Molecular adaptations underlying susceptibility and resistance to social defeat in brain reward regions

While stressful life events are an important cause of psychopathology, most individuals exposed to adversity maintain normal psychological functioning. The molecular mechanisms underlying such resilience are poorly understood. Here, we demonstrate that an inbred population of mice subjected to social defeat can be separated into susceptible and unsusceptible subpopulations that differ along several behavioral and physiological domains. By a combination of molecular and electrophysiological techniques, we identify signature adaptations within the mesolimbic dopamine circuit that are uniquely associated with vulnerability or insusceptibility. We show that molecular recapitulations of three prototypical adaptations associated with the unsusceptible phenotype are each sufficient to promote resistant behavior. Our results validate a multidisciplinary approach to examine the neurobiological mechanisms of variations in stress resistance, and illustrate the importance of plasticity within the brain's reward circuits in actively maintaining an emotional homeostasis.

Dynamic BDNF activity in nucleus accumbens with cocaine use increases self-administration and relapse

A single exposure to cocaine rapidly induces the brief activation of several immediate early genes, but the role of such short-term regulation in the enduring consequences of cocaine use is poorly understood. We found that 4 h of intravenous cocaine self-administration in rats induced a transient increase in brain-derived neurotrophic factor (BDNF) and activation of TrkB-mediated signaling in the nucleus accumbens (NAc). Augmenting this dynamic regulation with five daily NAc BDNF infusions caused enduring increases in cocaine self-administration, and facilitated relapse to cocaine seeking in withdrawal. In contrast, neutralizing endogenous BDNF regulation with intra-NAc infusions of antibody to BDNF subsequently reduced cocaine self-administration and attenuated relapse. Using localized inducible BDNF knockout in mice, we found that BDNF originating from NAc neurons was necessary for maintaining increased cocaine self-administration. These findings suggest that dynamic induction and release of BDNF from NAc neurons during cocaine use promotes the development and persistence of addictive behavior.

Region-specific tolerance to cocaine-regulated cAMP-dependent protein phosphorylation following chronic self-administration

Chronic cocaine self-administration can produce either tolerance or sensitization to certain cocaine-regulated behaviours, but whether differential alterations develop in the biochemical response to cocaine is less clear. We measured cocaine-induced phosphorylation of multiple cAMP-dependent and -independent protein substrates in mesolimbic dopamine terminal regions following chronic self-administration. Changes in self-administering rats were compared to changes produced by passive yoked injection to identify reinforcement-related regulation, whereas acute and chronic yoked groups were compared to identify the development tolerance or sensitization in the biochemical response to cocaine. Microwave-fixed brain tissue was collected immediately following 4 h of intravenous cocaine administration, and subjected to Western blot analysis of phosphorylated and total protein substrates. Chronic cocaine produced region- and substrate-specific tolerance to cAMP-dependent protein phosphorylation, including GluR1(S845) phosphorylation in striatal and amygdala subregions and NR1(S897) phosphorylation in the CA1 subregion of the hippocampus. Tolerance also developed to cAMP-independent GluR1(S831) phosphorylation in the prefrontal cortex. In contrast, sensitization to presynaptic regulation of synapsin(S9) phosphorylation developed in the hippocampal CA3 subregion while cAMP-dependent tyrosine hydroxylase(S40) phosphorylation decreased in striatal dopamine terminals. Cocaine-induced ERK and CREB(S133) phosphorylation were dissociated in many brain regions and failed to develop either tolerance or sensitization with chronic administration. Positive reinforcement-related correlations between cocaine intake and protein phosphorylation were found only in self-administering animals, while negative dose-related correlations were found primarily with yoked administration. These regional- and substrate-specific adaptations in cocaine-induced protein phosphorylation are discussed in view of their potential impact on the development of cocaine addiction.

Differential ability of D1 and D2 dopamine receptor agonists to induce and modulate expression and reinstatement of cocaine place preference in rats

RATIONALE

D1-Like agonists are self-administered by drug-naive animals, whereas D2-like agonists reinstate cocaine-seeking behavior, but the rewarding and reinstating effects of D1- and D2-like agonists in pavlovian-based conditioned place preference are equivocal.

