury was assessed by serum transaminase levels (ALT) and liver histology (hematoxylin and eosin). Neutrophil infiltration was estimated by confocal liver intravital microscopy. Coagulopathy was evaluated using prolonged prothrombin and partial thromboplastin time. Hemodynamic parameters were measured through tail cuff. Ammonia levels were quantified in serum and brain samples. Electroencephalography (EEG) and psychomotor activity score were performed to show brain function. Brain edema was evaluated using magnetic resonance imaging. RESULTS: Mice submitted to the TAA regime developed massive liver injury, as shown by elevation of serum ALT levels and a high degree of liver necrosis. An intense hepatic neutrophil accumulation occurred in response to TAA-induced liver injury. This led to mice mortality and weight loss, which was associated with severe coagulopathy. Furthermore, TAA-treated mice presented with increased serum and cerebral levels of ammonia, in parallel with alterations in EEG spectrum and discrete brain edema, as shown by magnetic resonance imaging. In agreement with this, neuropsychomotor abnormalities ensued 36 h after TAA, fulfilling several HE features observed in humans. In this context of liver injury and neurological dysfunction, we observed lung inflammation and alterations in blood pressure and heart rate that were indicative of multiple organ dysfunction syndrome. CONCLUSION: In summary, we describe a new murine model of hepatic encephalopathy comprising multiple features of the disease in humans, which may provide new insights for treatment.status: publishe

Increased cholinergic signaling improves cardiac function in mice with sympathetic hyperactivity-induced heart failure.

<p><b>A–B</b>. Percentage increase in left ventricular ejection fraction and fractional shortening measured by echocardiography. Systolic tension (<b>C</b>) and cardiomyocyte shortening (<b>D</b>) measurements were performed in WT and α_2A/α_2C-KO mice treated or not with pyridostigmine. Cholinesterase inhibition therapy restored cardiac function and and cellular contractile function of α_2A/α_2C–KO mice to control levels. *p<0.05 when compared to WT and α_2A/α_2C–KO/PYR.</p

Echocardiographic parameters.

<p>Echocardiographic measurements of cardiac parameters in rats following isoproterenol injection for 7 days. Pyridostigmine treatment of ISO-rats attenuated the development of cardiac remodeling induced by isoproterenol. n = number of rats analysed in each experimental group.</p><p>* = p<0.05 versus CT,</p><p>& = p<0.05 versus ISO,</p><p># = p<0.05 versus ISO+PYR.</p