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PubMed1984

Effects of hippocampal stimulation on retention and extinction of one way active avoidance response in cats.

We found previously that hippocampal stimulation (HiSt) at 20 cps, 100 mikroA, applied jointly with a tone (500 Hz) CS in the course of retention test, improved the performance and retarded the extinction of one way active avoidance response (AAR) in cats. During this test failures to perform the AAR were not punished in all but two trials it the beginning of each session. The first experiment of the present studies demonstrated that - (i) the AAR facilitating the effect of HiSt might be prevented by m all electrolytic lesions made around the tips of the stimulating electrodes, (ii) large lesions of the hippocampus exerted little effect on the AAR acquisition, but the response was extinguished faster during the retention test. In the second experiment two response prevention trials (non-reinforced presentations of the CS with no possibility to make the AAR) were run at the beginning of each session after the end of training. In these conditions the HiSt resulted in a faster extinction of the AAR as compared with implanted unstimulated animals. Large lesions of the hippocampus had no effect on the extinction rate. We conclude that the facilitation of retrieval from memory may be responsible for the effects of HiSt on conditioned behavior.

Animals↗
PubMedDate not supplied

[Interaction between neurons of the visual and sensomotor areas of the neocortex during elaboration and extinction of a conditioned defense reflex].

Cooperation in activities of pairs of neurones situated in projection cortical areas of conditioned and unconditioned stimuli was studied in rabbits during intertrial intervals at different stages of elaboration and extinction of conditioned defensive response by means of auto- and crosscorrelation analysis of impulse fluxes. At the stage of generalization the number of pairs of neurones discharging in correlation was shown to increase a little (64 per cent) in comparison to that at the initial stage of conditioning (50 per cent) and pseudoconditioning (54 per cent). At the stage of stabilization and during extinction the number of pairs of neurones discharging in correlation decreased correspondingly to 34 and 32 per cent. Parallel analysis of correlation in neuronal discharges and simultaneously recorded electroencephalogram allowed to suppose that excitatory synchronizing influences and inhibitory cortical system play a great part in synchronization of activities of cortical neurones. Participation of these two systems is not the same at different stages of conditioning and extinction.

Animals↗
PubMed1978

Stimulus intensity effects of acute extinction of the CER in rats.

Two groups of 9 rats were trained in the conditioned emotional response (CER) consisting of suppression of food-motivated behavior as a consequence of the pairing of white noise with unavoidable shock. One group was trained and then extinguished with an 80 dB white noise value and the other with the 50 dB white noise intensity as the conditioned stimulus (CS). The CER acquisition was faster with the more intense CS, however, on the last training day, conditioned suppression reached the same asymptotic level in both groups. Then an acute extinction procedure was introduced, wherein the CS was presented only once a day and lasted continuously until the end of the session with no US presentation during this period. This procedure was repeated over several consecutive days. During the first prolonged CS action, CER extinction was more rapid in the 50- than in 80-dB group. However, on the next extinction day the amount of suppression was less with the more intense CS. The results were discussed in terms of CS intensity effects on learning and performance of the conditioned response.

Acoustic Stimulation↗
PubMed1981

Responses eliminated by noncontingent or negatively contingent reinforcement recover in extinction.

Autoshaped key pecking in pigeons was eliminated by presenting reinforcers only during non-CS periods (negatively contingent reinforcement) or in both non-CS and CS periods (noncontingent reinforcement). In either case, when all reinforcers were subsequently removed (simple extinction), responding recovered strongly (Experiment 1). Recovery in extinction occurred only if the CS was in a conditioned state when non-CS reinforcers were introduced (Experiment 2). Recovery from noncontingent reinforcement was virtually complete, since total responding in extinction after response elimination was not less than in control groups extinguished without an intervening response-elimination phase (Experiment 3). Recovery also occurred for nonautoshapable, instrumentally reinforced key pecking (Experiment 4). The hypothesis that recovery is due to reinstatement of the non-CS stimulus conditions of acquisition (absence of food) was not supported (Experiments 5 and 6). Other accounts of recovery are considered.

Animals↗
PubMedDate not supplied

[Dynamics of the space-time organization of cortical potentials upon extinction of electro-defensive conditioned reflexes in rabbits].

