Increase In Freezing Research Articles

Effect of freeze\u2013thaw cycle on physical and mechanical properties and damage characteristics of sandstone

Rock deterioration under freeze–thaw cycles is a concern for in-service tunnel in cold regions. Previous studies focused on the change of rock mechanical properties under unidirectional stress, but the natural rock mass is under three dimensional stresses. This paper investigates influences of the number of freeze–thaw cycle on sandstone under low confining pressure. Twelve sandstone samples were tested subjected to triaxial compression. Additionally, the damage characteristics of sandstone internal microstructure were obtained by using acoustic emission (AE) and mercury intrusion porosimetry. Results indicated that the mechanical properties of sandstone were significantly reduced by freeze–thaw effect. Sandstone’ peak strength and elastic modulus were 7.28–37.96% and 6.38–40.87% less than for the control, respectively. The proportion of super-large pore and large pore in sandstone increased by 19.53–81.19%. We attributed the reduced sandstone’ mechanical properties to the degenerated sandstone microstructure, which, in turn, was associated with increased sandstone macropores. The macroscopic failure pattern of sandstone changed from splitting failure to shear failure with an increasing of freeze–thaw cycles. Moreover, the activity of AE signal increased at each stage, and the cumulative ringing count also showed upward trend with the increase of freeze–thaw number.

Influence of Freeze-Thaw Cycles and Binder Dosage on the Engineering Properties of Compound Solidified/Stabilized Lead-Contaminated Soils.

The solidification/stabilization (S/S) method is the usual technique for the remediation of soils polluted by heavy metal in recent years. However, freeze–thaw cycles, an important physical process producing weathering of materials, will affect the long-term stability of engineering characteristics in solidified contaminated soil. In addition, it is still questionable whether using large dosages of binders can enhance the engineering properties of solidified/stabilized contaminated soils. In this study, the three most commonly used binders (i.e., cement, quicklime, and fly ash), alone and mixed in different ratios, were thus added to lead-contaminated soil in various dosages, making a series of cured lead-contaminated soils with different dosages of binders. Afterward, unconfined compression strength tests, direct shear tests, and permeability tests were employed on the resulting samples to find the unconfined compressive strength (UCS), secant modulus (), internal friction angle (), cohesion (), and permeability coefficient () of each solidified/stabilized lead-contaminated soil after 0, 3, 7, and 14 days of freeze–thaw cycles. This procedure was aimed at evaluating the influence of freeze–thaw cycle and binder dosage on engineering properties of solidified/stabilized lead-contaminated soils. Results of our experiments showed that cement/quicklime/fly ash could remediate lead-contaminated soils. However, it did not mean that the more the dosage of binder, the better the curing effect. There was a critical dosage. Excessive cementation of contaminated soils caused by too much binder would result in loss of strength and an increase in permeability. Furthermore, it was found that UCS, , , and values generally decreased with the increase in freeze–thaw cycle time—a deterioration effect on the engineering characteristics of solidified lead-contaminated soils. Avoiding excessive cementation, 2.5% cement or quicklime was favorable for the value of while a 2.5% fly ash additive was beneficial for the value. It is also suggested that if the freeze–thaw cycle continues beyond the period supported by excessive cementation, such a cycle will rapidly destroy the original structure of the soil and create large cracks, leading to an increase in permeability. The results also showed that the contaminated soils with a larger dosage of binders exhibited more significant deterioration during freeze–thaw cycles.

Revisiting the autoconditioning hypothesis for acquired reactivity to ultrasonic alarm calls.

Rats emit 22 kHz ultrasonic vocalizations (USVs) in association with pain, fear, or distress. Whereas the capacity to produce USVs is innate, reactivity to them appears to require experience. Specifically, 22 kHz USVs fail to elicit freezing behavior in naïve laboratory rats. However, these "alarm calls" do elicit freezing in rats that previously experienced foot shocks. These findings led to the hypothesis that acquired reactivity is based on "autoconditioning"-learning in which self-generated 22 kHz USVs serve as Pavlovian cues that become associated with foot shocks. The current study tested the autoconditioning hypothesis by devocalizing rats through a unilateral transection of the recurrent laryngeal nerve (Experimental group). Subsequently, animals in both the Experimental and sham-operated Control groups received five unsignaled foot shocks. One or two days later, both groups were tested for USV-elicited freezing in a novel context. Recurrent laryngeal nerve transection failed to prevent or even diminish USV-elicited freezing. In fact, both groups showed large and comparable increases in freezing to USV presentations. A subset of Control animals failed to vocalize during conditioning, while some Experimental animals did vocalize during conditioning. Animals were therefore re-grouped and reanalyzed based on whether they vocalized during conditioning. Again, both groups showed large and comparable increases in USV-elicited freezing. These results disconfirm the essential tenet or prediction of the autoconditioning hypothesis. Alternative mechanisms for acquired reactivity to 22 kHz USVs are therefore considered.

