Orientational alignment of amyloidogenic proteins in pre-aggregated solutions.

In the present study we combine dielectric relaxation spectroscopy with generalized Born simulations to explore the role of orientational order for protein aggregation in solutions of bovine pancreatic insulin at various pH conditions. Under aggregation-prone conditions at low pH, insulin monomers prefer antiparallel dipole alignments, which are consistent with the orientation of the monomeric subunits in the dimer structure. This alignment is also true for two dimers, suggesting that already at moderate protein concentrations the species assemble in equilibrium clusters, in which the molecules adopt preferred orientations also found for the protomers of the corresponding oligomers.

Human serial learning: enhancement with arecholine and choline impairment with scopolamine.

Arecholine (4 milligrams), a cholinergic agonist, and choline (10 grams), a precursor of acetylcholine, significantly enhanced serial learning in normal human subjects. The subjects received methscopolamine prior to both arecholine and placebo injections. Conversely, scopolamine (0.5 milligram), a cholinergic antagonist, impaired learning and this impairment was reversed by arecholine and choline and the impairment after scopolamine were inversely proportional to the subject's performance on placebo; that is, "poor" performers were more vulnerable to both the enhancing effect of cholinergic agonist and precursor and the impairment after cholinergic antagonist than "good" performers.

Effects of serotonin on memory impairments produced by ethanol.

Subjects treated with low or high doses of ethanol demonstrated impaired memory, particularly in tests involving the recall of poorly learned information. Zimelidine, an inhibitor of serotonin reuptake, reversed this ethanol-induced impairment. The serotonin neurotransmitter system may mediate learning and memory in humans and may determine some of the effects of alcohol on higher mental functions.

Forms of memory failure.

Memory may fail in a variety of ways. Patients with Korsakoff's syndrome demonstrate global memory deficits similar to those seen in patients with early progressive dementia. Korsakoff's patients, however, may recall rules and principles for organizing information and can gain access to their previously acquired knowledge (semantic memory), whereas recent memory may be grossly impaired. In contrast, dementia patients may have little access to previously acquired knowledge and therefore have great difficulty in organizing and encoding ongoing events. These contrasting forms of memory failure have implications for understanding the structure and mechanisms of memory and learning, particularly the relationship between episodic and semantic memory, as well as the development of therapeutic strategies for cognitive impairments.

Dextroamphetamine: cognitive and behavioral effects in normal prepubertal boys.

The behavioral, cognitive, and electrophysiological effect of a single dose of dextroamphetamine (0.5 milligram per kilogram of body weight) or placebo was examined in 14 normal prepubertal boys (mean age, 10 years 11 months) in a double-blind study. When amphetamine was given, the group showed a marked decrease in motor activity and reaction time and improved performance on cognitive tests. The similarity of the response observed in normal children to that reported in children with "hyperactivity" or minimal brain dysfunction casts doubt on pathophysiological models of minimal brain dysfunction which assume that children with this syndrome have a clinically specific or "paradoxical" response to stimulants.

Effects on humans of 9 -tetrahydrocannabinol administered by smoking.

Twelve chronic marijuana users received triangle up(9)-tetrahydrocannabinol by smoking. The magnitude of their pulse increment was highly correlated with their subjective experiences. Three of the 12 subjects subsequently received triangle up(9)-tetrahydrocannabinol labeled with carbon-14; the time course of its concentration in plasma was highly correlated with the pulse increment. Subjective symptoms, however, appeared later and dissipated more slowly.

Effects of vasopressin on human memory functions.

Arginine vasopressin and a number of its synthetic analogs augment memory functions in experimental animals. One of these analogs, 1-desamino-8-D-arginine vasopressin (DDAVP), influences human learning and memory. Cognitively unimpaired, as well as cognitively impaired adults, treated with DDAVP for a period of several days, learn information more effectively, as measured by the completeness, organization, and consistency (reliability) of recall. DDAVP also appears to reverse partially the retrograde amnesia that follows electroconvulsive treatment.

A psychobiologic analysis of cognitive failures. Structure and mechanisms.

Impairments in memory, learning, and related cognitive functions can vary in most psychiatric or neuropsychiatric disorders. Although many methods have been used to measure the presence and severity of cognitive symptoms, little progress has been made in defining and contrasting possible determinants of cognitive dysfunction. We propose a theoretical framework that describes impairments of higher mental functions in terms of both "extrinsic" noncognitive processes and "intrinsic" cognitive processes. The latter include effort (capacity) demanding processes; automatic processes; episodic (recent biographical) memory; and processes involved in accessing previously acquired knowledge. Noncognitive processes include sensitivity to reinforcement, activation, sensorimotor function, and mood. Each of these processes can be expressed at the time of information acquisition or retrieval from memory. Findings from clinical studies of patients suffering amnestic disorders, progressive dementias, and mood disorders illustrate the utility of such a model for understanding some of the determinants of cognitive dysfunction, for developing diagnostic tools, and for considering therapeutic strategies that may be useful in treating cognitive dysfunctions.

Thinking disorder in depression.

