Homeostatic shutdown of long-term potentiation in the adult hippocampus.

Homeostasis is a key concept in biology. It enables ecosystems, organisms, organs, and cells to adjust their operating range to values that ensure optimal performance. Homeostatic regulation of the strength of neuronal connections has been shown to play an important role in the development of the nervous system. Here we investigate whether mature neurons also possess mechanisms to prevent the strengthening of input synapses once the limit of their operating range has been reached. Using electrophysiological recordings in hippocampal slices, we show that such a mechanism exists but comes into play only after a considerable number of synapses have been potentiated. Thus, adult neurons can sustain a substantial amount of synaptic strengthening but, once a certain threshold of potentiation is exceeded, homeostatic regulation ensures that no further strengthening can occur.