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Cortical neurons are often functionally heterogeneous even for molecularly defined subtypes. In sensory cortices, physiological responses to natural stimuli can be sparse and vary widely even for neighboring neurons. It is thus difficult to parse out circuits that encode specific stimuli for further experimentation. Here, we report the development of a Cre-reporter mouse that allows recombination for cellular labeling and genetic manipulation, and use it with an activity-dependent Fos-CreERT2 driver to identify functionally active circuits in the auditory cortex. In vivo targeted patch recordings validate our method for neurons responding to physiologically relevant natural sounds such as pup wriggling calls and ultrasonic vocalizations (USVs). Using this system to investigate cortical responses in postpartum mothers, we find a transient recruitment of neurons highly responsive to USVs. This subpopulation of neurons has distinct physiological properties that improve the coding efficiency for pup USV calls, implicating it as a unique signature in parental plasticity. [ABSTRACT FROM AUTHOR]

Local interneurons are essential in information processing by neural circuits. Here we present a comprehensive genetic, anatomical and electrophysiological analysis of local interneurons (LNs) in the Drosophila melanogaster antennal lobe, the first olfactory processing center in the brain. We found LNs to be diverse in their neurotransmitter profiles, connectivity and physiological properties. Analysis of >1,500 individual LNs revealed principal morphological classes characterized by coarsely stereotyped glomerular innervation patterns. Some of these morphological classes showed distinct physiological properties. However, the finer-scale connectivity of an individual LN varied considerably across brains, and there was notable physiological variability within each morphological or genetic class. Finally, LN innervation required interaction with olfactory receptor neurons during development, and some individual variability also likely reflected LN–LN interactions. Our results reveal an unexpected degree of complexity and individual variation in an invertebrate neural circuit, a result that creates challenges for solving the Drosophila connectome. [ABSTRACT FROM AUTHOR]

Olfactory systems utilize discrete neural pathways to process and integrate odorant information. In Drosophila, axons of first-order olfactory receptor neurons (ORNs) and dendrites of second-order projection neurons (PNs) form class-specific synaptic connections at ∼50 glomeruli. The mechanisms underlying PN dendrite targeting to distinct glomeruli in a three-dimensional discrete neural map are unclear. We found that the leucine-rich repeat (LRR) transmembrane protein Capricious (Caps) was differentially expressed in different classes of PNs. Loss-of-function and gain-of-function studies indicated that Caps instructs the segregation of Caps-positive and Caps-negative PN dendrites to discrete glomerular targets. Moreover, Caps-mediated PN dendrite targeting was independent of presynaptic ORNs and did not involve homophilic interactions. The closely related protein Tartan was partially redundant with Caps. These LRR proteins are probably part of a combinatorial cell-surface code that instructs discrete olfactory map formation. [ABSTRACT FROM AUTHOR]

In the olfactory system of Drosophila melanogaster, axons of olfactory receptor neurons (ORNs) and dendrites of second-order projection neurons typically target 1 of ∼50 glomeruli. Dscam, an immunoglobulin superfamily protein, acts in ORNs to regulate axon targeting. Here we show that Dscam acts in projection neurons and local interneurons to control the elaboration of dendritic fields. The removal of Dscam selectively from projection neurons or local interneurons led to clumped dendrites and marked reduction in their dendritic field size. Overexpression of Dscam in projection neurons caused dendrites to be more diffuse during development and shifted their relative position in adulthood. Notably, the positional shift of projection neuron dendrites caused a corresponding shift of its partner ORN axons, thus maintaining the connection specificity. This observation provides evidence for a pre- and postsynaptic matching mechanism independent of precise glomerular positioning. [ABSTRACT FROM AUTHOR]

Examines the Rac guanosine triphosphatase (GTPase) in controlling axon growth, guidance and branching. Regulation of actin cytoskeleton; Administration of mosaic analysis for Rac GTPase; Sensitivity of axon branching to the loss of Rac GTPase activity.

Examines the Rac guanosine triphosphatase in regulating actin cytoskeleton to control changes in cell shape. Use of dominant mutant isoforms in analyzing Rac; Importance of guanine nucleotide exchange factor in axon growth and guidance; Pattern of overlapping functions in diverse process for C. elegans.

Analyzes the action of neurons in the olfactory map of Drosophila. Projection of olfactory receptor neurons (ORN) to glomerular targets in olfactory bulb; Prespecification of neurons by lineage and birth order; Linkage between ORN and projection neurons.

The article offers information on the neural basis of aggression. A study conducted on fighting flies revealed that a small cluster of octopaminergic neurons can make a fly mad. Octopaminergic neuron is inferred to be responsible for aggressive behavior of the fighting fly. Induced aggression varies depending on the levels of octopamine.

The article discusses several studies relating to the retinotopic map, the framework that describes the movement of nerve fibers from the retina to their destination in the brain. An investigation proposed that the chemicals on retinal ganglion cells (RGC) axons could specify different positions. Another study provide evidence that Ryk-mediated repulsion in response is responsible for RGC axon targeting along the medial-lateral axis.

Comments on C. Rogers and colleagues' study identifying the ligands for the NPR-1 receptor and showing that these ligands differentially activate the solitary versus social variants of NPR-1. Ability of synthesized FaRP peptides to activate NPR-1 215GV and NPR-1 215F in a heterologous Xenopus laevis oocyte system; Expression pattern of the NPR-1 ligands.