OBJECTIVE

To compare the ability of D1 and D2 agonists to produce conditioned place preference with their modulation of expression and reinstatement of an established cocaine place preference.

METHODS

Using an unbiased procedure, we measured the place preference induced by the D1 receptor agonist SKF 81297 and the D2/D3 receptor agonist quinpirole in drug-naive or cocaine-exposed rats. The rewarding effects of the D1 agonists SKF 82958, ABT-431, A-77636, and the D2/D3 receptor agonist 7-OH-DPAT were also tested. Additionally, we tested the ability of SKF 81297 and quinpirole to modulate expression and reinstatement of an established cocaine place preference.

RESULTS

The D1 receptor agonists SKF 81297, SKF 82958, and ABT-431 produced dose-dependent conditioned place preferences, whereas A-77636 produced only place aversion, and the D2/D3 agonists quinpirole and 7-OH-DPAT were without effect in drug naive rats. In cocaine-treated rats, SKF-81297-induced place preference was reduced, whereas quinpirole-induced place preference was revealed. Pretreatment using either D1 or D2/D3 agonists blocked expression of an established cocaine place preference, but only the D1 agonist SKF 81297 and cocaine dose-dependently reinstated an extinguished cocaine place preference, whereas the D2/D3 agonist quinpirole induced place aversion but failed to alter cocaine-induced reinstatement.

CONCLUSIONS

D1, but not D2/D3, agonists mediate rewarding effects and reinstatement of cocaine place preference, but the reinstating effects differ markedly from self-administration paradigms.

Periadolescent exposure to ethanol and diazepam alters the aversive properties of ethanol in adult mice

Evidence suggests that the developing adolescent brain may be especially vulnerable to long-term neurobehavioral consequences following ethanol exposure and withdrawal. In the present study, we examined the long-term effect of adolescent ethanol withdrawal on a subsequent EtOH-induced conditioned taste aversion (CTA). Periadolescent and adult C3H mice were exposed to 64 h of continuous (single withdrawal) or intermittent (multiple withdrawal) ethanol vapor. Following each ethanol exposure, animals received either 0, 1, 2, or 3 mg/kg diazepam (DZP) in an attempt to counteract the possible effect of ethanol withdrawal. About 6 weeks following ethanol and DZP treatment, animals were tested for an EtOH-induced CTA. As expected, exposure to EtOH during adolescence attenuated the EtOH-induced CTA as compared to controls. Unexpectedly, administration of DZP during withdrawal did not spare but rather mimicked the attenuation of the EtOH-induced CTA seen in animals exposed to ethanol in adolescence. This attenuation was not evident when EtOH and/or DZP was administered in adulthood. Given the similar mode of action of EtOH and DZP on the GABA system, the principal implication of the present findings is that the intoxicating effect of ethanol on the developing brain can result in long-term changes in the aversive properties of EtOH.

Antisense-induced reduction in nucleus accumbens cyclic AMP response element binding protein attenuates cocaine reinforcement

