Subanesthetic effects of the noncompetitive NMDA antagonist, ketamine, in humans. Psychotomimetic, perceptual, cognitive, and neuroendocrine responses.
BACKGROUND
To characterize further behavioral, cognitive, neuroendocrine, and physiological effects of subanesthetic doses of ketamine hydrochloride in healthy human subjects. Ketamine, a phencyclidine hydrochloride derivative, is a dissociative anesthetic and a noncompetitive antagonist of the N-methyl-D-aspartate subtype of excitatory amino acid receptor.


METHODS
Nineteen healthy subjects recruited by advertisements from the community participated in this randomized, double-blind, placebo-controlled study. Subjects completed three test days involving the 40-minute intravenous administration of placebo, ketamine hydrochloride (0.1 mg/kg), or ketamine hydrochloride (0.5 mg/kg). Behaviors associated with the positive and negative symptoms of schizophrenia were assessed by using the Brief Psychiatric Rating Scale. Changes in perception and behaviors associated with dissociative states were assessed by the Perceptual Aberration Subscale of the Wisconsin Psychosis Proneness Scale and the Clinician-Administered Dissociative States Scale. Cognitive function was assessed by using the (1) Mini-Mental State Examination; (2) tests sensitive to frontal cortical dysfunction, including a continuous performance vigilance task, a verbal fluency task, and the Wisconsin Card Sorting Test; and (3) tests of immediate and delayed recall. Plasma levels of cortisol, prolactin, homovanillic acid, and 3-methoxy-4-hydroxyphenethyleneglycol were measured.


RESULTS
Ketamine (1) produced behaviors similar to the positive and negative symptoms of schizophrenia; (2) elicited alterations in perception; (3) impaired performance on tests of vigilance, verbal fluency, and the Wisconsin Card Sorting Test; (4) evoked symptoms similar to dissociative states; and (5) preferentially disrupted delayed word recall, sparing immediate recall and postdistraction recall. Ketamine had no significant effect on the Mini-Mental State Examination at the doses studied. Ketamine also had no effect on plasma 3-methoxy-4-hydroxyphenethyleneglycol levels, although it blunted a test day decline in plasma homovanillic acid levels at the higher dose. It also dose dependently increased plasma cortisol and prolactin levels. Ketamine produced small dose-dependent increases in blood pressure.


CONCLUSIONS
These data indicate that N-methyl-D-aspartate antagonists produce a broad range of symptoms, behaviors, and cognitive deficits that resemble aspects of endogenous psychoses, particularly schizophrenia and dissociative states.
Krystal
J H
JH
Department of Psychiatry, Yale University School of Medicine, New Haven, Conn.
Karper
L P
LP
Seibyl
J P
JP
Freeman
G K
GK
Delaney
R
R
Bremner
J D
JD
Heninger
G R
GR
Bowers
M B
MB
Charney
D S
DS
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D003071:Cognition / Q000187:drug effects; D004213:Dissociative Disorders / Q000139:chemically induced / Q000175:diagnosis / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D005625:Frontal Lobe / Q000187:drug effects / Q000502:physiology; D006719:Homovanillic Acid / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000097:blood; D009483:Neuropsychological Tests; D010465:Perception / Q000187:drug effects; D011388:Prolactin / Q000097:blood; D011569:Psychiatric Status Rating Scales; D011605:Psychoses, Substance-Induced / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D011674:Pulse / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects* / Q000502:physiology; D012559:Schizophrenia / Q000139:chemically induced* / Q000175:diagnosis / Q000503:physiopathology; D012565:Schizophrenic Psychology
D016194:Receptors, N-Methyl-D-Aspartate; D008734:Methoxyhydroxyphenylglycol; D007649:Ketamine; D011388:Prolactin; D006854:Hydrocortisone; D006719:Homovanillic Acid