Assessment of the Effect of Post-natal Lead Exposure on the Hippocampus of Developing Wistar Rats

Assessment of the Effect of Post-natal Lead Exposure on the Hippocampus of Developing Wistar Rats

CHAPTER ONE

Objectives of the Study

The research objectives are to assess the effect of post-natal lead exposure on the:

body weight, brain weight and brain somatic index of the Wistar rat
concentration of lead deposit in the brain using Atomic Absorption Spectrophotometer- lamp
changes in oxidative stress markers such assuperoxide dismutase activity (SOD), reduced glutathione (GSH) and malondialdehyde (MDA) concentration using chemical
CA3 regions of the hippocampus of the pups using H and E and Cresyl fast violet
cytoarchitecture of microglia in the hippocampus of the pups using Tomato lectin
volume of the hippocampus of the pups and number of activated microglia in the hippocampus of the pups using Cavalieri estimator and physical fractionator probe respectively.

CHAPTER TWO

LITERATURE REVIEW

Heavy Metals

Improvements in technology has enhanced the standards of living, but have led to new challenges with respect to ecological safety. Human safety has been threatened due to industrialization and urbanization without proper emission controls and pollution abatement (Arif et al., 2015). A necessity for economic growth that relies basically on agricultural and industrial development has largely circumvented environmental protection guidelines and as such continually exposes humans to heavy metals. There is no widely agreed criterion-based definition of a heavy metal and which elements should properly be classified as such, some have based the definition on atomic weight; others, on a specific gravity of greater than 5.0 and chemical behaviour, however heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers (Morris, 1992; Hawkes, 1997).

Even though heavy metals are naturally occurring in the earth‘s crust, exposure to them result mostly from anthropogenic activities (Figure 2.1) such as mining and smelting operations, industrial production and use, domestic and agricultural use of metals (Herawati et al., 2000; He et al., 2005). Significant contribution to heavy metal pollution by weathering and volcanic eruptions, metal corrosion, soil erosion of metal ions, leaching of heavy metals, Industrial sources (such as metal processing in refineries, coal burning in power plants, petroleum combustion, nuclear power stations, plastics, textiles)(Figure 2.1) have also been reported (Pacyna et al., 1996; He et al., 2005; Arruti, et al., 2010; Sträter et al., 2010).

CHAPTER THREE

MATERIALS AND METHODS

Materials

Ethical approval

Ethical approval was obtained from Ahmadu Bello University Ethics Committee on Animal Use and Care with approval number ABUCAUC/2018/047 (Appendix I).

Experimental animals

Nine (9) non pregnant and three (3) male Wistar rats weighing between 120g to 150g were obtained from the Animal House Centre, Faculty of Pharmaceutical Sciences, Ahmadu Bello University, Zaria – Nigeria. The rats were housed in different rat cages, fed rodent chow and water ad libitum without administration of lead for two weeks (14 days) to acclimatize them prior to experimental study.

CHAPTER FOUR

RESULTS

Body Weight, Brain Weight and Brain Somatic Index

Body weight of Wistar rat pups from dams exposed lead acetate

There was a significant (p<0.05) decrease in body weight of Wistar rat pups in group 2 (16.53±0.28g) and group 3 (15.71±0.35g) exposed to lead acetate via lactation from dams administered 60mg/kg and 90mg/kg bwt of lead acetate respectively from PND 1-21 when compared with the control (21.16±0.56g) (Table 4.1). The decrease in body weight of the pups in the group 3 (15.71±0.35g) administered 90mg/kg bwt of lead acetate when compared to group 2 (16.53±0.28g)treated with 60mg/kg bwt lead acetate via lactation from PND 1-21 was not significant (p>0.05)

CHAPTER FIVE

DISCUSSION

Previous research suggested that Pb exposure promotes neuroimmune disruption via diverse mechanisms, and possibly chronic microglial activation and microglial proliferation (Kraft and Harry, 2011). A number of studies have revealed that Lead metal causes toxicity in living cells either by ionic mechanism or that of oxidative stress (Flora et al., 2012). Compared to adults, children are more predisposed to its toxicity due the greater absorptive capacity of their gastrointestinal tracts (CDC, 2005). The present study was designed to assess the effects of maternal exposure to different doses of lead acetate during lactation on the hippocampus of developing Wistar rats.

