Antidepressant-like effect of lead in adult mice.

It has been reported that lead can cause behavioral impairment by inhibiting the N-methyl-D-aspartate (NMDA) receptor complex. MK-801, a noncompetitive NMDA receptor antagonist, exhibits an antidepressant-like action in the forced swimming test. The purpose of the present study was to determine whether subacute lead exposure in adult male Swiss mice weighing 30-35 g causes an antidepressant-like action in a forced swimming test. Mice were injected intraperitoneally (ip) with 10 mg/kg lead acetate or saline daily for 7 consecutive days. Twenty-four hours after the last treatment, the saline and lead-treated mice received an injection of MK-801 (0.01 mg/kg, ip) or saline and were tested in forced swimming and in open-field tests. Immobility time was similarly reduced in the saline-MK-801, Pb-saline and Pb-MK-801 groups compared to the saline-saline group (mean +/- SEM; 197.3 +/- 18.5, 193.5 +/- 15.8, 191.3 +/- 12.3 and 264.0 +/- 14.4 s, respectively; N = 9). These data indicate that lead may exert its effect on the forced swimming test by directly or indirectly inhibiting the NMDA receptor complex. Lead treatment caused no deficit in memory of habituation and did not affect locomotor activity in an open-field (N = 14). However, mice that received MK-801 after lead exhibited a deficit in habituation (22% reduction in rearing responses between session 3 and 1; N = 14) as compared to control (41% reduction in rearing responses; N = 15), further suggesting that lead may have affected the NMDA receptor activity. Forced-swim immobility in a basin in two daily consecutive sessions was also significantly decreased by lead exposure (mean +/- SEM; day 1 = 10.6 +/- 3.2, day 2 = 19.6 +/- 3.6; N = 16) as compared to control (day 1 = 18.4 +/- 3.8, day 2 = 34.0 +/- 3.7; N = 17), whereas the number of crossings was not affected by lead treatment, further indicating a specific antidepressant-like action of lead.