Neurological phenotype and synaptic function in mice lacking the CaV1.3 alpha subunit of neuronal L-type voltage-dependent Ca2+ channels

Neuronal L-type calcium channels have been implicated in pain perception and neuronal synaptic plasticity. To investigate this we have examined the effect of disrupting the gene encoding the CaV1.3 (alpha 1D) alpha subunit of L-type Ca2+ channels on neurological function, acute nociceptive behavior, and hippocampal synaptic function in mice. CaV1.3 alpha 1 subunit knockout (CaV1.3 alpha 1(-/-)) mice had relatively normal neurological function with the exception of reduced auditory evoked behavioral responses and lower body weight. Baseline thermal and mechanical thresholds were unaltered in these animals. CaV1.3 alpha 1(-/-) mice were also examined for differences in N-methyl-D-aspartate (NMDA) receptor-dependent (100 Hz tetanization for 1 s) and NMDA receptor-independent (200 Hz in 100 microM DL-2-amino-5-phosphopentanoic acid) long-term potentiation within the CA1 region of the hippocampus. Both NMDA receptor-dependent and NMDA receptor-independent forms of long-term potentiation were expressed normally. Radioligand binding studies revealed that the density of (+)[3H]isradipine binding sites in brain homogenates was reduced by 20-25% in CaV1.3 alpha 1(-/-) mice, without any detectable change in CaV1.2 (alpha 1C) protein levels as detected using Western blot analysis. Taken together these data indicate that following loss of CaV1.3 alpha 1 subunit expression there is sufficient residual activity of other Ca2+ channel subtypes to support NMDA receptor-independent long-term potentiation and some forms of sensory behavior/function.

Hippocampal synaptic plasticity in mice carrying the rd mutation in the gene encoding cGMP phosphodiesterase type 6 (PDE6)

Cyclic GMP (cGMP) has been implicated in the modulation of long-term potentiation (LTP) and depression (LTD) in the hippocampus. Transcripts for subunits of several types of cGMP specific phosphodiesterase are found in the mammalian brain but their relative role in hippocampal function is unclear. The retinal degeneration (rd) mutation in the gene encoding the PDE6B subunit causes a loss of function in PDE6 enzyme and in adult mice homozygous to the mutation it causes blindness. We have used this natural mutation, and the cGMP phosphodiesterase inhibitor zaprinast, in wild-type and rd/rd mouse littermates to investigate whether PDE5 and/or PDE6 regulates excitatory synaptic transmission in the hippocampus. Mice were genotyped using two independent PCR methods. Glutamate-mediated synaptic transmission in the CA1 region or dentate gyrus was unaffected in hippocampal brain slices from mice carrying the rd mutation. Similarly the facilitation of synaptic events by paired-pulse stimuli, and LTP induced by a theta-burst (10 bursts of four events at 100 Hz with a 200-ms inter-burst interval) were normal in rd/rd mice. Inhibition of cGMP-specific PDE activity by zaprinast (10 microM, an inhibitor of PDE5 and PDE6) induced a slowly developing and sustained depression of field synaptic potentials that was quantitatively similar in both wild-type and rd/rd mice. Thus in the CA1 region synaptic plasticity is likely to be regulated by the PDE5 rather than the PDE6 isoform.

The familial hemiplegic migraine mutation R192Q reduces G-protein-mediated inhibition of P/Q-type (Ca(V)2.1) calcium channels expressed in human embryonic kidney cells

Familial hemiplegic migraine is associated with at least 13 different missense mutations in the alpha1A Ca(2+) channel subunit. Some of these mutations have been shown to affect the biophysical properties of alpha1A currents. To date, no study has examined the influence of such mutations on the G-protein regulation of channel function. Because G-proteins inhibit movement of the voltage sensor, we examined the effects of the R192Q mutation, which neutralizes a positive charge in the first S4 segment. Human wild-type (WT) or R192Q mutant channels were expressed in human embryonic kidney tsA-201 cells along with dopamine D2 receptors. Application of quinpirole induced fast (approximately 1 s), pertussis toxin-sensitive inhibition of alpha1A(WT) and alpha1A(R192Q) Ca(2+) currents, consistent with the activation of a membrane-delimited pathway. alpha1A(WT) Ca(2+) currents were inhibited by 62.9 +/- 0.9 % (n = 27), whereas alpha1A(R192Q) Ca(2+) currents were inhibited by only 47.9 +/- 1.8 % (n = 35; P < 0.001). Concentration-response analysis showed that only the extent of inhibition was affected, with no change in agonist potency (EC(50) = 1 nM). Prepulse facilitation, which is a characteristic of voltage-dependent inhibition, was also reduced by the R192Q mutation. However, the kinetics of facilitation and slow activation were not affected, suggesting that G-protein-Ca(2+) channel affinity was unchanged. These results show that the R192Q mutation reduces the G-protein inhibition of P/Q-type Ca(2+) channels, probably by altering mechanisms by which Gbetagamma subunit binding induces a change in channel gating. Altered G-protein modulation and the consequent reduced presynaptic inhibition may contribute to migraine attacks by favouring a persistent state of hyperexcitability.

