Chromosomal localization of glutamate receptor genes: relationship to familial amyotrophic lateral sclerosis and other neurological disorders of mice and humans

Receptors for the major excitatory neurotransmitter glutamate may play key roles in neurodegeneration. The mouse Glur-5 gene maps to chromosome 16 between App and Sod-1. The homologous human GLUR5 gene maps to the corresponding region of human chromosome 21, which contains the locus for familial amyotrophic lateral sclerosis. This location, and other features, render GLUR5 a possible candidate gene for familial amyotrophic lateral sclerosis. In addition, dosage imbalance of GLUR5 may have a role in the trisomy 21 (Down syndrome). Further characterization of the murine glutamate receptor family includes mapping of Glur-1 to the same region as neurological mutants spasmodic, shaker-2, tipsy, and vibrator on chromosome 11; Glur-2 near spastic on chromosome 3; Glur-6 near waltzer and Jackson circler on chromosome 10; and Glur-7 near clasper on chromosome 4.

Identification and classification of celery cultivars with RAPD markers

Twenty-one celery (Apium graveolens L. var. dulce) cultivars, one celeriac (var. rapaceum) and one annual smallage (var. secalinum) cultivar were screened for polymorphic RAPD (Random Amplified Polymorphic DNA) markers with 28 arbitrary 10-mer primers. Among a total of 309 bands observed, 29 (9.3%) were polymorphic in the 23 cultivars screened, but only 19 (6.1%) markers were polymorphic within the 21 type dulce cultivars. These markers were sufficient to distinguish each of the cultivars used. The average marker difference was 6.4 between two celery cultivars, 16.7 between celery and annual smallage, 14.7 between celery and celeriac, and 12.0 between annual smallage and celeriac. The celery cultivars surveyed were classified into three groups based on the marker differences. The relationship among the dulce-type cultivars concluded from this research is basically consistent with the known lineage of the cultivars and the previous study using stem protein and isozyme markers. RAPD technology provides a new alternative for cultivar identification and classification in celery.

The role of a Drosophila POU homeo domain gene in the specification of neural precursor cell identity in the developing embryonic central nervous system

The Drosophila embryonic central nervous system (CNS) is derived from a stereotypic array of progenitor stem cells called neuroblasts (NBs). Each of the approximately 25 NBs per hemisegment undergoes repeated asymmetric divisions to produce, on average, 5-10 smaller ganglion mother cells (GMCs); each GMC, in turn, divides to produce two neurons. We demonstrate that the protein product encoded by a POU homeo domain gene (dPOU28/pdm-2) is expressed in the cell nuclei of a subset of NBs and GMCs. In the wild-type animal, GMC-1 is the only identified cell in the NB4-2 lineage that expresses dPOU28 protein to a high level, and it divides to produce the RP2 neuron and a second cell of unknown fate. Our results suggest that the presence of ectopically induced dPOU28/pdm-2 protein in the progeny of GMC-1 is sufficient to cause both of these cells to adopt their parental GMC-1 cell fate, leading to duplication of the RP2 neuron (and its sister cell) on the basis of both immunological and morphological criteria. These observations clearly implicate a role for dPOU28/pdm-2 in the specification of GMC-1 cell identity in the NB4-2 lineage and possibly in the specification of cell fate in other NB lineages in the developing embryonic CNS.

[Study on determination of gentamycin by enhanced chemiluminescent immunoassay]

Gentamycin was determined by solid antigen competition inhibition method of chemiluminescet immunoassay, in which luminol-(p-hydroxydiphenyl)-H2O2 was used a the chemiluminescence system and p-hydroxydiphenyl as the chemiluminescent enhancer. Solid antigen was synthesized by a method in which gentamycin was immobilized covalently on microcrystalline cellulose previously activated by 1,1'-carbonyldiimidazole. The rabbit anti-gentamycin IgG and the HRP-donkey anti-rabbit IgG were used as the first antibody and labelled second antibody, respectively. The linear range of the gentamycin (with blank serum) was 0.03-1 micrograms/tube and the correlation coefficient of the log-log regression equation [r[ was 0.981 +/- 0.016 with a limit of detection 3.3-11.4 ng/tube and the recovery of gentamycin 88.2 +/- 4.5%.

