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The effect of the neurotransmitter serotonin on autistic symptoms

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Biology 202
2000 Second Web Report
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The effect of the neurotransmitter serotonin on autistic symptoms

Emily Hollister

In a previous report, I described the symptoms of autism and the research that has been carried out to illustrate the existence of a connection between the neurotransmitter serotonin and autism, a pervasive developmental disorder. This report is more closely focussed on the actual effects that serotonin has on the manifestation of autistic symptoms and the debates that surround the relevance of serotonin to autism. In the previous report, it was also noted that "changes in the level of serotonin synthesis do not affect all symptoms of autism." (1) Reasons for this and the implications that it presents are examined here.

Serotonin (5-Hydroxytryptanamine) originates in the midbrain region where the cerebral hemispheres and thalamus-hypothalamus are bridged to the spinal cord, and distributed throughout the brain. The thalamus regulates sensory integration and motor integration. The hypothalamus regulates body temperature, emotions, hunger, thirst, and Circadian rhythms. Many of the functions associated with these structures are affected in autism. For example, poor sensory integration and dysfunctional emotional behavior are characteristic of autism. It's difficult to know whether differences in the structure of the thalamus and the hypothalamus cause these symptoms or if they affect production of serotonin levels which in turn triggers autistic symptoms.

Autism is a complicated disorder that affects many different aspects of a person and cannot be traced to one unique cause. Autism is increasingly thought to have causes rooted in a range of problems. Research has uncovered evidence of genetic abnormalities, viruses are thought by some to cause autism, as are toxins that pollute the environment. Autism is also attributed to physical abnormalities of various brain structures. These can be divided into two classifications: neural structure differences and abnormal brain chemistry. (2) The connection between the latter two is most significant to an understanding of serotonin production and synthesis. The former possible causes are likely to cause the abnormalities in neural structure and brain chemistry. These abnormalities in turn bring about the behaviors that are characteristic of autism. Serotonin levels are only one of autism's many contributing factors. This neurotransmitter is not necessarily a cause, however, but abnormal levels of serotonin can be understood as a primary symptom that is the base for observable symptoms. Therefore, drug therapy can limit certain symptoms that are related to serotonin levels, but it does not eliminate the causes of autism.

The role of serotonin is to regulate mood, regulate food intake by stimulating GIT smooth muscles, regulate sleep, and to stimulate or inhibit the release of various hormones. (2) As can be seen, serotonin functions in a variety of ways and works in conjunction with other chemicals. One implication of this multi-functioning capacity is that we cannot accurately determine how much to alter serotonin production, absorption or synthesis in order to produce the desired effect. Because many different brain structures with varying functions are affected in autism and symptoms vary from individual to individual, drugs affecting the serotonergic system can only be part of how autism is dealt with.

Some controversy over the relevance of serotonin levels to autism exists. A study published in the November Archives of General Psychiatry, researchers found that low levels of serotonin . (3) in adults contributed to a lessening in the intensity of autistic symptoms. Other researchers have the idea that low levels of serotonin would have the opposite effect and induce abnormal mood regulation. Celia M. Bibby states that autistic children have abnormally high levels of serotonin and that high levels of serotonin in general cause more intense autistic symptoms (4,5) . It's important to remember, however, that normal serotonin change according to age and are generally higher in children than they are in adults.

In the studies described in the earlier report, serotonin levels had varying affects on the patients that were part of the studies; however, both children and adults with autism have been known to benefit from drug therapy that affects serotonin levels in the blood. "There will always be a part of the brain that uses serotonin in a different way, a receptor that activates neurons differently." (5) The needs of autistic patients vary so widely that it is difficult to determine what the exact effects of serotonin levels will be in autism patients. 

WWW Sources

1) Autism and its Connection with the Neurotransmitter Serotonin

2) Overview of Autism: Causes

3) Autism: the Serotonin Connection

4) Autism: A Conditioned Response to Biochemical Toxicity?"

5) Mechanisms of LSD: a Glimpse into the Serotonergic System



Comments made prior to 2007

Please list my novel as a research tool on autism, and the efficacy of LSD in the treatment thereof. I have always suspected the efficacy of LSD as a remedy for autism and other developmental abnormalities. In 2000 I published the novel entitled "The Closer's Song" about an autistic child who grew up in Sleepy Hollow NY. It was a story about an abused child with learning disabilities, who encounters a Hippie who befriends him as an adolescent circa 1967. He is introduced to LSD in the book and his mental and psychological states begins to alter. The book chronicles his developement and transcendence into adulthood as of all things, an oustanding and successful automobile salesman. This book is largely autobiographical and based on firsthand knowledge. I have long suspected that the life changing, reality altering properties of LSD, have the potential of moving an autistic person off the spectrum toward a higher psychological development. I in no way encourage or endorse the use of LSD without a legal, controlled and medical supervision, as the complications and dangers are apparent ... Christopher Cole, 15 November 2007


visitor's picture

i have an 5 years old

i have an 5 years old autistic brother my mother had him when she was a little old
so any antidepressant could help him or any molecular diagnosis for him ?

