Low-Density Water Structure Observed in a Nanosegregated Cryoprotectant Solution at Low Temperatures from 285 to 238 K.

The structure of liquid water is defined by its molecular association through hydrogen bonding. Two different structures have been proposed for liquid water at low temperatures: low-density liquid (LDL) and high-density liquid (HDL) water. Here, we demonstrate a platform that can be exploited to experimentally probe the structure of liquid water in equilibrium at temperatures down to 238 K. We make use of a cryoprotectant molecule, glycerol, that, when mixed with water, lowers the freezing temperature of the solution nonmonotonically with glycerol concentration. We use a combination of neutron diffraction measurements and computational modeling to examine the structure of water in glycerol-water liquid mixtures at low temperatures from 285 to 238 K. We confirm that the mixtures are nanosegregated into regions of glycerol-rich and water-rich clusters. We examine the water structure and reveal that, at the temperatures studied here, water forms a low-density water structure that is more tetrahedral than the structure at room temperature. We postulate that nanosegregation allows water to form a low-density structure that is protected by an extensive and encapsulating glycerol interface.

Molecular insight into the hydrogen bonding and micro-segregation of a cryoprotectant molecule.

Glycerol-water liquid mixtures are intriguing hydrogen-bonded systems and essential in many fields of chemistry, ranging from basic molecular research to widespread use in industrial and biomedical applications as cryoprotective solutions. Despite much research on these mixtures, the details of their microscopic structure are still not understood. One common notion is that glycerol acts to diminish the hydrogen bonding ability of water, a recurring hypothesis that remains untested by direct experimental approaches. The present work characterizes the structure of glycerol-water mixtures, across the concentration range, using a combination of neutron diffraction experiments and computational modeling. Contrary to previous expectations, we show that the hydrogen bonding ability of water is not diminished in the presence of glycerol. We show that glycerol-water hydrogen bonds effectively take the place of water-water hydrogen bonds, allowing water to maintain its full hydrogen bonding capacity regardless of the quantity of glycerol in the environment. We provide a quantitative measurement of all hydrogen bonding in the system and reveal a concentration range where a microsegregated, bipercolating liquid mixture exists in coexistence with a considerable interface region. This work highlights the role of hydrogen bonding connectivity rather than water structuring/destructuring effects in these important cryoprotective systems.

Structural examination of the impact of glycerol on water structure.

The sugar alcohol glycerol is essential for cryopreservation, an important process used for the storage of biological molecules, cells, or tissues at low temperatures. A key hypothesis for the cryoprotective action of glycerol is that the glycerol molecule acts to modify the hydrogen bonding ability of water molecules, thus inhibiting ice formation. In this study, high-resolution neutron diffraction has been used in conjunction with hydrogen/deuterium isotopic labeling to determine with unprecedented detail the structure of a dilute aqueous glycerol solution. Contrary to some expectations, at the first neighbor level no modification in the position of the coordination shell of water is observed. However, at the second neighbor level the presence of only small quantities of glycerol in the solution has the same impact on water structure as increasing the pressure. Evidence is also found of more glycerol monomers than would be expected in the solution. This prevalence of isolated glycerol molecules results in a very well mixed solution with glycerol-water hydrogen bond interactions being very favorable. Our results indicate that while the local structure of water is relatively unperturbed by the presence of glycerol, the hydrogen bonded network is highly mixed between glycerol and water. These results indicate that efforts to explain the action of glycerol should focus on not just local water structure, but the extended hydrogen bonded network in the system.

Preference for isolated water molecules in a concentrated glycerol-water mixture.

