Effects of Schistocephalus solidus infection on brain monoaminergic activity in female three-spined sticklebacks Gasterosteus aculeatus

The three-spined stickleback Gasterosteus aculeatus is an intermediate host of the tapeworm Schistocephalus solidus. Changes in predator avoidance, fo raging and shoaling behaviour have been reported in sticklebacks infested w ith S. solidus, but the mechanisms underlying parasite-induced behavioural changes are not understood. Monoamine neurotransmitters are involved in the control of behaviour and central monoaminergic systems are sensitive to va rious stressors. Thus, the behavioural effects of S. solidus infestation mi ght be a reflection of changes in brain monoaminergic activity in the stick leback host. The concentrations of 5-hydroxytryptamine (5-HT), dopamine (DA ), norepinephrine (NE) and their metabolites 5-hydroxy-indoleacetic acid (5 -HIAA), homovanilic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) w ere measured in the telecephalons, hypothalami and brainstems of parasitize d and non-parasitized female sticklebacks held in the laboratory. The ratio s of 5-HIAA:5-HT were significantly elevated in both the hypothalami and br ainstems of infected sticklebacks. The concentrations of 5-HT and NE were s ignificantly reduced in the telencephalons of infected fish as compared wit h controls, but there was no elevation of metabolite concentrations. The re sults are consistent with chronic stress in infected fish, but may also ref lect other alteration of neuroendocrine status resulting from parasite infe ction.