Conditioned opioid release in ten-day-old rats.

Ten-day-old rats, for whom an orange scent predicted morphine injections at 5 days of age, exhibited a marked preference for orange that was fully naltrexone reversible. Moreover, such rats, when smelling orange during a heat-escape task, exhibited a higher pain threshold than control rats. Together, these findings suggest that the orange odor in conditioned rats caused a release of endogenous opioids that both sustained choice behavior and modulated pain systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned and unconditioned fear inhibition in rats.

Conducted 3 experiments with a total of 74 male Fisher344 rats in which tone stimuli suppressed avoidance responding despite the fact that they had never been administered to the Ss previously. These same stimuli attenuated the conditioned emotional response suppression of operant responding for water reinforcement. The stimuli thus appear to have unconditioned fear inhibitory properties. These unconditioned effects were compared with conditioned ones. It is suggested that results of some conditioning procedures (e.g., extinction below zero) may depend upon the unconditioned properties of the stimuli used as conditioned stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned odor potentiation of startle in rats.

An odor previously paired with shock was shown to be an effective stimulus for potentiating the startle response in rats; (Experiments 1 and 2). This effect required more than 1 odor-shock pairing (Experiment 3), was relatively long lasting (Experiment 4), and was specific to the odor previously paired with shock (Experiment 5). The implications of these findings for the startle probe procedure and for neural models of learning and memory based on results obtained with that procedure are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Endogenous cholecystokinin reduces vocalization in isolated 10-day-old rats.

Devazepide, the cholecystokinin (CCK) receptor blocker, markedly and specifically affected the behavior of 10-day-old rats isolated from mother and siblings. Whereas intraoral infusions of milk or fat, which cause CCK release, calmed infants, that is, reduced levels of ultrasonic vocalization, devazepide fully blocked this reduction. Devazepide did not reduce the elevated pain limen caused by milk or fat infusions. These data parallel earlier findings obtained with administration of exogenous CCK and implicate endogenous CCK in the maintenance of infant steady state and calm. The possibility that CCK contributes to the normal development of mother–infant affectional systems is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned insulin secretion and meal feeding in rats.

Previous researchers have reported that rats placed upon a feeding regimen such that they receive only 2 hrs of food/day (meal-fed rats) develop hyperinsulinemia at the time of the day associated with feeding, even in the absence of food. Controls fed ad lib show no such response. In the 3 experiments reported here, the 74 meal-fed Charles River rats had elevated insulin levels at only the specific time of the day associated with feeding, and the increment of insulin at that time could be eliminated with atropine. The 58 free-feeding controls, on the other hand, always had higher insulin levels than the meal-fed rats, did not have an elevation of insulin at the time of the day that the meal-fed rats normally ate, and had insulin values that were unaffected by atropine. Further experimentation showed that hyperinsulinemia could become associated with arbitrary stimuli always associated with eating for meal-fed rats. It is concluded that the hyperinsulinemia of meal-fed rats associated with their feeding time is a learned response. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipation of rewarding electrical brain stimulation evokes ultrasonic vocalization in rats.

Adult rats emit increased rates of 50-kHz ultrasonic vocalizations (USVs) before receiving social and pharmacological rewards. This study sought to determine whether anticipation of rewarding electrical stimulation of the brain (ESB) would also elicit these vocalizations. In Experiments 1 and 2, rats showed increased 50-kHz USVs before receiving experimenter-delivered ventral tegmental area (VTA) and lateral hypothalamic (LHy) ESB on a fixed time 20-s schedule. In Experiments 3 and 4, rats increased their rate of 50-kHz USVs in response to cues that predicted the opportunity to self-stimulate the VTA or LHy. Interestingly, unexpected termination of either type of ESB evoked 20-kHz, rather than 50-kHz, USVs. In Experiment 5, a cue that predicted daily 1-hr feeding sessions increased 50-kHz USVs, whereas a cue that predicted footshock decreased 50-kHz USVs. These effects could not be explained simply by changes in locomotor activity or general arousal. Together, these findings support the hypothesis that short 50-kHz USVs may selectively index a state of reward anticipation in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversions and neophobia in rats with hippocampal lesions.

In Exp I extensive hippocampal lesions retarded, but did not prohibit, the conditioning of a strong taste aversion to physiological saline (the CS) in 16 male Holtzman albino rats when illness (the UCS) was induced by apomorphine injection 15 min following ingestion of the saline. In Exp II hippocampal lesions reduced the aversiveness of novelty in a drinking fluid for 21 thirsty Ss. It is suggested that the mild impairment of taste aversion learning in Ss with hippocampal lesions was not the result of destruction of mnemonic mechanisms that serve to span the long CS-UCS interval but rather that the reduced intensity of the aversion resulted from a lesion-altered neophobic disposition that weakened the saliency of the novel flavor CS. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned brain-stimulation reward attenuates the acoustic startle reflex in rats.

