Monoamines suppress the phytohemagglutinin wattle response in chickens

The influence of the biogenic amines serotonin (5-HT), dopamine (DA) and norepinephrine (NE) on the phytohemagglutinin (PHA) wattle response was studied in three populations derived from line UNH 105 New Hampshire chickens. At 3 or 6 weeks of age, chicks were injected intravenously with either 5-HT, DA, NE, or a saline control. Thirty minutes after monoamine injection, 100 ug PHA-P was injected in the wattle and the thickness increase was calculated 24 hr later. Analysis of variance showed significant monoamine effects compared to controls but no difference in response among the three populations. 5-HT and NE each depressed significantly the wattle response in 3 and 6 week old chicks. DA reduced the response in both ages also but the significantly greater reduction in 6 than in 3 week old chicks indicated an age effect. These results suggest a regulatory role for monoamines in the PHA wattle response.