Human immunodeficiency virus-1 coat protein gp120 impairs contextual fear conditioning: a potential role in AIDS related learning and memory impairments.

Many AIDS patients suffer from cognitive impairments including deficits in learning and memory. The Human Immunodeficiency Virus-1 (HIV-1) envelope glycoprotein gp120 is one possible mediator of these impairments. This is because gp120 activates brain microglial cells and astrocytes, and in vivo activation of glia leads to the release of the proinflammatory cytokine interleukin-1 beta (IL-1beta). gp120 induced IL-1beta release could be involved in producing memory impairments associated with AIDS because central IL-1beta activity adversely affects cognitive function. The reported experiments evaluated the effects of i.c.v. gp120 administration and subsequent IL-1beta activity on learning and memory processes in the rat. Intracerebroventricular gp120 produced memory impairments on hippocampally dependent contextual fear conditioning, but not hippocampally independent auditory-cue fear conditioning following post-conditioning gp120 administration. Central gp120 administration also caused increases in IL-1beta protein levels in the hippocampus and frontal cortex but not in the hypothalamus. gp120 induced memory impairments were blocked by 2 different IL-1 antagonists, alpha melanocyte stimulating hormone (alphaMSH) and interleukin-1 receptor antagonist (IL-1ra). Finally, heat denaturation of the tertiary structure of gp120 abolished its effects on fear conditioning, suggesting that gp120 impairs contextual fear conditioning by binding to its receptors on glia.

Evaluation of change in blood flow by contrast-enhanced power Doppler imaging during norepinephrine-induced renal vasoconstriction.

We evaluated the changes in flow induced by intrarenal infusion of norepinephrine by an ultrasonographic contrast agent and power Doppler imaging. Hypoperfusion was induced in dogs (N = 5) by infusing norepinephrine directly into the renal artery for 30 min at doses of 0.7 microg/kg/min, 1.0 microg/kg/min, and 1.9 microg/kg/min. Contrast agent injections were made before and after each infusion of norepinephrine. The transit of contrast agent through the kidney and color enhancement were measured by computer analysis of power Doppler images. Mean transit time and effective renal plasma flow were measured. The effective renal plasma flow decreased by 29%, 30%, and 64%, respectively, with the increasing doses of norepinephrine. Paralleling this change, the mean transit time, which corresponds to reduction in renal blood flow, increased by 26%, 43%, and 77%, respectively, from the preinfusion value. Regression analysis shows renal blood flow to decrease exponentially with norepinephrine dose. Renal blood flow changes measured by contrast-enhanced imaging correlated closely with the effective renal plasma flow measurements. Computer analysis of contrast-enhanced power Doppler images allowed measurement of renal blood flow. This technique may be useful in assessing renal perfusion during pharmacologic and other therapeutic interventional procedures.

Role of interleukin-1 beta in impairment of contextual fear conditioning caused by social isolation.

Isolating rats immediately after conditioning impairs contextual but not auditory-cue fear conditioning. The reported experiments examine the involvement of brain interleukin-1beta (IL-1beta) in the impairment in contextual fear conditioning caused by social isolation. As measured by the conditioned freezing response, 5 h of social isolation after conditioning, impaired contextual but not auditory-cue fear conditioning in adult male Sprague-Dawley rats. Social isolation for 1 or 3 h after conditioning also increased IL-1beta protein in the hippocampus and cerebral cortex. No differences in IL-1beta protein levels were found in the pituitary or the hypothalamus. Intracerebroventricular (ICV) IL-1 receptor antagonist (IL-1ra) given after conditioning prevented the impairment in contextual fear conditioning caused by isolation. ICV IL-1ra had no effect on auditory-cue fear conditioning in these same animals, nor did it affect the level of contextual fear conditioning displayed by home cage controls. Like isolation, ICV IL-1beta (10 or 20 ng) after conditioning also impaired contextual but not auditory-cue fear conditioning. These results suggest that increased levels of brain IL-1beta play a role in producing the impairment in contextual fear conditioning produced by social isolation. These findings also add to the generality of the idea that stressors induce IL-1beta activity in the brain and that IL-1beta may play physiological roles in the uninjured brain.

