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Biomedical subjects

A Urbano

Publications and source records attributed to A Urbano.

At least 55 records · Page 3Linked to original sources
PubMed1982

Interpositus nucleus influences on pyramidal tract neurons in the cat.

The influences of the interpositus nucleus on pyramidal tract neurons were investigated by stimulating, in unanesthetized cats, interpositus nucleus foci which activated single muscles in limbs, while recording unitary discharges of pyramidal tract neurons located in foci (area 4 gamma) from which contraction was obtained in the same muscles as those excited from interpositus nucleus (agonist pyramidal tract neurons), in their antagonist (antagonist pyramidal tract neurons), or in heteronymous muscles (heteronymous pyramidal tract neurons). It was found that agonist pyramidal tract neurons were inhibited from the interpositus nucleus, whereas antagonist pyramidal tract neurons displayed a pure excitatory or an excitatory-inhibitory pattern, and the heteronymous neurons were not significantly influenced. A direct activation of interposito-thalamic efferents could be responsible for these effects. In fact, unitary discharge changes of pyramidal tract neurons, elicited from interpositus nucleus stimulation, persisted after chronic intermediate cortex ablation and dentate nucleus lesions, and disappeared following coagulations in the ventrolateral nucleus of the thalamus. These results suggest that interpositus nucleus efferents, which activate a given muscle, via the rubrospinal pathway, could inhibit the discharge of pyramidal neurons controlling that muscle, via collaterals direct to the thalamic ventrolateral nucleus.

Animals↗
PubMed1980

Single muscle organization of interposito-rubral projections.

In unanesthetized neuraxis intact cats microstimulation of the interpositus nucleus (IN) which activated a single flexor or extensor muscle in limbs, was used to investigate changes of unitary discharged of rubrospinal (RST) cells. Recordings were made from sites the stimulation of which excited the same muscle activated by the IN (agonist cells), its antagonist (antagonist cells) or heteronymous muscles (heteronymous cells). Cats submitted to chronic cerebellar decortication, acute brachium conjunctivum (BC) section, acute prerubral hemidecerebration or chronic prerubral hemidecerebration and contralateral BC section, were used as controls. It was shown that agonist RST cells were monosynaptically fired from IN, while antagonist cells were inhibited and the heteronymous ones were not influenced. Cerebellar efferents within the BC mediate both excitatory and inhibitory effects, but cerebellar cortex and prerubral structures were not involved in their production.

Animals↗
PubMed1979

[Value of hemophagocytosis in the morphological examination of the bone marrow (author's transl)].

The hemophagocytosis or the process of ingestion of blood cells by phagocytes and macrophages of the mononuclear phagocytic system (MFS), is a phenomenon that rarely could be observed in the morphological examination of the bone marrow aspirate. Occasionally it is present in certain pathologic conditions such as, malignant histiocitosis, autimmune hemolytic anemia, or some chronic inflammatory diseases. The capacity of ingestion is not an exlusive property of the phagocytes and macrophages of the MFS, so that different neoplastic cells can show it too. This study analyzes the presence of hemophagocytosis by neoplastic cells in a total of 552 bone marrow aspirates corresponding to a series of 130 patients with acute leukemia and 422 patients with diverse solid tumors. In the group of patients with acute leukemia, hemophagocytosis by blastic cells was observed in five cases with acute monocytic leukemia. In the other group with solid tumors, hemophagocytosis was present in three patients with oat-cell lung carcinomas and diffuse bone marrow metastases. The interest of the evaluation of hemophagocytosis by neoplastic cells in the morphological examination of the bone marrow is stressed, as well as it possible value in the cytological diagnosis of acute monocytic leukemia. However, in these circumstances a sdiffuse metastases by solid tumors should be always discarded, since their cytomorphological characteristics are in most cases superimposed to those of the leukemic bone marrow infiltrate.

Bone Marrow↗
PubMed1979

A computer model of intermediate cerebellum dynamic operations in motor control.

An intermediate cerebellum theoretical model for processing central programming discharges and muscle force signals is described which can perform a correct motor task under different peripheral perturbations (loads). An indispensable condition is that the simulated interpositus nucleus cells controlling a given effector (muscle) are inhibited by impulses coming from that effector (negative feedback from muscle force detectors). The hypothesis is proposed that the intermediate cerebellum can act via the rubrospinal tract as an interface between programming and executing motor structures.

Cerebellum↗
PubMed1978

Computer simulated discharges of thalamic ventrobasal neurones during sleep and wakefulness.

A theoretical model is described which in response to combinations of poissonian pulse trains with different mean frequencies on three independent incoming lines, generated output signals simulating spontaneous discharges of thalamic ventrobasal (VB) neurones during sleep and wakefulness. Some dynamic neuronal properties as refractoriness, facilitation, short term memory were simulated and characteristics of response to single pulses on different lines properly selected to reproduce those exhibited by VB neurones upon artificial stimulation of thalamic afferent systems. The data obtained from the model are briefly discussed in relation to possible contributions of specific and nonspecific afferent systems in producing spontaneous VB discharges characteristic of different levels of vigilance.

Action Potentials↗
PubMed1978

Motor responses evoked by microstimulation of restiform body in the cat.

Motor effects produced by microstimulation of restiform body (RB) were studied in acute unanesthetized cats, using tungsten electrodes for stimulating the peduncle and bipolar steel electrodes for recording muscular activity (EMG). The main results were the following. 1. Threshold microstimulation (18.24 microA +/- 8.77 S.D.) of effective foci within RB elicited single muscle contractions of ipsilateral limbs, primarily of forelimb; overthreshold activation (32.83 microA +/- 9.25S.D.) of the same points produced complex movements in 61.54% of cases that involved muscles of shoulder, neck, and trunk. 2. Single muscle contractions exhibited a mean latency (20.09 msec +/- 2.04 S.D.) which was significantly longer than that shown by complex movements (10.00 msec +/- 3.10 S.D.). Furthermore, a decrease in frequency of stimulating train below 300 Hz and a reduction in duration below 30 msec caused a steep rise of threshold for single muscle responses that was not observed when studying complex movements. 3. Acute RB interruption between stimulating electrode and cerebellum abolished single muscle contractions; conversely, complex movements remained unmodified even when the RB was lesioned in cats chronically submitted to interruption of brachium conjunctivum (BC). 4. The pathway involved in promoting RB induced single muscle activation includes interpositus nucleus, BC and rubrospinal tract. Possible modalities of RB afferent participation to the motor control are briefly discussed.

Animals↗