Chlorpromazine  is a typical
phenothiazine antipsychotic drug, which act as antagonist to dopamine D2
receptor that used to treat schizophrenia.

Ø  Normally, dopamine is released by the
presynaptic membrane in the mesolimbic pathway of the brain and binds to dopaminergic D2 receptors,
which are the GPCR coupled to inhibitory G-protein, dopamine binding consequences
in dissociation of the G-protein to G?i. G?i ? inhibit AC ? inhibits cAMP ? inhibit
PKA from being activated ? less Ca release (Tritsch et al., 2015). In schizophrenic brain, the
receptors on the postsynaptic membrane are too sensitive to its effect,
resulting in an over receptivity to dopamine. Chlorpromazine acts as an
antagonist on dopaminergic receptors, therefore, preventing the over activity
of dopamine, which leads to the blocking of the positive symptoms of schizophrenia (e.g., delusions, hallucinations and disorganized speech) (Bernard et al., 2008).

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For the short
term management of anxiety, agitation or disturbed behavior of psychiatric
conditions, chlorpromazine antagonizes two receptors: 5HT-2 receptor and H1
receptor.

Ø  Serotonin binds to (5HT-2) receptors which are GPCR coupled to Gq protein, then PIP2 is cleaved by PLC to DAG and IP3 (results in release of Ca)( Roth,
 2015).Serotonin participates in
modulating glutamate release, stimulates stress hormone release and activates CRF,
that consequence in anxiogenic effects(Ciranna, 2006). Chlorpromazine blocks the
serotonin receptors, subsequently, lowering both glutamate and stress hormone
release, which results in reducing aggression, anxiety and disturbed behaviors.

 

Ø  Histamine (H1) receptors, H1 receptors are coupled to Gq proteins, then PIP2 is cleaved by PLC to DAG and IP3 (results in release of Ca) (Billington et al., 2003). H1 receptor can
inhibit k channels in neurons, leading to depolarization and thus increasing
neuronal excitation. Chlorpromazine acts as histamine antagonist, consequently,
decrease histamine effects and k channels are no longer inhibited and no
neuronal excitation, which results in reducing aggression, anxiety and
disturbed behaviors (Sergeeva,
2009).