Biomedical subjects

M W Kalichman

Publications and source records attributed to M W Kalichman.

At least 19 recordsLinked to original sources

PubMed1999

Histomorphometric analysis of optic nerve changes in experimental glaucoma.

PURPOSE: To assess relative changes in different tissue components of optic nerve and their relationship to nerve fiber loss in the experimental monkey model of glaucoma. METHODS: Chronic intraocular pressure (IOP) elevation was induced by laser trabeculoplasty in the right eye of eight monkeys (Macaca fascicularis). Both experimental right optic nerves and control left optic nerves were studied. Histomorphometric analysis was performed on optic nerve cross-sections using bright field microscopy with camera lucida. Cross-sectional areas of optic nerve tissue components were estimated by point counting. Nerve fiber density was estimated by unbiased random sampling. Nerve fiber number was calculated by multiplying nerve fiber density with neuroglial area. RESULTS: Varying degrees of nerve fiber loss were seen in eight optic nerves with chronic IOP elevation. More than 50% nerve fiber loss was noted in four of eight experimental optic nerves. In these severely affected optic nerves, total optic nerve area was significantly decreased compared with control optic nerves. Among the optic nerve tissue components, only the ratio of myelinated fiber area to total optic nerve area was significantly decreased. The ratio of extraaxonal area to total optic nerve area was significantly increased, whereas the ratio of interfascicular septal area to total optic nerve area did not change significantly. For all optic nerves, differences in nerve fiber count between control and experimental optic nerves showed the strongest correlation with differences in myelinated fiber area, followed by differences in extraaxonal area and total optic nerve area. CONCLUSION: This histomorphometric study suggests the validity of the experimental monkey model of glaucoma in studying changes occurring in the nonaxonal optic nerve tissue components in human glaucomatous optic neuropathy. Glial scar tissue area was significantly increased in optic nerves with severe glaucomatous damage. Although a decrease in total optic nerve area was observed, among the optic nerve tissue components only myelinated nerve fiber area decreased significantly. Myelinated nerve fiber area also showed the strongest association with nerve fiber loss in experimental glaucoma.

Animals↗

PubMed1998

Nerve conduction velocity, laser Doppler flow, and axonal caliber in galactose and streptozotocin diabetes.

In an initial study, the effects of galactose intoxication on nerve laser Doppler blood flow (NLDF) and nerve conduction velocity (NCV) were assessed after 1-16 weeks of galactose feeding in pentobarbital-anesthetized rats. NLDF was not significantly changed at any time point. NCV was significantly reduced after 16, but not 1 or 4, weeks of galactose feeding. In a second study, NLDF was not significantly changed by 4 weeks of galactose intoxication, but streptozotocin-diabetic NLDF was significantly reduced compared to both control (P<0.001) and galactose-intoxicated rats (P<0.05). Compared to control animals, sciatic motor NCV was significantly (P<0.001) reduced in the galactose group, while sciatic and saphenous sensory NCVs were not significantly changed. In the streptozotocin-diabetic rats, motor and sensory NCVs were all significantly reduced (P<0.001). In contrast to the NCV findings, mean caliber of myelinated axons in both the saphenous and sciatic nerves was reduced in galactose-intoxicated, but not streptozotocin-diabetic rats. The observed sequence of changes associated with these two models of diabetic neuropathy is not consistent with the proposed roles of ischemia and axonal dwindling in the reported nerve conduction deficits.

Animals↗

PubMed1998

Tactile hyperesthesia, altered epidermal innervation and plantar nerve injury in the hindfeet of rats housed on wire grates.

The effects of wire grates on nerve injury and recovery were examined in rats housed in cages with sawdust-covered solid flooring. For the first 3 weeks of the study, 20 rats were housed on sawdust alone and 20 rats were housed in cages with wire grates placed over the sawdust. For the remaining 9 weeks, 10 animals housed on sawdust had wire grates added to their cages, while grates were removed from the cages of 10 animals. The effects of tactile stimulation on hindpaw plantar skin was measured weekly using the Von Frey filament test. Intraepidermal innervation using PGP 9.5 immunostaining and plantar nerve histology were assessed at the end of the 12-week study. After just 1 week on grates, hindpaw withdrawal thresholds were already markedly decreased and remained low until the grates were removed at 3 weeks. Thresholds returned to normal by 4 weeks after removal of the grates. Wire grates also induced increases in PGP 9.5 immunoreactive intraepidermal fine nerve endings that were normalized after grate removal. Demyelination, Wallerian degeneration and Renaut bodies were induced in the medial plantar nerve in rats housed in cages with wire-grate flooring. Nerve injury was largely resolved after 9 weeks on sawdust flooring. These data demonstrate that wire grates rapidly induce hindpaw tactile hyperesthesia and plantar neuropathy in rats and emphasize a risk of using wire-grate cage flooring in studies assessing hindlimb function and structure.

