Effects of repeated reversal of the light-dark cycle on the peripheral nervous system, blood and spontaneous activity of lead-exposed rat

Abstract

The purpose of the experiment was to investigate if biological effects on lead acetate (Pb(AcO)+2)-exposed rats under the reversal light-dark (LD) cycle (12∶12) could be different from those under the normal LD cycle (L: 0700-1900, D: 1900-0700). The reversal of LD condition was repeatedly produced by alternation of LD cycle every 3 days for 53 days. Motor nerve conduction velocity (MCV), Ht and Hb, lead contents in blood and sciatic nerve tissue, and spontaneous activity were measured. Either 10 mg or 20 mg (Pb(AcO)+2) was i.p. injected once a week, 8 times in total. The pattern of spontaneous activity under the reversal rhythm became desynchronized with the LD cycle, while that under the normal rhythm synchronized with the LD cycle through the experiment. From the 5th week, the MCV in the lead-exposed groups under the reversal rhythm decreased significantly compared with that in the control under the normal rhythm. From the 6th week, there were also significant differences in MCV of the 20-mg groups between the normal and reversal rhythms. However, there were not significant differences between the normal and the reversal rhythms in the body weight, the lead contents of the blood and the sciatic nerve, Ht, and Hb in any of the control, 10-mg and 20-mg groups.