. Mating behavior is controlled by acute changes in metabolic fuels. Am J Physiol Regulatory Integrative Comp Physiol 282: R782-R790, 2002; 10.1152/ajpregu.00383.2001.-Mild food restriction for 48 h inhibits mating behavior in female musk shrews (Suncus murinus). However, mating behavior is restored after a 90-min feeding bout. In this series of experiments, we examined the role of metabolic fuels in this behavioral restoration. First, drugs reported to block glycolysis or fatty acid oxidation were given 2 h before mating. Both treatments inhibited mating in food-restricted females that were refed after treatment. Blood glucose levels were assessed in females that were fed ad libitum, food restricted, or food restricted and refed for 90 min. Food restriction significantly lowered blood glucose compared with ad libitum feeding or food restriction in combination with 90 min of refeeding. However, neither glucose nor fat alone could substitute for food and promote mating behavior in food-restricted females. In addition, analysis of ketone bodies and body composition in females demonstrated low or undetectable levels of these energy substrates. Our data suggest that musk shrews have relatively little stored energy. Therefore, female musk shrews rely on continuous food intake and monitor multiple cues acutely, including glucose availability and fatty acid oxidation. This ensures that mating does not occur when adequate energy is unavailable. nutrition; glucose; fatty acids; anorexia; emesis SUCCESSFUL REPRODUCTION REQUIRES energy, typically attained by ingesting food consisting of proteins, fats, and carbohydrates. These macromolecules are broken down into amino acids, glycerol, fatty acids, and simple sugars. The brain almost exclusively uses glucose for energy production, while glucose and fatty acid oxidation are used in the periphery (18). In cases where glucose availability is inadequate (e.g., starvation and diabetes), ketone bodies can be used for neural energy. When food intake is limited, compensatory changes ensure that metabolic homeostasis is maintained (30). Initially, stored glycogen is broken down into glucose. With continued deprivation, the micromolecules in the liver are used to form glucose via gluconeogenesis. Next, fatty acid oxidation becomes the primary energy source in the periphery, and glucose or ketone bodies are shunted to the brain.During metabolic challenges, energy can be conserved by inhibition of processes that are unnecessary for immediate survival. For example, restricted food availability or limitations of specific metabolic fuels inhibit sexual behavior (5,14,17,20), hypothalamic gonadotropin-releasing hormone secretion (13), gonadotropin secretion (3, 4, 19), estrous cyclicity (22,23,28,29), and steroidogenesis (17, 19) in a wide variety of species (reviewed in Ref. 37). This is a reversible mechanism that allows females to maximize reproductive efficacy and synchronize reproduction with nutritional resources. Although estrous cycles and ovarian steroid secretion in Syrian hamst...