SPONTANEOUS LOCOMOTOR-ACTIVITY IN ARCTIC CHARR MEASURED BY A COMPUTERIZED IMAGING TECHNIQUE - ROLE OF BRAIN SEROTONERGIC ACTIVITY

Using a computerized video-image analysis system, spontaneous locomoto r activity was measured in dominant and subordinate individuals of Arc tic charr (Salvelinus alpinus) and in individuals treated with inhibit ors of serotonin (5-HT) synthesis and reuptake. Arctic charr were put together in pairs. After 1 week, subordinate individuals were found to have elevated brain levels of 5-hydroxyindoleacetic acid, a major 5-H T metabolite, suggesting an increase in serotonergic activity. The sub ordinate individuals had significantly lower spontaneous locomotor act ivity than the dominant fish. Similarly, Arctic charr displayed a sign ificantly reduced locomotor activity when their serotonergic activity was stimulated by the specific 5-HT re-uptake inhibitor zimeldine. In contrast, fish treated with the 5-HT synthesis inhibitor p-chloropheny lalanine showed a significant increase in locomotor activity. Dominant , subordinate and pharmacologically treated fish all had very similar activity rhythms for the 18 h test period. Thus, neither the previous social experience nor the pharmacological treatment seemed to affect t he diurnal activity rhythm per se. Taken together, these results sugge st that the brain serotonergic system inhibits locomotor activity and support the possibility that 5-HT is involved in the inhibition of loc omotor activity displayed by subordinate fish.