Schizophrenia: Neurotransmitter Tracts & Other Causes – Psychiatry | Lecturio

Schizophrenia: Neurotransmitter Tracts & Other Causes – Psychiatry | Lecturio


Now, we’re going to talk about one of the
most important of the psychotic disorders, which is schizophrenia. So what is schizophrenia? It’s a psychiatric disorder characterized by a
constellation of abnormalities in thinking, in
motion, and behavior. Here’s some facts about schizophrenia. It affects approximately 1% of
people over their lifetime. Men and women are equally affected. Men present with a disorder
around 20 years of age whereas women tend to present a little
bit older, around 30 years of age. It’s very rare for someone to present
with symptoms of schizophrenia before age 15 or
after the age of 45. Here’s a question for you, what season of birth is associated
with higher rates of schizophrenia? Winter birth. And there are a few thoughts
about why this is. Maybe because environmental
stressors such as cold weather, nutritional deficiencies or
exposure to infectious agents during this time of year occur. There are a lot of different hypotheses in
terms of the pathogenesis of schizophrenia. The most prominent of which are the
dopaminergic pathway hypotheses. So being that there’s a disruption
in either the mesolimbic pathway, which creates what we call positive
symptoms of schizophrenia, the mesocortical pathway, which
produces negative symptoms, the nigrostriatal pathway, which is
involved in extrapyramidal symptoms and also tardive dyskinesia, or the tuberoinfundibular pathway
involved in hyperprolactinemia. We’ll go through each of these
in a little bit more detail now. The mesolimbic pathway plays
a key and complex role in our motivation, emotions, reward and positive symptoms,
therefore, of schizophrenia. The mesocortical pathway is
relevant to the physiology of cognition and
executive function. This is in the dorsolateral
prefrontal cortex. Emotions and affect are involved in
the ventromedial prefrontal cortex and hypofunction of this
pathway might be related to the cognitive and negative symptoms
that are seen in schizophrenia. The nigrostriatal pathway contains
about 80% of the brain’s dopamine, a very important neurotransmitter
that we think is highly dysregulated in individuals who have psychotic
disorders especially schizophrenia. The nigrostriatal pathway is
involved in motor planning and dopaminergic neurons
stimulate purposeful movements. Dopaminergic projections in the
tuberoinfundibular pathway influence the release
of prolactin. The dopamine is released
into the portal circulation connecting the median eminence
with the anterior pituitary gland. The role of dopamine release in
the tuberoinfundibular pathway is to tonically inhibit
prolactin release. And so when this
pathway is disrupted, that’s why we think people
get hyperprolactinemia. Other causes of schizophrenia include
the downward drift hypothesis, which is where individuals who
are affected by the illness tend to follow a downward
trajectory in terms of not always being very highly educated, not being able to
sustain stable jobs and then basically
deteriorating and drifting downward in the
socioeconomic stratosphere, which then perpetuates
meeting someone and producing children who are going
to be more susceptible to the illness. Other neurotransmitters
that are implicated include serotonin, histamine, norepinephrine
and GABA and glutamate. You might ask why is glutamate an
excitatory amino acid neurotransmitter of any interest in
schizophrenia research? The answer is that the NMDA glutamate
receptor is blocked by PCP and produces a clinical syndrome
similar to schizophrenia including the positive and negative symptoms
as well as formal thought disorder. Here’s a question as well, what are the psychiatric indications
for neuroimaging studies? You want to do neuroimaging studies
such as a CT scan of the brain or MRI in any person who’s presenting with
a first time psychotic episode. Again, it’s very important to
rule out medical problems. You also want to do head imaging
when somebody’s acutely confused, if there’s dementia of unknown
cause, prolonged catatonia, if there’s a movement
disorder of unknown origin or a personality change in
someone over the age of 55. These are all indications
to do head imaging. Another question to consider here, what is the most consistent
functional neuroimaging study finding in people with schizophrenia? The answer is hypofrontality.

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