A sex-specific switch between visual and olfactory inputs underlies adaptive sex differences in behavior.

Although males and females largely share the same genome and nervous system, they differ profoundly in reproductive investments and require distinct behavioral, morphological, and physiological adaptations. How can the nervous system, while bound by both developmental and biophysical constraints, produce these sex differences in behavior? Here, we uncover a novel dimorphism in Drosophila melanogaster that allows deployment of completely different behavioral repertoires in males and females with minimum changes to circuit architecture. Sexual differentiation of only a small number of higher order neurons in the brain leads to a change in connectivity related to the primary reproductive needs of both sexes-courtship pursuit in males and communal oviposition in females. This study explains how an apparently similar brain generates distinct behavioral repertoires in the two sexes and presents a fundamental principle of neural circuit organization that may be extended to other species.

To court or not to court - a multimodal sensory decision in Drosophila males.

When Drosophila males encounter another fly, they have to make a rapid assessment to ensure the appropriate response: should they court, fight or pursue a different action entirely? Previous work has focused on the significance of sensory cues detected by the male during these encounters; however, recent evidence highlights the importance of the male's own internal state in shaping his responses. Additionally, once triggered, courtship is not a rigid sequence of motor actions, but rather a finely tuned behavioural display that must continually update in response to sensory feedback. Here, we review recent findings highlighting how sensory information and internal states are integrated ensuring appropriate action selection, and how they sustain and fine-tune motor output. We further discuss recent advances in our understanding of species differences in sensory processing that may contribute to reproductive isolation.

Drosophila Courtship: Love Is Not Blind.

Animals rely on sensory cues to help them find suitable mates. Visual cues are particularly useful for locating mates during the day. A new study has revealed key visual neurons in male Drosophila used to identify and pursue potential mates.

Monitoring Ca2+ elevations in individual astrocytes upon local release of amyloid beta in acute brain slices.

The pathogenesis of Alzheimer's disease (AD) is thought to involve acute neurotoxic effects exerted by oligomeric forms of amyloid-ß 1-42 (Aß). Application of Aß oligomers in physiological concentrations have been shown to transiently elevate internal Ca2+ in cultured astroglia. While the cellular machinery involved has been extensively explored, to what degree this important signalling cascade occurs in organised brain tissue has remained unclear. Here we adapted two-photon excitation microscopy and calibrated time-resolved imaging (FLIM), coupled with patch-clamp electrophysiology, to monitor Ca2+ concentration ([Ca2+]) inside individual astrocytes and principal neurons in acute brain slices. Inside the slice tissue local micro-ejection of Aß in sub-micromolar concentrations triggered prominent [Ca2+] elevations in an adjacent astrocyte translated as an approximately two-fold increase (averaged over ∼5min) in basal [Ca2+]. This elevation did not spread to neighbouring cells and appeared comparable in amplitude with commonly documented spontaneous [Ca2+] rises in astroglia. Principal nerve cells (pyramidal neurons) also showed Ca2+ sensitivity, albeit to a lesser degree. These observations shed light on the extent and dynamics of the acute physiological effects of Aß on brain cells in situ, in the context of AD.

Ultrafast action potentials mediate kilohertz signaling at a central synapse.

Fast synaptic transmission is important for rapid information processing. To explore the maximal rate of neuronal signaling and to analyze the presynaptic mechanisms, we focused on the input layer of the cerebellar cortex, where exceptionally high action potential (AP) frequencies have been reported in vivo. With paired recordings between presynaptic cerebellar mossy fiber boutons and postsynaptic granule cells, we demonstrate reliable neurotransmission up to ∼1 kHz. Presynaptic APs are ultrafast, with ∼100 µs half-duration. Both Kv1 and Kv3 potassium channels mediate the fast repolarization, rapidly inactivating sodium channels ensure metabolic efficiency, and little AP broadening occurs during bursts of up to 1.5 kHz. Presynaptic Cav2.1 (P/Q-type) calcium channels open efficiently during ultrafast APs. Furthermore, a subset of synaptic vesicles is tightly coupled to Ca(2+) channels, and vesicles are rapidly recruited to the release site. These data reveal mechanisms of presynaptic AP generation and transmitter release underlying neuronal kHz signaling.

Quantitative super-resolution imaging of Bruchpilot distinguishes active zone states.

The precise molecular architecture of synaptic active zones (AZs) gives rise to different structural and functional AZ states that fundamentally shape chemical neurotransmission. However, elucidating the nanoscopic protein arrangement at AZs is impeded by the diffraction-limited resolution of conventional light microscopy. Here we introduce new approaches to quantify endogenous protein organization at single-molecule resolution in situ with super-resolution imaging by direct stochastic optical reconstruction microscopy (dSTORM). Focusing on the Drosophila neuromuscular junction (NMJ), we find that the AZ cytomatrix (CAZ) is composed of units containing ~137 Bruchpilot (Brp) proteins, three quarters of which are organized into about 15 heptameric clusters. We test for a quantitative relationship between CAZ ultrastructure and neurotransmitter release properties by engaging Drosophila mutants and electrophysiology. Our results indicate that the precise nanoscopic organization of Brp distinguishes different physiological AZ states and link functional diversification to a heretofore unrecognized neuronal gradient of the CAZ ultrastructure.