Effects of subchronic exposure to benzo[a]pyrene (B[a]P) on learning and memory, and neurotransmitters in male Sprague-Dawley rat.

The harmful effects of the environmental carcinogen, benzo[a]pyrene (B[a]P), on mammalian neurodevelopment and behavior as yet remain unclear. Several studies have suggested that B[a]P impairs learning and memory. In the present investigation, we investigated the effects of subchronic exposure to B[a]P on rats. Male rats received daily injection of B[a]P (0, 1.0, 2.5, and 6.25 mg/kg, i.p.) or vehicle for 13 weeks. Employing the Morris water maze (MWM) test, we observed that rats exposed to either 2.5 mg/kg or 6.25 mg/kg B[a]P had modified behavior compared to controls as indicated by the increased mean latencies, the decreased number of crossing platform and the decreased swimming time in the target area. B[a]P treatment decreased the levels of malondialdehyde (MDA), nitric oxide (NO), nitric oxide synthase (NOS), superoxide dismutase (SOD), acetylcholine (ACh), choline acetyltransferase (ChAT), and increased the activity of acetylcholinesterase (AChE). Endogenous monoamine levels, norepinephrine (NE), adrenaline (A), dopamine (DA) and 5-hydroxytryptamine (5-HT) and their selected metabolites dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus were measured using high performance liquid chromatography (HPLC). B[a]P at both doses, 2.5 and 6.25 mg/kg, increased NE, DA, DOPAC and 5-HT content in the hippocampus. Our results suggested a close link between the modified levels of neurotransmitters in the hippocampus and the impaired behavioral performance, indicating that B[a]P is a potential neurotoxic pollutant.