HMG proteins and DNA flexibility in transcription activation.

The relative stiffness of naked DNA is evident from measured values of longitudinal persistence length (approximately 150 bp) and torsional persistence length (approximately 180 bp). These parameters predict that certain arrangements of eukaryotic transcription activator proteins in gene promoters should be much more effective than others in fostering protein-protein interactions with the basal RNA polymerase II transcription apparatus. Thus, if such interactions require some kind of DNA looping, DNA loop energies should depend sensitively on helical phasing of protein binding sites, loop size, and intrinsic DNA curvature within the loop. Using families of artificial transcription templates where these parameters were varied, we were surprised to find that the degree of transcription activation by arrays of Gal4-VP1 transcription activators in HeLa cell nuclear extract was sensitive only to the linear distance separating a basal promoter from an array of bound activators on DNA templates. We now examine the hypothesis that this unexpected result is due to factors in the extract that act to enhance apparent DNA flexibility. We demonstrate that HeLa cell nuclear extract is rich in a heat-resistant activity that dramatically enhances apparent DNA longitudinal and torsional flexibility. Recombinant mammalian high-mobility group 2 (HMG-2) protein can substitute for this activity. We propose that the abundance of HMG proteins in eukaryotic nuclei provides an environment in which DNA is made sufficiently flexible to remove many constraints on protein binding site arrangements that would otherwise limit efficient transcription activation to certain promoter geometries.

Improved quantitation of DNA curvature using ligation ladders.

It is often desirable to estimate accurately the local shape of DNA molecules. Such measurements are useful in understanding the intrinsic contribution of DNA sequence to curvature, as well as in assessing the effects of chemical modifications. We have been investigating the effects of asymmetric phosphate neutralization on DNA shape using the well-characterized ligation ladder approach developed by Crothers and co-workers [D.M. Crothers and J.Drak (1992) Meth. Enzymol.,212, 46-71]. This technique is remarkably sensitive to differences in DNA shape. We now report a general quantitative assay of DNA curvature that we have validated using a set of phased A(5)tract standards. This approach allows simultaneous estimation of helix axis deflection magnitude and direction when a test sequence is monitored in at least three phasings relative to a reference A(5-6)tract in short DNA duplexes. Analysis using this improved approach confirms our published data on DNA curvature due to electrostatic effects.

DNA constraints on transcription activation in vitro.

Activators of eukaryotic transcription often function over a range of distances. It is commonly hypothesized that the intervening DNA between the transcription start site and the activator binding sites forms a loop in order to allow the activators to interact with the basal transcription apparatus, either directly or through mediators. If this hypothesis is correct, activation should be sensitive to the presence of intrinsic bends in the intervening DNA. Similarly, the precise helical phasing of such DNA bends and of the activator binding sites relative to the basal promoter should affect the degree of transcription activation. To explore these considerations, we designed transcription templates based on the adenovirus E4 promoter supplemented with upstream Gal4 activator binding sites. Surprisingly, we found that neither insertion of intrinsically curved DNA sequences between the activator binding sites and the basal promoter, nor alteration of the relative helical alignment of the activator binding sites and the basal promoter significantly affected in vitro transcription activation in HeLa cell nuclear extract. In all cases, the degree of transcription activation was a simple inverse function of the length of intervening DNA. Possible implications of these unexpected results are discussed.

Diagnosis and neuroanatomical correlates of depression in brain-damaged patients. Implications for a neurology of depression.

Recognizing depression in brain-damaged patients poses considerable problems. The standard diagnostic criteria often are not applicable since the neurological lesion may distort or even obliterate salient features of depression. Patients actually may deny being depressed or dysphoric, not have a depressive affect, or be totally unaware of abnormal vegetative behaviors. Furthermore, brain lesions themselves may produce striking behavioral alterations that can be mistakenly attributed to depression, or striking behavioral changes due to depression may be mistakenly attributed to the brain lesion. Based on five case studies, several clinical guidelines for recognizing and diagnosing depression in brain-damaged patients are offered. These cases also provide a data base to generate initial hypotheses about the neuroanatomical basis of the depressive syndrome. By observing how focal brain lesions modify the signs and symptoms of depression, inferences are made about brain areas crucial for modulating the various features of the depressive syndrome.

