The effects of serotonin metabolites on tonic immobility in chickens (Gallus gallus): Dose and time response curves

Abstract

The effects of melatonin and 5-hydroxyindole acetic acid (5-HIAA) on tonic immobility in chickens were examined at various dosages and after several different postinjection time periods. Both of these metabolic byproducts of serotonin produced increases in duration of immobility at 10 min postinjection, but melatonin was much more potent than 5-HIAA. In addition, melatonin produced a decrease in the duration of tonic immobility at 120 min postinjection, while 5-HIAA produced a decrease at 60 min postinjection, which was followed by another increase in duration of immobility at 120 min. These results are discussed in terms of possible neurotransmitters and a central feedback system between brain levels of serotonin, its metabolites, and duration of tonic immobility.