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PubMed1997

Escape of human immunodeficiency virus from immune control.

Cytotoxic T lymphocytes (CTL) play a crucial role in the attempt to control infection with human immunodeficiency virus (HIV). Variation in epitopes recognized by CTL is common and frequently offers potential escape routes for mutant virus. Proof of escape, however, requires demonstration of increased frequency of virus particles or provirus that carry the escape sequence. There are now several recorded examples of virus variants that escape from CTL and are then selected. Most dramatic are those in which the CTL response has been dominated by CTL recognizing a single epitope that has suddenly changed, resulting in escape to fixation. This has been seen both early and late in the infection, leaving no doubt that escape occurs. Such escape is likely to be favored when the antiviral CTL response is oligoclonal and focused on a small number of immunodominant epitopes. The heterogeneous CTL response seen in many HIV-infected patients may result from successive waves of virus escape followed by new CTL responses specific for subdominant epitopes. Mutant virus can escape by several different routes, including failure of the mutated peptide to bind to the presenting HLA molecule and altered interactions with T cell receptors (TCR), including antagonism.

Acute Disease↗
PubMed1994

Atrial natriuretic factor significantly contributes to the mineralocorticoid escape phenomenon. Evidence for a guanylate cyclase-mediated pathway.

The mechanism underlying the mineralocorticoid escape phenomenon remains unknown. To assess the possible contribution of natriuretic peptides to mineralocorticoid escape, rats were injected with 5 mg deoxycorticosterone acetate for 3 d. Plasma atrial natriuretic factor (ANF) rose to twice basal levels and atrial ANF content decreased significantly by 24 h of treatment. This coincided with renal escape and with a significant increase in urinary cGMP excretion. Plasma ANF remained elevated and atrial ANF content continued to decline by 48 and 72 h while atrial ANF mRNA levels increased significantly only at 72 h. Plasma brain natriuretic peptide did not increase during escape although atrial brain natriuretic peptide mRNA levels increased significantly. Chronically administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled natriuretic peptide receptors, significantly and dose-dependently impaired the escape phenomenon. The highest dose of HS completely suppressed the increase in urinary cGMP. Despite the continued suppression, partial escape was observed by the end of the observation period. HS alone influenced neither plasma nor tissue or urine parameters. These findings show that despite activation of atrial ANF, blockade of the guanylate cyclase-coupled natriuretic peptide receptors impairs the ability of the kidney to escape the Na+ retaining effect of excess mineralocorticoid in a dose-dependent fashion. Later-acting, unknown mechanisms eventually come into play to mediate the escape phenomenon through a guanylate cyclase-independent pathway. Therefore, ANF of cardiac origin appears to be a major factor initiating mineralocorticoid escape through a guanylate cyclase-dependent pathway.

Animals↗
PubMed2003

High-speed video analysis of the escape responses of the copepod Acartia tonsa to shadows.

The copepod Acartia tonsa exhibits a vigorous escape jump in response to rapid decreases in light intensity, such as those produced by the shadow of an object passing above it. In the laboratory, decreases in light intensity were produced using a fiber optic lamp and an electronic shutter to abruptly either nearly eliminate visible light or reduce light intensity to a constant proportion of its original intensity. The escape responses of A. tonsa to these rapid decreases in visible light were recorded on high-speed video using infrared illumination. The speed, acceleration, and direction of movement of the escape response were quantified from videotape by using automated motion analysis techniques. A. tonsa typically responds to decreases in light intensity with an escape jump comprising an initial reorientation followed by multiple power strokes of the swimming legs. These escape jumps can result in maximum speeds of over 800 mm s(-1) and maximum accelerations of over 200 m s(-2). In A. tonsa, photically stimulated escape responses differ from hydrodynamically stimulated responses mainly in the longer latencies of photically stimulated responses and in the increased number of power strokes, even when the stimulus is near threshold; these factors result in longer escape jumps covering greater distances. The latency of responses of A. tonsa to this photic stimulus ranged from a minimum of about 30 ms to a maximum of more than 150 ms, compared to about 4 ms for hydrodynamically stimulated escape jumps. Average response latency decreased with increasing light intensity or increasing proportion of light eliminated. Little change was observed in the vigor of the escape response to rapid decreases in visible light over a wide range of adaptation intensities.

