title: Looping circuit: a novel mechanism for prolonged spontaneous [Ca2+]i increases in developing embryonic mouse brainstem.
abstract: Most cells maintain [Ca(2+)]i at extremely low levels; calcium entry usually occurs briefly, and within seconds it is cleared. However, at embryonic day 12.5 in the mouse brainstem, trains of spontaneous events occur with [Ca(2+)]i staying close to peak value, well above baseline, for minutes; we termed this 'bash bursts'. Here, we investigate the mechanism of this unusual activity using calcium imaging and electrophysiology. Bash bursts are triggered by an event originating at the mid-line of the rostral hindbrain and are usually the result of that event propagating repeatedly along a defined circular path. The looping circuit can either encompass both the midbrain and hindbrain or remain in the hindbrain only, and the type of loop determines the duration of a single lap time, 5 or 3 s, respectively. Bash bursts are supported by high membrane excitability of mid-line cells and are regulated by persistent inward 'window current' at rest, contributing to spontaneous activity. This looping circuit is an effective means for increasing [Ca(2+)]i at brief, regular intervals. Bash bursts disappear by embryonic day 13.5 via alteration of the looping circuit, curtailing the short epoch of bash bursts. The resulting sustained [Ca(2+)]i may influence development of raphe serotonergic and ventral tegmental dopaminergic neurons by modulating gene expression.
authors.affiliation: Department of Biology, Box 351800, University of Washington, Seattle, WA 98195, USA.    martibee@uw.edu.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Watari
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Tose
authors.forename: Martha M
authors.initials: MM
authors.lastname: Bosma
mesh_terms: D000200:Action Potentials; D000818:Animals; D001933:Brain Stem / Q000196:embryology / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D051379:Mice
chemical_list: D002118:Calcium