Lipid raft microdomain compartmentalization of TC10 is required for insulin signaling and GLUT4 translocation.

Recent studies indicate that insulin stimulation of glucose transporter (GLUT)4 translocation requires at least two distinct insulin receptor-mediated signals: one leading to the activation of phosphatidylinositol 3 (PI-3) kinase and the other to the activation of the small GTP binding protein TC10. We now demonstrate that TC10 is processed through the secretory membrane trafficking system and localizes to caveolin-enriched lipid raft microdomains. Although insulin activated the wild-type TC10 protein and a TC10/H-Ras chimera that were targeted to lipid raft microdomains, it was unable to activate a TC10/K-Ras chimera that was directed to the nonlipid raft domains. Similarly, only the lipid raft-localized TC10/ H-Ras chimera inhibited GLUT4 translocation, whereas the TC10/K-Ras chimera showed no significant inhibitory activity. Furthermore, disruption of lipid raft microdomains by expression of a dominant-interfering caveolin 3 mutant (Cav3/DGV) inhibited the insulin stimulation of GLUT4 translocation and TC10 lipid raft localization and activation without affecting PI-3 kinase signaling. These data demonstrate that the insulin stimulation of GLUT4 translocation in adipocytes requires the spatial separation and distinct compartmentalization of the PI-3 kinase and TC10 signaling pathways.

Calmodulin antagonists inhibit insulin-stimulated GLUT4 (glucose transporter 4) translocation by preventing the formation of phosphatidylinositol 3,4,5-trisphosphate in 3T3L1 adipocytes.

It has been previously reported that calmodulin plays a regulatory role in the insulin stimulation of glucose transport. To examine the basis for this observation, we examined the effect of a panel of calmodulin antagonists that demonstrated a specific inhibition of insulin-stimulated glucose transporter 4 (GLUT4) but not insulin- or platelet-derived growth factor (PDGF)-stimulated GLUT1 translocation in 3T3L1 adipocytes. These treatments had no effect on insulin receptor autophosphorylation or tyrosine phosphorylation of insulin receptor substrate 1 (IRS1). Furthermore, IRS1 or phosphotyrosine antibody immunoprecipitation of phosphatidylinositol (PI) 3-kinase activity was not affected. Despite the marked insulin and PDGF stimulation of PI 3-kinase activity, there was a near complete inhibition of protein kinase B activation. Using a fusion protein of the Grp1 pleckstrin homology (PH) domain with the enhanced green fluorescent protein, we found that the calmodulin antagonists prevented the insulin stimulation of phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] formation in vivo. Similarly, although PDGF stimulation increased PI 3-kinase activity in in vitro immunoprecipitation assays, there was also no significant formation of PI(3,4,5)P3 in vivo. These data demonstrate that calmodulin antagonists prevent insulin-stimulated GLUT4 translocation by inhibiting the in vivo production of PI(3,4,5)P3 without directly affecting IRS1- or phosphotyrosine-associated PI 3-kinase activity. This phenomenon is similar to that observed for the PDGF stimulation of 3T3L1 adipocytes.

Changes in the symptoms of neglect induced by changing task strategy.

Six patients with left side unilateral neglect from lesions of the right cerebral hemisphere were tested with verbal and visuospatial crossing-out tasks. The symptoms of neglect were less severe with the visuospatial than with verbal tasks. We hypothesize that changes in the symptoms of neglect were produced because the tasks altered hemispheric arousal.

Loss of spontaneous blinking in a patient with Balint's syndrome.

A patient with Balint's syndrome caused by bilateral parieto-occipital lesions lost spontaneous blinking, suggesting that humans, like nonhuman primates, have parietal lobe neurons that are important for blinking. Although the functions of spontaneous blinking are not known, they may help initiate some saccades and, like saccades, be involved in the cancellation of thalamic inhibitory postsynaptic potentials, thereby facilitating processing of new foveal targets. Spontaneous blinking may also facilitate sensory relay during sustained attention and, therefore, help prevent fading of a retinal image.

Thalamic neglect. Possible role of the medial thalamus and nucleus reticularis in behavior.

