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Figure 4 Synaptic activity regulates presynaptic excitablility. Muscle activation leads to release of retrograde factors that modulate excitability of the presynaptic neurons. These effects are mediated by the neurotrophin, NT-3. a, The refractory period was measured using a two-pulse protocol with a longer interpulse interval for each successive trial. Three trials are superimposed for each condition. In the presence of a-BgTX, APs did not overshoot the stimulus artifact. b, Co-application of NT-3 with a-BgTX rescued the effects of the toxin. Reprinted by permission from Macmillan Publishers Ltd: Nat. Neurosci. (Nick, T. A. and Ribera, A. B. 2000. Synaptic activity modulates presynaptic excitability. Nat. Neurosci. 3, 142-149), copyright (2000).

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Figure 4 Synaptic activity regulates presynaptic excitablility. Muscle activation leads to release of retrograde factors that modulate excitability of the presynaptic neurons. These effects are mediated by the neurotrophin, NT-3. a, The refractory period was measured using a two-pulse protocol with a longer interpulse interval for each successive trial. Three trials are superimposed for each condition. In the presence of a-BgTX, APs did not overshoot the stimulus artifact. b, Co-application of NT-3 with a-BgTX rescued the effects of the toxin. Reprinted by permission from Macmillan Publishers Ltd: Nat. Neurosci. (Nick, T. A. and Ribera, A. B. 2000. Synaptic activity modulates presynaptic excitability. Nat. Neurosci. 3, 142-149), copyright (2000).

Okamura, 1998). Their results indicated that, in both the unfertilized and the newly fertilized egg, APs were generated. Further, AP generation required the function of voltage-gated sodium and/ or calcium channels. In contrast, differentiated muscle fibers showed a predominantly calcium-dependent AP. These observations suggested that, during early embryonic differentiation: (1) some types of ion channels are eliminated; (2) some types of ion channels increase in density; and (3) new channel types appear.

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