Forebrain patterns of c-Fos and FosB induction during cancer-associated anorexia–cachexia in rat Jan Pieter Konsman 1,2 and Anders Blomqvist 1 1 Department of Cell Biology, Faculty of Health Sciences, University of Linko ¨ ping, S-581 85 Linko ¨ ping, Sweden 2 Neurobiologie Inte ´ grative, CNRS FRE 2723 ⁄ INRA-UR 1244 ⁄ Universite ´ Bordeaux2, Institut Franc ¸ois Magendie, 146 Rue Le ´o Saignat, 33077 Bordeaux Cedex, France Keywords: anorexia, cancer, Fos, hypothalamus, ventral striatum Abstract Forebrain structures are necessary for the initiation of food intake and its coupling to energy expenditure. The cancer-related anorexia–cachexia syndrome is typified by a prolonged increase in metabolic rate resulting in body weight loss which, paradoxically, is accompanied by reduced food intake. The aim of the present work was to study the forebrain expression of Fos proteins as activation markers and thus to identify potential neurobiological mechanisms favouring catabolic processes or modulating food intake in rats suffering from cancer-related anorexia–cachexia. Neurons in forebrain structures showing most pronounced induction of Fos proteins were further identified neurochemically. To provoke anorexia–cachexia, cultured Morris hepatoma 7777 cells were injected subcutaneously in Buffalo rats. This resulted in a slowly growing tumour inducing  7% body weight loss and a 20% reduction in food intake when the tumour represented 1–2% of body mass. Anorexia-cachexia in these animals was found to be accompanied by Fos induction in several hypothalamic nuclei including the paraventricular and ventromedial hypothalamus, in the parastrial nucleus, the amygdala, the bed nucleus of the stria terminalis, ventral striatal structures and the piriform and somatosensory cortices. Neurochemical identification revealed that the vast majority of FosB-positive neurons in the nucleus accumbens, ventral caudate– putamen and other ventral striatal structures contained prodynorphin or proenkephalin mRNA. These findings indicate that forebrain structures that are part of neuronal networks modulating catabolic pathways and food ingestion are activated during tumour- associated anorexia–cachexia and may contribute to the lack of compensatory eating in response to weight loss characterizing this syndrome. Introduction The cancer-associated anorexia–cachexia syndrome is typified by a rise in energy expenditure which paradoxically is often accompanied by decreased food intake and thus leads to progressive depletion of fat reserves and breakdown of skeletal muscle protein (Nelson, 2000; Tisdale, 2002). This syndrome is observed in the majority of advanced cancer patients and constitutes a common cause of cancer deaths (Nelson, 2000). Despite clinical trials with various drugs, none has proven satisfactory so far in restoring both fat and muscle mass. The emerging view is that metabolic abnormalities due to tumour by-products or the host response underlie weight loss in cancer patients (Tisdale, 2002). Although the extent to which energy intake is actually reduced remains debatable (Lindsey & Piper, 1985; Weston et al., 1989; Tchekmedyian et al., 1992; Bosaeus et al., 2001), loss of appetite or early satiety occurs in  50% of cancer patients irrespective of chemotherapy (Grosvenor et al., 1989). It is thus clear that the expected up-regulation of dietary intake in response to weight loss is lost in cancer patients (Bosaeus et al., 2001) and prevents them from regaining weight. Cancer-related anorexia–cachexia is therefore characterized by uncoupling of food intake from energy expenditure. Experiments with chronic decerebrate animals show that the initiation of food intake and coupling of food intake to energy expenditure requires forebrain structures (Grill & Norgren, 1978; Kaplan et al., 1993), among which the striatum and the hypothalamus are most important (Saper et al., 2002). However, despite our increased understanding of the central nervous control of food intake and energy expenditure, no study has examined the activation of brain structures during cancer-associated anorexia–cachexia. In the present study we addressed this issue by studying the induction patterns of the transcription factors c-Fos and FosB in the forebrain as a first approach to identifying neurobiological mechanisms favouring catabolic pro- cesses or modulating food intake in rats suffering from cancer-related anorexia–cachexia. We focused on the ventral striatal opioid system because of its role in motivated behaviour including food intake (Bodnar et al., 1995; Pecina & Berridge, 2000; Kelley, 2004), but we also identified changes in other forebrain structures that may be relevant to uncoupling of food intake and energy expenditure characterizing the anorexia–cachexia syndrome. To provoke anorexia–cachexia experimentally a tumour from a donor animal is typically transplanted. The main drawback of this approach is that anorexia–cachexia generally occurs when the tumour represents 5–10% of body weight (Strelkov et al., 1989; McCarthy, 1999; Cahlin et al., 2000). In this case, substrate consumption by the tumour alone is likely to play an important role in the metabolic derangement typical of anorexia–cachexia (Ohnuma, 2000). To avoid biases due to large tumour mass, rats were injected with cultured tumour cells in the present study. This approach resulted in anorexia– cachexia when the tumour represented 1–2% of body weight. Correspondence: Dr Jan Pieter Konsman, 2 Neurobiologie Inte ´grative, as above. E-mail: konsman@bordeaux.inserm.fr Received 9 December 2004, revised 20 February 2005, accepted 12 March 2005 European Journal of Neuroscience, Vol. 21, pp. 2752–2766, 2005 ª Federation of European Neuroscience Societies doi:10.1111/j.1460-9568.2005.04102.x