A BEHAVIORAL-ASSESSMENT OF TS65DN MICE - A PUTATIVE DOWN-SYNDROME MODEL

Mice which are trisomic for only the human chromosome (Chr) 21-homolog ous segment of mouse Chr 16 (segmental trisomy), including a portion o f the Down syndrome region of human Chr 21, have recently been develop ed. Since these segmentally trisomic mice, designated Ts(17(16))65Dn, survive to adulthood, they may represent a mouse model for the study o f Down syndrome. A partial characterization of their behavioral phenot ype was undertaken by evaluating the sensorimotor reflexes, exploratio n, locomotor activity, emotionality and spatial learning in 16 male Ts 65Dn mice (TS) and 16 control (GO) littermates. No sensorimotor defici ts appeared in TS compared to CO mice. By contrast, head-dipping behav iour in the hole board was increased in TS mice with respect to the CO group, showing a higher repetition rate of previously explored holes. Crossings in the open field and total arm entries in the plus maze we re higher in TS than in the CO group during the dark phase of the ligh t-dark (LD) cycle under red light, but not during the light phase of t he LD cycle under white light. Entries into the open arms of the plus maze were increased overall in TS mice when compared to CO mice, but n o differences were found in time spent in the open arms. TS mice showe d impaired place learning in the Morris water maze, whereas they were able to reach the same performance as CO animals in cued learning. Thu s, absence of sensorimotor deficits, increased exploration, hyperactiv ity under certain experimental conditions and a moderate impairment of spatial learning were the principal characteristics observed in TS mi ce compared to their CO littermates.