Infants later diagnosed with autism have lower canonical babbling ratios in the first year of life

BACKGROUND

Canonical babbling-producing syllables with a mature consonant, full vowel, and smooth transition-is an important developmental milestone that typically occurs in the first year of life. Some studies indicate delayed or reduced canonical babbling in infants at high familial likelihood for autism spectrum disorder (ASD) or who later receive an ASD diagnosis, but evidence is mixed. More refined characterization of babbling in the first year of life in infants with high likelihood for ASD is needed.

METHODS

Vocalizations produced at 6 and 12 months by infants (n = 267) taking part in a longitudinal study were coded for canonical and non-canonical syllables. Infants were categorized as low familial likelihood (LL), high familial likelihood diagnosed with ASD at 24 months (HL-ASD) or not diagnosed (HL-Neg). Language delay was assessed based on 24-month expressive and receptive language scores. Canonical babble ratio (CBR) was calculated by dividing the number of canonical syllables by the number of total syllables. Generalized linear (mixed) models were used to assess the relationship between group membership and CBR, controlling for site, sex, and maternal education. Logistic regression was used to assess whether canonical babbling ratios at 6 and 12 months predict 24-month diagnostic outcome.

RESULTS

No diagnostic group differences in CBR were detected at 6 months, but HL-ASD infants produced significantly lower CBR than both the HL-Neg and LL groups at 12 months. HL-Neg infants with language delay also showed reduced CBR at 12 months. Neither 6- nor 12-month CBR was significant predictors of 24-month diagnostic outcome (ASD versus no ASD) in logistic regression.

LIMITATIONS

Small numbers of vocalizations produced by infants at 6 months may limit the reliability of CBR estimates. It is not known if results generalize to infants who are not at high familial likelihood, or infants from more diverse racial and socioeconomic backgrounds.

CONCLUSIONS

Lower canonical babbling ratios are apparent by the end of the first year of life in ASD regardless of later language delay, but are also observed for infants with later language delay without ASD. Canonical babbling may lack specificity as an early marker when used on its own.

Characterizing Social Functioning in School-Age Children with Sensory Processing Abnormalities

Children with sensory abnormalities (SAs) have a variety of social problems resulting in poorer social functioning than children with typical development (TD). We describe the relationship between SAs and social functioning in school-age children with SAs, children with TD and a clinical comparison sample of children with autism spectrum disorder (ASD). Children with SAs demonstrated impaired social functioning on standardized measures. Children with SAs demonstrated worse social functioning than children with TD and equivalent social functioning to children with ASD. Increased SAs were associated with poorer social functioning across all groups. The results suggest that children with SAs experience clinically significant problems with social functioning and future research is needed to develop interventions to support social functioning in this population.

A voxel-wise assessment of growth differences in infants developing autism spectrum disorder

•

Pediatric neuroimaging study of Autism Spectrum Disorder.

•

Longitudinal Tensor Based Morphometry of the presymptomatic period of ASD.

•

Differences in voxelwise growth trajectories of children with ASD.

•

Regions with differences have been implicated in the core symptoms of ASD.

Autism Spectrum Disorder (ASD) is a phenotypically and etiologically heterogeneous developmental disorder typically diagnosed around 4 years of age. The development of biomarkers to help in earlier, presymptomatic diagnosis could facilitate earlier identification and therefore earlier intervention and may lead to better outcomes, as well as providing information to help better understand the underlying mechanisms of ASD. In this study, magnetic resonance imaging (MRI) scans of infants at high familial risk, from the Infant Brain Imaging Study (IBIS), at 6, 12 and 24 months of age were included in a morphological analysis, fitting a mixed-effects model to Tensor Based Morphometry (TBM) results to obtain voxel-wise growth trajectories. Subjects were grouped by familial risk and clinical diagnosis at 2 years of age. Several regions, including the posterior cingulate gyrus, the cingulum, the fusiform gyrus, and the precentral gyrus, showed a significant effect for the interaction of group and age associated with ASD, either as an increased or a decreased growth rate of the cerebrum. In general, our results showed increased growth rate within white matter with decreased growth rate found mostly in grey matter. Overall, the regions showing increased growth rate were larger and more numerous than those with decreased growth rate. These results detail, at the voxel level, differences in brain growth trajectories in ASD during the first years of life, previously reported in terms of overall brain volume and surface area.

Astrocytic water channel aquaporin-4 modulates brain plasticity in both mice and humans: a potential gliogenetic mechanism underlying language-associated learning

The role of astrocytes in brain plasticity has not been extensively studied compared with that of neurons. Here we adopted integrative translational and reverse-translational approaches to explore the role of an astrocyte-specific major water channel in the brain, aquaporin-4 (AQP4), in brain plasticity and learning. We initially identified the most prevalent genetic variant of AQP4 (single nucleotide polymorphism of rs162008 with C or T variation, which has a minor allele frequency of 0.21) from a human database (n=60 706) and examined its functionality in modulating the expression level of AQP4 in an in vitro luciferase reporter assay. In the following experiments, AQP4 knock-down in mice not only impaired hippocampal volumetric plasticity after exposure to enriched environment but also caused loss of long-term potentiation after theta-burst stimulation. In humans, there was a cross-sectional association of rs162008 with gray matter (GM) volume variation in cortices, including the vicinity of the Perisylvian heteromodal language area (Sample 1, n=650). GM volume variation in these brain regions was positively associated with the semantic verbal fluency. In a prospective follow-up study (Sample 2, n=45), the effects of an intensive 5-week foreign language (English) learning experience on regional GM volume increase were modulated by this AQP4 variant, which was also associated with verbal learning capacity change. We then delineated in mice mechanisms that included AQP4-dependent transient astrocytic volume changes and astrocytic structural elaboration. We believe our study provides the first integrative evidence for a gliogenetic basis that involves AQP4, underlying language-associated brain plasticity.

Shape mapping of the hippocampus in young children with autism spectrum disorder

BACKGROUND AND PURPOSE

We hypothesized the occurrence of characteristic hippocampal-shape alterations in young children with autistic spectrum disorder (ASD) who also exhibit deficits on neuropsychologic tests of medial temporal lobe (MTL) function.

MATERIALS AND METHODS

Coronal 3D MR images were acquired from 3- to 4-year-old children with ASD (n = 45) and age-matched children with typical development (n = 13). Children with ASD were further subclassified into those with autism disorder (AD, n = 29) or pervasive developmental disorder-not otherwise specified (PDD-NOS) (n = 16). Variations in hippocampal shape were evaluated by using large-deformation high-dimensional brain mapping.

