GABA(B) receptor-mediated modulation of hypocretin/orexin neurones in mouse hypothalamus.
Hypocretin/orexin (Hcrt) is a critical neurotransmitter for the maintenance of wakefulness and has been implicated in several other functions, including energy metabolism and reward. Using whole-cell patch-clamp recordings from transgenic mice in which enhanced green fluorescent protein was linked to the Hcrt promoter, we investigated GABAergic control of the Hcrt neurones in hypothalamic slices. Bath application of GABA or muscimol caused an early hyperpolarization mediated by Cl(-) and a late depolarization mediated by the efflux of bicarbonate. These GABA(A) receptor-mediated responses were blocked by picrotoxin and bicuculline. Under the GABA(A) blockade condition, GABA produced consistent hyperpolarization, decreased firing rate and input resistance. The selective GABA(B) agonist (R)-baclofen caused a similar response with an EC(50) of 7.1 mum. The effects of (R)-baclofen were blocked by the GABA(B) antagonist CGP 52432 but persisted in the presence of tetrodotoxin, suggesting direct postsynaptic effects. The existence of GABA(B) modulation was supported by GABA(B(1)) subunit immunoreactivity on Hcrt cells colabelled with antisera to the Hcrt-2 peptide. Furthermore, GABA(B) receptor activation inhibited the presynaptic release of both glutamate and GABA. (R)-Baclofen depressed the amplitude of evoked excitatory postsynaptic currents (EPSCs) and inhibitory synaptic currents (IPSCs), and also decreased the frequency of both spontaneous and miniature EPSCs and IPSCs with a modest effect on their amplitudes. These data suggest that GABA(B) receptors modulate Hcrt neuronal activity via both pre- and postsynaptic mechanisms, which may underlie the promotion of non-rapid eye movement sleep and have implications for the use of GABA(B) agonists in the treatment of substance addiction through direct interaction with the Hcrt system.
Xie
Xinmin
X
Biosciences Division, SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025, USA. xinmin.xie@sri.com
Crowder
Tara L
TL
Yamanaka
Akihiro
A
Morairty
Stephen R
SR
Lewinter
Robin D
RD
Sakurai
Takeshi
T
Kilduff
Thomas S
TS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D007031:Hypothalamus / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000032:analysis*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000737:chemistry* / Q000502:physiology*; D009479:Neuropeptides / Q000032:analysis*; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology; D018080:Receptors, GABA-B / Q000187:drug effects / Q000502:physiology*; D018013:Receptors, Neuropeptide; D012890:Sleep / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D014851:Wakefulness / Q000502:physiology
D018755:GABA Agonists; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D058788:GABA-B Receptor Antagonists; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D018013:Receptors, Neuropeptide