Multiple mechanisms of bursting in a conditional bursting neuron

The anterior burster (AB) neuron in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus, is a conditional burster in the pyloric motor circuit. Bath application of the monoamines dopamine, serotonin, and octopamine induces rhythmic bursting pacemaker potentials in a silent, synaptically isolated AB cell. However, each amine produces a unique and characteristic burst shape, resulting from different ionic dependences of the burst mechanisms. Bursting induced by serotonin or octopamine is critically dependent upon sodium entry through tetrodotoxin-sensitive channels; dopamine-induced bursting is not TTX-sensitive. Dopamine-induced bursting is abolished when extracellular calcium is reduced to 25% of normal; serotonin- and octopamine-induced bursts continue in this saline, although they are abolished in salines with calcium reduced to 10% or less of normal. Quantitative differences between the amines are also seen in the tetraethylammonium (TEA) sensitivity of the burst amplitude and in the dependence of the interburst hyperpolarization on extracellular potassium. These experiments demonstrate that there are both quantitative and qualitative differences in the ionic currents underlying every phase of the bursts induced by the 3 amines. Thus, a single neuron can burst via more than one ionic mechanism.