RESULTS

Hippocampal shape measures distinguished children with ASD from those with typical development; within the ASD sample, children with AD were distinguished from those with PDD-NOS. Hippocampal-shape alterations in children with ASD were correlated with degree of mental retardation and performance deficits on tests of MTL function.

CONCLUSIONS

Children with ASD exhibited an alteration of hippocampal shape consistent with inward deformation of the subiculum. This pattern of hippocampal-shape deformations in the children with ASD was accentuated in the more severely affected subgroup of children with AD and was associated with deficits on neuropsychologic tests of MTL but not prefrontal function. Hippocampal-shape deformation in the children with ASD was observed to be similar to a pattern of hippocampal shape deformation previously reported in adults with MTL epilepsy. Although the children with ASD, and those with AD in particular, PDD-NOS are at high risk for epilepsy as they enter adolescence, the specificity and causal relationship of this pattern of hippocampal-shape deformation to the development of seizures is not yet known.

Gray matter abnormalities in autism spectrum disorder revealed by T2 relaxation

OBJECTIVE

To perform quantitative T2 relaxation measurements to evaluate cerebral water content in children with autism.

METHODS

Sixty 2- to 4-year-old children with autism spectrum disorder (ASD), 16 age-matched children with idiopathic developmental delay (DD), and 10 children with typical development (TD) were scanned on a 1.5 T GE MRI scanner to obtain dual-echo fast spin echo images (2.5 mm thick, 0-mm gap). Images were segmented into gray and white matter and used to mask regions of interest for calculating T2 for each tissue type. Analysis of variance, covarying for age and sex, was used to compare T2 between groups, and correlations were used to compare T2 to IQ measures.

RESULTS

Children with ASD had prolonged cortical gray matter T2, but white matter T2 was not significantly different, compared with the children with TD. T2 was prolonged in cortical gray matter and white matter in children with DD compared with children with ASD or TD. Significant interactions between T2 measures and IQ were not observed.

CONCLUSIONS

Prolonged gray and white matter T2 in the children with developmental delay likely represents a delay in neuronal development and maturation. Prolonged T2 in gray matter, but not white matter, observed in children with autism spectrum disorder may signify abnormal developmental processes specific to autism.

Regional brain chemical alterations in young children with autism spectrum disorder

OBJECTIVE

The authors evaluated regional brain chemistry for evidence of increased neuronal packing density in autism.

METHODS

Forty-five 3- to 4-year-old children with autism spectrum disorder (ASD), 13 children with typical development (TD), and 15 children with delayed development (DD) were studied using dual-echo proton echoplanar spectroscopic imaging (32 x 32 matrix-1 cm(3) voxels) to measure brain chemical concentrations and relaxation times. Chemical quantification was corrected for tissue partial volume and relative measures of chemical relaxation (T(2r)) were calculated from the paired echoes. Measures from averaged and individual regions were compared using analysis of variance corrected for multiple comparisons.

RESULTS

ASD subjects demonstrated reduced N-acetylaspartate (NAA) (-10%), creatine (Cre) (-8%), and myo-inositol (-13%) concentrations compared to TD controls and prolonged NAA T(2r) relative to TD (7%) and DD (9%) groups. Compared to DD subjects, children with ASD also demonstrated prolonged T(2r) for choline (10%) and Cre (9%). Regional analyses demonstrated subtle patterns of chemical alterations in ASD compared to the TD and DD groups.

CONCLUSIONS

Brain chemical abnormalities are present in ASD at 3 to 4 years of age. However, the direction and widespread distribution of these abnormalities do not support hypothesis of diffuse increased neuronal packing density in ASD.

Brain structural abnormalities in young children with autism spectrum disorder

OBJECTIVE

To explore the specific gross neuroanatomic substrates of this brain developmental disorder, the authors examine brain morphometric features in a large sample of carefully diagnosed 3- to 4-year-old children with autism spectrum disorder (ASD) compared with age-matched control groups of typically developing (TD) children and developmentally delayed (DD) children.

METHODS

Volumes of the cerebrum, cerebellum, amygdala, and hippocampus were measured from three-dimensional coronal MR images acquired from 45 children with ASD, 26 TD children, and 14 DD children. The volumes were analyzed with respect to age, sex, volume of the cerebrum, and clinical status.

RESULTS

Children with ASD were found to have significantly increased cerebral volumes compared with TD and DD children. Cerebellar volume for the ASD group was increased in comparison with the TD group, but this increase was proportional to overall increases in cerebral volume. The DD group had smaller cerebellar volumes compared with both of the other groups. Measurements of amygdalae and hippocampi in this group of young children with ASD revealed enlargement bilaterally that was proportional to overall increases in total cerebral volume. There were similar findings of cerebral enlargement for both girls and boys with ASD. For subregion analyses, structural abnormalities were observed primarily in boys, although this may reflect low statistical power issues because of the small sample (seven girls with ASD) studied. Among the ASD group, structural findings were independent of nonverbal IQ. In a subgroup of children with ASD with strictly defined autism, amygdalar enlargement was in excess of increased cerebral volume.

CONCLUSIONS

These structural findings suggest abnormal brain developmental processes early in the clinical course of autism. Research currently is underway to better elucidate mechanisms underlying these structural abnormalities and their longitudinal progression.

Brain metabolic changes during lactate-induced panic: effects of gabapentin treatment

Six subjects with panic disorder underwent sodium lactate infusions in conjunction with magnetic resonance spectroscopic imaging (MRSI) at study entrance when actively symptomatic and after clinical improvement while under treatment with gabapentin. MRSI was used to serially measure regional brain lactate levels from an axial section at the level of the lateral ventricles at baseline, during lactate infusion and postlactate infusion. Gabapentin treatment appeared to be effective in blocking a lactate-induced panic response but did not alter the magnitude or time course of an abnormal brain lactate response to lactate infusion in all subjects. Additionally, two subjects were reinfused while clinically improved on double-blind placebo and demonstrated a consistent pattern of abnormal brain lactate response.

Magnetization transfer of fluoxetine in the human brain using fluorine magnetic resonance spectroscopy

Fluorine magnetic resonance spectroscopy ((19)F MRS) measurements of fluoxetine and metabolite concentration in the human brain underestimate true drug levels because of a bound, MRS-"invisible" pool of drug molecules. Magnetization transfer (MT) spectroscopy may be a useful technique for characterizing this bound pool of fluoxetine in the brain. Six subjects on consistent daily doses of fluoxetine underwent (19)F MT spectroscopy on a 1.5-T scanner using a train of three preparation pulses at -3000 Hz off resonance with 0.5 W of peak power deposition in tissue. One subject was scanned at multiple time points after initiation of drug therapy. Magnetization transfer signal contrast was quantified using VARPRO-based time domain fitting software. Magnetization transfer signal contrast was quantifiable with mean MT signal depression of 12.5% (SD = 5.0, n = 6). An inverse relationship between brain concentration and the MT signal contrast of fluoxetine was found (r = -.82, Spearman coefficient =.007). This study is the first in vivo application of (19)F MT spectroscopy and the first to demonstrate a quantifiable MT effect for a psychotropic medication in the human brain. Findings suggest that fluoxetine is substantially bound in the brain and that individual differences, inversely related to brain concentration, can be detected in the magnitude of MT contrast.

