Faculty Bibliography

BACKGROUND: Neuroimaging studies of schizophrenic subjects performing working memory (WM) tasks have demonstrated a relative hypoactivity of prefrontal cortex compared with normal subjects. METHODS: Using functional magnetic resonance imaging (fMRI), we compared dorsolateral prefrontal cortex (DLPFC) activation in 12 schizophrenic and 10 normal subjects during rewarded performance of a WM task. Subjects performed a modified version of the Sternberg Item Recognition Paradigm (SIRP), a continuous performance, choice reaction time (RT) task that requires WM. We compared a high WM load condition with a nonWM choice RT condition and with a low WM load condition. RESULTS: Schizophrenic subjects performed the tasks better than chance but worse than normal subjects. They showed greater activation than normal subjects in the left DLPFC but did not differ in the right DLPFC or in the control region. In the schizophrenic group, left DLPFC activation was inversely correlated with task performance, as measured by errors. CONCLUSIONS: These findings contrast with previous studies that demonstrated task-related hypofrontality in schizophrenia. Task parameters that may contribute to this difference are discussed. We hypothesize that the performance and activation differences we observed are also manifestations of prefrontal dysfunction in schizophrenia. They reflect inefficient functioning of the neural circuitry involved in WM.

BACKGROUND: D-Cycloserine, a partial agonist at the glycine recognition site of the NMDA receptor, has previously been shown to improve negative symptoms when added to conventional antipsychotics and, in one preliminary dose-finding study, worsened negative symptoms when added to clozapine. METHODS: Seventeen schizophrenia outpatients treated with clozapine were assigned in random order to 6-week trials of D-cycloserine 50 mg/day and placebo in a crossover design separated by a 1 week placebo washout. RESULTS: Eleven patients competed the 13-week study. D-Cycloserine significantly worsened ratings of negative symptoms compared to placebo but did not significantly affect ratings of psychotic symptoms. CONCLUSIONS: The differing effects of D-cycloserine on negative symptoms when added to clozapine compared to conventional antipsychotics suggests that activation of the glycine recognition site may play a role in clozapine's efficacy for negative symptoms.

BACKGROUND: In a preliminary dose-finding study, D-cycloserine, a partial agonist at the glycine modulatory site of the glutamatergic N-methyl-D-aspartate (NMDA) receptor, improved negative symptoms and cognitive function when added to conventional neuroleptics at a dose of 50 mg/d. METHODS: Forty-seven patients with schizophrenia meeting criteria for deficit syndrome were randomized to D-cycloserine, 50 mg/d (n=23) or placebo (n=24) added to their conventional neuroleptic for an 8-week, double-blind trial. Clinical assessments were performed at baseline and at weeks 1, 2, 4, 6, and 8. Serum concentrations of D-cycloserine, relevant amino acids, and homovanillic acid were assayed at baseline and at weeks 4 and 8. A cognitive battery was performed at baseline and at week 8. RESULTS: Thirty-nine patients completed the 8-week trial. Seven dropouts occurred in the D-cycloserine group and 1 in the placebo group. The mean reduction in negative symptoms with D-cycloserine (23%) was significantly greater than with placebo (7%) as calculated by slopes representing Scale for the Assessment of Negative Symptoms (SANS) total scores. Improvement of negative symptoms was predicted by low neuroleptic dose and low baseline SANS total score. No differences were found in performance on any cognitive test between groups or in changes in any other clinical measure. Clinical response did not correlate significantly with serum amino acid concentrations at baseline or with concentrations of D-cycloserine at weeks 4 and 8. CONCLUSION: These results support the hypothesis that agents acting at the glycine modulatory site of the NMDA receptor improve primary negative symptoms.

Evidence from lesioning studies and neuroimaging has linked negative symptoms to dysfunction of the prefrontal cortex, the limbic system, and the basal ganglia. Although such symptoms have been most strongly associated with dopaminergic hypoactivity in the prefrontal cortex, other neurotransmitters including norepinephrine, serotonin, and the excitatory amino acids may also play a role. In some patients moderate doses of conventional neuroleptics clearly improve negative symptoms; the response of such symptoms is relatively greater with clozapine and probably with certain serotonin-dopamine antagonists. Recent studies demonstrating improvement of negative symptoms when conventional neuroleptics are augmented with selective serotonin-reuptake inhibitors or with agents active at the glycine-modulatory site of the glutamatergic N-methyl-D-aspartate receptor complex suggest that further amelioration of primary negative symptoms may be possible through pharmacological strategies involving multiple neurotransmitter systems.

Schizophrenic outpatients (62 females, 59 males) were evaluated to examine the relationships between menstrual status, gender, clinical measures of psychopathology and drug side effects. Menstrual status was determined for 55 female patients. Blood from 44 female subjects, drawn before the AM dose of neuroleptic, was assayed for prolactin concentrations. In 27 premenopausal women (age < 45 years), six (22%) reported irregular menses and one (4%) reported amenorrhea. Women with irregular menses did not differ in their prolactin levels or neuroleptic dose, from women with regular menses. Amenorrheic women (n = 22) were significantly older than men (n = 59) and menstruating women (n = 33). After controlling for age, menstruating women did not differ in clinical measures of psychopathology, drug side effects, or neuroleptic dose compared to amenorrheic women or men. Comparison of 15 age-matched pairs of menstruating females and amenorrheic females revealed significantly lower levels of akathisia and depression in the menstruating group and a trend towards lower serum prolactin concentrations (P = 0.08). In female subjects, prolactin levels correlated significantly with neuroleptic dose (r = 0.36, P < 0.005). Our results only partially support hypothesized relationships between menstrual status, prolactin levels and neuroleptic effects and serve to emphasize the importance of controlling for age when comparing these clinical variables.

OBJECTIVE: Tardive dyskinesia is a movement disorder affecting 20%-40% of patients treated chronically with neuroleptic drugs. The dopamine supersensitivity hypothesis cannot account for the time course of tardive dyskinesia or for the persistence of tardive dyskinesia and the associated structural changes after neuroleptics are discontinued. The authors hypothesized that neuroleptics enhance striatal glutamatergic neurotransmission by blocking presynaptic dopamine receptors, which causes neuronal damage as a consequence of oxidative stress. METHOD: CSF was obtained from 20 patients with schizophrenia, 11 of whom had tardive dyskinesia. Markers for oxidative stress, including superoxide dismutase, lipid hydroperoxide, and protein carbonyl groups, and markers for excitatory neurotransmission, including N-acetylaspartate, N-acetylaspartylglutamate, aspartate, and glutamate, were measured in the CSF specimens. Patients were also rated for tardive dyskinesia symptoms with the Abnormal Involuntary Movement Scale. RESULTS: Tardive dyskinesia patients had significantly higher concentrations of N-acetylaspartate, N-acetylaspartylglutamate, and aspartate in their CSF than patients without tardive dyskinesia when age and neuroleptic dose were controlled for. The significance of the higher levels of protein-oxidized products associated with tardive dyskinesia did not pass Bonferroni correction, however. Tardive dyskinesia symptoms correlated positively with markers of excitatory neurotransmission and protein carbonyl group and negatively with CSF superoxide dismutase activity. CONCLUSIONS: These findings suggest that there are elevated levels of oxidative stress and glutamatergic neurotransmission in tardive dyskinesia, both of which may be relevant to the pathophysiology of tardive dyskinesia.