Isolation reduces contextual but not auditory-cue fear conditioning: a role for endogenous opioids.

Isolation for several hours after fear conditioning reduces contextual but not auditory-cue fear conditioning (J. W. Rudy, 1996). This isolation effect is reversed by both, centrally and peripherally acting opioid receptor antagonists. As in isolation, systemically administered morphine given immediately after conditioning also reduces contextual fear conditioning. Morphine's effect is also reversed by both centrally and peripherally acting opioid receptor antagonists. Exposure to the conditioning context has been shown to eliminate the effect of isolation on contextual fear conditioning (J. W. Rudy, 1996). Context preexposure also eliminated the effect of morphine on contextual fear conditioning. These results imply that opioids released in the periphery play an important role in producing the isolation effect and that they do so by disrupting the postconditioning memory consolidation processes.

Comparison of power Doppler and B-scan sonography for renal imaging using a sonographic contrast agent.

The goal of this study was to evaluate the relative performance of power Doppler and B-scan imaging modes in detecting vascular perfusion changes resulting from injection of a contrast agent. To allow this comparison the imaging plane and the contrast agent injection must be the same for both modes. We achieved this by using a rigid transducer holder and simultaneously recording power Doppler and B-scan images on separate videotapes. The kidneys of five adult beagles were scanned to allow a comparison of how power Doppler and B-scan imaging methods monitor changes during the injection of 0.1 ml/kg of a contrast agent, EchoGen emulsion (Sonus Pharmaceuticals, Bothell, WA). The changes in the images were assessed qualitatively by three radiologists and quantitatively using a custom-designed image analysis software. All of the radiologists agreed that no visually detectable changes occurred in B-scan images but that significant changes could be observed in power Doppler images. Image analysis also indicated a difference between power Doppler and B-scan images. The change in mean color level of power Doppler images could be displayed as an indicator dilution curve with a peak enhancement of 46 +/- 16 above the preinjection value. The time at which mean color level peaked was 18 +/- 13 s. The mean color level returned to half of the peak value by 69 +/- 42 s and returned to the preinjection baseline value by 148 +/- 73 s. Conversely, B-scan images showed statistically insignificant changes, and time measurements could not be made. By all measures used to evaluate images, power Doppler imaging had a greater sensitivity in detecting changes resulting from contrast agent injection than B-scan imaging. This finding indicates that power Doppler imaging of contrast agent injections can be used to map regional differences in flow as well as quantitative measurements of a contrast agent's transit time and has the potential to assess kidney abnormalities associated with renal blood flow.

Selective effects of peripheral lipopolysaccharide administration on contextual and auditory-cue fear conditioning.

The reported experiments explore the effects of peripheral LPS administration on learning and memory processes. As measured by the conditioned freezing response, intraperitoneal LPS administration given after conditioning impaired contextual but not auditory-cue fear conditioning in both juvenile (hooded Long Evans) and adult rats (albino Sprague Dawley) of two different strains. This impairment in contextual fear conditioning was not dependent on the presence of the tone. Preexposure to the context eliminated the effect of LPS on contextual fear conditioning, and in addition, LPS given after context preexposure negated the beneficial effects of preexposure on contextual fear. These results suggest that LPS disrupts posttrial memory consolidation processes. In support of the hypothesis that LPS-induced proinflammatory cytokine release is involved in producing the impairment in contextual fear caused by LPS, peripheral interleukin-1 receptor antagonist (IL-1ra) administered subcutaneously at a dose of 100 mg/kg prevented the impairment in contextual fear caused by LPS. These experiments provide evidence for a role of immune activation and cytokine activity in learning and memory processes.

Time of conditioning selectively influences contextual fear conditioning: further support for a multiple-memory systems view of fear conditioning.