A patient had an ischemic infarction of the right medial thalamus, with a resultant contralateral neglect syndrome. We propose that the medial thalamic nuclei, particularly centromedian and parafascicularis (CMPF), are normally involved in the arousal-activation process by which an organism can be aroused by and respond to novel or important stimuli. Specifically, we propose that (1) the mesencephalic reticular formation subserves tonic arousal to novel or painful stimuli by inhibiting the nucleus reticularis thalami (NR) and (2) that selective attention is mediated by cortical input to NR. The CMPF is closely associated with motor systems (basal ganglia, ventrolateral nucleus of the thalamus [VL], and frontal lobes). A pathway involving CMPF, the frontal cortex, and the portion of NR associated with VL may be important in preparing the tonically aroused organism for action. Unilateral lesions of CMPF therefore induce an asymmetric hypokinesia, and bilateral lesions may induce akinetic mutism.

Evoked potential in neglect.

The evoked potential was studied in Macaca speciosa before and after they received a lesion inducing neglect. Significant evoked potential changes associated with neglect were seen only in late components (N2, P3). These observations support the hypothesis of the arousal-attention mechanism of neglect.

Posterior neocortical systems subserving awareness and neglect. Neglect associated with superior temporal sulcus but not area 7 lesions.

OBJECTIVE: In humans and monkeys, the intraparietal sulcus separates the superior parietal lobule from the inferior parietal lobule (IPL). Whereas in humans Brodmann's area 7 is above this sulcus, in monkeys it is below and therefore part of the IPL. In humans, the IPL consists of Brodmann's areas 39 and 40. Some investigators contend that the monkey homologue of the human IPL (areas 39 and 40) is the monkey's IPL (area 7). Others contend that it is, at least in part, in the monkey's superior temporal sulcus (STS). In humans, IPL lesions induce neglect. Although IPL lesions in monkeys also have been reported to induce neglect, the STS was involved in these lesions. We sought to learn which of these two areas, when ablated, produces neglect. DESIGN: Study of five adult stump-tailed macaque monkeys by making five isolated STS and six IPL lesions. RESULTS: Inferior parietal lobule lesions were associated with misreaching but not with unilateral neglect. Neglect was observed in association with five of the six STS lesions. CONCLUSIONS: With regard to neglect, STS may be the monkey homologue of the human IPL. Animals with STS lesions and humans with IPL lesions may manifest unilateral neglect because these areas are necessary for normal awareness of external stimuli. This awareness may result from the integration of the areas important in stimulus localization (the "where is it?" system) and stimulus identification (the "what is it?" system), as well as the areas important in defining the biologic importance of stimuli, such as the frontal lobes and limbic areas.

Reaction times in Parkinson disease.

Ten hypokinetic parkinsonian patients and ten age- and sex-matched controls were tested, using reaction times with and without a warning signal. The time difference between each was used as a measure of phasic arousal. Both groups' reaction times improved with a warning signal, but there were no differences in reaction-time reduction between the parkinsonian and control groups. These results suggest either that hypokinesia in parkinsonism is not caused by an arousal defect or it is caused by a defect in the "autoevoked" arousal system.

Apraxia and the supplementary motor area.

Anatomical, electrophysiological, and cerebral blood flow studies suggest that the supplementary motor area (SMA) may be important for programming certain skilled motor acts of the limbs. However, to our knowledge, abnormalities of complex distal motor behavior following SMA lesions have not been reported. We have studied two patients with left mesial hemisphere infarctions that included the SMA. These patients had bilateral ideomotor apraxia for transitive limb movements without buccofacial apraxia. The observations suggest that the types of skilled motor acts programmed by the left SMA are learned transitive limb movements.

Response time in monkeys with unilateral neglect.

Four monkeys were trained to open a door with either the right or left hand in response to a tactile stimulus to either leg. After unilateral frontal arcuate ablation inducing unilateral neglect, the response time on this task increased most when the monkey responded with the hand contralateral to the lesion, but also increased when the monkey used the hand ipsilateral to the lesion. The side of stimulation had no effect on response time. Control (anterior superior temporal) lesions did not cause neglect and only affected response time slightly in one monkey (using the limb contralateral to the lesion). We conclude that response time is increased in animals with unilateral neglect and that the increase results from a defect in intention to act (motor neglect) rather than from sensory neglect.

TIA, stroke, and mitral valve prolapse.

Eight patients with transient ischemic attacks, and three with partial nonprogressive strokes associated with mitral valve prolapse, are reported. No other etiology for their ischemic events was found. Only one episode of ischemia recurred on aspirin treatment, whereas none recurred on sodium warfarin therapy.

Thalamic neglect.

Three patients with right thalamic hemorrhage showed contralateral neglect and limb akinesia. They also had anosognosia, visuospatial disorders, and emotional flattening. In animals, neglect can be induced by lesions along a cortico-limbic-reticular loop including the intralaminar thalamic nuclei. We propose that an activation defect is responsible not only for the neglect and akinesia, but also for the visuospatial and emotional defects usually associated with right-hemisphere cortical dysfunction.