The consequences of changes in the structure of loess as a result of cyclic freezing and thawing

The effects of freeze/thaw cycles change the structure of loess, which causes the deterioration of the specimen strength, leading to the occurrence of engineering disasters. In order to study the structure changes of loess body under freezing/thawing environment, taking Yanan city in Huangling County loess as the test object, this paper investigates the changes of the structure under different initial water content and different freezing/thawing cycles, and then analyzes the test results based on computer image processing technology, defines the damage variables, and quantitatively evaluates the damage state of the specimen. The results show that, with the increase of freezing and thawing times: the frost heaving force appears continuously; in the pores, the ice-water phase change volume expands; the local micropore stress concentration causes the specimen skeleton connection mode to change, from the surface–plane contact to the point–surface, point–point contact; the specimen structure is damaged by the number of fissures; and the total area changes. Therefore, this paper defines the porosity as a damage variable. As long as the damage variable and its evolution rule are known, the damage behavior of the material can be described, the damage variable increases with the increase of the freezing/thawing cycle, the specimen structure deteriorates, and the high density area of the specimen decreases, the low density area increases, and the integrity of the loess decreases. The continuous development of specimen porosity and fissure makes the migration channel change continuously, causing transfer channel elongation, widening, and new channel generation, resulting in the increase of ice generation.

Effects of Freezing and Thawing Cycle on Mechanical Properties and Stability of Soft Rock Slope

To explore the variation laws of mechanical parameters of soft rock and the formed slope stability, an experiment was carried out with collected soft rock material specimens and freezing and thawing cycle was designed. Meanwhile, a computational simulation analysis of the freezing-thawing slope stability was implemented. Key factors that influence the strength of frozen rock specimens were analyzed. Results showed that moisture content and the number of freezing-thawing cycles influenced mechanical parameters of soft rock significantly. With the increase of moisture content, cohesion of frozen soft rock specimens presents a quadratic function decrease and the internal friction angle shows a negative exponential decrease. The stability coefficient of soft rock material slope in seasonal freeze soil area declines continuously. With the increase of freezing and thawing cycle, both cohesion and internal friction angle of soft rock decrease exponentially. The higher the moisture content, the quicker the reduction. Such stability coefficient presents a negative exponential reduction. After three freezing and thawing cycles, the slope stability coefficient only changes slightly. Findings were finally verified by the filed database.

Uni-axial compressive stress-strain relation of recycled coarse aggregate concrete after freezing and thawing cycles

The mass loss, compressive strength, dynamic elastic modulus and stress-strain relationship of recycled coarse aggregate concrete under different cycles of freezing and thawing were investigated by comparison with normal concrete in the research reported in this paper. Forty-eight prism specimens with the size of 100mm×100mm×300mm and ninety-six cubic specimens with the size of 100mm×100mm×100mm were fabricated and tested. Test results show that, the mass loss of recycled coarse aggregate concrete decreased first then increased with the increase of freezing and thawing cycles; the relative cubic compressive strength and the relative dynamic elastic modulus of recycled aggregate coarse concrete decreased linearly with the increase of freezing and thawing cycles. The stress-strain curve of recycled aggregate concrete first ascended rapidly and then descended rapidly after exceeding the peak stress till to 1.5 times of the peak strain, finally turned into a slow decrease process. The ductility of recycled coarse aggregate concrete became worse with the increase of freezing and thawing cycles. Theoretic stress-strain curve of recycled coarse aggregate concrete after different cycles of freezing and thawing was presented and it was in good agreement with the experimental results from the other researcher.

