There are several known and researched neurotransmitters in the brain and body. Drugs are said to in some way produce an effect on these neurotransmitters and therefore cause a change in brain function that allows for psychological effects. I will attempt to briefly elaborate on each one and describe basic changes in brain and body function as a result of consuming drugs that allegedly alter these neurotransmitters.
A Canadian source will be used primarily to identify how neurotransmitters and drugs function in the brain. This source contains information made explicit in French Canada. Fortunately, I know some French and also have access to a translator that can assist me. Information will be provided accordingly!
Before getting into neurotransmitters in the brain, first a look at brain synapse connections will be briefly explained. A synapse is a junction point between two neurons [BrainCA]. It is noted that a nerve impulse can also be transmitted from a sensory cell, such as a neuron to a muscular cell (Neuromuscular) or from a neuron to the endocrine gland where a hormone is secreted (Neuroglandular), but the focus will be primarily in just connections within the brain. In a typical chemical synapse between neurons, the neuron where the impulse arrives is the presynaptic neuron. The neuron which the neurotransmitters bind to is the post synaptic neuron. A neurotransmitter is a kind of chemical messenger [BrainCA].
The terminal button of the presynaptic neuron's axon contains mitochondria as well as microtubules that transport the neurotransmitters from the body of the cell, where they are produced and then go to the tip of the axon. The terminal button (ending cell) also contains vesicles filled with neurotransmitters. There is a very narrow synaptic gap (space between the cells) where the neurotransmitters have to transport themselves. The width of this gap between cells is about 0.02 microns. After the neurotransmitters bind to the membrane receptors (Large proteins that anchor in the cell membrane of the post-synaptic neuron), when viewed through an electron microscope it can be observed that an accumulation of opaque material which consists of the cluster of receptors and other signaling proteins that are essential for chemical neurotransmission [BrainCA].
Each neurotransmitter has different sub-types of receptors that are specific to it. It is the presense or absence of these certain sub-types that causes a chemical reaction in the postsynaptic neuron. The reactions can be either excitatory or inhibatory [BrainCA].
As for the actual neurotransmitters there are six major types detailed in this source: Acetylcholine, Dopamine, GABA (Gamma-aminobutyric Acid), Glutamate, Norepinephrine, and Serotonin.
Acetylcholine is a very widely distributed excitatory neurotransmitter that generally triggers muscle contraction and stimulates the excretion of certain hormones. In the central nervous system, it is involved in wakefulness, attentiveness, anger, aggression, sexuality, as well as thirst and other things [BrainCA (1)].
Dopamine is a neuroransmitter involved in controlling movement and posture. It is also a modulator of mood and plays a role in positive reinforcement and dependency. Some description of positive reinforcement and dependency is necessary. Different theories have developed based on a traditional hedonist principle that people seek pleasure and avoid pain. [BrainCA (2)].
GABA is in inhibitory neurotransmitter that is very widely distributed in neurons of the cortex. GABA contributes to motor control, vision, and many other cortical functions. Anxiety is also heavily regulated by this neurotransmitter [BrainCA (1)].
Glutamate is an excitatory neurotransmitter mainly associated with learning and memory [BrainCA (1)]. Glutamate is an interesting excitatory neurotransmitter that seems to be able to excite nearly any neuron in the brain which is why it is sometimes called the "master switch" [Stahl 2008, pg 287]. The NMDA receptors is a sub-receptor type of Glutamate that is antagonized by several dissociative drugs including Ketamine and Phencyclidine (PCP) [Stahl 2008, pg 286-289].
Norepinephrine is a neurotransmitter that is most important for attentiveness, sleeping, learning and emotional state. It is also released as a hormone into the blood, where it causes blood vessels to contract and heart rate to increase [BrainCA].
Serotonin is a contributing neurotransmitter to various functions such as body temperature regulation, sleep, mood, apetite, and pain [BrainCA (1)]. Having the name 5-Hydroxy Tryptophan, serotonin receptors are commonly referred to as 5-HT receptors, with subtypes such as 5-HT-2A, 2B, 2C among others.
We also possess Endogenous Opiate Neurotransmitters. There are a variety of these receptors, most importantly mu, delta, and kappa. Endogenous opiate-like substances are peptides derived from precursor proteins called pro-opiomelanocortin, proenkephanin, and prodynorphin [Stahl 2008, pg 980]. Euphroia and relaxation are common effects of stimulating these receptors. By stimulating these receptors with opiate-like drugs a user may have begun on a "quest for euphoria" but is now on a quest to avoid withdrawal [Stahl 2008, pg 980].
Stahl 2008
Stahl's Essential Psychopharmacology - Neuroscientific Basis and Practical Applications
Stephen M. Stahl - Third Edition
BrainCA
(1) http://thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.html
(2) http://thebrain.mcgill.ca/flash/a/a_03/a_03_p/a_03_p_par/a_03_p_par.html#2
No comments:
Post a Comment