Time of conditioning influences long-term retention of contextual but not auditory-cue fear conditioning. Long-Evans rats (Rattus norvegicus) conditioned at 12 noon displayed reduced contextual fear conditioning compared to rats conditioned at 8 a.m. or 4 p.m. This effect was eliminated by exposure to the context 24 hr prior to conditioning and by a posttrial injection of corticosterone (1.0 mg/kg). Time of conditioning did not influence short-term retention of contextual fear. These results suggest that time of conditioning influences the posttrial processes that construct a memory representation of the context. They also support the view that contextual and auditory-cue fear conditioning depend on different processes. These results are discussed in relation to the concept of memory storage modulators.

A selective role for corticosterone in contextual-fear conditioning.

The contribution of corticosterone to contextual- and auditory-cue fear conditioning was examined. Adrenalectomized rats showed reduced contextual-fear conditioning when tested 24 hr after conditioning; however, neither immediate contextual- nor auditory-cue fear conditioning was impaired. Contextual-fear conditioning in adrenalectomized rats with corticosterone replacement during the 4-day interval separating surgery and conditioning matched the level of controls. Moreover, rats exposed to the context prior to adrenalectomy showed normal long-term contextual-fear conditioning. Corticosterone replacement administered after the conditioning episode also negated the effects of adrenalectomy. Thus, corticosterone's role in fear conditioning is selective: It appears to contribute to the neural processes that support the consolidation of a long-term memory representation of the context.

DHEA-S selectively impairs contextual-fear conditioning: support for the antiglucocorticoid hypothesis.

The authors had reported that glucocorticoids play a selective role in fear conditioning. The adrenal steroid dehydroepiandrosterone (DHEA) has been reported to act as a functional antiglucocorticoid. If DHEA has antiglucocorticoid properties, then its effects on fear conditioning might resemble those produced by adrenalectomy. The authors now report that chronic exposure to high levels of dehydroepiandrosterone sulfate (DHEA-S; converted in vivo to DHEA) produced the same pattern of results as adrenalectomy. Specifically, treatment with DHEA-S impaired contextual fear conditioning 24 hr after conditioning but not immediately after conditioning, and like adrenalectomy, DHEA-S had no effect on auditory-cue fear conditioning. Preexposure to the context before drug treatment eliminated the amnestic effects of DHEA-S, suggesting that, like adrenalectomy, DHEA-S exerted its effect by interfering with the construction of a contextual memory representation. Thus, DHEA appears to act as a functional antiglucocorticoid in the processes that mediate learning and memory.

Type II glucocorticoid receptor antagonists impair contextual but not auditory-cue fear conditioning in juvenile rats.

There is evidence that glucocorticoids may play a role in learning and memory. To further explore this possibility, we examined the effect of the Type II glucocorticoid antagonists on contextual fear conditioning. This conditioning task is dependent on the hippocampal formation, a brain structure known to be rich in glucocorticoid receptors. Rats systemically injected with a Type II antagonist either 1 h prior to conditioning (RU 38486 and RU 40555) or immediately after conditioning displayed less contextual fear conditioning than rats injected with vehicle. Although RU impaired contextual fear conditioning, it had no effect on auditory fear conditioning. These data are consistent with other reports that contextual fear conditioning and auditory-cue fear conditioning depend on different processes and with the hypothesis that glucocorticoid activity contributes to the processes involved in the consolidation of some forms of memory.

Use of power Doppler ultrasound-guided biopsies to locate regions of tumour hypoxia.

The purpose of this study was to determine whether power Doppler ultrasound techniques could be used to direct biopsies into tumour regions with relatively low red blood cell flux, and therefore preferentially sample regions that were relatively hypoxic. Subcutaneous 9L glioma rat tumours were biopsied using power Doppler ultrasound guidance. Immunohistochemical detection of the 2-nitroimidazole EF5 was performed to determine the presence and level of hypoxia in the biopsy samples. Comparisons between the power Doppler-determined red blood cell flux and EF5 binding were made. In seven out of eight tumours studied, power Doppler ultrasound allowed differentiation of a relatively hypoxic region from a relatively oxic region by localizing relatively low vs high red blood cell flux areas respectively. In one of these seven tumours, RBC flux was high in both biopsied sites and hypoxia was not present in either. In two of these seven tumours, hypoxia was present in each biopsy and both of the red blood cell flux measurements were low. In the eighth tumour, both the EF5 binding and the red blood cell flux measurements were low. In this tumour, low EF5 binding was due to the dominance of necrotic cells, which will not reduce or bind EF5 in the biopsy specimen. Using EF5-binding techniques, we have confirmed that regions of relatively low red blood cell flux are more hypoxic than those with relatively high red blood cell flux. Counterstaining specimens with haematoxylin and eosin allows differentiation of low EF5-binding regions due to oxia vs necrosis. These methods have clinical implications for the expanded use of power Doppler ultrasound as a means to direct tissue sampling when it is important to identify the presence of hypoxia.

