Reward behaviour is regulated by the strength of hippocampus–nucleus accumbens synapses
LeGates TA, Kvarta MD, Tooley JR, et al. Reward behaviour is regulated by the strength of hippocampus–nucleus accumbens synapses. Nature. 2018. https://doi.org/10.1038/s41586-018-0740-8.
Reward drives motivated behaviours and is essential for survival, and therefore there is strong evolutionary pressure to retain contextual information about rewarding stimuli. This drive may be abnormally strong, such as in addiction, or weak, such as in depression, in which anhedonia (loss of pleasure in response to rewarding stimuli) is a prominent symptom. Hippocampal input to the shell of the nucleus accumbens (NAc) is important for driving NAc activity1,2 and activity-dependent modulation of the strength of this input may contribute to the proper regulation of goal-directed behaviours. However, there have been few robust descriptions of the mechanisms that underlie the induction or expression of long-term potentiation (LTP) at these synapses, and there is, to our knowledge, no evidence about whether such plasticity contributes to reward-related behaviour. Here we show that high-frequency activity induces LTP at hippocampus–NAc synapses in mice via canonical, but dopamine-independent, mechanisms. The induction of LTP at this synapse in vivo drives conditioned place preference, and activity at this synapse is required for conditioned place preference in response to a natural reward. Conversely, chronic stress, which induces anhedonia, decreases the strength of this synapse and impairs LTP, whereas antidepressant treatment is accompanied by a reversal of these stress-induced changes. We conclude that hippocampus–NAc synapses show activity-dependent plasticity and suggest that their strength may be critical for contextual reward behaviour.
Neuropsychiatric Symptoms and the Diagnostic Stability of Mild Cognitive Impairment
Sugarman MA, Alosco ML, Tripodis Y, Steinberg EG, Stern RA. Neuropsychiatric symptoms and the diagnostic stability of mild cognitive impairment. Journal of Alzheimer’s Disease. 2018:1-15. doi: 10.3233/JAD-170527.
Mild cognitive impairment (MCI) is an intermediate diagnosis between normal cognition (NC) and dementia, including Alzheimer’s disease (AD) dementia. However, MCI is heterogeneous; many individuals subsequently revert to NC while others remain stable at MCI for several years. Identifying factors associated with this diagnostic instability could assist in defining clinical populations and determining cognitive prognoses.
The current study examined whether neuropsychiatric symptoms could partially account for the temporal instability in cognitive diagnoses.
The sample included 6,763 participants from the National Alzheimer’s Coordinating Center Uniform Data Set. All participants had NC at baseline, completed at least two follow-up visits (mean duration: 5.5 years), and had no recent neurological conditions. Generalized linear models estimated by generalized estimating equations examined associations between changes in cognitive diagnoses and symptoms on the Neuropsychiatric Inventory Questionnaire (NPI-Q) and Geriatric Depression Scale (GDS-15).
1,121 participants converted from NC to MCI; 324 reverted back to NC and 242 progressed to AD dementia. Higher symptoms on the GDS-15 and circumscribed symptom domains on the NPI-Q were associated with conversion from NC to MCI and a decreased likelihood of reversion from MCI to NC. Individuals with higher symptoms on NPI-Q Hyperactivity and Mood items were more likely to progress to AD dementia.
The temporal instability of MCI can be partially explained by neuropsychiatric symptoms. Individuals with higher levels of specific symptoms are more likely to progress to AD dementia and less likely to revert to NC. Identification and treatment of these symptoms might support cognitive functioning in older adults.
Loss of eIF4E Phosphorylation Engenders Depression-like Behaviors via Selective mRNA Translation
Amorim IS, Kedia S, Kouloulia S, et al. Loss of eIF4E phosphorylation engenders depression-like behaviors via selective mRNA translation. J Neurosci. 2018;38(8):2118-2133. doi: 10.1523/JNEUROSCI.2673-17.2018.
The MAPK/ERK (mitogen-activated protein kinases/extracellular signal-regulated kinase) pathway is a cardinal regulator of synaptic plasticity, learning, and memory in the hippocampus. One of major endpoints of this signaling cascade is the 5′ mRNA cap binding protein eIF4E (eukaryotic Initiation Factor 4E), which is phosphorylated on Ser 209 by MNK (MAPK-interacting protein kinases) and controls mRNA translation. The precise role of phospho-eIF4E in the brain is yet to be determined. Herein, we demonstrate that ablation of eIF4E phosphorylation in male mice (4Eki mice) does not impair long-term spatial or contextual fear memory, or the late phase of LTP. Using unbiased translational profiling in mouse brain, we show that phospho-eIF4E differentially regulates the translation of a subset of mRNAs linked to inflammation, the extracellular matrix, pituitary hormones, and the serotonin pathway. Consequently, 4Eki male mice display exaggerated inflammatory responses and reduced levels of serotonin, concomitant with depression and anxiety-like behaviors. Remarkably, eIF4E phosphorylation is required for the chronic antidepressant action of the selective serotonin reuptake inhibitor fluoxetine. Finally, we propose a novel phospho-eIF4E-dependent translational control mechanism in the brain, via the GAIT complex (gamma IFN activated inhibitor of translation). In summary, our work proposes a novel translational control mechanism involved in the regulation of inflammation and depression, which could be exploited to design novel therapeutics.
