Variation of brain and serum cholinesterase activity with age in wild small mammals.

Abstract

The use of organophosphate (OP) and carbamate pesticides can result in exposure, and in some cases mortality, of non-target vertebrates such as small mammals (Westlake et al. 1980; Johnson et al. 1991; Hardy et al. 1993). These pesticides are anticholinesterases and inhibition of blood cholinesterase (ChE) activity is widely used as a biomarker to assess exposure in vertebrates (Thompson 1991); inhibition of brain acetylcholinesterase (AChE) activity by more than 40% is generally considered to be associated with impaired physiological function and altered behaviour (Grue et al. 1991). Determination of the degree to which ChE activity has been inhibited requires good base-line knowledge of normal (control) activity levels. While normal levels of ChE activity have been measured in a variety of wild species (Westlake et al. 1983), the data have been obtained from a relatively small number of individuals. The difficulties in defining control activity levels from limited data have been highlighted by a long-term study in which normal brain ChE activity in wild-trapped wood mice Apodemus sylvaticus was found to vary by up to 33% during a twelve year period (Greig-Smith 1991). Such large-scale variation makes it difficult to identify when pesticide-mediated inhibition of activity has occurred.