Frontal cortex neuron types categorically encode single decision variables.

Individual neurons in many cortical regions have been found to encode specific, identifiable features of the environment or body that pertain to the function of the region1-3. However, in frontal cortex, which is involved in cognition, neural responses display baffling complexity, carrying seemingly disordered mixtures of sensory, motor and other task-related variables4-13. This complexity has led to the suggestion that representations in individual frontal neurons are randomly mixed and can only be understood at the neural population level14,15. Here we show that neural activity in rat orbitofrontal cortex (OFC) is instead highly structured: single neuron activity co-varies with individual variables in computational models that explain choice behaviour. To characterize neural responses across a large behavioural space, we trained rats on a behavioural task that combines perceptual and value-guided decisions. An unbiased, model-free clustering analysis identified distinct groups of OFC neurons, each with a particular response profile in task-variable space. Applying a simple model of choice behaviour to these categorical response profiles revealed that each profile quantitatively corresponds to a specific decision variable, such as decision confidence. Additionally, we demonstrate that a connectivity-defined cell type, orbitofrontal neurons projecting to the striatum, carries a selective and temporally sustained representation of a single decision variable: integrated value. We propose that neurons in frontal cortex, as in other cortical regions, form a sparse and overcomplete representation of features relevant to the region's function, and that they distribute this information selectively to downstream regions to support behaviour.

Sex and the single cell. II. There is a time and place for sex.

The Drosophila melanogaster sex hierarchy controls sexual differentiation of somatic cells via the activities of the terminal genes in the hierarchy, doublesex (dsx) and fruitless (fru). We have targeted an insertion of GAL4 into the dsx gene, allowing us to visualize dsx-expressing cells in both sexes. Developmentally and as adults, we find that both XX and XY individuals are fine mosaics of cells and tissues that express dsx and/or fruitless (fru(M)), and hence have the potential to sexually differentiate, and those that don't. Evolutionary considerations suggest such a mosaic expression of sexuality is likely to be a property of other animal species having two sexes. These results have also led to a major revision of our view of how sex-specific functions are regulated by the sex hierarchy in flies. Rather than there being a single regulatory event that governs the activities of all downstream sex determination regulatory genes-turning on Sex lethal (Sxl) RNA splicing activity in females while leaving it turned off in males-there are, in addition, elaborate temporal and spatial transcriptional controls on the expression of the terminal regulatory genes, dsx and fru. Thus tissue-specific aspects of sexual development are jointly specified by post-transcriptional control by Sxl and by the transcriptional controls of dsx and fru expression.

A Viral Receptor Complementation Strategy to Overcome CAV-2 Tropism for Efficient Retrograde Targeting of Neurons.

Retrogradely transported neurotropic viruses enable genetic access to neurons based on their long-range projections and have become indispensable tools for linking neural connectivity with function. A major limitation of viral techniques is that they rely on cell-type-specific molecules for uptake and transport. Consequently, viruses fail to infect variable subsets of neurons depending on the complement of surface receptors expressed (viral tropism). We report a receptor complementation strategy to overcome this by potentiating neurons for the infection of the virus of interest-in this case, canine adenovirus type-2 (CAV-2). We designed AAV vectors for expressing the coxsackievirus and adenovirus receptor (CAR) throughout candidate projection neurons. CAR expression greatly increased retrograde-labeling rates, which we demonstrate for several long-range projections, including some resistant to other retrograde-labeling techniques. Our results demonstrate a receptor complementation strategy to abrogate endogenous viral tropism and thereby facilitate efficient retrograde targeting for functional analysis of neural circuits.

Rapid and tunable method to temporally control gene editing based on conditional Cas9 stabilization.

The CRISPR/Cas9 system is a powerful tool for studying gene function. Here, we describe a method that allows temporal control of CRISPR/Cas9 activity based on conditional Cas9 destabilization. We demonstrate that fusing an FKBP12-derived destabilizing domain to Cas9 (DD-Cas9) enables conditional Cas9 expression and temporal control of gene editing in the presence of an FKBP12 synthetic ligand. This system can be easily adapted to co-express, from the same promoter, DD-Cas9 with any other gene of interest without co-modulation of the latter. In particular, when co-expressed with inducible Cre-ERT2, our system enables parallel, independent manipulation of alleles targeted by Cas9 and traditional recombinase with single-cell specificity. We anticipate this platform will be used for the systematic characterization and identification of essential genes, as well as the investigation of the interactions between functional genes.

Central neural circuitry mediating courtship song perception in male Drosophila.