SIGNIFICANCE STATEMENT We demonstrate that downstream of the MAPK (mitogen-activated protein kinase) pathway, eukaryotic Initiation Factor 4E (eIF4E) Ser209 phosphorylation is not required for classical forms of hippocampal LTP and memory. We reveal a novel role for eIF4E phosphorylation in inflammatory responses and depression-like behaviors. eIF4E phosphorylation is required for the chronic action of antidepressants, such as fluoxetine in mice. These phenotypes are accompanied by selective translation of extracellular matrix, pituitary hormones, and serotonin pathway genes, in eIF4E phospho-mutant mice. We also describe a previously unidentified translational control mechanism in the brain, whereby eIF4E phosphorylation is required for inhibiting the translation of gamma IFN activated inhibitor of translation element-containing mRNAs. These findings can be used to design novel therapeutics for depression.
Adjunctive Bright Light Therapy for Bipolar Depression: A Randomized Double-Blind Placebo-Controlled Trial
Sit, D. K., McGowan, J., Wiltrout, C., Diler, R. S., Dills, J., et al. (2017). Adjunctive bright light therapy for bipolar depression: A randomized double-blind placebo-controlled trial. American Journal of Psychiatry. doi:10.1176/appi.ajp.2017.16101200
Patients with bipolar disorder have recurrent major depression, residual mood symptoms, and limited treatment options. Building on promising pilot data, the authors conducted a 6-week randomized double-blind placebo-controlled trial to investigate the efficacy of adjunctive bright light therapy at midday for bipolar depression. The aims were to determine remission rate, depression symptom level, and rate of mood polarity switch, as well as to explore sleep quality.
The study enrolled depressed adults with bipolar I or II disorder who were receiving stable dosages of antimanic medication (excluding patients with hypomania or mania, mixed symptoms, or rapid cycling). Patients were randomly assigned to treatment with either 7,000-lux bright white light or 50-lux dim red placebo light (N=23 for each group). Symptoms were assessed weekly with the Structured Interview Guide for the Hamilton Depression Scale With Atypical Depression Supplement (SIGH-ADS), the Mania Rating Scale, and the Pittsburgh Sleep Quality Index. Remission was defined as having a SIGH-ADS score of 8 or less.
At baseline, both groups had moderate depression and no hypomanic or manic symptoms. Compared with the placebo light group, the group treated with bright white light experienced a significantly higher remission rate (68.2% compared with 22.2%; adjusted odds ratio=12.6) at weeks 4–6 and significantly lower depression scores (9.2 [SD=6.6] compared with 14.9 [SD=9.2]; adjusted β=–5.91) at the endpoint visit. No mood polarity switches were observed. Sleep quality improved in both groups and did not differ significantly between them.
The data from this study provide robust evidence that supports the efficacy of midday bright light therapy for bipolar depression.
Consistently altered expression of gene sets in postmortem brains of individuals with major psychiatric disorders
Darby M,M., Yolken R,H., Sabunciyan S. Consistently altered expression of gene sets in postmortem brains of individuals with major psychiatric disorders. Transl Psychiatry. 2016;6:e890. http://dx.doi.org/10.1038/tp.2016.173.
The measurement of gene expression in postmortem brain is an important tool for understanding the pathogenesis of serious psychiatric disorders. We hypothesized that major molecular deficits associated with psychiatric disease would affect the entire brain, and such deficits may be shared across disorders. We performed RNA sequencing and quantified gene expression in the hippocampus of 100 brains in the Stanley Array Collection followed by replication in the orbitofrontal cortex of 57 brains in the Stanley Neuropathology Consortium. We then identified genes and canonical pathway gene sets with significantly altered expression in schizophrenia and bipolar disorder in the hippocampus and in schizophrenia, bipolar disorder and major depression in the orbitofrontal cortex. Although expression of individual genes varied, gene sets were significantly enriched in both of the brain regions, and many of these were consistent across diagnostic groups. Further examination of core gene sets with consistently increased or decreased expression in both of the brain regions and across target disorders revealed that ribosomal genes are overexpressed while genes involved in neuronal processes, GABAergic signaling, endocytosis and antigen processing have predominantly decreased expression in affected individuals compared to controls without a psychiatric disorder. Our results highlight pathways of central importance to psychiatric health and emphasize messenger RNA processing and protein synthesis as potential therapeutic targets for all three of the disorders.