Repeated cocaine exposure up-regulates cyclic AMP signaling and increases the transcriptional activity of cyclic AMP response element binding protein (CREB) in the nucleus accumbens. To study the possibility that nucleus accumbens CREB activity regulates self-administration behavior, we tested the effects of a single, bilateral infusion of CREB antisense oligonucleotide into nucleus accumbens core and shell sub-regions on cocaine self-administration in rats. Nucleus accumbens core infusions of CREB antisense reduced CREB and the CREB-regulated immediate early gene brain-derived neurotrophic factor by 31 and 27%, respectively, but failed to alter levels of the homologous CREB family proteins cyclic AMP response element modulator and activating transcription factor 1, and had no effect on CREB levels in adjacent nucleus accumbens shell tissue. Similar infusions of CREB antisense in either core or shell produced a transient downward shift in cocaine self-administration dose-response curves on a fixed ratio 5 (five responses/injection) reinforcement schedule, indicating a reduction in cocaine reinforcement that fully recovered 3 days after treatment. CREB antisense also increased the threshold dose of cocaine required for reinstating cocaine self-administration, indicating that nucleus accumbens CREB levels regulate the incentive properties of cocaine. When access to cocaine was less restricted on a fixed ratio 1 schedule, infusion of CREB antisense in the core, but not shell, caused a transient (1-2 days) reduction in stabilized cocaine self-administration, but had no effect on responding maintained by sucrose pellets, indicating that basal CREB levels in the nucleus accumbens core regulate drug intake. None of these effects were produced by nucleus accumbens infusions of complementary sense oligonucleotide. These results suggest a necessary role for nucleus accumbens CREB activity in cocaine reinforcement, and, by converse analogy, up-regulation in CREB activity after chronic cocaine use could contribute to addiction-related increases in cocaine self-administration.

Regulation of anxiety and initiation of sexual behavior by CREB in the nucleus accumbens

Sexual deficits and other behavioral disturbances such as anxiety-like behaviors can be observed in animals that have undergone social isolation, especially in species having important social interactions. Using a model of protracted social isolation in adult rats, we observed increased anxiety-like behavior and deficits in both the latency to initiate sexual behavior and the latency to ejaculate. We show, using transgenic cAMP response element (CRE)-LacZ reporter mice, that protracted social isolation also reduces CRE-dependent transcription within the nucleus accumbens. This decrease in CRE-dependent transcription can be mimicked in nonisolated animals by local viral gene transfer of a dominant negative mutant of CRE-binding protein (CREB). We previously showed that this manipulation increases anxiety-like behavior. We show here that it also impairs initiation of sexual behavior in nonisolated animals, a deficit that can be corrected by anxiolytic drug treatment. This local reduction in CREB activity, however, has no influence on ejaculation parameters. Reciprocally, we used the viral transgenic approach to overexpress CREB in the nucleus accumbens of isolated animals. We show that this local increase in CREB activity completely rescued the anxiety phenotype of the isolated animals, as well as their deficit in initiating sexual behavior, but failed to rescue the deficit in ejaculation. Our data suggest a role for the nucleus accumbens in anxiety responses and in specific aspects of sexual behavior. The results also provide insight into the molecular mechanisms by which social interactions affect brain plasticity and behavior.

High sensitivity detection of molecular recognition using magnetically labelled biomolecules and magnetoresistive sensors

Small magnetoresistive spin valve sensors (2 x 6 microm(2)) were used to detect the binding of single streptavidin functionalized 2 microm magnetic microspheres to a biotinylated sensor surface. The sensor signals, using 8 mA sense current, were in the order of 150-400 microV for a single microsphere depending on sensor sensitivity and the thickness of the passivation layer over the sensor surface. Sensor saturation signals were 1-2 mV representing an estimated 6-20 microspheres, with a noise level of approximately 10 microV. The detection of biomolecular recognition for the streptavidin-biotin model was shown using both single and differential sensor architectures. The signal data compares favourably with previously reported signals for high numbers of magnetic microspheres detected using larger multilayered giant magnetoresistance sensors. A wide range of applications is foreseen for this system in the development of biochips, high sensitivity biosensors and the detection of single molecules and single molecule interactions.

Application of beta-galactosidase enzyme complementation technology as a high throughput screening format for antagonists of the epidermal growth factor receptor

