Pre-exposure Group Research Articles

Latent Inhibition: Attention through Response-Contingent Shock in Rats

Abstract The inhibitory effect of repeated nonreinforced preexposure of a to-be-conditioned stimulus (latent inhibition) was studied in a 2 × 2 factorial design. In conditioning trials, response-contingent shock facilitated conditioning and had a relatively greater effect in stimulus preexposure groups than in control groups without preexposure. Response-contingent shock significantly decreased the response rate during conditioning trials, suggesting that responses other than arousal may account for the facilitative effects of shock on conditioning.

Aversive stimulus properties of morphine: evaluation using the drug preexposure conditioned taste aversion paradigm

Interpretation of the finding that positive-reinforcing drugs such as morphine also possess possible aversive properties, as revealed by their ability to induce a conditioned taste aversion (CTA), remains problematic. This issue was addressed in the present study using the drug preexposure CTA paradigm. Water-deprived rats were given noncontingent preexposure to one of three doses of morphine (2.5, 5.0, or 15.0 mg/kg) or drug vehicle. Subsequently, animals in each of these preexposure groups were presented with a novel 0.1% saccharin-flavored solution followed immediately by injection with one of the same three morphine doses or drug vehicle. This procedure was repeated at 5-day intervals until six saccharin presentations had been performed. Results indicated that while the three morphine doses were differentially potent as taste aversion-conditioning agents, they were equipotent as preexposure agents serving to disrupt CTA. These data suggest that preexposure to morphine's predominantly positive-reinforcing (and non-CTA-inducing) properties is sufficient for preexposure disruption of subsequent morphine CTA. A second experiment indicated that the minimal effective preexposure dose is between 0.3 and 1.25 mg/kg of morphine. It is suggested that an important commonality may exist between the discriminative stimulus properties of morphine as a CTA-inducing agent and as a positive reinforcer.

Effects of conditioned stimulus preexposure on human electrodermal conditioning

Two experiments investigated the effects of conditioned stimulus (CS) preexposure on Pavlovian differential conditioning and extinction of the skin conductance response. In both experiments, half the subjects were exposed to 20 presentations each of the CS+ and CS-, and the other half were exposed to control stimuli. CS duration was 8 sec. The unconditioned stimulus in Experiment 1 ( N= 48) was a 1000 Hz tone of 80 dB which signalled a reaction time requirement, and in Experiment 2 ( N = 48), it was a 1 sec burst of white noise at 105 dB. The results of Experiment 1 indicated that no-preexposure groups displayed more CS+ /CS- differentiation than preexposure groups during acquisition and more resistance to extinction, at least for the first interval anticipatory response. In addition, the results of Experiment 2 indicated that no-preexposure groups displayed more differentiation than preexposure groups in terms of the second interval anticipatory response. These data constitute a demonstration of the latent inhibition effect with human subjects, and imply that there is an intrinsic relationship between the orienting response and the conditioning process.

Cadmium acclimation and limb regeneration in the fiddler crab, Uca pugilator: Sex differences

Abstract After multiple autotomy in the fiddler crab, Uca pugilator, cadmium retards limb regeneration and ecdysis. To study the effects of pre-exposure to lower levels of cadmium, groups were pre-exposed to 0·1, 0·5 or 1·0 mg liter−1 for a week prior to autotomy. Crabs were then placed in 1·0 mg liter−1 for regeneration. Pre-exposed groups were compared with groups of crabs which had not been pre-exposed to Cd. It was found that males pre-exposed to 0·5 mg liter−1 regenerated more rapidly in 1·0 mg liter−1 than those not pre-exposed. This phenomenon was not observed in females, in which none of the three pre-exposure concentrations were able to accelerate regeneration in 1·0 mg liter−1 relative to those not pre-exposed. In the pre-exposed males in which regeneration was accelerated and was comparable to control levels, no accompanying decrease of time until molting was observed. Therefore, the protective effect of pre-exposure would seem to be on the regeneration processes themselves and is not dependent on the neuroendocrine system which controls the molt cycle.

Effects of metergoline and quipazine on locomotor activity of rats in novel and familiar environments

Many studies have investigated the effects on locomotor activity of various manipulations of the brain's serotonin (5-hydroxytryptamine, 5-HT) systems but the results have not been consistent. However, besides employing different techniques for manipulating brain 5-HT, previous studies have differed in size of apparatus, amount of apparatus pre-exposure and length of session. To test the possibility that apparatus familiarity interacts with the effects of 5-HT manipulations on locomotor activity, this variable was manipulated in groups of rats treated with the 5-HT receptor blocker, metergoline or the agonist, quipazine. Within each drug treatment group, 18 rats had prior experience with the activity monitoring photocell chambers (pre-exposed condition) and 18 were not previously exposed (novel condition); each condition was further subdivided into 3 dose subgroups ( n=6). Testing consisted of 3 30-min sessions with subgroups receiving metergoline (0, 2.5, 5.0 mg/kg) or quipazine (0, 2.5, 5.0 mg/kg) 30 min before. Results with metergoline treatment revealed no significant drug effect in the pre-exposed groups but a decrease in activity in the novel condition. Quipazine, on the other hand, had no significant effect in the novel condition but produced a time-dependent effect on activity in the pre-exposed condition. These results suggest that the effects on locomotor activity of compounds affecting 5-HT neurotransmission may interact with the familiarity of the test apparatus and with the duration of testing. Interexperiment differences in these variables may account for some of the inconsistencies previously reported.

