Subregion-specific rules govern the distribution of neuronal immediate-early gene induction.

The induction of immediate-early gene (IEG) expression in brain nuclei in response to an experience is necessary for the formation of long-term memories. Additionally, the rapid dynamics of IEG induction and decay motivates the common use of IEG expression as markers for identification of neuronal assemblies ("ensembles") encoding recent experience. However, major gaps remain in understanding the rules governing the distribution of IEGs within neuronal assemblies. Thus, the extent of correlation between coexpressed IEGs, the cell specificity of IEG expression, and the spatial distribution of IEG expression have not been comprehensively studied. To address these gaps, we utilized quantitative multiplexed single-molecule fluorescence in situ hybridization (smFISH) and measured the expression of IEGs (Arc, Egr2, and Nr4a1) within spiny projection neurons (SPNs) in the dorsal striatum of mice following acute exposure to cocaine. Exploring the relevance of our observations to other brain structures and stimuli, we also analyzed data from a study of single-cell RNA sequencing of mouse cortical neurons. We found that while IEG expression is graded, the expression of multiple IEGs is tightly correlated at the level of individual neurons. Interestingly, we observed that region-specific rules govern the induction of IEGs in SPN subtypes within striatal subdomains. We further observed that IEG-expressing assemblies form spatially defined clusters within which the extent of IEG expression correlates with cluster size. Together, our results suggest the existence of IEG-expressing neuronal "superensembles," which are associated in spatial clusters and characterized by coherent and robust expression of multiple IEGs.

Neuronatin-mediated aberrant calcium signaling and endoplasmic reticulum stress underlie neuropathology in Lafora disease.

Lafora disease (LD) is a teenage-onset inherited progressive myoclonus epilepsy characterized by the accumulations of intracellular inclusions called Lafora bodies and caused by mutations in protein phosphatase laforin or ubiquitin ligase malin. But how the loss of function of either laforin or malin causes disease pathogenesis is poorly understood. Recently, neuronatin was identified as a novel substrate of malin that regulates glycogen synthesis. Here we demonstrate that the level of neuronatin is significantly up-regulated in the skin biopsy sample of LD patients having mutations in both malin and laforin. Neuronatin is highly expressed in human fetal brain with gradual decrease in expression in developing and adult brain. However, in adult brain, neuronatin is predominantly expressed in parvalbumin-positive GABAergic interneurons and localized in their processes. The level of neuronatin is increased and accumulated as insoluble aggregates in the cortical area of LD brain biopsy samples, and there is also a dramatic loss of parvalbumin-positive GABAergic interneurons. Ectopic expression of neuronatin in cultured neuronal cells results in increased intracellular Ca(2+), endoplasmic reticulum stress, proteasomal dysfunction, and cell death that can be partially rescued by malin. These findings suggest that the neuronatin-induced aberrant Ca(2+) signaling and endoplasmic reticulum stress might underlie LD pathogenesis.

Malin regulates Wnt signaling pathway through degradation of dishevelled2.

Using yeast-two hybrid screening followed by co-immunoprecipitation assay, we have found that the Lafora disease ubiquitin ligase malin interacts with dishevelled2, a key mediator of Wnt signaling pathway. Overexpression of malin enhances the degradation of dishevelled2 and inhibits Wnt signaling, which is evident from the down-regulation of ß-catenin target genes and the decrease in ß-catenin-mediated transcriptional activity. Partial knockdown of malin significantly increases the level of dishevelled2 and up-regulates Wnt signaling. Several malin mutants are found to be ineffective in degrading dishevelled2 and regulating the Wnt pathway. We have also found that malin enhances K48- and K63-linked ubiquitination of dishevelled2 that could lead to its degradation through both proteasome and autophagy. Altogether, our results indicate that malin regulates Wnt signaling pathway through the degradation of dishevelled2 and suggest possible deregulation of Wnt signaling in Lafora disease.

Claustral neurons projecting to frontal cortex restrict opioid consumption.

