The Endocannabinoid System
This post is part of the series Examining the Use of Medical Marijuana for ASD Treatment.
Scientists have identified an endocannabinoid system within the brain. It is so called because the naturally occurring neurotransmitters (chemical messengers that control the function of nerve cells in the brain) that control the endocannabinoid system resemble the active compounds, cannabinoids, found in plants of the genus Cannabis. The two known endocannabinoid neurotransmitters are anandamide and 2-arachidonyglycerol, thankfully referred to as 2AG for those not comfortable with the language of organic chemistry. They are classified as unconventional or atypical neurotransmitters because they do not behave as more familiar neurotransmitters do. There are likely more endocannabinoids that have not yet been identified.
The endocannabinoids interact with specific receptors (gates in the membranes of nerve cells made of proteins that open and close under specific circumstances) distributed throughout the brain. These are the cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptors, so named because they were found to interact with the psychoactive ingredients in marijuana. The CB1 receptor is found in many areas of the brain. These areas include:
· cerebellum: responsible for producing smooth, well-coordinated, multi-jointed movements (e.g. walking, running, writing), learning skilled movements (e.g. playing an instrument)
· hippocampus: memory
· basal ganglia: organization and guidance of complex motor functions, regulate cognitive functions (memory and learning), regulate emotional and motivated behavior
· cortex: sensory and motor function, sensory processing, learning, planning and decision making, language processing, attention, cognition
· brainstem: regulation of upper and lower body movements (balance, posture, gaze), sensory and motor functions of head and neck, regulates the level consciousness
· thalamus: amplifies, computes, and communicates sensory and motor information to the cortex; mediates attention, mood change, behavioral arousal, and transitions in sleep and wakefulness
· hypothalamus: regulates internal states (blood pressure, body temperature, emergency responses, etc.)
The CB2 receptor is more limited in its distribution but can also be found in the brainstem. The wide distribution of the CB1 receptor means that it has significant influence on just about every function of the brain. Just as there are likely other endocannabinoids yet to be discovered there are likely other unidentified receptors that are part of the endocannabinoid system.
Anandamide and 2AG serve as traffic regulators at the synapses where they are found. They are released by neurons when electrical signals come into the cell. The endocannabinoids slow down the signals traveling across a synapse by telling the previous neuron in the sequence of neurons to stop sending signals across the synapse. The effects of these endocannabinoids can last for seconds, minutes, or hours depending on what type of neuron is being inhibited.
In addition to the endocannabinoids and their receptors the brain also has a mechanism for dispensing with the endocannabinoids once they have done their job. There are a number of enzymes that break down anandamide and 2AG once their function is no longer needed. Researchers have been exploring ways to exploit the various parts of the endocannabinoid system in order to treat and control chronic pain, anxiety, depression, and obesity.
Next in the series, The Cannabinoids.
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