Topography of the human corpus callosum.

This study was undertaken to determine the topographical organization of fibers coursing through the human corpus callosum. We correlated the distribution of Wallerian degeneration in the corpus callosum with the anatomical sites of focal cortical lesions due to ischemic infarctions or circumscribed contusions. Fibers from the inferior frontal and anterior inferior parietal regions course through the rostrum and genu of the corpus callosum. Callosal connections from the temporo-parieto-occipital junctional region course through the splenium and caudal portion of the body of the corpus callosum. Both the superior parietal lobule and the occipital cortex give rise to interhemispheric fibers that course exclusively through the splenium of the corpus callosum. No callosal degeneration was associated with a cortical lesion in the anterior superior frontal region. The topographical organization of fibers in the human corpus callosum appears to be fairly similar to that found in the rhesus monkey (Macaca mulatta).

Sensory-specific and fractional disorders of recent memory in man. II. Unilateral loss of tactile recent memory.

Three patients were found to have unilateral tactile recent memory loss on examination. In two patients the loss occurred in the right hand and was accompanied by a disorder of verbal recent memory; in the third patient the loss occurred in the left hand and was not accompanied by any other disturbance in recent memory. An acute unilateral lesion, either structural or functional, in the medial temporal lobe contralateral to the tactile recent memory disturbance was the common denominator in all three cases. The proper methods for diagnosing a unilateral tactile disturbance of recent memory and other forms of fractional disorders of recent memory are discussed. Based on computerized tomography scans and behavioral and anatomical data in man and monkey, an anatomical explanation is offered to account for the syndromes of right and left unilateral tactile recent memory loss. The possible existence of other forms of fractional disturbances of recent memory and the role of the cerebral commissures in recent memory functions are discussed.

Sensory-specific and fractional disorders of recent memory in man. I. Isolated loss of visual recent memory.

Two patients who lost, in isolation, visual recent memory following bilateral posterior cerebral artery infarctions are described. Tactile, verbal, and nonverbal auditory recent memory functions were preserved in both patients. Based on computerized tomography scans and behavioral and anatomical data in monkey, isolated loss of visual recent memory in man is best understood as a bilateral disconnection syndrome between the striate cortex and the structures in the medial temporal lobe that are involved with recent memory. The possible existence of two other sensory-specific disorders of recent memory, tactile and auditory, is postulated, and the clinical relationship of prosopagnosia, achromatopsia, and spatial disorientation to visual recent memory loss is discussed.

The aprosodias. Functional-anatomic organization of the affective components of language in the right hemisphere.

It was recently proposed that the affective components of language, encompassing prosody and emotional gesturing, are a dominant function of the right hemisphere, and that their functional-anatomic organization in the right hemisphere mirrors that of propositional language in the left hemisphere. Ten right-handed patients with focal lesions of the right hemisphere and disorders of affective language are described. Observations were made about each patient's spontaneous prosody, prosodic repetition, prosodic comprehension, and comprehension of emotional gesturing. Using this particular examination strategy, which is derived from the usual bedside approach to aphasic disorders, the organization of affective language in the right hemisphere does mirror the organization of propositional language in the left hemisphere. Furthermore, the disorders of affective language seem to be classifiable in the same manner as the aphasias. Thus, the term "aprosodia," preceded by specific modifiers such as motor, global, transcortical sensory, etc, seems appropriate when classifying the various disorders of affective language that occur following-right-hemisphere damage. The relationships between affect, mood, pathologic laughing and crying, and depression are also discussed.

Sensory aprosodia with left hemiparesis from subcortical infarction. Right hemisphere analogue of sensory-type aphasia with right hemiparesis?

We report a case of sensory aprosodia with left hemiparesis following an ischemic infarction of the right thalamus and posterior limb of the internal capsule. Bedside evaluation, confirmed by special quantitative tests, demonstrated normal spontaneous affective prosody and gesturing with marked impairment of affective repetition and comprehension of affective prosody and gestures. A left hemiparesis with sensory loss was also present. This combination of deficits appears to represent the right-side analog to the unusual syndrome of Wernicke-type aphasia with right hemiparesis occasionally observed following left subcortical injury, thus providing further support for the hypothesis that the functional-anatomic organization of affective language in the right hemisphere mirrors that of propositional language in the left.

