NEUROPEPTIDE-Y ATTENUATES SATIETY - EVIDENCE FROM A DETAILED ANALYSISOF PATTERNS INGESTION

Centrally injected neuropeptide Y (NPY) is a potent stimulant of inges tive behavior capable of augmenting both food and fluid intake in full y satiated animals. To gain further insight into NPY's mechanism of ac tion, we recorded patterns of licking behavior in rats drinking sweete ned condensed milk solutions immediately after lateral ventricular inj ection of NPY (10 mu g) or vehicle. In a separate study, we examined l icking patterns after 23 h food deprivation (FD) that produced approxi mately the same total intake as NPY. Consistent with previous reports, we found NPY stimulated intake by increasing total ingestion time and total volume consumed during a l-h test. Although NPY increased the n umber of bouts of licking and shortened pauses between bouts, it also decreased mean bout size, bout duration and within-bout lick rate (loc al rate). It had no significant effect on start latency or lick effici ency (licks/ml). Further analyses revealed that NPY attenuated satiety (reduced slope of lick-rate functions with session time) but had no s ignificant effect on the beginning lick rate, a measure related to oro sensory excitation. In contrast to NPY, FD increased both the beginnin g lick rate and individual bout size without changing either the mean number of bouts or the pause between bouts. In general, NPY stimulated an intermittent pattern of licking and delayed satiation whereas FD i ncreased the initial rate of licking and the size of individual bouts without changing the basic licking pattern. The increase in initial li ck rate suggests that FD, unlike NPY, enhances orosensory stimulation. These data compliment previous results showing that NPY increases the motivation to eat. In particular, the present data suggest that NPY a lso promotes ingestion by producing a distinctive pattern of ingestion and slowing the rate of satiation.