Excitatory effect of bradykinin on intrinsic neurons of the rat heart

Peptides Isolated from Amphibian Skin Secretions with Emphasis on Antimicrobial Peptides

The skin of amphibians is a tissue with biological functions, such as defense, respiration, and excretion. In recent years, researchers have discovered a large number of peptides in the skin secretions of amphibians, including antimicrobial peptides, antioxidant peptides, bradykinins, insulin-releasing peptides, and other peptides. This review focuses on the origin, primary structure, secondary structure, length, and functions of peptides secreted from amphibians' skin. We hope that this review will provide further information and promote the further study of amphibian skin secretions, in order to provide reference for expanding the research and application of amphibian bioactive peptides.

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, which participate to the neuronal regulation of cardiac functions and which are involved in the initiation of cardiac arrhythmias. Therefore, deciphering its role in cardiac physiology and physiopathology is mandatory.

OBJECTIVE

The aim of this study is to provide a phenotypic, electrophysiological and pharmacological characterization of the mouse ICNS, which is still poorly characterized.

METHODS

Global cardiac innervation and phenotypic diversity were investigated using 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 have identified the expression of seven distinct neuronal markers within mouse ICNS, thus proving the neurochemical diversity of this network. Of note, it was the first time that the existence of neurons expressing the calcium binding protein calbindin, the neuropeptide Y (NPY) and the cocain and amphetamine regulated transcript (CART) peptide, was described in the mouse. Electrophysiological studies also revealed the existence of four different neuronal populations based on their electrical behavior. Finally, we showed that these neurons can be modulated by several neuromodulators.

CONCLUSION

This study showed that mouse ICNS presents a molecular and functional complexity similar to other species, and is therefore a suitable model to decipher the role of individual neuronal subtypes regarding the modulation of cardiac function and the initiation of cardiac arrhythmias.

Involvement of TRPC5 channels, inwardly rectifying K+ channels, PLCβ and PIP2 in vasopressin-mediated excitation of medial central amygdala neurons

KEY POINTS

Activation of V_1a vasopressin receptors facilitates neuronal excitability in the medial nucleus of central amygdala (CeM) V_1a receptor activation excites about 80% CeM neurons by opening a cationic conductance and about 20% CeM neurons by suppressing an inwardly rectifying K⁺ (Kir) channel The cationic conductance activated by V_1a receptors is identified as TRPC5 channels PLCβ-mediated depletion of PIP₂ is involved in V_1a receptor-elicited excitation of CeM neurons Intracellular Ca²⁺ release and PKC are unnecessary for V_1a receptor-mediated excitation of CeM neurons ABSTRACT: Arginine vasopressin (AVP) serves as a hormone in the periphery to modulate water homeostasis and a neuromodulator in the brain to regulate a diverse range of functions including anxiety, social behaviour, cognitive activities and nociception. The amygdala is an essential brain region involved in modulating defensive and appetitive behaviours, pain and alcohol use disorders. Whereas activation of V_1a receptors in the medial nucleus of the central amygdala (CeM) increases neuronal excitability, the involved ionic and signalling mechanisms have not been determined. We found that activation of V_1a receptors in the CeM facilitated neuronal excitability predominantly by opening TRPC5 channels, although AVP excited about one fifth of the CeM neurons via suppressing an inwardly rectifying K⁺ (Kir) channel. G proteins and phospholipase Cβ (PLCβ) were required for AVP-elicited excitation of CeM neurons, whereas intracellular Ca²⁺ release and the activity of protein kinase C were unnecessary. Prevention of the depletion of phosphatidylinositol 4,5-bisphosphate (PIP₂ ) blocked AVP-induced excitation of CeM neurons, suggesting that PLCβ-mediated depletion of PIP₂ is involved in AVP-mediated excitation of CeM neurons. Our results may provide a cellular and molecular mechanism to explain the anxiogenic effects of AVP in the amygdala.

Functional plasticity of cardiac efferent neurons contributes to traumatic brain injury-induced cardiac autonomic dysfunction

Traumatic brain injury (TBI) frequently causes cardiac autonomic dysfunction (CAD), irrespective of its severity, which is associated with an increased morbidity and mortality in patients. Despite the significance of probing the cellular mechanism underlying TBI-induced CAD, animal studies on this mechanism are lacking. In the current study, we tested whether TBI-induced CAD is associated with functional plasticity in cardiac efferent neurons. In this regard, TBI was induced by a controlled cortical impact in rats. Assessment of heart rate variability and baroreflex sensitivity indicated that CAD was developed in the sub-acute period after moderate and severe TBI. The cell excitability was increased in the stellate ganglion (SG) neurons and decreased in the intracardiac ganglion (ICG) neurons in TBI rats, compared with the sham-operated rats. The transient A-type K+ (KA) currents, but not the delayed rectifying K+ currents were significantly decreased in SG neurons in TBI rats, compared with sham-operated rats. Consistent with these electrophysiological data, the transcripts encoding the Kv4 α subunits were significantly downregulated in SG neurons in TBI rats, compared with sham-operated rats. TBI causes downregulation and upregulation of M-type K+ (KM) currents and the KCNQ2 mRNA transcripts, which may contribute to the hyperexcitability of the SG neurons and the hypoexcitability of the ICG neurons, respectively. In conclusion, the key cellular mechanism underlying the TBI-induced CAD may be the functional plasticity of the cardiac efferent neurons, which is caused by the regulation of the KA and/or KM currents.

Histamine depolarizes rat intracardiac ganglion neurons through the activation of TRPC non-selective cation channels

The cardiac plexus, which contains parasympathetic ganglia, plays an important role in regulating cardiac function. Histamine is known to excite intracardiac ganglion neurons, but the underlying mechanism is obscure. In the present study, therefore, the effect of histamine on rat intracardiac ganglion neurons was investigated using perforated patch-clamp recordings. Histamine depolarized acutely isolated neurons with a half-maximal effective concentration of 4.5 μM. This depolarization was markedly inhibited by the H₁ receptor antagonist triprolidine and mimicked by the H₁ receptor agonist 2-pyridylethylamine, thus implicating histamine H₁ receptors. Consistently, reverse transcription-PCR (RT-PCR) and Western blot analyses confirmed H₁ receptor expression in the intracardiac ganglia. Under voltage-clamp conditions, histamine evoked an inward current that was potentiated by extracellular Ca²⁺ removal and attenuated by extracellular Na⁺ replacement with N-methyl-D-glucamine. This implicated the involvement of non-selective cation channels, which given the link between H₁ receptors and G_q/11-protein-phospholipase C signalling, were suspected to be transient receptor potential canonical (TRPC) channels. This was confirmed by the marked inhibition of the inward current through the pharmacological disruption of either G_q/11 signalling or intracellular Ca²⁺ release and by the application of the TRPC blockers Pyr3, Gd³⁺ and ML204. Consistently, RT-PCR analysis revealed the expression of several TRPC subtypes in the intracardiac ganglia. Whilst histamine was also separately found to inhibit the M-current, the histamine-induced depolarization was only significantly inhibited by the TRPC blockers Gd³⁺ and ML204, and not by the M-current blocker XE991. These results suggest that TRPC channels serve as the predominant mediator of neuronal excitation by histamine.