Functional properties of the high-affinity TRPV1 (VR1) vanilloid receptor antagonist (4-hydroxy-5-iodo-3-methoxyphenylacetate ester) iodo-resiniferatoxin

We have synthesized iodinated resiniferatoxin bearing a 4-hydroxy-5-iodo-3-methoxyphenylacetate ester (I-RTX) and have characterized its activity on rat and human TRPV1 (VR1) receptors, as well as in behavioral assays of nociception. In whole cell patch-clamp recordings from transfected cells the functional activity of I-RTX was determined. Currents activated by capsaicin exhibited characteristic outward rectification and were antagonized by capsazepine and I-RTX. On rat TRPV1 the affinity of I-RTX was 800-fold higher than that of capsazepine (IC50 = 0.7 and 562 nM, respectively) and 10-fold higher on rat versus human receptors (IC50 = 0.7 and 5.4 nM, respectively). The same difference was observed when comparing the inhibition of [3H]RTX binding to rat and human TRPV1 membranes for both RTX and I-RTX. Additional pharmacological differences were revealed using protons as the stimulus. Under these conditions capsazepine only partly blocked currents through rat TRPV1 receptors (by 70 to 80% block), yet was a full antagonist on human receptors. In contrast, I-RTX completely blocked proton-induced currents in both species and that activated by noxious heat. I-RTX also blocked capsaicin-induced firing of C-fibers in a rat in vitro skin-nerve assay. Despite this activity and the high affinity of I-RTX for rat TRPV1, only capsazepine proved to be an effective antagonist of capsaicin-induced paw flinching in rats. Thus, although I-RTX has limited utility for in vivo behavioral studies it is a high-affinity TRPV1 receptor antagonist that will be useful to characterize the functional properties of cloned and native vanilloid receptor subtypes in vitro.

Estrogen receptor ligands affect mitochondrial activity in SH-SY5Y human neuroblastoma cells

We have studied the pharmacological regulation of mitochondrial activity in a human neuroblastoma cell line. Cyclosporin A was found to directly alter mitochondrial membrane potential and to decrease mitochondrial permeability as measured using calcein. The estrogen receptor ligands tamoxifen, nafoxidine and clomiphene were identified as agents which affect mitochondrial membrane potential in a cyclosporin A-like manner. Also when mitochondrial permeability was measured using calcein, tamoxifen, nafoxidine and clomiphene were effective in inhibiting dye loss from mitochondria. Nafoxidine and cyclosporin A inhibit effects of mastoparan on SH-SY5Y mitochondria. These studies indicate that estrogen receptor ligands appear to affect mitochondria in a cyclosporin A-like manner in human neuroblastoma cells.

Chronic substance P (NK1) receptor antagonist and conventional antidepressant treatment increases burst firing of monoamine neurones in the locus coeruleus

The mechanism of action of conventional antidepressants (e.g. imipramine) has been linked to modulation of central monoamine systems. Substance P (NK1) receptor antagonists may have antidepressant and anxiolytic effects in patients with major depressive disorder and high anxiety but, unlike conventional antidepressants, are independent of activity at monoamine reuptake sites, transporters, receptors, or monoamine oxidase. To investigate the possibility that substance P receptor antagonists influence central monoamine systems indirectly, we have compared the effects of chronic administration of imipramine with that of the substance P receptor antagonist L-760735 on the spontaneous firing activity of locus coeruleus neurones. Electrophysiological recordings were made from brain slices prepared from guinea-pigs that had been dosed orally every day for 4 weeks with either L-760735 (3 mg/kg), imipramine (10 mg/kg), or vehicle (water), or naive animals. Chronic, but not acute, treatment with the substance P receptor antagonist L-760735, induced burst firing of neurones in the locus coeruleus. This effect resembles that of the conventional antidepressant imipramine. However, their effects are dissociable since, in contrast to chronic imipramine treatment, chronic L-760735 treatment does not cause functional desensitisation of somatic alpha2 adrenoceptors. The mechanism by which chronic substance P receptor antagonist or conventional antidepressant treatment influences the pattern of firing activity of norepinephrine neurones remains to be elucidated. However, an indirect action in the periphery or distant brain nuclei has been excluded by the use of the in vitro slice preparation, suggesting a local site of action in the locus coeruleus.