[A comparative study of "angioblastic meningioma", hemangiopericytoma and cerebellar hemangioblastoma]

Forty-nine cases of the so-called "angioblastic meningioma", six cases of cerebellar hemangioblastoma, and four cases of soft tissue hemangiopericytoma were studied with HE, reticulin stainings, and immunohistochemical reaction with Vimentin, EMA, GFAP, S-100, and UEA-1 antibodies. The results showed that among the three subtypes of "angioblastic meningioma", namely, the hemangiomatous (H), the hemangioblastic (AB), and the hemangiopericytic (P) types, (1) type H belongs to true meningioma; (2) most of type P are almost identical with soft tissue hemangiopericytoma and different from true meningiomas, therefore belong to hemangiopericytoma arising from pericytes; however (3) some true meningiomas may appear as hemangiopericytoma histologically; (4) a few of AB are very similar to cerebellar hemangioblastoma and thus should be considered as supratentorial hemangioblastoma, while most of AB are still true meningiomas.

Plasmid diversity in senescent and nonsenescent strains of Neurospora

A sample of 171 natural isolates of Neurospora crassa and Neurospora intermedia was tested for senescence. Of these, 28 strains senesced within the duration of the experiment. These senescent strains, together with a selection of nonsenescent strains, were examined for the presence of mitochondrial plasmids. This was done by digesting mitochondrial DNA preparations with proteinase K, and running these samples on agarose gels. Most of the strains examined, both senescent and nonsenescent, contained plasmids, many of them new. Some new plasmids were linear, as inferred from their resistance to 5' exonuclease and sensitivity to 3' exonuclease. New circular plasmids were also found. Some strains carry several plasmids, and mixtures of circular and linear elements were common. A cross-homology study was performed on a sample of plasmid-bearing strains, and several cases of apparent relatedness were found, some between strains from distant geographical locations. Linear plasmids homologous to the maranhar linear senescence plasmid were quite common. A new member of the LaBelle circular plasmid homology group was found. In the sample tested for homology, no strains contained elements related to the kalilo linear senescence plasmid. The relationship of the new plasmids to senescence is not known. In addition to plasmid monomers, several different types of derivatives were found. The kalilo linear plasmid was found to occur in linear and circular forms of low mobility, presumed to be giant concatamers, and, in some strains, variant sibling structures and ladders of short derivatives were found. Circular plasmids also gave rise to extensive ladders on electrophoresis, probably representing different relaxation states and head-to-tail concatameric series. Some such forms migrated more slowly than mitochondrial DNA. One unique type of plasmid modification observed was a pair of linear elements that had apparently arisen de novo which showed homology to a circular plasmid.

Repertoire diversity of antibody response to bacterial antigens in aged mice. III. Phosphorylcholine antibody from young and aged mice differ in structure and protective activity against infection with Streptococcus pneumoniae

Aging in mice is accompanied by qualitative changes in the antibody repertoire to phosphorylcholine (PC), a natural epitope of certain pneumococci. The PC-specific mAb from young/adult (2-4 mo) BALB/c mice are uniformly encoded by the canonical IgV genes of T15 family, whereas the antibody from aged mice (> or = 20 mo) are molecularly heterogeneous, being encoded by various VH and VL genes of non-T15 families. Interestingly the young/adult and aged BALB/c mice produce comparable amounts of antibodies to PC regardless of the molecular shift in the antibody repertoire. This finding prompted our study on the relative ability of PC antibodies from young and aged donors to protect mice against virulent infection with type 3 pneumococci. Passive administration (i.p.) of pooled, PC-specific mAb generated from young donors (all from the T15 Ig gene family) protected the recipients against subsequent i.p. challenge with a lethal dose of Streptococcus pneumoniae strain WU2, in a dose-dependent manner. In contrast, a mixture of PC mAb from aged donors (all from non-T15 families) failed to protect the mice against the infection, even at the highest amount of administered (100 micrograms of mAb/recipient). Average affinity of the aged mAb for the free hapten (PC-chloride) as well as their binding to the bacteria was lower than that of the young mAb. Similarly, affinity-purified serum PC antibody from S. pneumoniae vaccine-immunized young mice afforded a measurable degree of passive protection against the pneumococcal infection whereas a similar dose of serum PC antibody from aged mice did not. Further experiments showed that PC mAb from young donors were equally protective in either young or aged recipients challenged with the bacteria. These results demonstrate that the aged immune system may, in some instances, produce high levels of antibody that are structurally different and less protective against microbial infection.