Comparison of fMRI and PEPSI during language processing in children

The present study explored the correlation between lactate as detected by MR spectroscopy (MRS) and blood oxygenation level dependent (BOLD) responses in male children during auditory-based language tasks. All subjects (N = 8) participated in one proton echo planar spectroscopic imaging (PEPSI) and one functional magnetic resonance imaging (fMRI) session that required phonological and lexical judgments to aurally presented stimuli. Valid PEPSI data was limited in the frontal areas of the brain due to the magnetic susceptibility of the eye orbits and frontal sinuses. Findings from the remainder of the brain indicate that subjects show a significant consistency across imaging techniques in the left temporal area during the lexical task, but not in any other measurable area or during the phonological task. Magn Reson Med 45:217-225, 2001.

Brain imaging and the effects of caffeine and nicotine

Caffeine and nicotine are the most common psychostimulant drugs used worldwide. Structural neuroimaging findings associated with caffeine and nicotine consumption are limited and primarily reflect the putative relationship between smoking and white matter hyperintensities (WMH), a finding that warrants further appraisal of its clinical implications. The application of newer brain imaging modalities that measure subtle haemodynamic changes or tissue-based chemistry in order to better elucidate brain functional processes, including mechanisms underlying addiction to nicotine and caffeine and the brain functional consequences, provide intriguing findings. Potential influences of caffeine and nicotine on the functional contrast, or metabolic response, to neural activation also necessitates the careful appraisal of the effects that these commonly used drugs may have on the results of functional imaging.

Placebo-controlled study of gabapentin treatment of panic disorder

A randomized, double-blind, placebo-controlled, parallel-group study was conducted to evaluate the efficacy and safety of gabapentin in relieving the symptoms of panic disorder. One hundred three patients were randomly assigned to receive double-blind treatment with either gabapentin (dosed flexibly between 600 and 3,600 mg/day) or placebo for 8 weeks. No overall drug/placebo difference was observed in scores on the Panic and Agoraphobia Scale (PAS) (p = 0.606). A post hoc analysis was used to evaluate the more severely ill patients as defined by the primary outcome measure (PAS score > or = 20). In this population, the gabapentin-treated patients showed significant improvement in the PAS change score (p = 0.04). In patients with a PAS score of 20 or greater, women showed a greater response than men regardless of treatment. Adverse events were consistent with the known side effect profile of gabapentin and included somnolence, headache, and dizziness. One patient experienced a serious adverse event during the study. No deaths were reported. The results of this study suggest that gabapentin may have anxiolytic effects in more severely ill patients with panic disorder.

Effects of a phonologically driven treatment for dyslexia on lactate levels measured by proton MR spectroscopic imaging

BACKGROUND AND PURPOSE

Dyslexia is a language disorder in which reading ability is compromised because of poor phonologic skills. The purpose of this study was to measure the effect of a phonologically driven treatment for dyslexia on brain lactate response to language stimulation as measured by proton MR spectroscopic imaging.

METHODS

Brain lactate metabolism was measured at two different time points (1 year apart) during four different cognitive tasks (three language tasks and one nonlanguage task) in dyslexic participants (n = 8) and in control participants (n = 7) by using a fast MR spectroscopic imaging technique called proton echo-planar spectroscopic imaging (1 cm3 voxel resolution). The age range for both dyslexic and control participants was 10 to 13 years. Between the first and second imaging sessions, the dyslexic boys participated in an instructional intervention, which was a reading/science workshop.

RESULTS

Before treatment, the dyslexic boys showed significantly greater lactate elevation compared with a control group in the left anterior quadrant (analysis of variance, P = .05) of the brain during a phonologic task. After treatment, however, brain lactate elevation was not significantly different from that of the control group in the left anterior quadrant during the same phonologic task. Behaviorally, the dyslexic participants improved in the phonologic aspects of reading.

CONCLUSION

Instructional intervention that improved phonologic performance in dyslexic boys was associated with changes in brain lactate levels as measured by proton echo-planar spectroscopic imaging.

Modeling brain compartmental lactate response to metabolic challenge: a feasibility study

Magnetic resonance spectroscopy has been used to characterize abnormal brain lactate response in panic disorder (PD) subjects following lactate infusion. The present study integrated water quantification and tissue segmentation to evaluate compartmental lactate response within brain and cerebrospinal fluid (CSF). As there is evidence of brain parenchymal pH changes during lactate infusion, water scans were collected at baseline and post-infusion to address brain water stability. Water levels remained essentially stable across the protocol suggesting internal water provides an improved reference signal for measuring dynamic changes in response to metabolic challenge paradigms such as lactate infusion. To model brain lactate changes by compartments, we took the null hypothesis that lactate rises occur only in tissue. The approach referenced lactate amplitude (potentially from both compartments) to 'voxel' water (water scan corrected for differential T(2) between CSF brain at long-echo times - synonymous to a short-echo water scan). If the magnitude of lactate rise in CSF was equal to or greater than brain, voxels with substantial CSF fractions should demonstrate an equivalent or elevated response to voxels comprised only of tissue. The magnitude of lactate increases paralleled voxel tissue fraction suggesting the abnormal lactate rise observed in PD is tissue-based. The feasibility of lactate quantification and compartmental modeling are discussed.

Dyslexic children have abnormal brain lactate response to reading-related language tasks

BACKGROUND AND PURPOSE

Children with dyslexia have difficulty learning to recognize written words owing to subtle deficits in oral language related to processing sounds and accessing words automatically. The purpose of this study was to compare regional changes in brain lactate between dyslexic children and control subjects during oral language activation.

METHODS

Brain lactate metabolism was measured during four different cognitive tasks (three language tasks and one nonlanguage task) in six dyslexic boys and in seven control subjects (age- and IQ-matched right-handed boys who are good readers) using a fast MR spectroscopic imaging technique called proton echo-planar spectroscopic imaging (1-cm3 voxel resolution). The area under the N-acetylaspartate (NAA) and lactate peaks was measured to calculate the lactate/NAA ratio in each voxel.

