Non-dopaminergic catecholaminergic neurons of mesencephalic and medullary nuclei contain different levels of dopamine.
The present study addresses the question whether metabolic dopamine can be immunocytochemically detected within non-dopaminergic catecholaminergic axonal fibers. For this purpose, confocal microscopy was used to analyze sections treated for the double fluorescence immunostaining of dopamine and either noradrenaline or phenylethanolamine-N- methyltransferase (the enzyme in adrenergic neurons that converts noradrenaline into adrenaline). Our data demonstrate that throughout the brain and spinal cord, the majority of the axonal fibers that reacted with the anti-phenylethanolamine-N-methyltransferase antibodies also exhibited faint to intense dopamine immunoreactivity. Similarly noradrenaline and dopamine immunoreactivities were frequently colocalized within axonal fibers innervating brain and spinal cord regions that receive a dense innervation from medullary noradrenergic neurons. On the contrary, dopamine was rarely detected within noradrenaline-immunoreactive fibers in those regions where the noradrenergic innervation essentially arises from noradrenergic neurons of the locus coeruleus. A similar differential dopamine immunostaining was observed in the corresponding neuronal perikarya of the medulla oblongata and the locus coeruleus. These data indicate that two types of non-dopaminergic catecholaminergic neurons can be distinguished according to their content in dopamine: (i) the noradrenergic and adrenergic neurons located in the medulla oblongata, whose cell bodies and axons contain high concentrations of metabolic dopamine and (ii) the noradrenergic neurons located in the mesencephalon, which contain low levels of metabolic dopamine.
Alonso
G
G
INSERM U 336, Dévelopement, Plasticité et Vieillissement du Système Nerveux, University of Montpellier II, France.
Brun
O
O
Ridet
J L
JL
Geffard
M
M
Chauvet
N
N
D000320:Adrenergic Fibers / Q000737:chemistry*; D000818:Animals; D001369:Axons / Q000737:chemistry; D004298:Dopamine / Q000032:analysis* / Q000502:physiology; D019084:Fluorescent Antibody Technique, Indirect; D007074:Immunoglobulin G / Q000276:immunology; D008297:Male; D008526:Medulla Oblongata / Q000737:chemistry* / Q000166:cytology; D008636:Mesencephalon / Q000737:chemistry* / Q000166:cytology; D018613:Microscopy, Confocal; D009474:Neurons / Q000737:chemistry*; D009638:Norepinephrine / Q000032:analysis*; D010625:Phenylethanolamine N-Methyltransferase / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry
D007074:Immunoglobulin G; D010625:Phenylethanolamine N-Methyltransferase; D004298:Dopamine; D009638:Norepinephrine