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 inject ed in the central nervous system and especially in the hypothalamus. T he major site of NPY synthesis in the hypothalamus is the arcuate nucl eus which projects to the paraventricular nucleus. These two nuclei fo rm 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 sta ndard artificial cerebrospinal fluid (CSF) as medium and hyperosmotic CSF obtained by addition of potassium chloride (55 mM). Hyperosmotic p erfusion 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/t ube. The potassium perfusion produced an increase in the release of ne uropeptide Y (peak at 71.4 +/- 7.1 pg/tube; p < 0.01), and this phenom enon was reproduced with the second potassium stimulation (peak at 47. 7 +/- 2.3 vs pg/tube; p < 0.05). Neuropeptide Y release returned to no rmal values after or between stimulations. Behavioral analysis showed that these stimulations were associated with an increase in food intak e. Neuropeptide Y is therefore physiologically released into the parav entricular nucleus of the hypothalamus. This release is associated wit h ingestive behavior and might be induced through voltage-dependent ch annels sensible to the high depolarisation associated with potassium e xcess in the extracellular fluid.