Lectures food and brain health
Week 1: Introduction to the course
Brain basics
One can study the brain from several directions:
- Frontal view: from the front.
- Lateral view: from the side.
- Medial view: from the inside of one hemisphere out (eye ear).
- Dorsal view: from the top.
- Ventral view: from the bottom. Mainly used when studying the cerebral vasculature.
It becomes more and more clear that the complete brain is involved in all tasks which are performed.
However, the brain is still divided in a more classic anatomy, showing that certain brain regions play a
(larger) role in certain tasks.
Basal ganglia
Involved in (eye) movement, learning, and decision making.
In Parkinson’s disease, the network in the basal ganglia is
disturbed. Other diseases related to the basal ganglia include
addiction, Huntington’s disease, depression, OCD, and
schizophrenia. The basal ganglia is a term for several brain
regions which tightly work together in a network. The basal
ganglia consist of the following brain regions: nucleus
accumbens, globus pallidus, caudate nucleus (covers the
ventricle), putamen, substantia nigra, and the subthalamic
nucleus.
- The nucleus accumbens in related to addiction.
- The substantia nigra is important in Parkinson’s disease.
- The putamen and globulus pallidus together form the lentiform nucleus.
In Parkinson’s disease the dopaminergic neurons
within the substantia nigra degenerate. The
dopaminergic neurons contain the black pigment
melatonin if there are many dopaminergic neurons
the substantia nigra is dark. During aging the
dopaminergic neurons slowly break down. However,
in Parkinson’s disease the dopaminergic neurons in
the substantia nigra degenerate at a high rate. The
substantia nigra will lose its colour. When 70% of
these neurons is lost, the first symptoms of Parkinson
will arise. Because of the degeneration of these
neurons, the network within the basal ganglia is
disturbed and movement control changes. This result in symptoms including tremor and shuffling
walk. The most effective treatment for Parkinson’s disease is levodopa treatment. Levodopa is a
dopamine precursor. Levodopa is taken up into the blood, transported over the blood-brain-barrier
(BBB) and converted into dopamine. This can reduce some symptoms for a maximum of 5 years. The
treatment gets less effective over time because the patients lose dopamine receptors as well. Also,
because the dopamine levels in the brain are fluctuating because of this treatment, the dopamine
levels are hard to predict and therefore symptoms can fluctuate as well. Before levodopa reaches the
,brain, it has to pass several barriers. Nutrition can be combined with levodopa intak0065 to increase
the amount of levodopa reaching the brain. For example, when taking levodopa together with
protein, the uptake of levodopa is severely reduced Parkinson’s patients should not take their
medication with a high protein meal.
Limbic system
The limbic system covers many brain regions. It
regulates emotion, memory, reward/pleasure,
olfaction, and automatic processes like energy intake
and sleep. The limbic system is related to multiple
disorders including addiction (eating disorders and
cocaine addiction), depression, aggression, ADHD,
autism, post-traumatic stress disorder (PTSD), and
Alzheimer’s disease (AD).
- PTSD is related to the amygdala. The
amygdala is close to the hippocampus and is
involved in emotion regulation.
The limbic system consists of many structures:
- The cingulate gyrus is present in the limbic
system. It covers the corpus collosum, which
is a white matter structure connecting the left
and right hemisphere.
- The dentate gyrus is a part of the hippocampus.
- The fornix is a white matter structure which provides information from and to the
hippocampus.
- The hypothalamus regulates food intake (e.g. leptin and ghrelin), the stress axis, and puberty.
The hypothalamus forms a connection to the periphery.
- The entorhinal cortex lies just below the hippocampus and is important in memory
formation.
- Epithalamus.
- Amygdala.
- Hippocampus is responsible for short-term memory
formation, which is further explained below.
The hippocampus consists of multiple regions, including the
dentate gyrus. There is a pathway between these areas to
store the short-term memory. When certain information is
repeated several times, the hippocampus stores this
information in the neocortex (long-term memory). The hippocampus receives information from the
cingulate gyrus and the amygdala (centre for emotion) a particularly happy or sad day is easier to
remember than a neutral day. The hippocampus transports information to the neocortex via the
fornix and the entorhinal cortex. Long term memories can be retrieved via the entorhinal cortex. In
AD or dementia, the hippocampus degenerates, resulting in memory problems. Patients with these
diseases can retrieve long-term memories, but they are unable to store new information. Symptoms
include amyloid beta-plugs and tangles formed in the hippocampus. Besides symptoms like
forgetfulness and spatial disorientation, doctors diagnose patients based on an MRI scan. In the
figure on the top right, patient A is healthy, but patient B (Alzheimer’s disease) has dark spaces
around the hippocampus. The hippocampus and entorhinal cortex are reduced in size. The large
black hole in patient B is the third ventricle; the hippocampus is close to the third ventricle. The third
ventricle did not increase in size, the hippocampus decreases in size.
