1.1. Background to the Study
The single-dose acute
oral toxicity test is used in preliminary evaluation of virtually all
substances of suspected biological activity. The test is based on
administration of graded dosage of chemical in relation to body mass.
Malathion is an organophosphate insecticide which is registered for
agricultural uses and for landscape maintenance, vector control, and
structural pest control (Cheeseman et al., 2004). This
assessment of potential dietary exposures addresses the residues that
may occur as a result of agricultural uses of malathion. Organophosphate
compounds inhibit the activity of cholinesterase which is an enzyme
present in several body tissues and essential for the normal function of
Selenium belongs to essential
microelements. Being a constituent of one of the main antioxidant
enzymes – glutathione peroxidase - it is considered to be an antioxidant
(Cheeseman et al., 2004). Its possible application as a
protective agent against toxic metals and compounds as well as against
oxidative stress have already been studied and the outcomes have seemed
to be encouraging (Brugh, 2008). Selenium alone or in combination with
vitamin E has already been found to prevent oxidative stress in brain of
animals exposed to cigarette smoke (Tiwaryand, 2005) chromium
(Chowdhury et al., 2005) and mercury (Oser, 2005).
In living systems, oxidation is a basic
part of the normal metabolic process, in which reactive oxygen species
(hydrogen peroxide and hypochlorous acid) and many free radicals
(hydroxyl radical (OH) and superoxide anion) are generated. Rapid
production of free radicals may cause alteration in the structure and
function of cell constituents and membranes and can results in human
neurologic and other disorders such as cancer, diabetes, inflammatory
disease, asthma, cardiovascular, neurodegenerative diseases, and
premature aging. Therefore, the prevention of the above conditions
requires the presence of antioxidants or the free radical scavenging
molecules in the body.
1.2. Statement of the Problem
Exposure of test animals or humans to
sufficient dosages of malathion and its primary active metabolite,
malaoxon, may result in subsequent signs of toxicity, such as salivation
and sweating. Antioxidants are natural or synthetic compounds, produced
in vivo, normal cell constituents, ordelivered in diets, whose main
function is to fight against oxidative stress (Creighton et al.,
2003), being thus able to either delay or prevent the oxidation of
substrates, such as proteins, deoxyribonucleic acid (DNA), lipids, DNA
mutations, malignant transformations, as well as other parameters of
cell damage (Luna, 2008).
Due to the role of hepatocytes in the
metabolism of drugs, xenobiotics and endogenous compounds, these cells
become the target of reactive oxygen and nitrogen species (ROS/RNS),
giving reactive oxygenated metabolites (ROM), requiring, therefore, an
important antioxidant defense system (Krzystyniak et al., 2005).
Among these antioxidant systems, stands out glutathione (GSH), the most
abundant cellular thiol antioxidant, which exhibits numerous and
versatile functions and therefore protects cells against toxicity
(Prescott et al., 2002).From the above background, the study
therefore examine Subacute malathion toxicity and amelioration of
selenium and antioxidant on brain histology of male wistar rat
1.3 Aim / Objective of Study
To study the antioxidant effect of selenium on malathion toxicity on the brain of male wistar rat.
1.3.1. Specific Objectives
Its specific objectives are;
- To evaluate effects of malathion in the brain of male wistar rats.
- To evaluate ameliorating effects of selenium on malathion in the brain of male wistarrats.
- To examine microstructural changes in the brain of male wistar rats administered with malathion.
Subacute administration of malathion on male wistar rat may change the enzymatic activities of antioxidant the brain.
1.5 Scope of Study
The scope of this project work involves
the investigation of malathion toxicity and antioxidant activity of
selenium on the brain of male wistar rats.
1.6 Significance of the Study
The relevance of this study lies on the
importance it provides on the ameliorating effect of selenium regarding
the toxicity of malathion in the brain which could be useful to the