The development of chemosensitivity in extrasynaptic areas of the neuronal surface after denervation of parasympathetic ganglion cells in the heart of the frog

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Abstract
1. The vagosympathetic trunks innervating the heart of the frog were cut on both sides. Two to 28 days following this denervation the chemosensitivity of the surface of the denervated neurons was explored with iontophoretic microapplication of ACh to restricted areas. 2. While in normally innervated neurons the synaptic areas alone are highly chemosensitive, after denervation the whole cell surface becomes sensitive to ACh. Synaptic transmission fails on the second day (30 to 40 h) after denervation (in frogs kept at 22 to 24 °C) and at the same time new chemoreceptive areas start to appear. After 4 to 8 days this development of chemosensitivity has reached a peak and remains at the same level for 4 weeks (the longest period of the present tests). 3. Measurements of chemosensitivity from different cells in different animals were compared. The finely localized chemosensitivity at synaptic areas in normally innervated neurons was of similar magnitude as the uniformly distributed sensitivity in denervated neurons.