Input-specific synaptic plasticity in the nucleus accumbens evoked by inhibition of angiotensin-converting enzyme

PROJECT SUMMARY Substance use disorders (SUDs) impair the health and well-being of over 40 million Americans and claim 106,000 lives each year due to a lack of effective treatments. The nucleus accumbens (NAc), which consists of medium spiny neurons (MSNs) marked by expression of Dopamine-1 or -2 receptors (D1 or D2, respectively),

is a reward center of the brain that exhibits changes in synaptic plasticity that drive addiction. D1-MSNs drive rewarding behaviors, such as addiction, while D2-MSNs drive aversive behaviors. Thus, identifying precise molecular targets that modulate D1-MSN synaptic signaling would hold promising therapeutic potential for SUDs.

Angiotensin converting enzyme (ACE) is selectively expressed in D1-MSNs within the NAc. In the brain, ACE hydrolyzes numerous neuropeptides, including the enkephalin Met-enkephalin-Arg-Phe (MERF), which has a high affinity for opioid receptors. ACE inhibition (ACEi) increases levels of MERF in the NAc, which acts in a -

opioid receptor (MOR) dependent manner at excitatory presynaptic inputs to drive long-term depression (ACEi- LTD) specifically onto D1-MSNs. However, it has not yet been determined which specific excitatory and inhibitory presynaptic inputs express ACEi-LTD, as NAc MSNs receive a diverse array of long-range excitatory and local

inhibitory inputs. The main goal of this proposal is to determine which specific excitatory and inhibitory presynaptic inputs to NAc MSNs express ACEi-LTD, revealing the circuit-specific synaptic plasticity mechanisms evoked by ACEi which is critical for developing circuit-informed therapies for SUDs. Towards this, excitatory opsins will be

expressed virally in an input and cell type-specific manner in individual inputs to the NAc. Whole-cell patch-clamp electrophysiological recordings will be taken from D1- and D2-MSNs while optogenetically stimulating individual excitatory or inhibitory inputs. Optically- and electrically-evoked postsynaptic currents will be measured before,

during, and after application of an ACE inhibitor to determine which specific excitatory and inhibitory inputs exhibit ACEi-LTD. The MOR-dependence of ACEi-LTD will be determined using pharmacological and genetic blockade of MOR signaling. Since thalamic inputs to the NAc are known to drive opiate dependence, and since prior

studies suggest that ACEi modulates cortical excitatory inputs to the NAc, Aim 1 will investigate the ACEi sensitivity of thalamic and cortical excitatory inputs onto MSNs. Additionally, since fast-spiking interneurons (FSIs) provide the most robust regulation of MSN output, and since low-threshold spiking interneurons (LTSIs)

are known to decrease presynaptic release upon MOR-agonist treatment, Aim 2 will investigate the ACEi sensitivity of FSI and LTSI inhibitory inputs onto MSNs. This proposal will reveal the circuit-specific effects of ACEi, which selectively targets D1-MSNs of the NAc that drive reward and contribute to addictive behaviors.

Since ACEi attenuates fentanyl preference in mice, ACE may be a precise and safe therapeutic target for the prevention and/or treatment of SUDs such as opioid use disorder.