Direct and indirect control of orexin/hypocretin neurons by glycine receptors.
Hypothalamic hypocretin/orexin (hcrt/orx) neurons promote arousal and reward seeking, while reduction in their activity has been linked to narcolepsy, obesity and depression. However, the mechanisms influencing the activity of hcrt/orx networks in situ are not fully understood. Here we show that glycine, a neurotransmitter best known for its actions in the brainstem and spinal cord, elicits dose dependent postsynaptic Cl⁻ currents in hcrt/orx cells in acute mouse brain slices. The effect was blocked by the glycine receptor (GLyR) antagonist strychnine and mimicked by the GlyR agonist alanine. Postsynaptic GlyRs on hcrt/orx cells remained functional during both early postnatal and adult periods, and gramicidin-perforated patch-clamp recordings revealed that they progressively switch from excitatory to inhibitory during the first two postnatal weeks. The pharmacological profile of the glycine response suggested that developed hcrt/orx neurons contain α/β-heteromeric GlyRs that lack α2-subunits, whereas α2-subunits, whereas α2-subunits are present in early postnatal hcrt/orx neurons. All postsynaptic currents (PSCs) in developed hcrt/orx cells were blocked by inhibitors of GABA and glutamate receptors, with no evidence of GlyR-mediated PSCs. However, the frequency but not amplitude of miniature PSCs was reduced by strychnine and increased by glycine in ~50% of hcrt/orx neurons. Together, these results provide the first evidence for functional GlyRs in identified hcrt/orx circuits and suggest that the activity of developed hcrt/orx cells is regulated by two GlyR pools: inhibitory extrasynaptic GlyRs located on all hcrt/orx cells and excitatory GlyRs located on presynaptic terminals contacting some hcrt/orx cells.
University of Cambridge, Department of Pharmacology, Cambridge, UK. mmk37@cam.ac.uk
Mahesh M
MM
Karnani
Anne
A
Venner
Lise T
LT
Jensen
Lars
L
Fugger
Denis
D
Burdakov
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000375:Aging / Q000502:physiology; D000409:Alanine / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001581:Benzothiadiazines / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology; D055724:Electrophysiological Phenomena / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D005998:Glycine / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism*; D000068797:Orexins; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D011724:Pyridazines / Q000494:pharmacology; D018079:Receptors, GABA / Q000502:physiology; D017470:Receptors, Glutamate / Q000502:physiology; D018009:Receptors, Glycine / Q000037:antagonists & inhibitors / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology; D055366:Synaptic Potentials / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000409:Alanine; D001581:Benzothiadiazines; D018118:Chloride Channels; D018756:GABA Antagonists; D018698:Glutamic Acid; D005998:Glycine; D049452:Green Fluorescent Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D010852:Picrotoxin; D011724:Pyridazines; D018079:Receptors, GABA; D017470:Receptors, Glutamate; D018009:Receptors, Glycine; D013331:Strychnine; D005680:gamma-Aminobutyric Acid; C485184:enhanced green fluorescent protein; C049853:gabazine; C004639:cyclothiazide