We have applied enzyme complementation technology to develop a screen for antagonists of the epidermal growth factor (EGF) receptor. Chimeric proteins containing two weakly complementing deletion mutants of Escherichia coli beta-galactosidase (beta-gal), each fused to the EGF receptor extracellular and transmembrane domains, have been stably expressed in C2C12 cells. In this cell line, formation of active beta-gal is dependent on agonist-stimulated dimerization of the EGF receptor. We have developed a homogenous 384-well assay protocol and have applied this to characterize the pharmacology of the receptor and to develop a high throughput screen (HTS) for EGF receptor antagonists. The assay is tolerant to DMSO concentrations of up to 2% and, across 21 passages in culture, exhibits an EC(50) for EGF of 5.4 +/- 3.6 ng/ml (n = 11) and a Z' of 0.55 +/- 0.13 (n = 11). A random set of 1,280 compounds was screened in duplicate at 11 microM to examine the robustness of enzyme complementation technology and to characterize the false-positive hit rate in the assay. Using a cutoff of 40% inhibition of EGF-promoted beta-gal activity, the hit rate on day 1 was 2.5% and on day 2 was 1.9%. After retesting the active compounds, the hit rate was reduced to 0.4%, of which one of the compounds was identified as a beta-gal inhibitor and the remainder appeared to be nonspecific inhibitors in the assay. This technology is amenable to automated screen workstations, there are highly sensitive chemiluminescent and fluorescent beta-gal assay reagents amenable to detection in miniaturized plate formats, and the assay benefits from a low false-positive hit rate. Enzyme complementation technology may have wide application within the HTS environment for the detection of modulators of receptor activation or inhibitors of protein-protein interactions in mammalian cells.

A method to measure the interaction of Rac/Cdc42 with their binding partners using fluorescence resonance energy transfer between mutants of green fluorescent protein

Enhanced blue fluorescent protein (EBFP) and enhanced green fluorescent protein (EGFP) mutants of GFP in close proximity to one another can act as a fluorescence resonance energy transfer (FRET) pair. Unstructured amino acid linkers of varying length were inserted between EBFP and EGFP, revealing that linkers even as long as 50 amino acids can be accommodated and still allow FRET to occur. This led to the development of a novel biosensor for Rac/Cdc42 binding to their effector proteins based on the insertion of amino acids 75-118 of p21-activated kinase (PAK) between the GFP mutants. We demonstrate that this protein construct allows significant FRET between EBFP and EGFP and retains the ability to bind to Rac in its GTP-bound form with a binding affinity similar to the uncomplexed PAK fragment, and furthermore, on binding to Rac or Cdc42 a marked change in FRET takes place. This forms the basis for a simple, sensitive, and rapid method to measure binding of Rac/Cdc42 to their effector proteins. Since the signal is dependent upon the interaction with active GTP-bound forms it acts as a biosensor for the activation of Rac/Cdc42. It has the potential for use in live cells and for identifying localization of Rac/Cdc42 within subcellular compartments.

Effect of IGFBP-3 on IGF- and IGF-analogue-induced insulin-like growth factor-I receptor (IGFIR) signalling

Insulin-like growth factor binding protein-3 (IGFBP-3) binds IGF-I and IGF-II with high affinity, at least an order of magnitude higher than the affiniy of the IGFs for the IGFIR. It has been hypothesized that IGFBP-3 inhibits IGF binding to the IGFIR via a mechanism independent of its ability to sequester IGFs. In the present study, we examined the effects of IGFBP-3 and its proteolytic fragments on the initial events of the IGFIR signalling pathway. IGFBP-3 inhibited IGF-I-, IGF-II-, Des(1-3)IGF-I- and Long(R3)IGF-I-induced IGFIR phosphorylation in a dose-dependent manner at similar concentration range but not QAYL-induced IGFIR-P. The((1-97))IGFBP-3 fragment was able to inhibit only IGF-I-induced IGFIR-P. The((1-97))IGFBP-3 fragment but not intact IGFBP-3 inhibited insulin-induced IGFIR-P. Monolayer cross-linking with [(125)I]IGFBP-3 indicated that there is no direct interaction of IGFBP-3 with the IGFIR. This study demonstrates that the effect on the initial step of IGFIR signalling by IGFBP-3 is largely due to its ability to sequester IGF and the IGF analogues in the extracellular milieu and not the result of any interaction of IGFBP-3 with the IGFIR or a mechanism independent of its ability to bind IGFs.