Spatio-temporal distribution of cortical potentials formed by non-reinforced conditioned stimuli in 10 unrestrained rabbits, was studied in the course of extinction of a conditioned defense ear-shaking reaction to flickering light, by means of comparison of successive electroencephalotopograms. The first signs of the extinction were characterized by a periodical reversion of the momentary sagittal gradient of values of simultaneous cortical potentials, going on with the frequency of light stimulation (4 cps). Under these conditions, the probability of motor reaction to light was reduced. At a late stage of the extinction the potential gradient reversion had lower frequency characteristics for passive wakefulness and drowsiness of the rabbits.

Animals↗
PubMedDate not supplied

[The evoked activity of the lateral hypothalamus during extinction and differential inhibition].

Character of interaction between symmetric points of the cat's auditory cortex (A1) and the lateral hypothalamus (HL) was determined by calculating Spearman correlation coefficients between averaged summed sound-evoked activity (AEP) of the structures before, during elaboration, extinction and restoration, as well as differentiation of food-procuring conditioned reflex and in the eating full. Close mutual co-tuning between the cortex and hypothalamus characteristic for stable conditioned reflex was found to disrupted during its extinction, elaboration of differentiation and fullness eat inhibition due to entire reduction of hypothalamic AEP and disappearance of correlated with negativity of HL AEP "doubling" of the first positive wave of A1 AEP. Hyperactivity stage, expressed at the beginning of extinction and at the end of differentiation, preceded inactivation of hypothalamic afferents during elaboration of conditioned inhibition. The stage of hyperactivity, initiated by the elevated emotional state of the animal, testifies to an important role of emotional brain structures in the process of internal inhibition. The stage of HL and A1 hyperactivity initiated by emotional stress of the animal and following HL inactivation during inhibition of the conditioned response point to an important role of emotional subcortical brain structures in the mechanisms of inhibitory conditioning.

Acoustic Stimulation↗
PubMed1994

The NMDA receptor antagonist MK-801 blocks acquisition and extinction of conditioned hypoalgesic responses in the rat.

The role of the N-methyl-D-aspartate (NMDA) receptor in Pavlovian conditioning of hypoalgesic responses in the hotplate apparatus was examined using the non-competitive NMDA antagonist MK-801. Either MK-801 or saline were administered before the training phase, test phase, or both, and MK-801 disrupted the acquisition and extinction but not the expression of conditioned hypoalgesic responses. All rats received counterbalanced injections of both MK-801 and saline after the training phase, therefore the learning decrements could not be attributed to a delayed, non-specific action of the drug. MK-801 did not augment paw-lick latencies on either the training or test days, indicating that its behavioural effects are not due to alterations in nociceptive sensitivity or motor performance. Similarly, MK-801's effects upon acquisition and extinction could not be attributed to state-dependent generalization decrement or impairments in processing of the hot-plate apparatus cues during training, as rats displayed normal hypoalgesic responses when tested with MK-801, and MK-801-treated animals displayed normal habituation of novelty-induced hypoalgesia in the hot-plate apparatus. These data suggest that the NMDA receptor system is involved in the acquisition and extinction, but not the expression of conditioned hypoalgesia and parallels the effects of NMDA receptor antagonists on the acquisition and expression of long-term potentiation (LTP) both in vitro and in vivo. It is plausible that an endogenous NMDA-mediated form of LTP plays a vital role in the acquisition and storage of aversive representations mediating conditioned hypoalgesic responses.

Animals↗
PubMed1999

Pinta in Austria (or Cuba?): import of an extinct disease?

BACKGROUND: Pinta, 1 of the 3 nonvenereal treponematoses, is supposed to be extinct in most areas in South and Central America, where it was once endemic. Only scattered foci may still remain in remote areas in the Brazilian rain forest, and the last case from Cuba was reported in 1975. OBSERVATION: A native Austrian woman, who had lived for 7 years in Cuba and was married to a Cuban native, developed a singular psoriasiform plaque on her trunk and several brownish papulosquamous lesions on her palms and soles during a visit to her home in Austria. Positive serological findings for active syphilis and the detection of spirochetes in the trunk lesion indicated early secondary syphilis, but an extensive case history and the clinical appearance fulfilled all criteria for pinta. CONCLUSION: The acquisition of a distinct clinical entity, pinta, in a country where it was formerly endemic but now is believed to be extinct raises the question of whether the disease is in fact extinct or whether syphilis and pinta are so similar that no definite distinction is possible in certain cases.

Adult↗
PubMed2004

Is telomere erosion a mechanism of species extinction?