Repertoire diversity of antibody response to bacterial antigens in aged mice. III. Phosphorylcholine antibody from young and aged mice differ in structure and protective activity against infection with Streptococcus pneumoniae

Aging in mice is accompanied by qualitative changes in the antibody repertoire to phosphorylcholine (PC), a natural epitope of certain pneumococci. The PC-specific mAb from young/adult (2-4 mo) BALB/c mice are uniformly encoded by the canonical IgV genes of T15 family, whereas the antibody from aged mice (> or = 20 mo) are molecularly heterogeneous, being encoded by various VH and VL genes of non-T15 families. Interestingly the young/adult and aged BALB/c mice produce comparable amounts of antibodies to PC regardless of the molecular shift in the antibody repertoire. This finding prompted our study on the relative ability of PC antibodies from young and aged donors to protect mice against virulent infection with type 3 pneumococci. Passive administration (i.p.) of pooled, PC-specific mAb generated from young donors (all from the T15 Ig gene family) protected the recipients against subsequent i.p. challenge with a lethal dose of Streptococcus pneumoniae strain WU2, in a dose-dependent manner. In contrast, a mixture of PC mAb from aged donors (all from non-T15 families) failed to protect the mice against the infection, even at the highest amount of administered (100 micrograms of mAb/recipient). Average affinity of the aged mAb for the free hapten (PC-chloride) as well as their binding to the bacteria was lower than that of the young mAb. Similarly, affinity-purified serum PC antibody from S. pneumoniae vaccine-immunized young mice afforded a measurable degree of passive protection against the pneumococcal infection whereas a similar dose of serum PC antibody from aged mice did not. Further experiments showed that PC mAb from young donors were equally protective in either young or aged recipients challenged with the bacteria. These results demonstrate that the aged immune system may, in some instances, produce high levels of antibody that are structurally different and less protective against microbial infection.

Concomitant defect in internal release and influx of calcium in patients with congenital platelet dysfunction and impaired agonist-induced calcium mobilization. Thromboxane production is not required for internal release of calcium

The rise in cytoplasmic ionized calcium concentration ([Ca2+]i) on platelet activation is a combination of Ca2+ release from internal stores and influx of extracellular Ca2+. To understand the underlying mechanisms, we studied internal release and influx of Ca2+ in platelets from four patients with impaired agonist-induced Ca2+ mobilization and abnormal platelet aggregation and secretion responses. In normal platelets, thrombin caused a dose-dependent increase in internal release and influx; aspirin inhibited the total rise in [Ca2+]i and influx but not internal release, indicating that internal release occurs independent of cyclooxygenase products. In the four patients, both internal release and influx of Ca2+ induced by thrombin and adenosine diphosphate were diminished; the defect was more striking at lower agonist concentrations. To determine whether the Ca2+ storage organelles of these platelets had a diminished responsiveness to inositol 1,4,5-triphosphate (IP3) we studied IP3 (0.05 to 5 mumol/L) induced Ca2+ release and found it to be normal in all patients. We conclude that the impaired Ca2+ mobilization in our patients is due to abnormalities in both internal release and influx and that it is unlikely to be due to impaired platelet responsiveness to IP3 or defective thromboxane production. The impaired Ca2+ mobilization may be due to defects in phospholipase C activation and IP3 production. These patients provide direct evidence that internal release and influx of Ca2+ on platelet activation are closely interrelated.

Allergen-specific modulation of cytokine synthesis patterns and IgE responses in vivo with chemically modified allergen

Hypersensitivity and IgE synthesis are highly dependent on the balance in which production of IL-4 and IFN-gamma is induced. An immunologic approach that alters the dominant pattern of cytokine synthesis and antibody production that is elicited after exposure to native allergen is described. High M(r), glutaraldehyde-polymerized OVA administered (i.p.) before or after immunization with unmodified OVA induces > or = 95% inhibition of specific IgE synthesis concomitant with 300- to 800-fold increases in IgG2a production in C57BL/6 mice. These changes result from a genetically controlled shift in the pattern of cytokine production within the allergen-specific T cell repertoire as demonstrated by i) susceptibility of the changes induced upon administration of modified allergen to in vivo treatment with anti-IFN-gamma mAb and ii) a 5- to 7-fold increase in the ratio of IFN-gamma:IL-4 synthesis after overnight culture directly ex vivo. This system should prove useful in identification of the factors which are influential in the commitment of T cells to Th1- or Th2-like patterns of cytokine synthesis. Moreover, as defective induction of IFN-gamma by allergen-specific T cells appears to play a role in elevated IgE synthesis and human allergy, this approach may have therapeutic potential.

