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Biomedical subjects

R D Skinner

Publications and source records attributed to R D Skinner.

87 records · Page 5Linked to original sources
PubMed1979

Cells of origin of long descending propriospinal fibers connecting the spinal enlargements in cat and monkey determined by horseradish peroxidase and electrophysiological techniques.

The cells of origin of the long descending propriospinal tract (LDPT) in the cervical enlargement were studied in cat and monkey by using the retrograde transport of horseradish peroxidase (HRP). Their distribution was confirmed electrophysiologically in cat by recording their antidromic action potentials. In cats and monkeys unilateral injections of HRP were made into the gray matter of the lumbosacral enlargement, but there was some spread to the contralateral side. In cats labeled somas were found in greatest numbers in lamina VIII and medial lamina VII, bilaterally. Labeled cells also were found bilaterally in laminae I, IV--VI, and X, but few were in IV and VI. Those in lamina V were usually in the lateral part of the lamina near the reticulated region. The cross-sectional areas of 20 neurons from each of laminae I and V--VIII were measured. Cells in lamina I were smallest and the largest were in VII and VIII. In cats with the spinal cord hemisected between the injection site and the cervical enlargement containing the somas, the bilaterality of the LDPT neurons in laminae VII and VIII was confirmed anatomically and physiologically. Contralaterally projecting neurons in laminae VIII and medial VII constituted a majority of LDPT cells in those laminae. The LDPT neurons in the dorsal horn appeared to project mainly ipsilaterally, but the number of labeled dorsal horn cells in these preparations was small. The distribution of antidromically localized cells of the LDPT was found to be in good agreement with the anatomical results. Their conduction velocity was 59 +/- 22 m/s (mean +/- s.d., n = 245). Histograms of the conduction velocity by laminae are given. In monkey the distribution of labeled somas was similar to that in the cat, except that the concentration of labeled somas in the ventral horn was more medially and dorsally located. Labeled somas were found bilaterally in laminae I, IV--VIII, and X, but more appeared to be ipsilateral to the side of the injection, especially in the dorsal horn. The bilaterality of the LDPT in the monkey was not tested with hemisections of the spinal cord. Neurons of the LDPT are ideally situated for conveying sensory information from the forelimb for eliciting reflexes in the hindlimb, as has been observed after stimulating afferents in the forelimb, and for coordinating, in general, motor functions between the two pairs of limbs.

Action Potentials↗
PubMed1979

Intraspinal non-neuronal cellular responses to peripheral nerve injury.

The accumulation of non-vascular, non-neuronal cells (designated herein as reactive cells) in association with perikarya of axotomized motor neurons has been described by many investigators. Recently Gilmore ('75) found that sciatic axotomy in immature rats resulted in the occurrence of reactive cells not only in the spinal ventral gray matter but also in the dorsal gray matter. To determine if the presence of these cells in the dorsal gray matter, a finding not reported by others, was related to the immaturity of the animal, sciatic axotomy was performed in rats ranging in age from 17 days to 16 months in the present study. Light microscopic evaluation of the spinal cords three or seven days post-operatively showed that the reactive cells occurred consistently in both dorsal and ventral gray matter irrespective of age. Transection of tibial nerve or the nerve to the medial head of the gastrocnemius muscle elicited a cellular response in both dorsal and ventral gray matter, although transection of the latter nerve resulted in a much less obvious response. Crushing of the sciatic nerve was followed by a response of reactive cells not qualitatively different from that noted following transection. Transection of the sural nerve, primarily a sensory nerve, resulted in the presence of reactive cells in dorsal gray matter but not in the environs of motor neurons in the ventral gray matter. These findings suggest that the reactive cells in the dorsal gray matter of the spinal cord are associated with altered central processes of dorsal root ganglion cells.

Aging↗
PubMed1978

Pontomedullary reticular projections into the region of the ascending medial longitudinal fasciculus in cat.

The medial longitudinal fasciculus (MLF) and immediately adjacent reticular formation were stimulated electrically just caudal to the trochlear nucleus in the cat. In the pontomedullary reticular formation within 1.5 mm of the midline, antidromically excited neurons were detected in (1) the contralateral abducens nucleus, (2) the contralateral reticular formation just caudal and caudoventral to the abducens nucleus, and (3) the ipsilateral nucleus reticularis pontis caudalis beneath and rostral to the abducens nucleus. The possible involvement of these neurons in eye or body movements is discussed.

Abducens Nerve↗
PubMedDate not supplied

In vivo and in vitro evidence supporting a role for the inflammatory cytokine interleukin-1 as a driving force in Alzheimer pathogenesis.

Interleukin-1 (IL-1), an inflammatory cytokine overexpressed in the neuritic plaques of Alzheimer's disease, activates astrocytes and enhances production and processing of beta-amyloid precursor protein (beta-APP). Activated astrocytes, overexpressing S100 beta, are a prominent feature of these neuritic plaques, and the neurite growth-promoting properties of S100 beta have been implicated in the formation of dystrophic neurites overexpressing beta-APP in neuritic plaques. These facts collectively suggest that elevated levels of the inflammatory cytokine IL-1 drive S100 beta and beta-APP overexpression and dystrophic neurite formation in Alzheimer's disease. To more directly assess this driver potential for IL-1, we analyzed IL-1 induction of S100 beta expression in vivo and in vitro, and of beta-APP expression in vivo. Synthetic IL-1 beta was injected into the right cerebral hemispheres of 13 rats. Nine additional rats were injected with phosphate-buffered saline, and seven rats served as uninjected controls. The number of astrocytes expressing detectable levels of S100 beta in tissue sections from IL-1-injected brains was 1.5 fold that of either control group (p < 0.01), while tissue S100 beta levels were approximately threefold that of controls (p < 0.05). The tissue levels of two beta-APP isoforms (approximately 130 and 135 kDa) were also significantly elevated in IL-1-injected brains (p < 0.05). C6 glioma cells, treated in vitro for 24 h with either IL-1 beta or IL-1 alpha, showed significant increases in both S100 beta and S100 beta mRNA levels. These results provide evidence that IL-1 upregulates both S100 beta and beta-APP expression, in vivo and vitro, and support the idea that overexpression of IL-1 in Alzheimer's disease drives astrocytic overexpression of S100 beta, favoring the growth of dystrophic neurites necessary for evolution of diffuse amyloid deposits into neuritic beta-amyloid plaques.

Alzheimer Disease↗
PubMedDate not supplied

Locomotor projections from the pedunculopontine nucleus to the spinal cord.

Following injections of retrograde tracers into the spinal cord enlargements, the mesencephalic locomotor region (MLR) was electrically stimulated to induce locomotion in decerebrate rats. MLR sites coincided with cholinergic pedunculopontine nucleus (PPN) neurons, which were selectively labelled using NADPH diaphorase histochemistry. Retrogradely labelled (spinal-projecting) PPN neurons were scattered among cholinergic PPN neurons. The absence of retrogradely labelled, NADPH diaphorase positive PPN neurons indicates that spinal enlargement projections are non-cholinergic.

Animals↗
PubMedDate not supplied

Locomotor projections from the pedunculopontine nucleus to the medioventral medulla.

Retrograde tracers were injected into the rat medioventral medulla (MED) and the injection site was identified as a locomotion- inducing area by electrical stimulation in the decerebrate preparation. Histological reconstructions showed that about 10% of cholinergic pedunculopontine (PPN) and laterodorsal tegmental (LDT) neurons project to the MED. Also, large numbers of non-cholinergic cells in and around the PPN and LDT were found to project to the MED.

Animals↗