According to the fossil record, 99.9% of all species that have ever lived on Earth have disappeared. However, only about 4% died out during the five mass extinction events, whereas it seems that the majority of species vanished without any signs of significant earthbound or extraterrestrial physical threats. Clearly, biological extinction mechanisms are by far the most important, but they are subject to serious limitations concerning the worldwide disappearance of species. In view of that, species-inherent mechanisms, which could lead to the worldwide destabilization of a population, might be worth reconsideration. Telomeres, the protective caps of chromosome ends, and the enzyme telomerase have been well preserved in plants and animals during evolution. In the absence of telomerase activity, telomeric DNA has been shown to shorten every time a cell divides. The concept of a mitotic clock based on the gradual erosion of telomeres is now generally accepted and has been confirmed in numerous plants and animals. Chromosomal rearrangements are the hallmarks of two completely different biological phenomena, cancer and speciation. In premalignant cells, gradual telomere erosion beyond a critical threshold is a well-known inducer of chromosomal instability. The species clock hypothesis, as presented here, is based on the idea of a tiny loss of mean telomere length per generation. This mechanism would not rapidly endanger the survival of a particular species. Yet, after many thousands of generations, critically short telomeres could lead to the weakening and even the extinction of old species and would simultaneously create the unstable chromosomal environment that might result in the origination of new species.

Biodiversity↗
PubMed1996

A comparison of measured and calculated single- and double-stranded oligodeoxynucleotide extinction coefficients.

The hyperchromicity resulting from exhaustive hydrolysis of several single-stranded and double-stranded oligodeoxynucleotides (ODN) with snake venom phosphodiesterase or snake venom phosphodiesterase/DNase I was used to measure the ODN's extinction coefficient at 260 nm. These extinction coefficients were compared with those obtained using nonempirical approximations. For the oligodeoxynucleotides investigated, the nonempirical approximations yielded extinction coefficients within 20% of the measured values.

Base Composition↗
PubMed2000

Extinction-like effects in normals: independence of localization and response selection.

An extinction-like effect in normal subjects was previously elicited when a low-salience target in the left was simultaneously presented with a highly salient distractor in the right visual hemifield, but not vice versa (Pollmann, 1996). We investigated in four experiments whether this extinction-like effect depends on (a) explicit localization and (b) response competition. It was found that the extinction-like effect could be replicated in the absence of both. In contradistinction to our previous results, low-salience distractors had no effect on pop-out target search. This showed that explicit spatial localization demands lead to low-salience distractor interference on pop-out search.

Adult↗
PubMed1995

Amino acid racemization on Mars: implications for the preservation of biomolecules from an extinct martian biota.

Using kinetic data, we have estimated the racemization half-lives and times for total racemization of amino acids under conditions relevant to the surface of Mars. Amino acids from an extinct martian biota maintained in a dry, cold (<250 K) environment would not have racemized significantly over the lifetime of the planet. Racemization would have taken place in environments where liquid water was present even for time periods of only a few million years following biotic extinction. The best preservation of both amino acid homochirality and nucleic acid genetic information associated with extinct martian life would be in the polar regions.

Amino Acids↗
PubMed1996

A model for evolution and extinction.

We present a model for evolution and extinction in large ecosystems. The model incorporates the effects of interactions between species and the influences of abiotic environmental factors. We study the properties of the model by approximate analytic solution and also by numerical simulation, and use it to make predictions about the distribution of extinctions and species lifetimes that we would expect to see in real ecosystems. It should be possible to test these predictions against the fossil record. The model indicates that a possible mechanism for mass extinction is the coincidence of a large coevolutionary avalanche in the ecosystem with a severe environmental disturbance.

Animals↗
PubMed1998

A mathematical model for Neanderthal extinction.

A simple mathematical homogeneous model of competition is used to describe Neanderthal extinction in Europe. It considers two interacting species, Neanderthals and Early Modern Men, in the same ecological niche. Using paleontological data we claim that the parameter of similarity, between both species, fluctuates between 0.992 and 0.997. An extension of the model including migration (diffusion) is also discussed; nevertheless, extinction of Neanderthal seems unavoidable. Numerical analysis of travelling wave solutions (fronts) confirms the extinction. The wave-front-velocity is estimated from linear analysis and numerical simulations confirm this estimation. We conjecture a mathematical formulation for the principle of exclusion between competitive interacting species (Gause).

Animals↗
PubMed2001

Are certain life histories particularly prone to local extinction?

