1. Complex behavior induced by egg-laying hormone in Aplysia
S M Bernheim, E Mayeri J Comp Physiol A. 1995 Jan;176(1):131-6. doi: 10.1007/BF00197759.
Previous studies have described a pattern of complex behavior that occurs in the marine mollusc Aplysia during egg laying. Egg laying and the behavior are initiated by a burst of impulse activity in the neuroendocrine bag cells of the abdominal ganglion or by injection of bag cell extract. To more precisely identify the factors responsible for inducing the behavior we injected animals with egg laying hormone (ELH), one of the neuropeptides secreted by the bag cells. We found that ELH causes a behavior pattern similar to what occurs during spontaneous egg laying. This includes a temporal pattern of head movements consisting of waves and undulations, followed near the beginning of egg deposition by a transition to head weaves and tamps and inhibition of locomotion. There was also a small decrease in respiratory pumping. Except for respiratory pumping, a similar pattern occurred in a second group of animals injected with atrial gland homogenate, which is presumed to induce bag cell activity, but not in controls. These results further implicate ELH in regulation of the behavior. We discuss possible sites of action of ELH and the neural mechanisms by which the behavior is controlled.
2. Egg-laying hormone: direct action on the ovotestis of Aplysia
B S Rothman, G Weir, F E Dudek Gen Comp Endocrinol. 1983 Oct;52(1):134-41. doi: 10.1016/0016-6480(83)90166-1.
The bag cells are a group of neuroendocrine cells located in the abdominal ganglion of Aplysia californica. These cells induce egg laying in the animal through the release of neurohormone(s). Previous experiments established that an extract of bag cells releases eggs from isolated ovotestis fragments in a dose-dependent manner. (F. E. Dudek and S. S. Tobe, 1978, Gen. Comp. Endocrinol. 36, 618-627.) Experiments presented here were conducted to purify and identify the component(s) of bag cell extract with the egg-releasing activity. Bag cell extracts were fractionated by means of gel-filtration chromatography followed by cation-exchange chromatography. Column eluates were assayed for egg-release activity on isolated ovotestis fragments by the method of Dudek and Tobe (1978). Only one component purified from the crude extract had egg-releasing activity. This component was identified as egg-laying hormone (ELH) based on its purification characteristics, effects on neuronal activity, and migration on thin-layer chromatography. In dose-response studies egg release increased with the concentration of ELH and had a threshold of 8 X 10(-10) M or less. ELH had the same dose-response relationship in egg release assays when present in purified form or as a component of bag cell extract. These data show that ELH acts directly on the ovotestis and that ELH is the only component of bag cell extract with egg-release activity. Taken with the results of other studies (W. D. Branton, S. Arch, T. Smock, and E. Mayeri, 1978. Proc. Nat. Acad. Sci. USA 75, 5732-5736. B. S. Rothman, P. Brownell, and E. Mayeri, 1979. Soc. Neurosci. Abstr. 5, 260. E. Mayeri and B. S. Rothman, 1982.(ABSTRACT TRUNCATED AT 250 WORDS)
3. Egg-laying hormone of Aplysia induces a voltage-dependent slow inward current carried by Na+ in an identified motoneuron
M D Kirk, R H Scheller Proc Natl Acad Sci U S A. 1986 May;83(9):3017-21. doi: 10.1073/pnas.83.9.3017.
This report presents studies on ionic currents in Aplysia motoneuron B16 that are modulated by the neuropeptide egg-laying hormone (ELH) of Aplysia. ELH induces an inward current that persists in the presence of the peptide and that decays slowly after ELH is removed from the bath. The effect is not due to a decrease in the delayed potassium current, the calcium-activated potassium current, or the transient potassium current. Current-voltage measurements indicate that ELH produces increased inward currents from -80 mV to approximately equal to 0 mV. The effect is particularly enhanced in the region from -40 mV to -25 mV where a negative slope conductance due to voltage-dependent slow inward current is observed. The slow inward current and the response to ELH persist in saline solutions in which Ca2+ is replaced with Co2+ but are eliminated when Na+ is replaced with equimolar concentrations of either Tris or N-methyl-D-glucamine. The response to ELH is unaffected by replacing chloride with equimolar acetate; by increasing the potassium concentration; or by adding tetraethylammonium chloride, CsCl, 4-amino-pyridine, or tetrodotoxin to the saline bath. In addition, the reversal potentials for the ELH response (range, -28 to +46 mV), obtained from difference current-voltage relationships, are consistent with an increase in the Na+-dependent slow inward current. We conclude that at least one of the effects of ELH on B16 is to increase a slow inward current carried by Na+.
