Regional innervation of the heart in the goldfish, Carassius auratus: A confocal microscopy study

Abstract

The intracardiac nervous system represents the final common pathway for autonomic control of the vertebrate heart in maintaining cardiovascular homeostasis. In teleost fishes, details of the organization of this system are not well understood. Here we investigated innervation patterns in the heart of the goldfish, a species representative of a large group of cyprinids. We used antibodies against the neuronal markers zn-12, acetylated tubulin, and human neuronal protein C/D, as well as choline acetyltransferase, tyrosine hydroxylase, nitric oxide synthetase, and vasoactive intestinal polypeptide (VIP) to detect neural elements and their transmitter contents in wholemounts and sections of cardiac tissue. All chambers of the heart were innervated by choline acetyltransferase-positive axons, implying cholinergic regulation; and by tyrosine hydroxylase-containing axons, implying adrenergic regulation. The mean total number of intracardiac neurons was 713 ± 78 (SE), nearly half of which were cholinergic. Neuronal somata were mainly located in a ganglionated plexus around the sinoatrial valves. Somata were contacted by cholinergic, adrenergic, nitrergic, and VIP-positive terminals. Putative pacemaker cells, identified by immunoreactivity for hyperpolarization activated, cyclic nucleotide-gated channel 4, were located in the base of the sinoatrial valves, and this region was densely innervated by cholinergic and adrenergic terminals. We have shown that the goldfish heart possesses the necessary neuroanatomical substrate for fine, region-by-region autonomic control of the myocardial effectors that are involved in determining cardiac output.

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

“…The general procedures used for immunohistochemistry in this study were similar to those we have described in previous publications on cyprinid neuroanatomy (Finney et al, 2006;Robertson et al, 2008;Dumbarton et al, 2010;Newton et al, 2014). Briefly, fixed tissues were rinsed in PBS; transferred to a PBS solution containing 2% Triton X-100 (X100; Sigma Aldrich), 1% bovine serum albumin (BSA; A9576; Sigma Aldrich), and 1% normal goat serum (NGS; G9023; Sigma Aldrich) for 48 hours at 4 C with agitation; and then incubated with primary antibodies (see below for descriptions).…”

“…To begin addressing this issue we recently investigated the neuroanatomy of the ICNS in the goldfish (Newton et al, 2014). This study provided, for the first time in any teleost species, details of the general innervation pattern, the neurotransmitter phenotypes, and the distribution of axons and neuronal somata within the heart.…”

“…These authors also described the expression of the transcription factor Islet-1 (Isl1) in putative pacemaker cells. Newton et al (2014) used immunohistochemical methods in the goldfish heart to show that HCN4 channel protein is present in small cells in sinoatrial valve leaflets, an area that is richly innervated.…”

The temperature dependence of electrical excitability in fish hearts

“…In contrast to the elongated shape of the mammalian sinoatrial node, the sinoatrial tissue of most fish hearts is a ring-shaped aggregation of cardiac myocytes (Laurent, 1962;Haverinen and Vornanen, 2007;Zaccone et al, 2010;Tessadori et al, 2012;Newton et al, 2014) (Fig. 1).…”

Effects of prolonged anoxia on electrical activity of the heart in Crucian carp (Carassius carassius)

“…In fish, the rate and rhythm of the heartbeat are determined by spontaneous activity of the ring-shaped pacemaker tissue at the border zone between the sinus venosus and the atrium (Yamauchi and Burnstock, 1968;Saito, 1969;Haverinen and Vornanen, 2007;Newton et al, 2014); a fast propagating atrial action potential (AP) provokes atrial systole. Impulse transmission is delayed at the atrioventricular canal to allow sufficient time for ventricular filling, before a fast propagating AP occurs and contraction is elicited in the ventricular wall (Saito and Tenma, 1976;Sedmera et al, 2003).…”