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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