Dysfunction of Orbitofrontal GABAergic Interneurons Leads to Impaired Reversal Learning in a Mouse Model of Obsessive-Compulsive Disorder.

Cognitive inflexibility is a cardinal symptom of obsessive-compulsive disorder (OCD) and often manifests as impaired reversal learning. Abnormal recruitment of the orbitofrontal cortex (OFC)-striatal circuit is implicated in reversal learning deficits in patients with OCD. However, the precise circuitry mechanism underlying normal and impaired reversal learning remains elusive. Using fiber photometry and optogenetics, we demonstrated cell-type-specific activity dynamics in the OFC-striatal circuit underlying normal reversal learning and cell-type-specific dysfunctions that causally lead to impaired reversal learning in an OCD mouse model (Sapap3 knockout mice). After contingency reversal, OFC GABAergic interneurons increase the activity in response to previously rewarded but currently non-reward cues to inhibit the elevated activity of OFC excitatory neurons encoding inappropriate cue-reward association. Striatal direct-pathway medium spiny neurons (D1-MSNs) gradually re-establish their response preference for rewarded versus non-reward cues. These activity dynamics together mediated normal reversal learning. In Sapap3 knockout OCD mouse model, the increase in activity of OFC GABAergic interneurons in response to previously rewarded but currently non-reward cues after contingency reversal was reduced, which resulted in insufficient inhibition on OFC excitatory neurons, which in turn led to a more severe inversion of the response preference of D1-MSNs for rewarded versus non-reward cues, ultimately resulting in slower reversal learning. These dysfunctions were causally involved in reversal learning impairments. Our findings identified OFC GABAergic interneurons as the key therapeutic target to treat cognitive inflexibility in OCD and may be generally applicable to cognitive inflexibility in other neuropsychiatric disorders.

Lateral orbitofrontal dysfunction in the Sapap3 knockout mouse model of obsessive­compulsive disorder

Background: Obsessive­compulsive disorder (OCD) is a common psychiatric disorder that affects about 2% of the population, but the underlying neuropathophysiology of OCD is not well understood. Although increasing lines of evidence implicate dysfunction of the orbitofrontal cortex (OFC) in OCD, a detailed understanding of the functional alterations in different neuronal types in the OFC is still elusive. Methods: We investigated detailed activity pattern changes in putative pyramidal neurons and interneurons, as well as local field potential oscillations, in the lateral OFC underlying OCD-relevant phenotypes. We applied in vivo multichannel recording in an awake OCD mouse model that carried a deletion of the Sapap3 gene, and in wildtype littermates. Results: Compared with wildtype mice, the lateral OFC of Sapap3 knockout mice exhibited network dysfunction, demonstrated by decreased power of local field potential oscillations. The activity of inhibitory and excitatory neurons in the lateral OFC showed distinct perturbations in Sapap3 knockout mice: putative interneurons exhibited increased activity; putative pyramidal neurons exhibited enhanced bursting activity; and both putative pyramidal neurons and interneurons exhibited enhanced discharge variability and altered synchronization. Limitations: To exclude motor activity confounders, this study examined functional alterations in lateral OFC neurons only when the mice were stationary. Conclusion: We provide, to our knowledge, the first direct in vivo electrophysiological evidence of detailed functional alterations in different neuronal types in the lateral OFC of an OCD mouse model. These findings may help in understanding the underlying neuropathophysiology and circuitry mechanisms for phenotypes relevant to OCD, and may help generate and refine hypotheses about potential biomarkers for further investigation.

SAPAP4 Deletion Causes Synaptic Dysfunction in the nucleus accumbens.

SAP90/PSD95-associated proteins (SAPAPs) are one type of scaffold protein in the postsynaptic density (PSD). Scaffold proteins play an important role in synaptic function. Recently, many studies have shown that mutations associated with scaffold proteins cause dysfunction in neuronal circuitry and in behavior. SAPAP4, as a protein in the SAPAP family, may have an impact on synaptic functions and on behaviors. To test this hypothesis, mice with a genetic deletion of SAPAP4 were used in our study. SAPAP4-/- mice displayed decreased cocaine sensitivity behavior after an acute injection of 20 mg/kg cocaine. We also found that the spine density of medium spiny neurons (MSNs) in the nucleus accumbens (NAc) shell was reduced in SAPAP4-/- mice. Furthermore, SAPAP4-/- mice displayed altered synaptic transmission and a decreased frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) in the NAc. Our findings demonstrate that SAPAP4 plays a critical role in cocaine-related behavior and in the synaptic function of the NAc.

Neuronal activity pattern defects in the striatum in awake mouse model of Parkinson's disease.