Magnesium fluoride-dependent binding of small G proteins to their GTPase-activating proteins

GTPase-activating proteins (GAPs) enhance the intrinsic GTPase activity of small G proteins, such as Ras and Rho, by contributing a catalytic arginine to the active site. An intramolecular arginine plays a similar role in heterotrimeric G proteins. Aluminum fluoride activates the GDP form of heterotrimeric G proteins, and enhances binding of the GDP form of small G proteins to their GAPs. The resultant complexes have been interpreted as analogues of the transition state of the hydrolytic reaction. Here, equilibrium binding has been measured using scintillation proximity assays to provide quantitative information on the fluoride-mediated interaction of Ras and Rho proteins with their respective GAPs, neurofibromin (NF1) and RhoGAP. High-affinity fluoride-mediated complex formation between Rho.GDP and RhoGAP occurred in the absence of aluminum; however, under these conditions, magnesium was required. Additionally, the novel observation was made of magnesium-dependent, fluoride-mediated binding of Ras.GDP to NF1 in the absence of aluminum. Aluminum was required for complex formation when the concentration of magnesium was low. Thus, either aluminum fluoride or magnesium fluoride can mediate the high-affinity binding of Rho. GDP or Ras.GDP to GAPs. It has been reported that magnesium fluoride can activate heterotrimeric G proteins. Thus, magnesium-dependent fluoride effects might be a general phenomenon with G proteins. Moreover, these data suggest that some protein.nucleotide complexes previously reported to contain aluminum fluoride may in fact contain magnesium fluoride.

Oxacillin-induced tissue necrosis

OBJECTIVE

To report a case of oxacillin-induced tissue necrosis in which recommended concentration guidelines for dilution and administration were used. Oxacillin concentration data, potential risk factors, and treatment options for extravasation injuries are also briefly reviewed.

CASE SUMMARY

Oxacillin was infused peripherally by infusion pump in a 79-year-old white woman as prophylactic antibiotic coverage for permanent pacemaker placement. Oxacillin extravasation occurred after the second postoperative dose. A dime-sized area of necrosis was noted at the heparin-lock insertion site.

DISCUSSION

Only one case of oxacillin-induced necrosis has been reported. The degree of damage and concentration of drug used were not specifically described. Concentration may play a role in the appearance or absence of tissue damage after an antibiotic extravasation and should be taken into consideration when evaluating a drug's tissue toxicity potential.

CONCLUSIONS

The potential exists for oxacillin 50 mg/mL to cause tissue damage in humans if an extravasation occurs. This reaction may be avoided with use of a less-concentrated preparation, avoidance of infusion pump administration, and identification of high-risk patients.

Genetic diversity in twenty variants of the avian polyomavirus

To determine if different pathotypes of the avian polyomavirus (APV) exist and to compare the genomes of APVs originating from different geographic areas, dates, and species of birds, the partial sequences of 18 APVs were determined. New viral sequences were compared with three published APV sequences. Two of the new viruses had identical sequences. Forty point mutations were found at 31 loci. A 27-bp deletion was found in the VP2 and VP3 open reading frames of one virus. A duplication of the putative origin of replication and adjacent enhancer region was previously reported in one APV. Smaller duplications involving the origin in one APV and a second enhancer region in another were discovered. All duplications were in tissue culture-adapted viruses, suggesting they occurred during the isolation process. Excluding duplications and the deletion, maximum variation between viruses was small (11 bp). A maximum parsimony tree was constructed that contained three major branches. The three earliest isolates were on separate branches. The European viruses were confined to branch I, but APVs from the United States were on all three branches. Lovebird, budgerigar, and macaw APVs were also on each of the three branches, suggesting that species-specific pathotypes have not developed. Most nonsynonymous mutations occurred in a small portion of the VP2 and VP3 open reading frames, demonstrating a selection for these mutations. That a glycine at VP2 221 will inhibit virus replication in chicken embryo fibroblasts (CEFs) has been previously reported. In contrast, six of seven of the new APVs isolated in CEFs had a glycine at VP2 221.