Animals↗
PubMed2002

Submarine escape trials 1999-2001--provision of medical support.

Since the early 1960s all Royal Navy submarines have been fitted with an escape system comprising a single escape tower (SET) and submarine escape immersion suit (SEIS). This system enables escape from a submarine at a depth of 180 metres (1.9 MPa) provided that the submarine compartment is at a pressure of no greater than 1 bar (0.1 MPa). Due to a variety of causes which may include flooding and leakage of high pressure air systems it is the highly probable that the submarine compartment will be at a pressure in excess of 1 bar (0.1 MPa) at the time of the escape. To investigate and determine what constitutes a 'safe' maximum escape depth from any given compartment pressure (the safe to escape curve), a purpose built chamber complex, the Submarine Escape Simulator (SES) has been constructed at the QinetiQ, formerly the Defence Evaluation and Research Agency (DERA), Alverstoke site. Unlike escapes from a submarine where once released from the submarine the escapee's ascent can not be halted, within the SES it is possible to halt the ascent phase. This article describes the systems and procedures developed to enable medical support to be provided rapidly to a subject at any stage of the compression decompression profile. The article also provides details of the results to date that have been obtained from this work.

Decompression↗
PubMedDate not supplied

Submarine escape breathing air. A review and analysis of animal and human experiments by the Royal Navy.

The contribution of the Royal Navy to the development of modern submarine escape by free ascent, breathing air, from 1945 to the present time, is described. Much of the work is unpublished. Experiments in which goats were exposed to simulated escape pressure profiles while breathing air from 90 m to 300 m are described. The gradual testing of human subjects during such escape profiles is also reported up to real escapes by subjects from submarines lying at 180 m. Thus escapes are now feasible from almost anywhere on the continental shelf. Possible techniques of even deeper escape, i.e. hyperoxygenated air breathing, oxygen breathing, propulsion + retropulsion of the escaper, drogues + pressure retaining (2 atm abs) escape suits are briefly considered. The figures illustrate the Royal Navy series of animal and human, simulated and real escapes. Table I gives full details on human testing. Tables containing details of all goat exposures can be obtained from author.

Animals↗
PubMed1989

Electrical stimulation of the medial prefrontal cortex supports both 'pure reward' and 'reward-escape' behavior in rats.

In female Sprague-Dawley rats, 8 of 12 medial prefrontal cortex (MPFC) sites that yielded criterion self-stimulation behavior supported only self-stimulation, i.e. were 'pure reward' in type. The remaining 4 sites supported behavior to escape from experimenter-administered stimulation of the same parameters as well, i.e. were 'reward-escape' in type. 'Pure reward' and 'reward-escape' sites in the MPFC were distinguished by both the magnitude and temporal form of the escape response functions generated, and by the prevalence of 'pounce-back', a vigorous and repetitive barpressing during the 3-s MPFC stimulation-escape interval produced by an effective barpress. The finding that both 'pure reward' and 'reward-escape' patterns of behavior can be elicited by stimulation of the MPFC provides a basis for further assessment of similarities and differences in medial prefrontal cortical and lateral hypothalamic (LH) 'reward' systems. It is suggested that 'reward-escape' in the MPFC may be mediated by the activity of 'reward' neurons which respond to stimulus offset, rather than by a secondary aversive process as is proposed to underlie 'reward-escape' in the LH.

Animals↗
PubMed1990

Thyroparathyroidectomy produces a progressive escape deficit in rats.

Abnormal thyroid status and affective disorders have been associated in the human clinical literature. It has recently been shown that pretreatment with thyroid hormone can prevent escape deficits produced by inescapable shock in an animal analogue of depression. In this report we provide evidence that hypothyroid status can produce an escape deficit in rats. While sham-operated rats improved their performance on a simple escape task over three days of testing, thyroparathyroidectomized rats showed a pronounced decrease in their responses. Markov transition analysis was used to obtain conditional probabilities of escaping given a prior escape or failure to escape for the two groups. This analysis shows that the structure of the data set may be similar for the two groups. These results suggest that if intact rats learn to escape, then hypothyroid rats may learn not to escape.