Adaptations of enchytraeids to single and combined effects of physical and chemical stressors

Climate changes are expected to be greatest in the polar and temperate areas, where predictions point to an increase in freeze–thaw events and changes in precipitation, evaporation, and salinity patterns. These events will therefore affect biological activity of the soil compartment that may result in large impacts in ecosystem functioning and dynamics therein. This concern becomes even more important when considering the presence of contaminants due to intense anthropogenic activity, which may lead to synergistic or antagonistic effects and increase or decrease the impact on natural ecosystems. This paper reviews the effect of physical and chemical stressors on enchytraeids, with special emphasis on Enchytraeus albidus because most relevant studies have involved this species. E. albidus is a freeze-tolerant and euryhaline organism and several studies suggest that the absence of salinity may have important (negative) consequences not only for their freeze tolerance ability but also for their reproduction and capacity to deal with the presence of contaminants, such as metals and fungicides. Single and joint effects of constant freezing or freeze–thaw cycles and surfactants, such as 4-nonylphenol, affected negatively E. albidus freeze tolerance by decreasing the levels of cryoprotectants, membrane fluidity and interfering with cellular energy allocation. Because enchytraeids are of ecological significance in many important habitats along the Artic and cold-temperate environments, a reduction in abundance may result in disturbances of the decomposition processes in soils. The knowledge of the biological, physiological, and biochemical limits of enchytraeids to combined effect of physical and chemical stressors are crucial to provide a scientific basis for improving the setting of safety factors when extrapolating from controlled (and optimal) laboratory conditions to natural soil ecosystems. Therefore, there is a need to expand and evolve experiments that more realistically mimic the situation in the field, where interactions between factors are highly relevant. The synergistic or antagonistic interactions identified in the present review may also represent a stepping stone in the evaluation and possible inclusion of natural factors, like cold and salinity, in standardized enchytraeid test guidelines and consequently in risk assessment of chemicals.

THE INFLUENCE OF FREEZE–THAW CYCLES ON UNCONFINED COMPRESSIVE STRENGTH OF CLAY SOILS TREATED WITH LIME

There are several questions that are not well understood with respect to the long-term stability characteristics of lime-treated clay soils in spite of being used as a conventional technique to improve the properties of clay soils. This paper investigates the influence of freeze-thaw cycles on the unconfined compressive strength of kaolinite and illite mixed with silica sand. The results of this study show that an increase in the number of freeze-thaw cycles decreases the unconfined compressive strength. The role of lime increasing the soil strength is more significant in the case of samples exposed to freeze-thaw cycles compared to those not exposed to freeze-thaw cycles. The effect of freeze-thaw cycles on the dry unit weight and moisture content is insignificant compared to unexposed samples. The maximum volumetric changes occurred in the first freeze-thaw cycle, and afterward, the rate of volume change decreased with an increase in freeze—thaw cycles.

Alterations in affective behavior during the time course of alcohol hangover

Alcohol hangover is a temporary state described as the unpleasant next-day effects after binge-like drinking. Hangover begins when ethanol is absent in plasma and is characterized by physical and psychological symptoms. Affective behavior is impaired during the acute phase of alcohol intoxication; however, no reports indicate if similar effects are observed during withdrawal. The aim of this work was to study the time-extension and possible fluctuations in affective behavior during a hangover episode. Male Swiss mice were injected i.p. either with saline (control group) or with ethanol (3.8g/kg BW) (hangover group). Anxiety, fear-related behavior and despair phenotype were evaluated at a basal point (ZT0) and every 2h up to 20h after blood alcohol levels were close to zero (hangover onset). Also, anhedonia signs and pain perception disabilities were studied. Mice exhibited an increase in anxiety-like behavior during 4h and 14h after hangover onset when evaluated by the elevated-plus maze and open field test respectively (p<0.05). Fear-related behavior was detected in hangover animals by the increase of freezing and decrease of line crossings and rearing frequency during 16h after hangover onset (p<0.001). Depression signs were found in hangover mice during 14h (p<0.05). Hangover mice showed a significant decrease in pain perception when tested by tail immersion test at the beginning of hangover (p<0.05). Our findings demonstrate a time-extension between 14 and 16h for hangover affective impairments. This study shows the long lasting effects of hangover over the phase of ethanol intoxication.

