Meeting Abstract

S1.7  Tuesday, Jan. 4  Forty years of gastropod feeding: multiple buccal motor patterns but conservation of apparently homologous neuronal circuitry in rasping heterobranchs. RAMAKRISHNAN, S; YASHINA, I; MURPHY, A/D*; Univ. of Illinois at Chicago; Univ. of Illinois at Chicago; Univ. of Illinois at Chicago dmurphy@uic.edu

Feeding in the snail, Helisoma, was originally described as a biphasic behavior with radular protraction followed by retraction. An “elegant” central pattern generator (CPG) that consisted of a single set of electrotonically coupled neurons was proposed. That “CPG” would generate repetitive bursts of spikes that simultaneously excited retractor neurons and inhibited protractor neurons which subsequently were excited by post-inhibitory rebound. However that proposed CPG was actually a set of pre-motor neurons at the sensory-motor interface. These neurons receive chemo- and mechanosensations from a variety of sources and either excite or inhibit motor and CPG neurons. These pre-moter neurons help to select and configure one of several possible motor patterns (eg. for feeding, rejection of food, or substrate cleaning for egg laying). The actual CPG consists of three semi-independent conditional oscillators physiologically linked in different sequences to produce different motor patterns. This CPG is widely conserved. A comparison of thirty identified motor and CPG neurons in the planorbid snails, Helisoma trivolvis and Biomphalaria glabrata showed them to be essentially identical. One motor neuron was found to have an axonal projection that was bilateral in Helisoma and ipsilateral in Biomphalaria. Strikingly, the key CPG interneurons of Helisoma appear to have homologs in the opisthobranch, Aplysia. Thus the CPG for rasping seems conserved in the heterobranchs. However with the wide diversity of feeding niches and mechanisms in the opisthobranchs, this group offers opportunities for addressing both evolutionary conservation and diversification of neuronal circuitry.