Allergen-dependent induction of interleukin-4 synthesis in vivo

The ability of freshly derived T cells to produce interleukin-4 (IL-4) remains controversial. Many groups report that freshly derived antigen-, allogen- or mitogen-activated CD4 T cells produce almost exclusively IL-2, acquiring the capacity to produce a spectrum of cytokines following culture, rest and restimulation. In contrast, it is demonstrated here that in vivo exposure to protein allergens induces rapid, co-ordinate activation of IL-4 and interferon-gamma (IFN-gamma) gene expression. Overnight culture of spleen cells obtained from mice immunized with ovalbumin (OVA) or ragweed extract (RAG) in alum adjuvant elicits strong IL-2 and IL-4 responses within 14 hr of culture. T cells from mice immunized with allergen in complete Freund's adjuvant (CFA) generate strong IL-2 and IFN-gamma production, but virtually no IL-4, while unimmunized mice do not respond detectably to allergen in vitro (< 1 U). Unlike the differential pattern of cytokine synthesis observed following antigen-specific in vitro restimulation, cultures derived from naive and allergen-primed animals yield virtually equivalent IL-4, IL-2 and IFN-gamma synthesis upon polyclonal restimulation with anti-CD3 mAb 145-2C11 or concanavalin A (Con A), a finding which underlines the importance of the experimental conditions selected for in vitro analysis of in vivo cytokine gene expression. Collectively, the results indicate that the mode of immunization is critical to the pattern of cytokine response elicited and consequently to the type of antibody response which develops.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine oocyte development following different oocyte maturation and sperm capacitation procedures

Various procedures have been reported for successful in vitro maturation and in vitro fertilization (IVM/IVF) of bovine follicular oocytes. Direct comparisons of these different recommended procedures have been rare. In this research, involving a total of 5,128 oocytes, a series of experiments were conducted to compare oocyte maturation, fertilization, and development in vitro with 2 maturation systems (with or without added hormones) and 3 types of sperm treatment procedures. Oocytes were collected from ovarian antral follicles (2-7 mm in diameter) within 3 hr after slaughter of cows or heifers. Those with intact or at least 4 layers of cumulus cells were selected for IVM/IVF. Oocytes were incubated for 22 hr in either Medium 199 with 7.5% fetal calf serum (M199 + FCS) alone or M199 + FCS with added hormones (M199 + FCS + H; oFSH 0.5 micrograms/ml, oLH 5.0 micrograms/ml, and E2 1.0 micrograms/ml) at 39 degrees C in 5% CO2 and 95% air. For IVF, frozen-thawed sperm were treated with either 0.1 microM calcium ionophore A23187 (A23187) for 1 min, or 10 or 100 micrograms/ml heparin (H10 or H100) for 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Allergen-specific modulation of cytokine synthesis patterns and IgE responses in vivo with chemically modified allergen

Hypersensitivity and IgE synthesis are highly dependent on the balance in which production of IL-4 and IFN-gamma is induced. An immunologic approach that alters the dominant pattern of cytokine synthesis and antibody production that is elicited after exposure to native allergen is described. High M(r), glutaraldehyde-polymerized OVA administered (i.p.) before or after immunization with unmodified OVA induces &gt; or = 95% inhibition of specific IgE synthesis concomitant with 300- to 800-fold increases in IgG2a production in C57BL/6 mice. These changes result from a genetically controlled shift in the pattern of cytokine production within the allergen-specific T cell repertoire as demonstrated by i) susceptibility of the changes induced upon administration of modified allergen to in vivo treatment with anti-IFN-gamma mAb and ii) a 5- to 7-fold increase in the ratio of IFN-gamma:IL-4 synthesis after overnight culture directly ex vivo. This system should prove useful in identification of the factors which are influential in the commitment of T cells to Th1- or Th2-like patterns of cytokine synthesis. Moreover, as defective induction of IFN-gamma by allergen-specific T cells appears to play a role in elevated IgE synthesis and human allergy, this approach may have therapeutic potential.

