Immunohistochemical Assessment of Thalamic Region in Rat Brain Following Bonny Light Crude Oil Administration

Environmental and occupational exposure to heavy metal-containing products, such as crude oil, poses serious global health concerns. The bioaccumulation of crude oil constituents in humans has been reported to be toxic to the brain, however, much is still unknown about the neurotoxic mechanism of crude oil. The thalamus is a key sensory neuro relay station to various cortical regions involved in numerous cognitive and sensorimotor functions. In the present study, we investigated thalamic glial and neuronal response to Bonny Light crude oil (BLCO) exposure in rats by immunohistochemical evaluations of selected neuro markers, including GFAP, Iba1, Nrf2, parvalbumin, and NeuN. Adult Wistar rats (n = 6) were orally administered either distilled water (control), 1 or 2 ml/kg BLCO for 21 days. Following administration, we performed immunohistochemistry protocols for the markers mentioned above. BLCO induced a marked decrease in Iba1 expression levels with a contrasting increase in GFAP levels reflective of the involvement of glial activity. In contrast, BLCO exposure did not alter Nrf2 levels suggestive of the lack of influence on oxidative stress regulation by the Nrf2 pathway. Furthermore, there was overexpression of thalamic parvalbumin, which could indicate an aberrant increase in inhibitory activity by parvalbumin-expressing GABAergic interneurons, thus possibly disrupting the brain's excitatory-inhibitory balance. Additionally, there was a significant reduction in the number of NeuN-positive cells but no change in immunoreactivity levels, signifying a reduction in thalamic neuronal density in BLCO-exposed rats. Overall, our results suggest that BLCO exposure could alter glial and neuronal functions in the thalamic region of the brain.

Key Words: Crude oil, thalamus, neurotoxicity, GFAP, Iba1, Nrf2, parvalbumin, NeuN