RESULTS

Dyslexic boys showed a greater area of brain lactate elevation (2.33+/-SE 0.843 voxels) as compared with the control group (0.57+/-SE 0.30 voxels) during a phonological task in the left anterior quadrant. No significant differences were observed in the nonlanguage tasks.

CONCLUSION

Dyslexic and control children differ in brain lactate metabolism when performing language tasks, but do not differ in nonlanguage auditory tasks.

Enhancement of BOLD-contrast sensitivity by single-shot multi-echo functional MR imaging

Improved data acquisition and processing strategies for blood oxygenation level-dependent (BOLD)-contrast functional magnetic resonance imaging (fMRI), which enhance the functional contrast-to-noise ratio (CNR) by sampling multiple echo times in a single shot, are described. The dependence of the CNR on T2*, the image encoding time, and the number of sampled echo times are investigated for exponential fitting, echo summation, weighted echo summation, and averaging of correlation maps obtained at different echo times. The method is validated in vivo using visual stimulation and turbo proton echoplanar spectroscopic imaging (turbo-PEPSI), a new single-shot multi-slice MR spectroscopic imaging technique, which acquires up to 12 consecutive echoplanar images with echo times ranging from 12 to 213 msec. Quantitative T2*-mapping significantly increases the measured extent of activation and the mean correlation coefficient compared with conventional echoplanar imaging. The sensitivity gain with echo summation, which is computationally efficient provides similar sensitivity as fitting. For all data processing methods sensitivity is optimum when echo times up to 3.2 T2* are sampled. This methodology has implications for comparing functional sensitivity at different magnetic field strengths and between brain regions with different magnetic field inhomogeneities.

Characterization of human brain pharmacokinetics using a two-compartment model

We developed a two-compartment pharmacokinetic model to systematically characterize 19F magnetic resonance spectroscopy (19F MRS) data on the concentration time course of psychotropic compounds measured in human brain. Using this model, brain volume of distribution and clearance were calculated for fluvoxamine as an index compound. Our interest in formalizing a multicompartment model was motivated by recent advances in the field of brain spectroscopy that allow the noninvasive characterization of brain uptake and elimination half-lives of fluorinated psychotropic compounds. Differences between central compartment single-dose and steady-state half-lives and the peripheral elimination half-life at steady state were used to formulate the model. Application of the model is illustrated using previously published data on the elimination half-lives of fluvoxamine from plasma and brain at steady state, along with the literature values for single-dose plasma elimination half-life. Applying the model, brain volume of distribution (1.12 L/kg +/- 0.2 SEM) and clearance (1.01 L/hour +/- 0.12 SEM) were calculated for fluvoxamine. The bioavailability of fluvoxamine to the brain from plasma was 1.85 +/- 0.23 SEM. The underlying multicompartment pharmacokinetics of fluvoxamine were reflected by the difference between brain and plasma elimination half-lives from steady state. This method to derive pharmacokinetic parameters using 19F MRS measurements of drug concentration in brain can be applied to characterize the pharmacokinetics of other fluorinated psychotropic compounds.

Effects of myo-inositol ingestion on human brain myo-inositol levels: a proton magnetic resonance spectroscopic imaging study

BACKGROUND

Cerebrospinal fluid levels of myo-Inositol (m-Ino) are reported to be decreased in patients with affective disorder, and dietary supplements of m-Ino have been shown to reduce the symptoms of major depression. Myo-Inositol transport across the blood-brain barrier is mediated by a low capacity, saturable system. This study tests whether dietary m-Ino increases brain m-Ino or changes brain metabolism of m-Ino, possibly explaining the ability of this compound to alter mood.

METHODS

Using proton magnetic resonance spectroscopic imaging, we measured m-Ino levels in occipital gray and parietal white matter of seventeen healthy subjects. Magnetic resonance spectroscopic imaging was performed twice at baseline as well as at day 4 and day 8 while subjects ingested 6 g of m-Ino twice a day.

RESULTS

Following 4 days of m-Ino, m-Ino/Cr was 20% higher than baseline levels in occipital gray matter (p < 0.04) and 8% higher in parietal white matter (p = ns). By day 8, m-Ino/Cr ratios had returned to baseline values.

CONCLUSIONS

Brain m-Ino levels initially increase during m-Ino administration and subsequently return to baseline levels. The time-limited increases observed for brain m-Ino may reflect homeostatic mechanisms, possibly associated with the role of m-Ino as a cerebral osmolyte, or with changes in brain phosphoinositide metabolism.

Human brain metabolic response to caffeine and the effects of tolerance

OBJECTIVE

Since there is limited information concerning caffeine's metabolic effects on the human brain, the authors applied a rapid proton echo-planar spectroscopic imaging technique to dynamically measure regional brain metabolic responses to caffeine ingestion. They specifically measured changes in brain lactate due to the combined effects of caffeine's stimulation of glycolysis and reduction of cerebral blood flow.

METHOD

Nine heavy caffeine users and nine caffeine-intolerant individuals, who had previously discontinued or substantially curtailed use of caffeinated products because of associated anxiety and discomforting physiological arousal, were studied at baseline and then during 1 hour following ingestion of caffeine citrate (10 mg/kg). To assess state-trait contributions and the effects of caffeine tolerance, five of the caffeine users were restudied after a 1- to 2-month caffeine holiday.

RESULTS

The caffeine-intolerant individuals, but not the regular caffeine users, experienced substantial psychological and physiological distress in response to caffeine ingestion. Significant increases in global and regionally specific brain lactate were observed only among the caffeine-intolerant subjects. Reexposure of the regular caffeine users to caffeine after a caffeine holiday resulted in little or no adverse clinical reaction but significant rises in brain lactate which were of a magnitude similar to that observed for the caffeine-intolerant group.

CONCLUSIONS

These results provide direct evidence for the loss of caffeine tolerance in the human brain subsequent to caffeine discontinuation and suggest mechanisms for the phenomenon of caffeine intolerance other than its metabolic effects on elevating brain lactate.

Neuropsychological function in retired workers with previous long-term occupational exposure to solvents

OBJECTIVES

It is plausible that neurodegenerative processes of aging might have a contributing role in the development of chronic effects of exposure to organic solvents. This study evaluated the risk for neuropsychological deficits among retired workers, relative to their histories of exposure to occupational solvents.

METHODS

This cross sectional study evaluated retired male workers, 62-74 years of age, including 89 people with previous long-term occupational exposure to solvents (67 retired painters and 22 retired aerospace manufacturing workers), and 126 retired carpenters with relatively minimal previous exposure to solvents. Subjects completed a standardised neuropsychological evaluation and psychiatric interview, structured interviews for histories of occupational exposure and alcohol consumption, and questionnaires assessing neurological and depressive symptoms.

