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Hypothalamic orexin-A binding sites are downregulated by chronic nicotine treatment in the rat
1Department of Pharmacology, University of Tennessee College of Medicine, 874 Union Avenue, TN 38163, Memphis, USA.
Abstract:
Chronic nicotine treatment (4 mg/kg per day; 14 days) significantly reduced the affinity and density of orexin-A binding sites in the anterior hypothalamus of rat brain. There was a significantly lower sensitivity of orexin-A binding to orexin peptides, to the related secretin and pituitary adenylate cyclase activating peptide, and to unrelated neuropeptide Y (NPY). This change correlated with selective downregulation of a fraction of hypothalamic NPY Y(1) receptors. In previous studies, we have demonstrated an increase in the levels of orexin-A peptide and NPY in discrete hypothalamic areas upon nicotine treatment. This finding contradicts an expected increase in the production of these orexigenic peptides in a model where an inverse relationship is observed between food consumption and nicotine treatment. This study provides a possible explanation to this inconsistency in that a decrease in affinity of orexin-A binding could reduce neural orexin signaling, which may contribute to decreased food intake observed in smokers and animals chronically treated with nicotine.
Insights
Chronic nicotine exposure reduces orexin-A binding site affinity and density in rat brains. This may explain reduced food intake in smokers by decreasing neural orexin signaling.
Area of Science:
- Neuroscience
- Endocrinology
- Pharmacology
Background:
- Nicotine exposure is known to affect appetite regulation.
- Orexin-A and Neuropeptide Y (NPY) are key orexigenic peptides involved in feeding behavior.
- Previous studies showed increased orexin-A and NPY levels with nicotine, contradicting observed reduced food intake.
Purpose of the Study:
- To investigate the impact of chronic nicotine treatment on orexin-A binding characteristics in the rat hypothalamus.
- To explore the relationship between nicotine-induced changes in orexin-A binding and NPY receptor expression.
- To elucidate the mechanism behind nicotine's effect on appetite regulation.
Main Methods:
- Rats received chronic nicotine treatment (4 mg/kg/day for 14 days).
- Orexin-A binding affinity and density were measured in the anterior hypothalamus.
- Sensitivity of orexin-A binding to various peptides and NPY Y(1) receptor downregulation were assessed.
Main Results:
- Chronic nicotine significantly reduced orexin-A binding affinity and density in the anterior hypothalamus.
- Orexin-A binding showed decreased sensitivity to orexin peptides, secretin, pituitary adenylate cyclase-activating peptide, and NPY.
- A selective downregulation of hypothalamic NPY Y(1) receptors was observed, correlating with binding changes.
Conclusions:
- Reduced orexin-A binding affinity and density following chronic nicotine treatment may impair neural orexin signaling.
- This impaired signaling offers a potential explanation for the decreased food intake observed in smokers and nicotine-treated animals.
- The findings reconcile the paradox of increased orexigenic peptide levels with decreased food consumption under nicotine exposure.