Kynurenic acid and schizophrenia

Area of Science:

• Neuroscience
• Psychiatry
• Pharmacology

Background:

• The dopamine (DA) hypothesis of schizophrenia is evolving to include the role of glutamatergic neurotransmission.
• Schizophrenia may be characterized as a glutamate deficiency disorder.
• Kynurenic acid (KYNA), an endogenous N-methyl D-aspartate (NMDA) receptor antagonist, influences neurophysiology.

Purpose of the Study:

• To investigate the role of kynurenic acid (KYNA) in schizophrenia pathogenesis.
• To examine the association between elevated KYNA levels and psychotomimetic effects.
• To explore how KYNA affects dopamine neuron activity and antipsychotic drug response.

Main Methods:

• Pharmacologically elevated KYNA levels in rats using PNU 156561A.
• Administration of PCP or ketamine to assess psychotomimetic effects.
• Measurement of cerebrospinal fluid (CSF) KYNA levels in schizophrenic patients and healthy controls.
• Evaluation of clozapine's effect on dopamine neurons in rats with varying KYNA levels.

Main Results:

• Pharmacologically elevated KYNA in rats increased midbrain dopamine (DA) neuron firing and burst activity, mimicking PCP/ketamine effects.
• Cerebrospinal fluid (CSF) KYNA levels were significantly higher in first-episode schizophrenic patients compared to controls.
• Elevated brain KYNA reversed clozapine's typical excitatory effect on DA neurons to an inhibitory response.

Conclusions:

• Elevated kynurenic acid (KYNA) contributes to schizophrenia pathogenesis.
• This finding links the dopamine hypothesis with the concept of glutamate deficiency in schizophrenia.
• KYNA may be a key factor in the altered neurophysiology observed in schizophrenia.