Immobilization stress-induced changes in brain acetylcholinesterase activity and cognitive function in mice

In the present study, the effect of acute and chronic immobilization stress on brain acetyl-cholinesterase (AChE) enzyme activity and cognitive functi on in mice was investigated. Mice were immobilized by strapping for 150 min . One group of mice were only immobilized once (acute stress) while in anot her group mice were immobilized (150 min) daily for 5 consecutive days (chr onic stress). Specific AChE enzyme activity (mu mol min(-1) mg(-1)) was est imated by a spectrophotometric method ill the whole brain of mice subjected to acute and chronic stress. In the acute stress group, AChE activity (0.2 4922 +/- 0.011) in the detergent-soluble fraction was found to be significa ntly decreased in comparison to the control group (0.33561 +/- 0.022). Chro nic stress did not cause any significant change in AChE activity in the det ergent-soluble fraction. In the salt-soluble fraction, AChE activity was si gnificantly decreased only in the chronic stress group (0.08791 +/- 0.011) as compared to the control group (0.12051 +/- 0.011). A passive avoidance t est was used to assess cognitive function. The transfer latency time (TLT) from a light to dark chamber was recorded in the control and acute stress g roups (30 min after immobilization is over) on day 1 (Trial I) and the foll owing day (Trial II). The acute stress group showed an increase (178%) in T LT From Trial I to Trial II, which was significantly higher than that of th e non-stress control group (75%). In the chronic stress group, Trial I was undertaken 30 min after the last immobilization, i.e. on day 5 and 24 hr la ter, Trial II. However, the chronically stressed mice showed an increase (7 0%) in TLT similar to the control group. Thus this study shows that acute i mmobilization stress may enhance cognitive function in mice which may be at tributed to a decrease in AChE activity leading to an increase in cholinerg ic activity in the brain. (C) 2000 Academic Press.