Hippocampus innervation modulates formation of aversive memories

Hippocampus innervation modulates formation of aversive memories

The neurotransmitter dopamine is thought to play an important role in memory and learning through its modulation of the hippocampus. However, the origin and mode of action of dopamine on hippocampus-dependent memory are unclear.

The researchers used viral tracing methods to identify and label a population of dopaminergic neurons near the border of the lateral ventral tegmental area and substantia nigra pars compacta of the midbrain that directly innervate the dorsal hippocampus.

The authors used optogenetic manipulations to enhance dopamine release from the midbrain and found that this release facilitated aversive learning. In contrast, pharmacological inhibition of dopamine signaling in dorsal CA1 was found to reduce contextual fear conditioning acquisition.

Thus, dopamine can bidirectionally regulate context-dependent associative fear learning in the hippocampus.

Additionally, genetic ablation of catecholamine production exclusively in norepinephrine neurons showed that midbrain dopamine is sufficient to maintain normal contextual fear memory formation, with no locus coeruleus dopamine contribution.

The findings indicate that a cluster of midbrain dopamine neurons send direct projections to the hippocampus, and midbrain dopaminergic innervation of the dorsal hippocampus helps modulate aversive memory formation, according to the authors.