Methylmercury induced alterations in brain amine syntheses in rats

Behavioral and neurochemical sensitization to amphetamine following early postnatal administration of methylmercury (MeHg)

Perinatal exposure to methylmercury (MeHg) in rodents has been linked to changes in sensitivity to dopaminergic agents later in life. In an effort to determine the behavioral and neurochemical response to the indirect dopaminergic and serotonergic agonist amphetamine following neonatal exposure to MeHg, male BALB/c mice were administered MeHg during critical periods of neural development and challenged with amphetamine as adults. Mice were observed 15, 30 and 60 min after a single amphetamine injection (7.5 mg/kg i.p.) for presence of stereotypic and self-injurious behaviors, abnormal posture, and hyperthermia. Mice treated with 2 or 4 mg/kg MeHg on alternate days 3-15 of life demonstrated an increase in body temperature and the appearance of stereotypic and self-injurious behaviors not observed when amphetamine was administered to either vehicle-exposed mice or those treated with an equivalent total amount of MeHg administered on postnatal days 13 and 15. Neurochemical analysis of MeHg- and vehicle-exposed mice challenged with amphetamine or saline revealed alterations in dopaminergic and serotonergic activity which corresponded to the sensitized behavioral response to amphetamine. These observations demonstrate a critical window for MeHg exposure affecting the later appearance of amphetamine-induced self-injurious behavior and support the hypothesis that early exposure to environmental neurotoxicants may predispose individuals to engage in aberrant, intrusive behaviors later in life.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

Chronic effects of methylmercury on the cerebral function in rats

We studied the effects of the long-term and small-dose administration of methylmercury chloride (MMC) on the cerebral function in rats. MMC, at a dose of 0.7 mg/kg/day, was subcutaneously injected for 85 consecutive days in nine adult male Sprague-Dawley rats. They were then sacrificed on the final day of exposure (MMC group) after both completing observations on behavioral changes and also determining the local cerebral glucose utilization (LCGU) as an indicator of the cerebral neuronal activities. Histological examinations of the brain and the sciatic nerve were also performed. In addition, seven rats who received physiological saline also served as a control. LCGU significantly decreased in the visual cortex, lateral geniculate nucleus and medial geniculate nucleus without any accompanying histological alterations. Severe axonal degeneration of the sciatic nerve was also observed, which corresponded to the previously described crossed leg phenomenon. The present results suggest that the damage to the peripheral nerve was much more severe than that to the brain, which caused behavioral changes. Although no cerebral morphological changes were observed, brain dysfunction showed a selective involvement of the visual and auditory systems. This finding suggests that LCGU is a sensitive method for detecting the subclinical cerebral dysfunction caused by long-term and small-dose MMC intoxication in the rat brain.