Role of 3,4-dihydroxyphenyl alanine in the nodulation response of silkwormBombyx mori L. to bacterial infection

The relationship between nodulation response to bacterial infection and exo genous application of 3,4-DL-dihydroxyphenyl alanine has been examined in t he silkworm Bombyx mori. Intrahaemocoelic injections of the bacteria Bacill us thuringiensis var. sotto, to fifth instar larvae, followed immediately b y injections of 3,4-dopa resulted in significant (P < 0.01) depletion of ha emocytes from general circulation in comparison to infected vehicle-treated controls. The nodulation response of the insect was also enhanced. Treatme nt with haloperidol, a dopamine receptor inhibitor, impaired the nodulation response as well as deployment of haemocytes in the defensive process. The inhibitory effects on nodulation were seen Ih after infection, which was e videnced by lesser cellular aggregates and nodules. On the other hand, trea tment with dopa + haloperidol following infection neutralized the effect of dopa (or dopamine). These findings are indicative of a specific role for d opa in the discrete cellular events leading to nodulation.