Behavioral and cellular effects of serotonin on locomotion and male mating posture in Ascaris suum (Nematoda)

Abstract

The site and mode of action of serotonin on locomotion were investigated in the parasitic nematode Ascaris suum. Injection of serotonin into Ascaris immediately caused paralysis in animals that were generating locomotory waveforms. Injected serotonin also increased body length and decreased the number of propagating body waves. Similar injections into the male tail produced a ventral tail curl. Injection of N-acetyl-serotonin had no effect on the generation of locomotory waveforms, but increased the body length and decreased the number of body waves in the waveform. Other biogenic amines were also tested but were much less potent. Serotonin decreased the amplitude of a submaximal acetylcholine-induced muscle contraction and increased the time to attain this contraction. The time course of this effect on the response to ACh was much slower than the action of injected serotonin on locomotory waveforms, suggesting that additional elements are involved in the action of serotonin on locomotory behavior. Serotonin abolished spontaneous slow potentials in VI motor neurons and decreased the frequency of EPSPs in DE2 motor neurons, probably by a pre-synaptic mechanism. In the male tail, serotonin depolarized the male-specific transverse ventral muscle cells, but did not affect either dorsal or ventral longitudinal muscle cells.

Changes in cyclic nucleotides, locomotory behavior, and body length produced by novel endogenous neuropeptides in the parasitic nematode Ascaris suum

“…The utility of a head ligature for inducing the stereotypical Head-Restricted Behavior [39] was first discovered when we were attempting to refine the markedly varied behavior observed when A. suum is placed in a large beaker of PBS. In this environment, the locomotory behavior is largely unpredictable, consisting of alternating bouts, of variable duration, of forwards- and backwards-moving waveforms, superimposed upon apparently random body bends that can sometimes form knots.…”

“…10-fold dilution in the region of the injection, so that target cells were exposed to ca. 1 μM peptide [39]. After observing general behavioral effects, namely body tonus immediately after injection (stiff or relaxed), the shape of the body (straight or curved) and whether or not propagating waveforms were affected, the worms were frozen in liquid nitrogen 5 – 7 minutes after injection.…”

“…To establish a baseline of locomotory behavior, all A. suum used in this study were ligatured at the head with surgical thread, which induces stereotypical anteriorly-propagating body waves [28, 39]. These waves are initiated in the region of the gonopore in females.…”

Neuronal localization of serotonin inAscaris suum

“…Jorgensen, personal communication). In adult Ascaris 5-HT has comparable effects on locomotion and male mating (Buchanan and Stretton, 1991;Reinitz and Stretton, 1996). The egg-laying effects have been convincingly associated with the HSN neurons (Trent et al, 1983;Desai et al, 1988;Desai and Horvitz, 1989) as have the male mating effects with the CP neurons (Loer and Kenyon.…”

“…Serotonin also causes an increase in cyclic AMP levels, an activation of phosphorylase and an inactivation of glycogen synthase (Donahue et al, 1981a,b). Recently it was shown that when 5-HT is injected into A. suum it produces a reversible paralysis of the worm (Buchanan and Stretton, 1991;Reinitz and Stretton, 1996), suggesting that serotonin plays a role in regulating locomotion. In C. elegans 5-HT stimulates egglaying, decreases locomotion, stimulates pharyngeal pumping, and affects male mating behavior (Avery and Horvitz, 1990;Horvitz et al, 1982;Loer and Kenyon, 1993).…”