Power, spectral, and color flow Doppler enhancement by a new ultrasonographic contrast agent.

The ability of EchoGen contrast agent (Sonus Pharmaceuticals, Bothell, WA) to enhance aortic, renal, and scrotal spectral Doppler, color flow, and power Doppler sonography at doses from 0.01 ml/kg to 0.65 ml/kg was evaluated in dogs. Videotaped images were digitized and analyzed for Doppler signal strength at known postinjection times. Contrast agent increased aortic spectral Doppler peak height, spectral width, and brightness. Contrast agent increased renal and testicular color flow and power Doppler sonographic signal and enhanced the visualization of vascular anatomy. Intensity and duration of these effects increased with increasing dose of contrast agent. Enhancement effect varied in different organs. At higher doses, blooming and Doppler shift artifacts were observed and are believed to be due to machine limitation.

A comparison of contextual and generalized auditory-cue fear conditioning: evidence for similar memory processes.

A number of variables influence contextual, but not auditory-cue, fear conditioning. However, several of these variables (isolation, stimulus preexposure, retention interval, and age) affect generalized auditory-cue fear. More generalized fear was found when (a) rats were isolated in a novel environment than when returned to their home cages, (b) the retention interval was 3 hr rather than 24 hr, and (c) in 18-day-old compared with 25-day-old rats. Moreover, preexposure to the auditory cue eliminated the isolation effect. At a behavioral-psychological level, these variables may exert their effects by influencing the processes that construct a memory representation of the stimulus. At a neural systems level, they may influence processing carried out in the thalamo-corticoamygdaloid auditory pathway.

A developmental analysis of contextual fear conditioning.

Contextual fear conditioning by 18- and 23-day-old rats was compared in two training contexts, a transparent Plexiglas chamber or a black Plexiglas chamber. As measured by a conditioned defensive freezing response, older rats displayed more contextual fear than younger rats. At both ages conditioning was (a) stronger in the black chamber than in the clear chamber, (b) a nonmonotonic function of retention interval, with freezing being greater at the immediate and 24-hr retention interval than at the 10-min interval, and (c) preexposure to the context 24 hr before conditioning enhanced conditioned freezing observed at the 10-min retention interval. Additional experiments suggest that rats at both ages acquire independent representations of the visual and tactile features of the context. These results support Rudy and Morledge's (1994) hypothesis that contextual fear conditioning is mediated by both a short-term and a long-term memory system and that long-term memory for contextual fear requires the consolidation of a representation of the context. They challenge their view that there is a qualitative developmental difference in long-term memory processes between 18- and 23-day-old rats.

Influence of postprocessing curves on contrast-echographic imaging: preliminary studies.

The aim of this study was to evaluate the influence of postprocessing curves on the visual and quantitative enhancement of image brightness caused by the injection of a contrast agent. A fixed dose (0.45 ml/kg) of contrast agent EchoGen was injected into three dogs, and images of the kidney were investigated using one linear (A) and three nonlinear (B, C, D) postprocessing curves. Curve D gave the best gray scale images and was generally used for diagnostic imaging. Images were analyzed qualitatively in three dogs and quantitatively in one dog for brightness change caused by contrast agent injection. Visually the changes were most identifiable with curve C and least by curve D. Video intensity time curves reflected the qualitative changes. Peak contrast and area under the video density curve changed in the order curve D < curve B approximately curve A < curve C. Choice of the postprocessing curve can have a marked influence on the enhancement of image brightness by a contrast agent. Postprocessing curves optimized to display a wide range of echo levels may not always be an ideal choice for contrast sonography.