Dominant language functions of the right hemisphere? Prosody and emotional gesturing.

Two patients lost the ability to impart affective qualities to their speech following lesions in the right hemisphere. Arguments are given to support the idea that the right or "minor" hemisphere has a dominant role in modulating the affective components of speech. The anatomical organization of the cortical areas subserving affective speech in the right hemisphere seem to be similar to the organization of cortical areas subserving propositional speech in the left or "major" hemisphere.

Crossed aprosodia in strongly dextral patients.

Two strongly right-handed patients with aprosodia following left hemisphere strokes are described. These patients appear to represent the aprosodia analogue of crossed aphasia--crossed aprosodia--and provide further evidence that the organization of the effective components of language is functionally and anatomically similar to the organization of the propositional components of language in the brain. In addition, both patients evidenced "double-crossed" agraphia involving the left hand.

How the brain integrates affective and propositional language into a unified behavioral function. Hypothesis based on clinicoanatomic evidence.

Recent publications suggest that the right hemisphere dominates in modulating the affective components of language. Disorders of language form right-sided focal brain lesions have been called "aprosodias" and can be classified in a manner similar to the aphasias. We describe a patient with motor aprosodia who subsequently died and underwent neuropathologic examination. From the neuropathologic findings and recent observations concerning the neurology of depression, we hypothesize that the motor integration of propositional and affective language takes place in the brainstem, whereas their higher-order integration takes place via the callosal connections between Wernicke's area on the left and its homologue on the right. Direct application of these functional and anatomic relations can help clinicians to properly interpret the often incongruous and disparate behavioral and language responses encountered in brain-damaged patients.

Localization of the pyramidal tract in the internal capsule by whole brain dissection.

Six human brains were dissected by blunt technique and sectioned horizontally to establish the three-dimensional relationships of the pyramidal tract and the internal capsule. In all instances, the pyramidal tract entered the rostral capsule in the anterior half of the posterior limb and progressively shifted into the posterior half of the posterior limb in the more caudal horizontal sections. These observations resolve the current controversy about the exact anatomic location of the pyramidal tract in the posterior limb of the internal capsule. This controversy arose because previous authors failed to consider the changing rostrocaudal/anterior-posterior anatomy of the pyramidal tract as it courses through the posterior limb.

Left medial parietal lobe and receptive language functions: mixed transcortical aphasia after left anterior cerebral artery infarction.

Three aphasic patients with infarctions involving the left anterior cerebral artery have been studied. Two had trancortical motor aphasia, and one had mixed transcortical (or isolation) aphasia. Based on computerized tomography in two patients and whole-brain sections in one, the patient with mixed transcortical aphasia had a lesion that went beyond the rolandic fissure to involve the anterior precuneus lobule of the left medial parietal lobe. In the patients with transcortical motor aphasia, the lesion was confined to the frontal lobe. From these cases and other data, it seems likely that the left medial parietal lobe has receptive language functions analogous to the motor language functions of the left medial frontal lobe, thus accounting for the mixed transcortical aphasia observed in the patient whose left anterior cerebral artery infarction involved both the medial parietal and medial frontal lobes.

Left-handed mirror writing following right anterior cerebral artery infarction: evidence for nonmirror transformation of motor programs by right supplementary motor area.

A patient with acquired, pathologic left-handed mirror writing and mirror movements during bimanual coordination is reported. CT demonstrated an ischemic infarction involving the right supplementary motor area, medial prefrontal cortex, and anterior cingulate gyrus with nearly total sparing of the corpus callosum. This case, together with recent experimental findings in monkeys, supports the hypothesis that the supplementary motor area may be responsible for nonmirror transformation of motor programs originating in the left hemisphere prior to execution by the primary motor area in the right hemisphere.

Impaired affective prosody in AD: relationship to aphasic deficits and emotional behaviors.