Body Weight Assessment

In this study a significant decrease in body weight was observed in Wistar rats pups of group 2 and group 3 exposed to lead acetate via lactation from dams administered 60mg/kg and 90mg/kg bwt of lead acetate respectively from PND 1-21 when compared with the control. Wistar rat pups in group 3 exposed to lead acetate via lactation from dams administered 90mg/kg bwt of lead acetate also showed a decrease in body weight when compared to group 2 exposed to lead acetate via lactation from dams treated with 60mg/kg bwt lead acetate from PND 1-21. This suggests that exposure to lead may cause serious loss of body weight in developing infants. The decrease in body weight may be as a result of decline in the consumption of food (anorexia) which is induced by heavy metal consumption. Another possible explanation for the loss of body weight may be the decreased muscle mass and cachexia due to the oxidative stress induced by lead (Zaheer et al., 2013). Aprioku and Siminialayi, (2013) reported significant and time-dependent reductions in body weight after perinatal exposure to 4 or 8 mg/kg lead acetate respectively. In a related study, weight reductions was also reported in neonates of female rats that received daily injections of 5 mg/kg lead acetate at different stages of pregnancy (Chandra et al., 1983). Ronis et al., (1998) also reported that the treatment of pregnant rats at doses of Pb between 0.05% and 0.45% w/v causes disturbances in pups‘ body weight at birth, and growth suppression during the pre-puberty and the puberty periods by causing a decrease in the plasma concentration of IGF (Insulin‐like growth factor) and the rate of pituitary growth hormone (GH) production. The result from the present study is dissimilar to the findings of Lewis and Pitts, (2004) who reported an insignificant decrease in body weight of Wistar rat pups after 3-week post-natal exposure to lead acetate at (50, or 250 ppm) when compared with the control. The difference observed in the result of Lewis and Pitts, (2004) with that of the present study may be due to the differences in the doses used in the studies.

CHAPTER SIX

SUMMARY, CONCLUSIONAND RECOMMENDATIONS

Summary

The results obtained from the present study revealed that post-natal exposure of Wistar rat pups to lead via lactation from dams administered lead acetate orally from PND 1-21 caused:

a significant decrease in body weight, significant increase in brain somatic index and an insignificant decrease in the brain weight
a significant accumulation of lead in the brain
oxidative stress in the brain by causing a significant decrease in antioxidant enzymes (SOD and GSH) level and a significant increase in MD distortion of the cytoarchitecture of the CA3 region of the an insignificant increase in the volume of the
an in significant increase in the number of activated microglia cells in the hippocampus.

Conclusion

The effect of maternal exposure to different doses of lead acetate during lactation on the hippocampus of developing Wistar rats was evaluated in this study. With respect to the findings of the present study, it can be inferred that exposure to increasing doses of lead acetate from post-natal day 1-21 did not significantly trigger microglia activation but caused distortion in the cytoarchitecture of the CA3 region of the hippocampus of Wistar rat pups.

Contribution to Knowledge

This study established that Wistar rat pups exposed to lead via lactation from dams administered lead acetate orally at a dose of 60 mg/kg and 90 mg/kg bwt respectively from PND 1-21 caused:

significant increase (p<0.05) in lead accumulation in brain tissues with values of (0.04±0.01ppm) and (0.11±0.03ppm) respectively when compared with the control (- 0.05±0.02ppm).
significant increase (p<0.05)in MDA levels(25.20±0.80nmol/mg protein) and (30.23±1.96nmol/mg protein) respectively when compared with the control (23.07±0.63nmol/mg protein),significant decrease (p<0.05) in SOD levels(17.90±0.25 U/ml) and (16.50±0.46 U/ml) respectively when compared with the control (20.60±0.56 U/ml) anda significant decrease (p<0.05) in reduced glutathione (GSH) in Wistar rat pups exposed to lead acetate via lactation from dams administered lead acetate orally at a dose 90 mg/kg bwt(11.40±0.99 ug/ml) respectively when compared with the control (16.50±1.48ug/ml).
an insignificant increase (p>0.05) in the number of activated microglia cells with values of 1.92×10⁶±6.10×10⁵(CE = 0.10)and 2.80×10⁶±1.11×10⁶(CE = 0.16) respectively when compared with the control1.22×10⁶±3.01×10⁵ (CE = 18).

Recommendations

The present study recommends:

that lactating mothers should avoid exposure to Lead
further studies on the effect of higher doses and longer duration of post-natal lead exposure on the developing brain
further studies on the effect of post-natal lead exposure on learning and memory using neurobehavioural test
that future studies could also examine the effects of brain Pb after post-natal exposure on expression of P2X7 since studies have suggested that the P2X7 receptor is critical for microglial proliferation during activation

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