Serotoninergic block in the ventromedial nucleus of hypothalamus improves food intake in anorectic tumor bearing rats

Molecular and neuroendocrine mechanisms of cancer cachexia

Cancer and its morbidities, such as cancer cachexia, constitute a major public health problem. Although cancer cachexia has afflicted humanity for centuries, its underlying multifactorial and complex physiopathology has hindered the understanding of its mechanism. During the last few decades we have witnessed a dramatic increase in the understanding of cancer cachexia pathophysiology. Anorexia and muscle and adipose tissue wasting are the main features of cancer cachexia. These apparently independent symptoms have humoral factors secreted by the tumor as a common cause. Importantly, the hypothalamus has emerged as an organ that senses the peripheral signals emanating from the tumoral environment, and not only elicits anorexia but also contributes to the development of muscle and adipose tissue loss. Herein, we review the roles of factors secreted by the tumor and its effects on the hypothalamus, muscle and adipose tissue, as well as highlighting the key targets that are being exploited for cancer cachexia treatment.

The anabolic-androgenic steroid nandrolone induces alterations in the density of serotonergic 5HT1B and 5HT2 receptors in the male rat brain

Anabolic-androgenic steroids (AAS) are partly misused by males in order to become brave and intoxicated and these agents are highly associated with psychosis, disinhibition, aggression and acts of violence. Since such behavioral states have been related to an imbalanced serotonergic system and the involvement of the serotonergic 5HT(1B) and the 5HT(2) receptors, it was important to discern the impact of AAS on these receptors. The objective of our study was to investigate the effects of 2 weeks of treatment with the AAS nandrolone decanoate at three different doses (1, 5, 15 mg/kg/day) on the total specific binding of the radioligands [(125)I]-(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (5HT(2) receptors) by autoradiography. All doses caused a significant down-regulation of the 5HT(1B) receptor density in the hippocampal CA(1) and in the medial globus pallidus and a significant up-regulation of the 5HT(2) receptor density in the nucleus accumbens shell. Alterations in receptor density were also observed in the lateral globus pallidus, ventromedial hypothalamus, the amygdala and in the intermediate layers of various cortex regions. In conclusion, serotonergic 5HT(1B) or 5HT(2) receptors are likely to play important roles in mediating observed emotional states and behavioral changes among AAS abusers.

Lack of effects by tricyclic antidepressant and serotonin inhibitors on anorexia in MCG 101 tumor-bearing mice with eicosanoid-related cachexia

OBJECTIVES

Anorexia is a major clinical problem in large number of patients with advanced cancer disease. Serotonergic mechanisms are assumed to play a role in the process of feeding behavior during normal and pathologic circumstances, which may also involve cancer anorexia according to previous experimental and clinical studies.

METHODS

In the present study, we evaluated the effect of the tricyclic antidepressants desipramine (7.5 mg x kg(-1) x d(-1), intraperitoneal) and imipramine (2 to 5 mg. kg(-1) x d(-1), intraperitoneal) the serotonin synthesis inhibitor para-chlorophenylalanine (300 mg x kg(-1) x d(-1), intraperitoneal), the serotonin receptor 5-HT(2C) antagonist cyproheptadine (5 mg x kg(-1) x d(-1), intraperitoneal) and the selective serotonin reuptake inhibitor citalopram (20 mg x kg(-1) x d(-1), intraperitoneal) on anorexia in MCG-101 tumor-bearing mice, a model with significant anorexia and cachexia sensitive to cyclooxygenase inhibition. Also, MCG 101-bearing mice develop well-recognized alterations in brain tryptophan/serotonin metabolism as increased Trp, 5-HPT, and 5-HIAA during tumor progression.

RESULTS

Daily provision of desipramine, imipramine, para-chloropheylalanine, cyproheptadine, and citalopram at doses that cause behavioral and metabolic alterations in normal mice did not alter food intake or body weight in tumor-bearing and healthy control mice. Also, the treatments did not decrease elevated plasma concentrations of interleukin-6 and prostaglandin E(2) in the tumor-bearing mice.

CONCLUSIONS

Thus, our results do not support previous observations that serotonin metabolism itself is a major factor behind anorexia in tumor-bearing animals in general. Rather, other mechanisms, such as eicosanoid and nitric oxide-dependent pathways, seem to be more important for induction of anorexia along tumor progression in the present model.