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Google searched my name

The comment that I had added years ago is out dated under right to be forgotten name and address on Google search engines, please remove it for me please.

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Name removed

Dear friend of serendip,

I’ve removed your name from the comment, and search engines will now re-index the page so it will be removed from their caches. This holds true of all search engines, not just Google.

Best wishes,


Serendip Visitor's picture

Depression drugs, autism and serotonin

Evidence now links SSRIs, depression drugs, with serotonin levels and autism in children born of mothers who used SSRIs during 1st trimester of pregnancy. An FYI.

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Re: Autism and Bipolar Nurotransmitters In Brain

Autism is something that we are born with like myself I was diagnosed in just having autism as I was born with it the Psychologist told me. Autism Psychologist looked to see if anything else is going on in my mind which nothing else was their? When I was a kid I get creative dreams and always sleep as a child and thought that I more than likely to have bipolar more than autism. I did remember when I was very young that I just could not speak and I was screaming and a lady in the 1970's was folding her arms saying that she don't want me back here again as a bad kid. I went back to her again and she helped me and was never diagnosed with autism. I was diagnosed at a later date as I had ripped off a woman's hijab in the street Exeter and she went to the police. But with Bipolar it would happen all the time I guess.

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Serotonin and Autism Studies?

Interesting to follow this. If you have any other references on this, please share it with me. I am interested to update my page on serotonin.

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further research

Dear Emilly,
This is fascinating have you done further research on this please advise , we have genomics company looking to work on this field please advise how i can follow your work

Tanvir Khandaker M.D.

TPowell's picture


My boyfriend and his mom seem to think my daughter may be autistic. She will be 5 in Nov and still sucks her thumb and is attached to her "lovey". She also seems to not understand or hear questions asked directly to her. If anyone else has experenced these symtoms in their child, or has an autistic child and can offer suggestions please feel free to e-mail me.


SMurray's picture

Did you ever get an answer to

Did you ever get an answer to this? Obviously, it's been three years...just curious if you still wanted some incite. I have a 6-year old autistic daughter.

Anonymous's picture

Anemia due to ingestion of lead

Anemia can be caused by an ingestion of heavy metal such as lead and is common in children exposed to lead products. Chelation (removal of toxic metals from the body) may be something that you want to look into. You will have better luck working with a doctor who has both an MD license but, also understands natural health and medicine. The metallic/chemical taste in your mouth probably is due to some sort of chemical/metal exposure. There is a new way of detoxing the body that is quite rapid and uses the latest technologies such as laser light. It's amazing! But, you will want to hurry and do something because your body is paying the price of being toxic with a chemical that is unknown to you. And possibly quite poison. Good luck!

VA's picture

brain cracking sounds

I have been suffering for 7-8 months a metallic taste or smell and chemical taste in my mouth consistent for 7-8 months. It has progressed and along with the base of my neck hurts like on the spine part and my brain sounds like its cracking. Everything I smell - smells like chemicals/metallic. I have been to numerous of doctors but dont feel I'm seeing the right doctor. I have a neurologist and he give me depression medication but acknowledge that I truly experiencing the symstoms??? I have had numerous MRI's, CT but all clear as well as a variety of blood work. The lest is I'm anmenic. I believe something more is wrong and it fears me to not know what doctor to consult with.

thanks, please help - VA

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metallic taste in mouth

If you have dental fillings that are amalgam (look like silver), definitely have them removed and replaced with fillings made of non-metal, composite material. Amalgam fillings are loaded with mercury, which is highly toxic. I had my two fillings removed and my life turned around. I had chronic fatigue before. The fillings leak. The mercury ruins your digestion and affects your mental state.

Amool's picture


Hello i have seen your letter regaring Sounds cracking in ur brain. The thing is i also have the same problem, but i just tend to ignore it because i dont know whether itz bad or good.
The problem is verses parts of my bone hurt me,i feel my breath had be taken away if i walk fast,i also have cracking sounds in my brain like weird sounds not paper being torned. something else
But i dont smell any weird things