Title

Role of GnRH as a neuromodulator during egg-laying behavior in two pulmonate snails: Helisoma (Planorbidae) and Lymnaea (Lymnaeidae).

Document Type

Presentation or Lecture

Publication Date

10-25-2004

Conference or Event

Society for Neuroscience

Department

Neuroscience

Abstract

Egg-laying behavior in snails is comprised of elaborate stereotypical oral and locomotory behaviors preceding oviposition. Here we propose a role for gonadotropin releasing-hormone(GnRH), a peptide known for its importance in vertebrate reproduction, as a neuromodulator during egg-laying in two species of snails. During egg-laying, snails clean a small area of the substrate using their oral apparatus. This substrate cleaning behavior is accompanied by constant shell turning in Lymnaeids, while among Planorbids it is associated with an extension of the pseudobranch. In both cases, these supposedly help the movement of eggs through the reproductive tract. Previous studies have shown that lesions to the intestinal nerve (IN), which connects the central nervous system(CNS) to the reproductive system, effectively abolishes shell turning and substrate cleaning behavior in Lymnaea. Further, IN stimulation causes excitation of pedal cells necessary for shell turning behavior. It has been hypothesized that the movement of the eggs through the reproductive tract is signaled through the IN to the CNS, to allow synchronization during egg-laying. The mechanism of signaling involved and its modulatory effects on the buccal and the pedal central pattern generators (CPGs) is as yet unknown. Here we suggest that GnRH acts as a signaling molecule from the IN to the CNS and modulates the buccal CPG in both Lymnaeids and Planorbids. Using immunohistochemistry and electrophysiology we show – 1.the presence of GnRH, in both Lymnaeid and Planorbid nervous systems; 2.that IN stimulation elicits similar long-term rhythmic patterns in the buccal CPG of both families of snails; 3.this long term buccal motor pattern is similar to that obtained on bath application of GnRH. This study will help us comprehend better the role of GnRH as a neuromodulator in patterned behaviors