MODULATION OF OSCILLATOR INTERACTIONS IN THE CRAB STOMATOGASTRIC GANGLION BY CRUSTACEAN CARDIOACTIVE PEPTIDE

The modulation of the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis, by crustacean cardioactive peptide (CCAP) is described. CCAP activated pyloric rhythms in most silent preparatio ns, and altered the phase relationships of pyloric motor neuron firing in all preparations. In CCAP, the pyloric rhythms were characterized by long lateral pyloric (LP) neuron bursts of action potentials. The t hreshold for CCAP action was similar to 10(-10) M, with increasing eff ects at higher CCAP concentrations. The changes in motor pattern evoke d by CCAP produced significant changes in LP-innervated muscle movemen t. These movements were additionally potentiated by CCAP applications to isolated nerve-muscle preparations. Thus, enhanced motor neuron fir ing and increase of the gain of the neuromuscular junctions are likely to operate coordinately in response to hormonally released CCAP. High CCAP concentrations sometimes resulted in modification of the normal 1:1 alternation between the pyloric dilator (PD) and LP neurons to pat terns of 2:1, 3:1, or 4:1 alternation. CCAP seems to activate slow int rinsic oscillations in the LP neuron, as well as enhance faster oscill ations in the pacemaker group of PD/anterior burster (AB) neurons. Sim ulations of fast and slow oscillators with reciprocal inhibitory coupl ing suggest mechanisms that could account for the mode switch from 1:1 alternation to multiple PD bursts alternating with one LP neuron burs t.