This experiment demonstrated abstract reasoning deficits in depressed patients and detailed some of the components of cognition that may determine such deficits. Subjects were given a discrimination learning problem in which possible solutions had to be formulated and tested against new information. Depressed subjects performed more poorly on the task than controls. Two types of errors--inability to narrow down the set of possible solutions (poor "focusing") and perseveration on disconfirmed hypotheses--hampered the performance of depressed but not control subjects. While logic, memory, and attention were intact at an elementary level, the inability to coordinate these functions in a complex task appeared to be an important feature of the depressive impairment.

Huntington's dementia. Clinical and neuropsychological features.

The neuropsychiatric syndrome of Huntington's disease is outlined in this report with an emphasis on the cognitive deficits that lend themselves to future neurobehavioral research. Eighteen patients without disabling cognitive or psychiatric symptoms were evaluated for a period of 3 to 15 weeks, with assessment of their cognitive disorder, psychiatric, and neurological symptoms. Neuropsychological examination included repeated mental status examination, the Wechsler Adult Intelligence Scale (WAIS), and, for some, parietal lobe testing. In addition to suffering from a loss of finely detailed memories, patients demonstrated impaired organizing, sequencing, planning, and recalling of information on request. On the WAIS, mean verbal and performance scores were not significantly different. Neuropsychological findings suggested that the Huntington's disease pattern of cognitive impairment is not initially diffuse and homogeneous, but characterized by a relative sparing of several higher cortical functions. Many patients had increased irritability and labile affect. The similarity of Huntington's disease to frontal lobe syndromes is also discussed.

Anticholinergic sensitivity in patients with dementia of the Alzheimer type and age-matched controls. A dose-response study.

We compared the cognitive and behavioral responses to three intravenous doses of scopolamine (0.1, 0.25, and 0.5 mg) and placebo of ten patients with dementia of the Alzheimer type (DAT) and ten age- and sex-matched elderly control subjects. The patients with DAT showed significant behavioral and cognitive but not physiologic changes at a lower scopolamine dose (0.25 mg) than did the normal elderly controls. Cognitive tests of new learning and semantic knowledge revealed significant impairments at the 0.25-mg scopolamine dose in the patients with DAT, while the responses of the control population were essentially unchanged. Behaviorally, mild euphoria, motor incoordination, and hostility occurred in the patients with DAT but not the controls at the 0.25-mg dose. These differences were unrelated to peripheral physiologic changes produced by the different scopolamine doses. These results indicate that central nervous system functions such as cognition and certain elements of behavior are more sensitive to temporary cholinergic blockade in patients with DAT than in normal age-matched controls. We review implications concerning the status of central cholinergic function in patients with DAT in light of neuropathologically demonstrated cholinergic system lesions in DAT.

Benzodiazepine sensitivity in normal human subjects.

Increasing intravenous doses of diazepam or placebo were administered to ten healthy normal volunteers, and the changes in saccadic eye velocity, self-rated sedation and anxiety, and plasma cortisol and growth hormone concentrations were measured. Diazepam administration (4.4 to 140 micrograms/kg, cumulative dose) resulted in a dose-dependent decrease in saccadic eye velocity and plasma cortisol level as well as a dose-dependent increase in self-rated sedation and plasma growth hormone level. Self-rated anxiety was unaffected in these relatively nonanxious subjects. The diazepam-induced changes in saccadic eye velocity, sedation, and growth hormone and cortisol levels were highly correlated with each other and with increasing plasma diazepam concentration. These results are consistent with a benzodiazepine receptor-mediated action of diazepam. The highly quantifiable and dose-dependent decrease in saccadic eye velocity by benzodiazepines should make this a useful measure of benzodiazepine receptor sensitivity in humans.

Cognitive processes in depression.

During depressive episodes, patients show both qualitative and quantitative changes in how information is processed. Depressed patients appear to use weak or incomplete encoding strategies to organize and transform events to be remembered. This makes these events less memorable. If the depressed patient is provided organization and structure, then learning-memory deficits are not apparent. Disruptions in arousal-activation in depression can account for these cognitive impairments.

Effort and cognition in depression.

Motor performance and cognitive function were examined in depressed patients and controls. Increasing severity of depression was strongly associated with decrements in performance in both motor and memory tasks. Greatest depression-related impairment was found on those cognitive and motor tasks that required sustained effort. We discuss these results in terms of a generalized deficit in the central motivational state of depressed individuals.

High-dose naloxone infusions in normals. Dose-dependent behavioral, hormonal, and physiological responses.

Hypotheses of involvement of the endogenous opioid system (EOS) in the regulation of human behavior suggest that functional blockade of the EOS should have behavioral consequences. Clinical administration of the opiate receptor antagonist naloxone hydrochloride, however, has had little or inconsistent behavioral effects in normals. This may be attributable to the use of doses insufficient to yield a complete EOS blockade. To assess this explanation, normals were administered increasing doses of naloxone hydrochloride (0.3 to 4 mg/kg) in a single-blind design. Significant dose-dependent behavioral, hormonal, and physiological effects were found. With increasing doses of naloxone, volunteers demonstrated increasingly dysphoric affects, a deterioration of performance on memory testing, increasing systolic BP and respiratory rate, and increasing plasma cortisol and growth hormone levels. These results are consistent with the expected effects of increasing EOS blockade, and thus suggest that lower doses of naloxone used in previous clinical studies may not have been sufficient to produce a complete EOS blockade. Specifically, they suggest involvement of the EOS in the tonic regulation of normal human mood, memory, BP, respirations, and plasma growth hormone and cortisol levels.