Uptake of antisense oligonucleotides and functional block of acetylcholine receptor subunit gene expression in primary embryonic neurons

Several recent studies have used antisense oligonucleotides in the nervous system to probe the functional role of particular gene products. Since antisense oligonucleotide-mediated block of gene expression typically involves uptake of the oligonucleotides, we have characterized the mechanism of this uptake into developing neurons from embryonic chickens. Antisense oligonucleotides (15 mers) added to the bathing media are taken up into the embryonic chicken sympathetic neurons maintained in vitro. A portion of the oligonucleotide uptake is temperature dependent and saturates at extracellular oligonucleotide concentrations > or = 20 microM. This temperature sensitive, saturable component is effectively completed by single nucleotides of ATP and AMP and is reminiscent of receptor-mediated endocytosis of oligonucleotides described in non-neuronal cells. The efficiency of the oligonucleotide uptake system is dependent on the developmental stage of the animal but independent of the number of days that the neurons are maintained in vitro. Following the uptake of antisense oligonucleotides directed against ion channel subunit genes expressed by these neurons (nicotinic acetylcholine receptor subunit alpha 3; nAChR alpha 3), biophysical assays reveal that the functional expression of the target gene is largely blocked. Thus the number of wild type nAChR channels expressed is decreased by approximately 80%-90%. Furthermore, following antisense deletion of alpha 3, "mutant" nAChRs with distinct functional characteristics are expressed. In sum, these studies characterize the uptake of antisense oligonucleotide and demonstrate the functional block of specific gene expression in primary developing neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Warm versus cold blood cardioplegia--is there a difference?

This experimental study sought to compare the effectiveness of warm blood cardioplegia versus cold blood cardioplegia in protecting areas of ischemic myocardium during urgent coronary revascularization. In 40 adult pigs, the second and third diagonal vessels were occluded with snares for 90 minutes. All animals were then placed on cardiopulmonary bypass and underwent 45 minutes of cardioplegic arrest followed by 3 hours of reperfusion during which time the coronary snares were released. During the period of cardioplegic arrest, 10 pigs received antegrade continuous warm blood cardioplegic solution (37 degrees C) at 100 ml/min; 10 animals received retrograde warm blood cardioplegic solution at 100 ml/min; 10 received intermittent, antegrade cold blood cardioplegic solution (4 degrees C), and 10 animals received intermittent, antegrade/retrograde cold blood cardioplegic solution. Hearts protected with antegrade warm blood cardioplegic solution had the lowest pH values in the area at risk (6.59 +/- 0.10 antegrade warm blood cardioplegia versus 6.80 +/- 0.10 retrograde warm blood cardioplegia versus 6.72 +/- 0.18 antegrade cold blood cardioplegia versus 6.85 +/- 0.15 antegrade/retrograde cold blood cardioplegia and the highest area of necrosis (42% +/- 3% antegrade warm blood cardioplegia versus 26% +/- 2% [p < 0.05 from antegrade warm blood cardioplegia] retrograde warm blood cardioplegia versus 31% +/- 2% [p < 0.05 from antegrade warm blood cardioplegia] antegrade cold blood cardioplegia versus 21% +/- 2% [p < 0.05 from antegrade warm blood cardioplegia] antegrade/retrograde cold blood cardioplegia). We conclude that in the presence of an acute coronary occlusion with ischemic myocardium, warm blood cardioplegic solution should be given in a continuous retrograde fashion and does not result in myocardial protection superior to the protection that can be achieved with antegrade/retrograde cold blood cardioplegic solution.

