Altered benzodiazepine receptor sensitivity in alcoholism: a study with fMRI and acute lorazepam challenge

Restoration of mammillothalamic functional connectivity through thiamine replacement therapy in Wernicke's encephalopathy

Resting-state functional MRI (fMRI) is now providing further understanding of neuropsychiatric illnesses. However, its practical applicability in the clinical realms is still questionable. Here we report three consecutive followed-up resting-state fMRI data in a single case with Wernicke encephalopathy before and after high-dose thiamine replacement therapy ranging over 20 months. We measured the mammillothalamic functional connectivity strength between the first ROI (mammillary body) and a voxel which showed the highest co-activation among voxels within the anterior thalamus (the second ROI) to enhance the specificity of the functional connectivity data. We found that the time-series changes in the mammillothalamic functional connectivity generally paralleled to the changes in delayed verbal and nonverbal recall memory scores in the left and right hemisphere, respectively. Among these, the left-side connectivity and delayed verbal recall score seemed to be related to the overall clinical status change. Modified directed transfer function (dDTF) analysis also identified significant information flows with mammillary-to-thalamic direction except at the acute illness state. Our findings, though preliminary in nature, suggest the practical applicability of resting-state fMRI to trace an effect of thiamine replacement therapy on the memory tract function in Wernicke encephalopathy at single-patient level.

The impact of alcoholism on sleep evoked Delta frequency responses

BACKGROUND

K-complexes (KCs) are evoked delta frequency electroencephalogram (EEG) responses during sleep that occur when large numbers of healthy cortical cells burst fire in a synchronized manner. The KC amplitude and incidence are sensitive measures of normal healthy brain aging. Given the known neurodegenerative consequences of alcohol abuse it was hypothesized that alcoholism would be associated with further KC amplitude and incidence reductions.

METHODS

Eighty-four subjects (42 alcoholics) screened for medical, psychiatric, and sleep problems participated. The protocol involved the presentation of auditory stimuli during stage 2 sleep throughout a night in the laboratory. The KCs were identified and averaged, to enable measurement of the P2, N550, and P900 peaks.

RESULTS

Compared with control subjects, alcoholic men and women had lower KC incidence (p < .001) and P2 (p < .001), N550 (p < .05), and P900 (p < .05) amplitudes. There was a significant diagnosis x site interaction (p < .001), indicating the group difference was largest at frontal sites. Longer sobriety correlated with increased N550 amplitude (p < .01).

CONCLUSIONS

The KC incidence and amplitude were negatively impacted in alcoholic men and women with exacerbation of the normal aging effects, particularly over frontal scalp regions. The observed relationship between improvements in KC measures and increased time of abstinence suggests that these measures might provide a useful marker of brain recovery with continued abstinence from alcohol.

GABA-A receptors and the response to CO(2) inhalation - a translational trans-species model of anxiety?

The mechanisms by which the inhalation of carbon dioxide (CO(2)) produces anxiety and panic are not fully understood, although more recently there is evidence to suggest the involvement of a neural 'fear circuit'. We have suggested that this neural fear circuit is partly mediated by the brain noradrenaline network [Bailey, J.E., Argyropoulos, S.V., Lightman, S.L. and Nutt, D.J., (2003) Does the brain noradrenaline network mediate the effects of the CO(2) challenge? J Psychopharmacol 17(3): 252-259.]. However, we now review evidence that GABA-A may also play an important role in the modulation of CO(2)-induced anxiety. The review of this evidence starts with a key publication showing that 1 min of 35% CO(2)/65% air produced anxiogenic effects in a rat model of anxiety, to a similar extent to the anxiogenic betacarboline derivative FG7142, a benzodiazepine receptor inverse agonist. The effects of both anxiogenic stimuli were abolished with pre-treatment with alprazolam (0.5 mg/kg), but only those of FG7142, not CO(2), was blocked by a benzodiazepine antagonist [Cuccheddu, T., Floris, S., Serra, M., Porceddu, L., Sanna, E., Biggio, G., (1995) Proconflict effect of carbon dioxide inhalation in rats. Life Sci 56: PL 321-324.]. Although the evidence from this study did not conclusively prove that CO(2) had an action to reduce GABA function, it was an experiment designed to be translational to compare what was known about CO(2)-induced anxiety in patients, and to also to explore if GABA mechanisms are involved. Additional evidence from the literature is found in the association between GABA and chemoreceptors, both in laboratory and human studies and GABA and anxiety disorders. Evidence of this association is found across species from stress-induced change in GABA levels in plants and insects to humans, where there is now much evidence of abnormalities in GABA/benzodiazepine receptors in anxiety and other psychiatric disorders. This paper reviews some of the evidence and attempts to relate and compare these findings across species from the human to the Drosophila.