RESULTS

By comparison with the carpenters, the painters on average reported greater cumulative alcohol consumption and had lower scores on the WAIS-R vocabulary subtest, usually presumed to reflect premorbid intellectual functioning. These findings, however, were not sufficient to account for the other study findings. Controlling for age, education, vocabulary score, and alcohol use, the painters had lower mean scores on test measures of motor, memory, and reasoning ability; and a subgroup of aerospace workers with moderate to high cumulative exposure to solvents (n = 8) had lower mean scores on measures of visuomotor speed, and motor, attention, memory, and reasoning ability. Subjects were more likely to have an increased number of relatively abnormal test scores (three or more outlier scores on 17 test measures) among both the painter group (odds ratio (OR), 3.1; 95% confidence interval (95% CI) 1.5 to 6.2) and the subgroup of aerospace workers with higher cumulative exposure (OR 5.6; 95% CI 1.0 to 38). The painters, but not the aerospace workers, reported significantly more neurological and depressive symptoms.

CONCLUSIONS

The findings are consistent with residual central nervous system dysfunction from long-term exposure to organic solvents, persisting years after the end of exposure.

Two-dimensional proton echo-planar spectroscopic imaging of brain metabolic changes during lactate-induced panic

BACKGROUND

A fast, proton echo-planar spectroscopic imaging (PEPSI) technique, capable of simultaneously measuring metabolites from multiple brain regions, was used to investigate the anatomical distribution and magnitude of brain lactate responses to intravenous lactate infusion among subjects with panic disorder and control subjects.

METHODS

Fifteen subjects with panic disorder and 10 control subjects were studied. All subjects were medication free and met DSM-IV criteria for panic disorder, or, for controls, no Axis I psychiatric disorder. Two-dimensional axial metabolite images having 1-cm3 spatial resolution were acquired at 61/2-minute intervals during 3 conditions: a 20-minute baseline, 20-minute 0.5-mol/L sodium lactate infusion, and 15-minute postinfusion period.

RESULTS

Intravenous lactate infusion increased brain lactate levels throughout the axial brain section studied in all subjects. Panic-disordered subjects had significantly greater global brain lactate increases in response to lactate infusion. Lateralization of brain lactate response did not occur, nor were discrete regional loci of elevated lactate observed. Cerebrospinal fluid lactate changes corresponded to lactate changes in brain tissue. Severity of symptoms provoked by lactate infusion did not directly correlate with brain lactate response.

CONCLUSIONS

Greater overall rises in brain lactate among subjects with panic disorder compared with controls occurred in response to lactate infusion. We were unable to detect a distinct regional pattern for magnitude differences in brain lactate rise by which to identify a specific neuroanatomical substrate underlying a lactate-induced panic response. The wide anatomical distribution of these brain lactate increases suggest metabolic and/or neurovascular mechanisms for the abnormal rise in subjects with panic disorder.

Functional MR spectroscopy of the brain

Functional MR spectroscopy is a technique for measuring brain activation that is based on metabolic changes in MR spectroscopy-detectable metabolites. This article covers functional MR spectroscopy applications in visual stimulation, auditory stimulation, language activation, cerebral metabolic rate, water MR spectroscopy, and in psychiatric disorders. Functional MR spectroscopy offers the ability to measure changes in the brain during neuronal activation that may be a more direct measure of cellular activation than functional magnetic resonance imaging. MR spectroscopy-detectable chemicals that are currently of greatest interest for measuring brain activation are also discussed.

Brain elimination half-life of fluvoxamine measured by 19F magnetic resonance spectroscopy

OBJECTIVE

This study used fluorine-19 magnetic resonance spectroscopy (19F MRS) to characterize the elimination of fluvoxamine from the human brain after abrupt drug discontinuation. The elimination half-lives of fluvoxamine in brain and plasma were determined to assess their interdependence and the relationship of brain half-life to the clinical practice of drug holidays and reports of acute withdrawal symptoms.

METHODS

Six subjects completing clinical treatment with fluvoxamine were enrolled in the study. Spectroscopic quantification of whole brain fluvoxamine concentrations and chromatographic determination of plasma fluvoxamine levels were performed serially for up to 10 days after drug withdrawal. Psychiatric evaluation to assess withdrawal symptoms was also done at each scanning session.

RESULTS

Elimination of fluvoxamine in the brain and plasma was optimally described by first-order kinetics; the mean elimination half-lives were 58 hours and 26 hours, respectively. The mean ratio of fluvoxamine brain elimination half-life to plasma half-life was 2.4. Three of the six subjects experienced mild to moderate withdrawal symptoms between the third and fifth days of the study, which corresponded to between one and two brain half-lives of fluvoxamine.

CONCLUSIONS

The brain elimination half-life for fluorinated psychotropic compounds can be measured noninvasively by 19F MRS. The elimination half-life of fluvoxamine was found to be substantially longer for the brain than for plasma. The time course of withdrawal symptom onset and the rationale for drug holidays with fluvoxamine appear to be well explained by the brain elimination half-life.

Single-voxel 1H-MRS investigation of brain metabolic changes during lactate-induced panic

Intravenous sodium lactate infusion is a robust laboratory technique for eliciting panic in susceptible individuals. The objective for this study was to replicate previous work which found differential brain lactate rises among lactate-sensitive panic subjects relative to control subjects using single-voxel 1H-magnetic resonance spectroscopy (MRS). Single-voxel 1H-MRS was used to measure brain lactate changes in the insular cortex region among 13 panic disorder subjects and 10 healthy control subjects during the infusion. One panic subject prematurely terminated the study due to a panic response during lactate infusion. Data from two additional control subjects and one panic subject were lost due to technical problems. Four panic subjects were reinfused with lactate while panic-free under treatment with fluoxetine (20 mg/day). At the time of initial infusion, all subjects were medication-free for at least 1 month. Ten panic subjects, but no control subjects, panicked during lactate infusion. In comparison to control subjects, panic subjects demonstrated significantly greater and prolonged brain lactate rises in the insular cortex region. Three of four medicated panic subjects experienced blockage of panic symptoms during lactate reinfusion but all exhibited persistent excesses in brain lactate rise. Consistent with our prior observations, greater and prolonged lactate rises in the insular brain region occur during and following lactate infusion among panic subjects compared to control subjects. This differential brain metabolic response did not appear to normalize when a small subset of panic patients were reinfused following resolution of panic symptoms during treatment over 3-4 months with fluoxetine.

Regional dynamic signal changes during controlled hyperventilation assessed with blood oxygen level-dependent functional MR imaging

PURPOSE

To quantitate the amplitude changes and temporal dynamics of regional functional MR imaging signals during voluntary hyperventilation using blood oxygen level-dependent contrast echo-planar imaging.

