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 an imals exhibit more pronounced stressor-provoked alterations of central amines relative to younger animals, it was of interest to determine w hether immune challenge would similarly induce more pronounced central amine variations in older animals. Fifteen-month old CD-1 mice challe nged with 10(7) sheep red blood cells (SRBC) revealed an equivalent pe ak splenic plaque-forming cell response (4 days after antigen challeng e) to that of 3-month-old mice challenged with 10(6) cells. Neither pl asma adrenocorticotropic hormone (ACTH) nor corticosterone levels vari ed over days following immunization, although ACTH levels were general ly higher in the older mice. In both age groups reductions of hypothal amic and locus coeruleus norepinephrine (NE) and increased accumulatio n of the metabolite MHPG coincided with (or preceded by 24 h) the peak immune response. However, increased accumulation of MHPG in the hypot halamus was greater and occurred earlier in the locus coeruleus of the aged mice. Likewise, at or about the time of peak immune responses nu cleus accumbens dopamine (DA) levels were reduced and metabolites elev ated in both age groups, while in the prefrontal cortex only DA metabo lite levels were elevated. These data are commensurate with previous f indings showing that SRBC inoculation may influence central neurotrans mitters and that such effects correspond with the time of the peak imm une responses. Moreover, in so far as hypothalamic NE utilization is c oncerned, it seems that the effects of SRBC inoculation are more prono unced in aged animals.