Cholinergic and peptidergic responses of pedal A cluster cells of the pond snail lymnaea stagnalis

Abstract

The cardioexcitatory neuropeptide FMRFamide was first identified and characterised by Price and Greenberg in the mollusc Macrocallista nirnbosa. Since then the peptide has been investigated in species representing every molluscan class except Scaphopoda
The main classical neurotransmitters within molluscs are acetylcholine (ACh), 5-hydroxytryptamine and dopamine. It has been postulated that for every neurotransmitter there is an associated neuropeptide which mimics its action. In the pulmonate freshwater snail Lyinnaea stagnalis ACh and FMRFamide have been investigated in the neurones of the respiratory, locomotory and feeding systems.
The aim of this investigation is to characterise the effects of ACh and FMRFamide, and candidate antagonists on Pedal A cluster cells Electrophysiological experiments were performed on the isolated brain of Lymnaea stagnalis. FMlRFamide resulted in significant inhibition of spike frequency. This response was variable, and this was attributed to seasonal differences within snail neurotransmitter content. ACh also exhibited a trend that was attributed to seasonal variation.
Neither of the candidate antagonists investigated in this study had a significant effect on firing frequency. Propanthelene (the ACh antagonist) however, caused a significant increase in the response of PeA cells to ACh. This suggests that propanthelene was acting as an agonist in this preparation rather than an antagonist. This is a common observation in molluscan preparations, where receptors do not follow the typical mammalian classifications.
There is wide scope for future investigation within the response of PeA cells to both FMRFamide and ACh. The type of receptors mediating the response, and other possible antagonists could be investigated. The responses of associated cells could also be investigated, such as VD4, and various methods such as pressure ejection and cell culture be implemented.