Bannon: Antipsychotic Drugs Flashcards
Schizophrenia
Epidemiology:
- Affect 1% of the population worldwide
- 30% of all homeless people
- 30% of all hospitalizations
.
Schizophrenia Psychotic Symptoms (Positive/Cognitive Symptoms): (3)
Psychotic Symptoms (Positive/Cognitive Symptoms): emerge in late teens
o Loss of reality
o Delusions and hallucinations (usually auditory)
o Disordered thinking and memory
.
Schizophrenia Prodromal Signs (Negative Symptoms): (5)
Prodromal Signs (Negative Symptoms): poorer prognosis associated with prominent negative symptoms o Social isolation and withdrawal o Poverty of speech o Odd behavior/ideas o Blunted affect o Lack of motivation
Schizophrenia
Biological Findings: (3)
Biological Findings: especially associated with negative symptoms
- Decreased blood flow in frontal lobe and caudate during working memory tasks
- Reduced hippocampal and medial temporal lobe volume
- Enlarged ventricles
Schizophrenia
Genetic Predisposition:
15% incidence in first degree relatives (compared to 1% incidence in the general population)
17% concordance in DZ twins; ~50% concordance in MZ twins
Complex polygenic disorder (as evidenced by high frequency and partial penetrance)
Schizophrenia
Dopamine Hypothesis
Evidence for the Involvement of DA: (3)
- Dopamine agonists can induce/exacerbate psychosis
- Clinically effective APDs block DA receptors
- DA receptor expression increased in schizophrenia (has since been proven UNTRUE)
Dopamine Receptors:
Dopamine Receptors: G-protein coupled receptors
D1 Family includes:
D1 Family: includes D1 and D5 (less prominent)
D1 Family
Location:
Location:
- D1: striatum and neocortex*
- D5: hippocampus and hypothalamus
D1 Family Second Messengers (Gq):
Second Messengers (Gq):
- Increase cAMP
- Increase PIP2 hydrolysis (PKC activation and Ca++ mobilization)
D2 Family includes:
D2 Family: D2, D3 and D4 (latter 2 less prominent)
D2 Family
Location:
D2: striatum, substantia nigra and pituitary gland*
D3: olfactory tubercle, nucleus accumbens, hypothalamus
D4: frontal cortex, medulla, midbrain
D2 Family Second Messengers (Gi):
Decrease cAMP
Increase K+ currents
Decrease voltage-gated Ca++ currents
Dopamine Pathways: single source divergent systems
Nigrostriatal DA:
Mesolimbic DA:
Nigrostriatal DA: modulates movement and learned habits; 80% of total DA
Mesolimbic DA: modulates motivation, goal-directed thinking, affect and reward
Dopamine Pathways: single source divergent systems
Mesocortical DA:
Hypothalamic DA:
Area postrema:
Mesocortical DA: modulates cognition
Hypothalamic DA: hormone regulation
Area postrema: located outside the BBB; mediates emesis (very sensitive to DA drugs)
Dopamine Pathways and their Relation to Psychotic Symptoms
Mesolimbic/Mesocortical DA:
Mesolimbic/Mesocortical DA: overactive –>possibly related to positive Sx
Dopamine Pathways and their Relation to Psychotic Symptoms
Mesocortical DA:
Mesocortical DA: hypofunction –> possibly related to negative Sx (DA blockade not helpful for these)
Dopamine Pathways and their Relation to Psychotic Symptoms
Nigrostriatal DA:
Nigrostriatal DA: highest DA content and related to extrapyramidal (motor) SEs and tardive dyskinesia
Dopamine Pathways and their Relation to Psychotic Symptoms
Tuberoinfundibular/Hypothalamic DA:
Tuberoinfundibular/Hypothalamic DA: related to endocrine effects
D2R Blockade and Clinical Efficacy:
D2R Blockade and Clinical Efficacy: strong correlation between blockage for these R and efficacy
Original D2 Blocking Agents (ie. Chlorpromazine):
Original D2 Blocking Agents (ie. Chlorpromazine): not a real high affinity for D2 receptors and therefore needed very high doses to achieve desired effects (lots of SE)
Newer D2 Blocking Agents with Higher Affinity (ie. Spiroperidol):
Newer D2 Blocking Agents with Higher Affinity (ie. Spiroperidol): although higher affinity, do not have improved efficacy over earlier agents; however, will have different SE profiles
Commonality in APDs Relevant to Antipsychotic Effects
Possibilities
5HT2A:
D4 in cortex:
5HT2A: typical APDs occupy most striatal D2 receptors while atypical APDs occupy a lower proportion of D2 R and more 5HT2A; however, role for 5HT2A receptors in psychosis not clear
D4 in cortex: but not all block here (ie. quetiapine)
Commonality in APDs Relevant to Antipsychotic Effects
Possibilities
Fast dissociation relative to R binding allows better modulation of function (ie. high Kd at D2):
Fast dissociation relative to R binding allows better modulation of function (ie. high Kd at D2): but then atypical APDs should look like low-affinity typical APDs (not the case)
Commonality in APDs Relevant to Antipsychotic Effects
Another issue:
Another issue: blockade of receptors is immediate but effects are delayed
Commonality in APDs Relevant to Antipsychotic Effects
BOTTOM LINE:
Antipsychotic MOA(s) still not really understood
However, D2 DA receptor blockade is a commonality to all agents