,There are many different types of dementia: AD, vascular dementia, combinations with Parkinson’s
disease. Sometimes it is difficult to diagnose the specific type of dementia, and in some cases, this
can only be done post-mortem.
Neurons and glia cells
The brain tissue contains around 100 billion neurons, many blood vessels and
glia cells. There are different types of glia cells:
- Astrocytes are present in the CNS and important for support.
Astrocytes have projections (end-feet) on the complete neurons. These
end-feet sense what the neurons need, e.g. glucose. These end-feet are
also important in maintaining the BBB.
- Oligodendrocytes are present in the CNS and important for myelin
production and action potentials.
- Microglia are present in the CNS and important for neuroinflammation
(the immune system of the brain). Other cells are involved in this
reaction as well, and microglia can provoke infiltration of T-cells and
mast cells. Microglia change in size when active versus non-active.
- Ependymal cells are present in the CNS and present on the outside of
the brain and the inner site of the ventricles. They produce the
cerebrospinal fluid (CBS).
- Schwann cells are present in the PNS and important for myelin production.
- Satellite cells are present in the PNS and important for support.
Most neurons are present in the cerebellum. The
cerebellum is the only brain area which directly
projects on the motor cortex; all other signals have
to travel through the thalamus. The cerebellum is
important for the feedback of movement, e.g. for
perfecting a specific technique in sports. Survival
without the cerebellum is possible, but these people
have difficulty walking (“drunk walk”), and they have
problems to optimize movement.
There are different types of neurons. The multipolar
neuron is the most common. It contains a dendrite
(receives the signal) the cell body decides
whether the signal is proceeded towards other
neurons, or if the signal is terminated. If the signal is proceeded signal towards the axon, which
transports the signal to another neuron via neurotransmitters.
Neurocommunication
If an action potential reaches the synapse membrane
depolarization calcium influx into the pre-synapse.
Neurotransmitters are stored in vesicles in the pre-
synapse.
- Examples of neurotransmitters are serotonin,
dopamine, and glutamate.
Depolarization + calcium influx triggers the vesicle to dock
towards the cell membrane vesicle opens
neurotransmitters are released into the synaptic cleft.
, At the post-synapse – which can be another neuron or another astrocyte – the neurotransmitter can
bind to a receptor signal towards the cell body when enough neurotransmitter is bound.
Depression
In depression the medicine Prozac can be used. Prozac is an SSRI (selective serotonin reuptake
inhibitor): serotonin levels in the synaptic cleft are low in depression and SSRI blocks the reuptake
mechanism of serotonin.
- Normal: serotonin is released in the synaptic cleft signal reuptake into vesicles in the
synapse.
- Prozac: high levels of serotonin will remain in the synaptic cleft. Serotonin can bind to the
receptor multiple times and therefore trigger multiple signals and reduce the symptoms of
depression.
Cocaine
Cocaine blocks the reuptake of dopamine, by competing with the
reuptake mechanism. A high level of dopamine remains in the
synaptic cleft.
Endocannabinoids
Endocannabinoids are fatty acids which are formed from
phospholipids within the neuronal membrane. They are instantly
formed: when an action potential arrives, the post synapse can
decide whether endocannabinoids are produced. When produced,
omega-6 fatty-acids are converted to an endocannabinoid and
released into the extracellular space. Here, the endocannabinoid
can bind an endocannabinoid receptor and inhibit the release of
glutamate and GABA. Endocannabinoids are not taken up again;
they are degenerated in the extracellular space. They can
communicate with the pre-synapse sending the signal and with astrocytes.
Endocannabinoids are for example involved in taste: high level of endocannabinoids preference
for sweet taste (high caloric foods).
Marihuana
When smoking marihuana or weed some people start craving a certain type of food. These foods are
often high in calories, fat, sugary, and sweet. This can be explained because a molecule in marihuana
(cannabinoid) can bind the endocannabinoid receptor 1 (CB1R). Thereby, it triggers the same
responses as endocannabinoids, and triggers a preference for sweet taste.
Synaptic plasticity
Synaptic plasticity is important in memory formation.
Upon an initial trigger, a certain number of
neurotransmitters are released, triggering a certain
response. Once the trigger is repeated, the long-term
potentiation will result in a more solid connection
between synapses through formation of more synapses,
higher release of neurotransmitters and more receptors.
Once a subject is memorized, there are stable activated synapses formed, which are able to directly
communicate.
Brain tissue
