Ventral Tegmental Area Dopamine Neurons Regulated by the Parabrachial Nucleus Mediate Long-Term Aversive Memory

Ventral tegmental area (VTA) dopamine (DA) neurons are intermixed with glutamate and GABA (gamma-aminobutyric acid) neurons, which have been implicated in aversion. While the neuronal circuitry involved in regulation of different VTA neurons that mediate aversion is unclear, a potential component of this circuitry is the parabrachial nucleus (PBN), which is involved in encoding threats and innervating the VTA.

To characterize synaptic connectivity between VTA neurons and PBN inputs, we applied neuronal tract tracing, RNAscope, immunohistochemistry, electron microscopy, and ex vivo electrophysiology. To test the role of different types of VTA neurons and PBN inputs in behavior, we applied a combination of behavioral assays, photometry recordings, optogenetics, pharmacology, and neuronal genetic ablation.

We found that lateral PBN (LPBN) glutamatergic neurons innervate the VTA and photoactivation of this pathway induced long-term aversive memory, and whereas LPBN neurons innervating VTA increased their activity in response to innate or learned threats, their genetic ablation eliminated responses to threats. We determined that LPBN-glutamatergic neurons established monosynaptic connections with VTA-DA, VTA-GABA, and VTA-glutamate neurons. However, VTA-DA neurons, but not VTA-GABA or VTA-glutamate neurons, via their regulation by LPBN-glutamatergic neurons mediated long-term aversive memory to innate and learned threats, blocked by a VTA D₁ receptor antagonist.

Our findings indicate that while different types of VTA neurons are regulated by LPBN-glutamate neurons, the LPBN neurons relay information on threatening stimuli to VTA-DA neurons. This pathway mediates the acquisition and expression of long-term aversive memory via a mechanism that involves somatodendritic release of DA and activation of VTA D₁ receptors.