Monoamine- and histamine-synthesizing enzymes and neurotransmitters withinneurons of adult human cardiac ganglia

Background-Cardiac ganglia were originally thought to contain only choliner gic neurons relaying parasympathetic information from preganglionic brain s tem neurons to the heart. Accumulating evidence, however, suggests that car diac ganglia contain a heterogeneous population of neurons that synthesize or respond to several different neurotransmitters and neuropeptides. Report s regarding monoamine and histamine synthesis and neurotransmission within cardiac ganglia, however, present conflicting information or are limited in number. Furthermore, very few studies have examined the neurochemistry of adult human cardiac ganglia. The purpose of this study was, therefore, to d etermine whether monoamine- and histamine-synthesizing enzymes and neurotra nsmitters exist within neurons of adult human cardiac ganglia. Methods and Results-Human heart tissue containing cardiac ganglia was obtai ned during autopsies of patients without cardiovascular pathology. Avidin-b iotin complex immunohistochemistry was used to demonstrate tyrosine hydroxy lase, L-dopa decarboxylase, dopamine beta-hydroxylase, phenylethanolamine-N -methyltransferase, tryptophan hydroxylase, and histidine decarboxylase imm unoreactivity within neurons of cardiac ganglia. Dopamine, norepinephrine, serotonin, and histamine immunoreactivity was also found in ganglionic neur ons. Omission or preadsorption of primary antibodies from the antisera and subsequent incubation with cardiac ganglia abolished specific staining in a ll cases examined. Conclusions-Our results suggest that neurons within cardiac ganglia contain enzymes involved in the synthesis of monoamines and histamine and that the y contain dopamine, norepinephrine, serotonin, and histamine immunoreactivi ty. Our findings suggest a putative role for monoamine and histamine neurot ransmission within adult human cardiac ganglia. Additional, functional evid ence will be necessary to evaluate what the physiological role of monoamine s and histamine may be in neural control of the adult human heart.