Effects of subchronic d-fenfluramine on splenic immune functions in young and old male and female Fischer 344 rats

The analgesic drug tramadol prevents the effect of surgery on natural killer cell activity and metastatic colonization in rats

Surgery stress has been shown to be associated in rat with decreased natural killer (NK) cell activity and enhancement of tumor metastasis. We have previously shown that the analgesic drug tramadol stimulates NK activity both in the rodent and in the human. In the present study, we analyze, in the rat, tramadol ability to prevent the effect of experimental surgery on NK activity and on the enhancement of metastatic diffusion to the lung of the NK sensitive tumor model MADB106. The administration of tramadol (20 and 40 mg/kg) before and after laparatomy significantly blocked the enhancement of lung metastasis induced by surgery. In contrast, the administration of 10 mg/kg of morphine was not able to modify this enhancement. The modulation of NK activity seemed to play a central role in the effect of tramadol on MADB106 cells. In fact, both doses of tramadol were able to prevent surgery-induced NK activity suppression, while the drug significantly increased NK activity in normal non-operated animals. Morphine, that in normal rats significantly decreased NK cytotoxicity, did not prevent surgery-induced immunosuppression. The good analgesic efficacy of tramadol combined with its intrinsic immunostimulatory properties suggests that this analgesic drug can be particularly indicated in the control of peri-operative pain in cancer patients.

Effects of repeated fluoxetine and citalopram administration on cytokine release in C57BL/6 mice

This study examines the effects of repeated administration of the selective serotonin reuptake inhibitors (SSRIs), fluoxetine and citalopram (10 mg/kg, i.p.), on immunoreactivity in C57BL/6 mice. Immune functions were evaluated by the ability of splenocytes to reduce a tetrazolium salt to formazan (MTT test), to proliferate, and to produce cytokines, including interleukin (IL)-1, IL-2, IL-4, IL-6, IL-10 and interferon gamma (IFN gamma). Citalopram administered for 1, 2 and 4 weeks stimulates the proliferative activity of splenocytes and suppresses their ability to secrete the anti-inflammatory cytokine IL-4. Fluoxetine administration for 1 and 2 weeks, but not 4 weeks, stimulates the proliferative activity of splenocytes, whereas a 4-week administration of fluoxetine suppresses the secretion of IL-4. Four weeks of prolonged administration of citalopram and fluoxetine induces a significant increase in the production of IL-6 and IL-10, a cytokine with immunosuppressive and anti-inflammatory activities. The results show that, in C57BL/6 mice, the immunomodulatory effects of SSRIs depend on the SSRI used and the duration of administration.

An assessment of the acute effects of the serotonin releasers methylenedioxymethamphetamine, methylenedioxyamphetamine and fenfluramine on immunity in rats

The purpose of the present study was to examine the effect of the serotonin releasing amphetamine derivatives methylenedioxymethamphetamine (MDMA), methylenedioxyamphetamine (MDA) and fenfluramine (FEN) on immunity in rats. Similar to MDA and MDMA, FEN reduced the number of circulating lymphocytes, provoked a suppression of Con A-stimulated lymphocyte proliferation and total IFN-gamma and IL-10 production in diluted whole blood cultures. Thus the non-psychostimulant amphetamine derivative FEN, shares the ability of the psychostimulant methylenedioxy-substituted amphetamine derivatives to alter these indices of immune function in the rat. However, when Con A-stimulated cytokine production was normalised for the number of lymphocytes in culture in order to examine cytokine production at a cellular level, the effect of the amphetamine derivatives begins to diverge. FEN shares with MDMA and MDA the ability to suppress production of the Th2 type cytokine IL-10. However the effect of these drugs on Th1 type cytokine secretion was much more complex. While the methylendioxy-substituted amphetamines increases the secretion of the Th1 type cytokine IL-2 without altering the related Th1 type cytokine IFN-gamma, FEN did not alter IL-2 secretion, but suppressed IFN-gamma secretion. In addition to these effects on T-cell responses, all three drugs inhibited LPS-induced TNF-alpha secretion from diluted whole blood cultures suggesting that macrophage activity is impaired following treatment. In all, these data extend our previous findings concerning the effects of MDMA on the immune system and demonstrate that the related serotonin releasers MDA and FEN also provoke immunological changes in rats.

