Characterization of an identified cerebrobuccal neuron containing the neuropeptide APGWamide (Ala-Pro-Gly-Trp-NH2) in the snail Lymnaea stagnalis

Abstract

A bilaterally symmetrical pair of cerebrobuccal neurons in Lymnaea stagnalis shows immunoreactivity for the molluscan neuropeptide APGWamide. The neuron somata are whitish in colour and located on the ventral surface of each cerebral ganglion between the roots of the labial nerves. A single axon travels via the ipsilateral cerebrobuccal connective into the buccal ganglia, where it gives rise to fine neuritic branching. Based upon these characteristics, the neuron has been named the cerebrobuccal white cell (CBWC). In isolated CNS preparations, in the absence of feeding motor output, the CBWC is silent and receives few, low amplitude, synaptic inputs. During generation of fictive feeding, the CBWC bursts in phase with cycles of feeding motor output. Tonic or phasic stimulation of CBWC leads to initiation of rhythmic feeding motor output. However, evoked bursts of activity in CBWC, which mimic its normal burst pattern, cannot entrain the buccal rhythm, suggesting that CBWC is not itself a major component of the feeding central pattern generator (CPG). Strong stimulation of CBWC during ongoing feeding motor output leads to a reduction in frequency and/or intensity of the buccal rhythm. Bath application of synthetic APGWamide (10(-7)M-10(-4)M) to the isolated CNS can activate feeding motor output in quiescent preparations after a delay, but disrupts ongoing buccal rhythms. This study represents the first description of a peptidergic cerebrobuccal neuron in the well described gastropod feeding system and also provides new information about the role of a novel molluscan neuropeptide.