Cognitive flexibility relies on a balance between parallel cortico-striatal circuits that govern motivated behavior. Inflexible or habitual behaviors rely primarily on the sensorimotor cortico-basal ganglia circuit that includes the premotor, motor, and somatosensory cortices and the striatal putamen. Chronic alcohol consumption can bias an increase in putamen output, as well as, result in an over-reliance on habitual behaviors. In this study, young adult rhesus macaques (n=12) had Gi-coupled designer receptors exclusively activated by designer drugs (AAV2-hsyn-HA-hM4Di) bilaterally inserted into the putamen. A longitudinal assessment of a novel attentional set-shifting task that increases in difficulty and incorporates sensory motor challenge. Our results suggest putamen inhibition did not alter performance under established parameters but improves adaptation to a sensory-motor challenge when compared to the performance of ethanol-naïve macaques (n=3).

As a first step in examining the primate brain circuitry that mediates ethanol’s interoceptive effects, DREADD receptors (AAV1-hsyn-hM4Di-mCherry) were injected into the nucleus accumbens core (NAcC) and activated with the DREADD actuator, clozapine-n-oxide (CNO-HCl; 1.7-5.6 mg/kg, i.m.), following ethanol administration in monkeys trained to discriminate 1.0 g/kg ethanol. Ethanol potency (ED50) was calculated before and during hM4Di activation followed by post hoc examination of density and spread of hM4Di (observed by mCherry expression) in the NAcC core and its downstream projection. There were wide individual differences in hM4Di-induced changes in ethanol ED50 (range: 0-200% from baseline, n=7 adult male rhesus monkeys) that had a trend association (p=0.057) with hM4Di receptor density within the NAcC. These data provide the first evidence of NAcC involvement in an assay of interoceptive-stimulus associated behavior in primates.

A recently developed ligand-gated ion channels (LGICs) chemogenetic tools called “pharmacologically selective actuator molecules” (PSAMs), consist of the extracellular ligand-binding domain of the α7-nicotinic acetylcholine receptor, engineered to not recognize its endogenous activator acetylcholine, but to be selectively activated by exogenous ligands (termed “Pharmacologically selective effector molecules” or PSEMs). However, prior to establishing it’s use in nonhuman primates, we need to understand the pharmacokinetics and potential off-target side effects of the activating ligand PSEM-817. We found that 0.1mg/kg subcutaneous injection of PSEM-817 readily crosses the blood brain barrier peaking in CSF (2.67ng/ml or 6.4nM) at 30min post-injection, remained stable for 2hours post-injection, and appears to be inert with no impact heart rate or activity levels compared to a vehicle injection. These studies will provide basic information to use PSAMs in monkeys, offering a new LGIC chemogenetic tool for tight modulation of neuronal activity patterns for non-human primate model research.

We recently developed a highly-potent DREADD actuator, deschloroclozapine (DCZ), which rapidly modifies neuronal activity and behavior and can be used as a PET-imaging prove for DREADDs in monkeys. The dual utility of DCZ offers us to non-invasively visualize the hM4Di-positive prefronto-subcortical projections, namely the dorsolateral prefrontal cortex to the mediodorsal thalamus and the caudate nucleus in macaques, and silences these circuits independently by local agonist infusion. We also show that orally delivered DCZ induces rotation behavior in the marmosets expressing hM3Dq in the unilateral nigrostriatal dopaminergic neurons, representing minimally-invasive strategies for circuit manipulation in non-human primates.