The conserved arginine in rho-GTPase-activating protein is essential for efficient catalysis but not for complex formation with Rho.GDP and aluminum fluoride

The Rho family of small GTP-binding proteins are downregulated by an intrinsic GTPase, which is enhanced by GTPase-activating proteins (GAPs). RhoGAPs contain a single conserved arginine residue that has been proposed to be involved in catalysis. Here, the role of this arginine has been elucidated by mutagenesis followed by determination of catalytic and equilibrium binding constants using single-turnover kinetics, isothermal titration calorimetry, and scintillation proximity assays. The turnover numbers for wild-type, R282A, and R282K RhoGAPs were 5.4, 0.023, and 0.010 s-1, respectively. Thus, the function of this arginine could not be replaced by lysine or alanine. Nevertheless, the R282A mutation had a minimal effect on the binding affinity of RhoGAP for either Rho. GTP or Rho.GMPPNP, which confirms the importance of the arginine residue for catalysis as opposed to formation of the protein-protein complex. The R282A mutant RhoGAP still increased the hydrolysis rate of Rho.GTP by 160-fold, whereas the wild-type enzyme increased it by 38000-fold. We conclude that this arginine contributes half of the total reduction of activation energy of catalysis. In the presence of aluminum fluoride, the R282A mutant RhoGAP binds almost as well as the wild type to Rho.GDP, demonstrating that the conserved arginine is not required for this interaction. The affinity of wild-type RhoGAP for the triphosphate form of Rho is similar to that for Rho.GDP with aluminum fluoride. These last two observations show that this complex is not associated with the free energy changes expected for the transition state, although the Rho.GDP.AlF4-.RhoGAP complex might well be a close structural approximation.

Reticuloendotheliosis in captive greater and Attwater's prairie chickens

Reticuloendotheliosis in captive greater (Tympanuchus cupido pinnatus) and Attwater's (T. cupido attwateri) prairie chickens is reported for the first time. Between September 1993 and August 1994, two adult female wild-caught greater prairie chickens housed at Texas A&M University (College Station, Texas, USA) were observed with multiple subcutaneous nodules. Both birds were euthanatized. Complete necropsy examinations revealed lesions limited to the skin of each bird. Histopathologic examination of lesions revealed pleomorphic lymphoreticular cells suggestive of reticuloendotheliosis and reticuloendotheliosis virus (REV) was demonstrated in tumor tissue by polymerase chain reaction and virus isolation. Between September 1994 and June 1995, five additional greater prairie chickens and two Attwater's prairie chickens were euthanatized or found dead with evidence of lymphoreticular neoplasia in multiple organ systems. Initial testing of the captive flock in December 1994 for evidence of viremia and antibody to reticuloendotheliosis virus revealed over 50% of the tested birds were viremic, but none developed antibodies. Subsequent testing between January 1995 and January 1996 indicated that once infected with reticuloendotheliosis virus, Attwater's prairie chickens tended to remain outwardly healthy despite persistent viremia compared to infected greater prairie chickens which had higher morbidity and mortality rates within 60 to 90 days after initial detection of viremia and did not usually develop persistent viremia. Antibodies to REV were detected in only three captive greater prairie chickens and only in 1995. Six of the nine birds that were euthanatized or found dead due to reticuloendotheliosis developed viremia prior to death; three birds were not tested prior to death. Testing of free-ranging greater and Attwater's prairie chickens for reticuloendotheliosis is recommended prior to translocation or release.

