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(Treating Anxiety Disorders may help depression).
Info on neurotransmitters from http://www.csuchico.edu/psy/
Dopamine (DA) is a neurotransmitter which is involved in
many behaviors; as examples:
One of the most significant findings of the last decade
has been that of the association between the release
of dopamine in the brain and reward or reinforcement.
Animals will push levers to deliver electric stimuli to
their brains if those stimuli cause the release of
dopamine. Also, cocaine, opiates, and alcohol produce
rewarding effects in part due to their abilities to
promote the release of dopamine.
Parkinson's Disease (PD) is accompanied by a selective
destruction of dopamine neurons in the substantia nigra
of the midbrain which send their axon terminals to the
striatum which is involved in motor control. PD is treated
with L-dopa which is a precursor for the production of
dopamine in the brain. The discovery that fetal brain
cells can be transplanted to the human brain to repair
the damage of Parkinson's Disease has launched a bioethical
debate in the scientific community and world at large.
Schizophrenia is treated with drugs which block the
binding of dopamine to its postsynaptic receptor
sites. The better the drug is at blocking dopamine,
the better it is at reducing the schizophrenia. The
dopamine hypothesis of schizophrenia is that there
is excessive dopamine stimulation in the frontal
lobe due to a combination of genes and some as yet
unknown aspect of the environment such as a perinatal virus or toxin.
Serotonin (5HT) is a neurotransmitter which is involved
in many behaviors; as examples:
Human mood disorders (depressions) are effectively
treated with drugs which specifically block the
reuptake of serotonin into the presynaptic axon
terminal, for example fluoxetine (Prozac). The
resultant enhanced serotonin activation brings
about a cascade of events ultimately resulting
in a reduced sensitivity of presynaptic autoreceptors
for serotonin and reduced serotonin synthesis.
This suggests that neurotransmitter dysregulation
may be involved in depressive disorders.
Human OCD (Obsessive Compulsive Disorder) is
effectively treated by serotonin reuptake
inhibitors suggesting that this condition
may also be due to dysregulation in serotonin synapses.
Human violence, aggressive behaviors,
and suicide have all been associated
with reduced levels of serotonin in the brain.
Sleep onset latency is reduced with tryptophan which
is the amino acid needed by the brain for the synthesis
of serotonin. This finding suggests that serotonin
may play a role in sleep induction. Grandmother's
suggestion to drink a glass of warm milk before
sleep may be sound, since milk is a good source
Some drugs which distort perception (e.g. LSD)
bind to one type of serotonin receptor
(5-HT2). Serotonin synapses are abundant
in the cerebral cortex making it likely
that they are involved in the processes
of perception in some way.
Norepinephrine (NE) is a neurotransmitter
involved in many behaviors; as examples:
Norepinephrine plays a role in attention and
general arousal level. Waking behavior is
enhanced by drugs which activate norepinephrine
systems while REM sleep (dream sleep) occurs when
norepinephrine systems are at their lowest level of activity.
Brain norepinephrine is depleted in states of
chronic stress and this depletion may contribute
to the harmful effects of stress. Exercise of a
chronic aerobic nature appears to enhance the
brain's ability to deal with stress and protect
it from depletion of norepinephrine.
Norepinephrine is involved in mood states.
Some of the drugs which are used to treat
depressive disorders (tricyclic antidepressants)
block the reuptake of norepinephrine at the synapse.
Norepinephrine is also released as a hormone
from the adrenal glands during stress. This
hormonal norepinephrine acts as an amplifier
for the sympathetic nervous system "fight or
flight" response and is an important aspect
of adaptive behavior in times of challenge.
Interestingly, this hormonal norepinephrine i
s important for learning and the formation of memory.
Amino Acids - Some Examples:
GABA (gamma-aminobutyric acid): GABA is the main
inhibitory neurotransmitter in the brain. Its
actions, which are anxiety reduction, are mediated
by the entry of chloride into a cell when GABA
binds to its postsynaptic receptor site. Drugs
such as Valium which act as anxiolytics (anti-anxiety)
produce their effects by enhancing the effects
of GABA at the synapse. The brain produces
substances which enhance anxiety (beta-carbolines)
as well as substances which reduce anxiety
(e.g. allopregnanolone). All of these substances
seem to modify the GABA receptor in the brain
to produce their effects.
GLU (glutamate): Glutamate is the main excitatory
neurotransmitter in the brain. Its actions are
mediated at two types of receptor sites (NMDA and
AMPA). At the NMDA receptor glutamate binding will
cause calcium to flow into a neuron (but only in
large amounts when the AMPA receptors are also
activated). These receptors are involved in the
process of memory formation in the brain. Curiously,
glutamate is also involved in a "suicidal" response
when the brain is damaged such as in a stroke.
Excess glutamate is neurotoxic and neurons are
killed by the excessive calcium which enters
the cell due to glutamate binding. It is
glutamate which is produced excessively in
ALS (Lou Gherig's Disease) and which causes
the death of neurons in the spinal cord and brainstem.
Peptides - Some Examples:
Endorphins/Enkephalins: Endorphins and enkephalins
are endogenous opiate peptide neurotransmitters
found in a variety of places in the brain
(limbic system, midbrain). They are also
produced by the pituitary gland and released
as hormones. They are involved in pain reduction,
pleasure (they enhance the release of dopamine),
and hibernation as well as a number of other
behaviors. Opiates of the world (natural and synthetic)
all work to alter behavior because of their
ability to bind to endorphin and enkephalin
receptors in the brain.
Substance P: Substance P is one of the
neurotransmitters which mediates the
experience of pain. It is found throughout
the pain pathway and its release can be
blocked by enkephalins.
Neuropeptide Y/Polypeptide YY: NPY and
PPYY are neurotransmitters found in the
hypothalamus, particularly the paraventricular
nucleus. These neurotransmitters bring about
excessive food intake and fat storage and have
been linked with human eating disorders.
Some other neurotransmitters:
Acetylcholine (ACh) is a neurotransmitter
which is involved in many behaviors; as examples:
Movement: Each time you move a muscle it
is because acetylcholine has been released
from a neuron to activate muscle fibers.
Acetylcholine releasing neurons in the pons
are very active in REM sleep (dreaming),
Learning and memory are blocked by drugs which
impair the synthesis and release of acetylcholine,
and in certain cases choline (an amino acid
necessary for the synthesis of acetylcholine)
has been found to improve learning and memory.
Alzheimer's Disease is associated with a 90%
loss in the brain's production of the
neurotransmitter acetylcholine in the
basal forebrain and hippocampus.