METHODS

Seven male subjects were studied during voluntary hyperventilation (PetCO2 = 20 mm Hg) regulated by capnometry. Measurements were made on multisection echo-planar MR images obtained with parameters of 1000/66 (repetition time/echo time), flip angle of 30 degrees, and voxel size of 3 x 3 x 5 mm3. Sensitivity of the functional MR imaging signal to changes in PetCO2, time delays in relation to PetCO2 changes, and time constants of functional MR imaging signal changes were assessed on a region-by-region basis.

RESULTS

Within 20 seconds of starting hyperventilation, rapid and substantial decreases in the functional MR imaging signal (by as much as 10%) were measured in areas of gray matter, which were significantly greater than the modest changes observed in white matter. Regional-specific effects in areas of the frontal, occipital, and parietooccipital cortex were stronger than in subcortical regions or in the cerebellum. Signal decreases measured with functional MR imaging were significantly delayed with respect to the reduction in PetCO2. Apparent differences between regional time constants did not reach statistical significance.

CONCLUSION

Regional and gray-white matter differences in functional MR imaging signal changes during controlled hyperventilation may reflect differences in metabolic activity, vascular regulation, and/or capillary density. When measuring brain activation with functional MR imaging, arterial PCO2 differences due to unregulated respiration may confound interpretation of activation-related functional MR imaging signal changes.

In vivo measurement of regional brain metabolic response to hyperventilation using magnetic resonance: proton echo planar spectroscopic imaging (PEPSI)

A new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2-dimensional distribution of brain lactate increases during hyperventilation on a conventional clinical scanner equipped with a head surface coil phased array. PEPSI images (nominal voxel size: 1.125 cm3) in five healthy subjects from an axial section approximately 20 mm inferior to the intercommissural line were obtained during an 8.5-min baseline period of normocapnia and during the final 8.5 min of a 10-min period of capnometry-controlled hyperventilation (end-tidal PCO2 of 20 mmHg). The lactate/N-acetyl aspartate signal increased significantly from baseline during hyperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemisphere, but not in the basal ganglia. Regional or hemispheric right-to-left differences were not found. The study extends previous work using single-voxel MR spectroscopy to dynamically study hyperventilation effects on brain metabolism.

19F magnetic resonance spectroscopy investigation in vivo of acute and steady-state brain fluvoxamine levels in obsessive-compulsive disorder

OBJECTIVE

The purpose of this study was to investigate the pharmacokinetics of fluvoxamine in the human brain by using fluorine-19 magnetic resonance spectroscopy (19F MRS) and to assess the relationships among fluvoxamine brain levels, fluvoxamine plasma levels, and clinical efficacy.

METHOD

Eight subjects with DSM-IV obsessive-compulsive disorder were entered into a prospective, open-label treatment trial of fluvoxamine. 19F MRS measurements of whole brain drug and metabolite concentrations and spin-lattice (T1) relaxation times were performed serially in seven subjects for up to 5 months. A psychiatric determination of clinical response and a blood sample for plasma fluvoxamine measurement were obtained at each 19F MRS session.

RESULTS

The subjects achieved steady-state brain concentrations of fluvoxamine within 30 days after consistent daily dosing, as determined by stabilization of brain fluvoxamine concentrations. The mean brain-to-plasma ratio at steady state was 24 to 1. Brain fluvoxamine T1 values from 140 to 230 msec were observed. All but one subject experienced substantial improvement in symptoms. The one nonresponder exhibited several-fold higher plasma and brain fluvoxamine levels.

CONCLUSIONS

Brain fluvoxamine levels were substantially higher than plasma levels. Steady-state brain levels correlated to plasma levels but not to dose. Systematic assessment of treatment response in relation to brain or plasma fluvoxamine level was not feasible because of the marked and rapid clinical response during open-label treatment. These data suggest that fluvoxamine attains brain steady-state levels substantially faster than fluoxetine, with corresponding clinical implications.

Application of a novel fiber-optic biosensor in situ to investigate the metabolic effect of lactate infusion

Recently developed biosensor technology, which allows near real-time measurement in situ of gas tension (pCO2 and pO2) and of pH, was applied to arterial blood, cerebrospinal fluid (CSF), and brain parenchyma during intravenous lactate infusion in monkeys. Comparison of simultaneous biosensor measurements and discrete arterial blood sampling for traditional blood gas analyses indicated a high level of correlation for pCO2, pO2, and pH. Arterial pO2 and pH values were significantly higher and pCO2 significantly lower than corresponding CSF and brain parenchyma values at baseline, during and following lactate infusion. There was a divergence between arterial and brain parenchyma pH and pO2 measurements. Lactate infusion was associated with progressive arterial pH rises, consistent with the production of a metabolic alkalosis. Cerebrospinal fluid pCO2 remained unchanged during and following lactate infusion. Brain parenchyma exhibited a complex pattern of response characterized by a trend for pO2 and pH to decrease during lactate infusion, which reversed following completion of the infusion. These observations are suggestive of a transient hypoxia from decreased cerebral blood flow and/or reduced oxyhemoglobin dissociation during lactate infusion, but verification of these results is required.

Proton magnetic resonance spectroscopy investigation of hyperventilation in subjects with panic disorder and comparison subjects

OBJECTIVE

The purpose of this study was to investigate differential effects of hyperventilation on brain lactate in patients with panic disorder and comparison subjects as a possible mechanism for explaining previous observations of an excess rise in brain lactate among panic disorder subjects during lactate infusion.

METHOD

Seven treatment-responsive patients with panic disorder and seven healthy comparison subjects were studied with proton magnetic resonance spectroscopy to measure brain lactate during controlled, voluntary hyperventilation over a period of 20 minutes. Hyperventilation was regulated with the use of capnometry to maintain end-tidal PCO2 at approximately 20 mm Hg during the period of hyperventilation. Blood lactate was measured prior to and at the end of hyperventilation.

RESULTS

At baseline the two groups had similar brain lactate levels. Panic disorder subjects exhibited significantly greater rises in brain lactate than comparison subjects in response to the same level of hyperventilation. Blood lactate levels before and after 20 minutes of hyperventilation were not significantly different between groups.

CONCLUSIONS

Controlled hyperventilation increases brain lactate and does so disproportionately in subjects with panic disorder. This increase in brain lactate may result from decreased cerebral blood flow due to hypocapnia, and individuals with panic disorder may have greater sensitivity to this regulatory mechanism.

Preliminary application of magnetic resonance spectroscopy to investigate lactate-induced panic

OBJECTIVE

To characterize changes associated with lactate-induced panic, proton magnetic resonance spectroscopy (MRS) was used to measure brain lactate during intravenous infusion of 0.5-M sodium lactate in panic disorder patients and comparison subjects.

