GABA-mediated control of hypocretin- but not melanin-concentrating hormone-immunoreactive neurones during sleep in rats.
The perifornical-lateral hypothalamic area (PF-LHA) has been implicated in the regulation of behavioural arousal. The PF-LHA contains several cell types including neurones expressing the peptides, hypocretin (HCRT; also called orexin) and melanin-concentrating hormone (MCH). Evidence suggests that most of the PF-LHA neurones, including HCRT neurones, are active during waking and quiescent during non-rapid eye movement (non-NREM) sleep. The PF-LHA contains local GABAergic interneurones and also receives GABAergic inputs from sleep-promoting regions in the preoptic area of the hypothalamus. We hypothesized that increased GABA-mediated inhibition within PF-LHA contributes to the suppression of neuronal activity during non-REM sleep. EEG and EMG activity of rats were monitored for 2 h during microdialytic delivery of artificial cerebrospinal fluid (aCSF) or bicuculline, a GABAA receptor antagonist, into the PF-LHA in spontaneously sleeping rats during the lights-on period. At the end of aCSF or bicuculline perfusion, rats were killed and c-Fos immunoreactivity (Fos-IR) in HCRT, MCH and other PF-LHA neurones was quantified. In response to bicuculline perfusion into the PF-LHA, rats exhibited a dose-dependent decrease in non-REM and REM sleep time and an increase in time awake. The number of HCRT, MCH and non-HCRT/non-MCH neurones exhibiting Fos-IR adjacent to the microdialysis probe also increased dose-dependently in response to bicuculline. However, significantly fewer MCH neurones exhibited Fos-IR in response to bicuculline as compared to HCRT and other PF-LHA neurones. These results support the hypothesis that PF-LHA neurones, including HCRT neurones, are subject to increased endogenous GABAergic inhibition during sleep. In contrast, MCH neurones appear to be subject to weaker GABAergic control during sleep.
Alam
Md Noor
MN
Research Service (151A3), Veteran Affairs Greater Los Angeles Healthcare System, Sepulveda, CA 91343, USA. noor@ucla.edu
Kumar
Sunil
S
Bashir
Tariq
T
Suntsova
Natalia
N
Methippara
Melvi M
MM
Szymusiak
Ronald
R
McGinty
Dennis
D
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D016762:Genes, fos / Q000502:physiology; D007026:Hypothalamic Area, Lateral / Q000502:physiology / Q000648:ultrastructure; D007028:Hypothalamic Hormones / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D008297:Male; D008543:Melanins / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009479:Neuropeptides / Q000502:physiology*; D000068797:Orexins; D010907:Pituitary Hormones / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012894:Sleep Stages / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D007028:Hypothalamic Hormones; D047908:Intracellular Signaling Peptides and Proteins; D008543:Melanins; D009479:Neuropeptides; D000068797:Orexins; D010907:Pituitary Hormones; D005680:gamma-Aminobutyric Acid; C019463:melanin-concentrating hormone; D001640:Bicuculline