The organization of the cardiac ganglion of the axolotl (Ambystoma mexicanum)

Catecholamines are present in larval Xenopus laevis: a potential source for cardiac control

Changes in noradrenaline (NA), adrenaline (A), and dopamine (DA) levels in the heart, kidneys, and whole body (without heart and kidneys) during embryonic development were investigated in the frog, Xenopus laevis using high-performance liquid chromatography (HPLC). In addition, the presence of cells immunoreactive to tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and/or phenylethanolamine-N-methyltransferase (PNMT) in the heart of Xenopus larvae was investigated using immunohistochemical techniques. The presence of nerve fibers was visualized using antibodies against acetylated tubulin (AcT). NA and DA concentrations in the heart were low and steady in NF 40-56, showed an increased value at NF 57, and decreased again in froglets. A trend toward higher concentrations of A was observed at NF 43-49 and NF 57. Cells immunoreactive to TH, DBH, and PNMT were found in the heart from NF 40, and the TH immunoreactive cells became more abundant in the whole heart at later stages. The presence of catecholamines in the non-innervated larval heart together with the finding of TH/DBH/PNMT immunoreactive cells suggests that catecholamines are synthesized and stored in the heart and could therefore have a paracrine role in cardiac control in Xenopus larvae. Detectable concentrations of catecholamines were also found in kidneys and whole bodies (except heart and kidneys). Therefore, catecholamine-producing cells outside the heart can be an important source of circulating catecholamines involved in adrenergic cardiac control in Xenopus larvae.

Electrophysiological properties of in vitro intrinsic cardiac neurons in the pig (Sus scrofa)

Physiological properties and synaptically mediated responses of 34 ganglionated plexus neurons from the right atrium of the pig heart were studied with in vitro intracellular recording techniques. Whole-cell input resistance of these neurons was lower, time constant was shorter, and threshold for directly evoked action potentials was higher than the same properties in extracardiac autonomic neurons. Long intracellular depolarizing current pulses (400-500 ms) failed to generate more than one or two action potentials. Nicotinic and non-nicotinic synapses were present on neurons in cardiac ganglia and neuronal properties could be modified by norepinephrine. Based on their physiological properties, cardiac ganglionated plexus neurons in the pig appear to represent a distinct population of autonomic neurons that may be capable of intracardiac integration of efferent information to the heart.

Histochemical study of the heart of the axolotl (Ambystoma mexicanum)

We have investigated the presence of cells containing monoamines, substance P, and neuron-specific enolase (NSE) in the heart and in the pericardial wall of a urodele amphibian, the axolotl. Fibers containing substance P-like immunoreactivity were present in the heart but not in the pericardial wall. Also present in the heart were small branched cells, which stained metachromatically with toluidine blue. Similar cells were found in the peritoneum and were tentatively identified as mast cells. NSE-immunoreactive fibers were found both in the heart and in the pericardial wall. Small intensely fluorescent (SIF) cells of the pericardial wall contained a high concentration of norepinephrine but no other monoamines, substance P, or NSE. Comparison with data available for the mudpuppy, Necturus maculosus, a closely related amphibian species, suggests that the innervation of the heart in the axolotl is substantially different.