METHOD

Eight panic disorder subjects, five medicated and three unmedicated, and eight healthy comparison subjects were studied at baseline, during lactate infusion (5 meq/kg over 20 minutes), and after infusion. Localized proton MRS was used to acquire averaged spectra every 5 minutes from a 27-ml sampling volume in the insular cortex and adjacent regions. Brain lactate levels, quantitatively estimated in relationship to N-acetyl aspartate, were compared to blood lactate levels.

RESULTS

The procedure was generally well tolerated; one panic subject requested early termination before lactate infusion. Significant rises in brain lactate levels occurred for all subjects during infusion. The panic patients who responded to lactate (N = 3) had significantly higher brain lactate levels before, during, and after infusion than did the comparison subjects (N = 8) and medicated patients who were lactate nonresponders (N = 4). After infusion the panic patients with lactate-induced panic exhibited a striking dissociation between decreasing blood lactate and further increases in brain lactate levels.

CONCLUSIONS

These preliminary observations indicate that brain lactate increases during a standard lactate infusion. Lactate-induced panic is associated with greater increases than in comparison subjects and with prolonged elevations in brain lactate that are decoupled from falling blood lactate levels after completion of lactate infusion. Further investigation is necessary to clarify the mechanism(s) responsible for these findings and establish whether a causal relationship to the occurrence of lactate-induced panic exists.

Dawn simulation treatment of winter depression: a controlled study

OBJECTIVE

This study sought to determine whether dawn simulation was superior to a shorter dimmer "placebo" dawn signal in treating winter depression.

METHOD

In a randomized, parallel design, 22 patients with winter depression were treated with either 1 week of a 2-hour dawn simulation peaking at 250 lux or 1 week of a 30-minute dawn simulation peaking at 0.2 lux. The subjects were told that they would receive either a "gradual" dawn or a "rapid" dawn reaching an intensity that would be dimmer than standard bright light treatment. At the end of both the baseline week and the treatment week, subjects were assessed in a blind manner with the Hamilton Rating Scale for Depression. Analysis of covariance was used to compare the two dawn treatments.

RESULTS

The 2-hour, 250-lux dawn simulation resulted in Hamilton depression scale scores that were significantly lower than scores after the 30-minute, 0.2-lux dawn simulation.

CONCLUSIONS

This study indicates that dawn simulation is an effective treatment for winter depression.

MRS detection of whole brain lactate rise during 1 M sodium lactate infusion in rats

Proton magnetic resonance spectroscopy (1H MRS) performed in vivo on nine Sprague Dawley rats detected a threefold increase in whole brain lactate during intravenous 1 mol/L sodium lactate infusion. Significant increases in whole brain lactate were detected within 5 min after starting lactate infusion, progressively rose to a maximum level estimated at 3.2 +/- 1.5 mmol/L (all values +/- SD) immediately postinfusion, then decreased towards baseline levels during the next hr. Venous lactate concentration, increasing from 2.3 +/- 2.4 mmol/L to 43.0 +/- 8.0 mmol/L during the infusion, exhibited a steeper rise and then decreased more rapidly in comparison to changes in whole brain lactate. These data suggest MRS can be used in vivo to study acute changes in brain lactate associated with increasing blood lactate concentrations.

The relationship between anxiety and depression: a clinical comparison of generalized anxiety disorder, dysthymic disorder, panic disorder, and major depressive disorder

This study examined the relationship between the chronic disorders, generalized anxiety disorder (GAD) and dysthymic disorder (DD), and the more acute disorders, panic disorder (PD) and major depressive disorder (MDD) in 110 psychiatric outpatients with diagnoses of either PD, MDD, GAD, or DD. Pure, mixed, and early-/late-onset forms of the chronic disorders were compared with each other and then with PD and MDD on clinical measures and psychiatric history. Minimal differences were found between pure GAD and mixed GAD or between pure DD and mixed DD. The chronic disorders, DD and GAD, had distinct clinical symptom profiles when compared with each other and appeared more closely related to their parent disorders than to each other. However, despite these similarities, there were significant differences between DD and MDD in contrast to the minimal differences between GAD and PD, providing less support for GAD as a valid diagnostic category separate from PD. Comparisons of early-/late-onset DD and GAD showed more severe symptoms in late-onset DD, in contrast to more severe symptoms in early-onset GAD. These varying patterns of symptom severity may warrant study for further syndromal delineation.

Applications of magnetic resonance spectroscopy to the investigation of neuropsychiatric disorders

Magnetic resonance spectroscopy (MRS) can noninvasively characterize tissue composition and metabolism in vivo without the need for radioactive isotope administration. For the neuropsychiatrist interested in the functional basis of disease, MRS offers an investigative tool capable of studying a wide variety of neuropsychiatric disorders. This report provides an overview of how MRS works, current and potential clinical applications for specific psychiatric populations, and limitations of the technology.

Localized magnetic resonance spectroscopy measurement of brain lactate during intravenous lactate infusion in healthy volunteers

Proton magnetic resonance spectroscopy (1H MRS) localized to the left temporal-parietal region in 8 healthy volunteers detected a 2.1-fold +/- 0.7-fold increase (all values +/-SD) in brain lactate during intravenous infusion of 0.5 molar (M) sodium lactate (5 meq/kg over 20 minutes). Significant increases in brain lactate occurred within 5-10 minutes after starting lactate infusion, progressively rose during the infusion, then decreased towards baseline levels during 30 minutes post-infusion. Venous lactate concentration increased from 0.8 +/- 0.2 mM to 10.9 +/- 4.1 mM or 13.6-fold during the infusion. Flow phantom findings in vitro suggest attenuation of 1H MRS blood lactate signal from arteries and veins as a result of flow velocity effects. Correlations between paired blood and brain lactate measurements at each sampling time indicate a non-linear relationship between compartments during lactate infusion.

Lactate vulnerability after alprazolam versus placebo treatment of panic disorder

Thirty-six patients with panic disorder underwent sodium lactate infusion before and after 8 weeks of treatment with alprazolam or placebo. With reinfusion, those patients panic-free with chronic alprazolam treatment displayed significantly decreased reactivity to lactate, as measured by subjective symptom ratings, duration of infusion before developing peak lactate-induced symptoms, and the proportion of patients experiencing lactate-induced anxiety or panic. Patients panic-free on placebo, as well as nonresponders to alprazolam treatment, displayed some, although less striking, decreases in reactivity to lactate with reinfusion. As a group, patients clinically unchanged with placebo treatment showed no systematic change in lactate response with reinfusion. Although the small numbers of patients in each treatment outcome group prohibit drawing definitive conclusions, these findings suggest that decreases in lactate-induced panic after successful alprazolam treatment of panic may result from a combination of changes in clinical state and direct effects of the medication.

