Two sources of dopamine for the hippocampus.

McNamara CG
Dupret D

This article describes three recent papers that together suggest that novelty signalling in the brain's memory centre arises from two different brain pathways, whereas up until recently it was thought to originate from only one. Both pathways use a chemical messenger called dopamine.

Scientific Abstract

Dopaminergic signalling is established as playing an important role in novelty related modulation of hippocampal memory. Two recent studies have identified the noradrenergic fibres originating in the locus coeruleus as an additional source of neurotransmitter acting on dopaminergic receptors in the hippocampus.

Dopaminergic axons in the hippocampus
Dopaminergic axons in the dorsal CA1 subfield of the hippocampus visualized through green fluorescent protein expression after transfection with an AAV at the cell bodies in the VTA. Inserts show anti tyrosine hydroxylase staining for the same axonal segments in magenta. Cell nuclei (white) show the location of the pyramidal cell layer.
2017. Trends Neurosci., 40(7):383-384.