6,7-Dihydro-2-benzothiophen-4(5H)-ones: a novel class of GABA-A alpha5 receptor inverse agonists

Nonselective inverse agonists at the benzodiazepine binding site on the GABA-A chloride ion channel enhance cognitive performance in animals but cannot be used in the treatment of cognitive disorders because of anxiogenic and convulsant side effects. We have identified a novel series of GABA-A alpha5 receptor ligands during our search for alpha5 receptor inverse agonists as potential cognition enhancers. In particular, 6,6-dimethyl-3-(2-hydroxyethyl)thio-1-(thiazol-2-yl)-6,7-dihydro-2-benzothiophen-4(5H)-one (26) has been identified as a functionally selective GABA-A alpha5 inverse agonist.

Impairment in hippocampal long-term potentiation in mice under-expressing the Alzheimer's disease related gene presenilin-1

Presenilin-1 (PS1) is intimately involved in cleavage of amyloid precursor protein to form beta-amyloid peptides, certain forms of which aggregate in the brains of patients with Alzheimer's disease (AD). The function(s) of PS1 and its precise involvement in the development of cognitive deficits associated with AD are unclear. We have utilised genetically modified mice that under-express PS1 (PS1(+/-) mice) to investigate the role of PS1 in hippocampal synaptic plasticity. Field excitatory postsynaptic responses elicited by baseline stimulation were indistinguishable between PS1(+/-) mice and wild-type controls. Likewise, a measure of short-term plasticity, paired-pulse facilitation, was normal in PS1(+/-) mice. However, long-term potentiation induced by multiple tetanus trains was reduced in PS1(+/-) animals. These results demonstrate that chronic reduction of PS1 activity leads to impaired synaptic plasticity, thus suggesting a role for PS1 in normal cognitive function.

Role of the histidine residue at position 105 in the human alpha 5 containing GABA(A) receptor on the affinity and efficacy of benzodiazepine site ligands

1. A histidine residue in the N-terminal extracellular region of alpha 1,2,3,5 subunits of the human GABA(A) receptor, which is replaced by an arginine in alpha 4 and alpha 6 subunits, is a major determinant for high affinity binding of classical benzodiazepine (BZ)-site ligands. The effect of mutating this histidine at position 105 in the alpha 5 subunit to an arginine (alpha 5H105R) on BZ-site pharmacology has been investigated using radioligand binding on HEK293 and L(tk-) cells and two electrode voltage clamp recording on Xenopus oocytes in which GABA(A) receptors of subtypes alpha 5, alpha 5H105R, alpha 4 and alpha 6 were co-expressed with beta 3 gamma 2s. 2. The classical BZs, diazepam and flunitrazepam (full agonists on the alpha 5 receptor) showed negligible affinity and therefore negligible efficacy on alpha 5H105R receptors. The beta-carbolines DMCM and beta CCE (inverse agonists on the alpha 5 receptor) retained some affinity but did not exhibit inverse agonist efficacy at alpha 5H105R receptors. Therefore, the alpha 5H105R mutation confers an alpha 4/alpha 6-like pharmacology to the classical BZs and beta-carbolines. 3. Ro15-4513, flumazenil, bretazenil and FG8094, which share a common imidazobenzodiazepine core structure, retained high affinity and were higher efficacy agonists on alpha 5H105R receptors than would be predicted from an alpha 4/alpha 6 pharmacological profile. This effect was antagonized by DMCM, which competes for the BZ-site and therefore is likely to be mediated via the BZ-site. 4. These data indicate that the conserved histidine residue in the alpha subunit is not only a key determinant in the affinity of BZ-site ligands on alpha 5 containing GABA(A) receptors, but also influences ligand efficacy.

