BDNF HAS OPPOSITE EFFECTS ON THE QUANTAL AMPLITUDE OF PYRAMIDAL NEURON AND INTERNEURON EXCITATORY SYNAPSES

Recently, we have identified a novel form of synaptic plasticity that acts to stabilize neocortical firing rates by scaling the quantal ampl itude of AMPA-mediated synaptic inputs up or down as a function of neu ronal activity. Here, we show that the effects of activity blockade on quantal amplitude are mediated through the neurotrophin brain-derived neurotrophic factor (BDNF). Exogenous BDNF prevented, and a TrkB-IgG fusion protein reproduced, the effects of activity blockade on pyramid al quantal amplitude. BDNF had opposite effects on pyramidal neuron an d interneuron quantal amplitudes and modified the ratio of pyramidal n euron to interneuron firing rates. These data demonstrate a novel role for BDNF in the homeostatic regulation of excitatory synaptic strengt hs and in the maintenance of the balance of cortical excitation and in hibition.