The acoustic startle reflex (ASR) in rats is attenuated by a light paired with food or, in humans, by "pleasant" pictures. Rats were trained to barpress for lateral hypothalamus (LH) stimulation. ASR amplitudes were then measured at 4 intensities, with or without a light. Control rats that did not receive brain-stimulation reward (BSR) showed initially lower ASR amplitudes than did rats exposed to BSR, but both groups responded similarly with or without light. Next, experimental rats were given BSR in the presence of light but not in its absence. After conditioning, ASR amplitudes were reduced, and ASR thresholds were raised by a mean of 2.6 dB in the light but remained at preconditioning levels without light. No such change was found for control rats or rats with placements outside the LH. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned cyclosporine effects but not conditioned taste aversion in immunized rats.

In 2 experiments, the development of adjuvant arthritis (an experimental autoimmune disease) was inhibited by exposing rats to a flavored solution that had previously been paired with injections of cyclosporine (an immunodepressive drug) compared with rats with the same history but exposed to a flavored solution that had previously not been paired with drug injections. In contrast to earlier experiments on conditioned cyclophosphamide effects, rats did not avoid the taste that had previously been paired with drug administration. Thus, conditioned immunopharmacologic effects were not confounded with taste aversion. These observations are interpreted as reflecting an associative learning process that affected the development of an autoimmmune disease. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned and unconditioned behavioral-cognitive effects of a dopamine antagonist in rats.

Many drugs need to be taken multiple times to achieve a therapeutic effect. Researchers have identified several mechanisms to account for the slow onset of drug action, including drug accumulation and structural changes induced by drugs. This article provides an example of a new mechanism to account for this change in drug action. Stimuli that accompany drug administration may come to evoke conditioned responses (CRs), and these CRs may be the basis for changes in drug efficacy. Specifically, this research shows that a dopamine antagonist, pimozide, changes response rates through the direct action of the drug but changes time perception through the CRs elicited by drug administration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned fear and postshock emotionality in vicious circle behavior of rats.

Gave 64 female hooded Long-Evans rats 15 shock-escape trials in a runway (1 trial/day), followed by 30 extinction trials. Half of the Ss received regular extinction treatment, while the others received a punishing shock if they ran. The Ss' level of activity (or freezing) before the trial was used as an index of conditioned fear. In acquisition, these shocked Ss were less active before the trial than 56 additional Ss receiving identical treatment, but without shock. During extinction, punished Ss both ran longer and showed less pretrial activity. This directly supports the vicious circle hypothesis that punishment for running maintains the fear motivating the running. When postshock emotionality was induced before a trial, it tended to suppress vicious circle behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned and unconditioned suppression as a function of age in rats.

Examined age differences in a cer paradigm. 72 sprague-dawley albino rats were treated at 15, 22, 35, or 70 days of age in 1 of 3 ways: (a) paired tone-light and shock trials; (b) unpaired tone-light and shock trials; or (c) no treatment at all. Subsequent tests in a suppression of drinking situation show that only the 15-day old ss failed to acquire a cer, as measured by the difference between paired and unpaired groups. Older ss extinguished more quickly than younger ss and also habituated an unconditioned suppression response more quickly. Results are related to thompson's model, and to the literature on the development of learning abilities. (french summary) (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned aversions and their memories in 5-day-old rats during suckling.

In 4 experiments, 216 5-day-old Sprague-Dawley rat pups equipped with tongue cannulae placed either 2 mm rostral or 4–6 mm caudal to the intermolar eminence received sweet or salty solutions while suckling. This ingestion was followed by intraperitoneal injections of .3 M LiCl or isotonic saline. Ss with anterior cannulae took in considerably less fluid than controls when tested 5 or 16 days later. A series of control groups demonstrated that this acquired aversion was associative in nature. Ss with posterior cannulae did not form the association. It is suggested that the failure of 5-day-old Ss with posterior cannulae to form associations while suckling was not due to the prevention of conditioning by the act of suckling but instead resulted from the failure of the fluid to reach anterior taste receptors when injected into the posterior oropharynx, where the nipple normally empties its contents. Findings are discussed in terms of the transfer of information obtained during suckling to feeding and drinking during and after weaning. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned hypoglycemia.

Conducted a pilot study with 32 male Charles River rats to determine the amount of glucose which, when simultaneously administered with insulin, would reliably prevent hypoglycemia. This amount was then used in an experiment in which 24 rats were given ip injections of saline, insulin, glucose, or glucose plus insulin as the UCS in a classical conditioning paradigm. It was found that a change of blood glucose need not occur on the conditioning trials in order to obtain successful conditioning of a hypoglycemic response; rather, an increase of insulin was all that was necessary. An explanation of conditioned hypoglycemia as the logical response of glucoregulatory centers of the CNS in proposed. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduction of dopamine synaptic activity: Degradation of 50-khz ultrasonic vocalization in rats.

