Evidence for an Annelid Neuroendocrine System

Abstract

Hormonal processes along with enzymatic processing similar to that found in vertebrates occur in annelids. Amino acid sequence determination of annelids precursor gene products reveals the presence of the respective peptides that exhibit high sequence identity to their mammalian counterparts. Furthermore, these neuropeptides exert similar physiological function in annelids than the ones found in vertebrates. In this respect, the high conservation in course of evolution of these molecules families reflects their importance. Nevertheless, some specific neuropeptides to annelids or invertebrates have also been in these animals.

A Hormone-Activated Central Pattern Generator for Courtship

“…Examples of twisting induced by all three molecules may be found in Supplemental Movie 1. Quantitatively, conopressin was just as potent as hirudotocin, a peptide actually produced by Hirudo [8], and these two peptides produced stronger responses at a given dose than did annetocin, a peptide produced by earthworms [9]. For instance, the latency to the first characteristic twisting of a leech after injecting peptide (5 nanomoles/gram of body weight) was 4.1 ± 1.7 minutes for conopressin and 4.7 ± 2.7 minutes for hirudotocin (mean ± SD, N = 6 animals for each peptide; not significantly different).…”

“…First, immunocytochemical staining indicates the presence of a vasopressin homolog, presumably hirudotocin, in neurons of the central nervous system of Hirudo spp. [16, 8]. Second, the peptides did not induce a single, simple behavior, but a whole sequence of behaviors—first twisting and mouth flaring as in mate exploration, then periodic thrusting and retraction of the anterior body as in cocoon deposition—and the elicited behaviors disappeared completely after 24–48 hours or less, depending on dose.…”

“…In annelids, too, hormones in this family evoke responses related to reproduction (and water balance) [27, 28], and several of them have been reported in leeches [16, 29, 8]. The association of (Arg 8 )-conopressin G, hirudotocin, and annetocin with reproductive behavior in the leech fits well in this general pattern: a different conopressin produces related effects on the pond snail Lymnaea stagnalis [30], and annetocin induces egg-laying behavior in earthworms [31].…”

“…Electrophysiological recording from semi-intact leeches during mating is thus impossible. However, we here report that several members of the vasopressin/oxytocin family of peptide hormones, specifically (Arg 8 )-conopressin G [7], hirudotocin [8], and annetocin [9], elicit in Hirudo a sequence of behaviors that closely resemble elements of spontaneous courtship and cocoon deposition, but that are almost totally resistant to external disturbances. Using a series of progressively reduced preparations, we demonstrate that one of these behaviors, a highly stereotyped twisting that is a critical part of preparation for copulation, is driven by one or more physiologically accessible central pattern generators.…”

A classic model animal in the 21st century: recent lessons from the leech nervous system

“…This situation improved when a chance discovery revealed that hirudotocin (Salzet, 2006) and conopressin (Cruz et al, 1987), two members of the vasopressin/oxytocin family of peptide hormones, elicit motor behaviors in leeches that are associated with procreation (Wagenaar et al, 2010). This made it possible to determine that these behaviors are controlled by linked CPGs located in the 4th, 5th and 6th segmental ganglia.…”