Neutron diffraction coupled with hydrogen/deuterium isotopic substitution has been used to investigate the structure of a concentrated glycerol water (4:1 mole fraction) solution. The neutron diffraction data were used to constrain a three-dimensional computational model that is experimentally relevant using the empirical potential structure refinement technique. From interrogation of this model, we find that glycerol-glycerol hydrogen bonding is largely unperturbed by the presence of water in the solution. We find that glycerol-water hydrogen bonding is prevalent, suggesting that water molecules effectively take the place of glycerol molecules in this concentrated solution. In contrast, we find that water-water hydrogen bonding is significantly perturbed. While the first coordination shell of water in the concentrated solution remains similar to that of pure water, water-water hydrogen bonding is greatly diminished beyond the first neighbor distance. Interestingly, the majority of water molecules exist as single monomers in the concentrated glycerol solution. The preference of isolated water molecules results in a solution that is well mixed with optimal glycerol-water hydrogen bonding. These results highlight the importance of preferential hydrogen bonding in aqueous solutions and suggest a mechanism for cryoprotection by which glycerol effectively hydrogen bonds with water, resulting in a disrupted hydrogen-bonded water network.

The structure of glycerol in the liquid state: a neutron diffraction study.

Neutron diffraction coupled with hydrogen/deuterium isotopic substitution has been used to investigate the structure of the pure cryoprotectant glycerol in the liquid state at 298 K and 1 atm. The neutron diffraction data were used to constrain a 3 dimensional computational model that is experimentally relevant using the empirical potential structure refinement (EPSR) technique. These simulations lead to a model structure of the glycerol molecule that is consistent with the experimental data. Interestingly, from interrogation of this structure, it is found that the number of hydrogen bonds per molecule is larger than had previously been suggested. Furthermore, converse to previous work, no evidence for intra-molecular hydrogen bonds is found. These results highlight the importance and relevance of using experimental data to inform computational modelling of even simple liquid systems.

Symptom provocation alters behavioral ratings and brain electrical activity in obsessive-compulsive disorder: a preliminary study.

Regional brain activity was measured using quantitative electroencephalography (EEG) in six patients with obsessive-compulsive disorder (OCD) during live and imaginal exposure to feared contaminants. OCD symptoms increased significantly from baseline levels during live and imaginal exposures. However, live exposure provoked significantly more OCD symptoms than imaginal exposure. There was a significant change in the anterior-to-posterior scalp distribution of alpha power during live exposure. These preliminary results suggest that: (1) live exposure is more effective than imaginal exposure in altering behavioral and electrophysiological measures; and (2) live exposure is associated with regional EEG changes in OCD.

Response- and stimulus-related ERP asymmetries in a tonal oddball task: a Laplacian analysis.

Previous studies have found greater P3 amplitude over right than left hemisphere sites in a tonal oddball task with a reaction time (RT) response. This asymmetry had a central topography, and interacted with response hand. Identification of the processes underlying these asymmetries requires the use of additional methods for separating response- and stimulus-related contributions. We applied local Hjorth and spherical spline algorithms to compute surface Laplacian topographies of ERP data recorded from 30 scalp electrodes in a pooled sample of 46 right-handed healthy adults. For both methods, the current sources underlying the late positive complex were largest at medial parietal regions, but were asymmetric at central and frontocentral sites. Although a frontocentral sink contralateral to the response hand contributed to the asymmetry of the classic P3 peak, the source asymmetry was most robust after the sink had resolved. The late source was largest at electrode C4 for right hand responses, and was further enhanced in subjects showing a dichotic left ear advantage, but was unrelated to response speed. We conclude that the right hemisphere source reflects an interaction of response-related asymmetries with right hemisphere processes responsible for pitch discrimination.

Brain ERPs of depressed patients to complex tones in an oddball task: relation of reduced P3 asymmetry to physical anhedonia.

Event-related potentials to binaural complex tones were recorded from 40 depressed outpatients and 22 normal control participants at 30 electrode sites. Patients did not differ from control participants in N1 or P3 amplitude but showed greater N2. N2 was greater over right than over the left hemisphere at lateral sites in patients and control participants. A P3 asymmetry was found for control participants and patients with low scores on a physical anhedonia scale, but not for patients with high anhedonia scores. Topographic (local Laplacian) maps corresponding to P3 showed greater radial current flow over right than over left central regions in control participants. Patients with high anhedonia did not show this asymmetry, whereas patients with low anhedonia showed an intermediate asymmetry. These findings support the hypothesis that anhedonic depression is associated with dysfunction of right hemisphere mechanisms mediating the processing of complex pitch information.

