An equimolal single dose (1 mmole/kg) of
leptophos or
cyanofenphos was given orally to chickens to assay the clinical and biochemical neurotoxic effects of these two organophosphorus
insecticides.
Parathion and
TOCP at 2 and 1000 mg/kg of chicken
body weight were tested in the same manner as negative and positive neurotoxicants, respectively. Three birds of each of five groups tested were sacrificed 1,2,3,7,14,21 and 28 days
after treatment and the brains were taken for the biochemical tests.
Acetylcholinesterase (AChE) and
neurotoxic esterase (NTE) activities were determined in the brain microsomal fractions. In addition, the AChE activity in the brain soluble fractions was measured. Clinical observations indicated that
leptophos-,
cyanofenphos- and
parathion-treated chickens became acutely poisoned but recovered from the typical
cholinergic signs in a day or two. However, about 10 to 15 days later
leptophos- and
cyanofenphos-treated chickens developed the characteristic leg weakness and unrecoverable
ataxia seen in birds given
TOCP. The biochemical results indicated that
cyanofenphos followed by
leptophos and
parathion produced more in vivo AChE inhibition than that produced by
TOCP in both chicken brain soluble and microsomal fractions. Results suggested that there are no correlations between the in vivo effect of
TOCP,
leptophos and
cyanofenphos on AChE and
phenyl valerate-total hydrolyzing activities and the ability of these chemicals to produce neuropathy in hens. The results obtained from this study of the in vivo effect of the tested compounds on chicken brain NTE activity present an acceptable correlation between the inhibition of this
enzyme and the ability of these chemicals to induce neuropathy. The mechanism and explanation for this correlation are presented. The in vivo effect of the tested compounds on the chicken brain NTE activity was determined using the indirect and a new direct method. The data presented in this report suggested that the new direct technique of assaying NTE activity using
4-nitrophenyl valerate (4-NPV) as substrate, can be useful in the in vivo screening studies of
organophosphates for their ability to induce neuropathy in hens.