Constant Amplitude of Postsynaptic Responses for Single Presynaptic Action Potentials But Not Bursting Input during Growth of an Identified Neuromuscular Junction in the Lobster, Homarus americanus

ABSTRACT: As lobsters grow from early juveniles to adults their body size increases more than 20-fold, raising the question of how function is maintained dur-ing these ongoing changes in size. To address this ques-tion we studied the pyloric 1 (p1) muscle of the stomach of the lobster, Homarus americanus. The p1 muscle re-ceives multiterminal innervation from one motor neu-ron, the lateral pyloric neuron of the stomatogastric ganglion. Staining with antibodies raised against synap-totagmin showed that as the muscle fibers increased in length, the spacing between the terminal innervation increased proportionally, so the number of synaptic con-tact regions/muscle fiber did not change. Muscle fibers were electrically coupled in both juveniles and adults. The amplitude of single intracellularly recorded excita-tory junctional potentials evoked by motor nerve stim-ulation was the same in both juveniles and adults. None-theless, the peak depolarizations reached in response to ongoing pyloric rhythm activity or in response to high-frequency trains of stimuli similar to those produced during the pyloric rhythm were approximately twofold larger in juveniles than in adults. This suggests that homeostatic regulation of synaptic connections may op-erate at the level of the amplitude of the single synaptic potential rather than on the summed depolarization evoked during strong rhythmic activity. © 2004 Wile