Journal of Neurophysiology 79: 1450-1460, 1998.
The amount of synaptic activity was much lower in brain slices (at 34oC) as the standard deviation of the intracellular signal was 10-17 times lower in vitro than in vivo. Rins measured in vivo during relatively quiescent epochs ('control Rins') could be reduced by up to 70% during periods of intense spontaneous activity. Further, the 'control Rins' were increased by about 30-70% following TTX application in vivo, approaching in vitro values. In contrast, TTX produced negligible Rin changes in vitro (about 4%).
These results indicate that, compared to the in vitro situation, the background synaptic activity present in intact networks dramatically reduces the electrical compactness of cortical neurons and modifies their integrative properties. The impact of the spontaneous synaptic bombardment should be taken into account when extrapolating in vitro findings to the intact brain.