Regional brain asymmetries in major depression with or without an anxiety disorder: a quantitative electroencephalographic study.

Studies of brain activity in affective disorders need to distinguish between effects of depression and anxiety because of the substantial comorbidity of these disorders. Based on a model of asymmetric hemispheric activity in depression and anxiety, it was predicted that anxious and nonanxious depressed patients would differ on electroencephalographic (EEG) measures of parietotemporal activity. Resting EEG (eyes closed and eyes open) was recorded from 44 unmedicated outpatients having a unipolar major depressive disorder (19 with and 25 without an anxiety disorder), and 26 normal controls using 30 scalp electrodes (13 homologous pairs over the two hemispheres and four midline sites). As predicted, depressed patients with an anxiety disorder differed from those without an anxiety disorder in alpha asymmetry. Nonanxious depressed patients showed an alpha asymmetry indicative of less activation over right than left posterior sites, whereas anxious depressed patients showed evidence of greater activation over right than left anterior and posterior sites. The findings are discussed in terms of a model in which specific symptom features of depression and anxiety are related to different patterns of regional brain activity.

Abnormality of EEG alpha asymmetry in female adolescent suicide attempters.

Abnormal electroencephalographic (EEG) activity has been associated with various psychiatric disorders and behaviors, including depression, suicide, and aggression. We examined quantitative resting EEG in Hispanic female adolescent suicide attempters and matched normal controls. Computerized EEG measures were recorded at 11 scalp sites during eyes open and eyes closed periods from 16 suicide attempters and 22 normal controls. Suicide attempters differed from normal controls in alpha asymmetry. Normal adolescents had greater alpha (less activation) over right than left hemisphere, whereas suicidal adolescents had a nonsignificant asymmetry in the opposite direction. Nondepressed attempters were distinguished from depressed attempters in that they accounted for the preponderance of abnormal asymmetry, particularly in posterior regions. Alpha asymmetry over posterior regions was related to ratings of suicidal intent, but not depression severity. The alpha asymmetry in suicidal adolescents resembled that seen for depressed adults in its abnormal direction, but not in its regional distribution. Findings for suicidal adolescents are discussed in terms of a hypothesis of reduced left posterior activation, which is not related to depression but to suicidal or aggressive behavior.

Brain event-related potentials to complex tones in depressed patients: relations to perceptual asymmetry and clinical features.

Brain event-related potentials (ERPs) to probe tones in a dichotic complex tone test were recorded from right-handed depressed patients (n = 44) and normal subjects (n = 19) at homologous sites over left and right hemispheres (F3, F4; C3, C4; P3, P4; O1, O2). There were no differences between groups N1 or P2 amplitude, but patients had smaller P3 amplitude than did normal subjects. Depressed patients failed to show either the left ear advantage or behavior-related hemispheric asymmetry of P3 seen for normal subjects. Depressed patients also showed less difference in hemispheric asymmetry between same and different judgments. These findings indicate that the abnormal behavioral asymmetry for dichotic pitch discrimination in depressed patients reflects a reduction in hemispheric asymmetry and is related to relatively late stages of cognitive processing.

Smaller right ear (left hemisphere) advantage for dichotic fused words in patients with schizophrenia.

OBJECTIVE: The purposes of this study were to compare right ear (left hemisphere) advantage for dichotic words in schizophrenia and depression and to assess its association with antipsychotic medication, symptom ratings, and gender. METHOD: Thirty-two schizophrenic patients and 65 patients with major depression were given the Fused Rhymed Words Test, a dichotic listening measure of hemispheric dominance for language. RESULTS: An earlier finding of smaller left hemisphere advantage in schizophrenic patients was replicated. There was no significant change in ear advantage in a subgroup of the schizophrenic patients tested when they were taking neuroleptics and when they were not. The smaller left hemisphere advantage in the schizophrenic patients was not dependent on gender but was related to symptom ratings on the Positive and Negative Syndrome Scale. CONCLUSIONS: The findings are consistent with a left hemisphere dysfunction in schizophrenia, which is associated with positive symptoms.

