Histopathological alterations in the brain (optic tectum) of the fresh water teleost Channa punctatus in response to acute and subchronic exposure to the pesticide Chlorpyrifos

In the present investigation an attempt was made to assess the toxicity of the organophosphate pesticide Chlorpyrifos (0,0-diethyl-0-3,5,6-trichloro-2-pyridyl phosphorothioate; CPF) on the brain (optic tectum) of the teleost Channa punctatus (Bloch). Fish were exposed to acute (1.5, 3.0, 4.5, 6.0 and 7.5 μl/l) for 24 h and sublethal concentrations of CPF 1.79 μl/l (1/3 of LC50) and 0.538 μl/l (1/10 of LC50) for 3 and 7 days respectively. Several endpoints related to the histoarchitectural profile in the optic tectum were evaluated. Histological examination showed detachment in the superficial zone of the Stratum opticum, Str. marginale due to degeneration of neuronal cells. Spongiosis, congestion, necrosis and appearance of clear areas around the nucleus of mononuclear cells in the lining of the Str. fibrosum grisium superficiale, Str. griseum centrale, Str. album centrale were seen. Granular cells found in the innermost layer of optic tectum, i.e. the Str. periventriculare, were severely degenerated and vacuolized and they migrated toward the Torus semicircularis. The histopathological changes were more pronounced with higher concentrations of CPF. The degree of neurodegeneration found in the deep layers of the optic tectum in higher concentration treatment (6.0 and 7.5 μl/l) was more pronounced. These alterations of the optic tectum affected the functioning of motor coordination of the fish body, because CPF inhibited acetylcholine in neuronal synapses. Due to apoptosis in the superficial zone of the optic tectum, normal visual response was affected. Fish showed microphthalmia (reduced size and eye shrinkage in the eye orbit) because of detachment, necrosis, degeneration and vacuolization in different regions after CPF treatment. This study shows that CPF is highly toxic to fish and affect their population survival in environment.