Biomedical subjects

K L Holloway

Publications and source records attributed to K L Holloway.

12 recordsLinked to original sources

PubMed2006

Isolation of neuronal progenitor cells from the adult human neocortex.

BACKGROUND: The reliability of harvesting neuronal progenitor cells (NPCs) from the adult human neocortex has not been established, with respect to preparing autologous cell cultures for transplantation in stroke and traumatic brain injured patients. METHOD: Enriched NPC cultures have been generated from nonneurogenic regions of the adult rodent brain by buoyancy-dependent fractionation, but the feasibility of using such a method to isolate NPCs from the adult human cortex has not been reported previously. To determine if a starter population of human adult cortical NPCs could be isolated for in vitro expansion using this method, tissue samples from five patients undergoing cortical resection for either epilepsy or trauma were assayed. FINDINGS: Cultured cells generated from all patients predominately expressed both the NPC marker nestin and neuron-specific beta-tubulin III. The presence of NPCs was verified by in vitro BrdU/beta-tubulin III co-labeling and increasing beta-tubulin expression in differentiating conditions. Despite the formation of aggregates in monolayer culture, cell proliferation as measured by BrdU incorporation was not as prevalent as that reported from rodent cultures generated by this protocol. CONCLUSIONS: NPCs isolated from the adult human neocortex using this method expressed beta-tubulin III in larger percentages than has been previously reported for NPCs isolated using other methods. As such, these data suggest the possibility of culturing dividing neuroblasts from the adult neocortex for further manipulation as transplantable cells.

Adolescent↗

PubMed2000

Simplified approach to somatization disorder. When less may prove to be more.

Somatization disorders--manifestations of mental pain--take many forms and can be difficult to diagnose and treat. By definition, most patients with this condition do not want to be cured. Antidepressant or antianxiety medication and referral to a support group or psychiatrist can help patients who are willing to participate in their treatment. Other patients may receive the most benefit from primary care physicians who accept the limitations of treatment, listen to their patient's concerns, and provide reassurance.

Adolescent↗

PubMed1999

Human neuronal gamma-aminobutyric acid(A) receptors: coordinated subunit mRNA expression and functional correlates in individual dentate granule cells.

gamma-Aminobutyric acid(A) receptors (GABARs) are heteromeric proteins composed of multiple subunits. Numerous subunit subtypes are expressed in individual neurons, which assemble in specific preferred GABAR configurations. Little is known, however, about the coordination of subunit expression within individual neurons or the impact this may have on GABAR function. To investigate this, it is necessary to profile quantitatively the expression of multiple subunit mRNAs within individual cells. In this study, single-cell antisense RNA amplification was used to examine the expression of 14 different GABAR subunit mRNAs simultaneously in individual human dentate granule cells (DGCs) harvested during hippocampectomy for intractable epilepsy. alpha4, beta2, and delta-mRNA levels were tightly correlated within individual DGCs, indicating that these subunits are expressed coordinately. Levels of alpha3- and beta2-mRNAs, as well as epsilon- and beta1-mRNAs, also were strongly correlated. No other subunit correlations were identified. Coordinated expression could not be explained by the chromosomal clustering of GABAR genes and was observed in control and epileptic rats as well as in humans, suggesting that it was not species-specific or secondary to epileptogenesis. Benzodiazepine augmentation of GABA-evoked currents also was examined to determine whether levels of subunit mRNA expression correlated with receptor pharmacology. This analysis delineated two distinct cell populations that differed in clonazepam modulation and patterns of alpha-subunit expression. Clonazepam augmentation correlated positively with the relative expression of alpha1- and gamma2-mRNAs and negatively with alpha4- and delta-mRNAs. These data demonstrate that specific GABAR subunit mRNAs exhibit coordinated control of expression in individual DGCs, which has significant impact on inhibitory function.

Adolescent↗

PubMed1998

Physiological analysis of Rasmussen's encephalitis: patch clamp recordings of altered inhibitory neurotransmitter function in resected frontal cortical tissue.

Rasmussen's encephalitis (RE) is a progressive, rare childhood disease characterized by severe epilepsy, hemiplegia, dementia, and inflammation of the brain. While one mechanism underlying the pathogenesis of RE has been hypothesized to be mediated by production of excitotoxic GluR3 autoantibodies to the AMPA receptor, other neuropathological etiologies have also been indicated. Whole-cell patch clamp recordings of GABA(A) receptor mediated responses were conducted in neurons acutely isolated from an RE patient, and compared to properties of non-focal human temporal cortical neurons. RE neurons appeared similar anatomically to control cortical neurons. Significant differences in GABAergic responses were evident between RE and control neurons. GABA was significantly more potent in RE than in control cortical neurons (EC50 of 13 microM vs 23 microM, respectively). In addition, the overall efficacy of GABA was significantly decreased in RE neurons, associated with a decrease in postsynaptic GABA current density in RE neurons (5.1 pA/microm2) in comparison to controls (9.2 pA/microm2). Augmentation of GABA responses by the benzodiazepine, clonazepam (CNZ), was significantly reduced in RE in comparison to control neurons (34% vs 99% augmentation at 100 nM). The RE-associated reduced functional efficacy and altered pharmacology of neuronal GABA(A) receptors is consistent with overall disinhibition in RE neurons, and could contribute to the generation of the severe epileptic activity evident in this disorder.

