Introduction

Bisphenols are chemical compounds found in many plastic products around the world. Some of these products include Beverage can liners, food packaging, and water bottles. These plastics are dumped into treatment plants for degradation and as result these plasticizers are released into the environment posing a great threat to animal and human health. In recent years, science has shown bisphenol A (BPA) can disrupt endocrine system and induce neurobehavioral deficits in humans (Rosenfeld et al.,2015). Due to the backlash, many companies began implementing alternatives in their products such as bisphenol S (BPS), allowing them to place the BPA-free mark on bottles and other plastic materials. However, more extensive research showed exposure to these alternatives also may lead to impaired function and disruptions during development stages (Gu et al., 2019). In a recently published article, Dr.Machnik and collogues investigate for the first time the effects of BPS and BPA on neuro signaling in the adult vertebrate brain (Machnik et al., 2021). 

Background

Studies previously focused on the effects of bisphenol compounds in developmental stages and behavioral effects. BPS was found to disrupt the fetal brain development in rodent models. Results showed the bisphenol altered gene expression and reduced the serotonin concentrations in the placenta (Mao et al., 2020). In zebrafish, BPA and BPS exposure overstimulates the endocrine system during development which leads to premature birth (Qiu et al., 2016). However, none of the previous researchers have directed their efforts to the electrophysiological changes that occur in adult brains as a result of ingesting bisphenol compounds. Dr.Machnik and colleagues decided to do the research on goldfish because BPS is also highly soluble in water and has been detected in the aquatic environment (Fang et al., 2020). This research brings the idea that it is very possible for bisphenols to affect adult human brains and provides procedures and tests which can potentially be used for pre-testing alternative plasticizers. 

Methods

The researchers at University of Bayreuth conducted electrophysiological recordings in goldfish (N=98) after one month of exposure to BPA and BPS. The electrophysiology experiments were focused on the Mauthner neurons of the central nervous system due to their accessibility and large size. Mauthner neurons in fish and amphibians are responsible for the fast escape reflex from a threatening environment by integrating sensory stimuli. The researchers performed in vivo intracellular recordings in these neurons by electrically stimulating the axons and monitoring the backpropagating action potentials. The fish were also presented with acoustic and visual input in order to evaluate the electrophysiological changes after exposure to the plasticizers. For acoustic stimulation the scientists used loudspeakers under water to generate sound, and for visual stimulation they used LED light which was directly placed in front of the goldfish’s eye. 

Results and Interpretation 

The key results showed action potentials were altered in Mauthner neurons after exposure to BPA and BPS. Moreover, these plasticizers disrupted the coordination between Mauthner neurons which is essential for integrating the sensory stimuli. Synaptic transmission was altered which caused an imbalance between inhibitory and excitatory inputs. The changes in neurotransmission were found to interfere with the processing of acoustic and visual stimuli which is important for the survival of the fish. These results show that plasticizers can potentially affect the human brain in similar ways and cause neurological deficits, but no such studies have been conducted yet to confirm this claim. Moreover, the researchers emphasize the need of developing new plasticizers because even alternatives such as BPS present the same dangers as conventional plasticizers. The tests and protocol in this research are quick and efficient which can potentially be used to assess new plasticizers and their effects on neuronal function. This study provided concrete evidence on the negative aspects which plasticizers present. It would have been interesting to see the behavioral effects in the goldfish after the exposure to BPA and BPS for more than just a month. Further research needs to focus on primates which would be more indicative of what the effect of plasticizers has on humans.    

[+] References

[+] Other Work By Alex Tomceac