Effects of quinuronium sulfate pre-exposure on hepatic excretion of sulfobromophthalein (BSP) as measured by isolated perfused rat liver.

Effects of quinuronium sulphate pre-exposure on hepatic excretion of sulfobromophthalein (BSP) as measured by isolated perfused rat liver was investigated. Seventeen rats were used in the study. Rats were divided into controls (Group 1, n = 5), low quinuronium treated animals (Group 2, n = 6), and high quinuronium treated animals (Group 3, n = 6) receiving 0, 1.5 or 2.3 mg quinuronium sulphate/kg intraperitoneally, respectively. Each animal was dosed 30 min. before sacrifice. After 30 min. of equilibrium perfusion, BSP was introduced and the experiment continued for 2 hours. Perfusate and bile were collected at designated time intervals and the volume of bile was noted. BSP in perfusate and bile was assayed. Half-life in minutes (t 1/2 +/- S.E.) of BSP disappearance from perfusate in groups 1, 2 and 3 were 12.5 +/- 1.8, 13.7 +/- 1.0 and 16.8 +/- 3.3, respectively. Group 2 and 3 rats had a significant decrease of BSP excretion in bile (P less than 0.01) compared to group 1 rats. Bile volumes decreased in both quinuronium pre-exposed groups of rats compared to control rats. These observations indicate that quinuronium affects liver function.

Vulnerability of developing brain not explained by cell number/cell size hypothesis

Prenatal and postnatal exposure to cocaine can affect the development and function of the central nervous system in offspring. It also produces changes in cocaine-induced dopamine release and increases cocaine self-administration and cocaine-induced conditioned place preference. Further, prenatal cocaine exposure involves greater risk for development of a substance use disorder in adolescents. Therefore, the objective of this study was to determine the effect of prenatal and postnatal cocaine exposure on locomotor sensitization in rats. A group of pregnant female Wistar rats were administered daily from day GD0 to GD21 with cocaine (cocaine pre-exposure group) and another group pregnant female rats were administered daily with saline (saline pre-exposure group). During lactation (PND0 to PND21) pregnant rats also received cocaine administration or saline, respectively. Of the litters resulting of the cocaine pre-exposed and saline pre-exposed pregnant female groups, only the male rats were used for the recording of the locomotor activity induced by different doses of cocaine (1, 5, 10, 20 and 40 mg/Kg/day) during the induction and expression of locomotor sensitization at different postnatal ages (30, 60, 90 and 120 days), representative of adolescence and adult ages. The study found that prenatal and postnatal cocaine exposure enhanced locomotor activity and locomotor sensitization, and such increase was dose- and age-dependent. This suggests that prenatal and postnatal cocaine exposure can result in increased vulnerability to cocaine abuse in young and adult humans.

Effects of prior exposure on conditioned taste aversion in the rat: androgen- and estrogen-dependent events.

The effects of preexposure and gonadal hormone manipulation on the extinction of a conditioned taste aversion were investigated. In Experiment 1, male rats were given one prior exposure to sucrose at some selected time (Days 4, 2, or 1) before a second exposure (Day 0) to sucrose and an LiCl injection. Controls received no prior exposure to sucrose but experienced only the sucrose + LiCl condition (Day 0). under the single exposure condition (Day 0) castrated animals extinguished the aversion faster than either testosterone-treated castrated rats or sham-operated rats. Sham-operated and castrated rats that had received preexposure treatment (Days 4, 2, or 1) were not distinguishable on a within-groups comparison of behavior but differed from their respective controls by exhibiting faster rates of extinction. However, in the testosterone-treated group only the Day 4 preexposure group exhibited a faster extinction rate. In Experiment 2, estradiol, dihydrotestosterone, and testosterone were studied by using only a Day 1 preexposure condition. The testosterone-treated group maintained the aversion for the longest period of time, followed by dihydrotestosterone-treated, sham, castrated, and estradiol-treated groups. It appears that estradiol augments the castration effect whereas dihydrotestosterone attenuates the effect. In Experiment 3, estradiol was administered alone or in combination with two different doses of dihydrotestosterone, and a Day 1 preexposure condition was used. The findings indicate that the outcome of behavior is dependent on the ratio of estradiol to dihydrotestosterone, with variations in this ratio resulting in fast (estrogen effect) to slow (androgen effect) rates of extinction.

