Time-dependent in vivo mesolimbic dopamine variations following antigenic challenge

Administration of sheep red blood cells (SRBC: 5 × 10⁶) ro rats provoked an immune response which peaked 4 days following inoculation. Immune activation elicited an increase of in vivo extracellular dopamine (DA) in the nucleus accumbens, indicating increased release of DA from neurons. The DA alterations coincided with the time of the peak immune response, being significantly altered 4 days after inoculation, and declining to control levels thereafter. In contrast, the levels of serotonin metabolite, 5-hydroxyindoleacetic acid (5HIAA), were not affected by SRBC inoculation. These data are consistent with the supposition that antigenic challenge influences central neurotransmitters, and indicates that such effects are not restricted to the hypothalamus, but are apparent in mesolimbic regions. It is suggested that the antigenic challenge leads to effects comparable to those induced by stressors. As such, it might be expected that immune activation may come to produce behavioral alterations much like those engendered by stressors.