Impact of snowpack decrease on net nitrogen mineralization and nitrification in forest soil of northern Japan

Winter climate change is an important environmental driver that alters the biogeochemical processes of forest soils. The decrease in snowpack amplifies soil freeze–thaw cycles and decreases the snowmelt water supply to soil. This study examined how snow decrease affects nitrogen (N) mineralization and nitrification in forest soil in northern Japan by conducting an in situ experimental snowpack manipulation experiment and a laboratory incubation of soil with different moisture, temperature and freeze–thaw magnitudes. For the incubation studies, surface mineral soil (0–10 cm) was collected from a cool-temperate natural mixed forest and incubated using the resin core method during the winter. In the field, there were two treatments: 50 and 100 % snow removal and control plots. The increase in the soil freeze–thaw cycle increased net N mineralization and marginally decreased the net nitrification in soil. The dissolved organic carbon (DOC) and DOC/DON ratio in soil increased with the decrease in snowpack especially during the snow melt period. These results suggested that the change in substrate quality by the increase in freeze–thaw cycles caused the significant enhancement of microbial ammonium production in soil. The lower soil moisture and higher gross immobilization of inorganic N by soil microbes may be maintaining the slow net nitrification and low nitrate leaching in freeze–thaw cycles with less snowpack. The results indicate that winter climate change would strongly impact N biogeochemistry through the increase in ammonium availability in soil for plants and microbes, whereas it would be unlikely that nitrate loss from surface soil would be enhanced.

Effect of freeze–thaw cycles on the molecular weight and size distribution of gluten

Freezing processing is widely used in food industry, but some key scientific issue is still unclear. In this paper, the effects of freeze–thaw cycles on the molecular weight, radius of gyration, free amino group content, free sulphydryl group content and molecular conformation of gluten were investigated by size-exclusion chromatography in conjunction with multi-angle laser light scattering (SEC–MALLS), spectrophotometry and atomic force microscopy (AFM). The results showed that during the freeze–thaw cycles (frozen at −18°C with cycling to 0°C for 12h and then back to −18°C per 10days) the molecular weight and radius of gyration of the gluten proteins decreased with the increase in freeze–thaw cycles, implying a depolymerisation in the high-molecular-weight fraction of the gluten. The free amino group content changed only slightly, and the free sulphydryl group content of the gluten increased from 9.8μmol/g for the control to 13.87μmol/g for the gluten stored for 120days and submitted to 12 times freeze–thaw cycling, indicating that the depolymerisation of the gluten during freeze–thaw cycling was due to the breakage of disulphide bonds. AFM images showed that the gluten chain formed a fibril-like branched network which was weakened with increasing freeze–thaw cycles storage time. Some aggregation of the gluten chains was also observed in the AFM images.

Effect of freeze–thaw cycles on durability and strength of very soft clay soil stabilised with recycled Bassanite

Abstract This paper investigates the influence of freeze–thaw cycles on the unconfined compressive strength and durability of very soft clay soil stabilised with recycled Bassanite, which is produced from gypsum wastes. The results of this study show that an increase in the number of freeze–thaw cycles decreases the unconfined compressive strength and durability index. The presence and increase in the Bassanite content in the soil mixture has a significant effect on the improvement of strength, volume change and durability of samples subjected to freeze–thaw cycles. The role of Bassanite in increasing the soil strength and durability is more significant in the case of samples exposed to freeze–thaw cycles compared to those not exposed to freeze–thaw cycles. The dry unit weight increased, and moisture content decreased with the increase of Bassanite content in the soil mixture. The effect of freeze–thaw cycles on the dry unit weight and moisture content is insignificant compared to unexposed samples. The maximum volumetric changes occurred in the first freeze–thaw cycle, and afterward, the volume changes decreased with an increase in freeze–thaw cycles. The use of recycled Bassanite obtained from gypsum wastes as a stabiliser material for very soft clay soil achieves the acceptable durability and strength against the effects of freeze–thaw cycles.

