Participants

Among the 17 alcohol-dependent participants recruited, 10 met criteria for active AUDs, and seven were in full remission from alcohol use disorders (AUD-R) for at least 1 year. These participants were compared with a sample of 23 healthy controls recruited from the community. All procedures were conducted with the approval of the Human Research and Review Committee at the University Of New Mexico School Of Medicine. All participants provided informed consent. Basic demographic information on each group is provided in Table 1. General inclusion criteria for the study were as follows: (1) willingness to participate in all study components; (2) ability to provide informed consent; (3) ability to read, speak, and understand English at the sixth grade level; (4) ability to provide at least one contact person to assist with collateral interviews; (5) age between 21 and 45 years; (6) at least 48 h after last drink; and (7) a urine sample, free of the presence of cocaine, hallucinogens, barbiturates, benzodiazepines, and opiates.

Table 1 Descriptive Demographic Statistics by Group for Participants Included in Analysis of Glu and Gln Levels Full size table

General exclusion criteria for the study were as follows: (1) history of neurological disorder or disease; (2) history of traumatic brain injury with loss of consciousness for more than 5 min; (3) mental retardation, dementia, or other cognitive impairment of sufficient severity to render the individual incapable of providing informed consent; or (4) suicide attempt in the previous 6 months or current suicidal ideation. As part of a brief health screening interview, self-report of abnormal liver enzyme level or diagnosis of hepatic disease was noted. One participant with a reported history of abnormal liver enzymes was included in the AUD-R group.

The AUD and AUD-R groups were recruited from the University of New Mexico's Alcohol and Substance Abuse Program and Center for Alcoholism, Substance Abuse and Addictions (CASAA). Diagnoses were established using the Structured Clinical Interview for DSM Disorders (SCID), AUD inclusion criteria were: (1) diagnosis of alcohol abuse or dependence active within the past 1 month (ie, not in early or sustained full remission) and (2) two or more days of heavy drinking (five or more drinks for per occasion for a man, four or more drinks per occasion for a woman) in the last 30 days before screening. The AUD-R group met diagnostic criteria for lifetime alcohol dependence in sustained full remission, ie, not active in the previous year. Specific AUD and AUD-R exclusion criteria were: (1) presence of Axis-I schizophrenia spectrum disorders or (2) a first-degree relative with schizophrenia or other psychotic disorder. Healthy control participants were recruited through advertisements in local newspapers or from postings around the Albuquerque area. Control group members reported no history of substance abuse or dependence, with the exception of nicotine, or other Axis-I psychopathology upon interview.

Procedures

Study procedures were conducted at the CASAA and the Mind Research Network in Albuquerque, New Mexico. Clinical interviews typically took place 0–5 days before imaging. AUD and AUD-R participants were administered the DrInC (Miller et al, 1995) as a measure of negative consequences from drinking. DrInC total score was considered here as an estimate of long-term severity of alcohol abuse. Recent consumption data for alcohol and other substances were collected using the Form-90 (Miller and Del Boca, 1994), a timeline follow-back interview in which the participant reported his or her use of alcohol and other substances starting at 90 days preceding the most recent drink to the present. Drinks per drinking day (DPDD) and percentage days drinking (PDD) were chosen as the alcohol variables of interest in order to capture both the intensity and frequency of recent drinking.

Magnetic resonance imaging and MRS data acquisition

Magnetic resonance imaging and 1H-MRS were performed on a Siemens 3-Tesla TrioTIM scanner using the 12-channel radiofrequency head coil. T 1 -weighted images were collected in the sagittal plane using a five-echo 3-D MPRAGE sequence (TR/echo time (TE)/TI=2530/1.64, 3.5, 5.36, 7.22, 9.08/1200 ms, flip angle=7°, field of view=256 × 256 mm, matrix=256 × 256, 1 mm thick slice, 192 slices, GRAPPA acceleration factor=2). Using these images, a single 1H-MRS voxel was positioned in the bilateral medial frontal cortex directly superior to the corpus callosum, containing anterior cingulate, middle frontal, and superior frontal gyri (Figure 1). A point-resolved spectroscopy sequence (TR/TE=1.5 s/40 ms, voxel size=20 × 30 × 20 mm, averages=192) was collected, using an TE of 40 ms for improved detection of Glu (Mullins et al, 2008). An unsuppressed water sequence for use as a concentration reference and eddy current correction in post processing was collected with 16 averages and otherwise identical parameters for each single-voxel spectrum.

MRS data analysis

Raw time-domain 1H-MRS data from 4.0 to 1.0 p.p.m. in the spectral dimension were analyzed using LCModel (Provencher, 2001) with the unsuppressed waterscan as a concentration reference. Parameterized macromolecule intensities were included over the fitted spectral region (the LCModel macromolecule intensity set MM20). As a quality assurance measure, LCModel produces a Cramer-Rao lower bound (CRLB) of the fit to the peak of interest. If this value was greater than 20%, the fit was deemed unreliable and excluded from analysis. Metabolite concentrations in molality units of mmol/kg of tissue water were computed for total creatine plus phosphocreatine (Cre), total choline-containing compounds (Cho), myo-inositol (Ins), total N-acetylaspartate plus N-acetyl-aspartylglutamate (NAA), Glu, and Gln. T 1 -weighted images were segmented into gray matter, white matter, and cerebrospinal fluid (CSF) using SPM5. To calculate tissue and CSF fraction within the spectroscopic voxel, the spatial coordinates of the voxel and T 1 -weighted image were used to register the voxel volume to the segmentation maps generated from the T 1 -weighted image. Once this was performed, the gray matter, white matter, and CSF pixels from the segmentation maps that were included in the voxel volume were summed and normalized by the total number of pixels in the volume to arrive at the gray matter, white matter, and CSF fractions in the voxel. Metabolite concentrations were then computed, correcting for partial volume and T 1 and T 2 relaxation effects using methods described previously (Gasparovic et al, 2006). Figure 2 shows a representative spectrum from a control participant.

Figure 2 An example of a single control subject's spectra, with major metabolites labeled. PowerPoint slide Full size image

Statistical analyses

All statistical analyses were carried out using IBM SPSS, Version 16.0.1. χ2-tests were used to investigate the possible group differences on demographic variables. An omnibus ANOVA was used to test the group effect, with neurometabolites entered as dependent variables. Post-hoc t-tests using a Bonferroni adjustment were then applied to identify which group differences accounted for identified omnibus effects. Relationships between substance use and metabolite levels were explored using bivariate correlation and linear regression.