Extrasynaptic Release of Dopamine in a Retinal Neuron

Abstract

Extrasynaptic release of dopamine is well documented, but its relation to the physiological activity of the neuron is unclear. Here we show that in absence of presynaptic active zones, solitary cell bodies of retinal dopaminergic neurons release by exocytosis packets of approximately 40,000 molecules of dopamine at irregular intervals and low frequency. The release is triggered by the action potentials that the neurons generate in a rhythmic fashion upon removal of all synaptic influences and therefore depends upon the electrical events at the neuronal surface. Furthermore, it is stimulated by kainate and abolished by GABA and quinpirole, an agonist at the D(2) dopamine receptor. Since the somatic receptors for these ligands are extrasynaptic, we suggest that the composition of the extracellular fluid directly modulates extrasynaptic release.

Neuronal somatic ATP release triggers neuron–satellite glial cell communication in dorsal root ganglia

“…We (Fig. 2D) and others (7,10) have found that L-type Ca 2ϩ channels, which are known to be loosely associated with release machinery (34,35), mediate somatic exocytosis. In contrast, N-and P/Q types Ca 2ϩ channels, which are closely associated with fusion machinery, are involved in the exocytosis at synaptic terminals (34,36).…”

“…It has been assumed for a long time that the cell body (i.e., soma) of a neuron does not release transmitters in response to electrical stimulation. This assumption has been challenged by our and others' observations that neuronal somatic release indeed occurs (3)(4)(5)(6)(7)(8)(9)(10). Using carbon fibers, several groups have shown that somatic release of catecholamine occurs through vesicular mechanisms (3,(5)(6)(7).…”

“…This assumption has been challenged by our and others' observations that neuronal somatic release indeed occurs (3)(4)(5)(6)(7)(8)(9)(10). Using carbon fibers, several groups have shown that somatic release of catecholamine occurs through vesicular mechanisms (3,(5)(6)(7). Exocytosis in response to membrane depolarization has also been reported in the somata of dorsal root ganglion (DRG) neurons (4), a group of neurons responsible for transmitting touch, temperature and pain information from the periphery to the spinal cord (11).…”

“…Exocytosis in response to membrane depolarization has also been reported in the somata of dorsal root ganglion (DRG) neurons (4), a group of neurons responsible for transmitting touch, temperature and pain information from the periphery to the spinal cord (11). In most cases, soma release is triggered and enhanced by voltage-dependent Ca 2ϩ channels (4)(5)(6)(7)10). Despite these studies, it is not known whether vesicular release of fast-acting transmitters, e.g., ATP or glutamate, occurs in the somata.…”

Gene discovery in genetically labeled single dopaminergic neurons of the retina

“…granules (34). The distribution of organelles containing the vesicular monoamine transporter-2 suggests that dopamine-containing vesicles are of the agranular type.…”