Fentanyl and its analogues are increasingly responsible for drug overdose deaths in the United States and
worldwide. As a potent µ-opioid receptor (MOR) agonist, fentanyl is anticipated to exacerbate the pathobiology
of neuroHIV and HIV-associated neurocognitive disorder (HAND) via complex mechanisms involving direct
peripheral and CNS effects. Unlike typical opioids, fentanyl appears to also target non-opioid receptors causing
chest wall muscle rigidity, laryngospasm, and rapid death, and pronounced neuroimmune dysregulation. Our
preliminary data show that non-opioid receptor targets, especially α1-, α2-, and possibly β-adrenergic receptors
(ARs), widely expressed by astroglia in the striatum, are critical for the unique pathophysiologic effects of
fentanyl. We find that acute fentanyl (i) exposure differentially alters the firing rates of dopamine receptor D1-
and D2-expressing (D1 and D2) medium spiny neurons (MSNs), while sustained exposure (ii) nearly eliminates
spontaneous activity in MSNs if co-cultured with astroglia and (iii) increases inflammatory chemokines and
oxyradicals, and that (iv) many of fentanyl's sustained effects are likely mediated by α1AR-expressing astro-
and microglia. Xylazine, an α2AR agonist, which is increasingly combined with fentanyl to create “tranq”, is
highly excitotoxic to MSNs in mixed glial co-cultures and appears to have much more severe pathophysiologic
effects in neuroHIV models than the prototypical opioid morphine, or than fentanyl alone. We hypothesize
that, in addition to its effects at MORs and unlike typical opioids, fentanyl exacerbates HIV-induced
MSN dysfunction and injury through actions at αARs and that its unique pathological effects are
mediated by α1AR-, α2AR- (especially with xylazine), but not β2AR-, expressing astro- and microglia.
This hypothesis will be tested in the following Aims: Aim 1 will identify the MOR-, α1 and α2AR, and βAR
mechanisms by which fentanyl (with some comparisons to morphine) and Tat and infectious and replicative-
deficient HIV cause D1 and D2 MSN excitotoxicity and synaptodendritic injury in vitro. The role of MORs,
α1ARs, and α2ARs will be assessed in studies of MSN-mixed-glial co-cultures and human MSN iPSCs using
confocal microscopy and whole-cell and perforated-patch physiologic approaches. Aim 2 will determine the
MOR- and α1 and α2-AR mechanisms by which fentanyl and HIV interact to disrupt D1 and D2 MSN
synaptodendritic structure and function in control and Tat tg mice in vivo and using whole-cell neurophysiologic
approaches in ex vivo slices. Aim 3 will determine the MOR- and α1 and α2AR mechanisms by which fentanyl
and xylazine (“tranq”) combinations and Tat/HIV interact to disrupt D1 and D2 MSN synaptodendritic structure
and function in vitro and in vivo/ex vivo. This project will systematically explore and compare novel interactions
of fentanyl with HIV using well-established models used previously to characterize the effects of the
prototypical MOR-agonist opioid morphine in neuroHIV. If confirmed, our findings will establish a conceptual
framework for understanding how fentanyl, its synthetic analogues and xylazine impact neuroHIV.
