Presynaptic long-term potentiation in corticothalamic synapses.

The thalamus and neocortex are two highly organized and complex brain structures that work in concert with each other. The largest synaptic input to the thalamus arrives from the neocortex via corticothalamic fibers. Using brain slices, we describe long-term potentiation (LTP) in corticothalamic fibers contacting the ventrobasal thalamus. Corticothalamic LTP is input-specific, NMDA receptor-independent, and reversible. The induction of corticothalamic LTP is entirely presynaptic and Ca(2+)-dependent. The expression of corticothalamic LTP is associated with a decrease in paired-pulse facilitation (PPF) and blocked by an inhibitor of the cAMP-dependent protein kinase A (PKA). Consistent with an involvement of cAMP and PKA, activation of adenylyl cyclase induced a synaptic enhancement that was associated with a decrease in PPF and occluded LTP. Corticothalamic LTP may serve to enhance the efficacy of cortico-cortical communication via the thalamus and/or to mediate experience-dependent long-term modifications of thalamocortical receptive fields.