OBJECTIVE: To assess the ability of patients with AD to produce, repeat, and comprehend affective prosody in relationship to severity of dementia, aphasic deficits, and changes in emotional behaviors. METHODS: An Aprosodia Battery was used to assess affective-prosodic performance and to identify patterns of deficits in affective communication. In addition, the presence and severity of aberrant behaviors, depression, and aphasia were assessed using standardized assessment tools. RESULTS: Patients with AD had significant impairments in their ability to repeat, comprehend, and discriminate affective aspects of speech, but maintained normal spontaneous affective-prosodic performances. As dementia severity increased, performance on the comprehension tasks and, to a lesser degree, on the repetition tasks became more impaired; spontaneous affective prosody remained normal. In the current study, affective-prosodic comprehension impairments were present in patients with all stages of AD; comparable aphasic deficits were not observed until patients were severely demented. The majority of aphasic deficits involved anomia without loss of comprehension. Patients with AD with sensory aprosodia had increased frequency and severity of behavioral changes whereas patients with AD with normal affective-prosodic performance were significantly less demented, had normal linguistic ability, and displayed fewer aberrant psychiatric behaviors. CONCLUSION: Patients with mild AD are at considerable risk for affective-prosodic comprehension deficits. As patients become more demented and develop sensory aprosodia, they are at greater risk for disturbances in behavior and mood.

Progressive multifocal leukoencephalopathy in a renal transplant recipient. Increased diagnostic sensitivity of computed tomographic scanning by double-dose contrast with delayed films.

A progressive, deteriorating neurologic disorder developed in a 28-year-old white man 10 years after he successfully received a living related donor kidney transplant. An extensive neurologic evaluation was unrevealing, including normal results of computed tomographic scanning of the brain with and without contrast medium. Repeated computed tomographic scanning after a double dose of radiocontrast medium in conjunction with delayed imaging revealed multiple areas of abnormal enhancement. This technique helped to direct brain biopsy, which led to the early diagnosis of progressive multifocal leukoencephalopathy and the institution of specific therapy.

The significance of the Babinski sign in the newborn-a reappraisal.

A study of the clinical significance and the stimulus methods used to elicit the Babinski sign in normal newborns has been carried out. Although the most frequent response to cutaneous nociceptive stimulation of the lateral sole in neonates was extension of the great toe, a small but significant number of flexor responses were obtained. Consequently, the Babinski sign has limited clinical usefulness as a reflex indicating the presence or absence of neurological disease in the newborn. In reviewing previous studies in the literature, it was apparent that the widely differing percentages of extensor plantars reported in newborns was related directly to differences in the technique of examination.

Dexamethasone suppression test and onset of poststroke depression in patients with ischemic infarction.

BACKGROUND: Studies documenting abnormal results in the 1.0-mg dexamethasone suppression test (DST) and the prevalence of depression in stroke patients are usually accomplished between 1 and 6 months poststroke. One study, however, reported that 27% of patients met DSM-III criteria for major depression and 20% for minor depression 1 to 3 weeks poststroke even though previous research has indicated that the prevalence of poststroke depression was greatest at approximately 6 months. Therefore, we decided to assess DST abnormalities and depression within the first month of stroke. METHOD: Twelve patients with single, computed tomography (CT)-verified, ischemic infarctions were administered the DST at 1 and 3 weeks poststroke. Each patient also received a complete psychiatric evaluation, including a special clinical interview and the 17-item Hamilton Rating Scale for Depression (HAM-D). 3 to 4 weeks poststroke. RESULTS: DST results were abnormal in 75% of the patients at 1 week poststroke and 50% of the patients at 3 weeks poststroke. Those patients whose HAM-D scores revealed more depressive symptoms at 3 to 4 weeks were more likely to evidence abnormal DST results (cortisol nonsuppression). None of the patients, however, met either DSM-III or modified criteria for clinical depression at 3 to 4 weeks. CONCLUSION: Poststroke depression appears to have a delayed clinical onset. Abnormal DST results at 3 weeks poststroke may serve as a potential marker for those patients at risk for developing poststroke depression.