ILLUMINATING MOTIVATION AND REWARD CIRCUITRY - MULTIPHOTON INSIGHTS INTO STRIATAL NEUROTRANSMITTER DYNAMICS

Acetylcholine and dopamine are key neurotransmitters controlling motivation and reward, with the nucleus accumbens serving as a central hub in this circuitry. We employed the power of functional ex vivo brain slice imaging to study activity and neurotransmitter release with high temporal and spatial resolution.
Multiphoton functional imaging was performed in acute mouse brain slices using fluorescent calcium and neurotransmitter sensors (Cal520, GRAB-Acetylcholine, GRAB-Dopamine). Neuronal activity and transmitter release were assessed following pharmacological modulation of native presynaptically expressed receptors and channels (n=3-6 mice), knock-down of a specific ion channel via microRNA (n=5 mice), and chemogenetic inhibition of cholinergic interneurons (n=3-6 mice).
Recordings revealed that tonic acetylcholine and dopamine release in nucleus accumbens were altered by chemogenetic, pharmacological, and genetic manipulation. Chemogenetic inhibition of cholinergic interneurons reduced acetylcholine release and induced heterogeneous effects on neuronal activity at the population level. Additionally, pharmacological inhibition and knock-down of a presynaptically expressed, non-selective ion channel on cholinergic interneurons decreased acetylcholine release.
Dopamine release was enhanced either by direct activation of a Gs-coupled receptor located on dopaminergic terminals or indirectly through pharmacological inhibition of GABAergic interneurons.
This study demonstrates the power of combining multiphoton functional imaging with genetically encoded neurotransmitter sensors in acute brain slices to dissect local circuit mechanisms. The integration of chemogenetic, pharmacological, and knock-down approaches enabled precise manipulation at the synaptic, single cell and local network levels in the cholinergic and dopaminergic system, revealing their contributions to reward and motivation related circuitry.