Particulate acetylcholinesterase in amniotic fluid and its implications for neural tube defect screening

Acetylcholinesterase activity in mid-trimester amniotic fluid has been determined by a quantitative spectrophotometric method and a qualitative electrophoretic technique in a limited (76 samples) retrospective study. Differential centrifugation studies on amniotic fluid from normal pregnancies demonstrated the presence of particle-associated acetylcholinesterase sedimenting only at relatively high centrifugal forces. It is postulated that this particle-associated activity was a contributory factor to an observed false-positive incidence of 6.6% when quantitative acetylcholinesterase measurement was used to discriminate between normal pregnancies and those associated with neural tube defects. Discrimination on the basis of electrophoretic analysis of acetylcholinesterase resulted in no misclassification of pregnancies. Particulate acetylcholinesterase would not be expected to influence the interpretation of the electrophoretic pattern due to its size-related exclusion from gel pores. The implication of these observations in the accurate prenatal diagnosis of neural tube defects is discussed.

Orienting responses and locus of control

Few studies have attempted to relate the locus of control (Rotter, 1966) variable to physiological activity. This paper describes the heart-rate and skin conductance responses of 40 subjects exposed to a series of auditory stimuli, in relation to their locus of control scores. It was found that those scoring relatively 'externally' on the locus of control scale gave less decelerative and more accelerative heart-rate responses and tended to give larger skin conductance responses when there was a change in stimulus characteristics, than those scoring 'internally'. These results may be interpreted to support Lazarus' (1966) suggestions that control over a situation lessens the threat perceived in that situation. They also indicate that internal subjects tend to seek information to increase their control.

A Familial Tubular Absorption Defect of Glucose and Amino Acids

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