Some parasympathetic neurons in the guinea-pig heart express aspects of the catecholaminergic phenotype in vivo

Cell Tissue Res. 1990 Aug;261(2):275-85. doi: 10.1007/BF00318669.

Abstract

In a histochemical study of intrinsic cardiac ganglia of the guinea-pig in whole-mount preparations, it was found that some 70-80% of the neurons express aspects of the catecholaminergic phenotype. These neurons have an uptake mechanism for L-DOPA, and contain the enzymes for converting L-DOPA (but not D-DOPA) to dopamine and noradrenaline, i.e. aromatic L-aminoacid decarboxylase and dopamine beta-hydroxylase. Monoamine oxidase is also present within some of the neurons. In these respects, the neurons resemble noradrenergic neurons of sympathetic ganglia, so we refer to them as intrinsic cardiac amine-handling neurons. However, these neurons do not contain tyrosine hydroxylase and show little or no histochemically detectable uptake of alpha-methyldopa, dopamine or noradrenaline, even after depletion of endogenous stores of amines by pre-treatment with reserpine. Noradrenergic fibres from the sympathetic chain form pericellular baskets around nerve cell bodies. The uptake of L-DOPA into nerve cell bodies is not prevented by treatment with 6-hydroxydopamine sufficient to cause transmitter-depletion or degeneration of the extrinsic noradrenergic fibres. Such degeneration experiments suggest that axons of the amine-handling neurons project to cardiac muscle, blood vessels and other intrinsic neurons. The cardiac neurons do not show any immunohistochemically detectable serotonergic characteristics; there is no evidence for uptake of the precursors L-tryptophan and 5-hydroxytryptophan or 5-HT itself, whereas the extrinsic noradrenergic nerve fibres within the ganglia can take up 5-HT when it is applied in high concentrations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Catecholamines / biosynthesis*
  • Dopamine / pharmacology
  • Dopamine beta-Hydroxylase / analysis
  • Female
  • Ganglia, Autonomic / cytology*
  • Guinea Pigs
  • Heart / innervation*
  • Immunohistochemistry
  • Levodopa / metabolism
  • Male
  • Methyldopa / pharmacology
  • Neurons / drug effects
  • Neurons / metabolism*
  • Norepinephrine / pharmacology
  • Pargyline / pharmacology
  • Phenotype
  • Serotonin / analysis
  • Sympathectomy, Chemical
  • Tyrosine 3-Monooxygenase / analysis

Substances

  • Catecholamines
  • Serotonin
  • Levodopa
  • Methyldopa
  • Pargyline
  • Tyrosine 3-Monooxygenase
  • Dopamine beta-Hydroxylase
  • Dopamine
  • Norepinephrine