Modulation of chicken plaque-forming cells by serotonin and dopamine

Serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) are endogenous components of the central nervous and endocrine systems of the chicken. To determine the effects of these monoamines on antibody-mediated immunity. New Hampshire chickens of Line UNH 105 were injected intravenously with 5-HT (100 micrograms/kg of body weight) and DA (1 mg/kg of body weight). One milliliter of a 5% SRBC suspension was injected intravenously 30 min later. Both IgM and IgG splenic plaque-forming cells were assayed 5 days after antigen injection. For in vitro studies, spleen lymphocytes from SRBC-primed chicks were incubated with DA and 5-HT followed by quantitation of IgM and IgG plaque-forming cells. The in vivo incubation of splenic lymphocytes with specific antagonists was used to ascertain the presence of monoamine receptors on lymphocytes. The 5-HT significantly enhanced IgM plaque-forming cells compared with controls following in vivo [550 +/- 85 (SE) cells/10(6) splenic lymphocytes versus 359 +/- 44] but not in vitro exposure. The IgG plaque-forming cells were not affected by 5-HT. The DA significantly suppressed IgM plaque-forming cells responses following in vivo (284 +/- 46 versus 499 +/- 66) and in vitro (254 +/- 57 versus 451 +/- 51) exposure. Significant suppression of IgG plaque-forming cells was found in vivo (287 +/- 40 versus 462 +/- 75) and in vitro (153 +/- 36 versus 371 +/- 81) following treatment. Specific DA antagonists, apomorphine and metoclopramide, did not alleviate the in vitro suppressive effect of DA.