High-resolution mapping of sensory fibers at the healthy and post-myocardial infarct whole transgenic hearts.

The sensory nervous system is critical to maintain cardiac function. As opposed to efferent innervation, less is known about cardiac afferents. For this, we mapped the VGLUT2-expressing cardiac afferent fibers of spinal and vagal origin by using the VGLUT2::tdTomato double transgenic mouse as an approach to visualize the whole hearts both at the dorsal and ventral sides. For comparison, we colabeled mixed-sex transgenic hearts with either TUJ1 protein for global cardiac innervation or tyrosine hydroxylase for the sympathetic network at the healthy state or following ischemic injury. Interestingly, the nerve density for global and VGLUT2-expressing afferents was found significantly higher on the dorsal side compared to the ventral side. From the global nerve innervation detected by TUJ1 immunoreactivity, VGLUT2 afferent innervation was detected to be 15-25% of the total network. The detailed characterization of both the atria and the ventricles revealed a remarkable diversity of spinal afferent nerve ending morphologies of flower sprays, intramuscular endings, and end-net branches that innervate distinct anatomical parts of the heart. Using this integrative approach in a chronic myocardial infarct model, we showed a significant increase in hyperinnervation in the form of axonal sprouts for cardiac afferents at the infarct border zone, as well as denervation at distal sites of the ischemic area. The functional and physiological consequences of the abnormal sensory innervation remodeling post-ischemic injury should be further evaluated in future studies regarding their potential contribution to cardiac dysfunction.

Anatomical characterization of vagal nodose afferent innervation and ending morphologies at the murine heart using a transgenic approach.

Heart is an extensively innervated organ and its function is strictly coordinated by autonomic neural circuits. After pathological events such as myocardial infarction (MI), cardiac nerves undergo a structural and functional remodeling contributing to cardiac dysfunction. Although the efferent component of the cardiac nerves has been well described, sensory innervation of the heart has not been defined in detail. Considering its importance, comprehensive description of vagal afferent innervation on the whole heart would enable a better description of autonomic imbalances manifesting as sympathoexcitation and vagal withdrawal in post-ischemic states. To address this issue, we globally mapped the vagal nodose afferent fibers innervating the whole murine heart with unprecedented resolution. By using the Phox2b-Cre::tdTomato transgenic mouse line, we described the detailed distribution and distinct vagal sensory ending morphologies at both the dorsal and ventral sides of the mouse heart. By neural tracing analysis, we quantitated the distribution and prevalence of vagal afferent nerve fibers with varying diameters across dorsal and ventral surfaces of the heart. Moreover, we demonstrated that vagal afferents formed flower spray and end-net-like endings within the atria and ventricles. As distinct from the atria, vagal afferents formed intramuscular array-like endings within the ventricles. Furthermore, we showed that vagal afferents undergo structural remodeling by forming axonal sprouts around the infarct area in post-MI hearts. These findings improve our understanding of the potential effect of vagal afferent remodeling on autonomic imbalance and generation of cardiac arrhythmias and could prospectively contribute to the development of more effective neuromodulatory therapies.

Experimental data of labeling the heart and cardiac cultures with a retrograde tracer in vitro and in vivo.

Retrograde dyes are often used in basic research to investigate neuronal innervations of an organ. This article describes the experimental data on the application of retrograde dyes on the mouse heart in vivo and on the cardiac or neuronal cultures in vitro. By providing this information, cardiac or inneinnervations can be evaluated in vivo. Therefore, unknown cellular and molecular mechanisms and systemic interactions in the body can be investigated. In particular, we provided practical tips to lower mortality risks following the cardiac surgery and evaluated the staining capacity and fluorescent characteristics of the Di-8-ANEPPQ dye in the cardiac tissue and cell cultures. First, primary cultures of mouse nodose ganglia (NG) neurons and mouse neonatal cardiomyocytes were stained with Di-8-ANEPPQ. The Di-8-ANEPPQ signal from live cultures were visualized using spinning disk confocal microscopy to verify the lipophilic and fluorescent labeling capacity of Di-8-ANEPPQ. Next, the excitation and emission data of Di-8-ANEPPQ were collected between 415 nm and 690 nm using power spectrum module of confocal microscopy. This spectrum analysis could be useful for the researchers who plan to use Di-8-ANEPPQ in combination with other fluorescent dyes to eliminate any florescent overlap. In order to label the heart tissue with tracer dyes Di-8-ANEPPQ or DiI in vivo, the heart was exposed without damaging lungs or other tissues following anesthetization, then the retrograde dye was applied as a paste for DiI or injected to the apex of the heart for Di-8-ANEPPQ and the operation area was sutured. The surgical procedure required intubation to control the respiratory reflex without the need to perform a tracheotomy and yielded high viability. Following labeling the heart in vivo, the heart was dissected, and images of injection area were captured using confocal microscopy. All fluorescent images of Di-8-ANEPPQ labeled cells were analyzed by using the Fiji software. Overall, these data provide applicable data to other investigators to trace the sensory neurons innervating not only the heart but also other organs using Di-8-ANEPPQ. These data support the original research article titled "Evaluation of bilateral cardiac afferent distribution at the spinal and vagal ganglia by retrograde labeling" that was accepted for publication in Brain Research Journal [1].