The synthetic opioid fentanyl is a major contributor to the current opioid addiction crisis. We report that claustral neurons projecting to the frontal cortex limit oral fentanyl self-administration in mice. We found that fentanyl transcriptionally activates frontal-projecting claustrum neurons. These neurons also exhibit a unique suppression of Ca2+ activity upon initiation of bouts of fentanyl consumption. Optogenetic stimulation of frontal-projecting claustral neurons, intervening in this suppression, decreased bouts of fentanyl consumption. In contrast, constitutive inhibition of frontal-projecting claustral neurons in the context of a novel, group-housed self-administration procedure increased fentanyl bout consumption. This same manipulation also sensitized conditioned-place preference for fentanyl and enhanced the representation of fentanyl experience in the frontal cortex. Together, our results indicate that claustrum neurons exert inhibitory control over frontal cortical neurons to restrict oral fentanyl intake. Upregulation of activity in the claustro-frontal projection may be a promising strategy for reducing human opioid addiction.

Egr2 induction in spiny projection neurons of the ventrolateral striatum contributes to cocaine place preference in mice.

Drug addiction develops due to brain-wide plasticity within neuronal ensembles, mediated by dynamic gene expression. Though the most common approach to identify such ensembles relies on immediate early gene expression, little is known of how the activity of these genes is linked to modified behavior observed following repeated drug exposure. To address this gap, we present a broad-to-specific approach, beginning with a comprehensive investigation of brain-wide cocaine-driven gene expression, through the description of dynamic spatial patterns of gene induction in subregions of the striatum, and finally address functionality of region-specific gene induction in the development of cocaine preference. Our findings reveal differential cell-type specific dynamic transcriptional recruitment patterns within two subdomains of the dorsal striatum following repeated cocaine exposure. Furthermore, we demonstrate that induction of the IEG Egr2 in the ventrolateral striatum, as well as the cells within which it is expressed, are required for the development of cocaine seeking.

The human brain is ever changing, constantly rewiring itself in response to new experiences, knowledge or information from the environment. Addictive drugs such as cocaine can hijack the genetic mechanisms responsible for this plasticity, creating dangerous, obsessive drug-seeking and consuming behaviors. Cocaine-induced plasticity is difficult to apprehend, however, as brain regions or even cell populations can react differently to the compound. For instance, sub-regions in the striatum ­ the brain area that responds to rewards and helps to plan movement ­ show distinct responses during progressive exposure to cocaine. And while researchers know that the drug immediately changes how neurons switch certain genes on and off, it is still unclear how these genetic modifications later affect behavior. Mukherjee, Gonzales et al. explored these questions at different scales, first focusing on how progressive cocaine exposure changed the way various gene programs were activated across the entire brain. This revealed that programs in the striatum were the most affected by the drug. Examining this region more closely showed that cocaine switches on genes in specific 'spiny projection' neuron populations, depending on where these cells are located and the drug history of the mouse. Finally, Mukherjee, Gonzales et al. used genetically modified mice to piece together cocaine exposure, genetic changes and modifications in behavior. These experiments revealed that the drive to seek cocaine depended on activation of the Egr2 gene in populations of spiny projection neurons in a specific sub-region of the striatum. The gene, which codes for a protein that regulates how genes are switched on and off, was itself strongly activated by cocaine intake. Cocaine addiction can have devastating consequences for individuals. Grasping how this drug alters the brain could pave the way for new treatments, while also providing information on the basic mechanisms underlying brain plasticity.

Claustral Neurons Projecting to Frontal Cortex Mediate Contextual Association of Reward.

The claustrum is a small nucleus, exhibiting vast reciprocal connectivity with cortical, subcortical, and midbrain regions. Recent studies, including ours, implicate the claustrum in salience detection and attention. In the current study, we develop an iterative functional investigation of the claustrum, guided by quantitative spatial transcriptional analysis. Using this approach, we identify a circuit involving dopamine-receptor expressing claustral neurons projecting to frontal cortex necessary for context association of reward. We describe the recruitment of claustral neurons by cocaine and their role in drug sensitization. In order to characterize the circuit within which these neurons are embedded, we apply chemo- and opto-genetic manipulation of increasingly specified claustral subpopulations. This strategy resolves the role of a defined network of claustrum neurons expressing dopamine D1 receptors and projecting to frontal cortex in the acquisition of cocaine conditioned-place preference and real-time optogenetic conditioned-place preference. In sum, our results suggest a role for a claustrum-to-frontal cortex circuit in the attribution of incentive salience, allocating attention to reward-related contextual cues.

