There is increasing evidence of bidirectional communication between the nervous and the immune systems, but the age-related changes in this communication, including the effects of neurotransmitters on immune cells, have been scarcely studied. In the present work the in vitro effects, on several functions of leucocytes from adult (22 ± 2 weeks old), old (72 ± 2 weeks old) and very old (128 ± 2 weeks old) mice, of two neurotransmitter of the sympathetic nervous system, noradrenaline (NA) and neuropeptide Y (NPY), individually and jointly have been studied.

The concentrations of neurotransmitters used were: 10^-12, 10^-10 and 10^-8 M for NPY and 10^-12, 10^-10, 10^-8 and 10^-6 M for NA as well as these concentrations of NA plus 10^-10 M of NPY. Peritoneal leucocytes from BALB/c mice were obtained without killing of animals. Lymphoproliferation both spontaneous and in response to mitogens (concanavalin A (conA) and lypopolysaccharide (LPS)), and the release of cytokines such as interleukin 2 (IL-2) (measured in cultures with conA) and tumour necrosis factor α (TNFα) (measured in cultures with LPS), were the functions studied.

The results show a stimulatory effect of neurotransmitter on spontaneous lymphoproliferation at all ages studied. Lymphoproliferation in response to mitogens was lower in old than in adult mice. The proliferation of lymphocytes in the presence of ConA was inhibited, not influenced and stimulated by NPY and NA in cells from adult, old and very old mice, respectively. The same results were obtained for IL-2. The lymphoproliferation in response to LPS was stimulated, not affected and inhibited by the neurotransmitter in cells from adult, old and very old mice, respectively. The TNFα release was inhibited at all ages studied, but with all concentrations of neurotransmitter only in adult mice. Always, the effects shown in the joint presence of NPY and NA were more related to those shown with NA. These results suggest a modulatory role of sympathetic neurotransmitters such as NA and NPY, which changes with ageing.

The present work was supported by a FISS (99/0815) grant.