Affect↗
PubMed1982

Stimulus change influences escape performance: deficits induced by uncontrollable stress and by haloperidol.

Exposure to uncontrollable foot-shock or treatment with haloperidol was found to disrupt subsequent escape behavior. Performance among naive mice, as well as mice that had been exposed to inescapable shock or treated with haloperidol could be enhanced by either interrupting the shock train during escape testing or by presentation of a novel stimulus. The effectiveness of these treatments were dependent on the time at which the change in stimulation occurred. That is, shock interruption or cue presentation just prior to escape being possible enhanced performance, but the same manipulation several seconds prior to escape being possible had only a limited effect. In addition, the time of cue termination also influenced escape behavior. When cue offset coincided with or followed successful escape a performance enhancement was evident, but when cue offset occurred several seconds prior to escape, performance was not affected. It was suggested that inescapable shock and haloperidol treatment hinder performance by disrupting response maintenance. Shock interruption and novel cue presentation minimize disturbances of escape performance by altering the course of the decline of shock-elicited activity.

Animals↗
PubMed2003

Fos-like immunoreactive neurons following electrical stimulation of the dorsal periaqueductal gray at freezing and escape thresholds.

Electrical stimulation of the dorsal regions of the periaqueductal gray (PAG) leads to defensive reactions characterized as freezing and escape responses. Until recently it was thought that this freezing behavior could be due to the recruitment of neural circuits in the ventrolateral periaqueductal gray (vlPAG), while escape would be mediated by other pathways. Nowadays, this view has been changing mainly because of evidence that freezing and escape behaviors thus elicited are not altered after lesions of the vlPAG. It has been suggested that there are at least two pathways for periaqueductal gray-mediated defensive responses, one involving the hypothalamus and the cuneiform nucleus (CnF) which mediates responses to immediate danger and another one involving the amygdala and vlPAG which mediates cue-elicited responses, either learned or innate. To examine this issue further we measured Fos protein expression in brain areas activated by electrical stimulation of the dorsolateral PAG (dlPAG) at the freezing and escape thresholds. The data obtained showed that freezing-provoking stimulation caused increases in Fos expression in the dorsomedial PAG (dmPAG), while escape-provoking stimulation led to increases at both dmPAG and dlPAG. Surprisingly, neither escape- nor freezing-provoking stimulations altered Fos expression in the central nucleus of amygdala (CeA). Escape-provoking stimulation caused increased Fos expression in the ventromedial hypothalamus (VMH), dorsal premammilary nucleus (PMd) and in the cuneiform nucleus. Significant increases in Fos labeling were found in the dmPAG and PMd following freezing-provoking stimulation. Therefore, the present data support the notion of a neural segregation for defensive behaviors in the dorsal columns of PAG, with increased Fos expression in the dmPAG following freezing, while dlPAG is affected by both freezing and escape responses. dlPAG, CnF, VMH and PMd are part of a brain aversion network activated by fear unconditioned stimuli. The present data also suggests that the defensive responses generated at the dlPAG level do not recruit the neural circuits of the vlPAG and CeA usually activated by conditioned fear stimuli.

Animals↗
PubMed2002

Rapid evolution of escape ability in Trinidadian guppies (Poecilia reticulata).

Predators are widely assumed to create selection that shapes the evolution of prey escape abilities. However, this assumption is difficult to test directly due to the challenge of recording both predation and its evolutionary consequences in the wild. We examined these events by studying natural and experimental populations of Trinidadian guppies, Poecilia reticulata, which occur in distinct high-predation and low-predation environments within streams. Importantly, in the last two decades several populations of guppies have been experimentally introduced from one type of predatory environment into the other, allowing measurements of the consequences of change. We used this system to test two hypotheses: First, that changes in predatory environments create phenotypic selection favoring changes in escape ability of guppies, and second, that this selection can result in rapid evolution. For the first test we compared escape ability of wild caught guppies from high- versus low-predation environments by measuring survival rates during staged encounters with a major predator, the pike cichlid Crenicichla alta. We used guppies from three streams, comparing two within-stream pairs of natural populations and three within-stream pairs of an introduced population versus its natural source population. In every comparison, guppies from the high-predation population showed higher survival. These multiple, parallel divergences in guppy survival phenotype suggest that predatory environment does create selection of escape ability. We tested our second hypothesis by rearing guppies in common garden conditions in the laboratory, then repeating the earlier experiments using the F2 generation. As before, each comparison resulted in higher survival of guppies descended from the high-predation populations, demonstrating that population differences in escape ability have a genetic basis. These results also show that escape ability can evolve very rapidly in nature, that is, within 26-36 generations in the introduced populations. Interestingly, we found rapid evolutionary loss of escape ability in populations introduced into low-predation environments, suggesting that steep fitness trade-offs may influence the evolution of escape traits.

