Insecticide Impairs Gastrointestinal Function, May Increase Disease Risk

Researchers treated mice with oral low dose of a type of pyrethroid once a week

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by Andrea Lobo |

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Being exposed to insecticides impacts gastrointestinal function and might increase the risk of developing Parkinson’s disease, a new study in mice shows.

The research also shows exposure to a specific insecticide disrupts dopaminergic brain circuitries, and leads to motor deficits associated with Parkinson’s.

When it comes to neurological disorders, “[e]verything that happens in the gut has an impact in the brain. A better understanding of interactions between the gut and the brain will bring great opportunities for the diagnosis, treatment and prevention of diseases,” said Sonia Villapol, assistant professor of neurosurgery at Houston Methodist Research Institute, in a press release.

The research was presented in the scientific poster, “Low-dose, oral insecticide exposure impairs gastrointestinal function and disrupts nigrostriatal dopamine circuitry in mice,” at Neuroscience 2022, the annual meeting of the Society for Neuroscience, taking place online and live in S. Diego, Nov. 12–16.

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Gut Inflammation Helps Drive Disease, Mouse Study Indicates

Parkinson’s disease is marked by the loss of dopaminergic neurons, nerve cells that communicate with each other by releasing a signaling molecule, or neurotransmitter, called dopamine. This results in the progressive loss of motor function.

A hallmark of the disease is tht abnormal forms of the alpha-synuclein protein are produced and aggregate in toxic clumps inside dopaminergic neurons.

Everything that happens in the gut has an impact in the brain.

Exposure to pesticides and changes in the gut microbiome, or the community of microorganisms living in the gut, have been linked to an increased risk of developing Parkinson’s disease. Some patients have gastrointestinal disturbances decades before the onset of motor symptoms.

It’s hypothesized that some cases of Parkinson’s disease might be triggered within the gut after exposure to oral pesticides, such as commonly used insecticides, called pyrethroids.

A team of U.S. researchers treated mice with oral low doses of the insecticide deltamethrin, a type of pyrethroid, once a week, as a chronic model to assess its effects on gastrointestinal function and dopaminergic brain circuitry.

The results showed exposure to deltamethrin triggers gastrointestinal changes associated to increased constipation, including alterations in the gut microbiome, in male mice, but not females).

Moreover, levels of proteins associated with the function of dopaminergic neurons significantly changed in the mice exposed to the insecticide. Such proteins included tyrosine hydroxylase, important for dopamine production, and dopamine transporter, which regulates the reuptake, or absorption, of dopamine.

Motor functions were also altered in mice administered deltamethrin, as demonstrated by the mice’s performance in behavioral tests that evaluate several parameters of motor performance.

Taken together, the results suggest exposure to oral insecticides in adulthood can lead to molecular changes in the gut and the brain associated with gastrointestinal disturbances, disruption of dopamine signaling, and motor dysfunction. These effects are probably related to an increased risk of developing Parkinson’s disease.

These new data reinforce the link between the gut microbiome and the brain, and its potential contribution to developing Parkinson’s disease.