Fear memory for cue and context: Opposite and time-dependent effects of a physiological dose of corticosterone in male BALB/c and C57BL/6J mice

Highly emotional, stress reactive BALB/c mice secrete more corticosterone in response to fear conditioning than the low stress reactive C57BL/6J mice. Fear memory to cue and context differs between the strains. We injected corticosterone at physiological concentrations (250μg/kg i.p.) 30min before fear conditioning. Fear memory was tested 48 and 72h later. Although corticosterone had little effect on acquisition, it differentially affected fear memories in strain dependent manner: while BALB/c mice decreased freezing during cue and context episodes, C57BL/6J mice showed an overall increase in freezing. BALB/c mice showed extinction over days while no such extinction was seen in C57BL/6J mice. Evaluation of these data in the perspective of previous studies using the same fear conditioning paradigm with corticosterone injections 5min before or immediately after acquisition, revealed the impact of corticosterone during conditioning on the strength of fear memories. In C57BL/6J mice the overall increase in fear memories was higher if corticosterone was injected 30min pre acquisition than if injected 5min pre. In contrast, BALB/c mice showed reduced fear memories when injected 30min pre compared to that seen 5min pre acquisition. Both strains showed decreased fear memories compared to vehicle if corticosterone was administered immediately after acquisition. We conclude that the timing of physiologically relevant, stress levels increase in corticosterone is essential for the processing of aversive events and the formation of fear memories. However, the quality of the effect depends on the genetic background. These findings contribute to the understanding of the etiology of stress-related disorders.

Long‐term effects of differential early rearing in rhesus macaques: Behavioral reactivity in adulthood

Adverse early experiences are associated with a range of deleterious health outcomes in humans, including higher risk for affective disorders. Studies using a long-standing model of nonhuman primate model of early adversity have demonstrated that nursery-reared (NR) monkeys exhibit alterations in multiple aspects of biobehavioral development; however, few studies have evaluated the persistence of socioaffective behavioral changes through adulthood. We evaluated the effects of early rearing experience on adult animals' response to a well-validated assessment of anxiety-like behavior, the human intruder paradigm (HIP). We tested 22 rhesus monkeys who were either nursery-reared (NR) or reared with their mothers (mother-reared; MR). NR monkeys were inhibited in their behavior compared to MR monkeys, with reduced locomotion and exploratory behaviors. NR animals showed a marginal increase in freezing. Together these findings demonstrate that the consequences of differential infant rearing experience on socioaffective behavior persist into adulthood, with evidence of greater inhibition in NR monkeys.

Beam Test Research on Bond Behavior between Steel Bar and Concrete in Salt-Frost Environment

Salt-frost action is one of the main causes that induced the decrease of force resistance behavior of concrete structure in cold areas. By the freezing and thawing cycles of 0, 50, 100 and 200 times for the reinforcement concrete beam specimens in saline solution, the effects of freezing and thawing cycles on the bond behavior between steel bar and concrete are studied. The results show that: with the increase of freezing and thawing cycles, the bond strength and the bond stiffness trend to degenerate. The co-operating capacity between steel bar and concrete falls down. The ductility of the specimens reduces, and the bond failure presents brittle. The degradation speed of bond strength after salt-frosting is relevant to the size and stirrup ratio of specimens, the larger the specimen’s size is, and the higher the stirrup ratio is, The stronger the capacity of resisting freezing-thawing cycle is, the more slowly the bond property degenerate, the study using small specimens will probably underestimate the frost resistance of actual structure.

Sex-dependent effects of long-term oral methylphenidate treatment on spontaneous and learned fear behaviors

In previous studies, chronic low-dose methylphenidate (MPH) administration during early development has been shown to increase emotional responding in adulthood. However, most studies employed male subjects, which generally show enhanced fear relative to females in laboratory tests of anxious behaviors. The present study examined the sex-dependent effects of MPH treatment on innate and learned fear behaviors. Rats were treated for 4 weeks from periadolescence through early adulthood with oral MPH. In open field testing, females showed greater levels of activity than males, and MPH (5 mg/kg) decreased locomotion relative to control and 2 mg/kg treatment in both sexes. In contextual fear conditioning, females exhibited less freezing than males at all retention intervals. Both sexes treated with 5 mg/kg MPH showed increased fear to the shock context, although MPH treatment did not interfere with contextual discrimination in either sex. Upon reexposure to the shock context at 24 h, only females treated with 5 mg/kg MPH exhibited increases in freezing. MPH treatment did not disrupt extinction of contextual fear (48 h post-conditioning) in either sex. These findings illustrate subtle sex differences in the effects of prolonged MPH exposure on fear behaviors, and highlight the need to examine further the underlying mechanisms in both sexes.

