Medical marijuana use is becoming legal and accepted in a growing number of US states. A small but probably growing number of them are relaxing or eliminating laws against recreational use, too. As marijuana use becomes nothing more than a legal exercise in adult free will, like alcohol and tobacco, caution must be exercised during pregnancy, when a developing fetus is exposed to everything its mother consumes during that time.

The medical effects of tobacco and alcohol on fetal development are well documented but the study of marijuana’s effects on the fetal brain is limited at this time. Neuroscientist Tibor Harkany and his team of collaborators are changing that limited scope of knowledge.

Harkany’s advice to pregnant mothers is to avoid marijuana use during pregnancy. Harkany and his local team of researchers at the Karolinska Institute near Stockholm, Sweden, and their colleagues at Austria’s Medical University in Vienna found evidence of fetal brain defects in a recently conducted study and suggests the effects of prenatal exposure could last well into adulthood.

The Harkany team used marijuana’s active ingredient, THC (delta 9-tetrahydrocannabinol), in three different ways to test for effects:

  • Brain cells of lab mice were grown in the presence of THC
  • Pregnant lab mice were injected with THC
  • Examination of the brains of human fetuses electively aborted by women who had used marijuana during the pregnancy

A specific protein essential for the development of nerve connections (synapses) was identified in the study samples’ nerve cells - Superior Cervical Ganglion 10 (SCG10) - in an effort to analyze the brain’s “wiring” system. The protein is essential for healthy brain development.

The study team found lower levels of SCG10 in the human and mouse brains exposed to THC than they found in control-groups not exposed to THC. The area most affected was the cerebral cortex, which is responsible for forming memories and for higher-level thinking skills.

This finding indicates THC (marijuana) exposure does produce a specific adverse effect on a developing brain. Harkany suggests prenatal exposure to THC could cause the brain to be more sensitive to THC in the future and may increase the likelihood of neuropsychiatric illness even into adulthood.

In previous studies, the long-term effects of fetal THC exposure include a child’s increased risk of anxiety, attention deficit disorder (ADD), cognitive impairments, depression, and personal use of drugs.

The research team advises all pregnant women to discontinue use of the drug before conception, even when it is prescribed for medical reasons. According to Harkany, it takes the body only a few days to rid itself of THC and, although this study focuses on THC exposure only during pregnancy, its use before pregnancy may hinder a woman’s attempts at conception.

Source: Harkany, Tibor, et al. “Miswiring the brain: Delta-9-tetrahydrocannabinol disrupts cortical development by inducing an SCG10/stathmin-2 degradation pathway.” EMBOpress. The EMBO Journal / European Molecular Biology Organization. Jan 27, 2014. Web. Feb 4, 2014.

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