The orienting reaction during human eyelid conditioning following preconditioning exposures to the CS.

Two experiments on latent inhibition are described in which the electrodermal and alpha blocking components of the orienting reaction (OR) were measured during human eyelid conditioning. In the first experiment the 16 Ss in the experimental group received 20 CS pre-exposure trials. The OR habituated on those trials but reappeared fully after the first conditioning trial. Therefore, after that trial there was no difference in OR amplitude with a no pre-exposure control group. The two groups did not differ in conditioning performance either. In the second experiment two groups of 25 Ss received an equal number of CS pre-exposures but one group was conditioned during the performance of a masking task. This time the reappearance of the OR was only observed in the no-task group. The results of both experiments are discussed in relation to Sokolov's theory on the facilitative effect of the OR on conditioning.

Neutralizing and complement-fixing antibody responses in pre- and post-exposure vaccinees to a rabies vaccine produced in human diploid cells

Two hundred and eighty-three individuals, who were believed to have been exposed to rabies, were immunized pre- and post-exposure according to different schedules with a β-propiolactone-inactivated and concentrated rabies vaccine prepared in a human diploid cell strain. The vaccine was well tolerated and no major side effects were observed after primary immunization with three to six doses. The dynamics of neutralizing and complement-fixing antibody formation and the persistence of antibodies in three different groups of 89 vaccinees are described. The groups were vaccinated (I) pre-exposure on days 0, 28 and 56 (13 individuals); (II) on days 0, 7 and 14 (46 individuals), respectively, and one group of 30 individuals was vaccinated post-exposure on days 0, 3, 7, 14, 30 and 90. High levels of neutralizing and complement-fixing antibodies were obtained in all three groups and they persisted in the pre-exposure group I as well as in the post-exposure group for at least 18 months after initiation of vaccination. With the vaccine under study therefore the post-exposure vaccination schedule appears to be satisfactory. The complement-fixation test, using a concentrated and purified virion antigen, was shown to be highly specific for the follow-up of rabies virus antibody formation in vaccination subjects. As the complement-fixing and neutralizing rabies virus antibodies were both associated with protection then the complement-fixation test could replace the laborious, time-consuming and expensive neutralization test for such studies.

The effects of pre-exposure to scopolamine on subsequent drug state discrimination.

This experiment was done to test the prediction that preexposure to a drug state would increase the discriminability of that drug state when used as a cue in a discrimination task. Eight rats were pre-exposed to scopolamine for 20 days and 8 rats were given saline injections. The drug pre-exposed animals acquired a drug state discrimination more quickly than the controls. A difference was also found between the generalization gradients for each group with the pre-exposed group showing a steeper generalization gradient.

The inhibitory effect of preexposed olfactory cues on intermale aggression in mice

To explore the effect of preexposure of olfactory cues on aggressive behavior, adult male mice, isolated for 14 days prior to the experiment, were preexposed for 10 days to one of 3 odors: (1) that of the opponent encountered in the test trial; (2) that of a strange mouse not subsequently encountered; and, (3) that of a neutral substance. The results show the greatest amount of aggression, as measured by latency to attack, accumulated attacking time, number of attacks and intensity of fighting, in the neutral preexposure group; an intermediate amount of aggression in the group preexposed to the irrelevant mouse odor; and the least amount of aggression in the group preexposed to the odor of the future-opponent mouse. Furthermore, preexposed animals in the third condition did not respond to attack by assuming the characteristic submissive posture. Results are discussed in terms of learned habituation to the pheromone which purportedly elicits aggression in the mouse.

Preferences of rats given early temporal visual patterns.

20 albino rats were reared with one of two different temporal light patterns (Dash-Dot-Dot; Dot-Dash-Dot) for 60 days and subsequently tested for preference between their rearing pattern or a different pattern. The results indicated that both groups tended to prefer the Dash-Dot-Dot pattern. However, the effects of being reared with a particular pattern for 60 days did not significantly increase the preference of the pre-exposed group for their pattern compared to the results of a group not exposed to this pattern.

Critical periods for early experience in transfer of perceptual learning.

It has generally been found that early experience with stimuli enhances the subsequent discriminability of these forms. To determine if critical periods exist for yielding this early experience effect, albino rats were given either early (20 to 55 days of age) or late (55 to 90 days of age) stimulus experience. A third pre-exposure group received experience with the to-be-discriminated forms from 20 to 90 days of age. Control animals, with no stimulus pre-exposure, were run on the discrimination problem at either 55 or 90 days of age. The basic early experience effect was replicated in that early experience with stimuli facilitated their subsequent discriminability. However, no evidence for critical periods of early experience was obtained.