Paired-Pulse Inhibition and Disinhibition of the Dentate Gyrus Following Orexin Receptors Inactivation in the Basolateral Amygdala

The basolateral amygdala (BLA) has substantial effects on the neuronal transmission and synaptic plasticity processes through the dentate gyrus. Orexin neuropeptides play different roles in the sleep/wakefulness cycle, feeding, learning, and memory. The present study was conducted to investigate the function of the orexin receptors of the BLA in the hippocampal local interneuron circuits. For this, paired-pulse responses from dentate gyrus (DG) region were recorded. Within the procedure, SB-334867-A (12μg/0.5μl), and, TCS-OX2-29 (10μg/0.5μl (orexin 1 and 2 receptors antagonists, respectively), were administered into the both side of the BLA areas of the rat brain. Dimethyl sulfoxide (DMSO) was used as the solvent in the control animals with the volume of 0.5μl. Our data indicated that the paired-pulse (PP) responses were not affected by the inactivation of the orexin receptors of the BLA.

Thirst interneurons that promote water seeking and limit feeding behavior in Drosophila

Thirst is a motivational state that drives behaviors to obtain water for fluid homeostasis. We identified two types of central brain interneurons that regulate thirsty water seeking in Drosophila, that we term the Janu neurons. Janu-GABA, a local interneuron in the subesophageal zone, is activated by water deprivation and is specific to thirsty seeking. Janu-AstA projects from the subesophageal zone to the superior medial protocerebrum, a higher order processing area. Janu-AstA signals with the neuropeptide Allatostatin A to promote water seeking and to inhibit feeding behavior. NPF (Drosophila NPY) neurons are postsynaptic to Janu-AstA for water seeking and feeding through the AstA-R2 galanin-like receptor. NPF neurons use NPF to regulate thirst and hunger behaviors. Flies choose Janu neuron activation, suggesting that thirsty seeking up a humidity gradient is rewarding. These findings identify novel central brain circuit elements that coordinate internal state drives to selectively control motivated seeking behavior.

The wiring logic of an identified serotonergic neuron that spans sensory networks

Serotonergic neurons modulate diverse physiological and behavioral processes in a context-dependent manner, based on their complex connectivity. However, their connectivity has not been comprehensively explored at a single-cell resolution. Using a whole-brain EM dataset we determined the wiring logic of a broadly projecting serotonergic neuron (the “CSDn”) in Drosophila. Within the antennal lobe (AL; first-order olfactory region), the CSDn receives glomerulus-specific input and preferentially targets distinct local interneuron subtypes. Furthermore, the wiring logic of the CSDn differs between olfactory regions. The CSDn innervates the AL and lateral horn (LH), yet does not maintain the same synaptic relationship with individual projection neurons that also span both regions. Consistent with this, the CSDn has more distributed connectivity in the LH relative to the AL, preferentially synapsing with principal neuron types based on presumptive transmitter content. Lastly, we identify protocerebral neurons that provide abundant synaptic input to the CSDn. Our study demonstrates how an individual modulatory neuron can interact with local networks and integrate input from non-olfactory sources.

A segmentation scheme for complex neuronal arbors and application to vibration sensitive neurons in the honeybee brain

The morphology of a neuron is strongly related to its physiological properties, and thus to information processing functions. Optical microscope images are widely used for extracting the structure of neurons. Although several approaches have been proposed to trace and extract complex neuronal structures from microscopy images, available methods remain prone to errors. In this study, we present a practical scheme for processing confocal microscope images and reconstructing neuronal structures. We evaluated this scheme using image data samples and associated gold standard reconstructions from the BigNeuron Project. In these samples, dendritic arbors belonging to multiple projection branches of the same neuron overlapped in space, making it difficult to automatically and accurately trace their structural connectivity. Our proposed scheme, which combines several software tools for image masking and filtering with an existing tool for dendritic segmentation and tracing, outperformed state-of-the-art automatic methods in reconstructing such neuron structures. For evaluating our scheme, we applied it to a honeybee local interneuron, DL-Int-1, which has complex arbors and is considered to be a critical neuron for encoding the information indicated in the waggle dance of the honeybee.

Transmitter Co-Expression Reveals Key Organizational Principles of Local Interneuron Heterogeneity in the Olfactory System

Heterogeneity of individual neurons within a population expands the computational power of the entire neural network. However, the organizing principles that support heterogeneity within a neuronal class are often poorly understood. Here, we focus on a highly heterogeneous population of local interneurons whose traits co-vary seemingly at random. We asked if local interneurons (LNs) in the antennal lobe (AL) of Manduca sexta express fixed, predictable combinations of neurotransmitters, or if transmitter co-expression can be explained by random probability. We systematically determined the co-expression of neuropeptides and GABA by LNs and found variable patterns of co-expression for all neuropeptides, except for tachykininergic LNs which exhibited highly stereotyped co-expression on a neuron-by-neuron basis. To test if observed patterns of co-expression were random, we used a computational model and found that the probabilities of transmitter co-expression cannot be explained by independent expression of each transmitter. We also determined that setting a single rule in the model, while leaving the rest of the co-expression up to random probability, allowed the model to replicate the overall heterogeneity of transmitter co-expression across antennal lobe LNs. This implies that certain co-expression relationships contribute to the ground plan of the AL, but that otherwise, transmitter expression amongst LNs may be random, allowing heterogeneous co-expression patterns to emerge. Furthermore, neuropeptide receptor expression suggests that peptidergic signaling from LNs may simultaneously target olfactory receptor neurons, LNs and projection neurons, and thus the effects of different peptides do not segregate based on principal AL cell type. Our data suggest that while specific constraints may partially shape transmitter co-expression in LNs, a large amount of flexibility on a neuron-by-neuron basis produces heterogeneous network parameters.

Developmental experience-dependent plasticity in the first synapse of the Drosophila olfactory circuit

Evidence accumulating over the past 15 years soundly refutes the dogma that the Drosophila nervous system is hardwired. The preponderance of studies reveals activity-dependent neural circuit refinement driving optimization of behavioral outputs. We describe developmental, sensory input-dependent plasticity in the brain olfactory antennal lobe, which we term long-term central adaption (LTCA). LTCA is evoked by prolonged exposure to an odorant during the first week of posteclosion life, resulting in a persistently decreased response to aversive odors and an enhanced response to attractive odors. This limited window of early-use, experience-dependent plasticity represents a critical period of olfactory circuit refinement tuned by initial sensory input. Consequent behavioral adaptations have been associated with changes in the output of olfactory projection neurons to higher brain centers. Recent studies have indicated a central role for local interneuron signaling in LTCA presentation. Genetic and molecular analyses have implicated the mRNA-binding fragile X mental retardation protein and ataxin-2 regulators, Notch trans-synaptic signaling, and cAMP signal transduction as core regulatory steps driving LTCA. In this article, we discuss the structural, functional, and behavioral changes associated with LTCA and review our current understanding of the molecular pathways underlying these developmental, experience-dependent changes in the olfactory circuitry.