HIV Transgenic Rats Demonstrate Impaired Sensorimotor Gating But Are Insensitive to Cannabinoid (Δ9-Tetrahydrocannabinol)-Induced Deficits

Acute nicotine vapor normalizes sensorimotor gating and reduces locomotor activity deficits in HIV-1 transgenic rats

Rationale

Despite improved life expectancy of people with HIV (PWH), HIV-associated neurocognitive impairment (NCI) persists, alongside deficits in sensorimotor gating and neuroinflammation. PWH exhibit high smoking rates, possibly due to neuroprotective, anti-inflammatory, and cognitive-enhancing effects of nicotine, suggesting potential self-medication.

Objectives

Here, we tested the effects of acute nicotine vapor exposure on translatable measures of sensorimotor gating and exploratory behavior in the HIV-1 transgenic (HIV-1Tg) rat model of HIV.

Methods

Male and female HIV-1Tg and F344 control rats (n=57) were exposed to acute nicotine or vehicle vapor. Sensorimotor gating was assessed using prepulse inhibition (PPI) of the acoustic startle response, and exploratory behavior was evaluated using the behavioral pattern monitor (BPM).

Results

Vehicle-treated HIV-1Tg rats exhibited PPI deficits at low prepulse intensities compared to F344 controls, as seen previously. No PPI deficits were observed in nicotine-treated HIV1-Tg rats, however. HIV-1Tg rats were hypoactive in the BPM relative to controls, whilst nicotine vapor increased activity and exploratory behavior across genotypes. Cotinine analyses confirmed comparable levels of the primary metabolite of nicotine across genotypes.

Conclusions

Previous findings of PPI deficits in HIV-1Tg rats were replicated and, importantly, attenuated by acute nicotine vapor. Evidence for similar cotinine levels suggest a nicotine-specific effect in HIV-1Tg rats. HIV-1Tg rats had reduced exploratory behavior compared to controls, attenuated by acute nicotine vapor. Therefore, acute nicotine may be beneficial for remediating sensorimotor and locomotor activity deficits in PWH. Future studies should determine the long-term effects of nicotine vapor on similar HIV/NCI-relevant behaviors.

Effects of acute Δ9-tetrahydrocannabinol on behavior and the endocannabinoid system in HIV-1 Tat transgenic female and male mice

Cannabis use is highly prevalent especially among people living with HIV (PLWH). Activation of the anti-inflammatory and neuroprotective endocannabinoid system by phytocannabinoids, i.e. Δ9-tetrahydrocannabinol (THC), has been proposed to reduce HIV symptoms. However, THC's effects on HIV-related memory deficits are unclear. Using HIV-1 Tat transgenic mice, the current study investigates acute THC effects on various behavioral outcomes and the endocannabinoid system. For the rodent tetrad model, THC doses (1, 3, 10 mg/kg) induced known antinociceptive effects, with Tat induction increasing antinociceptive THC effects at 3 and 10 mg/kg doses. Only minor or no effects were noted for acute THC on body temperature, locomotor activity, and coordination. Increased anxiety-like behavior was found for females compared to males, but acute THC had no effect on anxiety. Object recognition memory was diminished by acute THC in Tat(-) females but not Tat(+) females, without affecting males. The endocannabinoid system and related lipids were not affected by acute THC, except for THC-induced decreases in CB1R protein expression levels in the spinal cord of Tat(-) mice. Female sex and Tat induction was associated with elevated 2-AG, AEA, AA, CB1R, CB2R, FAAH and/or MAGL expression in various brain regions. Further, AEA levels in the prefrontal cortex of Tat(+) females were negatively associated with object recognition memory. Overall, findings indicate that acute THC exerts differential effects on antinociception and memory, dependent on sex and HIV Tat expression, potentially in relation to an altered endocannabinoid system, which may be of relevance in view of potential cannabis-based treatment options for PLWH.

THC improves behavioural schizophrenia-like deficits that CBD fails to overcome: a comprehensive multilevel approach using the Poly I:C maternal immune activation

