Experimental model studies of pesticide exposure

The neurotoxic effects of Dimethoate (Dim), Dichlorvos (DDVP) and Methyl-Parathion (MP) respectively were investigated on the central nervous system (CNS) and peripheral nervous system (PNS) of rats after different treatment schedules at the macro and single unit cell level. At the macro investigations 1/25, 1/50 and 1/100 of the respective LD50 values of each pesticide were administered to different groups by gavage daily in the following programs: Pregnancy variation (P) to females from 5th to 15th days of pregnancy; Pregnancy and lactation variation (P+L): to females as above and during lactation for 4 weeks; Pregnancy+lactation+post weaning variation (P+L+P) as above plus to the young male rats (F1 generation) up to 8 weeks. Neurotoxicological investigations were conducted on the F1 rats at the age of 12 weeks. Spontaneous electrocorticograms (ECoG) were recorded on the anesthetized rats from the somatosensory, visual and auditory cortex. Cortical evoked potentials (EP) were recorded from the same areas subsequently. Conduction velocity and refractory periods of the tail nerve was investigated. Treatment by Dim, DDVP and MP during P and P+L of the mothers did not influence the bioelectric activity of the offsprings significantly. The same treatment by the P+L+P programme, resulted in significant changes. Frequency of the spontaneous ECoG waves grew significantly in all dose groups of P+L+P group. Latency time become shorter after somatosensory. light or acoustic stimuli respectively on one hand and the beginning of the of answer of these by the evoked potential (EP) waves on the other hand. Conduction velocity of the tail nerve diminished, refractory periods grew dose dependently and significantly at the P+L+P programs with all the three pesticides. Cortical single unit activity was studied after the i.p administration of 1/5 LD50 of the three organophosphates (OP). The decrease of the firing frequencies was observed. The amplitude of the hippocampal population spikes increased. The changes observed in these studies point toward a higher excitation state of the CNS and a disturbed conduction of the nervous impulses of the peripheral nerves. These results could be taken into consideration when deciding on human contaminations by OP-s.