PECAM-1/IgG attenuates peroxynitrite-mediated extremity reperfusion injury

OBJECTIVE

Neutrophil transendothelial migration, a key feature of skeletal muscle ischemia and reperfusion (I/R) injury, is mediated by the platelet endothelial cell adhesion molecule-1 (PECAM-1). Peroxynitrite anion, a toxic product of neutrophil superoxide anion and nitric oxide, contributes to oxidative skeletal muscle injury and can be quantified by measurement of protein tyrosine nitration after I/R. This study hypothesizes that administration of the PECAM-1/IgG antibody chimera will inhibit peroxynitrite-mediated injury after I/R.

METHODS

The study was composed of five groups: an I/R group (n = 4), a sham treatment group anesthetic control (n = 3), a treatment group receiving the PECAM-1/immunoglobulin G (IgG) antibody chimera with I/R (n = 9), a treatment group receiving human IgG with I/R as an antibody control (n = 6), and a treatment group receiving normal saline solution with I/R as a vehicle control (n = 5). The right hind limb in male New Zealand white rabbits was rendered ischemic by occluding the iliac and femoral arteries for 3 hours, followed by 2 hours of reperfusion (I/R). Sham-treated rabbits underwent arterial dissection without arterial occlusion. PECAM-1/IgG-treated rabbits and IgG-treated rabbits received an infusion of 1 mg/kg in normal saline solution 20 mL via an ear vein catheter during the last 5 minutes of ischemia and the first 15 minutes of reperfusion. Saline solution-treated rabbits similarly received normal saline solution 20 mL. The anterior tibialis muscle was harvested after reperfusion. Immunohistochemical staining for nitrotyrosine was performed with monoclonal antinitrotyrosine antibodies and fluorescently labeled secondary antibodies. Computed morphometric study was performed to calculate relative fluorescence scores for each histologic section. Averaged fluorescence scores were analyzed by one-way analysis of variance with Bonferroni post hoc comparison.

RESULTS

The averaged fluorescence scores (mean +/- SEM) for the sham-treated (2.88 +/- 0.78) and PECAM-1/IgG-treated (6.16 +/- 0.43) groups demonstrated a significant reduction in quantitative fluorescence compared with the IgG- (15.17 +/- 2.01) and saline solution-treated (17.46 +/- 3.71) control groups, and the I/R-treated (18.52 +/- 3.00) group, (P <.05).

CONCLUSIONS

These results suggest that PECAM-1/IgG diminishes peroxynitrite-mediated oxidative skeletal muscle injury by inhibiting neutrophil transendothelial migration and may therefore prove a useful therapeutic agent in the treatment of reperfusion injury.

Age-related impairment of synaptic transmission but normal long-term potentiation in transgenic mice that overexpress the human APP695SWE mutant form of amyloid precursor protein

We have studied synaptic function in a transgenic mouse strain relevant to Alzheimer's disease (AD), overexpressing the 695 amino acid isoform of human amyloid precursor protein with K670N and M671L mutations (APP(695)SWE mice), which is associated with early-onset familial AD. Aged-transgenic mice had substantially elevated levels of Abeta (up to 22 micromol/gm) and displayed characteristic Abeta plaques. Hippocampal slices from 12-month-old APP(695)SWE transgenic animals displayed reduced levels of synaptic transmission in the CA1 region when compared with wild-type littermate controls. Inclusion of the ionotropic glutamate receptor antagonist kynurenate during preparation of brain slices abolished this deficit. At 18 months of age, a selective deficit in basal synaptic transmission was observed in the CA1 region despite treatment with kynurenate. Paired-pulse facilitation and long-term potentiation (LTP) were normal in APP(695)SWE transgenic mice at both 12 and 18 months of age. Thus, although aged APP(695)SWE transgenic mice have greatly elevated levels of Abeta protein, increased numbers of plaques, and reduced basal synaptic transmission, LTP can still be induced and expressed normally. We conclude that increased susceptibility to excitotoxicity rather than a specific effect on LTP is the primary cause of cognitive deficits in APP(695)SWE mice.

Lessons learned in adopting endovascular techniques for treating abdominal aortic aneurysm

HYPOTHESIS

Endovascular exclusion of abdominal aortic and common iliac aneurysms can be performed safely, and in the short term represents a feasible alternative to traditional, open aneurysm repair.

PATIENTS AND METHODS

Forty-one patients were treated with endovascular grafts for 39 abdominal aortic and 2 common iliac artery aneurysms.

