Intrinsic and extrinsic innervation of the heart in zebrafish (Danio rerio)

Abstract

In the vertebrate heart the intracardiac nervous system is the final common pathway for autonomic control of cardiac output, but the neuroanatomy of this system is not well understood. In this study we investigated the innervation of the heart in a model vertebrate, the zebrafish. We used antibodies against acetylated tubulin, human neuronal protein C/D, choline acetyltransferase, tyrosine hydroxylase, neuronal nitric oxide synthase, and vasoactive intestinal polypeptide to visualize neural elements and their neurotransmitter content. Most neurons were located at the venous pole in a plexus around the sinoatrial valve; mean total number of cells was 197 ± 23, and 92% were choline acetyltransferase positive, implying a cholinergic role. The plexus contained cholinergic, adrenergic, and nitrergic axons and vasoactive intestinal polypeptide-positive terminals, some innervating somata. Putative pacemaker cells near the plexus showed immunoreactivity for hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) and the transcription factor Islet-1 (Isl1). The neurotracer neurobiotin showed that extrinsic axons from the left and right vagosympathetic trunks innervated the sinoatrial plexus proximal to their entry into the heart; some extrinsic axons from each trunk also projected into the medial dorsal plexus region. Extrinsic axons also innervated the atrial and ventricular walls. An extracardiac nerve trunk innervated the bulbus arteriosus and entered the arterial pole of the heart to innervate the proximal ventricle. We have shown that the intracardiac nervous system in the zebrafish is anatomically and neurochemically complex, providing a substrate for autonomic control of cardiac effectors in all chambers.

Zebrafish heart as a model to study the integrative autonomic control of pacemaker function

“…In a previous study (57), we described the basic structure of the ICNS in zebrafish, which is consistent with that of humans and other mammalian models (28,33,37,43,44). The isolated zebrafish heart thus has technical advantages that may be exploited to better understand the role of the ICNS in modulating chronotropy (57).…”

“…In zebrafish and mammalian species, HCN4 channels contribute a major portion of the diastolic depolarizing current in cardiac pacemaker cells (28,33,37,43,44). Immunohistochemical evi-dence also shows that juxta-pacemaker terminals contain the neurotransmitters acetylcholine (ACh; parasympathetic, cardio-inhibitory) and norepinephrine (NE; sympathetic, cardioexcitatory), providing the neuroeffector substrate for bidrectional autonomic control of pacemaker rate (57). At the atrioventricular region (AVR) a subpopulation of HCN4-expressing cells has been identified (57).…”

Distribution, Innervation, and Cellular Organization of Taste Buds in the Sea Catfish, <b><i>Plotosus japonicus</i></b>

“…These results are similar to those of a previous study utilizing scanning electron microscopy [Sakata et al, 2001]. To observe the innervation of the taste buds, we performed double immunohistochemistry with anti-calretinin and anti-acetylated tubulin antibodies; the later marks nerve fibers [Hagströme and Olsson, 2010;Stoyek et al, 2015]. Acetylated tubulinir nerve fibers formed polygonal networks bellow the barbel epithelium ( Fig.…”

Evidence for a role of heme oxygenase-1 in the control of cardiac function in zebrafish (Danio rerio) larvae exposed to hypoxia

“…However, there is no direct evidence as yet for the presence of HO-1 in the pacemaker cells of the mammalian heart. In zebrafish, the cardiac pacemaker cells are located at the sinoatrial boundary (Tessadori et al, 2012;Stoyek et al, 2015). In this study, we found evidence that HO-1 is located in the presumptive pacemaker cells of the developing zebrafish heart.…”