Mechanism of the hypertensive response to central injection of nicotine in conscious rats

The purpose of this study was to examine the effects of nicotine administered directly into the CNS on mean arterial pressure (MAP) and heart rate to avoid the direct peripheral action of the drug. Also, because nicotine has been reported to enhance the release of endogenous brain acetylcholine, we sought to determine the role of this mechanism in mediating the cardiovascular response. Normotensive Wistar rats were previously implanted with indwelling intracerebroventricular (ICV) cannula guides and an arterial line (iliac artery) for central injection of drugs and measurement of MAP and heart rate, respectively. Rats received a series of increasing doses of nicotine (or saline vehicle) from 2-100 micrograms (in a 10 microliter volume) with each dose separated by at least 1 day. MAP increased immediately following all doses of nicotine; however, the maximal response was obtained following the 50 micrograms dose (higher doses actually produced lower responses). In general, the hypertensive response began immediately after injection, peaked within 2-3 min and returned to baseline within about 20 min. Heart rate changes were often not dramatic and highly variable. In order to examine the dependence of the pressor response to nicotine on brain acetylcholine, rats were pretreated with 20 micrograms (ICV) of hemicholinium-3 (HC-3) 1 h prior to nicotine to deplete endogenous acetylcholine. HC-3 pretreatment resulted in a significant reduction in the magnitude and duration of the pressor response to nicotine. Likewise, pretreatment with atropine inhibited the pressor response to subsequent injection of nicotine. Nicotine enhanced the release of [3H]acetylcholine from brain slices in vitro at concentrations likely achieved in the in vivo studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Steerable optical waveguides formed in self-defocusing media by using dark spatial solitons

We demonstrate that steerable, two-dimensional, single-mode optical waveguides can be formed in defocusing media by exciting dark spatial solitons.

The effect of multi-glycosides of Tripterygium wilfordii Hook f. (GTW) on the survival time of cardiac allografts in rats

Heterotopic heart transplantation was carried out in rats and the influence of multi-glycosides of Tripterygium wilfordii Hook f. (GTW) and a subtherapeutic dose of cyclosporine A (CsA) on the mean survival time (MST) of the cardiac allografts was investigated. The results showed that the MSTs of cardiac allografts in both the GTW and CsA-treated groups were significantly prolonged (P < 0.01 vs control). The rate of allograft rejection in the drug-treated groups was much lower than that in the control group.

A comparison between in vitro fertilization and microinjection of immobilized spermatozoa from bulls producing spermatozoa with defects

The objectives of this study were to compare the fertilization rate of bovine in vitro matured oocytes by in vitro fertilization (IVF) and by microinjection of a single spermatozoon (MI) and to relate these rates with fertility reported for these bulls in artificial breeding. Bull A (Holstein) had a nonreturn rate of 75%. Semen from this bull is routinely used in our standard IVF procedure. Bull B (Ayrshire), used regularly in artificial breeding and related to bull D, had a nonreturn rate of 69.2%. Bull C (Brown Swiss), with a chromosomal translocation and trisomy, achieved a nonreturn rate of 42%. Bull D (Ayrshire) produced nonmotile spermatozoa (SPZ) and had an abnormality described as "tail stump defect." No pregnancies sired by bull D have been reported. Oocytes were either fertilized in vitro by capacitated SPZ or by microinjection of a single immobilized SPZ into the ooplasm. SPZ were treated with 0.1 microM A23187 and used for IVF. For microinjection SPZ were cocultured for 5 h with bovine oviduct epithelial cells (BOEC) and then immobilized by freezing and thawing twice without cryoprotectant. A single batch of killed SPZ (stored at -25 degrees C) was used for all microinjections. All oocytes were cultured in Medium 199 for 22 h at 39 degrees C and subsequently fixed, stained, and examined for evidence of fertilization (i.e., female and male pronucleus formation, SPZ decondensation). Fertilization rates following IVF with semen from bulls A, B, C, and D were 80%, 54%, 1%, and 2%, and following microinjection were 39%, 22%, 21%, and 34%, respectively.

[Experimental study on monitor of microcirculation of random skin flaps and early division of their pedicles]

In a series of 30 random skin flaps formed in pigs, the skin capillary blood flow was measured with laser doppler flowmetry (LDF) pre-, and postoperatively and within 48 hours after pedicle division. The results showed that the change in the microcirculation can be divided into three phases: (1) rapid rising, (2) plateau, and (3) slow rising. The plateau stage may be considered as the critical period. Division of the flap before this "critical" period causes flap necrosis, while division after the period resulted in flap survival (100 percent). Comparison of preoperative and postoperative LDF values can be regarded as a reliable objective criterion for division of the pedicle.