A mechanistic analysis of nondisruptive axonal injury: a review

Axons are particularly at risk in human diffuse head injury. Use of immunocytochemical labeling techniques has recently demonstrated that axonal injury (AI) and the ensuing reactive axonal change is, probably, more widespread and occurs over a longer posttraumatic time in the injured brain than had previously been appreciated. But the characterization of morphologic or reactive changes occurring after nondisruptive AI has largely been defined from animal models. The comparability of AI in animal models to human diffuse AI (DAI) is discussed and the conclusion drawn that, although animal models allow the analysis of morphologic changes, the spatial distribution within the brain and the time course of reactive axonal change differs to some extent both between species and with the mode of brain injury. Thus, the majority of animal models do not reproduce exactly the extent and time course of AI that occurs in human DAI. Nonetheless, these studies provide good insight into reactive axonal change. In addition, there is developing in the literature considerable variance in the terminology applied to injured axons or nerve fibers. We explain our current understanding of a number of terms now present in the literature and suggest the adoption of a common terminology. Recent work has provided a consensus that reactive axonal change is linked to pertubation of the axolemma resulting in disruption of ionic homeostatic mechanisms within injured nerve fibers. But quantitative data for changes for different ion species is lacking and is required before a better definition of this homeostatic disruption may be provided. Recent studies of responses by the axonal cytoskeleton after nondisruptive AI have demonstrated loss of axonal microtubules over a period up to 24 h after injury. The biochemical mechanisms resulting in loss of microtubules are, hypothetically, mediated both by posttraumatic influx of calcium and activation of calmodulin. This loss results in focal accumulation of membranous organelles in parts of the length of damaged axons where the axonal diameter is greater than normal to form axonal swellings. We distinguish, on morphologic grounds, between axonal swellings and axonal bulbs. There is also a growing consensus regarding responses by neurofilaments after nondisruptive AI. Initially, and rapidly after injury, there is reduced spacing or compaction of neurofilaments. This compaction is stable over at least 6 h and results from the loss or collapse of neurofilament sidearms but retention of the filamentous form of the neurofilaments. We posit that sidearm loss may be mediated either through proteolysis of sidearms via activation of microM calpain or sidearm dephosphorylation via posttraumatic, altered interaction between protein phosphatases and kinase(s), or a combination of these two, after calcium influx, which occurs, at least in part, as a result of changes in the structure and functional state of the axolemma. Evidence for proteolysis of neurofilaments has been obtained recently in the optic nerve stretch injury model and is correlated with disruption of the axolemma. But the earliest posttraumatic interval at which this was obtained was 4 h. Clearly, therefore, no evidence has been obtained to support the hypothesis that there is rapid, posttraumatic proteolysis of the whole axonal cytoskeleton mediated by calpains. Rather, we hypothesize that such proteolysis occurs only when intra-axonal calcium levels allow activation of mM calpain and suggest that such proteolysis, resulting in the loss of the filamentous structure of neurofilaments occurs either when the amount of deformation of the axolemma is so great at the time of injury to result in primary axotomy or, more commonly, is a terminal degenerative change that results in secondary axotomy or disconnection some hours after injury.

Characterization of the avian polyomavirus-associated glomerulopathy of nestling parrots

The glomerulopathy occurring in nestling nonbudgerigar parrots with avian polyomavirus (APV) disease was examined in 10 parrots. Glomerular lesions were characterized by the presence of dense, periodic acid-Schiff (PAS)-positive material that expanded the mesangium and that narrowed and at times occluded capillary lumina. PAS-staining was found to be more sensitive than hematoxylin and eosin in the detection of the lesions. Ultrastructurally, finely granular electron-dense material was found in massive intracapillary and mesangial condensates. Capillary endothelial cells exhibited changes consistent with cellular swelling. No evidence of chronic glomerular changes was observed. Immunofluorescent staining demonstrated that the PAS-positive, electron-dense condensates were complexes of IgG, avian polyomavirus antigen, and, in one bird, IgM. Viral DNA was detected in the serum of all six birds examined. Anti-APV antibodies were also present in all five serum samples examined. These findings suggested that the pathogenesis of this acute immune complex glomerulopathy and other APV-associated lesions depends on the presence of an appropriate ratio of circulating virus and anti-APV antibody.