Effects of tramadol and its enantiomers on Concanavalin-A induced-proliferation and NK activity of mouse splenocytes: involvement of serotonin

The centrally acting analgesic drug tramadol is a 1:1 racemic mixture of two enantiomers, with different pharmacological properties. The (-)-tramadol preferentially inhibits noradrenaline uptake, whereas the (+)-tramadol inhibits serotonin uptake and binds to opioid receptors. Since tramadol has been shown to stimulate some immune responses in mice, in the present work we analyzed the effects of its enantiomers on the same parameters, with the aim to better characterize the mechanisms involved in such action of tramadol. The acute administration of 20 and 40 mg/kg of racemic tramadol and of 10 and 20 mg/kg of (+)-tramadol induced a significant and comparable stimulation of Concanavalin-A (Con-A) induced proliferation and of Natural Killer (NK) activity of splenocytes. On the contrary, the (-)-tramadol was devoid of any effect. The pretreatment with the serotoninergic antagonist metergoline (3.0 mg/kg) completely blocked the effects of both tramadol and (+)-tramadol. We suggest that the enhancement of the serotoninergic tone could be at the basis of the stimulatory effects exerted by tramadol on Con-A induced lymphoproliferation and NK activity.

Effect of d-fenfluramine on the lymphocyte response of HIV+ humans

The objective of this study was to analyse the effect of d-dexfenfluramine (d-FEN) on the human lymphocyte response, in vitro. Experiments were designed to determine whether d-FEN augments specific human immune parameters associated with protection from opportunistic microbial pathogens and particularly focuses on d-FEN as a means by which to augment the function of CD8+ and CD4+ lymphocytes. Lymphocytes were examined for three reasons: (1) for their ability to inhibit the growth of Candida albicans; (2) for their ability to proliferate in response to a mitogen; and, (3) their cytokine profile (vis., production of IL-2, IFN-gamma and TNF-alpha). Peripheral blood mononuclear cells (PBMC) were obtained from 20 HIV+ patients. The patients were diagnosed as HIV+ within the past 0.5-9 years. d-FEN was found to augment the capacity of CD8+ lymphocytes to inhibit the growth of the opportunistic microbial pathogen, C. albicans. d-FEN enhanced the capacity of CD4+ lymphocytes to proliferate in response to the mitogen, Concanavalin A, and to increase the amount of IL-2 produced by CD4+ and CD8+ lymphocytes from AIDS patients. d-FEN increased the number of CD4+ and CD8+ lymphocytes that produced IFN-gamma from either non-AIDS or AIDS patients and increased the number of AIDS patient's CD8+ lymphocytes that produce TNF-alpha. These in vitro data suggest that d-FEN may be effective in enhancing immune function in immunocompromised individuals.

Role of serotonin in the immune system and in neuroimmune interactions

Serotonin (5-HT) is one of the most extensively studied neurotransmitters of the central nervous system. 5-HT is, however, also present in a variety of peripheral tissues including in constituents of the immune system. The function of 5-HT in the immune system has received increasing attention since about 1984, but has been reviewed only once, in 1985. In recent years, modern techniques of molecular biology such as reverse-transcriptase polymerase chain reaction and targeted gene disruption have made it possible to study new important aspects of 5-HT in the immune system. In the first part of the review, we explore whether 5-HT is involved in interactions between the central nervous and immune systems. It emerges that 5-HT may mediate interactions of these two systems by four different pathways. In the second part, we dissect the functional roles of 5-HT in the immune system. We describe the distribution of 5-HT receptors and the 5-HT transporter on immune cells and estimate which levels 5-HT may attain in the extracellular space in physiological conditions and under pathological circumstances such as inflammation, thrombosis, and ischemia. At these 5-HT concentrations, four major functions for 5-HT emerge. These include T cell and natural killer cell activation, delayed-type hypersensitivity responses, production of chemotactic factors, and natural immunity delivered by macrophages. Finally, we discuss promising future avenues to further advance knowledge of the role of 5-HT in the immune system and in neuroimmune interactions.

Aging and lymphocyte subsets in the spleen and peripheral blood of the Sprague-Dawley rat

This study was undertaken to determine the effects of aging on lymphocyte subsets in the peripheral blood and spleens of Sprague-Dawley rats. Rats aged 3,13 and 26 months were used in the study. Analyses of dual labeled lymphocytes from the 26 month animals show decreases in the numbers of lymphocytes due to decreased cellularity (spleen) or reduced lymphocyte percentages within the total white blood cell population (peripheral blood). In the spleens and blood of the oldest rats, there were reduced numbers of Total T, T helper/amplifier (Th/a), virgin Th and natural killer (NK) cells. Other changes were observed in the spleen but not peripheral blood. The numbers of T cytotoxic/suppressor cells (Tc/s) B cells, "autoimmune" B cells and NK cells were reduced in the spleen but remained within normal limits in peripheral blood. The data show aging exerts different effects on the peripheral blood and splenic compartments of the immune system. These differences may have teleological significance in relation to immune responses to xenobiotics and neoplastic cells.

