PubMed Health⌕ Search

Biomedical subjects

J M Kerns

Publications and source records attributed to J M Kerns.

32 records · Page 2Linked to original sources
PubMed1987

A twitch tension method to assess motor nerve function in rat.

A simple and quantitative method is described which assesses the motor function of the rat tibial nerve by recording the twitch tension developed by the digital flexors. Stimulating electrodes are placed at the proximal end of the sciatic nerve of anesthetized rats, and the associated foot is immobilized on a sliding stage. The middle digit is connected via a thread to a force-displacement transducer and the sciatic nerve is stimulated supramaximally. The resulting twitch tension curve is recorded on an oscilloscope and/or signal averager. Measurement of the area and amplitude of the twitch tension curve provides an estimate of the recovery of motor function. The method is illustrated by examining the return of motor function following either sciatic nerve crush, or sciatic transection and repair. The results obtained are compared with other assessments of sciatic nerve function, such as the toe-spreading reflex and the analysis of walking tracks. The results from the twitch tension method are more sensitive, unaffected by changes in sensory function, and less prone to variation than the other assessments.

Animals↗
PubMed1987

An experimental implant for applying a DC electrical field to peripheral nerve.

Several studies have shown that nerve fibers grow preferentially toward the cathode when placed in an electrical field. To study the effects of electrical stimulation on in vivo nerve regeneration, an inexpensive implantable current source has been developed which is able to reliably deliver a minute DC current (0.57 microA) via wick electrodes. The current density was measured directly with a vibrating probe and compared to the delivered current. The mean current density along the normal unoperated rat sciatic nerve was 0.19 microA/cm2, while the value along the nerve near the wick electrodes positioned 15 mm apart with an active in vivo implant was 23.39 microA/cm2. This application promises to provide a potentially useful means of enhancing nerve regeneration clinically.

Animals↗
PubMed1987

The effect of chronic subarachnoid bupivacaine infusion in dogs.

A functional and histologic examination of the effect of the continuous intrathecal administration of bupivacaine was made in five dogs. After a partial laminectomy at L5, a silicone rubber catheter was inserted into the subarachnoid space and advanced 10 cm cranially. A model 400 Infusaid pump, used for drug delivery, was placed in a subcutaneous pocket between the 13th rib and iliac crest. Drug infusions were individually adjusted and maintained at a concentration such that the animal just exhibited slight gait impairment. Daily bupivacaine doses ranged from 5.7-11.1 mg. Infusions were maintained for a period of 3-16 weeks. Light microscopic examination of spinal cord and roots revealed no abnormalities. A focal mononuclear cell infiltration of the leptomeninges was seen in two drug animals, as well as one catheter control animal. One of the 16-week animals had a residual limp upon drug removal. While we were not able to quantitatively assess the degree of sensory motor dissociation, the results of this study suggest that chronic intrathecal bupivacaine infusion through an implantable pump system may be a short-term alternative to intrathecal morphine in the control of cancer pain.

Anesthesia, Spinal↗
PubMed1986

Effect of repetitive lidocaine infusion on peripheral nerve.

Neurotoxicity in rat tibial nerve was assessed following injections of lidocaine through implanted catheters. Doses of 1 to 4% lidocaine in volumes sufficient to inhibit motor nerve function, were infused three times a day for 3 days. When 4% lidocaine was infused into a Silastic cuff surrounding the sciatic nerve, all function was lost and there was considerable nerve fiber degeneration. When 4% lidocaine was infused within the muscle pocket surrounding the nerve, but at some distance from the nerve, there was no measurable permanent loss of motor function, but occasional nerve fiber degeneration. In contrast, 1% lidocaine appeared to cause no neurotoxicity, even when infused within a surrounding cuff. In addition, 1% lidocaine injection did not cause damage to the underlying muscle. Therefore, intermittent nerve block with low concentrations of lidocaine appears to be nontoxic to nerve and muscle when administered during 3 days. However, long-term studies are needed before clinical usage can be considered, because there is the potential for nerve and muscle damage.

