Evidence for proportional synaptic scaling in neocortex of intact animals

Neocortical neurons in culture can modify their global synaptic strength ac cording to their recent activity level. This process has been termed synapt ic scaling. We explored possible effects of synaptic scaling in intact anim als by comparing EPSPs of two identified synaptic tracts on single cortical neurons in acute slices. We show that the amplitude and rise-time of unita ry thalamocortical and intracortical EPSPs vary among different neurons, bu t are highly correlated on single cells. Likewise, the AMPA-to-NMDA recepto r ratio in EPSPs evoked from the two tracts is correlated in single neurons , although intracortical pathways within layer 5 exhibit a significantly la rger NMDA component. These findings demonstrate that, under physiological c onditions, cortical neurons actively regulate their own response magnitude, regardless of the input source. NeuroReport 11:4027-4031 (C) 2000 Lippinco tt Williams & Wilkins.