Typically, DD mice given l-dopa experience an activity peak at 3 hours after which movement declines, until 12 hours after injection they hardly move at all. 2nd and 3rd waves of activity up to 56 hours after l-dopa injection, although it is not enough to simulate eating. When l-dopa was withdrawn from the double mutant mice, food consumption all but ceased and body weight dropped by 15 percent by day 3, even though they were very active during the period. The results show dopamine is required for food intake, even when leptin is absent. This indicates that dopamine suppresses the leptin-melanocortin pathway in controlling feeding.
Scientists are uncertain as to how dopamine functions to motivate food intake.
But Palmiter hypothesizes that dopamine-deficient mice are unable to process the signals that stimulate eating, and that the lack of signaling may prevent the strong appetite stimulus normally associated with low leptin levels. Szczypka MS, et al. Copyright 1997-2001, all rights reserved. All information in this publication is believed to be accurate and true. Publisher is not liable for omissions or inaccuracies.