Molecular and functional characterization of the mouse intracardiac nervous system

Background: The intracardiac nervous system (ICNS) refers to clusters of neurons, located within the heart, that participate to the neuronal regulation of cardiac functions and are involved in the initiation of cardiac arrhythmias. Therefore, deciphering the role of the ICNS in cardiac physiology and physiopathology is mandatory. Whereas transgenic mouse models represent powerful tools to reach this goal, the mouse ICNS is still poorly characterized. Objective: The objective of the present study was to provide a phenotypic, electrophysiological and pharmacological characterization of the mouse ICNS. Methods: Global cardiac innervation and phenotypic diversity was investigated by performing immunohistochemistry on cleared murine heart and on tissue sections. Patch clamp technique was used for electrophysiological and pharmacological characterization of isolated mouse intracardiac neurons. Results: We identified the expression of 7 distinct neuronal markers within mouse intracardiac neurons demonstrating the neurochemical diversity of this network. Of note, we described for the first time in mouse, the existence of neuron expressing the calcium binding protein calbindin, the neuropeptide Y (NPY) and the cocain and amphetamine regulated transcript (CART) peptide. Electrophysiological studies also revealed the existence of two different neuronal population based on their electrical behavior. Finally, we demonstrated that these neurons can be modulated by several neuromodulators. Conclusion: This study demonstrated that mouse ICNS shares similar molecular and functional complexity to that of other species and therefore is a suitable model to decipher the role of individual neuronal subtypes in the modulation of cardiac function and in the initiation of cardiac arrhythmias.

LPS immune challenge reduces arcuate nucleus TSHR and CART mRNA and elevates plasma CART peptides

Background The aim was to examine the impact of lipopolysaccharide-induced systemic inflammation on expression of mRNA for cocaine- and amphetamine-regulated transcript (CART) and the thyrotropin receptor (TSHR) and its ligands in CNS areas of relevance for feeding controls and metabolism. Lipopolysaccharide effects on plasma levels of TSH and CART peptides were also examined. Methods Lipopolysaccharide (150–200 μg/mouse) was injected in C57BL/6J mice and tissue and plasma samples taken after 24 h. To establish if plasma increase in CART peptide levels were prostanoid dependent, indomethacin was given via the drinking water beginning 48 h prior to LPS. We evaluated mRNA expression for CART, TSHR, TSHβ, and thyrostimulin in brain and pituitary extracts. Plasma levels of TSH, CARTp, and serum amyloid P component were analyzed by ELISA. Results Lipopolysaccharide suppressed TSHR mRNA expression in the arcuate nucleus and the pituitary. CART mRNA expression was reduced in the arcuate nucleus but elevated in the pituitary of mice treated with Lipopolysaccharide, whereas plasma TSH remained unchanged. Plasma CART peptide concentration increased after LPS treatment in a prostanoid-independent manner, and CART peptide levels correlated positively to degree of inflammation. Conclusions Our findings suggest that central and peripheral CART is affected by acute inflammation. Considering the role of the arcuate nucleus in feeding controls, our data highlight TSHR and CART as putative neuroendocrine signaling components that respond to inflammation, perhaps to maintain weight and metabolic homeostasis during states of disease.