Neuropeptide Y cotransmission with norepinephrine in the sympathetic nerve-macrophage interplay

The CNS modulates immune cells by direct synaptic-like contacts in the brai n and at peripheral sites, such as lymphoid organs. To study the nerve-macr ophage communication, a superfusion method was used to investigate cotransm ission of neuropeptide Y (NPY) with norepinephrine (NE), with interleukin ( IL)-6 secretion used as the macrophage read-out parameter. Spleen tissue sl ices spontaneously released NE, NPY, and IL-6 leading to a superfusate conc entration at 3-4 h of 1 nM, 10 pM, and 120 pg/ml, respectively. Under these conditions, NPY dose-dependently inhibited IL-6 secretion with a maximum e ffect at 10(-10) M (p = 0.012) and 10(-9) M (p < 0.001). Simultaneous addit ion of NPY at 10(-9) M and the <alpha>2-adrenergic agonist p-aminoclonidine further inhibited IL-6 secretion (p < 0.05). However, simultaneous adminis tration of NPY at 10(-9) M and the <beta>-adrenergic agonist isoproterenol at 10(-6) M Or NE at 10(-6) M significantly increased IL-6 secretion (p < 0 .005). To objectify these differential effects of NPY, electrical field sti mulation of spleen slices was applied to release endogenous NPY and NE. Ele ctrical field stimulation markedly reduced IL-6 secretion, which was attenu ated by the NPY Y1 receptor antagonist BIBP 3226 (10(-7) M, p = 0.039; 10(- 8) M, p = 0.035). This indicates that NPY increases the inhibitory effect o f endogenous NE, which is mediated at low NE concentrations via <alpha>-adr enoceptors. Blockade of alpha -adrenoceptors attenuated electrically induce d inhibition of IL-6 secretion (p < 0.001), which was dose-dependently abro gated by BIBP 3226. This indicates that under blockade of <alpha>-adrenocep tors endogenous NPY supports the stimulating effect of endogenous NE via be ta -adrenoceptors. These experiments demonstrate the ambiguity of NPY, whic h functions as a cotransmitter of NE in the nerve-macrophage interplay.