Fabian Rossi

Hand preference and transcranial magnetic stimulation asymmetry of cortical motor representation.

Human handedness may be associated with asymmetry in the corticospinal motor system. Previous studies measuring the threshold for eliciting motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) have provided evidence consistent with this hypothesis. However, TMS asymmetry observed in previous studies may have reflected cortical or spinal differences. We therefore undertook this investigation to test the hypothesis that handedness is associated with asymmetry in cortical motor representations. We used TMS to map contralateral cortical motor representations of the right and left abductor pollicis brevis (APB) and flexor carpi radialis (FCR) muscles in nine normal subjects (three left-handed). Using focal stimulation with a figure-of-8 shaped magnetic coil, we found no differences in MEP threshold or MEP size between the preferred and the nonpreferred hand. However, we observed that the number of scalp stimulation sites eliciting MEPs was statistically greater for APB and FCR muscles of the preferred limb. We found significant asymmetry between right-handed and left-handed subjects, such that in right-handers, the representation of the right APB was larger than that of the left APB, but in left-handers the representation of right APB was smaller than that of the left APB. These results suggest that handedness is associated with asymmetry in cortical motor representation.

Effect of Chronic Treatment with Losartan Potassium (DuP 753) on the Elevation of Blood Pressure during Chronic Exposure of Rats to Cold

Elevation of diastolic, systolic, and mean blood pressures and cardiac hypertrophy occur in rats exposed to cold (5 degrees C) for 1-3 weeks. The renin-angiotensin-aldosterone system is believed to play a role in the development of cold-induced hypertension since plasma renin activity increases within the first 2 weeks, presumably initiating the hypertensive process, and then returns to control level. The present study was designed to assess the role of angiotension II (Ang II) in the hypertensive process by chronic administration of losartan potassium, an Ang II1 receptor antagonist. Twenty-four rats were divided into four equal groups. After a 1-week control period, one group was kept at 25 degrees C while the remaining three groups were exposed to cold (5 degrees C). One of the cold-treated groups was untreated while the remaining two were given losartan in drinking water at a concentration calculated to provide 56 and 112 mg/kg/day. The untreated cold-exposed group had a significant elevation of systolic blood pressure within 1 week of exposure to cold. Losartan at both doses prevented the elevation of blood pressure and blocked both the dipsogenic and vascular responses to administration of Ang II. Exposure to cold increased food intake, urine output and water intake significantly above that of warm-adapted controls. Treatment with losartan tended to decrease each of these toward the level of controls. At the conclusion of the seventh week of exposure to cold, the rats were sacrificed and heart, kidneys, and brown fat removed and weighed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Chronic Treatment with Prazosin and L-Arginine on the Elevation of Blood Pressure during Cold Exposure

Chronic exposure to cold (5 degrees C) is well known to increase both tyrosine hydroxylase (TH) activity in brown adipose tissue and systemic blood pressure. The effect of chronic dietary administration of the alpha-adrenergic antagonist, prazosin, and the amino acid, L-arginine, on both the elevation of blood pressure during exposure to cold and on TH activity and expression of TH mRNA in the adrenal glands of rats was studied. As observed previously, chronic exposure to cold increased systolic blood pressure significantly and induced cardiac hypertrophy. Chronic dietary treatment with prazosin (8 mg/kg food) and arginine (20 g/kg food) returned blood pressure to control levels, did not affect body weight significantly, but failed to prevent cardiac hypertrophy. Both prazosin and L-arginine reduced the drinking response to administration of angiotensin II. Treatment with arginine and prazosin was accompanied by a significant increase in the urinary outputs of dopamine and L-DOPA. The 3 cold-treated groups (control, L-arginine and prazosin) had increases in plasma T3 and decreases in plasma T4 and plasma renin activity. Plasma concentrations of epinephrine and norepinephrine were increased significantly in the L-arginine-treated group. TH mRNA and TH activity in the adrenal glands were increased in the 3 cold-treated groups and these measures were correlated directly and significantly with plasma norepinephrine and epinephrine concentrations. Although both prazosin and arginine prevented the cold-induced elevation of blood pressure, they did not prevent the increase in TH mRNA, TH activity or epinephrine in plasma. The protective effect of arginine and prazosin in cold-induced hypertension may be related both to their reduction in plasma renin activity and to a reduced responsiveness to angiotensin II, as well as to their abilities to increase the secretion of dopamine.

Topographic differences in task-dependent facilitation of magnetic motor evoked potentials

Objective: To look for differences in task-dependent facilitation of magnetic motor evoked potentials (MEPs) in proximal and distal upper extremity muscles. Background: Postexercise facilitation of MEPs has been demonstrated repeatedly in forearm muscles. Proximal muscles are prominently involved in limb stabilization, a largely isometric activity. In contrast, distal hand muscles specialize in precision movements. Based on these functional differences between proximal and distal muscles, we postulated that there might be topographic differences in task-dependent facilitation of MEPs. Methods: We studied the effects of isometric exercise and a precision grip task on MEPs in proximal and distal upper extremity muscles. Results: Isometric exercise of the target muscle was associated with significant facilitation of MEPs in biceps and extensor carpi radialis muscles, but not in first dorsal interosseous or abductor digiti minimi muscles. In contrast, a precision grip task was associated with significant post-task facilitation of MEPs in first dorsal interosseous, but not in extensor carpi radialis. Conclusions: These differences in the facilitation of MEPs depending on the motor task and whether the muscle is proximal or distal may reflect the relative importance of proximal muscles in maintaining posture.

Listeria spinal cord abscess responsive to trimethoprim-sulfamethoxazole monotherapy

OBJECTIVE To describe an alternative antibiotic regimen for the treatment of central nervous system Listeria monocytogenes infection. BACKGROUND Classical treatment of listeria infections of the brain and spinal cord has included ampicillin in combination with gentamicin and chloramphenicol. Antibiotic resistance to L. monocytogenes is extraordinarily low, and the combined risks of nephrotoxicity, ototoxicity, and agranulocytosis in an already critically ill patient make the potential use of trimethoprim-sulfamethoxazole monotherapy for coverage or treatment of listeria an important alternative. METHODS Case report. RESULTS A 58-year-old woman presented with a two-week history of progressive quadriplegia. Gadolinium enhanced MRI showed diffuse edema of the cervical and thoracic spine with ring-enhancing lesions. Cerebrospinal fluid and blood cultures both grew L. monocytogenes. Spinal cord biopsy of the lesion revealed inflammation with necrosis and also grew listeria. Intravenous trimethoprim-sulfamethoxazole (8 mg/kg in four divided doses) was administered for six weeks with resultant arrest of neurological symptoms and stabilization of the clinical course. Although the patient was quadraparetic she was able to be discharged to a rehabilitation facility. CONCLUSIONS Trimethoprim-sulfamethoxazole monotherapy may be a potential alternative option for critically ill patients with central nervous system L. monocytogenes infection.