Cell Size↗

PubMed1998

GABA(A) receptor function in epileptic human dentate granule cells: comparison to epileptic and control rat.

Using patch clamp recording techniques in dentate granule cells (DGCs) isolated from patients undergoing temporal lobectomy for intractable epilepsy, we investigated basic properties of GABA(A) receptors (GABA(A)Rs) and pharmacological sensitivity of GABA-evoked currents to modulation by zinc and benzodiazepines (BZ). Properties of human DGC GABA(A)Rs were compared to DGC GABA(A)R properties in control and epileptic rats. Blockade of GABA evoked currents by zinc was significantly enhanced in epileptic human relative to control rat DGCs. Augmentation of the GABA(A)R current by the non-subunit selective BZ agonist, clonazepam (CNZ) and by the BZ1 specific agonist, zolpidem (ZOL), were not significantly different in human DGCs relative to control or epileptic rat. GABA potency was significantly higher in epileptic human DGCs than in control or epileptic rat DGCs. The significantly enhanced efficacy of zinc in blocking GABA currents in epileptic human DGCs mirrors that seen in epileptic rat DGCs, and was coupled with mossy fiber sprouting evident in both epileptic human and rat dentate gyrus. The aberrant mossy fibers provide a novel zinc delivery system within the epileptic dentate gyrus. The mossy fiber release of zinc onto DGCs coupled with the enhanced zinc sensitivity of GABA(A)Rs in epileptic DGCs, may lead to 'dynamic disinhibition' which could compromise inhibitory efficacy in the epileptic rat and human hippocampus.

Animals↗

PubMed1997

Intraoperative monitoring of substrate delivery during aneurysm and hematoma surgery: initial experience in 16 patients.

The effects of proximal occlusion of the parent artery during aneurysm surgery in humans are not fully understood, although this method is widely used. The reduction in substrate that can be tolerated by normal and subarachnoid hemorrhage (SAH)-affected brain is unknown. Therefore, the authors measured brain oxygen tension (brain PO2), carbon dioxide tension (brain PCO2), pH, and hemoglobin oxygen (HbO2) saturation before and after temporary occlusion in 12 patients with aneurysms. The effect of removal of a traumatic intracranial hematoma on cerebral oxygenation was also studied in four severely head injured patients. A multiparameter sensor was placed in the cortex of interest and locked by means of a specially designed skull bolt. The mean arterial blood pressure, inspired O2 fraction, and end-tidal PCO2 were analyzed. Brain PO2 and HbO2 saturation data were collected every 10 seconds. Descriptive and nonparametric analyses were used to analyze the data. A wide range in baseline PO2 was seen, although a decrease from baseline in brain PO2 was found in all patients. During temporary occlusion, brain PO2 in patients with unruptured aneurysm (seven patients) dropped significantly, from 60 +/- 31 to 27 +/- 17 mm Hg (p < 0.05). In the SAH group (five patients), the brain PO2 dropped from 106 +/- 74 to 87 +/- 73 mm Hg (not significant). Removal of intracranial hematomas in four severely head injured patients resulted in a significant increase in brain PO2, from 13 +/- 9 to 34 +/- 13 mm Hg (p < 0.05). The duration of safe temporary occlusion could not be determined from this group of patients, because none developed postoperative deterioration in their neurological status. However, the data indicate that this technique is useful to detect changes in substrate delivery during intraoperative maneuvers. This study also reemphasizes the need for emergency removal of intracranial hematomas to improve substrate delivery in severely head injured patients.

Adult↗

PubMed1996

Characterization of GABAA receptor function in human temporal cortical neurons.