Animals↗

PubMed1998

Relationship of optic disc topography to optic nerve fiber number in glaucoma.

OBJECTIVE: To assess the relationship between in vivo measurements of optic disc topography and histomorphometric measurements of optic nerve fiber number in glaucoma. METHODS: Both eyes of 10 monkeys (Macaca fascicularis) with laser-induced glaucoma in the right eye were studied. Optic disc topography was measured in vivo with a confocal scanning laser ophthalmoscope. Histomorphometry was performed on optic nerve cross sections using bright-field microscopy with camera lucida. Nerve fiber density was estimated by unbiased random sampling. Nerve fiber number was estimated for each sector by multiplying nerve fiber density with neuroglial area. Nerve fiber count was compared with each of 13 global optic disc topographic parameters. RESULTS: For neuroretinal measurements in the glaucomatous eyes, rim area, retinal nerve fiber layer (RNFL) cross-sectional area, rim volume, and RNFL thickness correlated significantly with optic nerve fiber number. Differences in nerve fiber count between control and glaucomatous optic nerves showed the strongest correlation with differences in mean height contour; this was followed by RNFL cross-sectional area, RNFL thickness, rim volume, and differences in rim area. For cup measurements in the glaucomatous eyes, cup volume below reference, cup area, mean cup depth, the ratio of cup area to disc area, and cup shape correlated significantly with nerve fiber number. Differences in nerve fiber number between control and glaucomatous optic nerves showed the strongest correlation with differences in cup shape; this was followed by mean cup depth, cup volume below reference, the ratio of cup area to disc area, cup area, and differences in cup volume below surface. No association was found between optic nerve fiber number and optic disc area in glaucomatous eyes. CONCLUSIONS: In experimental glaucoma, most optic disc topography measures correlated significantly with optic nerve fiber number. The results of this histomorphometric study support the use of confocal scanning laser ophthalmoscopy to evaluate optic nerve damage in glaucoma.

Animals↗

PubMed1998

Reactive, degenerative, and proliferative Schwann cell responses in experimental galactose and human diabetic neuropathy.

Despite early descriptions of hypertrophic Schwann cells and onion-bulb formation in patients with diabetic neuropathy, clinical and experimental studies have emphasized axonal pathology. In recent years, the Schwann cell has been further implicated in diabetic neuropathy because it is the primary intrafascicular location for the first enzyme of the polyol pathway, aldose reductase, which appears to have a role in modulating a variety of complications of diabetes, including diabetic neuropathy. To further explore the role of polyol pathway flux in the pathogenesis of Schwann cell injury, ultrastructural abnormalities of Schwann cells in human diabetic neuropathy (HDN) were compared with those in experimental galactose neuropathy (EGN), a well-characterized model of hyperglycemia without hypoinsulinemia. Similar to previous studies of EGN, reactive, degenerative and proliferative changes of Schwann cells were observed after 2, 4 and 24 months of galactose intoxication. Reactive changes included accumulation of lipid droplets, pi granules of Reich and glycogen granules, increased numbers of subplasmalemmal vesicles, cytoplasmic expansion, and capping. Degenerative changes included enlargement of mitochondria and effacement of cristae, and disintegration of both abaxonal and adaxonal cytosol and organelles. Both demyelination and onion-bulb formation were seen at all time points, although supernumerary Schwann cells and axonal degeneration were most numerous after 24 months of galactose feeding. In sural nerve biopsy samples from patients with diabetes and progressive worsening of neuropathy, ultrastructural abnormalities in Schwann cells encompassed the full range of reactive, degenerative and proliferative changes described in galactose-fed rats. The concordance of fine-structural observations in nerves from galactose-fed rats and these adult-onset diabetic patients emphasizes the role of flux through aldose reductase in the complex pathology of diabetic neuropathy and points to the utility of galactose intoxication in helping to understand this metabolic disorder.