RESULTS

All devices were successfully deployed. The size of the abdominal aortic aneurysms varied from 4.9 to 11.9 cm (average, 6.13 cm). The median procedure time was 195 minutes. There was one iliac artery rupture, which required celiotomy for repair. The hospital stay varied from 2 to 39 days (average, 6.7 days). The perioperative mortality rate was 2.4%. Sixteen patients (39%) had groin wound complications. Ten patients (24%) had evidence of contrast (endoleak) within the aneurysm sac on completion of the procedure. There were no obvious direct leaks from either the point of proximal or distal fixation. Seven of these endoleaks have resolved spontaneously. Two patients required additional procedures in the postoperative period to treat endoleak. The final patient has evidence of persistent endoleak on 3-month surveillance computed tomography scan. Major late problems occurred in 3 patients.

CONCLUSION

Patients with large abdominal aortic aneurysms and considerable cardiac comorbidity can safely undergo endovascular aneurysm repair. Femoral groin wound complications resulting in prolonged hospitalization remain the major cause of perioperative morbidity. In contradistinction to open aneurysm repair, long-term surveillance is essential to detect migration of the device and identify flow within the residual aneurysm sac-complications that could lead to aneurysm rupture following endovascular repair.

Substance P stimulates inhibitory synaptic transmission in the guinea pig basolateral amygdala in vitro

To determine the physiological role of tachykinin NK1 receptors in the basolateral nucleus of the amygdala (BLN) we have studied the electrophysiological effects of substance P (SP) in the absence and presence of selective tachykinin receptor antagonists in guinea pig brain slices. Recordings were made from two populations of neurones; spiny pyramidal and stellate neurones, both thought to be projection neurones. Activation of NK1 receptors with SP increased the frequency of spontaneous inhibitory postsynaptic potentials in the majority of cells. This effect was blocked by bicuculline or tetrodotoxin, but not ionotropic glutamate receptor antagonists. The enhanced synaptic activity induced by SP was antagonised by the NK1 receptor antagonist L-760,735 but not by the less active enantiomer L-781,773 or the NK3 receptor antagonist L-769,927. Thus in the basolateral nucleus of the guinea pig amygdala, NK1 receptor activation preferentially stimulates inhibitory synaptic activity. Consistent with this observation, immunohistochemistry revealed NK1 receptor immunoreactivity to be largely restricted to a subset of GABA interneurones. These studies support a physiological role for SP in the regulation of pathways involved in the control of emotional behaviour.

Identification of amino acid residues responsible for the alpha5 subunit binding selectivity of L-655,708, a benzodiazepine binding site ligand at the GABA(A) receptor

L-655,708 is a ligand for the benzodiazepine site of the gamma-aminobutyric acid type A (GABA(A)) receptor that exhibits a 100-fold higher affinity for alpha5-containing receptors compared with alpha1-containing receptors. Molecular biology approaches have been used to determine which residues in the alpha5 subunit are responsible for this selectivity. Two amino acids have been identified, alpha5Thr208 and alpha5Ile215, each of which individually confer approximately 10-fold binding selectivity for the ligand and which together account for the 100-fold higher affinity of this ligand at alpha5-containing receptors. L-655,708 is a partial inverse agonist at the GABA(A) receptor which exhibited no functional selectivity between alpha1- and alpha5-containing receptors and showed no change in efficacy at receptors containing alpha1 subunits where amino acids at both of the sites had been altered to their alpha5 counterparts (alpha1Ser205-Thr,Val212-Ile). In addition to determining the binding selectivity of L-655,708, these amino acid residues also influence the binding affinities of a number of other benzodiazepine (BZ) site ligands. They are thus important elements of the BZ site of the GABA(A) receptor, and further delineate a region just N-terminal to the first transmembrane domain of the receptor alpha subunit that contributes to this binding site.

Regulation of vascular surgery by the federal government

Governmental regulation of medicine seeks to protect patients and employees providing health care and to insure fair reimbursement for services. This report outlines workplace regulation of bloodborne pathogens and ergonomics. The investigation of potential Medicare fraud and abuse is reviewed. Mechanisms that control physician payment policy, including the Relative Base Resource Value System, the Correct Coding Initiative, and Current Procedural Terminology, are described.