Sonographic enhancement of renal cortex by contrast media.

The purpose of this study was to evaluate whether a phase shift contrast agent could enhance the renal cortex. Four doses of the contrast agent EchoGen ranging from 0.25 to 0.65 ml/kg were injected intravenously in three healthy dogs. Images of the kidney were recorded on a videotape before and after each injection. The images were evaluated visually and were computer-analyzed for brightness change caused by the contrast agent. Marked changes in cortical brightness were observed at the doses of 0.45 and 0.65 ml/kg. At lower doses the changes in image brightness were significantly reduced but measurable. The brightness peaked at 65 +/- 9 seconds after injection and gradually decreased to the baseline value in approximately 12 minutes. The video density varied nonlinearly with dose, and at low doses its value drifted below the baseline. This is believed to be due to attenuation of echoes by the contrast agent. The results of this study indicate that the microbubbles formed by phase shift contrast media are sufficiently small and persist long enough to enhance sonographic images of the cortex. Contrast media whose effect is based on the phenomenon of phase shift permit enhancement of the gray scale characteristic of the kidney. The enhancements last up to several minutes and have strong potential to allow investigation of perfusion in kidney.

Noncardiogenic pulmonary edema in dogs and cats: 26 cases (1987-1993)

Medical records of 23 dogs and 3 cats treated for noncardiogenic pulmonary edema (NPE) resulting from airway obstruction (n = 8), cranial trauma (7), electric shock (7), or seizures (4) between 1987 and 1993 were reviewed. There were 18 purebred dogs, 5 mixed-breed dogs, 2 domestic shorthair cats, and 1 Siamese. Sixteen animals were male, and 10 were female. All but 7 were less than 1 year old. Time between the inciting incident and onset of respiratory tract signs ranged from minutes to several hours. Respiratory distress was the primary clinical sign for all animals with NPE resulting from airway obstruction, cranial trauma, or seizures, and for 2 of the 7 animals with NPE resulting from electric shock. The only consistent clinicopathologic abnormality was hyperglycemia, which was detected in 12 animals. Arterial blood gas partial pressures were measured in 11 animals; 10 were hypoxemic. On thoracic radiographs, the predominant pattern of pulmonary infiltration was alveolar. Symmetry of involvement, which was assessed by examining dorsoventral or ventrodorsal radiographic projections, could be determined for 23 animals. In 18, involvement was asymmetric, and in 13 of those 18, the right side was predominantly involved. On lateral radiographic projections, the caudodorsal quadrant of the lung field was involved primarily or as part of a diffuse distribution in all but 1 animal. Generally, animals with NPE resulting from airway obstruction had the greatest degree of radiographic involvement, followed in decreasing order, by animals with NPE resulting from cranial trauma, animals with NPE resulting from seizures, and animals with NPE resulting from electric shock. Overall, 9 animals died.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonography as a tool for monitoring in ovo chicken development. 1. Technique and morphological findings.

Preliminary studies were performed to develop a method for using real-time, B-mode ultrasonography (US) to directly image the internal morphology of the chicken egg and developing embryo. Different soft tissue interfaces will reflect US waves differentially. These reflected waves, or echoes are then converted into a two-dimensional image of internal morphology. A major limitation of diagnostic US is its inability to penetrate through gas or hard tissue (bone, shell) interfaces. Methodology development to overcome the acoustic obstacle presented by the eggshell and air cell constituted the initial part of the preliminary study. An acoustical window was achieved by creating a 2-cm fenestration through the large end of the eggshell, then filling the air cell with sterile saline. Morphological features of the yolk and embryo were recorded at 0, 2, 6, 9, 14, and 17 days of incubation. The second part of the preliminary study explores whether the acoustic window, once created, could then be closed, and if closed, whether egg viability could be maintained. A second concurrent trial was conducted with 32 eggs that were fenestrated, imaged, recorded, reclosed, and incubated. Two methods of closure were attempted: one using dialysis membrane and tape; the other using an eggshell allograft. Hatchability was partially retained with both window closure methods.