Chronic intracerebroventricular administration of beta-endorphin augments natural killer cell cytotoxicity in rats

We have studied the effect of chronic intracerebroventricular (i.c.v.) infusion of different opioid peptides on natural killer (NK) cell mediated cytotoxicity in vivo in the spontaneously hypertensive rat (SHR). The in vivo NK cell activity was measured as the clearance of 51Cr-labelled YAC-l lymphoma cells from the lung tissues. Further, the phenotype of lymphocytes in spleen and peripheral blood was analysed by flow cytometry (FACS). All opioid drugs were administered i.c.v. for 6 days with osmotic minipumps releasing 1.0 microliter/h. beta-Endorphin (10 or 20 micrograms/rat per day) significantly increased NK cell cytotoxicity in vivo. The opioid receptor antagonist naloxone (10 mg/kg, i.p.) given immediately before the injection of YAC-lymphoma cells, completely abolished the effects of i.c.v. administered beta-endorphin. Corresponding doses of beta-endorphin administered subcutaneously (s.c.) with minipumps for 6 days did not significantly affect NK cell cytotoxicity. Neither Leu- or Met-enkephalin (20 micrograms/rat per day) nor dynorphin (20 micrograms/rat per day) administered i.c.v. had any significant effects on NK cell activity. In beta-endorphin treated SHR, the percentage of cells with NK cell phenotype (OX52+/CD5-) in peripheral blood was not significantly different from that of controls, while the percentage of cells with T cell phenotype (CD5+/OX52-) was significantly decreased. The percentage of splenic NK cells (OX52+/CD5-) and T cells (CD5+/OX52-) was also unchanged by beta-endorphin treatment i.c.v. These results suggest that of the opioid peptides administered i.c.v., only beta-endorphin augments in vivo NK cell mediated cytotoxicity. We thus conclude that these effects most probably are centrally and opioid receptor mediated effects, since beta-endorphin in the same dose administered peripherally does not influence in vivo NK cell cytotoxicity.

Responses to novelty stress in female F344 rats: effects of age and d-fenfluramine treatment

To elucidate some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with age in female rats, we administered the serotonin (5-HT) releaser and reuptake inhibitor, d-fenfluramine (d-FEN; 0.0 or 0.6 mg/kg/day, PO) for 30-38 days to young (4 month) and old (21 month) F-344 female rats. Animals were placed into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited significantly (p < 0.05) less exploratory behavior and a smaller CORT response to OF than young animals. d-FEN treatment had no effect on plasma ACTH and CORT levels or exploratory behavior. The old HC rats had significantly (p < 0.05) higher plasma levels of prolactin (PRL) than the young HC rats. A stress induced increase in PRL secretion was observed in the old rats only, which was attenuated by d-FEN treatment. In the OF groups, both the young and old rats showed elevated medial frontal cortex (MFC) dopamine turnover (DOPAC/DA ratio), but only the young rats exhibited an elevation in norepinephrine (NE) turnover (MHPG/NE ratio). d-FEN treatment blocked the stress-induced increase in NE turnover in the young rats and the increase in DA turnover in the old rats. These data suggest that 5-HT activity could be involved in the age-related changes in the MFC catecholamine and PRL responses to stress in female rats.

Effect of d-fenfluramine on the local immune response to the opportunistic microbial pathogen Candida albicans

In this study the effects of systemic administration of d-fenfluramine on the local lymphocyte response to Candida albicans was evaluated. Experimental animals were challenged intradermally with Candida albicans and then administered d-fenfluramine (d-FEN 1 mg/kg per day, i.p.) or a balanced salts solution. At successive time intervals, lymphocytes were derived from the draining lymph nodes and from the dermal sites of active microbial challenge. A CD8+ lymphocytosis was observed in all animals challenged with Candida albicans. The CD8+ lymphocytosis was augmented in animals that received d-FEN. Phenotypically, lymph nodes from d-FEN treated animals showed a marked increase in CD3+ and CD8+ lymphocytes, a modest increase in the numbers of NK1.1+ cells and a decrease in Ig+ lymphocytes. Functionally, lymphocytes from the site of active microbial challenge were capable of direct growth inhibition of Candida albicans. The anti-fungal activity was augmented in the animals that received d-FEN. These results suggest that d-FEN augments the local T lymphocyte response to an important microbial pathogen by increasing the number of T lymphocytes draining the site of microbial infection and by increasing the biological activity of the lymphocytes at the site of the infection.

