Hormonal modulation of two coordinated rhythmic motor patterns.

Neuromodulation is well known to provide plasticity in pattern generating circuits, but few details are available concerning modulation of motor pattern coordination. We are using the crustacean stomatogastric nervous system to examine how co-expressed rhythms are modulated to regulate frequency and maintain coordination. The system produces two related motor patterns, the gastric mill rhythm that regulates protraction and retraction of the teeth and the pyloric rhythm that filters food.

Divergent co-transmitter actions underlie motor pattern activation by a modulatory projection neuron.

Co-transmission is a common means of neuronal communication, but its consequences for neuronal signaling within a defined neuronal circuit remain unknown in most systems. We are addressing this issue in the crab stomatogastric nervous system by characterizing how the identified modulatory commissural neuron (MCN)1 uses its co-transmitters to activate the gastric mill (chewing) rhythm in the stomatogastric ganglion (STG). MCN1 contains gamma-aminobutyric acid (GABA) plus the peptides proctolin and Cancer borealis tachykinin-related peptide Ia (CabTRP Ia), which it co-releases during the retractor phase of the gastric mill rhythm to influence both retractor and protractor neurons.

Intercircuit control via rhythmic regulation of projection neuron activity.

Synaptic feedback from rhythmically active neuronal circuits commonly causes their descending inputs to exhibit the rhythmic activity pattern generated by that circuit. In most cases, however, the function of this rhythmic feedback is unknown. In fact, generally these inputs can still activate the target circuit when driven in a tonic activity pattern.

Extracellular peptidase activity tunes motor pattern modulation.

We are examining how extracellular peptidase activity sculpts the peptidergic actions of modulatory projection neurons on rhythmically active neuronal circuits, using the pyloric circuit in the stomatogastric ganglion (STG) of the crab Cancer borealis. Neurally released peptides can diffuse long distances to bind to their receptors. Hence, different neurons releasing the same neuropeptide into the same neuropil may reach the same receptor complement.