K(+)-stimulated neuropeptide Y release into the paraventricular nucleus and relation to feeding behavior in free-moving rats.

Neuropeptide Y (NPY) strongly stimulates food intake when it is injected in the central nervous system and especially in the hypothalamus. The major site of NPY synthesis in the hypothalamus is the arcuate nucleus which projects to the paraventricular nucleus. These two nuclei form the arcuate-paraventricular axis, a local circuit in the control of food intake. It was demonstrated that neuropeptide Y concentration in the paraventricular nucleus can be modified by ingestive or metabolic factors. Actually, these modifications cannot be associated with the existence of a release of neuropeptide Y in this nucleus. That is why we used push-pull perfusion during the light phase in freely-behaving rats with food and water available. Perfusates were collected with standard artificial cerebrospinal fluid (CSF) as medium and hyperosmotic CSF obtained by addition of potassium chloride (55 mM). Hyperosmotic perfusion was repeated a second time for some animals. Results clearly demonstrated that neuropeptide Y is released into the paraventricular nucleus during normal perfusion with a mean value of 35.5 +/- 1.5 pg/tube. The potassium perfusion produced an increase in the release of neuropeptide Y (peak at 71.4 +/- 7.1 pg/tube; p < 0.01), and this phenomenon was reproduced with the second potassium stimulation (peak at 47.7 +/- 2.3 vs pg/tube; p < 0.05). Neuropeptide Y release returned to normal values after or between stimulations. Behavioral analysis showed that these stimulations were associated with an increase in food intake. Neuropeptide Y is therefore physiologically released into the paraventricular nucleus of the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)