Adult↗

PubMed1998

NT-3 attenuates functional and structural disorders in sensory nerves of galactose-fed rats.

The present study investigated the effect of NT-3, a neurotrophin expressed in nerve and skeletal muscle, on myelinated fiber disorders of galactose-fed rats. Adult, female Sprague-Dawley rats were fed diets containing complete micronutrient supplements and either 0% D-galactose (control) or 40% D-galactose. Treated controls received 20 mg/kg NT-3 and treated galactose-fed rats received 1, 5, or 20 mg/kg NT-3 three times per week by subcutaneous injections. After 2 months, sciatic and saphenous sensory nerve conduction velocity (SNCV) and sciatic motor nerve conduction velocity (MNCV) were measured and the sciatic, sural, peroneal and saphenous nerves and dorsal and ventral roots processed for light microscopy. Treatment of control animals with NT-3 had no effect on any functional or structural parameter. Compared to control values, galactose feeding induced a sensory and motor nerve conduction deficit and a reduction in axonal caliber. Treatment with 5 and 20 mg/kg NT-3 ameliorated deficits in sciatic and saphenous SNCV in galactose-fed rats but had no effect on the MNCV deficit. NT-3 treatment also attenuated the decrease in mean axonal caliber in the dorsal root and sural nerve but not in the saphenous nerve, ventral root and peroneal nerve. These observations show that NT-3 can selectively attenuate the sensory conduction deficit of galactose neuropathy in a dose-dependent manner that depends only in part on restoration of axonal caliber of large-fiber sensory neurons.

Animals↗

PubMed1997

Effects of body and hindlimb temperature on laser Doppler blood flow and vascular conductance in rat sciatic nerve and skeletal muscle.

The role of body and hindlimb temperature in the control of blood flow in nerve and muscle was assessed by laser Doppler flowmetry. Following surgical exposure of nerve, initial measurements were taken for 5 min at hindlimb temperatures of 30-31 degrees C. A second set of identical measurements was then made either with or without warming to 37 degrees C. Without warming, nerve laser Doppler flow (NLDF) increased by 14.5+/-3.2% (mean+/-SEM) but, with warming, decreased by 40.9+/-8.2%. In contrast, adduccamerontor magnus muscle laser Doppler flow (MLDF) decreased without warming (14.7+/-1.0%) and increased with warming (20.4+/-12.8%). Because blood pressure was not significantly altered by changes in hindlimb temperature, the patterns of changes in vascular conductance (laser Doppler flow/blood pressure) were not significantly different from that seen with NLDF and MLDF. Thus, warming to physiological temperatures was associated with decreased NLDF and vascular conductance and increased MLDF and vascular conductance. These data may have implications for the interpretation of nerve blood flow data obtained at different hindlimb temperatures.

Adjuvants, Anesthesia↗

PubMed1996

Effects of seven days of galactose feeding and aldose reductase inhibition on mast cells and vessel morphometry in rat sciatic nerve.

The association between mast cells and vessel morphometry in sciatic nerve was examined after seven days in animals fed a diet of 40% D-galactose and compared to control rats and to galactose-fed animals treated with the aldose reductase inhibitor, Tolrestat. Electron microscopy revealed an increase in the total number of mast cells and the number of degranulated mast cells in galactose-fed animals (7.8 +/- 2.9; 2.6 +/- 2.9; mean +/- SD) compared to controls (4.6 +/- 2.1; degranulated mast cells were not seen in any control nerves) and Tolrestat-treated, galactose-fed animals (4.4 +/- 2.5; 0.1 +/- 0.4). Although no significant differences were noted in the numbers of vessels between the three groups, an index of vasoconstriction was significantly increased in the galactose-fed animals (0.115 +/- 0.048; mean +/- SD) compared to controls (0.068 +/- 0.011) and Tolrestat-treated, galactose-fed animals (0.075 +/- 0.20). These data suggest that mast cell degranulation is associated with the vascular constriction induced by seven days of galactose intoxication and that both may be prevented by inhibiting aldose reductase.

