Differential effects of cannabinoid CB1 inverse agonists and antagonists on impulsivity in male Sprague Dawley rats: identification of a possibly clinically relevant vulnerability involving the serotonin 5HT1A receptor.

RATIONALE: Cannabinoid CB1 inverse agonists hold therapeutic promise as appetite suppressants but have produced suicidal behaviors among a small subpopulation in clinical trials. Anatomical and pharmacological evidence implicate the 5HT1A serotonin receptor in suicide in humans and impulsivity in humans and animals. OBJECTIVE: The objective of the study is to assess whether 5HT1A blockade is necessary for CB1 ligands to produce impulsivity. METHODS: Sprague Dawley rats were administered the CB1 inverse agonist AM 251, the CB1 antagonist AM 6527, or the peripherally restricted antagonist AM 6545, with or without pretreatment with the 5HT1A antagonist WAY 100,635 (WAY) on the paced fixed consecutive number (FCN) task, which measures choice to terminate a chain of responses prematurely. As FCN is sensitive to changes in time perception, which have been demonstrated with CB1 blockade, a novel variable consecutive number task with discriminative stimulus (VCN-S D ) was also performed and proposed to be less sensitive to changes in timing. RESULTS: Pretreatment with WAY enabled mild but significant reductions in FCN accuracy for AM 251 and AM 6527. No effects were found for AM 6545. On the VCN-S D task, substantial impairments were found for the combination of WAY and AM 251. CONCLUSIONS: AM 251, but not the antagonists AM 6527 or AM 6545, produced impulsivity only following systemic 5HT1A blockade. Although preliminary, the results may indicate that disrupted serotonin signaling produces a vulnerability to undesirable effects of CB1 inverse agonists, which is not evident in the general population. Furthermore, neutral CB1 antagonists do not produce this effect and therefore may have greater safety.

Attenuation of PKR-like ER Kinase (PERK) Signaling Selectively Controls Endoplasmic Reticulum Stress-induced Inflammation Without Compromising Immunological Responses.

Inflammation and endoplasmic reticulum (ER) stress are associated with many neurological diseases. ER stress is brought on by the accumulation of misfolded proteins in the ER, which leads to activation of the unfolded protein response (UPR), a conserved pathway that transmits signals to restore homeostasis or eliminate the irreparably damaged cell. We provide evidence that inhibition or genetic haploinsufficiency of protein kinase R-like endoplasmic reticulum kinase (PERK) can selectively control inflammation brought on by ER stress without impinging on UPR-dependent survival and adaptive responses or normal immune responses. Using astrocytes lacking one or both alleles of PERK or the PERK inhibitor GSK2606414, we demonstrate that PERK haploinsufficiency or partial inhibition led to reduced ER stress-induced inflammation (IL-6, CCL2, and CCL20 expression) without compromising prosurvival responses. In contrast, complete loss of PERK blocked canonical PERK-dependent UPR genes and promoted apoptosis. Reversal of eIF2α-mediated translational repression using ISRIB potently suppressed PERK-dependent inflammatory gene expression, indicating that the selective modulation of inflammatory gene expression by PERK inhibition may be linked to attenuation of eIF2α phosphorylation and reveals a previously unknown link between translational repression and transcription of inflammatory genes. Additionally, ER-stressed astrocytes can drive an inflammatory M1-like phenotype in microglia, and this can be attenuated with inhibition of PERK. Importantly, targeting PERK neither disrupted normal cytokine signaling in astrocytes or microglia nor impaired macrophage phagocytosis or T cell polarization. Collectively, this work suggests that targeting PERK may provide a means for selective immunoregulation in the context of ER stress without disrupting normal immune function.