The role of patterned burst and interburst interval on the excitation-coupling mechanism in the isolated XXXX neural lobe.

@entity35 @entity398 @entity1951
Isolated @entity35 neural lobes were stimulated electrically and the release of @entity1951 and @entity398 was measured by radioimmunoassay. The neurohypophyses were stimulated with pulses given at a constant frequency or with a pulse pattern imitating the electrical activity, recorded in vivo, of @entity1951 - or @entity398 -containing magnocellular neurones. A single burst recorded from a ' @entity1951 ' cell with an intraburst mean frequency of 13 Hz evoked more @entity1951 release than the same number of stimuli delivered at a constant frequency of 13 Hz. The amount of @entity1951 release per pulse was much higher at the beginning than at the end of the burst. Series of bursts given with interburst silent periods released more hormone than bursts delivered without silent periods. The amount of hormone released by four ' @entity1951 ' bursts was significantly larger with silent periods of 21 s than with shorter intervals. Four pulses were much more effective in promoting hormone release when given with 60 ms interspike intervals at the beginning of each second than when delivered at a constant frequency of 4 Hz. Prolonged stimulation with ' @entity1951 ' bursts had a greater effect in inducing hormone release than the same number of pulses given in burst delivered at a constant frequency of 13 Hz. After an initial increase the rate of @entity1951 release declined rapidly whereas @entity398 release remained elevated for the first 20 min and only then decreased. The release of both @entity1951 and @entity398 remained, however, above the release from unstimulated neurohypophyses. 45Ca uptake in the neural lobe was larger when the neurohypophyses were stimulated with @entity1951 or @entity398 bursts delivered with silent intervals than when the silent periods were omitted, or when the tissue was stimulated with bursts with the same number of pulses but given at a constant frequency of 13 Hz. In conclusion, it is suggested that the interspike intervals in a burst and the silent intervals between bursts are two important determinants of the effectiveness of the burst pattern in promoting neuropeptide release.
