Probes for LONG

Abstract Background A parallel downregulation of brain-derived neurotrophic factor (BDNF) and somatostatin (SST), a marker of inhibitory γ-amino-butyric acid (GABA) interneurons which target pyramidal cell dendrites, has been reported in several brain areas of subjects with major depressive disorder (MDD), and rodent genetic studies suggests they are linked and both contribute to the illness. However, the mechanism by which they contribute to the pathophysiology of the illness has remained elusive. Methods With qPCR, we determined the expression level of BDNF transcript variants and synaptic markers in the prefrontal cortex (PFC) of MDD patients and matched controls (n=19/group) and of C57BL/6J mice exposed to chronic stress or control conditions (n=12/group). We next suppressed BDNF transcripts with long 3’ untranslated region (L-3’-UTR) using small hairpin RNA (shRNA) and investigated changes in cell morphology, gene expression and behavior. Results L-3’-UTR containing BDNF mRNAs, which migrate to distal dendrites of pyramidal neurons, are selectively reduced and highly correlated with SST expression in the PFC of MDD subjects. A similar downregulation occurs in mice submitted to chronic stress. We next show that Bdnf L-3’-UTR knockdown is sufficient to induce (i) dendritic shrinkage in cortical neurons, (ii) cell-specific MDD-like gene changes (including Sst downregulation), and (iii) depressive-/anxiety-like behaviors. The translational validity of the Bdnf L-3’-UTR shRNA-treated mice was confirmed by significant cross-species correlation of changes in MDD-associated gene expression. Conclusions These findings provide evidence for a novel MDD-related pathological mechanism linking local neurotrophic support, pyramidal cell structure, dendritic inhibition and mood regulation.

Neuroanatomists have long speculated that expanded primate brains contain an increased morphological diversity of inhibitory neurons (INs)1, and recent studies have identified primate-specific neuronal populations at the molecular level2. However, we know little about the developmental mechanisms that specify evolutionarily novel cell types in the brain. Here, we reconstruct gene expression trajectories specifying INs generated throughout the neurogenic period in macaques and mice by analysing the transcriptomes of 250,181 cells. We find that the initial classes of INs generated prenatally are largely conserved among mammals. Nonetheless, we identify two contrasting developmental mechanisms for specifying evolutionarily novel cell types during prenatal development. First, we show that recently identified primate-specific TAC3 striatal INs are specified by a unique transcriptional programme in progenitors followed by induction of a distinct suite of neuropeptides and neurotransmitter receptors in new-born neurons. Second, we find that multiple classes of transcriptionally conserved olfactory bulb (OB)-bound precursors are redirected to expanded primate white matter and striatum. These classes include a novel peristriatal class of striatum laureatum neurons that resemble dopaminergic periglomerular cells of the OB. We propose an evolutionary model in which conserved initial classes of neurons supplying the smaller primate OB are reused in the enlarged striatum and cortex. Together, our results provide a unified developmental taxonomy of initial classes of mammalian INs and reveal multiple developmental mechanisms for neural cell type evolution.

Ketamine, an N-methyl-D-aspartate (NMDA)-receptor antagonist, is a recently revitalized treatment for pain and depression, yet its actions at the molecular level remain incompletely defined. In this molecular-pharmacological investigation in the rat, we used short- and longer-term infusions of high dose ketamine to stimulate neuronal transcription processes. We hypothesized that a progressively stronger modulation of neuronal gene networks would occur over time in cortical and limbic pathways. A continuous intravenous administration paradigm for ketamine was developed in rat consisting of short (1 h) and long duration (10 h, and 10 h + 24 h recovery) infusions of anesthetic concentrations to activate or inhibit gene transcription in a pharmacokinetically controlled fashion. Transcription was measured by RNA-Seq in three brain regions: frontal cortex, hippocampus, and amygdala. Cellular level gene localization was performed with multiplex fluorescent in situ hybridization. Induction of a shared transcriptional regulatory network occurred within 1 h in all three brain regions consisting of (a) genes involved in stimulus-transcription factor coupling that are induced during altered synaptic activity (immediate early genes, IEGs, such as c-Fos, 9-12 significant genes per brain region, p < 0.01 per gene) and (b) the Nrf2 oxidative stress-antioxidant response pathway downstream from glutamate signaling (Nuclear Factor Erythroid-Derived 2-Like 2) containing 12-25 increasing genes (p < 0.01) per brain region. By 10 h of infusion, the acute results were further reinforced and consisted of more and stronger gene alterations reflecting a sustained and accentuated ketamine modulation of regional excitation and plasticity. At the cellular level, in situ hybridization localized up-regulation of the plasticity-associated gene Bdnf, and the transcription factors Nr4a1 and Fos, in cortical layers III and V. After 24 h recovery, we observed overshoot of transcriptional processes rather than a smooth return to homeostasis suggesting an oscillation of plasticity occurs during the transition to a new phase of neuronal regulation. These data elucidate critical molecular regulatory actions during and downstream of ketamine administration that may contribute to the unique drug actions of this anesthetic agent. These molecular investigations point to pathways linked to therapeutically useful attributes of ketamine.