Previous studies showed the loss of dopaminergic neurons directly leads to both changes in firing rate and neuronal synchrony in the striatum by pharmacogenetic approach, but physiological observation of striatal neurons in awake animal is rare up to now due to the limitation of recording methods. We use multichannel in vivo recording system, to record the activity pattern of both medium spiny projecting neurons (MSNs) and fast spiking interneurons (FSIs) in awake mouse model of Parkinson's disease (PD), created by injection of 6-hydroxyl-dopamine (6-OHDA) into dorsolateral striatum bilaterally and unilaterally. The abnormal discharge of neurons, including oscillations, burst activity and firing rate were systematically observed, and we used these index together to comprehensively analyse the functional change of striatal neurons in PD mouse model. We found that PD mouse model exhibited elevated synchronized oscillatory activity in ß frequency band and decreased firing rate of FSIs during movement. The firing rate and burst activity of MSNs clearly reduced during movement after bilateral dopamine depletion. The present study has novelly shown the firing pattern changes of the MSNs and FSIs in DL striatum in awake PD mouse model, by combination of electrophysiology with molecular biological technology. Our results may help to reveal a new circuitry mechanism of movement disorders in PD.

Axon guidance pathways served as common targets for human speech/language evolution and related disorders.

Human and several nonhuman species share the rare ability of modifying acoustic and/or syntactic features of sounds produced, i.e. vocal learning, which is the important neurobiological and behavioral substrate of human speech/language. This convergent trait was suggested to be associated with significant genomic convergence and best manifested at the ROBO-SLIT axon guidance pathway. Here we verified the significance of such genomic convergence and assessed its functional relevance to human speech/language using human genetic variation data. In normal human populations, we found the affected amino acid sites were well fixed and accompanied with significantly more associated protein-coding SNPs in the same genes than the rest genes. Diseased individuals with speech/language disorders have significant more low frequency protein coding SNPs but they preferentially occurred outside the affected genes. Such patients' SNPs were enriched in several functional categories including two axon guidance pathways (mediated by netrin and semaphorin) that interact with ROBO-SLITs. Four of the six patients have homozygous missense SNPs on PRAME gene family, one youngest gene family in human lineage, which possibly acts upon retinoic acid receptor signaling, similarly as FOXP2, to modulate axon guidance. Taken together, we suggest the axon guidance pathways (e.g. ROBO-SLIT, PRAME gene family) served as common targets for human speech/language evolution and related disorders.

Fusion of Ssm6a with a protein scaffold retains selectivity on NaV 1.7 and improves its therapeutic potential against chronic pain.

Voltage-gated sodium channel NaV 1.7 serves as an attractive target for chronic pain treatment. Several venom peptides were found to selectively inhibit NaV 1.7 but with intrinsic problems. Among them, Ssm6a, a recently discovered centipede venom peptide, shows the greatest selectivity against NaV 1.7, but dissociates from the target too fast and loses bioactivity in synthetic forms. As a disulfide-rich venom peptide, it is difficult to optimize Ssm6a by artificial mutagenesis and produce the peptide with common industrial manufacturing methods. Here, we developed a novel protein scaffold fusion strategy to address these concerns. Instead of directly mutating Ssm6a, we genetically fused Ssm6a with a protein scaffold engineered from human muscle fatty acid-binding protein. The resultant fusion protein, SP-TOX, maintained the selectivity and potency of Ssm6a upon NaV 1.7 but dissociated from target at least 10 times more slowly. SP-TOX dramatically reduced inflammatory pain in a rat model through DRG-targeted delivery. Importantly, SP-TOX can be expressed cytosolically in Escherichia coli and purified in a cost-effective way. In summary, our study provided the first example of cytosolically expressed fusion protein with high potency and selectivity on NaV 1.7. Our protein scaffold fusion approach may have its broad application in optimizing disulfide-rich venom peptides for therapeutic usage.

Manipulation of a central auditory representation shapes learned vocal output.

Learned vocalizations depend on the ear's ability to monitor and ultimately instruct the voice. Where is auditory feedback processed in the brain, and how does it modify motor networks for learned vocalizations? Here we addressed these questions using singing-triggered microstimulation and chronic recording methods in the singing zebra finch, a small songbird that relies on auditory feedback to learn and maintain its species-typical vocalizations. Manipulating the singing-related activity of feedback-sensitive thalamic neurons subsequently triggered vocal plasticity, constraining the central pathway and functional mechanisms through which feedback-related information shapes vocalization.

Synaptic integration of olfactory information in mouse anterior olfactory nucleus.

Individual odorants activate only a small fraction of mitral cells in the mouse main olfactory bulb (MOB). Odor mixtures are represented by a combination of activated mitral cells, forming reproducible activation maps in the olfactory bulb. However, how the activation of a cohort of narrowly tuned mitral cells by odor mixtures is read out synaptically by neurons in higher-level olfactory structures, such as the anterior olfactory nucleus (AON), is mostly unknown. In the current study, we used intracellular and extracellular recordings to examine and compare responses of AON neurons and MOB mitral cells to a panel of structurally diverse odorants presented either as mixtures or as individual components. We found that a majority of individual AON neurons could be synaptically activated by several mixtures of structurally dissimilar components and by several dissimilar components in an effective mixture. The suprathreshold response of an AON neuron to an effective mixture often exceeded the sum of its suprathreshold responses to all of the components in that mixture, indicating a nonlinear combinatorial interaction. In contrast to the broad responsiveness of AON neurons, the majority of mitral cells were activated by only one or two components in a single mixture. The broader responsiveness of AON neurons relative to mitral cells suggests that individual AON neurons synaptically integrate several functionally distinct mitral cell inputs.