Some parasympathetic neurons in the guinea-pig heart express aspects of the catecholaminergic phenotype in vivo.
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.
Bałuk
P
P
Department of Anatomy and Developmental Biology, University College, London, United Kingdom.
Gabella
G
G
D000818:Animals; D002395:Catecholamines / Q000096:biosynthesis*; D004298:Dopamine / Q000494:pharmacology; D004299:Dopamine beta-Hydroxylase / Q000032:analysis; D005260:Female; D005725:Ganglia, Autonomic / Q000166:cytology*; D006168:Guinea Pigs; D006321:Heart / Q000294:innervation*; D007150:Immunohistochemistry; D007980:Levodopa / Q000378:metabolism; D008297:Male; D008750:Methyldopa / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010293:Pargyline / Q000494:pharmacology; D010641:Phenotype; D012701:Serotonin / Q000032:analysis; D013563:Sympathectomy, Chemical; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis
D002395:Catecholamines; D012701:Serotonin; D007980:Levodopa; D008750:Methyldopa; D010293:Pargyline; D014446:Tyrosine 3-Monooxygenase; D004299:Dopamine beta-Hydroxylase; D004298:Dopamine; D009638:Norepinephrine