Neuropeptide Y increases the inhibitory effects of clonidine on potassium evoked 3H-noradrenaline but not 3H-5-hydroxytryptamine release from synaptosomes of the hypothalamus and the frontoparietal cortex of the male Sprague-Dawley rat.
The release of 3H-noradrenaline (3H-NA) and of 3H-5-hydroxytryptamine (3H-5-HT) evoked by high-K+ (15 mM) was studied in synaptosomes isolated from the hypothalamus and the frontoparietal cortex of the male Sprague-Dawley rat using a superfusion apparatus. Based on concentration-response curves obtained by analyzing the full-time course of the inhibitory effects of clonidine on 3H-NA and on 3H-5-HT release neuropeptide Y (NPY) (1 nM) was shown to significantly increase the ability of clonidine to inhibit 3H-NA release in synaptosomes isolated from the hypothalamus and from the frontoparietal cortex. NPY (1 nM) alone had no effect on K+-evoked 3H-NA release from these regions. In contrast, NPY (1 nM) did not modulate the inhibitory effects of clonidine on 3H-5-HT release in the above mentioned regions. These results indicate that NPY can increase the sensitivity of the alpha 2-autoreceptors belonging to hypothalamic NA and/or to adrenaline nerve terminals and to cortical NA nerve terminals, while the alpha 2-heteroreceptors inhibiting 3H-HT release in the same brain regions appear not to be regulated by high affinity NPY receptors. Thus, alpha 2-autoreceptors and alpha 2-heteroreceptors appear to be differentially controlled by high affinity NPY receptors at least with regard to regulation of 3H-NA and 3H-5-HT release, respectively.
Department of Pharmacology, Catholic University, Rome, Italy.
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D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D005625:Frontal Lobe / Q000187:drug effects / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009478:Neuropeptide Y / Q000494:pharmacology*; D009638:Norepinephrine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010296:Parietal Lobe / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012702:Serotonin Antagonists / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism
D009478:Neuropeptide Y; D012702:Serotonin Antagonists; D003000:Clonidine; D011188:Potassium; D009638:Norepinephrine