Locus coeruleus and dopaminergic consolidation of everyday memory

The retention of episodic-like memory is enhanced, in humans and animals, when something novel happens shortly before or after encoding. Using an everyday memory task in mice, we sought the neurons mediating this dopamine-dependent novelty effect, previously thought to originate exclusively from the tyrosine hydroxylase-expressing (TH(+)) neurons in the ventral tegmental area (VTA). We report that neuronal firing in the locus coeruleus (LC) is especially sensitive to environmental novelty, LC-TH(+) neurons project more profusely than VTA-TH(+) neurons to the hippocampus, optogenetic activation of LC-TH(+) neurons mimics the novelty effect, and this novelty-associated memory enhancement is unaffected by VTA inactivation. Surprisingly, two effects of LC-TH(+) photoactivation are sensitive to hippocampal D(1)/D(5) receptor blockade and resistant to adrenoceptors blockade – memory enhancement and long lasting potentiation of synaptic transmission in CA1 ex vivo. Thus, LC-TH(+) neurons can mediate post-encoding memory enhancement in a manner consistent with possible co-release of dopamine in hippocampus.