ABSTRACT
The lateral hypothalamus (LH) is a key regulator of multiple vital behaviors. The firing of brain-wide-projecting LH neurons releases neuropeptides promoting wakefulness (orexin/hypocretin; OH), or sleep (melanin-concentrating hormone; MCH). OH neurons, which coexpress glutamate and dynorphin, have been proposed to excite their neighbors, including MCH neurons, suggesting that LH may sometimes coengage its antagonistic outputs. However, it remains unclear if, when, and how OH actions promote temporal separation of the sleep and wake signals, a process that fails in narcolepsy caused by OH loss. To explore this directly, we paired optogenetic stimulation of OH cells (at rates that promoted awakening in vivo) with electrical monitoring of MCH cells in mouse brain slices. Membrane potential recordings showed that OH cell firing inhibited action potential firing in most MCH neurons, an effect that required GABAA but not dynorphin receptors. Membrane current analysis showed that OH cell firing increased the frequency of fast GABAergic currents in MCH cells, an effect blocked by antagonists of OH but not dynorphin or glutamate receptors, and mimicked by bath-applied OH peptide. In turn, neural network imaging with a calcium indicator genetically targeted to MCH neurons showed that excitation by bath-applied OH peptides occurs in a minority of MCH cells. Collectively, our data provide functional microcircuit evidence that intra-LH feedforward loops may facilitate appropriate switching between sleep and wake signals, potentially preventing sleep disorders.
Subject(s)
Hypothalamic Hormones/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Melanins/metabolism , Nerve Net/physiology , Neural Inhibition/physiology , Neurons/physiology , Neuropeptides/metabolism , Optogenetics , Pituitary Hormones/metabolism , Signal Transduction/physiology , Animals , Calcium/metabolism , Channelrhodopsins , Excitatory Amino Acid Antagonists/pharmacology , Hypothalamic Area, Lateral/cytology , Hypothalamic Area, Lateral/metabolism , Hypothalamic Hormones/genetics , In Vitro Techniques , Intracellular Signaling Peptides and Proteins/genetics , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Lysine/analogs & derivatives , Lysine/metabolism , Melanins/genetics , Membrane Potentials/drug effects , Membrane Potentials/physiology , Mice , Neural Inhibition/drug effects , Neuropeptides/genetics , Neuropeptides/pharmacology , Orexins , Patch-Clamp Techniques , Pituitary Hormones/genetics , Transduction, Genetic , gamma-Aminobutyric Acid/metabolism , Red Fluorescent ProteinABSTRACT
A three-dimensional wide-angle parabolic equation (3DPE) is used to model low frequency sound propagation in irregular urban canyons at low computational cost. This one-way wave equation is solved using the Alternating Direction Implicit method. A finite difference scheme adapted to the geometry of the urban environment is then developed. Abrupt variations of the street width are treated as a single scattering problem using the Kirchhoff approximation. Numerical results are compared with experimental data obtained on a scale model of a street. Comparisons show the ability of the 3DPE model to provide reliable transmitted fields even for large irregularities.
