Johannes Kohl

A Bidirectional Circuit Switch Reroutes Pheromone Signals in Male and Female Brains

Summary The Drosophila sex pheromone cVA elicits different behaviors in males and females. First- and second-order olfactory neurons show identical pheromone responses, suggesting that sex genes differentially wire circuits deeper in the brain. Using in vivo whole-cell electrophysiology, we now show that two clusters of third-order olfactory neurons have dimorphic pheromone responses. One cluster responds in females; the other responds in males. These clusters are present in both sexes and share a common input pathway, but sex-specific wiring reroutes pheromone information. Regulating dendritic position, the fruitless transcription factor both connects the male-responsive cluster and disconnects the female-responsive cluster from pheromone input. Selective masculinization of third-order neurons transforms their morphology and pheromone responses, demonstrating that circuits can be functionally rewired by the cell-autonomous action of a switch gene. This bidirectional switch, analogous to an electrical changeover switch, provides a simple circuit logic to activate different behaviors in males and females.

Mapping of Brain Activity by Automated Volume Analysis of Immediate Early Genes

Understanding how neural information is processed in physiological and pathological states would benefit from precise detection, localization, and quantification of the activity of all neurons across the entire brain, which has not, to date, been achieved in thexa0mammalian brain. We introduce a pipeline for high-speed acquisition of brain activity at cellular resolution through profiling immediate early gene expression using immunostaining and light-sheet fluorescence imaging, followed by automated mapping and analysis of activity by an open-source software program we term ClearMap. We validate the pipeline first by analysis of brain regions activated inxa0response to haloperidol. Next, we report new cortical regions downstream of whisker-evoked sensory processing during active exploration. Last, we combine activity mapping with axon tracing to uncover new brain regions differentially activated during parenting behavior. This pipeline is widely applicable to different experimental paradigms, including animal species for which transgenic activity reporters are not readily available.

Mobility of Calcium Channels in the Presynaptic Membrane

Unravelling principles underlying neurotransmitter release are key to understand neural signaling. Here, we describe how surface mobility of voltage-dependent calcium channels (VDCCs) modulates release probabilities (P(r)) of synaptic vesicles (SVs). Coupling distances of <10 to >100 nm have been reported for SVs and VDCCs in different synapses. Tracking individual VDCCs revealed that within hippocampal synapses, ∼60% of VDCCs are mobile while confined to presynaptic membrane compartments. Intracellular Ca(2+) chelation decreased VDCC mobility. Increasing VDCC surface populations by co-expression of the α2δ1 subunit did not alter channel mobility but led to enlarged active zones (AZs) rather than higher channel densities. VDCCs thus scale presynaptic scaffolds to maintain local mobility. We propose that dynamic coupling based on mobile VDCCs supports calcium domain cooperativity and tunes neurotransmitter release by equalizing Pr for docked SVs within AZs.

Pheromone processing in Drosophila

Understanding how sensory stimuli are processed in the brain to instruct appropriate behavior is a fundamental question in neuroscience. Drosophila has become a powerful model system to address this problem. Recent advances in characterizing the circuits underlying pheromone processing have put the field in a position to follow the transformation of these chemical signals all the way from the sensory periphery to decision making and motor output. Here we describe the latest advances, outline emerging principles of pheromone processing and discuss future questions.

Ultrafast tissue staining with chemical tags

Significance Cellular and subcellular structures in thick biological samples typically are visualized either by genetically encoded fluorescent proteins or by antibody staining against proteins of interest. However, both approaches have drawbacks. Fluorescent proteins do not survive treatments for tissue preservation well, are available in only a few colors, and often emit weak signals. Antibody stainings are slow, do not penetrate thick samples well, and often result in considerable background staining. We have overcome these limitations by using genetically encoded chemical tags that result in rapid, even staining of thick biological samples with high-signal and low-background labeling. We introduce tools for flies and mice that drastically improve the speed and specificity for labeling genetically marked cells in biological tissues. Genetically encoded fluorescent proteins and immunostaining are widely used to detect cellular and subcellular structures in fixed biological samples. However, for thick or whole-mount tissue, each approach suffers from limitations, including limited spectral flexibility and lower signal or slow speed, poor penetration, and high background labeling, respectively. We have overcome these limitations by using transgenically expressed chemical tags for rapid, even, high-signal and low-background labeling of thick biological tissues. We first construct a platform of widely applicable transgenic Drosophila reporter lines, demonstrating that chemical labeling can accelerate staining of whole-mount fly brains by a factor of 100. Using viral vectors to deliver chemical tags into the mouse brain, we then demonstrate that this labeling strategy works well in mice. Thus this tag-based approach drastically improves the speed and specificity of labeling genetically marked cells in intact and/or thick biological samples.