1. Surgically resected tissue from the tip of the human temporal lobe of seven patients undergoing temporal lobectomy was employed to study functional properties of GABAergic inhibition mediated through activation of GABAA receptors, using patch-clamp recording techniques in acutely isolated neurons and in slices of human temporal cortex. 2. Human temporal cortical pyramidal neurons from surgically resected tissue could be acutely isolated with the use of conventional methods. These neurons appeared normal in morphology, in their intrinsic membrane properties, and in their response to application of exogenous gamma-aminobutyric acid (GABA). 3. Application of GABA to acutely isolated human temporal cortical neurons elicited a large current with an average reversal potential of -65 mV, presumably mediated through a GABAA-activated chloride conductance. Application of varying concentrations of GABA generated a concentration/response relationship that could be well-fitted by a conventional sigmoidal curve, with an EC50 of 25.5 microM and a Hill coefficient of 1.0 4. Coapplication of the benzodiazepine clonazepam and 10 microM GABA augmented the amplitude of the GABA response. The concentration dependence of this benzodiazepine augmentation could be best-fitted by an equation assuming that the benzodiazepine interacted with two distinct binding sites, with differing potencies. The high-potency site had an EC50 of 0.06 nM and maximally contributed 38.5% augmentation to the total effect of clonazepam. The lower potency site had an EC50 of 16.4 nM, and contributed 66.1% maximal augmentation to the overall effect of clonazepam. These data derived from adult human temporal cortical neurons were very similar to our findings in adult rat sensory cortical neurons. 5. The effects of equimolar concentrations (100 nM) of clonazepam, a BZ1 and BZ2 agonist, and zolpidem, a selective BZ1 agonist, on acutely isolated human temporal cortical neurons were also investigated. Zolpidem and clonazepam were equally effective (71.5 vs. 65.0%, respectively) in potentiating GABA responses elicited by application of 10 microM GABA. This suggests that many of the functional benzodiazepine receptors in these neurons were of the BZ1 variety. 6. GABAergic synaptic inhibition was also studied with the use of patch-clamp recordings in slices of human temporal cortex. Extracellular stimulation at the white matter/gray matter border elicited compound synaptic events in layer II-V cortical neurons. These events usually consisted of an early excitatory postsynaptic potential (EPSP) and a late multiphasic inhibitory postsynaptic potential (IPSP). Application of either clonazepam or zolpidem (both at 100 nM) to the slice during extracellular stimulation reversibly augmented the late compound IPSP. 7. Spontaneous IPSPs were also recorded in approximately 50% of human temporal cortical neurons. These events did not have a preceding EPSP and were usually monopolar, with a single exponential rise and decay. This supported the idea that these events were triggered by spontaneous activity of GABAergic interneurons. Bath application of either clonazepam or zolpidem (both at 100nM) to the slice during ongoing spontaneous IPSP activity increased the amplitude and lengthened the time constant of decay of these events. 8. To our knowledge, this is one of the first detailed characterizations of the functional properties of GABAA-mediated inhibition in human cortical neurons using patch-clamp recordings in both isolated cells and slices of resected temporal cortex. Isolated pyramidal neurons exhibited GABAA-mediated currents that were comparable in many aspects with GABA currents recorded from adult rat cortical neurons, including similar GABA concentration/response curves, and similar two differing potency site effects for clonazepam augmentation of GABA currents. In addition, evoked and spontaneous IPSPs recorded in human cortical neurons appeared similar to IPSPs in rat cortical

Animals↗

PubMed1996

Ventriculostomy infections: the effect of monitoring duration and catheter exchange in 584 patients.

The investigators undertook a retrospective analysis of ventriculostomy infections to evaluate their relationship to monitoring duration and prophylactic catheter exchange. In 1984, the results of an epidemiological study of ventriculostomy-related infection were published. One of the conclusions of the paper was that the incidence of ventriculostomy-related infections rose after 5 days of monitoring. This led to the recommendation that catheters be prophylactically changed at 5-day intervals if prolonged monitoring was required. A recent randomized prospective study on central venous catheters showed no reduction in infection with prophylactic catheter exchanges. This has led the authors to reexamine their experience with ventriculostomy infections. Data on 584 severely head injured patients with ventriculostomies were prospectively collected in two data banks, The Traumatic Coma Data Bank and The Medical College of Virginia Neurocore Data Bank. These data were retrospectively analyzed for factors associated with ventriculostomy related infections. It was found that there is a relationship of ventriculitis to monitoring duration but it is not simple or linear. There is a rising risk of infection over the first 10 days, but infection then becomes very unlikely despite a population that continues to be at risk. Patients in whom catheters were replaced prior to 5 days did not have a lower infection rate than those whose catheters were exchanged at more than 5-day intervals. Based on these data, it is recommended that ventriculostomy catheters for intracranial pressure monitoring be removed as quickly as possible, and in circumstances in which prolonged monitoring is required, there appears to be no benefit from catheter exchange.

Adolescent↗

PubMed1995

Epilepsy surgery: removing the thorn from the lion's paw.

