Oscillations in local field potentials of the primate motor cortex during voluntary movement.

We investigated the occurrence and distribution of oscillatory activity in local field potentials (LFPs) recorded from the frontal motor cortex of behaving monkeys performing skilled voluntary movements. LFPs were recorded simultaneously from up to 12 sites distributed throughout motor cortex while monkeys performed a visually guided, instructed delay task using the wrist or digits. Oscillatory activity between 15 and 50 Hz was evident in the LFP recorded from both primary motor cortex and premotor areas. Oscillations occurred preferentially before the visual cue to initiate movement but were infrequent during movement. Oscillations typically stopped before movement initiation during the wrist task, although they often continued into the initial phases of movement during the digit task. The relationship of oscillations to task performance was consistent across trials over periods of many months, although the amplitude and duration of oscillations varied across trials and days. Interactions between pairs of LFP recordings, evaluated with cross-correlation analysis, revealed synchronous oscillations over long distances (> 7 mm) and across primary motor cortex and premotor recording sites. These studies demonstrate that oscillations recorded in the LFP in motor cortex during trained motor tasks are not related to the details of movement execution but may be related to aspects of movement preparation.     

Mode of action of the IgG inhibitor of erythropoiesis in transient erythroblastopenia of children

Twelve cases of transient erythroblastopenia of childhood (TEC) have been studied to evaluate their marrow cell erythropoiesis in vitro and the effect on it of their serum or IgG. The number of colony-forming units-erythroid (CFU-E) and burst-forming units-erythroid (BFU-E) in the bone marrow of nine cases was extremely variable and did not allow any conclusion regarding the pathogenesis of this anemia. An IgG inhibitor of growth of erythroid colonies or bursts was detected in 8/12 cases. This IgG inhibitor had no effect on the growth of granulocyte-macrophage colonies. Further studies on its mode of action indicated that the IgG did not have antierythropoietin antibody properties and did not affect the mature erythroblasts, as shown by a lack of inhibition of their responses to erythropoietin and by the lack of a cytotoxic effect on 59Fe-labeled erythroblasts. In four cases, preincubation studies demonstrated a direct effect of the IgG on the CFU-E, which was complement-mediated in three cases and complement- independent in one case. In two other cases, the IgG suppressed the growth of normal BFU-E only without affecting the growth of CFU-E. The IgG inhibitor was no longer present after the erythroblastopenia had remitted. These studies demonstrate that in the majority of cases of TEC, an IgG suppressor of erythropoiesis in vitro is present. Its mode of action is heterogeneous regarding its requirement for complement. Its target cells are the earlier or later erythroid progenitors, BFU-E or CFU-E, but not the differentiated erythroblasts.     

Erythropoietin induces association of the JAK2 protein tyrosine kinase with the erythropoietin receptor in vivo

Protein tyrosine phosphorylation has been hypothesized to play a key role in the growth signaling induced by erythropoietin (Epo), although the Epo receptor (EpoR), a member of the cytokine receptor superfamily, lacks a tyrosine kinase domain. Recently, the JAK2 tyrosine kinase was shown to be activated on Epo stimulation and to bind to the cytoplasmic domain of EpoR in vitro. To further explore the mechanisms of activation of JAK2 in EpoR-mediated signal transduction, we assessed the conditions for association of JAK2 with EpoR in vivo. Epo stimulation rapidly induced association of JAK2 with the EpoR in an interleukin 3 (IL-3)-dependent cell line transfected with the wild-type EpoR. On Epo stimulation JAK2 also associated with a truncated mutant EpoR (H-mutant), which is mitogenetically active but not tyrosine phosphorylated, indicating that association does not require receptor phosphorylation and occurs in the membrane proximal region. However, association was not detected with mutant receptors inactivated by an internal deletion or a point mutation, Trp282 to Arg, in a membrane- proximal cytoplasmic region (PB or PM4 mutant, respectively). Immune complex kinase assays of anti-EpoR immunoprecipitates also revealed that activated JAK2 associates with the EpoR in Epo-stimulated cells. By this approach, association also occurred with the mitogenically active H mutant but not with the mitogenically inactive PB or PM4 mutants. In the immune complex kinases assays, EpoR, JAK2, and a 150-kD protein were phosphorylated on tyrosine. Taken together, the results further support the hypothesis that, on Epo stimulation, JAK2 associates with the membrane-proximal cytoplasmic region of the EpoR to be activated and induces tyrosine phosphorylation of cellular substrates, including the EpoR, to transduce a growth signal.     

Value of chest radiography in excluding traumatic aortic rupture

A retrospective review of chest radiographs from 205 patients with blunt chest trauma who also underwent aortography was performed. Forty-one of the 205 had aortographically proved aortic rupture. Discriminant analysis of 16 radiographic signs indicated that the most discriminating signs were loss of the aorticopulmonary window, abnormality of the aortic arch, rightward tracheal shift, and widening of the left paraspinal line without associated fracture. No single or combination of radiographic signs demonstrated sufficient sensitivity to indicate all cases of traumatic aortic rupture on plain chest radiographs without the performance of a large number of aortographically negative studies. The bedside anteroposterior "erect" view of the chest proved far more valuable than the supine view in detecting true-negative studies. Despite significant reader variability in the interpretation of the various radiographic signs, in general the analysis confirmed the role of chest radiography in this clinical situation, but suggests that its most beneficial use is in excluding the diagnosis and eliminating unwarranted aortography rather than in predicting aortic rupture.