Figure 1.

Rats anticipate 3 or 4 daily meals. (A) Upper panel: Actogram depicting lever pressing for food in a rat (R03) with food available ad-libitum for 10 days (indicated by blue vertical bar to the upper left of the actogram), followed by 1 day of total food deprivation (pink shading, red vertical bar), 21 days of restricted feeding (green vertical bar; lever pressing reinforced for 30 min starting at ZT2, 10 and 18), and 60 h of total food deprivation (pink shading, red bar). Time of day (10 min bins) is plotted left to right and consecutive days are aligned vertically. Black bars represent time bins with activity. The height of each bar represents relative amount of activity (quintiles). Lower panels: Waveforms of lever pressing for rat R03 on days 18–21 of the 3-meal schedule, and during 60 h of food deprivation in constant dark (FD-DD). Mealtimes are denoted by green vertical bars during scheduled feeding (lever presses yield 20 mg food pellets) and by red vertical bars when lever presses were not reinforced (FD-DD). The fifth panel in the column is the average of the last 6 days of scheduled feeding prior to total food deprivation. Data were smoothed using a 40-min running average. (B) Upper panel: Actogram of operant nose-poking for food in rat R03 with 4 daily 15–30 min feeding opportunities, at ZT3, 9, 15, and 21. Lower panels: Waveforms of operant nose-poking for rat R03 on days 37–40 of the 4-meal schedule, and during the 2 days of total food deprivation (FD-DD). The fifth panel is the average of the last 6 days of scheduled feeding prior to the 2-day food deprivation. (C) Upper panel: Actogram of lever pressing in a representative SCN-ablated rat (Sx06), fed at 05:00 h, 13:00 h, and 21:00 h local time each day in constant dim light. Lower panels: Waveforms of lever pressing on days 22–24 of the 3-meal schedule, and during the 3 days of total food deprivation. Panel 4 is the average of the 6 days of scheduled mealtimes prior to total food deprivation.