Chronicity of depressive episode in relation to antidepressant-placebo response

Pooled data from three 6-week placebo-controlled, double-blind, phase III clinical trials, designed to assess the efficacy of newer antidepressants, were retrospectively analyzed to study the relationship between chronicity of presenting depressive episode and response to placebo, imipramine, and adinazolam. One hundred forty-six depressed outpatients met criteria for inclusion into this study; 80 received placebo treatment, 27 imipramine and 39 adinazolam treatment. Consistent with our hypothesis the response to placebo was low in subjects who were depressed for 1 year or longer (22.6%) as compared to a higher response rate (44.9%) among those who were not as chronically depressed. The response to imipramine and adinazolam was not related to the duration of presenting depressive episode. The implications of these findings are discussed.

Morning or evening bright light treatment of winter depression? The significance of hypersomnia

In a randomized crossover design 19 patients with winter depression were treated with 7 days of bright morning light (6:00 to 8:00 AM) and 7 days of evening light (7:00 to 9:00 PM). Bright light in the morning reduced the Hamilton Depression Rating Scale score from 22.3 to 5.5; bright light in the evening decreased the Hamilton score from 21.0 to 12.2. Improvement in the depression as measured by the Hamilton Depression Rating scores was greater with morning light compared with evening lights. Hypersomnia was associated (p less than 0.05) with a superior response to morning light.

Prevention of psychological disability after occupational respiratory exposures

"Psychological injury" in the workplace constitutes the fastest-growing sector of workers' compensation disability claims in several states. Most such claims pertain to effects of "occupational stress," including interpersonal conflicts with supervisors or co-workers, adaptation to changing work practices, and job insecurity. Of equal interest are the psychological consequences of chemical insults on the job. In the case of occupational respiratory exposures, psychological co-morbidity may occur along with a variety of acute, chronic, and latent illness states. Both predictable responses (such as adjustment reactions to disabling physical conditions) and idiopathic patterns (such as the development of odor-conditioned panic attacks or panic disorder) have been described. Physicians who evaluate and treat such patients need to be alert to the potential interaction of physiological and psychological stressors. Effective prevention and treatment requires not only an appreciation of the patient's view of the disease process, but also a recognition of the role of prognostic uncertainty in the subsequent development of anxiety symptoms. In some cases, exclusive attention to physical signs and symptoms may actually lead to a worsening of impairment and disability.

Bright light treatment of winter depression: morning versus evening light

In a randomized crossover design, 7 patients with winter depression were treated with 7 d of bright morning light (0600 to 0800) and 7 d of evening light (2000 to 2200). Bright lights in the morning significantly reduced the Hamilton Rating Scale for Depression (HRSD) score (18.4 to 5.0); the bright light in the evening moderately decreased the HRSD score (19.4 to 15.1). The improvement in the HRSD score was significantly greater with morning light than with evening light.

A case of bupropion-associated delirium

The authors report a case of bupropion-associated delirium characterized by disorganized thinking, memory impairment, fear, and agitation but not disorientation, delusions, hallucinations, or other perceptual distortions. Symptom onset appeared to be dose-related, and a sustained therapeutic response was subsequently obtained at a lower dose of bupropion without recurrence of delirium. Abnormal bupropion metabolism and elevated plasma metabolite levels did not account for the adverse reaction, which instead was hypothesized to reflect dopaminergic effects of bupropion.

Central nervous system effects of lactate infusion in primates

The concentration of total lactate in cisternal fluid increased threefold, from 12.3 +/- 2.1 to 37.6 +/- 8.9 mg/dl, during a 20-min intravenous infusion of 1 M racemic sodium lactate (10 mEq/kg) in 3 anesthetized, mechanically ventilated baboons. Rises in cisternal lactate lagged behind arterial lactate increases, but occurred during the time interval in which susceptible humans typically panic in response to lactate infusion. Subsequent to cisternal lactate increases, cisternal pH and HCO3- concentration progressively increased during a 105-min interval following lactate infusion. No consistent changes in cisternal pCO2 occurred during or subsequent to lactate infusion. These preliminary findings fail to support the hypothesis that lactate-induced panic is mediated by increasing central nervous system pCO2. Instead, these data demonstrate that lactate can rapidly increase in the central nervous system during lactate infusion, suggesting new lines of investigation for studying the mechanisms responsible for lactate-induced panic.

Response to sodium lactate infusion in alcoholics with panic attacks

The authors studied the response to sodium lactate infusion of 12 alcoholics with a history of panic attacks, 10 alcoholics without a history of panic attacks, and 16 nonalcoholic patients with panic disorder. The rate of lactate-induced panic was significantly higher in alcoholics with panic attacks than in alcoholics without panic attacks. Alcoholics with panic attacks were similar to nonalcoholic patients with panic disorder in their response to lactate. These findings support the specificity of lactate-induced panic for panic states and suggest that panic attacks in alcoholics resemble those in nonalcoholics. Lactate infusion may prove useful in the diagnosis of panic disorder in alcoholics.

Diagnostic reliability of M-mode echocardiography for detecting mitral valve prolapse in 50 consecutive panic patients

Fifty consecutive panic patients had M-mode echocardiographs read independently by two cardiologists with expertise in echocardiography. In this prospective study, there was poor interrater reliability (22 of 50; K = 0.11) for diagnosis of mitral valve prolapse (MVP). On repeat evaluation 10 months later there was also unacceptable intrarater reliability for each reader: 22 of 35 (K = 0.41) and 22 of 35 (K = 0.45). We conclude that M-mode echocardiography is clinically unreliable for establishing the diagnosis of mitral valve prolapse. These findings suggest that the variable reporting of M-mode-determined mitral valve prolapse in psychiatric populations may reflect differences among echocardiologists rather than differences in cardiac pathology. The clinical implications of these findings are discussed.

Relapse and rebound following discontinuation of benzodiazepine treatment of panic attacks: alprazolam versus diazepam

The authors assessed the effects of partial tapering followed by abrupt discontinuation of alprazolam, diazepam, and placebo in 40 patients with panic attacks. The anxiety scores and frequency of panic attacks of the three groups did not differ at the end of the initial 2-week taper, but 1 week after abrupt discontinuation of the remaining medication, patients formerly taking alprazolam had greater increases in anxiety but no more panic attacks than did the other patients. Because of low statistical power, differences in benzodiazepine half-lives, absence of multiple ratings, and imbalances between groups in clinical characteristics, these findings must be viewed as preliminary.