Subchronic and chronic exposure to d-fenfluramine dose-dependently enhances splenic immune functions in young and old male Fischer-344 rats

Serotonin (5-HT) has been shown to modulate various arms of the rodent immune system in an age- and sex-dependent fashion. Thus, only young (5-6 months) male and old (21-23 months) female Fischer-344 (F344) rats demonstrated an elevation in ex vivo assessed basal and IL-2 stimulated splenic NK activity as well as CON-A induced T cell proliferation after subchronic (30-44 days) administration of low doses (0.6-1.8 mg/kg per day, p.o.) of the 5-HT releaser and reuptake inhibitor, d-fenfluramine (d-FEN). In the present study when young male F344 rats were administered higher doses of d-FEN (3-9 mg/kg per day, p.o.) for 30-39 days, there was a dose-dependent decrease in basal NK activity which returned to control levels after overnight incubation with IL-2. Further, only the rats receiving 6 mg/kg per day of d-FEN exhibited an elevation (40%) in CON-A mitogenesis compared to controls. When 15-month-old male rats were treated with d-FEN (0.6 mg/kg per day, p.o.) for 8 months, their NK and T cell activities at 23 months were not statistically different from young (7 months old) control animals. Importantly, neither the old rats treated with d-FEN nor the young control animals evidenced splenic or hepatic hypertrophy and lesions. In contrast, the old control animals showed increased NK activity (250%) and decreased T cell mitogenesis (300%) which correlated with a high incidence of splenic pathology. Thus, long-term exposure to d-FEN appears to maintain the NK and T cell arms of the immune system at youthful levels and prophylactically reduce the splenic pathology associated with advancing age. These results suggest that long-term exposure to increased levels of 5-HT may be beneficial to the immune system of the aging male F344 rat.

Effects of a primary immune response to T-cell dependent antigen on serotonin metabolism in frontal cortex: in vivo microdialysis study in freely moving Fischer 344 rat

Antigenic challenge is known to influence brain catecholamine turnover, e.g. hypothalamic norepinephrine activity, but little is known about effects on the activity of serotoninergic neurons, i.e. the release of the neurotransmitter at nerve terminals. In the present study, we first investigated the changes of central serotonin (5-HT) metabolism in Fischer 344 male rats at 2, 3, 4 and 5 days following i.v. immunization with sheep red blood cell (SRBC). Major decreases in 5-HT levels were evident in the hypothalamus (Hy) and cortex (Cx) at a time which corresponded to the late phase of the production of specific antibodies to SRBC measured with a plaque-forming cell assay (PFC). A pretreatment with an immunosuppressive drug, cyclosporin A (CsA; 12.5 mg/kg by gavage for 7 days) prevented the decreases in cortical 5-HT levels. Concomitantly, a 2-fold increase in the basal 5-HT release at frontocortical nerve terminals was observed by using in vivo microdialysis in awake rats on Day 3 following SRBC inoculation. This effect was totally suppressed by CsA. Our data suggest that the decrease in brain 5-HT levels that occurs after antigen administration may reflect a specific short-lasting CsA-dependent-release of 5-HT at frontocortical nerve terminals at a time (Day 3 or 4) when the splenic immune response is maximal.

Neuroendocrine and neurochemical responses to novelty stress in young and old male F344 rats: effects of d-fenfluramine treatment

To understand some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with aging, we administered the serotonin [5-hydroxytryptamine (5-HT)] releaser and reuptake inhibitor d-fenfluramine (d-FEN; 0.0, 0.2, or 0.6 mg/kg/day, p.o) for 30-38 days to young (4 months) and old (22 months) F344 male rats. Rats were stressed by placement into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited less (p < 0.05) exploratory behavior than young rats, which was not altered by treatment with d-FEN. Old HC rats also had higher (p < 0.05) basal plasma levels of adrenocorticotropic hormone (ACTH) and prolactin (PRL) than young HC rats. Old OF rats showed higher (p < 0.05) levels of ACTH and corticosterone (CORT) than young OF animals. A stress-induced increase in PRL secretion was not observed in old rats. Subchronic low-dose d-FEN normalized the enhanced ACTH and CORT responses of old animals to novelty. In addition to these endocrine changes, stress-induced increases in medial frontal cortex (MFC) dopamine (DA) and norepinephrine (NE) turnover also were observed. The increase in NE turnover was greater (p < 0.01) in old than in young rats. d-FEN treatment blocked the stress-induced increase in MFC NE but not MFC DA turnover in both young and old rats. These data support a role for 5-HT and/or NE in some age-related neuroendocrine perturbations and suggest that increased 5-HT neurotransmission can normalize the hyperactivation of the hypothalamo-pituitary-adrenal axis of old male rats.