Endomorphin-2 is released from newborn rat primary sensory neurons in a frequency- and calcium-dependent manner.
Recent evidence indicates that endomorphins, endogenous mu-opioid receptor (MOR) agonists, modulate synaptic transmission in both somatic and visceral sensory pathways. Here we show that endomorphin-2 (END-2) is expressed in newborn rat dorsal root ganglion (DRG) and nodose-petrosal ganglion complex (NPG) neurons, and rarely co-localizes with brain-derived neurotrophic factor (BDNF). In order to examine activity-dependent release of END-2 from neurons, we established a model using dispersed cultures of DRG and NPG cells activated by patterned electrical field stimulation. To detect release of END-2, we developed a novel rapid capture enzyme-linked immunosorbent assay (ELISA), in which END-2 capture antibody was added to neuronal cultures shortly before their electrical stimulation. The conventional assay was effective at reliably detecting END-2 only when the cells were stimulated in the presence of CTAP, a MOR-selective antagonist. This suggests that the strength of the novel assay is related primarily to rapid capture of released END-2 before it binds to endogenous MORs. Using the rapid capture ELISA, we found that stimulation protocols known to induce plastic changes at sensory synapses were highly effective at releasing END-2. Removal of extracellular calcium or blocking voltage-activated calcium channels significantly reduced the release. Together, our data provide the first evidence that END-2 is expressed by newborn DRG neurons of all sizes found in this age group, and can be released from these, as well as from NPG neurons, in an activity-dependent manner. These results point to END-2 as a likely mediator of activity-dependent plasticity in sensory pathways.
Department of Integrative Biosciences, Oregon Health and Science University, Portland, OR 97239, USA.
Heather L
HL
Scanlin
Elizabeth A
EA
Carroll
Victoria K
VK
Jenkins
Agnieszka
A
Balkowiec
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D004558:Electric Stimulation; D004797:Enzyme-Linked Immunosorbent Assay; D017950:Ganglia, Sensory / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology; D009475:Neurons, Afferent / Q000166:cytology / Q000378:metabolism*; D009620:Nodose Ganglion / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D009842:Oligopeptides / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology
D019208:Brain-Derived Neurotrophic Factor; D009842:Oligopeptides; C105294:endomorphin 2