Effects of lactational exposure to benzo[α]pyrene (B[α]P) on postnatal neurodevelopment, neuronal receptor gene expression and behaviour in mice

The harmful effects of exposure to benzo[α]pyrene (B[α]P), which is a neurotoxic pollutant, on mammalian neurodevelopment and/or behaviour as yet remain widely unclear. In the present investigation, we evaluated the impact of the lactational exposure to B[α]P on postnatal development of pups and behaviour of young mice. The neurobiological effects of B[α]P during lactation were also evaluated on pups' brain. Here, we found that lactational exposure to B[α]P at 2 and 20 mg/kg affects the neuromaturation of pups by significantly decreasing their reflex as highlighted in surface righting reflex and negative geotaxis tests. However, we noted a significant increase in muscular strength of lactationally B[α]P mg/kg-exposed pups, which was probably due to the impact of the exposure to this toxic compound on body weight gain. At the pup stage, lactational exposure to B[α]P also provoked a neurobiological change, which was assessed by determination of neuronal receptor gene expression. Indeed, a significant reduction in gene expression of 5HT_1A receptors in pups exposed to B[α]P through lactation was found in comparison to controls. Additionally, attenuation in the expression of MOR₁ mRNA was observed, but statistically significant only in animals receiving the higher dose. Neither the expression levels of ADRA_1D nor GABA_A mRNA were altered. Interestingly, the harmful effects of lactational exposure to B[α]P on behaviour and cognitive function were still found despite a long post-weaning period. Young mice whose mothers were exposed to B[α]P displayed a disinhibition behaviour towards the aversive spaces of the elevated plus maze. Furthermore, a significant increase of spontaneous alternation in the Y-maze was observed, but only in young mice whose mothers were orally exposed to the lower dose of B[α]P. Our results suggest a close link between the neurobiological change highlighted in pups' brain and the different behavioural disturbances observed during postnatal development period until young adult stage.