Biomedical subjects

S G Siegel

Publications and source records attributed to S G Siegel.

4 recordsLinked to original sources

PubMed2000

Ciliary neurotrophic factor is required for motoneuron sprouting.

We used mutant mice that lack the gene for ciliary neurotrophic factor (CNTF) to test the hypothesis that it is an endogenous sprouting factor. Fibers in the lateral gastrocnemius muscle were either partially denervated by transection of one of the branches of its nerve or paralyzed by intramuscular injection of botulinum toxin. This results in a significant sprouting response at the terminals of intact motoneurons in normal animals. We did not detect sprouting produced by either stimulus in mice lacking CNTF. When exogenous CNTF was administered to CNTF knockout mice following partial muscle denervation, they mounted a typical sprouting response. Thus CNTF is a critical factor in the process of sprout formation after both partial denervation injury and neuromuscular paralysis. It may function as part of a cellular compensatory mechanism after neuronal injury.

Animals↗

PubMed1999

Reflex activation patterns in relation to multidirectional ankle torque in decerebrate cats.

Cutaneous reflexes have been described primarily according to their actions in the flexion/extension plane. It is shown here, by measuring electromyography and isometric force in decerebrate cats, that ankle muscles are activated in relation to their actions in the abduction/adduction plane during sural nerve (SNR) and crossed-extension (XER) reflexes. Ankle adductors (tibialis posterior, extensor digitorum longus, and flexors digitorum and hallucis longus) were active in XER, but not in SNR. Muscles producing ankle abduction (medial and lateral gastrocnemii and peroneus longus and brevis) were consistently more strongly activated in SNR than in XER. This differential pattern of muscle activation results in greater abduction torque at the ankle in SNR than in XER. These data demonstrate reflex organization in relation to the multidirectional torque generated by individual muscles.

Animals↗

PubMed1999

Recruitment order among motoneurons from different motor nuclei.

Recruitment order among motoneurons from different motor nuclei. The principles by which motoneurons (MNs) innervating different multiple muscles are organized into activity are not known. Here we test the hypothesis that coactivated MNs belonging to different muscles in the decerebrate cat are recruited in accordance with the size principle, i.e., that MNs with slow conduction velocity (CV) are recruited before MNs with higher CV. We studied MN recruitment in two muscle pairs, the lateral gastrocnemius (LG) and medial gastrocnemius (MG) muscles, and the MG and posterior biceps femoris (PBF) muscles because these pairs are coactivated reliably in stretch and cutaneous reflexes, respectively. For 29/34 MG-LG pairs of MNs, the MN with lower CV was recruited first either in all trials (548/548 trials for 22 pairs) or in most trials (225/246 trials for 7 pairs), whether the MG or the LG MN in a pair was recruited first. Intertrial variability in the force thresholds of MG and LG MNs recruited by stretch was relatively low (coefficient of variation = 18% on average). Finally, punctate stimulation of the skin over the heel recruited 4/4 pairs of MG-LG MNs in order by CV. By all of these measures, recruitment order is as consistent among MNs from these two ankle muscles as it is for MNs supplying the MG muscle alone. For MG-PBF pairings, the MN with lower CV was recruited first in the majority of trials for 13/24 pairs and in reverse order for 9/24 pairs. The recruitment sequence of coactive MNs supplying the MG and PBF muscles was, therefore, random with respect to axonal conduction velocity and not organized as predicted by the size principle. Taken together, these findings demonstrate for the first time, that the size principle can extend beyond the boundaries of a single muscle but does not coordinate all coactive muscles in a limb.

Animals↗

PubMed1997

Posttransplantation lymphoproliferative disorder: changing manifestations of disease in a renal transplant population.

OBJECTIVE: To review the changing manifestations of PTLD in patients with renal transplants. METHODS: Review of 1954 records of the renal transplantation clinic from 1971 to 1993 produced 17 patients with the diagnosis of PTLD. RESULTS: With changes in immunosuppression, the sites of involvement of PTLD have changed. Central nervous system involvement was the predominant site of disease prior to the use of cyclosporine. With the institution of cyclosporine, thoracic, and abdominal presentations became more common. PTLD isolated to the renal transplant is a new manifestation of disease that may be a result of immunosuppression with OKT3. Monomorphous PTLD was associated with a 78% PTLD related mortality. Polymorphous PTLD had a 0% PTLD related mortality. In patients with cross-sectional imaging abnormalities, PTLD presented as solitary or multiple masses in 78%. This is the finding most suggestive of PTLD in a transplant population. CONCLUSION: Posttransplantation lymphoproliferative disorder is a heterogeneous grouping of lymphoid proliferation with variable clinical and radiographic manifestations. An understanding of the range of manifestations may lead to improved diagnosis of this unusual disorder.

Abdomen↗