In the United States, 10,000 to 20,000 patients have epilepsy uncontrolled by medication. The addition of a second-line drug to the primary regimen has a 2% to 11% chance of controlling the seizures. We present a series of 35 patients with intractable epilepsy who had surgical resection of their seizure focus. Seventy-five percent of the patients with temporal lobe epilepsy were made seizure free, with an additional 14% sustaining a greater than 90% reduction in seizures (decrease in number and frequency). Seventy-one percent of the patients with extratemporal lobe epilepsy (seizures originating outside the temporal lobe) had a worthwhile reduction (> 90%) in their seizures. Two patients sustained permanent clinically significant deficits as a result of their presurgical evaluation or resection. There were no deaths. Epilepsy surgery offers a cure for the "incurable" patient with a morbidity of 5% to 6%.

Adolescent↗

PubMed1994

Ultrastructural studies of diffuse axonal injury in humans.

Diffuse axonal injury (DAI) is observed commonly in traumatically brain injured humans. However, traditional histologic methods have proven of limited use in identifying reactive axonal change early (< 12 h) in the posttraumatic course. Recently, we have reported, in both humans and animals, that antibodies targeting neurofilament subunits are useful in the light microscopic recognition of early reactive change. In the present study, we extend our previous efforts in humans by analyzing the progression of traumatic brain injury (TBI)-induced axonal change at the ultrastructural level. This effort was initiated to follow the subcellular progression of reactive axonal change in humans and to determine whether this progression parallels that described in animals. Two commercially prepared antibodies were used to recognize reactive axonal change in patients surviving from 6 to 88 h. The NR4 antibody was used to target the light neurofilament subunit (NF-L), and the SMI32 antibody was used to target the heavy neurofilament subunit (NF-H). Plastic-embedded tissue sections were screened for evidence of reactive axonal change, and once identified, this reactive change was analyzed at the ultrastructural level. At 6 h survival, focally enlarged, immunoreactive axons with axolemmal infolding or disordered neurofilaments were seen within fields of axons exhibiting no apparent abnormality. By 12 h, some axons exhibited continued neurofilamentous misalignment, pronounced immunoreactivity, vacuolization, and, occasionally, disconnection. At later stages, specifically 30 and 60 h survival, further accumulation of neurofilaments and organelles had led to the further expansion of the axis cylinder, and clearly disconnected reactive swellings were recognized. These contained a dense core of disordered immunoreactive neurofilaments partially encompassed by a cap of less densely aggregated organelles. At 88 h, the reactive axons were larger and elongated, consistent with the continued delivery of organelles by axoplasmic transport. At the later time points, considerable heterogeneity was observed, with focally enlarged disconnected axons being observed in relation to axons showing less advanced reactive change. Our findings suggest that neurofilamentous disruption is a pivotal event in axonal injury.

Adult↗

PubMed1990

Postoperative myeloneuropathy: a preventable complication in patients with B12 deficiency.

Two cases of postoperative neurological deterioration following routine neurosurgical procedures are presented. In each instance, the patient was found to have hematological abnormalities present preoperatively consistent with vitamin B12 deficiency and to have undergone general anesthesia involving N2O. This caused inactivation of the remaining marginal stores of B12 with resultant neurological decompensation. The frequent use of N2O in general anesthesia and the significant incidence of B12 deficiency make it imperative that the surgeon be aware of this complication and its easy prevention. The preoperative recognition of B12 deficiency and N2O-induced neurological deterioration in patients with B12 deficiency is reviewed.

Female↗

PubMedDate not supplied

Antibiotic prophylaxis during clean neurosurgery: a large, multicenter study using cefuroxime.

Cefuroxime is a second-generation cephalosporin with in vitro activity against the organisms that are commonly associated with neurosurgical wound infections. Other properties of cefuroxime are an elimination half-life of 1.3 hours, which yields prolonged serum concentrations, and its ability to penetrate the blood-brain barrier in proportion to the degree of inflammation. A prospective, multicenter, open-label study was conducted to evaluate the efficacy and safety of cefuroxime for antibiotic prophylaxis in patients undergoing clean neurosurgery. Cefuroxime 1.5 g was given intravenously 25 to 60 minutes before surgery; for procedures lasting more than 3 hours, cefuroxime 750 mg was given intravenously 8 hours after the initial dose. Patients were examined before surgery, daily during hospitalization, and at 8 weeks after surgery. A total of 956 adults were enrolled in the study. The most common procedures in study patients were laminectomy (41.8% of patients) or craniotomy (24.3%), and the mean duration of surgery was 3.2 hours. Infection occurred in 2 (0.3%) of 592 assessable patients by the time of discharge and in 1 additional patient by the 8-week follow-up evaluation for a total of 3 (0.5%) of 560 assessable patients. Drug-related adverse events occurred in 5 (0.5%) of 956 patients. These results indicate that antibiotic prophylaxis with cefuroxime is associated with a low incidence of postoperative wound infection and is well tolerated in patients undergoing clean neurosurgery.

Adult↗