Actions of centrally administered neuropeptide Y on EEG activity in different rat strains and in different phases of their circadian cycle

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Abstract
The effects of centrally administered neuropeptide Y (NPY) on the sleep-wakefulness cycle were studied by analyzing its action in different strains of rats with or without spontaneous hypertension and during 2 different phases of the circardian cycle. Normal adult Sprague-Dawley (SD), Wistar-Kyoto (WKy) and spontaneous hypertensive (SH) rats were used. By means of EEG electrodes the recording of the fronto-parietal electrocorticogram and the electromyogram could be made. Stainless steel cannula were also implanted into the lateral ventricle. The effects of an intraventricular injection of NPY (1.25 nmol/rat) was compared with the effects of the vehicle (saline) alone. The EEG patterns were classified as desynchronized, mixed or synchronized. In the SD rats NPY produced behavioral signs of sedation and a significant reduction of synchronized EEG activity as well as significant increase of synchronized and mixed EEG activities in comparison with the saline treated rats. In the WKy rats NPY administration produced an increaese of synchronized EEG activity during evening sessions. In SH rats NPY produced a significant increase of desynchronized EEG activity and a decrease in mixed EEG activity indicating an awakening effect of the peptide. In view of the NPY innervation of the locus ceruleus, it seems possible that the neuronal and hormonal regulation of the locus ceruleus noradrenaline [norepinephrine] nerve cells is different in the 2 strains of rats. The ability of NPY to increase wakefulness in hypertensive animals is probably related to abnormal changes in the .alpha.2-adrenoreceptors taking place in SH rats.

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