Salient experiences are represented by unique transcriptional signatures in the mouse brain.

It is well established that inducible transcription is essential for the consolidation of salient experiences into long-term memory. However, whether inducible transcription relays information about the identity and affective attributes of the experience being encoded, has not been explored. To this end, we analyzed transcription induced by a variety of rewarding and aversive experiences, across multiple brain regions. Our results describe the existence of robust transcriptional signatures uniquely representing distinct experiences, enabling near-perfect decoding of recent experiences. Furthermore, experiences with shared attributes display commonalities in their transcriptional signatures, exemplified in the representation of valence, habituation and reinforcement. This study introduces the concept of a neural transcriptional code, which represents the encoding of experiences in the mouse brain. This code is comprised of distinct transcriptional signatures that correlate to attributes of the experiences that are being committed to long-term memory.

Functional Plasticity of Odor Representations during Motherhood.

Motherhood is accompanied by new behaviors aimed at ensuring the wellbeing of the offspring. Olfaction plays a key role in guiding maternal behaviors during this transition. We studied functional changes in the main olfactory bulb (OB) of mothers in mice. Using in vivo two-photon calcium imaging, we studied the sensory representation of odors by mitral cells (MCs). We show that MC responses to monomolecular odors become sparser and weaker in mothers. In contrast, responses to biologically relevant odors are spared from sparsening or strengthen. MC responses to mixtures and to a range of concentrations suggest that these differences between odor responses cannot be accounted for by mixture suppressive effects or gain control mechanisms. In vitro whole-cell recordings show an increase in inhibitory synaptic drive onto MCs. The increase of inhibitory tone may contribute to the general decrease in responsiveness and concomitant enhanced representation of specific odors.

High on food: the interaction between the neural circuits for feeding and for reward.

Hunger, mostly initiated by a deficiency in energy, induces food seeking and intake. However, the drive toward food is not only regulated by physiological needs, but is motivated by the pleasure derived from ingestion of food, in particular palatable foods. Therefore, feeding is viewed as an adaptive motivated behavior that involves integrated communication between homeostatic feeding circuits and reward circuits. The initiation and termination of a feeding episode are instructed by a variety of neuronal signals, and maladaptive plasticity in almost any component of the network may lead to the development of pathological eating disorders. In this review we will summarize the latest understanding of how the feeding circuits and reward circuits in the brain interact. We will emphasize communication between the hypothalamus and the mesolimbic dopamine system and highlight complexities, discrepancies, open questions and future directions for the field.

Comprehensive analysis of transcription dynamics from brain samples following behavioral experience.

The encoding of experiences in the brain and the consolidation of long-term memories depend on gene transcription. Identifying the function of specific genes in encoding experience is one of the main objectives of molecular neuroscience. Furthermore, the functional association of defined genes with specific behaviors has implications for understanding the basis of neuropsychiatric disorders. Induction of robust transcription programs has been observed in the brains of mice following various behavioral manipulations. While some genetic elements are utilized recurrently following different behavioral manipulations and in different brain nuclei, transcriptional programs are overall unique to the inducing stimuli and the structure in which they are studied(1,2). In this publication, a protocol is described for robust and comprehensive transcriptional profiling from brain nuclei of mice in response to behavioral manipulation. The protocol is demonstrated in the context of analysis of gene expression dynamics in the nucleus accumbens following acute cocaine experience. Subsequent to a defined in vivo experience, the target neural tissue is dissected; followed by RNA purification, reverse transcription and utilization of microfluidic arrays for comprehensive qPCR analysis of multiple target genes. This protocol is geared towards comprehensive analysis (addressing 50-500 genes) of limiting quantities of starting material, such as small brain samples or even single cells. The protocol is most advantageous for parallel analysis of multiple samples (e.g. single cells, dynamic analysis following pharmaceutical, viral or behavioral perturbations). However, the protocol could also serve for the characterization and quality assurance of samples prior to whole-genome studies by microarrays or RNAseq, as well as validation of data obtained from whole-genome studies.