International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience
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Int. J. Dev. Neurosci. · Feb 2005
ReviewBehavioral and cellular consequences of increasing serotonergic activity during brain development: a role in autism?
The hypothesis explored in this review is that the high levels of serotonin in the blood seen in some autistic children (the so-called hyperserotonemia of autism) may lead to some of the behavioral and cellular changes also observed in the disorder. At early stages of development, when the blood-brain Barrier is not yet fully formed, the high levels of serotonin in the blood can enter the brain of a developing fetus and cause loss of serotonin terminals through a known negative feedback function of serotonin during development. The loss of serotonin innervation persists throughout subsequent development and the symptoms of autism appear. ⋯ Paraventricular nucleus of the hypothalamus, a brain region involved in social memory and bonding, where a decrease in oxytocin was found. Both of these cellular changes could result from loss of serotonin innervation, possibly due to loss of terminal outgrowth from the same cells of the raphe nuclei. Thus, increased serotonergic activity during development could damage neurocircuitry involved in emotional responding to social stressors and may have relevance to the symptoms of autism.