Physiology & Behavior, Vol. 17, pp. 367--371. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A. Prolonging Lateral Hypothalamic Anorexia by Tube-Feeding' RICHARD E. KEESEY, TERRY L. POWLEY 2 AND JOSEPH W. KEMNITZ University of Wisconsin, Madison, WI 53706 (Received 3 November 1975) KEESEY, R. E., T. L. POWLEY AND J. W. KEMNITZ. Prolonging lateral hypothalamic anorexia by tube-feeding. PHYSIOL. BEHAV. 17(3) 367-371, 1976.- Male rats sustaining lateral hypothalamic (LH) lesions were anorexic for approximately one week following surgery. They then maintained their body weight at a reduced level (approximately 20% below controls) for the remainder of an 8-week postlesion period of observation. By tube-feeding another group of LH animals, their body weight was held at a control level for the first week postlesion. Following tube-feeding, these animals were anorexic for several weeks while their body weights declined to the same reduced level as that of the LH animals not tube-fed. For both groups of LH animals, achievement of a lowered weight level, rather than a time-dependent recovery process, appeared to underlie the return of food intake to levels sufficient for maintaining body weight. By impeding the loss of body weight, tube-feeding can thus prolong the duration of LH anorexia. Lateral hypothalamus Weight regulation Tube-feeding IT IS common practice to feed animals by garage after lesioning the lateral hypothalamus (LH). The rationale for this procedure derives from the assumption that neural control over food intake is lacking following LH lesions and that such control is restored only after what is often a lengthy period of recovery [5,21]. Tube-feeding is thus seen as a procedure necessary for sustaining a dysphagic animal which might otherwise die of inanition. Recent observations raise the possibility, however, that tube-feeding some LH animals may be not only unnecessary but may actually delay the return of normal feeding. This possiblity is raised by work indicating that a chronic reduction in the level of weight maintenance is often a primary consequence of LH lesions [3, 7, 8, 9, 14, 17, 18]. Following the LH lesions used in these experiments, animals were aphagic and anorexic, but only until their body weight had been reduced to a lower maintenance level. They then defended this lower level in much the same way a nonlesioned animal defends a normal body weight. These observations suggest that the aphagia and anorexia following LH lesions can be a regulatory strategy employed by the animal to lower its body weight to a new set point established by the lesion. According to this view, the duration of aphagia and anorexia will be proportional to the amount of weight that must be lost to achieve this new maintenance level. If LH lesions lower the weight maintenance level, tube-feeding, by impeding weight loss and so opposing an animal's efforts to achieve this lower level, should prolong the normal periods of aphagia and anorexia. However, tube-feeding would not be expected to alter the amount of weight the animal loses over these periods, since that will be determined by how much the lesion has caused the maintenance level to be lowered. A more traditional interpretation of the LH feeding syndrome, in which it is assumed that aphagia and anorexia are direct or primary consequences of LH lesions, leads to opposite predictions. Tube-feeding should have little or no influence on the time required for neural control over feeding to be recovered, and should thus not affect the length of the postlesion aphagia and anorexia. Tube- feeding, however, should reduce the amount of weight lost during these periods of aphagia and anorexia. The present experiment was designed to put these differing predictions to test by examining the effect of tube-feeding upon both the duration of the anorexia following LH lesions and the postlesion level of maintained body weight. METHOD Animals and General Main tenance Procedure Twenty-five male Sprague-Dawley rats, 211 and 212 days of age at the time of surgery, were used. The animals were individually housed in double cages fitted with calibrated drinking tubes and were kept in an isolated room which was constantly illuminated. A highly palatable chocolate chip cookie mash [ 19] and a wet mash of ground Purina Laboratory Chow (70% water by weight) were used during an 1 l-day adaptation period t This research was supported by National Institute of Mental Health Research Grant MH-08909. The authors wish to thank Peter C. Boyle for his helpful criticism of an earlier version of this manuscript. Requests for reprints should be sent to Richard E. Keesey, Department of Psychology, University of Wisconsin, Madison, WI 53706. 2Now at Yale University, New Haven, CT 06510. 367