Brain event-related potential correlates of overfocused attention in obsessive-compulsive disorder.

A hypothesis of overfocused attention in obsessive-compulsive disorder was investigated by measuring auditory event-related potentials (ERPs) during a selective attention task. Unmedicated patients (n = 18) with this disorder showed significantly larger attention-related processing negativity (PN), with earlier onset and longer duration, than did normal controls (n = 15). In the N200 region (160-250 ms), PN was larger in patients with fewer nonspecific neurological soft signs. This task, however, did not yield any group differences in mismatch negativity (N2a) or classical N200 (N2b). P300 amplitudes for attended targets were smaller for patient than normal groups, but the reverse was true for P300 and positive slow wave amplitudes for unattended nontargets. Collectively, these ERP abnormalities suggest a misallocation of cognitive resources. Because of the importance of the frontal lobe in the control of selective attention, PN enhancement in patients with obsessive-compulsive disorder may reflect hyperactivation of this region. This conceptualization is consistent with recent functional neuroimaging findings.

Event-related potential and clinical correlates of neurodysfunction in obsessive-compulsive disorder.

The current study confirmed with increased sample sizes our preliminary findings of event-related potential (ERP) abnormalities in obsessive-compulsive disorder (OCD) (Towey et al., 1990) and examined their relationship to symptom severity, treatment response, and neurological soft signs. Unmedicated patients (n = 17) showed larger negativities in N200 and slow wave regions than normal control subjects (n = 16) to correctly detected auditory "oddball" stimuli. N200 amplitude was larger over left than right hemispheres of OCD patients, but not normal control subjects. Greater N200 amplitude correlated with less severe obsessions, better response to subsequent treatment with serotonin reuptake blockers, and fewer neurological soft signs in OCD. With increased task difficulty, N200 and P300 latencies lengthened for normal subjects, but not for OCD patients. The abnormal ERP pattern in OCD supports hypotheses of cortical hyperarousal and overfocused attention.

Correspondence between brain ERP and behavioral asymmetries in a dichotic complex tone test.

Electrophysiologic correlates of perceptual asymmetry for dichotic pitch discrimination were investigated in 20 normal subjects. Brain event-related potentials (ERPs) elicited by dichotic pairs and binaural probe tones in the Complex Tone Test (Sidtis, 1981) were recorded from homologous scalp locations over left and right hemispheres (F3, F4; C3, C4; P3, P4; O1, O2). Baseline-to-peak amplitudes were measured for N100, P200, and a late positive complex consisting of P350, P550, and slow wave. A left ear advantage (LEA) was evident in 70% of the subjects, and hemispheric asymmetries related to this behavioral asymmetry were found for P350 and P550 amplitudes to probe stimuli. Subjects with a strong LEA had greater amplitudes over the right hemisphere than the left, whereas subjects with little or no LEA showed a nonsignificant trend toward the opposite hemispheric asymmetry. Hemispheric asymmetry of these late ERPs at parietal and occipital sites was highly correlated with behavioral asymmetry. These findings suggest the utility of electrophysiological measures in assessing hemispheric asymmetries for processing complex pitch information.

Abnormal cerebral laterality in bipolar depression: convergence of behavioral and brain event-related potential findings.

Cerebral laterality in bipolar and unipolar major depression was compared using visual half-field and dichotic listening measures of perceptual asymmetry. The results replicate our prior finding of abnormal laterality in bipolar depressed patients on a visuospatial test. Bipolar patients (n = 11) failed to show the left visual field (right hemisphere) advantage for dot enumeration seen for both unipolar patients (n = 43) and normal controls (n = 24). Bipolar patients performed significantly poorer than unipolar patients on normal controls for left visual field, but not right visual field stimuli. An electrophysiological correlate of abnormal visual field asymmetry in bipolar depression was found in brain event-related potentials recorded during audiospatial and temporal discrimination tasks. Bipolar patients had smaller N100 amplitudes for test stimuli in the left than right hemifield, whereas unipolar patients and normals did not. The origins of left hemifield deficits in bipolar depression are discussed in terms of right-sided dysfunction of an arousal/attentional system involving temporoparietal and possibly frontal regions.

