In utero exposure to drugs that interact with neural pathways has been implicated as an important risk factor for ASD. Cannabis/ tetrahydrocannabinol (THC) is the most widely used psychotropic drug; its use has increased substantially over the past 20 years; moreover, more recent formulations of the drug display enhanced potency due to changes in preparation methods [17]. Currently, cannabis use during pregnancy is estimated at 10%. Recent studies by Passey et al. [18] and Shabani et al. [19] have shown that neural deficits can result from in utero cannabis exposure. Moreover, Siniscalco et al. [20] have suggested that the endocannabinoid (EC) system may play an important role in the integrated IS/CNS developmental pathway that is dysregulated in autism. Their research has shown that the cannabinoid receptor type 2(CBR2) signal pathway is upregulated in peripheral blood mononuclear cells (PBMCs) from children with ASD. This finding raises the possibility that the endocannabinoid (EC) system may be associated with ASD. In addition, the authors found reduced levels of bone marrow differentiated macrophages (BMDCs) in children with ASD that may be linked to altered CBR-2 levels.
Endogenous cannabinoids bind to type-1 cannabinoid receptors in the central nervous system (CNS) to guide neural pattern formation and network connectivity in the developing brain. Research by Cutando et al. provides evidence that THC binding of EC-1 receptors as a consequence of subchronic cannabis exposure may affect these signal pathways, at least in part, by activating microglial cells important to neural function [21]. Similar patterns of cerebellar microglial activation have been documented in the brains of autistic children, suggesting similar pathways may be involved. Tortoriello et al. [22] have recently determined that THC affects EC-1 receptor signaling in the developing fetal brain by altering fetal cortical circuitry, further implicating THC as a potential cause of autism.
Researchers from Georgetown University Medical Center combed through papers studying cannabinoids and their effect on human embryos, using mostly animal models published between 1975 and 2015. They found that Tetrahydrocannabinol or THC, the active ingredient in marijuana, can cross the placenta thus exposing the fetus to the chemical.
“We know from limited human studies that use of marijuana in early pregnancy is associated with many of the same risks as tobacco, including miscarriage, birth defects, developmental delays and learning disabilities, but animal research suggests the potential for many more developmental issues linked with the drug
Cannabinoids can affect the use of folic acid, which is important for normal growth and development of the placenta and the embryo. A deficiency in folic acid can cause low birth weight, increase the risk of spontaneous abortion and neural tube defects like spina bifida.
Over the course of two years, Dr. Lucy Troup studied the long-term effects of 70 participants who either smoked cannabis, smoked casually, or smoked chronically, according to self-reported data. The study took place in three parts: an implicit emotion test, an explicit emotion text, and an empathy test, where volunteers were asked to view a facial emotion—positive, neutral, or negative—and were rated on their ability to empathize. One of the most surprising results was that cannabis users generally had lower empathy ratings than the control group.
This result has opened up questions around weed and autism, though this current study has not looked directly at the link between the two. "I've been approached by a number of researchers who are very interested in the use of cannabis to treat autism and if the two are related or causal," Dr. Troup says. "We found that when you ask a cannabis user to think about other people's emotions and relate to them, it's harder for them. That inability to empathize would be a parallel to autistic-like behaviors.
Additionally, Dr. Troup also asked participants to undergo an implicit emotional task. Both the control group of non-smokers and the cannabis users were hooked up to an electroencephalogram (EEG) while they were shown faces with positive, neutral, and negative facial expressions, but asked to focus on the sex of the face displayed. Later they were asked to recall the emotions they were shown, and the cannabis users faired much worse with this task than non-cannabis users. From these results, Dr. Troup infers that weed inhibits a person's ability to intuitively identify emotions when they're not explicitly focusing on them.
Researchers also found that THC levels in marijuana that is smoked has increased 25-fold since 1970. The studies, however, did not analyze the harmful effects of smoking marijuana in the animals.
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