Bursting properties of caudal neurosecretory cells in the flounder Platichthys flesus, in vitro

Bursting activity in type 1 Dahlgren cells was studied using intra- and ext racellular recording from an in vitro preparation of the caudal neurosecret ory system of the euryhaline flounder. 45 % of cells showed spontaneous bur sts of approximately 120s duration and 380s cycle period. Similar bursts we re triggered by short duration (<5 s) depolarising or hyperpolarising pulse s. Cells displayed a characteristic depolarising after potential, following either an action potential with associated afterhyperpolarisation, or a hy perpolarising current pulse. This depolarising after potential was related to a 'sag' potential, which developed during the hyperpolarising pulse. Bot h the depolarising after potential and the sag potential occurred only in c ells at more depolarised (<60 mV) holding potentials. In addition, the ampl itude of the depolarising after potential was dependent on the amplitude an d the duration of the hyperpolarising pulse. The depolarising after potenti al following action potentials may provide a mechanism for facilitating rep etitive firing during a burst. Extracellular recording revealed similar bur sting in individual units which was not, however, synchronised between unit s. Spontaneous bursting activity recorded both intra- and extracellularly w as inhibited by application of a known neuromodulator of the system, 5-hydr oxytryptamine. This study provides a basis for investigating the relationsh ip between physiological status, Dahlgren cell activity and neuropeptide se cretion.