Egg laying hormone, a peptide neurohormone with an approximate molecular weight of 6000, was isolated from the region of the abdominal ganglion of Aplysia that contains the neuroendocrine bag cells and purified by gel filtration chromatography, isoelectric focusing, and dialysis. A 1-min local application of egg laying hormone to the identified neuron R15 produced prolonged (>1 hr) augmentation of impulse activity in this neuron. The distinctive quality and prolonged duration of the response are apparently identical to the previously described response to electrically elicited bag cell activity. The results provide evidence that egg laying hormone is the mediator of this prolonged neuronal interaction. The bag cells are a group of neurons located in the abdominal (parietovisceral) ganglion of the marine mollusk Aplysia. These cells are normally silent but, when stimulated with a brief train of electrical stimuli, they discharge in near synchrony with a burst of spike activity lasting approximately 20 min (1). The activity is accompanied by a calcium-dependent release of hormone which, when collected from the superfusate of the isolated ganglion and injected into intact animals, induces egg laying (2-4). The egg laying is apparently due to a hormonal action on gonadal tissue (5) and is associated with the release of a stereotyped behavior pattern (2, 6, 7). Stimulation of the bag cell discharge also produces various responses-some excitatory, others inhibitory-in various identified neurons of the abdominal ganglion. These neuronal responses, studied with intracellular recording techniques, differ from responses at conventional synapses in that they have slow, smoothly graded onsets and markedly prolonged durations; in some cells they result in the modulation of ongoing impulse activity for several hours (8-10).The bag cells send out extensive, granule-filled, axonal processes that end blindly near vascular spaces in the ganglionic sheath (11, 12). Some of the processes end in the sheath overlying the cell bodies of other ganglion neurons (7, 13), but ultrastructural studies have not revealed synaptic contacts between bag cell axonal processes and other neurons (11,12). When the release of bag cell neurosecretory product is simulated by local application of bag cell extract to identified cell R15, a response is produced that is apparently identical to the response produced by bag cell activity. It has therefore been proposed that the bag cell actions on central neurons are mediated by a process in which a hormone (or hormones) is dispersed locally into vascular and interstitial spaces to act on or near the cell bodies of the target neurons (10).Pulse-label studies with radioactive amino acids indicate that a large proportion of the protein synthesis in the bag cells is given over to the production of secretory peptides (13-16). A peptide with a molecular weight of approximately 6000 and an isoelectric point of approximately 9.3 has been isolated from the bag cell somata and identified as the egg laying hor...
It has been determined that the bag cells of Aplysia californica produce two polypeptide species that comigrate on electrophoretic gels containing sodium dodecyl sulfate. By this separation procedure both species can be assigned a molecular weight of approximately 6,000. One of these molecules has an Rf of 0.65 on alkaline discontinuous electrophoresis gels, an isoelectric point at pH 4.8, a gel filtration molecular weight of approximately 12,000, and has no known biological function. The other does not enter alkaline disk gels, has an isoelectric point at approximately pH 9.3, shows a gel filtration molecular weight consistent with that determined by SDS gel electrophoresis, and is the egg-laying hormone.
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