Animals use acoustic signals across a variety of social behaviors, particularly courtship. In Drosophila, song is detected by antennal mechanosensory neurons and further processed by second-order aPN1/aLN(al) neurons. However, little is known about the central pathways mediating courtship hearing. In this study, we identified a male-specific pathway for courtship hearing via third-order ventrolateral protocerebrum Projection Neuron 1 (vPN1) neurons and fourth-order pC1 neurons. Genetic inactivation of vPN1 or pC1 disrupts song-induced male-chaining behavior. Calcium imaging reveals that vPN1 responds preferentially to pulse song with long inter-pulse intervals (IPIs), while pC1 responses to pulse song closely match the behavioral chaining responses at different IPIs. Moreover, genetic activation of either vPN1 or pC1 induced courtship chaining, mimicking the behavioral response to song. These results outline the aPN1-vPN1-pC1 pathway as a labeled line for the processing and transformation of courtship song in males.

Neural pathways for the detection and discrimination of conspecific song in D. melanogaster.

BACKGROUND: During courtship, male Drosophila melanogaster sing a multipart courtship song to female flies. This song is of particular interest because (1) it is species specific and varies widely within the genus, (2) it is a gating stimulus for females, who are sensitive detectors of conspecific song, and (3) it is the only sexual signal that is under both neural and genetic control. This song is perceived via mechanosensory neurons in the antennal Johnston's organ, which innervate the antennal mechanosensory and motor center (AMMC) of the brain. However, AMMC outputs that are responsible for detection and discrimination of conspecific courtship song remain unknown. RESULTS: Using a large-scale anatomical screen of AMMC interneurons, we identify seven projection neurons (aPNs) and five local interneurons (aLNs) that outline a complex architecture for the ascending mechanosensory pathway. Neuronal inactivation and hyperactivation during behavior reveal that only two classes of interneurons are necessary for song responses--the projection neuron aPN1 and GABAergic interneuron aLN(al). These neurons are necessary in both male and female flies. Physiological recordings in aPN1 reveal the integration of courtship song as a function of pulse rate and outline an intracellular transfer function that likely facilitates the response to conspecific song. CONCLUSIONS: These results reveal a critical pathway for courtship hearing in male and female flies, in which both aLN(al) and aPN1 mediate the detection of conspecific song. The pathways arising from these neurons likely serve as a critical neural substrate for behavioral reproductive isolation in D. melanogaster.

Manipulation of an innate escape response in Drosophila: photoexcitation of acj6 neurons induces the escape response.

BACKGROUND: The genetic analysis of behavior in Drosophila melanogaster has linked genes controlling neuronal connectivity and physiology to specific neuronal circuits underlying a variety of innate behaviors. We investigated the circuitry underlying the adult startle response, using photoexcitation of neurons that produce the abnormal chemosensory jump 6 (acj6) transcription factor. This transcription factor has previously been shown to play a role in neuronal pathfinding and neurotransmitter modality, but the role of acj6 neurons in the adult startle response was largely unknown. PRINCIPAL FINDINGS: We show that the activity of these neurons is necessary for a wild-type startle response and that excitation is sufficient to generate a synthetic escape response. Further, we show that this synthetic response is still sensitive to the dose of acj6 suggesting that that acj6 mutation alters neuronal activity as well as connectivity and neurotransmitter production. RESULTS/SIGNIFICANCE: These results extend the understanding of the role of acj6 and of the adult startle response in general. They also demonstrate the usefulness of activity-dependent characterization of neuronal circuits underlying innate behaviors in Drosophila, and the utility of integrating genetic analysis into modern circuit analysis techniques.

Diagnosis and management of male breast cancer.

BACKGROUND: Male breast cancer (MBC) is rare with an incidence of 1% of all breast cancers. The evidence about the treatment is derived from the data on the management of the female breast cancer because conduction of randomized, controlled trials is impossible due to the rarity of the disease. In this study, we review the special features, overall management, diagnosis, and treatment of patients with MBC managed under our care with a brief review of the current literature. METHODS: During the period 1998 to 2006, we managed 1103 new patients with breast cancer in St Mary's Hospital. Among these, 14 patients were men. We retrospectively reviewed the case notes, histology, and follow-up notes of all the newly diagnosed patients with MBC. RESULTS: In this series, 28.6% had only in situ disease. Moreover, in 78.6% there was an in situ component present. One patient was found to have a cancer on the microdochectomy specimen after an operation for single duct nipple discharge, and in a second patient the cancer was found in the gynecomastia operation specimen. All ten invasive tumors were estrogen receptor positive (ER +ve), whereas eight were progesterone receptor positive (PgR +ve). With a median follow-up of 35 months, there was one locoregional recurrence and one disease-associated death. CONCLUSIONS: In situ cancer may not be as rare as previously reported among patients with MBC. Increased patient awareness and early assessment by a specialist is a key to early diagnosis and improved outcomes.