Animals↗
PubMed2006

Behavioral analyses of wind-evoked escape of the cricket, Gryllodes sigillatus.

The wind-evoked escape behavior of the cricket Gryllodes sigillatus was investigated using an air puff stimulus. A high velocity air puff elicited the escape behavior in many crickets. The crickets tended to escape away from the stimulus source, but the direction was not accurately oriented 180 degrees from the stimulus. After bilateral cercal ablation, only a few crickets showed wind-evoked escape behavior, and their response rates did not increase even 19 days after ablation. Therefore, information on air motion detected by cercal filiform hairs is essential for triggering wind-evoked behavior. After unilateral cercal ablation, the 81.3% response rate of intact crickets decreased to 16.5%, that is, it decreased to almost 20% that of intact crickets. One week after unilateral cercal ablation, the response rate recovered to more than 60% that of intact crickets. However, the accuracy rate of the escape direction of G. sigillatus showed no change even immediately after the unilateral cercal ablation. Therefore, both cerci are not necessarily required to determine the escape direction. The behavioral characteristics of wind-evoked escape of G. sigillatus are compared with those of another species of cricket, Gryllus bimaculatus. The two species of cricket employ different strategies for wind-evoked escape.

Animals↗
PubMed2000

Molt-related and size-dependent differences in the escape response and post-threat behavior of the American lobster, Homarus americanus.

Videotaped recordings of adult lobsters of different molt stages were analyzed. The escape response of adults was compared with that of juveniles recorded in an earlier study. Juvenile lobsters always respond to a threat with escape behavior irrespective of their molt stage, but in adults the probability of eliciting a response was a function of molt stage: more hard-shelled (intermolt stage C) and (premolt stage D) animals tailflipped than did soft-shelled (postmolt stages A and B) animals. The number, frequency, and duration of tailflips, and the average distance swum by animals in each molt stage were measured for the entire escape response, for the initial power swim, and for the subsequent swims. These measurements were used to compute several parameters: velocity, acceleration, force, and work; average distance traveled in a tailflip for each kilogram of body weight (distance/kg/tailflip); and average distance traveled for each bodylength (distance/bodylength). Among adults, intermolt (stage C) lobsters traveled significantly farther and faster than postmolt animals (stages A and B). Among juveniles, late postmolt (stage B) animals traveled farther. Among adults, although the total number of tailflips and the duration of the response were not significantly different among molt stages, the number of tailflips/second (frequency) and distance traveled/kg/tailflip were greater for intermolt animals. In juvenile intermolts, however, frequency and distance/kg/tailflip were markedly lower than in the premolt stages. Although values were lower than intermolts and premolts, postmolt adults sustained their swimming frequency, distance/kg/tailflip, and distance/bodylength for the entire escape distance (as did postmolt juveniles). These parameters then dropped off sharply for both adult and juvenile intermolt and premolt animals in the second half of the escape distance. Post-threat behaviors reveal that stage D animals have the highest aggression index and often attack the presented stimulus, whereas stage A animals are the least likely to approach the stimulus and typically back away in a non-aggressive posture. Thus, although effects of the molt cycle on adult and juvenile escape behavior are similar in some ways, other physical characteristics of adults, such as weight, allometry, and physiology, seem to become important in determining the likelihood of escape behavior and the characteristics of the escape swim in each molt stage.