Biophysical properties, pharmacology, and modulation of human, neuronal L-type (alpha(1D), Ca(V)1.3) voltage-dependent calcium currents

Voltage-dependent calcium channels (VDCCs) are multimeric complexes composed of a pore-forming alpha(1) subunit together with several accessory subunits, including alpha(2)delta, beta, and, in some cases, gamma subunits. A family of VDCCs known as the L-type channels are formed specifically from alpha(1S) (skeletal muscle), alpha(1C) (in heart and brain), alpha(1D) (mainly in brain, heart, and endocrine tissue), and alpha(1F) (retina). Neuroendocrine L-type currents have a significant role in the control of neurosecretion and can be inhibited by GTP-binding (G-) proteins. However, the subunit composition of the VDCCs underlying these G-protein-regulated neuroendocrine L-type currents is unknown. To investigate the biophysical and pharmacological properties and role of G-protein modulation of alpha(1D) calcium channels, we have examined calcium channel currents formed by the human neuronal L-type alpha(1D) subunit, co-expressed with alpha(2)delta-1 and beta(3a), stably expressed in a human embryonic kidney (HEK) 293 cell line, using whole cell and perforated patch-clamp techniques. The alpha(1D)-expressing cell line exhibited L-type currents with typical characteristics. The currents were high-voltage activated (peak at +20 mV in 20 mM Ba2+) and showed little inactivation in external Ba2+, while displaying rapid inactivation kinetics in external Ca2+. The L-type currents were inhibited by the 1,4 dihydropyridine (DHP) antagonists nifedipine and nicardipine and were enhanced by the DHP agonist BayK S-(-)8644. However, alpha(1D) L-type currents were not modulated by activation of a number of G-protein pathways. Activation of endogenous somatostatin receptor subtype 2 (sst2) by somatostatin-14 or activation of transiently transfected rat D2 dopamine receptors (rD2(long)) by quinpirole had no effect. Direct activation of G-proteins by the nonhydrolyzable GTP analogue, guanosine 5'-0-(3-thiotriphospate) also had no effect on the alpha(1D) currents. In contrast, in the same system, N-type currents, formed from transiently transfected alpha(1B)/alpha(2)delta-1/beta(3), showed strong G-protein-mediated inhibition. Furthermore, the I-II loop from the alpha(1D) clone, expressed as a glutathione-S-transferase (GST) fusion protein, did not bind Gbetagamma, unlike the alpha(1B) I-II loop fusion protein. These data show that the biophysical and pharmacological properties of recombinant human alpha(1D) L-type currents are similar to alpha(1C) currents, and these currents are also resistant to modulation by G(i/o)-linked G-protein-coupled receptors.

Shear force regulates matrix metalloproteinase activity in human saphenous vein organ culture

BACKGROUND

Development of vein graft intimal hyperplasia has been related both to shear force and to the activity of matrix metalloproteinases (MMPs). Little data are available regarding the effects of shear on MMP expression and activity. The aim of this study was to examine the relationship among shear force, metalloproteinase activity, and intimal thickening in human saphenous vein segments maintained in organ culture.

MATERIALS AND METHODS

Segments of human saphenous vein were cultured under static conditions, or perfused under low-flow and high-flow conditions in a perfusion apparatus for 7 days. Metalloproteinase levels and activities were measured using ELISA and substrate gel zymography, respectively. Intimal thickening was determined by morphometric analysis. Results were compared with control vein tissue, which was not subjected to organ culture, using a one-way ANOVA.

RESULTS

A 13% increase in proteolytic activity was noted on substrate gel zymography at 68-72 kDa in high-flow vein tissue. The protein content of MMP-2, MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and TIMP-2 was increased in high-flow vein tissue by 21%, 126%, more than 100-fold, and 86%, respectively. In culture media bathing the outside of the vein, TIMP-2 was increased in high-flow specimens, while TIMP-1 was inversely related to flow rate. Intimal thickening was directly related to flow rates, and was progressively increased in the low-flow and high-flow groups by 3-fold and 4-fold, respectively.

CONCLUSIONS

Metalloproteinase levels in human saphenous vein cultures are related to shear force. MMP levels and activity correlate with the degree of intimal thickening. This model may provide a valuable tool for the analysis of physical forces and their influence on intimal thickening in human saphenous vein.

