Cropper E C, Price D, Tenenbaum R, Kupfermann I, Weiss K R
Center for Neurobiology and Behavior, New York State Psychiatric Institute, NY 10032.
Proc Natl Acad Sci U S A. 1990 Feb;87(3):933-7. doi: 10.1073/pnas.87.3.933.
In previous studies, we demonstrated that B15, one of the two cholinergic motor neurons of the accessory radula closer muscle of Aplysia, synthesizes two peptides, small cardioactive peptides A and B (SCPA and SCPB), that, when exogenously applied, increase the size and relaxation rate of muscle contractions elicited by motor neuron stimulation. In the present experiments, we obtained evidence that the SCPs are released under physiological conditions. Specifically, we characterized firing patterns of motor neuron B15 during normal behavior, simulated them in vitro, and demonstrated that this type of neuronal activity produces decreases in SCP levels in neuronal processes and terminals. We also obtained evidence that suggests that enough SCP is released under physiological conditions to modulate neuromuscular activity in the accessory radula closer. We demonstrated that physiological activity of neuron B15 produces significant increases in muscle cAMP levels. Furthermore, increases in the size and relaxation rate of muscle contractions can be produced by changes in stimulation parameters that are also likely to maximize effects of released endogenous SCPA and SCPB.
在先前的研究中，我们证明，海兔副齿舌闭合肌的两个胆碱能运动神经元之一的B15，能合成两种肽，即小的心脏活性肽A和B（SCPA和SCPB），当外源性应用时，它们会增加运动神经元刺激引发的肌肉收缩的大小和松弛速率。在本实验中，我们获得了证据，表明SCPs在生理条件下会释放。具体而言，我们对正常行为期间运动神经元B15的放电模式进行了表征，在体外进行模拟，并证明这种类型的神经元活动会使神经元突起和终末中的SCP水平降低。我们还获得了证据，表明在生理条件下释放的SCP足以调节副齿舌闭合肌中的神经肌肉活动。我们证明，神经元B15的生理活动会使肌肉中的cAMP水平显著升高。此外，刺激参数的变化也可能使释放的内源性SCPA和SCPB的作用最大化，从而导致肌肉收缩的大小和松弛速率增加。