Aldehyde Reductase↗

PubMed1996

Polyol pathway and osmoregulation in JS1 Schwann cells grown in hyperglycemic and hyperosmotic conditions.

To test the osmoregulatory rules of Schwann cell aldose reductase (AR) and myo-inositol, JS1 Schwann cells were grown under control and hyperosmotic conditions with and without excess glucose or galactose. JS1 cells cultured in control conditions possessed AR protein and activity that were not altered by the inclusion of 25 mM glucose or galactose. Following culture with 100 mM NaCl, there was a decline in cell number accompanied by an increase in AR activity, both of which were attenuated by the addition of 25 mM glucose or galactose. Sorbitol was not detected in JS1 Schwann cells following culture in control, glucose-supplemented, or hyperosmotic medium, and dulcitol accumulated only following culture with galactose. However, both polyols were dramatically increased in JS1 cells cultured in hyperosmotic medium supplemented with 25 mM glucose or galactose. In contrast, myo-inositol levels were elevated only during hyperosmotic exposure but decreased when glucose or galactose was also present. These data are consistent with the use of polyol formation by JS1 Schwann cells as a means of responding to osmotic stress.

Aldehyde Reductase↗

PubMed1995

Mast cell degranulation and blood-nerve barrier permeability in rat sciatic nerve after 7 days of hyperglycemia.

The association between hyperglycemia and altered blood-nerve barrier permeability was examined after 7 days of experimental diabetes. In nerves of rats fed a diet of 40% galactose, permeability to [14C]mannitol [13.43 +/- 2.47 x 10(-5) (SD) ml.s-1.g dry wt-1] and water content [3.43 +/- 0.24 (SD) mg/mg dry wt] were significantly increased compared with control (9.24 +/- 2.09 x 10(-5) ml.s-1.g dry wt-1 and 2.15 +/- 0.28 mg/mg dry wt) and streptozotocin-diabetic animals (8.43 +/- 2.94 x 10(-5) ml.s.-1.g dry wt-1 and 2.35 +/- 0.56 mg/mg dry wt). Electron microscopy revealed significant increases in the number of degranulating perivascular mast cells and in an index of vasoconstriction in galactose-treated rats (3.8 +/- 1.6 and 0.160 +/- 0.062, respectively) compared with control (0.5 +/- 0.8 and 0.072 +/- 0.017, respectively) and diabetic animals (1.4 +/- 1.7 and 0.083 +/- 0.033, respectively). The data are consistent with a role for mast cells in permeability changes occurring after only 7 days of galactose intoxication.

Animals↗

PubMed1994

Aldose reductase inhibition, Doppler flux and conduction in diabetic rat nerve.

Two chemically distinct aldose reductase inhibitors, ponalrestat and tolrestat, were tested against laser Doppler blood flow and conduction deficits in the sciatic nerve of diabetic rats. The effects of two months of streptozotocin-induced diabetes and aldose reductase inhibition on body weight, plasma glucose, and nerve sugars and polyols were comparable to those reported previously. Nerve blood flow, reflected by laser Doppler flow measurements, and motor nerve conduction velocity were both significantly less in diabetic than in control animals. Both of these reductions were prevented by ponalrestat, but not tolrestat. Thus, either deficits in laser Doppler blood flow and conduction are not aldose reductase inhibitor-dependent or tolrestat has some other property which offsets the beneficial effects of aldose reductase inhibition. In either case, these data are consistent with the hypothesis that reduced nerve blood flow contributes to conduction deficits in diabetes.

Aldehyde Reductase↗

PubMed1994

Effects of cocaine on blood flow and prostaglandin metabolites in rat sciatic nerve.