Determinates of functional disability after complex upper extremity trauma

This is a retrospective chart review of 71 patients who were operated on for presumed upper extremity arterial trauma between June 1992 and June 1998. Penetrating trauma occurred in 50 (70%) patients, and blunt trauma in 21 (30%). There were 2 innominate, 6 subclavian, 13 axillary, 26 brachial, 5 radial, 6 ulnar, and 6 multiple arterial injuries. There were 7 negative explorations (4 venous injuries, 2 false-positive angiograms, and 1 branch artery injury). In addition to the vascular injury, 44 patients (69%) had another injury in the extremity, including 8 (12.5%) orthopedic injuries, 12 (19%) nerve injuries, and 24 (37.5%) combination nerve and orthopedic injuries. There were three arterial thromboses, one arterial disruption, and four amputations, resulting in a patency rate and limb salvage rate of 94%. Persistent disability was more common in those patients with blunt injury (p = 0.02) and in those patients with associated neurologic and orthopedic injuries (p < 0.05). Full functional recovery was seen in 21 (33%) patients, while some form of disability was noted in the remaining 67%. The magnitude of the concomitant neurologic injury was the major determinate of functional outcome in this patient population.

All-trans-retinoic acid decreases cell proliferation and increases apoptosis in an animal model of vein bypass grafting

BACKGROUND

We have previously demonstrated a decrease in intimal hyperplasia in vein bypass grafts from animals treated with all-trans-retinoic acid (atRA). The purpose of this study was to examine the effect of atRA on proliferation and apoptosis rates in healing vein bypass grafts.

METHODS

Interposition jugular vein bypass grafts were placed in the carotid artery of 30 New Zealand white rabbits. Animals received either atRA (10 mg/kg/d) or vehicle (corn oil) for a period of 2 weeks. Animals were killed at 3, 7, or 28 days after graft placement after having received 3 doses of 5-bromo-2'-¿Deoxyuridine (BRDU, 35 Mg/KG). Animals Were Perfusion Fixed, And Vein Grafts Were Prepared For Immunohistochemistry By Using Antibodies To Brdu, Proliferating Cell Nuclear Antigen, And Bcl-XL. Apoptosis Was Measured By Using The Tunel Assay. Histologic Sections Were Analyzed By A Pathologist Blinded To The Study, And An Index Of Positively Stained Cells Was Generated For Each Layer Of The Vein Graft Wall.

RESULTS

All-trans-retinoic acid reduced the proliferation index in the neointima of vein grafts during the first week after surgery. Apoptotic rates were higher in the intima of vein grafts from animals treated with atRA, which could not be explained by changes in bcl-xl expression. No differences were noted in the media or adventitia between the groups.

CONCLUSIONS

atRA decreased cell proliferation and increased apoptosis in the intima of healing vein bypass grafts. These effects contribute to decreased intimal hyperplasia, which has been previously noted.

Reduced long-term potentiation in hippocampal slices prepared using sucrose-based artificial cerebrospinal fluid

Sucrose-based artificial cerebrospinal fluid (aCSF) is sometimes used to prepare brain slices for in vitro electrophysiological experiments. This study compared the effect of preparing brain slices using chilled sucrose-based aCSF versus the conventional method using chilled aCSF on hippocampal synaptic plasticity. Brain slices from each treatment group were transferred to normal aCSF before electrophysiological recordings were made. The stimulus-response relationship of field excitatory postsynaptic potentials (fEPSPs) in the CA1 region was indistinguishable between the two treatment groups. However, the amount of LTP induced by either a &theta;-burst (four stimuli at 100 Hz repeated ten times at 200 ms intervals) or tetanic stimulation (100 Hz for 1 s) was significantly reduced in slices that had been prepared using sucrose-based aCSF. This was associated with reduced facilitation of the fEPSPs during the high frequency stimulus, reduced post-tetanic potentiation and short-term potentiation. In sucrose-cut slices the fEPSPs were slightly shorter in duration (29%, P<0.01), and during paired-pulse stimulation the broadening of the second fEPSP was enhanced. The LTP deficit in sucrose-cut slices was reversed by blocking GABA(A) receptor function with picrotoxin. These data suggest that the use of sucrose based aCSF better preserves GABA-mediated synaptic transmission, which limits the induction of LTP in hippocampal brain slices.

