Central modulation of croton oil induced subacute inflammation in rats

Earlier studies from this laboratory have indicated that CNS exerts a modulatory influence over acute inflammation in rats. The present study examines the existence of a similar modulatory effect of CNS on a subacute inflammatory paradigm, the croton oil-induced granuloma pouch in rats. The inflammatory exudate, collected on 6th day after croton oil administration, was found to be substantially less in intracerebroventricular (icv) cannulated and artificial cerebrospinal fluid administered rats as compared to their uncannulated saline (ip) administered counterparts. This effect may be due to stress induced by cannulation. Centrally administered pharmacological agents which attenuate central monoaminergic, cholinergic or prostaglandin systems had insignificant effects on the inflammatory exudate. However, induced increase in central noradrenergic activity was found to attenuate the inflammation when the treatment was done before, but not 48 hr after, the induction of the inflammation. In contrast, induced increase in central serotonergic activity had no effect on the volume of the inflammatory exudate at either time period. Steady state levels of rat brain noradrenaline and serotonin, but not dopamine, were enhanced by the inflammatory procedure. However, these effects may be attributed to the stress induced by croton oil inflammation. The investigation indicates that the modulatory influence of CNS remains limited to the acute phase of inflammation, being exerted mainly by the central noradrenergic system. Once the inflammation has progressed, this modulatory influence of CNS is no longer apparent.