Stimulation of chemosensory pathways and intracellular alkalinization mimic cAMP activation of endogenous bursting in feeding command neurones

Cyclic nucleotides modulate the activity of diverse types of excitable cells (Twarog & Muneoka, 1973; Berridge, 1975; Triestman & Levitan, 1976; Greengard, 1980; Bernier, Castellucci, Kandel & Schwartz, 1982; Gillette, Gillette & Davis, 1982b; Evans, 1984). In the carnivorous gastropod Pleurobranchaea, it would appear that cAMP modulation of a single pair of neurones effects the expression of a complex coordinated rhythmic behaviour. These neurones, the ventral white cells (VWCs), command vigorous motor output from the neuronal feeding oscillator through an intrinsic capacity to generate minutes-long high intensity bursts of action potentials (Gillette, Gillette & Davis, 1980). This high frequency firing causes the action potentials to increase in duration (broaden). The increase in action potential duration is a specific antecedent to enhanced motor output through a Ca²⁺-dependent mechanism (Gillette, Gillette & Davis, 1982a). Elevated intraneuronal cAMP is a specific activator of prolonged VWC bursting in both the isolated nervous system and the isolated VWC soma (Gillette et al. 1982b). The relationship between this endogenous effector (cAMP) and extrinsic activators of the motor programme has not been established.