To better understand the mechanisms of local anesthetic-reduced nerve blood flow and nerve blood flow regulation, the effects of cocaine on blood flow and vasoactive prostaglandins were tested in the sciatic nerve of anesthetized rats. After 30 min, nerve blood flow was significantly reduced from baseline by perineural injection of 160 mM cocaine [-29.4 +/- 4.0 (SD) laser-Doppler flow units (P < 0.001)] but not saline (1.6 +/- 11.3). These same nerves were removed and assayed for the stable metabolites 6-ketoprostaglandin F1 alpha and thromboxane B2 of the vasoactive eicosanoids prostacyclin and thromboxane A2, respectively. Both metabolites were reduced, but the ratio of thromboxane B2 to 6-ketoprostaglandin F1 alpha was greater (P < 0.05) in nerves pretreated with cocaine (6.1 +/- 3.2 vs. 2.4 +/- 1.1) and was inversely correlated (P < 0.01) with nerve blood flow. In a separate experiment, perineural injection of the prostaglandin synthesis inhibitor indomethacin (0.5 mg in 0.5 ml of either saline or 50% ethanol) reduced nerve blood flow as well (P < 0.05). These results are consistent with the proposal that cocaine inhibits nerve blood flow by effects on nerve prostaglandin metabolites.

6-Ketoprostaglandin F1 alpha↗

PubMed1993

Permeability and surface area of the blood-nerve barrier in galactose intoxication.

The blood-nerve movement of a small molecular weight non-electrolyte was studied in control and galactose-fed rats by measuring the permeability-surface area (PSA) product of the blood-nerve interface to [14C]mannitol in sciatic nerve using an in vivo injection method. PSA products were measured after 9 to 11 months of feeding control rats a diet containing 0% galactose and galactose-intoxicated rats a diet containing 40% galactose. Nerves of the galactose-fed group were hydrated as reflected by a significant increase in nerve water content and wet weight to dry weight ratio (both P < 0.05). Compared to controls, PSA products were increased by 51% (P < 0.01) in galactose-fed animals when referenced to nerve dry weight (13.59 +/- 2.90 x 10(-5) ml/s/g dry wt. versus 8.99 +/- 1.59 x 10(-5) ml/s/g dry wt.; mean +/- S.D.; galactose vs. control, respectively) or by 30% (P < 0.001) when referenced to nerve length (2.43 +/- 0.43 x 10(-5) ml/s/mm vs. 1.87 +/- 0.48 x 10(-5) ml/s/mm) but not when referenced to nerve wet weight. It is suggested that in galactose intoxication, where endoneurial volume changes reflect increases in nerve water content, PSA products are best normalized to dry weight or length, which are not affected by volume changes. Normalized to dry weight, the blood-nerve barrier surface area (i.e. vessels and perineurium) was determined by morphometric methods to be increased by 34% in the galactose-intoxicated group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Decreased endoneurial fluid electrolytes in normal rat sciatic nerve after aldose reductase inhibition.

The role of the enzyme aldose reductase in nerve homeostasis was examined by treating rats with an aldose reductase inhibitor. Female Sprague-Dawley rats were treated with Ponalrestat (25 mg/kg/day) or with excipient alone for 4 to 12 weeks before examining electrophysiologic function, endoneurial fluid electrolyte concentrations, nerve polyol levels, water content and (Na+,K+)-ATPase activity. Sorbitol, the product of glucose metabolism by aldose reductase, was detected in all nerves from control animals, whereas it was below detection limits in 7 of 11 nerves from Ponalrestat-treated rats. Ponalrestat treatment reduced endoneurial fluid sodium and chloride concentrations by 25% and 37%, respectively (both P < 0.001). No differences in nerve water content, conduction velocity, or ATPase activities were detected. These data, and previous studies demonstrating that increased flux through aldose reductase causes the accumulation of endoneurial electrolytes, suggest a role for this enzyme in modulation of the endoneurial microenvironment. However, short-term inhibition of aldose reductase does not appear to affect nerve function. Thus, our findings do not elicit concerns regarding the use of aldose reductase inhibitors in the treatment of clinical diabetic neuropathy.

Adenosine Triphosphatases↗

PubMed1993

Relative neural toxicity of local anesthetics.

In rat sciatic nerve, relative neural toxicity and relative motor nerve conduction blockade were assessed for two amide-linked local anesthetics (etidocaine and lidocaine) and two ester-linked local anesthetics (chloroprocaine and procaine). As measures of neural toxicity, nerve fiber injury and edema were assayed by light microscopic examination of nerve tissue sampled 2 days after perineural (next to the sciatic nerve) injection of various concentrations of the local anesthetics. Both nerve injury and edema increased with concentration of local anesthetics, but injury was frequently present in nerve fascicles with little or no edema. In parallel studies, the amplitude of the electrical activity elicited from the interosseous muscles of the foot following ipsilateral electrical stimulation at the sciatic notch was monitored for up to 15 minutes to assess the extent of motor nerve blockade. The resulting log concentration-response curves were analyzed for differences in potency. Both for injury and for conduction block, the order of decreasing potency was: etidocaine, lidocaine, chloroprocaine, procaine. These results are not consistent with the proposal that ester-linked agents are more likely than other local anesthetic agents to cause nerve injury.