Animals↗
PubMed2000

Escape flights of yellowhammers and greenfinches: more than just physics.

Wintering birds increase their fat reserves throughout the day, and impaired escape performance is often considered to be an important cost of fat reserves. Since lifting a larger mass requires more energy, if birds escape at maximum power output, an increase in mass will impair the escape flight. In this study we did not find support for mass-dependent escape performance for yellowhammers, Emberiza citrinella, and greenfinches, Carduelis chloris, with natural daily mass increases of 7-8%. This suggests either that the birds were not performing at maximum output at dawn, when light, or that maximum power output was higher at dusk, when heavy. Either way, the birds seemed to be able to put more effort into their escape flight when heavier. In both species, when alarmed, birds took off significantly faster and at a steeper angle than when not alarmed. Yellowhammers escaped at a higher speed and angle than greenfinches, and reacted faster to the predator model. This suggests that predator escape is more than just Newtonian physics, and may be influenced by behavioural, as well as morphological, adjustments. Different species may have evolved different responses to predation risk. Our results seem to be in disagreement with recent ideas about mass-dependent predation risk. However, to build up reserves, birds have to increase exposure time, which increases predation risk. This cost may be more important than impaired escape performance when relatively small, daily, changes in body mass are considered. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Studies of renal aquaporin-2 expression during renal escape from vasopressin-induced antidiuresis.

In animal models of the syndrome of inappropriate antidiuresis (SIADH), sustained administration of vasopressin and water results in free-water retention and progressive hyponatremia for several days, which is then followed by escape from the vasopressin-induced antidiuresis. With the onset of vasopressin escape, water excretion increases despite sustained administration of vasopressin, allowing water balance to be re-established and the serum sodium to be stabilized at a steady, albeit decreased, level. Studies from our laboratories have investigated whether this escape phenomenon can be attributed to altered regulation of aquaporin water channels. After four-day pre-treatment with 1-deamino-[8-D-arginine]-vasopressin (dDAVP) by osmotic minipump, rats were divided into control (continued dDAVP) and water-loaded (continued dDAVP plus a daily oral water load) groups. A significant increase in urine volume in the water-loaded rats was observed by the second day of water loading, indicating escape from antidiuresis. The onset of escape coincided temporally with a marked decrease in renal aquaporin-2 protein (measured by semi-quantitative immunoblotting), which began at day 2 and fell to 17% of control levels by day 3. In contrast, there was no decrease in the renal expression of aquaporins 1, 3, or 4. The marked suppression of whole kidney aquaporin-2 protein was accompanied by a concomitant suppression of whole kidney aquaporin-2 mRNA levels. Immunocytochemical localization and differential centrifugation studies demonstrated that trafficking of aquaporin-2 to the plasma membrane remained intact during vasopressin escape. Additional studies have indicated that the observed down-regulation of aquaporin-2 expression also occurs in the renal cortex as well as the inner and outer medullas, and can be reversed simply by water restriction despite maintenance of hyponatremia. Our results therefore suggest that escape from vasopressin-induced antidiuresis is attributable, at least in part, to a vasopressin-independent and osmolality-independent decrease in aquaporin-2 water channel expression in the renal collecting duct. Similar mechanisms likely contribute to the phenomenon of escape from antidiuresis seen clinically in patients with SIADH as well.

Animals↗
PubMed1978

Regional replication of the bacterial chromosome induced by derepression of prophage lambda. IV. Escape synthesis of gal operon in phage 82.

Derepression of prophage lambda in E. coli strain K12 results in constitutive synthesis of the enzymes directed by the nearby bacterial operon, gal (escape synthesis). Phage 82 fails to cause escape synthesis despite that it lysogenizes the strain K12 at the site identical to that of lambda on the host chromosome. The reason for the observed difference between 82 and lambda is studied in the light of the recent finding that escape synthesis in lambda-lysogen is closely associated to phage-promoted replication of bacterial chromosome contiguous to the prophage including gal operon (escape replication). Excision-defective mutants from 82, 82int or 82xis, do initiate escape synthesis, suggest that the prophage 82 is normally excised too quickly after induction to allow sufficient escape replication. In support of this, much more DNA hybridizable to bacterial DNA contained in lambdagal accumulates after induction if 82int than after induction of 82. Studies with various hybrid phages between 82 and lambda have suggested: 1. The occurrence of gal escape synthesis depends on the nature of the region between b2 and N in the lambda map. 2. Regions of the 82 genome on both sides of the attachment site contribute independently to prevent gal escape synthesis. Implications of these results are discussed with regard to the factors involved in the prophage excision.

