Serotonin Transporter in Lymphocytes of Rats Exposed to Physical Restraint Stress

Abstract

Objectives: Glucocorticoids and stress cause transcriptional and functional changes on the serotonin transporter (SERT) in the central nervous system. Stress can produce specific modifications of SERT in lymphocytes, which could be associated with alterations in immune response. The aim of this study was to evaluate the effect of a physical restraint stress protocol on (1) rat lymphocyte proliferation in the presence of the selective serotonin reuptake inhibitor fluoxetine and (2) SERT kinetic parameters, i.e. binding capacity (Bmax), affinity (Kd) and Hill coefficient (n_H). Methods: Male adult Sprague-Dawley rats were placed in Plexiglass boxes (5 h daily for 5 days), and blood was obtained by cardiac puncture on day 6. Serum corticosterone was quantitated by an immunoenzymatic assay. Lymphocytes were isolated by density gradients and adhesion to plastic, of which there was sufficient material for further experiments, then cultured with or without the mitogen concanavalin A (Con A, 2 μg/ml) and fluoxetine (1-50 μ<smlcap>M</smlcap>). Cell proliferation was measured with tetrazolium salts, and [³H]paroxetine was used as a SERT-specific ligand for binding assays. Results: Restraint produced a significant increase in serum corticosterone of stressed rats. The proliferative response to Con A was similar in the controls and stressed animals. Fluoxetine reduced cell proliferation with and without Con A. Restraint diminished the inhibitory effect of fluoxetine on proliferation. Restraint also increased Bmax and Kd, but decreased n_H. Treatment of rats with actinomycin D, a transcription inhibitor, reduced Bmax in stressed animals. Conclusions: Restraint stress modulated the effect of fluoxetine on cell proliferation, probably through the modification of the presence and the function of SERT.

5-HT₇ Receptors and Tryptophan Hydroxylase in Lymphocytes of Rats: Mitogen Activation, Physical Restraint or Treatment with Reserpine

“…injections were done on 2 consecutive days, 500 μg/kg (200-300 μl), between 08.00 and 09.30 h [3]. The rats were physically restricted in a different room in individual ventilated Plexiglass boxes, 16 × 7 × 6 cm, adjustable for length to 9, 11 or 14 cm, for 5 h per day between 09.00 and 14.00 h for 5 days [4,5]. Reserpine was injected i.p., 2.5 mg/kg daily for 3 consecutive days in 200-300 μl of 0.5% methylcellulose [23].…”

“…For instance concanavalin A (Con A) increases 5-HT 1A receptors in lymphocytes [3] and affects the effect of fluoxetine on proliferation [4]. Reserpine, acting on the sympathetic system as an inhibitor of vesicular transport of monoamines, constitutes a documented pharmacological stress [5] and alters the 5-HT transporter in lymphocytes [6]. Thus, this evidence stimulates the exploration of other 5-HT receptors involved in basic lymphocyte physiopathology by its presence and its susceptibility to stimulus, such as inflammatory, physical or pharmacological stress.…”

Fluoxetine Treatment in Rats Increases the Rate of Taurine Transport in Mononuclear Cells

“…After centrifugation at 300 g for 30 min, the mononuclear cell layer was taken and washed twice with Tyrode buffer at 150 g for 10 min. The integrity of the isolated cells was determined by a 50% Trypan blue exclusion test resuspended in phospate-buffered saline (PBS; Na + -K + 0.1 M, pH 7.4) at a final concentration of 0.4% [31] . The viability of the cells was >90%.…”

“…Fluoxetine, a selective serotonin reuptake inhibitor (SSRI) antidepressant, exerts a suppressor effect on lymphocyte proliferation in a time-and dose-dependent manner [29][30][31] . Fluoxetine and other SSRIs have become the drugs of choice for treating depression.…”

“…Fluoxetine and other SSRIs have become the drugs of choice for treating depression. Major depression is associated with endocrinal changes such as activation of the hypothalamic-pituitary-adrenal (HPA) axis [30,31] . Some studies have shown that humans with depression have impaired immune function, as reflected by overall leukocytosis, a mild reduction in absolute counts of NK cells and relative proportions of T cells [30] , higher concentrations of circulating neutrophils [32] , reduced mitogen-stimulated lymphocyte proliferation and neutrophil phagocytosis, moderate decreases in the functioning of T cells and NK cells, and reduced and altered monocyte activity [19,32,18] .…”