A switching mechanism in a neuronal rhythm synthesizer, the neurogenic pacemaker of lobster heart

The heart of lobsters includes a pacemaker ganglion (a neuronal rhythm synthesizer) consisted of nine bursting neurons ("bursters"). Their burst rates change with inflation of the heart since the bursters have stretch-sensitive dendrites; on the cardiac muscle. The cardiac neurons of the Japanese spiny lobster could be grouped into three different oscillators. The maximum burst rate correlated to cell size. The large bursters increased the rate up to 1.5 Hz while the middle and small ones did to 1 and 0.7 Hz, respectively. Furthermore, the nine bursters mutually connected with excitatory chemical and electrical synapses. Predominant activity in the ganglion was switched from the small to the large bursters according to the degree of input brought from heart inflation. In this process, at least five patterns of the ganglionic burst rhythm were distinguished. A switching mechanism was a positive feedback from the stretch sensors of large neurons.