Failure of maternally derived yolk IgG to reach detectable concentrations in the sera of nestling budgerigars (Melopsittacus undulatus)

Transfer of maternal immunoglobulin G (IgG) to the yolk and nestling was investigated in the budgerigar. Specific antibodies to avian polyomavirus and Newcastle disease virus could be detected in 82% of yolk extracts of eggs from seropositive hens. Using a double immunodiffusion assay with anti-chicken IgG antibodies, IgG could also be detected in yolk supernatants with virus neutralizing activity. In all assays, IgG concentrations in the yolk extracts were significantly less than those of the adult budgerigar serum. No antiviral activity was detected in nestling serum. Examination of nestling serum with the double immunodiffusion assay and an immuno-dot-blot technique specific for IgG showed that detectable concentrations of IgG are not present in nestling serum until after the yolk sac is fully absorbed. This observation, coupled with the absence of specific anti-viral antibody in nestlings of seropositive hens, indicated that none of the yolk sac antibody reached the nestling circulation.

Production of avian polyomavirus seronegative budgerigars (Melopsittacus undulatus) from seropositive adults

Adult budgerigars (Melopsittacus undulatus) with 2 years of breeding experience were removed from an aviary with enzootic avian polyomavirus (APV) disease and maintained in an isolation unit. Following a 7-month respite from breeding, these birds were allowed to breed without interruption for 2 years. Although the adults were seropositive both at the beginning and end of the experiment, all 102 of their offspring were seronegative. These data suggest that APV can be eliminated from a budgerigar aviary with the use of simple management techniques.

A scale for identifying "Stockholm syndrome" reactions in young dating women: factor structure, reliability, and validity

The factor structure, reliability, and validity of a 49-item scale designed to measure Stockholm Syndrome (also referred to as "traumatic bonding" and "terror bonding"), that is, bonding with an abusive partner, were assessed for college women in heterosexual dating relationships. Factor analysis identified three major factors: Core Stockholm Syndrome, characterized by cognitive distortions and other strategies for coping with abuse; Psychological Damage, marked by depression, low self-esteem, and loss of sense of self; and Love-Dependence, typified by the feeling that one cannot survive without one's partner's love. The scale and factors had excellent internal consistency and good test-retest reliabilities. They correlated negatively with the Marlowe-Crowne Social Desirability scale and positively with Horowitz, Wilner, & Alvarez' (1979) Impact of Event Scale, Hyler and Rieder's (1987) Borderline Personality Disorder Scale, Hatfield and Sprecher's (1986) Passionate Love Scale, and Straus' (1979) Verbal Aggression and Violence scales of the Conflict Tactics Scales.

Evaluation of the hepatobiliary excretion of technetium-99m-MAG3 and reconstitution factors affecting radiochemical purity

Technetium-99-MAG3 is a renal tubular function agent. However, sporadic liver and gallbladder visualization have raised questions about kit stability, impurities and nonrenal routes of excretion. To address these issues, studies were conducted to optimize the labeling efficiency of the TechneScan MAG3 kit and to evaluate the hepatobiliary excretion of the MAG3 complex.

METHODS

Thirty-six vials of the commercial formulation of 99mTc-MAG3 were prepared according to manufacturer's instructions and evaluated for radiochemical purity using two methods: a combination of high-performance liquid chromatography and paper chromatography (HPLC/PC); and the manufacturer's miniature chromatography system (Sep-Pak procedure).

RESULTS

The labeling efficiency was significantly higher when the kit was reconstituted with 10 ml (96.6%) of saline versus 5 ml (91.4%) (p < 0.01). The radiochemical purity of the kits remained stable for up to 6 hr, but the purity determined by Sep-Pak averaged 2.5% higher than that determined by HPLC procedures (p < 0.01). Rat studies to evaluate renal and hepatobiliary elimination of MAG3 showed no difference in the %ID excreted into the urine by 60 min in all groups of animals studied. However, the %ID excreted into the bile was significantly higher for the kit formulation than the HPLC-purified MAG3, 9.9% versus 6.6% (p = 0.0475).

CONCLUSION

The radiochemical purity of the TechneScan MAG3 kit can be improved by reconstituting with larger volumes. In addition, the studies in rats suggest that fasting or kit impurities may be a contributing factor to increased hepatobiliary visualization in patient studies.