SYSTEMIC administration of lipopolysaccharide (LPS), a non-specific activat
or of proinflammatory cytokine release from macrophages, provokes sickness
characterized by anorexia, soporific effects, and disturbances of locomotor
activity and exploration. In addition, endotoxin treatment may provoke an
anhedonic response. Assessment of anhedonia in appetitive paradigms, howeve
r, is compromised by the anorexia provoked resent investigation assessed by
the treatment. The LPS on rewarding lateral the anhedonic effects hypothal
amic brain stimulation. Using a simultaneous discrimination, current titrat
ion procedure in the assessment of intracranial self-stimulation (ICSS), it
was found that acute systemic administration of LPS (50 mu g, 100 mu g or
200 mu g) reduced ICSS during the ascending sequence of current presentatio
ns, but had little effect on responding to a series of descending currents.
In a parallel experiment, peripheral administration of LPS (100 mu g) incr
eased in vivo dopamine (DA) efflux from the nucleus accumbens, a region tho
ught to be involved in goal-directed responding to positively reinforcing s
timuli. It is suggested that LPS alters ICSS in a manner different than tha
t observed following stressor exposure or peripheral IL-2 treatment. Furthe
rmore, LPS may engender an anhedonic effect (possibly secondary to sickness
), and the decline of responding reflects the relation between the cost of
responding given in the face of sickness and the reward received for respon
ding. NeuroReport 9: 3797-3802 (C) 1998 Lippincott Williams & Wilkins.