To investigate the relationships between the central nervous system and interleukins, ventral mesencephalic cells from embryonic 17-day-old rats were cultured for 3 days in vitro (DIV) and exposed to interleukin-1 beta (IL-1 beta), interleukin-3 (IL-3), or interleukin-6 (IL-6) for the following 2 or 3 DIV with or without 2 microM 1-methyl-4-phenylpyridinium (MPP+). Thus, the survival of and the MPP+ neurotoxicity against the dopaminergic neurons immunostained with anti-tyrosine hydroxylase antibody were examined. For the survival studies, IL-1 beta has been shown to have a survival-promoting effect on dopaminergic neurons. This effect is initiated at a concentration between 0.1 and 1 ng/ml. In contrast to the effect of IL-1 beta, IL-3 and IL-6 failed to increase the survival of dopaminergic neurons. In MPP+ neurotoxicity analysis, only IL-6 among the three interleukins studied here has been shown to attenuate the MPP+ neurotoxicity against dopaminergic neurons in a dose-dependent manner; this neuro-protective action is apparent at a concentration of 10 ng/ml. In addition, these three interleukins did not promote glial proliferation. These findings suggest that the effects of IL-1 beta and IL-6 on dopaminergic neurons are not mediated by glial proliferation, that IL-1 beta acts as a neurotrophic factor on dopaminergic neurons, and that IL-6 is capable of protecting dopaminergic neurons from the neurotoxicity of MPP+.