Direct evidence for biphasic cAMP responsive element-binding protein phosphorylation during long-term potentiation in the rat dentate gyrus in vivo.

Phosphorylation of the transcription factor cAMP responsive element-binding protein (CREB) is thought to play a key role in synaptic plasticity and long-term memory. However, direct evidence for CREB phosphorylation during hippocampal long-term potentiation (LTP) in vivo is sparse. Here, we show that, in the intact animal, CREB is rapidly phosphorylated in response to high-frequency stimulation but not low-frequency stimulation of the perforant pathway. CREB phosphorylation occurred in a biphasic manner, with a first peak at 30 min and a second long-lasting peak beginning 2 hr after tetanic stimulation and lasting for at least 24 hr. Only stimuli that generated nondecremental LTP promoted a sustained hyperphosphorylation of CREB but not stimuli that produced decremental LTP. CREB phosphorylation was specifically triggered in the dentate gyrus, as well as the CA1, but not the CA3, hippocampal region. Pretreatment with the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate completely prevented activation of CREB. Together, we have resolved the spatial and temporal dynamics of CREB phosphorylation during hippocampal LTP, showing that the transcription factor CREB is specifically recruited at two distinct time points in some forms of hippocampal synaptic plasticity in vivo.