Anesthetics, Local↗

PubMed1992

Local anesthetic-induced conduction block and nerve fiber injury in streptozotocin-diabetic rats.

Patients with diabetes may have peripheral neuropathy, which may have clinical implications for the use of regional nerve block. The effects of local anesthetics on nerve conduction and nerve fiber injury were tested in control rats and at 4 weeks after the onset of diabetes in rats injected with streptozotocin (50 mg/kg intraperitoneally). Nerve conduction was assessed by recording evoked electrical activity in hindpaw muscles following ipsilateral electrical stimulation of the sciatic nerve near the hip. Block of motor nerve conduction was quantified by recording the amplitude of the evoked response at 1-min intervals for up to 15 min after the injection of 500 microliters 1% lidocaine HCl or procaine HCl into the midthigh next to the sciatic nerve. In control animals, procaine was much less effective than lidocaine in producing conduction block. The rate and magnitude of lidocaine-induced conduction block were not significantly different between control and diabetic groups. However, conduction block due to procaine was sufficiently enhanced in diabetic rats to become comparable to that of lidocaine-treated control nerves. Long-lasting injury was assessed in sciatic nerve harvested 2 days after the extraneural injection of saline or 2 or 4% lidocaine HCl. Using a light microscope with a superimposed grid, nerve edema was quantified as the proportion of intersection points falling on extracellular space. Lidocaine induced edema in both control and diabetic nerves, but 4% lidocaine induced significantly more edema in diabetic nerves than in controls. Nerve fiber injury, based on light microscopic scoring of axonal degeneration and demyelination, was not observed in saline-treated nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

A pilot study of biomedical trainees' perceptions concerning research ethics.

The authors surveyed 2,010 biomedical trainees in the fall of 1990 at the University of California, San Diego, regarding their perceptions about unethical practices in research and the extent of their training exposure to the ethics of scientific investigation; 549 responded, representing both clinical and basic science departments and including graduate students and postdoctoral fellows in addition to medical students, residents, and fellows. Of the 549 trainees, 129 (23%) responded that they had received no training in research ethics; 195 (36%), that they had observed some kind of scientific misconduct (although not necessarily in the sense of research fraud defined in federal regulations); and 81 (15%), that they would be willing to select, omit, or fabricate data to win a grant or publish a paper. The trainees planning an academic career were more likely to report having been aware of others' scientific misconduct. Reported exposure to ethics training was not associated with a difference in past or potential unethical behavior. The authors conclude that while the apparent ineffectiveness of past ethics instruction does not preclude the possibility that more systematic training may be useful, it does underscore the need to assess the efficacy of training activities.

California↗

PubMed1991

Experimental nerve ischemia and injury produced by cocaine and procaine.

The effects of ethanol, glycerol, procaine, and cocaine were tested on rat sciatic nerve blood flow. Blood flow measurements were made using a laser Doppler blood perfusion monitor with a 1 mm diameter probe. The local anesthetics procaine and cocaine produced a dose-dependent and time-dependent decrease in nerve blood flow, but 80% ethanol, 80% glycerol, and 0.9% saline did not significantly alter nerve blood flow either acutely (10 min) or for up to 4 h. For histopathologic studies, the same nerves were removed at 2 days after blood flow tests. Evidence of nerve injury (edema and nerve fiber pathology) was observed for the neurolytic agents ethanol and glycerol and for both local anesthetics. No relationship between nerve blood flow and injury was seen for either ethanol or glycerol; however, both local anesthetics exhibited a highly significant negative correlation (P less than 0.01) between blood flow at 4 h and injury at 2 days. These data provide additional evidence that local anesthetics can decrease nerve blood flow; and these results are consistent with an ischemic mechanism for local anesthetic-induced nerve injury.

Analysis of Variance↗