The neurobiology of parenting: A neural circuit perspective.

Social interactions are essential for animals to reproduce, defend their territory, and raise their young. The conserved nature of social behaviors across animal species suggests that the neural pathways underlying the motivation for, and the execution of, specific social responses are also maintained. Modern tools of neuroscience have offered new opportunities for dissecting the molecular and neural mechanisms controlling specific social responses. We will review here recent insights into the neural circuits underlying a particularly fascinating and important form of social interaction, that of parental care. We will discuss how these findings open new avenues to deconstruct infant‐directed behavioral control in males and females, and to help understand the neural basis of parenting in a variety of animal species, including humans.

Functional circuit architecture underlying parental behaviour

Parenting is essential for the survival and wellbeing of mammalian offspring. However, we lack a circuit-level understanding of how distinct components of this behaviour are coordinated. Here we investigate how galanin-expressing neurons in the medial preoptic area (MPOAGal) of the hypothalamus coordinate motor, motivational, hormonal and social aspects of parenting in mice. These neurons integrate inputs from a large number of brain areas and the activation of these inputs depends on the animal’s sex and reproductive state. Subsets of MPOAGal neurons form discrete pools that are defined by their projection sites. While the MPOAGal population is active during all episodes of parental behaviour, individual pools are tuned to characteristic aspects of parenting. Optogenetic manipulation of MPOAGal projections mirrors this specificity, affecting discrete parenting components. This functional organization, reminiscent of the control of motor sequences by pools of spinal cord neurons, provides a new model for how discrete elements of a social behaviour are generated at the circuit level.Galanin-expressing neurons in the medial preoptic area coordinate different aspects of motor, motivational, hormonal and social behaviour associated with parenting by projecting to different brain regions depending on the type of behaviour and sex and reproductive state of mice.

Neuroanatomy: Decoding the Fly Brain

Despite their relatively small brains, with only about 100,000 neurons, fruit flies show many complex behaviours. Understanding how these behaviours are generated will require a wiring diagram of the brain, and significant progress is being made towards this goal. One study has labelled 16,000 individual neurons and generated a coarse wiring diagram of the whole fly brain, identifying subnetworks that may carry out local information processing.

Functional and Anatomical Specificity in a Higher Olfactory Centre

Most sensory systems are organized into parallel neuronal pathways that process distinct aspects of incoming stimuli. For example, second order olfactory neurons make divergent projections onto functionally distinct brain areas relevant to different behaviors. In insects, one area, the mushroom body has been intensively studied for its role in olfactory learning while the lateral horn is proposed to mediate innate olfactory behavior. Some lateral horn neurons (LHNs) show selective responses to sex pheromones but its functional principles remain poorly understood. We have carried out a comprehensive anatomical analysis of the Drosophila lateral horn and identified genetic driver lines targeting many LHNs. We find that the lateral horn contains >1300 neurons and by combining genetic, anatomical and functional criteria, we identify >150 cell types. In particular we show that genetically labeled LHNs show stereotyped odor responses from one animal to the next. Although LHN tuning can be ultra-sparse (1/40 odors tested), as a population they respond to three times more odors than their inputs; this coding change can be rationalized by our observation that LHNs are better odor categorizers. Our results reveal some of the principles by which a higher sensory processing area can extract innate behavioral significance from sensory stimuli.

Neural control of parental behaviors

Parenting is a multicomponent social behavior that is essential for the survival of offspring in many species. Despite extensive characterization of individual brain areas involved in parental care, we do not fully understand how discrete aspects of this behavior are orchestrated at the neural circuit level. Recent progress in identifying genetically specified neuronal populations critical for parenting, and the use of genetic and viral tools for circuit-cracking now allow us to deconstruct the underlying circuitry and, thus, to elucidate how different aspects of parental care are controlled. Here we review the latest advances, outline possible organizational principles of parental circuits and discuss future challenges.