Animals↗
PubMed1986

Microwave irradiation of peripheral nerve following injury: a structural analysis of degeneration and regeneration.

Studies of the enhancement effect of pulsed energy irradiation on nerve regeneration following injury have produced variable results. The effect of microwave treatment on the rat peroneal nerve after transection and anastomosis was analyzed by light and electron microscopy. The hindquarters were irradiated 1 h/day during the first 10 days postoperative (dpo). The nerves were fixed in situ and prepared for microscopic analysis. At 10 dpo the distal segment of the degenerating nerve had several enlarged myelin sheath profiles devoid of axoplasm. The swelling was not significantly altered by microwave treatment, but the number and density of the empty myelin sheath profiles were three to four times greater in the treatment group. At 49 dpo the regenerating nerve segment had a 43% decrease in the nerve fiber diameter compared with a normal mean of 7 microns. The number and density of remyelinated fibers showed a 50% increase in both treatment and control groups. Histologic evidence indicated no permanent enhancement on nerve regeneration by microwave treatment, even though the treatment may have delayed Wallerian degeneration.

Animals↗
PubMed1981

Reversible microwave effects on the blood-brain barrier.

Low level microwave exposure of Chinese hamsters resulted in reversible permeability of the blood-brain barrier (BBB) to horseradish peroxidase (HRP). Lesions were grossly visible in random areas of the brain immediately following exposure, but were not as common following a 1 h recovery period and were absent after a 2 h recovery period. The apparent route of increased permeability was via endothelial vesicular transport, since reaction product was not seen passing through the endothelial tight junctions. In addition, endothelial flooding of HRP, platelet aggregation and perivascular edema were observed only in experimental animals. Possible mechanisms of the enhanced vesicular transport are discussed.

Animals↗
PubMed1981

Non-neuronal cells in the spinal cord of nude and heterozygous mice. I. Ventral horn neuroglia.

A quantitative light microscopic analysis of the ventral grey matter in the lumbar spinal cord of homozygous nude (nu/nu) and heterozygous (nu/+) mice was performed to determine the possible contribution of lymphocytes to normal C.N.S. tissue. If lymphocytes were present in the neuropil, they could be mistaken for neuroglial cells. Athymic nude mice offer a good model, since they lack T-lymphocytes and symptoms of neurological involvement. Mean cell counts from 1 micrometer sections were tested by analysis of variance. There were not strain differences for the area and number of neurons. The total neuroglial cell count was also similar, but the number of oligodendrocytes decreased 28%, astrocytes increased 51% and microglia were unchanged in the nude compared with the heterozygous mouse. There were no qualitative differences at the ultrastructural level among the neuroglia of either strain. Either the genetic defect retards and alters neuroglial cell development, or some of the small, round dark nuclei belong to lymphocytes, which have earlier migrated into the C.N.S. parenchyma. Lymphocytes could then participate in a cell-mediated immune response with brain macrophages, which are thought to be primarily derived from mononuclear leukocytes.

Animals↗
PubMed1981

Non-neuronal cells in the spinal cord of nude and heterozygous mice. II. Agranular leukocytes in the subarachnoid and perivascular space.

The lumbar spinal cord of the athymic nude mouse and its heterozygous control were examined at the light and electron microscopic levels for differences in the cellular constituents of the subarachnoid and perivascular spaces. Both macrophages and lymphocytes were found in these spaces associated with the adventitial and leptomeningeal cells. Occasionally, fixed-cells were associated with extensions of the basal lamina and subjacent astrocytic processes. The appearance of the basal lamina of the external glia limitans and perivascular space was enhanced by tannic acid treatment. There were twice as many macrophages as lymphocytes, but no significant strain differences. Comparison was made between cells in the lumina of incompletely perfused vessels and neuroglial cells in the spinal cord. The cellular morphology is distinct in each of these compartments and no cell migrations were observed between the blood, cerebrospinal fluid and C.N.S. interstitial space. The normal presence of both macrophages and lymphocytes in the subarachnoid and perivascular space suggests that these cells could penetrate the basal lamina and gain access to the C.N.S.

