Major depressive disorder is thought to arise in part from dysfunction of the brain's “reward circuitry,” consisting of the mesolimbic dopamine system and the glutamatergic and neuromodulatory inputs onto this system. Both chronic stress and antidepressant treatment regulate gene transcription in many of the brain regions that make up these circuits, but the exact nature of the transcription factors and target genes involved in these processes remain unclear. Here, we demonstrate induction of the FosB family of transcription factors in ∼25 distinct regions of adult mouse brain, including many parts of the reward circuitry, by chronic exposure to the antidepressant fluoxetine. We further uncover specific patterns of FosB gene product expression (i.e., differential expression of full-length FosB, ΔFosB, and Δ2ΔFosB) in brain regions associated with depression – the nucleus accumbens (NAc), prefrontal cortex (PFC), and hippocampus – in response to chronic fluoxetine treatment, and contrast these patterns with differential induction of FosB isoforms in the chronic social defeat stress model of depression with and without fluoxetine treatment. We find that chronic fluoxetine, in contrast to stress, causes induction of the unstable full-length FosB isoform in the NAc, PFC, and hippocampus even 24 hours following the final injection, indicating that these brain regions may undergo chronic activation when fluoxetine is on board, even in the absence of stress. We also find that only the stable ΔFosB isoform correlates with behavioral responses to stress. These data suggest that NAc, PFC, and hippocampus may present useful targets for directed intervention in mood disorders (ie, brain stimulation or gene therapy), and that determining the gene targets of FosB-mediated transcription in these brain regions in response to fluoxetine may yield novel inroads for pharmaceutical intervention in depressive disorders.

Stable changes in neuronal gene expression have been studied as mediators of addicted states. Of particular interest is the transcription factor ⌬FosB, a truncated and stable FosB gene product whose expression in nucleus accumbens (NAc), a key reward region, is induced by chronic exposure to virtually all drugs of abuse and regulates their psychomotor and rewarding effects. Phosphorylation at Ser 27 contributes to ⌬FosB's stability and accumulation following repeated exposure to drugs, and our recent work demonstrates that the protein kinase CaMKII␣ phosphorylates ⌬FosB at Ser 27 and regulates its stability in vivo. Here, we identify two additional sites on ⌬FosB that are phosphorylated in vitro by CaMKII␣, Thr 149 and Thr 180, and demonstrate their regulation in vivo by chronic cocaine. We show that phosphomimetic mutation of Thr 149 (T149D) dramatically increases AP-1 transcriptional activity while alanine mutation does not affect transcriptional activity when compared with wild-type (WT) ⌬FosB. Using in vivo viral-mediated gene transfer of ⌬FosB-T149D or ⌬FosB-T149A in mouse NAc, we determined that overexpression of ⌬FosB-T149D in NAc leads to greater locomotor activity in response to an initial low dose of cocaine than does WT ⌬FosB, while overexpression of ⌬FosB-T149A does not produce the psychomotor sensitization to chronic low-dose cocaine seen after overexpression of WT ⌬FosB and abrogates the sensitization seen in control animals at higher cocaine doses. We further demonstrate that mutation of Thr 149 does not affect the stability of ⌬FosB overexpressed in mouse NAc, suggesting that the behavioral effects of these mutations are driven by their altered transcriptional properties.

OBJECTIVES: The impact of opioids on anorectal function is poorly understood but potentially relevant to the pathogenesis of opioid-induced constipation (OIC). To evaluate anorectal function testing (AFT) characteristics, symptom burden, and quality of life in chronically constipated patients prescribed an opioid (OIC) in comparison with constipated patients who are not on an opioid (NOIC). METHODS: Retrospective analysis of prospectively collected data on 3,452 (OIC = 588 and NOIC = 2,864) chronically constipated patients (Rome 3) who completed AFT. AFT variables included anal sphincter pressure and response during simulated defecation, balloon expulsion test (BET), and rectal sensation. Dyssynergic defecation (DD) was defined as an inability to relax the anal sphincter during simulated defecation and an abnormal BET. Patients completed Patient Assessment of Constipation Symptoms (PAC-SYM) and Patient Assessment of Constipation Quality of Life (PAC-QOL) questionnaires. RESULTS: The mean age of the study cohort was 49 years. Most patients were women (82%) and whites (83%). Patients with OIC were older than NOIC patients (50.7 vs 48.3, P = 0.001). OIC patients were significantly more likely to have DD (28.6% vs 21.4%, P < 0.001), an abnormal simulated defecation response on anorectal manometry (59% vs 43.8%, P < 0.001), and an abnormal BET (48% vs 42.5%, P = 0.02) than NOIC patients. OIC patients reported more severe constipation symptoms (P < 0.02) and worse quality of life (P < 0.05) than NOIC patients. DISCUSSION: Chronically constipated patients who use opioids are more likely to have DD and more severe constipation symptoms than NOIC.