Ligand and electrically induced acitivation patterns in myenteric neuronal networks. Confocal calcium imaging as a bridge between basic and human physiology.
Confocal imaging in combination with fluorescent calcium indicators provides the possibility to study neuronal activation in entire neuronal networks. The experiments presented in this essay aimed at applying confocal calcium imaging to study activation patterns in neuronal networks of myenteric ganglia in situ. First we studied the response to electrical train stimulation (ETS). ETS induced Ca2+ transients in 52.2% and 65.4% of the neurons when applied orally and aborally respectively. We observed more responses during aboral ETS which is not in line with the hypothesis of neuronal polarity, suggesting complex neuronal activation patterns and neuronal interaction in ETS-induced activation in myenteric ganglia. We demonstrated that ghrelin has a direct excitatory effect on myenteric neurons in situ via ghrelin receptor activation. Ghrelin induced Ca2+ transients in one third of the myenteric neurons, involving release of Ca2+ from intracellular stores and direct GHS-receptor activation. We found that CRF activates one fifth of the myenteric neurons, via CRF1 receptor activation. These CRF induced Ca2+ signals involved somatic influx through (mainly R-type) voltage operated Ca2+ channels. Finally we set up human studies in healthy volunteers and dyspeptic patients to test the effect of ghrelin on gastrointestinal motility. Intravenous administration of ghrelin induced a premature phase 3 activity front that originated in the stomach and an increase in gastric tone. Ghrelin decreased gastric emptying time for fluids and reduced symptom scores for fullness and pain. These studies provide further evidence for a role of ghrelin in the regulation of gastrointestinal motility, and possibly provide new therapeutic approaches. Our studies show that confocal calcium imaging allows to assess neuronal activation of myenteric neurons. The influence of new hormones or new pharmaceutical compounds on the myenteric plexus can hereby be easily assessed.
Bisschops
R
R
Faculteit Geneeskunde, Dienst Gastro-enterologie, KULeuven, Herestraat 49, B 3000 Leuven.
D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005769:Gastrointestinal Motility / Q000187:drug effects; D054439:Ghrelin / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating; D009197:Myenteric Plexus / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*
D015220:Calcium Channels; D054439:Ghrelin