Animals↗
PubMed1980

Postnatal differentiation of the rat trochlear nerve.

A morphometric analysis of postnatal differentiation in the rat trochlear nerve was studied by light and electron microscopy as an initial basis for understanding motor unit heterogeneity in the extraocular muscles (EOM). A total of 35 animals were examined 7--90 days postnatal (dpn). The mean number of fibers increased from 222 to 7 dpn to 274 in the adult and the size distribution became bimodal at 21 dpn. In the adult 17% of the myelinated fibers had a mean diameter of 2.5 micrometer and 83% were 7.3 micrometer. The estimated number of unmyelinated axons decreased from about 40% at 7 dpn to 20% at 14 dpn and 16% in the adult. The myelinated fiber diameter was more highly correlated with age and body weight than was fiber number. Certain organelles characteristic of active membrane growth were present in the Schwann cell cytoplasm at the paranode region. Redundant loops were prominent at 10 dpn, when many axons were still in Schwann cell bundles. During the third postnatal week a number of alterations were noted which may reflect a loss of polyneuronal innervation. These included thicker myelin sheaths and ultrastructural evidence of axonal degeneration. Branching of myelinated fibers was limited to the intramuscular portions of the nerve at 18 dpn. The g-ratio of the largest fibers at selected ages was nearly constant at .71 and was correlated with fiber diameters (r = 0.40), except at 14 dpn. The periodicity of the myelin sheath had either an inverse or constant relationship to the number of lamellae. The significance of the results is discussed in relation to postnatal development, the size principle and heterogeneity in the EOM motor units.

Animals↗
PubMed1979

Oculomotor nerve regeneration after aneurysm surgery.

A 57-year-old woman had symptoms of oculomotor nerve palsy first appearing one year before successful surgical ligation of a saccular aneurysm arising from the right posterior cerebral artery. During the subsequent postoperative period of two years, oculomotor nerve functions improved as the result of regeneration. Extensive morphometric evaluation of the regenerated nerve was compared to the normal side at the light microscopic level. The affected nerve showed a reduction in the transverse area (62%), estimated number of fibers (49%), and mean diameter of myelinated axons (23%). The normal g-ratio of axon to total diameter was almost constant at 0.64, but on the regenerated side it increased to 0.73. An increase in unmyelinated axons and connective tissue endoneurium was evident at the ultrastructural level. The significance of these marked quantitative changes was compared to the partial return of oculomotor nerve function.

Axons↗
PubMed1974

Ultrastructure of a large ventro-lateral dendritic bundle in the rat ventral horn.

There is an extensive bundle of dendrites with a rostro-caudal axis in the ventro-lateral lamina of the sixth lumbar segment in each side of the rat spinal cord. Such a bundle has a diameter of about 250 mum and contains over 1400 parallel dendrites, each with a diameter of less than 8 mum, interspersed between neuronal somata. The volume fraction of dendrites in the bundle neuropil is about 55%, the remainder being equally distributed between astrocytes, synaptic boutons, and axons, most of which are unmyelinated. An analysis of the median percentage covering of dendrites by contiguous elements of the neuropil reveals that as the dendrite diameter decreases from 4 to 0.2 mum (mean equals 2 mum), astrocytes increase from 43 to 75%, axons decrease from 21% to zero, boutons decrease from 28% to zero, and dendrites decrease from 10% to zero. There is a mean of 18 synaptic boutons per 100 mum-2 of the overall dendritic surface, but larger boutons tend to be more frequent on larger dendritic profiles. Apposed dendrites and their somata may have either puncta adhaerentia or confronting subsurface cisternae. Synaptic types in the rat are similar to those reported for the cat. The morphological findings are discussed with respect to previously proposed interaction between neural elements.

Animals↗