Prepulse inhibition (PPI) of the startle reflex, a measure of sensorimotor gating, is decreased in
schizophrenia. The validity of a glutamatergic,
N-methyl-d-aspartate receptor (NMDAR)-mediated model of PPI disruption is presently equivocal. The NMDAR antagonist
ketamine disrupts PPI in rodents, but may increase PPI in healthy volunteers.
Glycine (GLY), which acts as an obligatory co-agonist at the NMDAR-GLY site, induces PPI deficits in rats although, consistent with the hypo-NMDAR hypothesis, improves negative and
cognitive symptoms in
schizophrenia patients. We assessed the hypothesis that GLY serum levels may affect PPI parameters in
schizophrenia. Forty-five
chronically ill medicated
schizophrenia patients and 37 matched healthy comparison subjects were tested for PPI of the eyeblink component of the startle reflex measured by electromyogram recording. Patients' demographic variables, symptom severity scores and GLY,
serine and
glutamate serum levels were obtained. Patients showed deficient PPI in blocks two and three of the PPI session and differed from controls in terms of change of degree of PPI as a function of the prepulse to eliciting stimulus interval. GLY levels correlated negatively with PPI parameters, such that patients with the highest GLY levels showed decreased PPI (rs=-0.4, p=0.03). These preliminary findings indirectly support previous observations on
ketamine effects upon PPI in humans and suggest a dissociation of symptomatology and PPI changes as function of NMDAR modulation in
schizophrenia.