Anorexia of infection: current prospects

The anorexia of infection is part of the host's acute phase response (APR). Despite being beneficial in the beginning, long lasting anorexia delays recovery and is ultimately deleterious. Microbial products such as bacterial cell wall compounds (e.g., lipopolysaccharides and peptidoglycans), microbial nucleic acids (e. g., bacterial DNA and viral double-stranded RNA), and viral glycoproteins trigger the APR and presumably also the anorexia during infections. Microbial products stimulate the production of proinflammatory cytokines (e.g., interleukins [ILs], tumor necrosis factor-alpha, interferons), which serve as endogenous mediators. Several microbial products and cytokines reduce food intake after parenteral administration, suggesting a role of these substances in the anorexia during infection. Microbial products are mainly released and cytokines are produced in the periphery during most infections; they might inhibit feeding through neural and humoral pathways activated by their peripheral actions. Activation of peripheral afferents by locally produced cytokines is involved in several cytokine effects, but is not crucial for the anorectic effect of microbial products and IL-1beta. Cytokines increase leptin expression in the adipose tissue, and leptin may contribute to, but is also not essential for, the anorectic effects of microbial products and cytokines. In addition, a direct action of cytokines and microbial products on the central nervous system (CNS) is presumably involved in the anorexia during infection. Cytokines can reach CNS receptors through circumventricular organs and through active or passive transport mechanisms or they can act through receptors on endothelial cells of the brain vasculature and stimulate the release of subsequent mediators such as eicosanoids. De novo CNS cytokine synthesis occurs in response to peripheral infections, but its role in the accompanying anorexia is still open to discussion. Central mediators of the anorexia during infection appear to be neurochemicals involved in the normal control of feeding, such as serotonin, dopamine, histamine, corticotropin releasing factor, neuropeptide Y, and alpha-melanocyte-stimulating hormone. Reciprocal, synergistic, and antagonistic interactions between various pleiotropic cytokines, and between cytokines and neurochemicals, form a complex network that mediates the anorexia during infection. Current knowledge on the mechanisms involved suggests some therapeutic options for treatment. Substances that block common key steps in cytokine synthesis or cytokine action, or inhibitors of eicosanoid synthesis, may hold more promise than attempts to antagonize specific cytokines. To target the neurochemical mediation of the anorexia during infection may be even more efficient. Future research should address these neurochemical mechanisms and the cytokine actions at the blood-brain barrier. Further unanswered questions concern the modulation of the anorexia during infection by gender and nutritional state.

The role of medial hypothalamic serotonin in the suppression of feeding in a rat model of colitis

BACKGROUND & AIMS

Experimental colitis is associated with anorexia that is attenuated by treatment with an interleukin (IL)-1 receptor antagonist. Serotonin (5-hydroxytryptamine [5-HT]) is a potent inhibitor of feeding, and its release from the hypothalamus is stimulated by IL-1. We have tested the hypotheses that anorexia associated with experimental colitis results from increased activity of hypothalamic 5-HT neurons and that the increase in activity occurs secondary to an increase in availability of tryptophan, the precursor of 5-HT.

METHODS

In vivo 5-HT release and regional hypothalamic 5-HT and tryptophan concentrations were measured in rats with 2,4,6,-trinitrobenzene sulfonic acid (TNBS)-induced colitis, healthy controls, and animals pair-fed to match the food intake of the colitic group. Food intake in the colitic group was assessed after depletion of brain 5-HT by p-chlorophenylalanine (PCPA).

RESULTS

In the colitic group, release of 5-HT from the hypothalamic paraventricular nucleus (PVN) was 3-fold (P = 0.01) and 14-fold (P < 0.001) higher than in control and pair-fed groups, respectively. Concentrations of tryptophan were similar in each group in all hypothalamic regions. Food intake was significantly increased in the colitic group after PCPA treatment but was not restored to control values.

CONCLUSIONS

In animals with TNBS-induced colitis, 5-HT release from the PVN is increased. The increase in food intake after depletion of brain 5-HT suggests that hypothalamic 5-HT contributes to anorexia but is not the only mediator. Increased 5-HT release in the colitic group was not driven by increased precursor availability.

