1. Introduction At the latest SfN meeting (1), we presented data showing that 10.0 and 1.5 mg/kg of estradiol valerate (EV) enhanced female rats’ appetite for chocolate cake mix batter (CCMB). That research was prompted by findings that EV enhanced intake of alcoholic beverages (2,3) and a highly palatable saccharin solution. The 10.0 mg/kg dose reduced intakes of a concentrated saccharin solution that was probably bittersweet (4). It appears that EV induces an enhanced appetite for only certain ingesta, for example, those that might be considered luxury ingesta (alcoholic beverage, saccharin sweet solutions, and cake mix). Following the work of Wade (5), a consensus has emerged that estradiol reduces appetite rather than enhancing it. Estradiol does reduce appetite across days after its administration, for even highly palatable solutions; but enhances appetite subsequently. It is the enhanced appetite for chocolate cake that is of interest here, because it seems relevant to overeating and, hence, obesity. In the first studies of EV and ingestion, the dose of EV was 2 mg a female or roughly 10.0 mg/kg. This dose was chosen because it selectively lesions the arcuate nucleus of the hypothalamus (6-8). The idea was to use EV to assess the role of  -endorphin, a product of the arcuate n., in ingestion of alcoholic beverages and, thereby, test certain theories of alcoholism. Smaller doses of EV might also be effective in inducing an enhanced appetite (see, e.g., 9) We, therefore, decided to test smaller doses of EV and measure intake of CCMB. Method Forty, female, Sprague-Dawley rats were purchased from Taconic Farms when they weighed about 185 g. Upon their arrival at the laboratory, they were housed in standard cages in a room maintained at 22 o C, lit 12 hr a day. They had standard lab chow and water always available. Shortly after their arrival, they were presented CCMB for 24 hr a day for 8 days. At the end of these 8 days all subjects were taking considerable amounts of CCMB daily. Nine days after withdrawal of CCMB, the subjects were injected. Six days after injections, they were again presented CCMB for 8 days. The rationale for providing CCMB for days before the injections was to ensure that neophobia would not confound measures of intake subsequent to injections. The time after first presentations were programmed to ensure that any effects of chocolate withdrawal (see below) were not apt to interact with the effects of injections. The time after injections was programmed to reduce the possibility of conditioned taste aversions emerging with disturbances in normal bodyweight gains that accompany larger doses of EV. There were 5 groups of subjects. Four groups received one of four doses of EV. One group got placebos. The doses of EV were 0.75, 0.375, 0.1875, 0.09375 mg/kg of bodyweight. The placebos were injections of sesame seed oil, the carrier of EV. Injections were given intramuscularly, 0.1 ml/kg. CCMB was a commercially available cake mix that consisted primarily of complex carbohydrates, fat, and cocoa powder. Water was added to the mix in the amount prescribed by a recipe for cake and the result was a batter that the rats did not spill and did not spoil. CCMB was presented in small jars. New batter replaced the amount eaten every day. To assess the amount of weight lost due to evaporation, some jars were presented to empty cages. The difference before and after each day’s presentation, corrected for evaporation, are the raw data of intakes. The rats were weighed daily. The grams of CCMB taken per kilogram of bodyweight are the data of interest. Results The results are summarized in Fig. 1 and 2. Notice in Fig. 1 that doses of EV, particularly the larger doses, interrupted the ordinary weight gain of these females (see the weight gain of placebo-controls). Notice the marked weight gain with the onset of CCMB availability. Also, notice the marked reduction in bodyweights associated with the end of opportunity to take CCMB. We have repeatedly seen this marked reduction in bodyweight with the end of intake of CCMB. The correlation between the degree of weight loss (difference between last day with CCMB and first day without CCMB) to the total amount of CCMB taken across 8 days is.54. Given this correlation and the observation that females receiving EV took more CCMB than controls, dose-relatedly, it is no surprise that the groups of subjects getting EV lost, reliably, more weight than placebo controls with the termination of availability of CCMB. EV, dose-relatedly, increased intake of CCMB. The placebo-controls of these subjects as well as those from