Chromosomes, Bacterial↗
PubMed1994

Adrenergic, purinergic, and endothelial mediators and modulators of norepinephrine-induced mesenteric autoregulatory escape.

We evaluated the effects of potential factors in autoregulatory escape from norepinephrine-induced vasoconstriction in rat anterior mesenteric artery. We determined mesenteric artery blood flow velocity with a pulsed Doppler, sonic flowmeter, and systemic arterial blood pressure with a transducer. A 4-min norepinephrine infusion (0.125-1.0 x 10(-8) M/min) intravenously evoked a dose-dependent, initial vasoconstriction that was followed by rapid escape of blood flow toward or above the control value during sustained norepinephrine administration. Neonatal capsaicin treatment enhanced vasoconstrictor responses to norepinephrine but failed to affect escape parameters. Propranolol decreased norepinephrine-induced escape dose dependently. Adenosine deaminase attenuated escape, and the combination of this enzyme plus propranolol nearly abolished escape from norepinephrine-induced vasoconstriction. Methylene blue also diminished autoregulatory escape. These findings suggest that norepinephrine-induced autoregulatory escape involves simultaneous beta-adrenoceptor, purinergic, and endothelial mediation. Norepinephrine-evoked mesenteric vasoconstriction appears to involve predominantly alpha 2-adrenoceptors and is modulated by peptidergic sensory nerves and adenosine.

Adenosine Deaminase↗
PubMed1992

Those cheating rats: male and female rats use odor trails in a water-escape "working memory" task.

Three-month-old Sprague-Dawley rats were trained on a working memory win-stay (spatial delayed matching-to-sample) water-escape task with the escape platform location the same for all subjects on a given trial, a procedure that maximizes the buildup of an odor trail to the escape platform. In subsequent tests during which the location of the escape platform varied randomly between subjects, the rats, especially the females, while continuing to perform above chance level, made increased errors. Varying the platform location between subjects eliminated odor trail as a nonambiguous cue for locating the escape platform. In a second experiment females performed better than males on a reference memory odor trail discrimination task which involved following the path of like-gender "pathmaker" rats to the escape platform. The relatively poor use of odor trails by the males was associated with a high frequency of choosing a preferred choice section or returning to the choice section selected first on the immediately preceding trial (perseveration). Collectively, the two experiments demonstrate that rats can use either working memory or odor trails to locate an escape platform in a water maze, and that they, especially females, will use odor trails in a working memory task if odor trails are available. Clearly, the location of the escape platform should be varied randomly between subjects in tests of working memory.

Analysis of Variance↗
PubMed2024

Quantification of escape from X chromosome inactivation with single-cell omics data reveals heterogeneity across cell types and tissues.

Several X-linked genes escape from X chromosome inactivation (XCI), while differences in escape across cell types and tissues are still poorly characterized. Here, we developed scLinaX for directly quantifying relative gene expression from the inactivated X chromosome with droplet-based single-cell RNA sequencing (scRNA-seq) data. The scLinaX and differentially expressed gene analyses with large-scale blood scRNA-seq datasets consistently identified the stronger escape in lymphocytes than in myeloid cells. An extension of scLinaX to a 10x multiome dataset (scLinaX-multi) suggested a stronger escape in lymphocytes than in myeloid cells at the chromatin-accessibility level. The scLinaX analysis of human multiple-organ scRNA-seq datasets also identified the relatively strong degree of escape from XCI in lymphoid tissues and lymphocytes. Finally, effect size comparisons of genome-wide association studies between sexes suggested the underlying impact of escape on the genotype-phenotype association. Overall, scLinaX and the quantified escape catalog identified the heterogeneity of escape across cell types and tissues.

X Chromosome Inactivation↗