Prenatal infections and cannabis use during adolescence are well-recognized risk factors for schizophrenia. As inflammation and oxidative stress (OS) contribute to this disorder, anti-inflammatory drugs have been proposed as potential therapies. This study aimed to evaluate the association between delta-9-tetrahydrocannabinol (THC) and schizophrenia-like abnormalities in a maternal immune activation (MIA) model. Additionally, we assessed the preventive effect of cannabidiol (CBD), a non-psychotropic/anti-inflammatory cannabinoid. THC and/or CBD were administered to Saline- and MIA-offspring during periadolescence. At adulthood, THC-exposed MIA-offspring showed significant improvements in sensorimotor gating deficits. Structural and metabolic brain changes were evaluated by magnetic resonance imaging, revealing cortical shrinkage in Saline- and enlargement in MIA-offspring after THC-exposure. Additionally, MIA-offspring displayed enlarged ventricles and decreased hippocampus, which were partially reverted by both cannabinoids. CBD prevented THC-induced reduction in the corpus callosum, despite affecting white matter structure. Post-mortem studies revealed detrimental effects of THC, including increased inflammation and oxidative stress. CBD partially reverted these pro-inflammatory alterations and modulated THC's effects on the endocannabinoid system. In conclusion, contrary to expectations, THC exhibited greater behavioural and morphometric benefits, despite promoting a pro-inflammatory state that CBD partially reverted. Further research is needed to elucidate the underlying mechanisms involved in the observed benefits of THC.

The Endocannabinoid System as a Potential Therapeutic Target for HIV-1-Associated Neurocognitive Disorder

Background: Despite the successful introduction of combined antiretroviral therapy, the prevalence of mild to moderate forms of HIV-associated neurocognitive disorders (HAND) remains high. It has been demonstrated that neuronal injury caused by HIV is excitotoxic and inflammatory, and it correlates with neurocognitive decline in HAND. Endocannabinoid system (ECS) protects the body from excitotoxicity and neuroinflammation on demand and presents a promising therapeutic target for treating HAND. Here, we firstly discuss the potential pathogenesis of HAND. We secondly discuss the structural and functional changes in the ECS that are currently known among HAND patients. We thirdly discuss current clinical and preclinical findings concerning the neuroprotective and anti-inflammatory properties of the ECS among HAND patients. Fourth, we will discuss the interactions between the ECS and neuroendocrine systems, including the hypothalamic-pituitary-adrenocortical (HPA) and hypothalamic-pituitary-gonadal (HPG) axes under the HAND conditions. Materials and Methods: We have carried out a review of the literature using PubMed to summarize the current state of knowledge on the association between ECS and HAND. Results: The ECS may be ideally suited for modulation of HAND pathophysiology. Direct activation of presynaptic cannabinoid receptor 1 or reduction of cannabinoid metabolism attenuates HAND excitotoxicity. Chronic neuroinflammation associated with HAND can be reduced by activating cannabinoid receptor 2 on immune cells. The sensitivity of the ECS to HIV may be enhanced by increased cannabinoid receptor expression in HAND. In addition, indirect regulation of the ECS through modulation of hormone-related receptors may be a potential strategy to influence the ECS and also alleviate the progression of HAND due to the reciprocal inhibition of the ECS by the HPA and HPG axes. Conclusions: Taken together, targeting the ECS may be a promising strategy to alleviate the inflammation and neurodegeneration caused by HIV-1 infection. Further studies are required to clarify the role of endocannabinoid signaling in HIV neurotoxicity. Strategies promoting endocannabinoid signaling may slow down cognitive decline of HAND are proposed.

Neurodegeneration Within the Amygdala Is Differentially Induced by Opioid and HIV-1 Tat Exposure

Opioid use disorder (OUD) is a critical problem that contributes to the spread of HIV and may intrinsically worsen neuroHIV. Despite the advent of combined antiretroviral therapies (cART), about half of persons infected with HIV (PWH) experience cognitive and emotional deficits that can be exacerbated by opioid abuse. HIV-1 Tat is expressed in the central nervous system (CNS) of PWH on cART and is thought to contribute to neuroHIV. The amygdala regulates emotion and memories associated with fear and stress and is important in addiction behavior. Notwithstanding its importance in emotional saliency, the effects of HIV and opioids in the amygdala are underexplored. To assess Tat- and morphine-induced neuropathology within the amygdala, male Tat transgenic mice were exposed to Tat for 8 weeks and administered saline and/or escalating doses of morphine twice daily (s.c.) during the last 2 weeks of Tat exposure. Eight weeks of Tat exposure decreased the acoustic startle response and the dendritic spine density in the basolateral amygdala, but not the central nucleus of the amygdala. In contrast, repeated exposure to morphine alone, but not Tat, increased the acoustic startle response and whole amygdalar levels of amyloid-β (Aβ) monomers and oligomers and tau phosphorylation at Ser396, but not neurofilament light chain levels. Co-exposure to Tat and morphine decreased habituation and prepulse inhibition to the acoustic startle response and potentiated the morphine-induced increase in Aβ monomers. Together, our findings indicate that sustained Tat and morphine exposure differentially promote synaptodendritic degeneration within the amygdala and alter sensorimotor processing.