Phasic firing enhances vasopressin release from the rat neurohypophysis.
TL;DR: Isolated rat neural lobes were incubated in vitro and electrically stimulated to release vasopressin and there was a reasonably good correlation between results obtained with this assay and those obtained by bioassay with the rat blood pressure method.
Abstract: 1. Isolated rat neural lobes were incubated in vitro and electrically stimulated to release vasopressin. The released vasopressin was assayed using a radioimmunoassay and there was a reasonably good correlation (r = 0.81) between results obtained with this assay and those obtained by bioassay with the rat blood pressure method.
2. Regular stimulation at frequencies of 5, 10 and 20 Hz released progressively more vasopressin and the release could be blocked by addition of tetrodotoxin to the incubation medium.
3. Stimulation with pulse patterns derived from tape recordings of phasically firing units in the supraoptic nucleus of dehydrated rats released more vasopressin than the same number of pulses regularly spaced in time. In the range 2-8 pulses/sec vasopressin release was related to the pulse frequency within the bursts (r = 0.90) and the number of short (< 100 msec) interpulse intervals (r = 0.92). Vasopressin released per pulse increased over the frequency range 3-6 pulses/sec, but above 6 pulses/sec vasopressin release per pulse tended to diminish.
4. We conclude that phasic firing of vasopressin neurosecretory cells may enhance vasopressin release in vivo and that an important factor in determining release is the number of short interspike intervals.
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...…the mechanism of secretion of many different neuropeptides from neurons and neuroendocrine cells, including vasopressin, oxytocin, luteinizing hormone releasing hormone (LHRH) and cat- echolamines (see, e.g.Dutton and Dyball, 1979; Ip and Zigmond, 1984; Cazalis et al., 1985; Gainer et al., 1986)....
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...POMC cells may also synthesize galanin-like peptide and cocaine and amphetamine related transcript (CART); all of these peptides may modulate food intake (Elmquist, 2001; Gundlach, 2002)....
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