The behavioural effects of lead

The investigation of the behavioural effects of lead in animals has drawn on all aspects of experimental psychology. Only studies employing rats or mice will be discussed here, although a large body of evidence is available for other animals (including fish, birds, sheep and primates). The behavioural effects of developmental lead exposure are summarized in Table 7. The doses and routes of administration for the studies outlined here are shown in Table 7. 

As shown in Table 7 the behavioural experiments can be divided into four main types, (a) simple behaviour and activity, (b) learning paradigms, (c) complex behaviour and (d) drug-induced behaviour. 

Behavioural test and parameter Result or effect Reference 

Appearance of hair Delayed (in mice) Silbergeld and Goldberg, 1973 1974b 

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The hypothesis that the behavioural effects of lead are mediated via a lead-hippocampus interaction has received much attention. Indeed, the evidence for the possible involvement of the hippocampus in lead intoxication is quite large, although it is mainly of an indirect nature. From these results, it is possible to assume that lead may cause an alteration in hippocampal function. However, some of the reported behavioural effects of lead do not correlate well with a hippocampal dysfunction, therefore it is also possible to conclude that the behavioural effects of lead cause a wide variety... 

The investigation into the possible behavioural effects of lead at low doses has produced an enormous literature. All disciplines and approaches have been used, and the numerous different effects reported covered a whole range of neurobiological function. However, the approach to these studies was essentially the same as the original encephalopathy reports. A dose of lead was given that would produce an effect. Non-specific complications were noted, but rarely considered important. Few reports attempted to characterize the model of lead administration employed, and the myriad effects reported were based on a wide range of doses and durations of exposure. 

In the last 10 years, the neurotoxicological effects of lead have received intense attention, and some of the conclusions reached have been discussed here. Effects of lead have been seen at the behavioural, neurochemical and structural levels in the brain. As it appears that atmospheric lead dispersal will now begin to fall, the emphasis of research into the effects of lead is likely to change again. 

In a blend of immiscible homopolymers, macrophase separation is favoured on decreasing the temperature in a blend with an upper critical solution temperature (UCST) or on increasing the temperature in a blend with a lower critical solution temperature (LCST). Addition of a block copolymer leads to competition between this macrophase separation and microphase separation of the copolymer. From a practical viewpoint, addition of a block copolymer can be used to suppress phase separation or to compatibilize the homopolymers. Indeed, this is one of the main applications of block copolymers. The compatibilization results from the reduction of interfacial tension that accompanies the segregation of block copolymers to the interface. From a more fundamental viewpoint, the competing effects of macrophase and microphase separation lead to a rich critical phenomenology. In addition to the ordinary critical points of macrophase separation, tricritical points exist where critical lines for the ternary system meet. A Lifshitz point is defined along the line of critical transitions, at the crossover between regimes of macrophase separation and microphase separation. This critical behaviour is discussed in more depth in Chapter 6. 

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