Alterations in central catecholamines associated with immune responding in adult and aged mice

Central catecholamine alterations associated with immune activity are similar to those seen following stressor exposure. Inasmuch as aged animals exhibit more pronounced stressor-provoked alterations of central amines relative to younger animals, it was of interest to determine whether immune challenge would similarly induce more pronounced central amine variations in older animals. Fifteen-month old CD-1 mice challenged with 10(7) sheep red blood cells (SRBC) revealed an equivalent peak splenic plaque-forming cell response (4 days after antigen challenge) to that of 3-month-old mice challenged with 10(6) cells. Neither plasma adrenocorticotropic hormone (ACTH) nor corticosterone levels varied over days following immunization, although ACTH levels were generally higher in the older mice. In both age groups reductions of hypothalamic and locus coeruleus norepinephrine (NE) and increased accumulation of the metabolite MHPG coincided with (or preceded by 24 h) the peak immune response. However, increased accumulation of MHPG in the hypothalamus was greater and occurred earlier in the locus coeruleus of the aged mice. Likewise, at or about the time of peak immune responses nucleus accumbens dopamine (DA) levels were reduced and metabolites elevated in both age groups, while in the prefrontal cortex only DA metabolite levels were elevated. These data are commensurate with previous findings showing that SRBC inoculation may influence central neurotransmitters and that such effects correspond with the time of the peak immune responses. Moreover, in so far as hypothalamic NE utilization is concerned, it seems that the effects of SRBC inoculation are more pronounced in aged animals.