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

Area of Science:

• Developmental biology
• Neuroendocrinology
• Comparative physiology

Background:

• Catecholamines, including noradrenaline, adrenaline, and dopamine, are crucial signaling molecules in vertebrates.
• Their roles and synthesis pathways during embryonic development, particularly in amphibians like Xenopus laevis, are not fully understood.
• The non-innervated larval heart presents a unique model to study potential paracrine roles of catecholamines.

Purpose of the Study:

• To investigate the developmental changes in catecholamine levels (noradrenaline, adrenaline, dopamine) in the heart, kidneys, and body of Xenopus laevis embryos.
• To identify the presence and distribution of catecholamine-synthesizing enzymes (tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine-N-methyltransferase) in the embryonic Xenopus heart.
• To explore the potential paracrine role of endogenously produced catecholamines in cardiac regulation during Xenopus larval development.

Main Methods:

• High-performance liquid chromatography (HPLC) was employed to quantify catecholamine concentrations in tissue extracts.
• Immunohistochemistry using antibodies against tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT) was used to detect enzyme-expressing cells.
• Antibodies against acetylated tubulin (AcT) were used to visualize nerve fibers.

Main Results:

• Noradrenaline and dopamine levels in the heart were low and stable, with a peak at NF 57. Adrenaline showed a trend toward higher concentrations at specific developmental stages (NF 43-49 and NF 57).
• Cells immunoreactive to TH, DBH, and PNMT were detected in the heart from stage NF 40, with TH-immunoreactive cells increasing in abundance later in development.
• Catecholamines were also found in kidneys and the rest of the body, indicating extra-cardiac sources.

Conclusions:

• The presence of catecholamines and synthesizing enzymes in the non-innervated larval heart suggests endogenous synthesis and storage, supporting a paracrine role in cardiac control.
• Catecholamine-producing cells outside the heart contribute to circulating levels, potentially influencing adrenergic cardiac control in Xenopus larvae.
• This study provides novel insights into the developmental neuroendocrinology of catecholamines in amphibians.