| Abstract: | In a crayfish phasic neuromuscular junction, we have demonstrated low-frequency depression (LFD), high-frequency depression (HFD), and long-term facilitation (LTF) in response to different regimens of stimulation. Chronic stimulation of the phasic axon supplying the closer muscle of the claw in Procambarus clarkii resulted in diminished expression of HFD and LTF. Conversely, when impulse production in the phasic motoneuron was reduced by claw immobilization, both HFD and LTF were enhanced. LFD was insensitive to these manipulations. These results provide further evidence for long-term adaptation of the phasic neuromuscular junction to ongoing levels of impulse activity and illustrate the importance of a neuron's past history for synaptic plasticity. The ability of the neuron to adjust its short-term plasticity in response to altered experience constitutes an adaptive response that could be of general significance. |
