The Noradrenergic Neuron, a Multipeptide Secretory Cell

Abstract

It is generally accepted that each neuron can secrete a classical transmitter and one or more peptides via small synaptic vesicles (SS Vs) and large dense-cored vesicles (LDCVs), respectively. According to the current concept both SSVs and LDCVs undergo regulated exocytosis but their release process is differentially regulated. However, this general concept of neurotransmitter release seemed not to hold for sympathetic neurons since the latter store their classical transmitter noradrenaline (NA) not in SSVs but in small dense-cored vesicles (SDCVs) and moreover also in LDCVs together with proteins and peptides. In addition, NA in sympathetic neurons was shown to be released, at least in part, by exocytosis from LDCVs, a finding long disputed but now supported by many recent physiological, pharmacological, electron microscopical and confocal immunomicroscopical studies (De Potter et al., 1997; Annaert et al., 1997). At present the debate merely concerns the part of NA released from SDCV and LDCV.