Histological Studies of the Effects of Monosodium Glutamate on the Superior Colliculus of Adult Wistar Rats

摘要

Histological effects of Monosodium glutamate (MSG) commonly used as food additive on one of the visual relay centre namely the superior colliculus (SC) of adult Wistar rat was carefully studied. The rats of both sexes (n=24), average weight of 185g were randomly assigned into two treatments (n=16) and control (n=8) groups. The rats in the treatment groups received 3g and 6g of MSG thoroughly mixed with their feeds for fourteen days, while the control rats received equal amounts of feeds without MSG added. The rats were fed with growers' mash purchased from Edo Feeds and Flour Mill Ltd, Ewu, Edo State and were given water liberally. The rats were sacrificed on day fifteen of the experiment. The superior colliculus was carefully dissected out and quickly fixed in 10% formal saline for routine histological study after H&E method.The histological findings after H&E method indicated that the treated section of the superior colliculus (SC) showed some varying degree of reduced cellular population based on its sparse distribution, degenerative changes, cellular hypertrophy, and intercellular vacuolations appearing in the stroma.These findings indicate that MSG consumption may have a deleterious effect on the neurons of the intracranial visual relay centre and this may probably have some adverse effects on visual sensibilities by its deleterious effects on the cells of the superior colliculus (SC) of adult Wistar rats. It is recommended that further studies aimed at corroborating these observations be carried out. Introduction Pathological processes frequently involve the body's normal responses to abnormal environmental influences. Such noxious external influences as pathogenic microorganisms, trauma, dietary deficiencies and hereditary factors acting alone or in a complex interaction with environmental factors, cause diseases1. Various environmental chemicals, industrial pollutants and food additives have been implicated as causing harmful effects2.Most food additives act either as preservatives or enhancer of palatability. One of such food additive is monosodium glutamate (MSG) and it is sold in most open markets and stores in Nigeria as “Ajinomoto” marketed by West African Seasoning Company Limited. The safety of MSG's usage has generated much controversy locally and globally3. In Nigeria, most communities and individuals often use MSG as a bleaching agent for the removal of stains from clothes. There is a growing apprehension that its bleaching properties could be harmful or injurious to the body, or worse still inducing terminal diseases in consumers when ingested as a flavor enhancer in food. Despite evidence of negative consumer response to MSG, reputable international organizations and nutritionist have continued to endorse MSG, reiterating that it has no adverse reactions in humans. Notably of such is the Directorate and Regulatory Affairs of Food and Drug Administration and Control (FDA&C) in Nigeria, now NAFDAC has also expressed the view that MSG is not injurious to health4. MSG improves the palatability of meals and thus influences the appetite centre positively with it resultant increase in body weight5. Though MSG improves taste stimulation and enhances appetite, reports indicate that it is toxic to human and experimental animals6. MSG has a toxic effect on the testis by causing a significant oligozoospermia and increase abnormal sperm morphology in a dose-dependent fashion in male Wistar rats7. It has been implicated in male infertility by causing testicular hemorrhage, degeneration and alteration of sperm cell population and morphology 8. It has been reported that MSG has neurotoxic effects resulting in brain cell damage, retinal degeneration, endocrine disorder and some pathological conditions such as addiction, stroke, epilepsy, brain trauma, neuropathic pain, schizophrenia, anxiety, depression, Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis9. It cannot be stated t