Abstract: The CNS modulates immune cells by direct synaptic‐likecontacts in the brain and at peripheral sites, such as lymphoid organs. Tostudy the nerve‐macrophage communication, a superfusion method was used toinvestigate cotransmission of neuropeptide Y (NPY) with norepinephrine (NE),with interleukin (IL)‐6 secretion used as the macrophage read‐out parameter.Spleen tissue slices spontaneously released NE, NPY, and IL‐6 leading to asuperfusate concentration at 3‐4 h of 1 nM, 10 pM, and 120pg/ml, respectively. Under these conditions, NPY dose‐dependently inhibitedIL‐6 secretion with a maximum effect at 10^‐10M(p = 0.012) and 10^‐9M (p < 0.001).Simultaneous addition of NPY at 10^‐9M and theα‐2‐adrenergic agonist p‐aminoclonidine further inhibited IL‐6secretion (p < 0.05). However, simultaneous administration of NPYat 10^‐9M and the β‐adrenergic agonist isoproterenolat 10^‐6M or NE at 10^‐6Msignificantly increased IL‐6 secretion (p < 0.005). To objectifythese differential effects of NPY, electrical field stimulation of spleenslices was applied to release endogenous NPY and NE. Electrical fieldstimulation markedly reduced IL‐6 secretion, which was attenuated by the NPYY1 receptor antagonist BIBP 3226 (10^‐7M, p = 0.039;10^‐8M, p = 0.035). This indicates that NPY increases theinhibitory effect of endogenous NE, which is mediated at low NE concentrationsvia α‐adrenoceptors. Blockade of α‐adrenoceptors attenuatedelectrically induced inhibition of IL‐6 secretion (p < 0.001),which was dose‐dependently abrogated by BIBP 3226. This indicates that underblockade of α‐adrenoceptors endogenous NPY supports the stimulatingeffect of endogenous NE via β‐adrenoceptors. These experimentsdemonstrate the ambiguity of NPY, which functions as a cotransmitter of NE inthe nerve‐macrophage interplay.