Vocal deficits are prevalent and debilitating in Parkinson's disease. These deficits may be related to the initial pathology of the nigrostriatal dopamine neurons and resulting dopamine depletion, which contributes to dysfunction of fine motor control in multiple functions. Although vocalization in animals and humans may differ in many respects, we evaluated complex (50-kHz) ultrasonic mate calls in 2 rat models of Parkinson's disease, including unilateral infusions of 6-hydroxydopamine to the medial forebrain bundle and peripheral administration of a nonakinesia dose of the dopamine antagonist haloperidol. We examined the effects of these treatments on multiple aspects of the acoustic signal. The number of trill-like (frequency modulated) 50-kHz calls was significantly reduced, and appeared to be replaced by simpler (flat) calls. The bandwidth and maximum intensity of simple and frequency-modulated calls were significantly decreased, but call duration was not. Our findings suggest that the nigrostriatal dopamine pathway is involved to some extent in fine sensorimotor function that includes USV production and complexity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tumor growth in rats: Conditioned suppression of food intake and preference.

In 4 experiments, 140 male syngeneic Wistar-Furth rats were implanted with tumors or received control incisions. Ss with experimental tumors developed strong aversions to a novel diet they consumed during tumor growth. Aversions were not evident when the food available during tumor growth was familiar laboratory chow. The impact of learned food aversions on tumor anorexia was evidenced by more severe and long-lasting hypophagia in tumor-bearing Ss maintained on a novel diet than in those maintained on laboratory chow. Thus, when a diet was a salient target for the development of learned aversions, the aversions that developed to it could make substantial contributions to the overall syndrome of tumor anorexia. Frequent changes of the diet offered to tumor-bearing Ss were associated with milder anorexia than that produced by a constant diet. Results suggest that, the prevention of learned food aversions, or the repeated replacement of aversive foods, can minimize the impact of learned food aversions and attentuate anorexia in tumor-bearing animals. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Female presence during postejaculatory interval facilitates penile erection and 22-kHz vocalization in male rats.

During the postejaculatory interval (PEI), male rats exhibit prolonged immobility, 22-kHz vocalization, and penile erections. To test whether females modulate these behaviors, females were removed after the first or second ejaculation or left in the test chamber. Female presence during the PEI delayed exploratory behavior and facilitated vocalization and erection. Female stimulation of vocalization is consistent with the hypothesis that vocalization has a communicative function, not just a thermoregulatory one. The timing of the effect of females on erection suggests that males are sexually arousable well before they resume copulation. Therefore, erection may be better than vocalization as an indicator of the male's sexual refractoriness. The findings also challenge the conventional view that the PEI comprises absolute and relative sexual refractory periods marked, respectively, by the presence and absence of 22-kHz vocalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned place preference for mating is preserved in rats with pelvic nerve transection.

Female rats exhibit a conditioned place preference (CPP) for a context paired with mating. The present experiment tested the hypothesis that the activation of the pelvic nerve mediates the reinforcing effects of mating for female rats. Rats underwent bilateral pelvic nerve or sham transection and then received paced mating, nonpaced mating, or the control treatment during a CPP procedure. Pelvic nerve transection did not affect the CPP for paced or nonpaced mating. In tests of paced mating behavior, contact-return latencies following intromissions were significantly shorter in rats with pelvic nerve transection than they were in rats with sham transections. These results show that the pathway conveying the reinforcing effects of mating stimulation does not depend on the integrity of the pelvic nerve, but that activation of the pelvic nerve contributes to the display of paced mating behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversion in lean and obese rats with ventromedial hypothalamic knife cuts.

Assessed the development of a conditioned taste aversion (CTA) in 60 female Sprague-Dawley rats made hyperphagic with parasagittal knife cuts in the ventromedial hypothalamus (VMH). Ss were water deprived and presented with a .1% saccharin solution paired with injections of either LiCl or NaCl. In Exp I, VMH Ss tested at a nonobese weight level did not differ from sham-operated controls in acquisition and extinction of the CTA. In Exp II, moderately obese VMH Ss displayed a stronger CTA than did sham-operated controls as evidenced by slower extinction. A 2nd group of obese VMH Ss given an amount of LiCl equivalent to that given to the controls also displayed retarded extinction of the CTA. Results reflect an obesity-induced suppression in appetitive motivation. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of gonadal hormones and sexual behavior on ultrasonic vocalization in rats: I. Treatment of females.

Ultrasonic vocalizations were measured when male Long-Evans rats were placed with ovariectomized females that had experienced various hormonal and behavioral treatment. In Exp I, 18 males were tested with females in each of the following conditions: nonestrous (OVX), estrogen treated (E), estrogen and progesterone treated (EP), and estrogen and progesterone treated and given 2 intromissions from a stud male prior to testing (EPI). Control conditions included clean cage (CL) and cage soiled by an estrous female (SOI). The treatments differed in effect on rate and maintenance of vocalization, in the order of greatest to least: EP, E, EPI, and OVX (equal), SOI, and CL. In tests in which males produced a high rate of vocalization, some males with short intromission latencies shifted from the normal 50-kHz pulse to a 22-kHz pulse. In Exp II, the effect of the female's vocalization and movement on the rate of and latency to vocalization was measured. 21 males were presented with each of the following stimulus conditions: estrous female with red light (EP), estrous female without red light (EP dark), estrous anesthetized female (EP anes), and nonestrous anesthetized female (OVX anes). Effects on vocalization of various treatments were in descending order: EP and EP-dark (equal), EP anes, and OVX anes. Data suggest that the 50-kHz vocalizations constitute a graded response influenced by the female's hormonal and sexual condition. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)