Frontal cortical dysfunction is thought to contribute to cognitive and behavioral features of autism spectrum disorders; however, underlying mechanisms are poorly understood. The present study sought to define how loss of Mecp2, the gene mutated in Rett syndrome (RTT), disrupts function in the murine medial prefrontal cortex (mPFC) using acute brain slices and behavioral testing. Compared with wildtype, pyramidal neurons in the Mecp2 null mPFC exhibit significant reductions in excitatory postsynaptic currents, the duration of excitatory UP-states, evoked population activity, and the ratio of NMDA:AMPA currents, as well as an increase in the relative fraction of NR2B currents. These functional changes are associated with reductions in the density of excitatory dendritic spines, the ratio of vesicular glutamate to GABA transporters and GluN1 expression. In contrast to recent reports on circuit defects in other brain regions, we observed no effect of Mecp2 loss on inhibitory synaptic currents or expression of the inhibitory marker parvalbumin. Consistent with mPFC hypofunction, Mecp2 nulls exhibit respiratory dysregulation in response to behavioral arousal. Our data highlight functional hypoconnectivity in the mPFC as a potential substrate for behavioral disruption in RTT and other disorders associated with reduced expression of Mecp2 in frontal cortical regions.

The HIV-1 transactivator of transcription (Tat) is a neurotoxin involved in the pathogenesis of HIV-1 associated neurocognitive disorders (HAND). The neurotoxic effects of Tat are mediated directly via AMPA/NMDA receptor activity and indirectly through neuroinflammatory signaling in glia. Emerging strategies in the development of neuroprotective agents involve the modulation of the endocannabinoid system. A major endocannabinoid, anandamide (N-arachidonoylethanolamine, AEA), is metabolized by fatty acid amide hydrolase (FAAH). Here we demonstrate using a murine prefrontal cortex primary culture model that the inhibition of FAAH, using PF3845, attenuates Tat-mediated increases in intracellular calcium, neuronal death, and dendritic degeneration via cannabinoid receptors (CBR and CBR). Live cell imaging was used to assess Tat-mediated increases in [Ca], which was significantly reduced by PF3845. A time-lapse assay revealed that Tat potentiates cell death while PF3845 blocks this effect. Additionally PF3845 blocked the Tat-mediated increase in activated caspase-3 (apoptotic marker) positive neurons. Dendritic degeneration was characterized by analyzing stained dendritic processes using Imaris and Tat was found to significantly decrease the size of processes while PF3845 inhibited this effect. Incubation with CBR and CBR antagonists (SR141716A and AM630) revealed that PF3845-mediated calcium effects were dependent on CBR, while reduced neuronal death and degeneration was CBR-mediated. PF3845 application led to increased levels of AEA, suggesting the observed effects are likely a result of increased endocannabinoid signaling at CBR/CBR. Our findings suggest that modulation of the endogenous cannabinoid system through inhibition of FAAH may be beneficial in treatment of HAND.

In the era of combined antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) is considered a chronic disease that specifically targets the brain and causes HIV-1-associated neurocognitive disorders (HAND). Endocannabinoids (eCBs) elicit neuroprotective and anti-inflammatory actions in several central nervous system (CNS) disease models, but their effects in HAND remain unknown. HIV-1 does not infect neurons, but produces viral toxins, such as transactivator of transcription (Tat), that disrupt neuronal calcium equilibrium and give rise to synaptodendritic injuries and cell death, the former being highly correlated with HAND. Consequently, we tested whether the eCBs N-arachidonoyl ethanolamine (anandamide/AEA) and 2-arachidonoyl-glycerol (2-AG) offer neuroprotective actions in a neuronal culture model. Specifically, we examined the neuroprotective actions of these eCBs on Tat excitotoxicity in primary cultures of prefrontal cortex neurons (PFC), and whether cannabinoid receptors mediate this neuroprotection. Tat-induced excitotoxicity was reflected by increased intracellular calcium levels, synaptodendritic damage, neuronal excitability, and neuronal death. Further, upregulation of cannabinoid 1 receptor (CB1R) protein levels was noted in the presence of HIV-1 Tat. The direct application of AEA and 2-AG reduced excitotoxic levels of intracellular calcium and promoted neuronal survival following Tat exposure, which was prevented by the CB1R antagonist rimonabant, but not by the CB2R antagonist AM630. Overall, our findings indicate that eCBs protect PFC neurons from Tat excitotoxicity in vitro via a CB1R-related mechanism. Thus, the eCB system possesses promising targets for treatment of neurodegenerative disorders associated with HIV-1 infection.

In the era of combined antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) is now considered a chronic disease that specifically targets the brain and causes HIV-1-associated neurocognitive disorders (HAND). Endocannabinoids exhibit neuroprotective and anti-inflammatory properties in several central nervous system (CNS) disease models, but their effects in HAND are poorly understood. To address this issue, whole-cell recordings were performed on young (14 – 21 day old) C57BL/6J mice. We investigated the actions of the synthetic cannabinoid WIN55,212-2 (1 μM) and the endocannabinoid N-arachidonoyl ethanolamine (anandamide; AEA, 1 μM) in the presence of HIV-1 Tat on GABAergic neurotransmission in mouse prefrontal cortex (PFC) slices. We found a Tat concentration dependent (5 – 50 nM) decrease in the frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). The cannabinoid 1 receptor (CB1R) antagonist rimonabant (1 μM) and zero extracellular calcium prevented the significant Tat-induced decrease in mIPSCs. Further, bath-applied WIN55,212-2 or AEA by itself, significantly decreased the frequency, but not amplitude of mIPSCs and/or spontaneous IPSCs (sIPSCs), and occluded a further down-regulation of IPSCs by Tat. Pretreatment with rimonabant but not the CB2R antagonist AM630 (1 μM) prevented the WIN55,212-2- and AEA-induced decrease in IPSCs frequency without any further Tat effect. Results indicated a Tat-induced decrease in GABAergic neurotransmission, which was occluded by cannabinoids via a CB1R-related mechanism. Understanding the relationship between Tat toxicity and endocannabinoid signaling has the potential to identify novel therapeutic interventions to benefit individuals suffering from HAND and other cognitive impairments.