From benign fasciculations and cramps to motor neuron disease.

Fasciculations and cramps may occur in motor neuron disease or as part of a more benign syndrome. A man with apparently benign fasciculations and cramps for 4 years developed progressive muscle weakness and wasting. Such a previously undocumented evolution of benign fasciculations and cramps to motor neuron disease may further implicate anterior horn cell dysfunction in the pathogenesis of muscle fasciculation-cramp syndromes.

Performance on hemispatial pointing task by patients with neglect syndrome.

Five patients with left hemispatial neglect and five aphasic control subjects were given a hemispatial pointing task. They were instructed to point to an imaginary point in space perpendicular to the midline of the chest. Right hemisphere-damaged subjects with neglect deviated more into the hemispace ipsilateral to the lesion than left hemisphere-damaged controls. This task did not require sensory input from left hemispace, and the defective performance cannot be attributed to sensory inattention or to impaired gaze or memory. The finding is compatible with hemispatial akinesia.

Myokymia, muscle hypertrophy and percussion "myotonia" in chronic recurrent polyneuropathy.

Three unusual features were observed in a patient with chronic relapsing polyneuropathy: myokymia, muscle hypertrophy, and prolonged contraction in response to muscle percussion. Low nerve conduction velocity and conduction block were demonstrated in all motor nerves tested, indicating a demyelinating peripheral neuropathy. Myokymia was caused by spontaneous motor unit activity which was shown to originate in peripheral nerves, since it persisted after nerve block and was abolished by regional curarization. Muscle hypertrophy was attributed to increased peripheral nerve activity, and the prolonged contraction of muscle in response to direct percussion was attributed to irritability of intramuscular nerve terminals.

Normal tactile threshold in monkeys with neglect.

To learn whether animals with parietotemporal lesions have sensory inattention or defective intention, we trained monkeys to respond with the contralateral limb to a threshold tactile stimulus. After parietotemporal lesions that induced neglect, the monkeys continued to respond normally to threshold stimuli on the side opposite the lesion (the neglected side), but made errors when stimulated on the normal side (ipsilateral to the lesion), often failing to use the contralateral extremity. On this learned task, there was no abnormality of sensory input or sensory attention. The problem was attributed to an impaired preparation to respond (intention).

Resolution of gumma with steroid therapy.

Antibiotic usage has rendered neurosyphilis uncommon, and cerebral gummas are rare. Reduced awareness of cerebral gummas and abolition of serologic screening can delay diagnosis of this treatable disease. Diagnostic confusion between syphilitic and nonsyphilitic cerebral mass lesions can be increased by apparent resolution of a gumma during steroid therapy. Such an occurrence in a young woman emphasizes the need for serologic testing for syphilis in diagnosing cerebral mass lesions. A trial of conservative therapy using penicillin (with or without prednisone) should be considered for patients with intracerebral mass lesions and positive serologic findings.

Hypoarousal in patients with the neglect syndrome and emotional indifference.

Physiologic theories of emotion suggest that activation is important in the experience of emotion; patients exhibiting "neglect" as a consequence of right parietotemporal of dysfunction show flattened affect. We studied arousal in patients with lesions of the right hemisphere who also exhibited emotional indifference, in aphasic patients with lesions of the left hemisphere, and in non-brain-damaged controls, by stimulating the forearm ipsilateral to the side of the brain lesion while recording galvanic skin responses (GSRs) from the fingers on the same side. The group exhibiting neglect had lower GSRs than aphasic patients or non-brain-damaged controls. Aphasic patients had higher GSRs than non-brain-damaged controls. These results suggest that neglect is associated with disturbances in bilateral arousal and that this disorder of arousal may be responsible in part for flattened affect. The heightened GSR in aphasic patients may reflect disinhibition, which might be partly responsible for increased emotionality in these patients.

Discrimination and evocation of affectively intoned speech in patients with right parietal disease.

Patients with right parietal disease have disturbed comprehension of affective speech. Ability to discriminate affective speech (make same/different discriminations) and ability to repeat emotionally bland sentences with affective tones were tested in three groups of subjects--patients with right parietal dysfunction and neglect, conduction aphasics with left hemispheric lesions, and patients without intracranial disease. Patients with right parietal dysfunction performed significantly poorer than did aphasic controls on both a recognition and discrimination task. Patients with right parietal dysfunction also scored poorer on the evocative task than the nonaphasic controls.