Figure 4.

Ca²⁺ is necessary and sufficient for long-term potentiation (LTP). A: in this series of experiments an extracellular electrode records the field potential LTP from a population of neurons (top). Simultaneously, an intracellular electrode monitors LTP from a single neuron (bottom). When the intracellular recording electrode is filled with the standard electrolyte, the magnitude of LTP is the same as that recorded with the field electrode. In contrast, when the intracellular electrode contains nitr-5, a nitrobenzhydrol tetracarboxylate (a Ca²⁺ chelator), LTP is absent (bottom) (177), indicating that Ca²⁺ is necessary for LTP. B: the experimental design involves stimulating 2 independent pathways and recording responses from a single cell (see inset). The stimuli to the 2 pathways were alternated to get a baseline for each pathway. The cell is depolarized to 0 mV and stimulation of pathway 1 continues, but stimulation of pathway 2 is stopped. The cell is then depolarized to +70 mV and stimulation to pathway 1 stopped, but stimulation of pathway 2 commences. After this pairing protocol, the cell is returned to −70 mV. Robust LTP is observed for pathway 1 but no LTP for pathway 2. Superimposed sample records of before and after pairing are shown below. The results indicate that a rise in Ca²⁺ through N-methyl-d-aspartate receptors (NMDARs) is instructive for LTP (178). C: a rise in postsynaptic Ca²⁺ is sufficient to potentiate synaptic transmission, Photo uncaging of Ca²⁺ from nitr-5, a nitrobenzhydrol tetracarboxylate Ca²⁺ chelator, enhances synaptic transmission (filled triangles) but fails to enhance synaptic transmission when the cage is not loaded with Ca²⁺ (open triangles) (177). EPSC, excitatory postsynaptic current; EPSP, excitatory postsynaptic potential. Images modified from Refs. 177 and 178, with permission from Science and Neuron, respectively.