similar studies take about 80 to 90 g/kg of CCMB daily. We believe that this is an extraordinarily large amount (i.e., a mean of 19.5 g of CCMB a day), yet the EV-treated, 0.38 mg/kg, females take more (i.e., 25.5 g). All subjects take ordinary lab chow in addition to CCMB. Discussion A recently published, comprehensive review of the literature on regulation of energy homeostasis stated “Gonadal steroids, including estradiol and testosterone, have also been long known to reduce appetite, increase energy expenditure, and decrease adiposity” (10, p. 236). In addition, it has been long known that ovariectomy leads to weight gains. There is a nice symmetry to these long known generalizations. However, with respect to estradiol, it appears the “long known” generalization that estradiol reduces appetite does not hold for CCMB. It is an overgeneralization to conclude that estradiol, particularly at pharmacological doses, reduces appetite. How does one reconcile the findings of these experiments with the long known generalization (i.e., estradiol reduces appetite)? Large doses of estradiol reduce appetite during the first days after their administration, but subsequently increase ingestion of at least some ingesta (i.e., CCMB, palatable saccharin solutions and alcoholic beverages) and probably many more. The combination of neophobia and conditioned taste aversions that might be induced by pairing presented ingesta with the weight loss (which probably signifies a malaise) that accompanies injections of estradiol probably account for the observations that estradiol reduces appetite. When these factors are controlled, as in this procedure, what is observed is a dose-related increase in appetite. We do not believe that the increased appetite is associated with all ingesta that might be presented to the females. Bittersweet solutions, for example, are taken less during the same time that similar injections are increasing appetite for sweet solutions (4). Our hypothesis is that the continuously high levels of estradiol produced by the EV mimic the events of pregnancy. It would be an advantageous adaptation for a female who is pregnant to have an enhanced appetite for highly rewarding substances (e.g., sweets) while avoiding risky foods (e.g., those that are bitter are correlated with poison-liability). This enhanced appetite would be preparation for the high energy demands of late term pregnancy and nursing. References 1. Boswell KJ, Caffalette CA, Lamb SA Stitt KT, Reid ML & Reid LD. Program Number 521.5 2003 Abstract Viewer / Itinerary Planner, Washing DC: Society for Neuroscience. 2. Marinelli PW, Quirion R & Gianoulakis C. Behav Brain Res 2003,139, 59-67. 3. Reid LD, Marinelli PW, Bennett SM, Fiscale LT, Narciso SP, Oparowski CJ, Reid ML, Merrigan BA, Moricone J, Hubbell CL & Gianoulakis C. Pharmacol Biochem & Behav 2002, 72, 601-616. 4. Reid ML, Boswell KJ, Fitch JV, Gentile BM & Reid LD. Paper presented at the Inter. Behav. Neurosci. Soc. Meeting, Capri, Italy, June 2002. 5. Wade GN. J Comp Physiol Psychol, 1975, 88, 183-193. 6. BrawerBrawer JR, Beaudet A, Desjardins GC & Schipper HM Biol Reprod 1993, 49, 647-52. 7. DesDesjardins GC, Beaudet A & Brawer JR Endocrinology 1990, 127, 2969-76. 8. Desjardins GC, Brawer, JR & Beaudet, A. Endocrinology 1993, 132, 86-93. 9. Ford MM, Eldridge JC & Samson HH. Alcohol Clin Exp Res 2004, 28,20-8. 10. Horvath TL, Diano S & Tsch  p M. The Neuroscientist, 2004, 10, 235-46. Fig. 2. The total intakes of chocolate cake mix batter taken across an 8-day period are depicted. The values are means for each group of subjects. The n for placebo is equal to 15 (7 from another group plus 8 of this group). The n for each of the other groups is 8. The single injections of EV (doses) were given intramuscularly 6 days before the 8 days of opportunity to take the batter. The mean intake in terms of grams of batter taken for the group receiving 0.375 mg of EV/kg of bodyweight during the 8 days was 203.4 grams which is nearly the mean weight of the females (217 g) at the beginning of the 8 days of opportunity to take batter. In other words, the EV treated females took nearly their weight in batter during an 8-day period of opportunity to do so (over 10% of their bodyweight daily). Fig. 1. The mean body weights for the five groups of females are depicted from the day before injections to six days after the removal of CCMB. Notice that the injections, dose-relatedly, disturb ordinary bodyweight gain (Days 2-6). Notice the marked reduction in bodyweights with the end of availability of CCMB (Days 15 to 16). Presented at IBNS meeting, 2004, Key West, FL, USA