Preparation and swelling behavior of polyvinyl alcohol physiological saline gel

Polyvinyl alochol(PVA) physiological saline gel was prepared using physiological saline solution of the polymer by freezing and thawing method. The influences of the concentration of PVA, freezing and thawing cycle times and solvent swelling media on the swelling properties of PVA saline gel were investigated. The result show that the electrolytical ions have great effect on the swelling behavior of PVA saline gel. The equilibrium swelling ratio of PVA saline gel in aqueous swelling media is larger than that in saline swelling media. Also, the equilibrium swelling ratios of PVA saline gel in aqueous and in saline media decrease with the increase of gel concentration and the increase of freezing and thawing cycle times. The decreasing speed of equilibrium swelling ratio with the increase of freezing and thawing cycle times of PVA gel in distilled water is faster than that in physiological saline. The swelling kinetic equation can sufficiently describe the swelling behavior of PVA physiological saline gel.

Ventral hippocampal muscimol disrupts context‐specific fear memory retrieval after extinction in rats

Research aimed at understanding Pavlovian fear memory extinction has yielded considerable insight into the conditions under which fear memories may become inhibited. After extinction, Pavlovian fear memory retrieval is context-specific. Fear memories are not expressed in the extinction context, but they are expressed in every other context. Research indicates that the dorsal hippocampus mediates the context-specific expression of fear memory, but the role of the ventral hippocampus in mediating this process is unknown. Insofar as the ventral hippocampus is involved in the acquisition and expression of both context and tone fear, we asked whether GABA systems in the ventral hippocampus mediate context-specific fear memory retrieval after extinction. Experiment 1 showed that ventral hippocampal inactivation with muscimol disrupted context-specific fear memory retrieval. Experiment 2 showed that rats infused with muscimol can discriminate a context in which they were shocked from a neutral context. Nonetheless, they do appear to have a mild impairment in this task. Experiment 3 showed that ventral hippocampal muscimol did not disrupt locomotor activity, but did result in a slight increase in freezing and grooming, an effect that cannot explain the context-specific retrieval deficit demonstrated in experiment 1. These data are consistent with a role for the ventral hippocampus in mediating context-specific fear memory retrieval.

Gel–sol transition of poly(vinyl alcohol) hydrogels formed by freezing and thawing

Poly(vinyl alcohol) (PVA) hydrogels were prepared by freezing and thawing. Freezing and thawing cycle ( n) was varied from 1 to 5. Gel–sol transition of the above hydrogels was measured using a highly sensitive differential scanning calorimeter (DSC). Phase transition of hydrogels was also investigated by simultaneous X-ray diffractometry (XRD) and DSC. Gel–sol transition temperature was observed in a temperature range from 55 to ca. 90 °C. Enthalpy of gel–sol transition was varied in a range from ca. 0.4 to 2 J g −1. Peak temperature and enthalpy of gel–sol transition increased with increasing n. By simultaneous measurement of X-ray diffractometry (XRD) and DSC, it is confirmed that no structural change is observed for either ice or water before and after gel formation. It is concluded that PVA molecules are aggregated during ice formation and hydrogen bonding is established between molecular chains. By increase of freezing and thawing cycle, residual free molecular chains are successively included in junction zones.

Effect of repeated methamphetamine pretreatment on freezing behavior induced by conditioned fear stress

The present study examined the effect of methamphetamine (MA) pretreatment on conditioned fear stress in male Wistar-King rats. Rats received MA or the vehicle according to the repeated escalating dose schedule (1.25, 2.5, 3.75, and 5 mg/kg SC × 2/every other day for a week). After a 5-day drug abstinent period, the rats were exposed to conditioned fear stress (exposure to an environment paired previously with foot shock). Repeated but not single MA pretreatment significantly increased conditioned freezing behavior, suggesting that rats previously exposed to chronic MA are hypersensitive to subsequent stress than control rats. Repeated MA treatment did not decrease basal dopamine or serotonin concentrations in the brain. Furthermore, coadministration of MK-801 (noncompetitive NMDA antagonist), amfonelic acid (dopamine reuptake inhibitor), or fluoxetine (serotonin reuptake inhibitor) with MA did not alter the enhanced freezing behavior. Taken together, it seems that MA-induced hypersensitivity to stress is not due to the neurotoxic effect of MA. Coadministration of nemonapride (D 2/3/4 antagonist) with MA prevented the MA-induced increase in freezing. These results suggest that D 2/3/4 receptors play an important role for MA-induced enhancement of fear or anxiety.