Dextroamphetamine. Its cognitive and behavioral effects in normal and hyperactive boys and normal men.

The effects of a single oral dose of dextroamphetamine sulfate on motor activity, vigilance, learning, and mood were compared for normal and hyperactive prepubertal boys and normal college-aged men using a double-blind crossover design. Both groups of boys and men showed decreased motor activity increased vigilance, and improvement on a learning task after taking the stimulant drug. The men reported euphoria, while the boys reported only feeling "tired# or "different# after taking the stimulant. It is not clear whether this difference in effect on mood between adults and children is due to differing experience with drugs, ability to report affect, or a true pharmacologic age-related effect. While there were some quantitative differences in drug effects on motor activity and vigilance between these different groups, stimulants appear to act similarly on normal and hyperactive children and adults.

Naloxone and Alzheimer's disease. Cognitive and behavioral effects of a range of doses.

There have been conflicting reports on the effects of naloxone hydrochloride in patients with dementia of the Alzheimer type (DAT). In addition, none of the naloxone studies in DAT used doses of 2.0 mg/kg or more, the amount necessary to produce reliable cognitive and behavioral changes in young normal subjects. In a randomized, double-blind, placebo-controlled study, 12 patients with DAT were administered naloxone hydrochloride in doses of 5 micrograms/kg, 0.1 mg/kg, and 2.0 mg/kg, with detailed evaluation of its behavioral and cognitive effects using measures selected for their potential relevance to DAT and the known effects of blockade of endogenous opiate systems. None of the measures of motor performance, attention, memory, learning, or recognition showed improvement with naloxone. Increased inappropriate verbal productions were noted after 0.1 mg/kg of naloxone hydrochloride. Patients became irritably activated after this dose, which may account for the altered verbal behavior in this study and also for some of the changes suggesting cognitive improvement in prior studies. Differences in the sensitivity and dose dependency of the behavioral effects in patients with DAT compared with prior studies in young normal subjects merit further investigation.

Effortful and automatic cognitive processes in depression.

Ten patients with major depression and ten age- and sex-matched normal controls were presented with two contrasting cognitive tasks: one required sustained effort and information processing, and the other required only superficial information processing that could be accomplished automatically, with little effort. Depressed patients performed more poorly only on the effort-demanding cognitive task.

Attention dysfunction and psychopathology in college men.

Four hundred college men were screened on a measure of vigilance, the Continuous Performance Test (CPT). The individuals with good and poor attention (the upper and lower 5% of the CPT score distribution) were compared on multiple measures of psychiatric disturbance, cognition, and psycho-physiologic function. The attention dysfunction group (lower 5%) had a higher incidence of symptoms of hyperactivity both in childhood and as adults, but had no higher incidence of other psychopathology as assessed with either the Research Diagnostic Criteria or the Minnesota Multiphasic Personality Inventory. Cognitive differences between the lower and upper CPT groups, including differences on Wechsler Adult Intelligence Scale subtests, the Stroop test, reaction time, and evoked potentials, substantiated an attention dysfunction syndrome. Thus, attentional dysfunction in young adults seems more closely linked to hyperactivity than to current psychopathology.

L-deprenyl in Alzheimer's disease. Preliminary evidence for behavioral change with monoamine oxidase B inhibition.

Since monoamine neurotransmitter disturbances exist in some cases of dementia of the Alzheimer's type (DAT), monoamine-enhancing drugs may ameliorate some symptoms of DAT. L-Deprenyl is a monoamine oxidase (MAO) inhibitor that is generally free of undesired effects. At low doses (10 mg/d) it selectively inhibits MAO-B, an enzyme whose level is elevated in the brains of patients with DAT who are studied post mortem. At higher doses it has more complex effects, including inhibition of MAO-A plus MAO-B. We administered 10 mg/d and 40 mg/d of L-deprenyl to 17 patients with DAT in a double-blind, placebo-controlled, serial treatment. Total Brief Psychiatric Rating Scale scores decreased significantly during 10-mg/d treatment, with decreases in measures of anxiety/depression, tension, and excitement. Approximately one half of the patients' conditions were judged to be improved clinically, with evidence of increased activity and social interaction along with reduced tension and retardation. Similar but smaller changes were observed during 40-mg/d treatment. The behavioral changes were associated with improvement in performance on a complex cognitive task requiring sustained effort. There were minimal physiologic and side effects. The greater effect of low-dose L-deprenyl therapy suggests that it is the inhibition of MAO-B, and not MAO-A, that may be important in the behavioral effects of L-deprenyl administration to patients with DAT.