Interleukins and tumor necrosis factor as inhibitors of food intake

Cytokines, such as interleukins and tumor necrosis factor-alpha (TNFalpha), are produced in response to immune stimulation and have systemic effects, mediated by the central nervous system (CNS). Interleukins, in particular interleukin [IL]-1beta, and TNFalpha reduce food intake after peripheral and central administration, suggesting that they contribute to the anorexia during various infectious, neoplastic and autoimmune diseases. Because cytokines are mainly produced in the periphery during most of these diseases, IL-1beta and TNFalpha may inhibit feeding indirectly through neural and humoral pathways activated by their peripheral actions. Activation of afferent nerve fibers by locally produced cytokines in the periphery is involved in several cytokine effects, but is not crucial for the anorectic effect of systemic immune stimulation. Cytokines increase OB protein (leptin) expression in the adipose tissue, and leptin may contribute to, but is also not essential for, the anorectic effects of cytokines. Finally, circulating IL-1beta and TNFalpha may act directly on the brain or cytokine synthesis in the brain may contribute to the anorectic effect of systemic immune stimulation. Central mediators of the anorectic effects of cytokines appear to be neurochemicals involved in the normal control of feeding, such as serotonin, corticotropin releasing factor, histamine, alpha-melanocyte stimulating hormone, and neuropeptide Y. The well-documented cytokine production in the gut in relation to feeding and the expression of TNFalpha by adipocytes suggest that IL-1beta and TNFalpha may also play a role in the control of normal feeding and energy balance. All in all, reciprocal, synergistic and antagonistic interactions between various pleiotropic cytokines and between cytokines and neurochemicals form a complex network that mediates the effects of cytokines on feeding and energy balance.

Use of recombinant human soluble TNF receptor in anorectic tumor-bearing rats

With progression of tumor growth, rats demonstrate anorexia and reduced food intake, a function of meal number and meal size. Tumor necrosis factor-alpha (TNF-alpha), a recognized anorectic agent, reacts with two different receptors (type I: 55 kDa; type II: 75 kDa). We used a dimeric, pegylated 55-kDa TNF receptor construct to test its effects on food intake, meal number, and meal size, which were continuously measured with a rat eater meter in 16 Fischer 344 male rats injected with 10(6) viable methylcholanthrene cells. When anorexia developed, rats received a subcutaneous injection of either 0.25 mg/kg body wt of soluble TNF receptor construct (study) or vehicle (tumor-bearing control). Before TNF inhibitor injection, no differences were observed in food intake, meal number, or meal size between the two groups. After the TNF inhibitor injection, study vs. control rats significantly improved food intake as a result of an increase in meal number and meal size. Rats also showed a significant improvement in body weight. These data suggest that TNF-alpha, in addition to other cytokines, contributes to the anorexia of tumor growth, probably mediated via the hypothalamus.

Potential strategies for ameliorating early cancer anorexia

BACKGROUND

Normally the lateral hypothalamic area (LHA) and the ventromedial nucleus (VMN) interact to regulate food intake (FI), the product of meal number (MN) and meal size (MZ), by changes in neurotransmitters, mainly dopamine and serotonin. Change in LHA dopamine influences meal size; while in VMN, decreasing dopamine and increasing serotonin levels influence meal number. Whether this situation exists in early cancer anorexia was tested in a series of studies to examine the role of the hypothalamus in the pathogenesis of early cancer anorexia.

MATERIALS AND METHODS

In experiment 1, male Fischer tumor-bearing (TB) rats and weight-matched controls had FI, MN, and MZ measured continuously via a computerized rat eater meter. At onset of anorexia, feeding patterns were measured. In experiment 2, the VMN was temporarily blocked with 0.32 microgram of colchicine in TB rats, while TB controls had an equal volume of intra-VMN saline, and changes in feeding patterns were measured. In experiment 3, changes in VMN dopamine and serotonin were measured via microdialysis at anorexia and after tumor resection.

RESULTS

In experiment 1, with the onset of anorexia, food intake decreased significantly in TB rats, initially by a decrease in MN and then by a decrease in both MN and MZ. No change occurred in controls, suggesting that VMN versus LHA played a more significant role in mediation of cancer anorexia. In experiment 2, following VMN block, FI increased significantly in anorectic TB rats, achieved by an almost exclusive increase in MN with minimal change in MZ, thus supporting the role of the VMN in anorexia. In experiment 3, at the onset of anorexia, FI decreased significantly in TB rats versus controls. TB rats had a significant increase in VMN serotonin and a significant decrease in VMN dopamine. After tumor resection, food intake improved and high levels of serotonin normalized with no change in dopamine.

CONCLUSION

Serotoninergic and dopaminergic systems are involved in the etiology of cancer anorexia. The changes in food intake are mediated via the VMN by a decrease in meal number.