Using stochastic simulations and elasticity analysis, we show that there are inherent differences in the risk of extinction between life histories with different demographies. Which life history is the most vulnerable depends on which vital rate varies. When juvenile survival varies semelparous organisms with delayed reproduction are the most vulnerable ones, while a varying developmental rate puts a greater threat to semelparous organisms with rapid development. Iteroparous organisms are the most vulnerable ones when adult survival varies. Generally, we do not expect to observe organisms in nature having variation in vital rates that produce a high risk of extinction. Given the results here we therefore predict that iteroparous organisms should show low variation in adult survival. Moreover, we predict that semelparous organisms should show low variation in juvenile survival and low variation in developmental rate. The effect of temporal correlation on extinction risk is most pronounced in organisms with semelparous life histories.

Animals↗
PubMed2002

Metapopulation models for extinction threshold in spatially correlated landscapes.

Simple analytical models assuming homogeneous space have been used to examine the effects of habitat loss and fragmentation on metapopulation size. The models predict an extinction threshold, a critical amount of suitable habitat below which the metapopulation goes deterministically extinct. The consequences of non-random loss of habitat for species with localized dispersal have been studied mainly numerically. In this paper, we present two analytical approaches to the study of habitat loss and its metapopulation dynamic consequences incorporating spatial correlation in both metapopulation dynamics as well as in the pattern of habitat destruction. One approach is based on a measure called metapopulation capacity, given by the dominant eigenvalue of a "landscape" matrix, which encapsulates the effects of landscape structure on population extinctions and colonizations. The other approach is based on pair approximation. These models allow us to examine analytically the effects of spatial structure in habitat loss on the equilibrium metapopulation size and the threshold condition for persistence. In contrast to the pair approximation based approaches, the metapopulation capacity based approach allows us to consider species with long as well as short dispersal range and landscapes with spatial correlation at different scales. The two methods make dissimilar assumptions, but the broad conclusions concerning the consequences of spatial correlation in the landscape structure are the same. Our results show that increasing correlation in the spatial arrangement of the remaining habitat increases patch occupancy, that this increase is more evident for species with short-range than long-range dispersal, and that to be most beneficial for metapopulation size, the range of spatial correlation in landscape structure should be at least a few times greater than the dispersal range of the species.

Algorithms↗
PubMed2004

Memory, reconsolidation and extinction in Lymnaea require the soma of RPeD1.

The central pattern generator (CPG) that drives aerial respiratory behaviour in Lymnaea consists of 3 neurons. One of these, RPeD1--the cell that initiates activity in the circuit, plays an absolutely necessary role as a site for memory formation, memory reconsolidation, and extinction. Using an operant conditioning training procedure that results in a long-term non-declarative memory (LTM), we decrease the occurrence of aerial respiratory behaviour. Since snails can still breathe cutaneously learning this procedure is not harmful. Concomitant with behavioural memory are changes in the spiking activity of RPeD1. Going beyond neural correlates of memory we directly show that RPeD1 is a necessary site for LTM formation. Expanding on this finding we show that this neuron is also a necessary site for memory reconsolidation and 'Pavlovian' extinction. As far as we can determine, this is the first time a single neuron has been shown to be a necessary site for these different aspects memory. RPeD1 is thus a key neuron mediating different hierarchical aspects of memory. We are now in a position to determine the necessary neuronal, molecular and proteomic events in this neuron that are causal to memory formation, reconsolidation and extinction.

Animals↗
PubMed1994

The interaction of inbreeding depression and environmental stochasticity in the risk of extinction of small populations.

Current population genetic and population dynamic models are inappropriate to judge the risk of extinction of small populations due to the combined effects of inbreeding, genetic drift, demographic stochasticity, and environmental stochasticity. Instead, a model based on the aggregated fates of individuals is advocated. The unequal distribution of resources over individuals is an essential part of this model. The model allows the incorporation of the mutation-selection dynamics of alleles leading to inbreeding effects and to fixation of slightly deleterious mutations as a result of genetic drift. The slightly deleterious mutations lower the conversion of resources into offspring. Whereas lethal alleles are rapidly eliminated by selection in small populations, the selection against mild deleterious effects depends strongly on effective population size and on the social system, that is, on the division of resources among individuals. The model allows for the study of rates at which processes occur while far away from equilibrium, which is crucial in understanding the extinction risks of threatened populations. One example of the latter is illustrated in simulations in which small populations become extinct between approximately 100 and 200 generations after they became small populations, due to a gradual accumulation of mildly deleterious mutations.

Alleles↗