Blood-brain barrier definition

The definition of neurotoxicity also indicates a potential difference between the developing and the mature nervous system, to underscore the fact that developmental neurotoxicity is an important aspect of neurotoxicology. Most known human neurotoxicants are indeed developmental neurotoxicants.4 In most, but not all cases, the developing nervous system is more sensitive to adverse effects than the adult nervous system, as indicated, for example, by the most deleterious effects of ethanol, methylmercury, or lead when exposure occurs in utero or during childhood. Furthermore, the blood-brain barrier (BBB), which protects the mature nervous system from the entry of a number of substances, appears to be poorly developed at birth and during the first few years of life.6... 

Neither Coppola [239] nor Donoso, Bishop, Fawcett, Krulich and McCann [231] found any definite role for 5-HT in the control of prolactin release. However, Kamberi, Mical and Porter [212] observed a rise in serum prolactin after injection of the amine into the third ventricle. The systemic injection of 5-HT does not alter serum prolactin levels in rats, presumably because it fafls to cross the blood brain barrier but a sin e injection of 5-hydroxytryptophan (5-HTP, a precursor of 5-HT) causes a marked rise in plasma prolactin concentration [240]. 

Two different methods have been used to determine the structure-activity relations of the neurotoxic action of the excitatory amino acids. With the first, the amino acids are administered by peripheral injection, which produces neuronal damage in areas of the brain to which the excitotoxins gain access. The second approach involves direct intracranial injection with analysis of the affected area to determine the scope and specificity of the lesion. While the latter method allows for more precise definition of toxic potencies and avoids variables such as metabolism and penetration of the blood-brain barrier, the systemic administration of these compounds was exploited first and continues to be used. 

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