Similar levels of long-term potentiation in amyloid precursor protein -null and wild-type mice in the CA1 region of picrotoxin treated slices

Although mutations in amyloid precursor protein (APP) are known to be involved in the development of Alzheimer's disease in some individuals, the role of this protein in normal brain function is poorly understood. We have reported previously that in APP-null mice long-term potentiation (LTP) in the CA1 region of the hippocampus is present but its magnitude is reduced compared to wild-type littermate controls. In the present study, we have confirmed this deficit using a different theta burst induction protocol. Significantly, however, we find that this deficit is no longer apparent when LTP experiments are performed following blockade of gamma-aminobutyric acid(A) receptors. These results suggest that the LTP process per se is not altered by the absence of APP. The deficit may therefore be an indirect consequence of other changes in the hippocampus that occur in the APP-null animal.

Pharmacology of recombinant human GABA(A) receptor subtypes measured using a novel pH-based high-throughput functional efficacy assay

To facilitate the discovery of novel compounds that modulate human GABA(A) receptor function, we have developed a high throughput functional assay using a fluorescence imaging system. L(tk-) cells expressing combinations of human GABA(A) receptor subunits were incubated with the pH-sensitive dye 2',7'bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein, then washed and placed in a 96-well real-time fluorescence plate reader. In buffer adjusted to pH 6.9 there was a robust and persisting acidification response to addition of GABA, which was antagonised by the GABA(A) receptor antagonist bicuculline. The concentration-response relationship for GABA was modulated by allosteric ligands, including benzodiazepine (BZ) site agonists and inverse agonists. The effects of BZ site ligands on the pH response to GABA for receptors containing alpha1beta3gamma2, alpha3beta3gamma2 or alpha5beta3gamma2 subunits were well correlated with results from electrophysiological studies on the same receptor subunit combinations expressed in Xenopus oocytes. Most modulatory compounds tested were found to be relatively unselective across the three subunit combinations tested; however, some showed subtype-dependent efficacy, such as diazepam, which had highest agonist effects on the alpha3beta3gamma2 subtype, substantial but lesser agonism on alpha1beta3gamma2 and still substantial but the least agonism on alpha5beta3gamma2. This indicates that the alpha subunit within the recombinant receptor expressed in L(tk-) cells can affect the efficacy of the response to some BZ compounds. Inhibitors of Na(+)/Cl(-) cotransport, anion/anion exchange and the gastric type of H(+)/K(+) ATPase potently inhibited GABA-evoked acidification, indicating that multiple transporters are involved in the GABA-evoked pH change. This novel fluorescence-based high throughput functional assay allows the rapid characterization of allosteric ligands acting on human GABA(A) receptors.

All-trans-retinoic acid decreases vein graft intimal hyperplasia and matrix metalloproteinase activity in vivo

BACKGROUND

Development of vein graft intimal hyperplasia has been associated with increased activity of matrix metalloproteinases (MMPs). All-trans-retinoic acid (atRA) decreases expression and activity of MMPs in tissue culture and has decreased intimal hyperplasia following arterial balloon catheter injury. We examined the effect of oral administration of atRA on intimal hyperplasia and MMP expression in an animal model of vein bypass grafting.

MATERIALS AND METHODS

Interposition jugular vein bypass grafts were placed in the carotid artery of New Zealand white rabbits. Animals received either atRA (10 mg/kg/day) or vehicle (corn oil) for a period of 2 weeks. Retinoic acid serum levels were determined by HPLC. Intimal and medial areas were measured using morphometric analysis of perfusion-fixed vein graft specimens, and intimal thickness was calculated using circumferential measurements. Expression of MMP-2, MMP-9, and TIMP-1 in vein grafts and unoperated control veins was determined using Northern analysis, and proteolytic activity was determined using substrate gel zymography.

RESULTS

Animals treated with atRA had significantly elevated serum levels of this compound and its metabolites. A decrease in intimal to medial ratio was noted after 28 days in vein grafts from treated animals (0.63 vs 0.88, P < 0.01), and a decrease in calculated intimal thickness was noted at 7 and 28 days. Expression of MMP-2 was decreased in treated animals 7 days following surgery, and expression of both MMP-2 and MMP-9 was decreased at 28 days. A decrease in proteolytic activity was noted on zymography at 68 kDa, 7 and 28 days following surgery in vein grafts from animals treated with atRA, corresponding with a decrease in the active form of MMP-2. Increased expression of TIMP-1 was noted in vein grafts from both the treated and the control groups, 7 and 28 days following graft placement.

CONCLUSIONS

Oral administration of all-trans-retinoic acid resulted in decreased intimal hyperplasia in an animal model of vein bypass grafting. This was associated with decreased expression and activity of MMP-2 in treated animals.