This article presents some recent work from our laboratory indicating
that multiple physiological systems play a role in conditioned immunom
odulation. The first study shows that naltrexone, but not N-methylnalt
rexone, blocks the suppressive effects of an aversive conditioned stim
ulus on Con-A-induced proliferation and natural killer cell activity o
f splenic lymphocytes. This Ending indicates that central opioid activ
ity is involved in the conditioned effects. The second study shows tha
t the beta-adrenergic antagonists atenolol and ICI-118,551 block the s
uppressive effects of an aversive conditioned stimulus on Con-A-induce
d proliferation, but have no effect on natural killer cell activity. T
his result indicates the involvement of the adrenergic system in a sub
set of the conditioned effects. Collectively, these experiments provid
e evidence that both the opioid system and the sympathetic nervous sys
tem are involved in conditioned immunomodulatory changes elicited by a
n aversive conditioned stimulus.