Left hemispheric activation in depersonalization disorder: a case report.

Depersonalization disorder is classified in DSM-III-R (APA 1987) as a dissociative disorder characterized by altered perception or experience of the self. To date, there are no known reports of the neurobiological features of this disorder. We report clinical and biological correlates in a patient with depersonalization disorder previously unresponsive to a variety of anticonvulsant, monoamine oxidase inhibitor, and tricyclic antidepressant trials, but for whom fluoxetine partially reduced depersonalization symptoms, but not associated anxiety and depression. Neurophysiological, neuroanatomical and neuropsychological findings revealed left hemispheric frontal-temporal activation and decreased left caudate perfusion. These findings suggest a similarity to the neuropsychiatric data reported in obsessive-compulsive disorder patients.

Event-related potentials in depression: influence of task, stimulus hemifield and clinical features on P3 latency.

P3 latency, a brain event-related potential (ERP) correlate of stimulus evaluation time, was measured in 25 unmedicated depressed patients and 27 normal controls during auditory temporal and spatial discrimination tasks. Patients were divided into two subgroups, one having a typical major depression (melancholia or simple mood reactive depression) and one having an atypical depression. Typical depressives had abnormally long P3 latency for the spatial task but not the temporal task. They also showed an abnormal lateral asymmetry, with longer P3 latency for stimuli in the right hemifield than the left. In contrast, atypical depressives did not differ from normals in either respect. Longer P3 latency correlated with ratings of insomnia, while abnormal lateral asymmetry correlated with reduced right visual field advantage for syllables. The P3 latency findings point to a task-related slowing of perceptual decisions in a subgroup of depression.

Endogenous event-related potentials in obsessive-compulsive disorder.

Brain event-related potentials (ERPs) were used to investigate central nervous system (CNS) correlates of cognitive function in obsessive-compulsive disorder (OCD). ERPs of 10 unmedicated OCD patients and 10 normal controls were measured in an auditory "oddball" task. Increasing task difficulty resulted in longer N200 and P300 latencies in normal subjects, but not in OCD patients. Moreover, OCD patients displayed shorter P300 latency than normal controls for the more difficult discrimination conditions. This replicates prior findings of Beech et al. (1983) for a visual task. For both levels of task difficulty, OCD patients also showed greater negativity than normal controls in the N200 region, which extended into the subsequent slow wave region. Negativities in the N200 and slow wave regions were larger at sites over the left hemisphere than the right hemisphere. The enhanced negativities and reduced P300 latency in OCD patients are discussed in terms of current theories postulating cortical hyperarousal and left hemisphere involvement in OCD.

Methadone during pregnancy: assessment of behavioral effects in the rat offspring.

Pregnant rats were administered methadone hydrochloride by gastric intubation. Beginning on day 8 of gestation, a drug group received 5 mg/kg/day; the daily maintenance dose was increased to 10 mg/kg after 4 days with the final dose given on day 22. An intubation control group received sterile water alone on the same gestation days and a nontreated control group was left undisturbed, All experimental and control litters were fostered at birth to untreated mothers, Body weights were low at birth among the methadone offspring but were similar to controls by weaning. During adulthood, offspring were tested on several operant tasks that included acquisition of a lever-pressing response, performance on a variable interval reinforcement schedule, acquisition and performance of an auditory-visual discrimination and response inhibition in a "punishment" paradigm. None of these measures revealed any learning or inhibitory impairments among the methadone-exposed offspring. The major behavioral effect produced by the treatment was a high response output which emerged for each sex in different phases of testing.