Conditioned suppression of humoral immunity in the rat.

180 Charles River rats were conditioned by pairing consumption of a novel sodium saccharin drinking solution with the effects of an ip injection of 75 mg/kg cyclophosphamide, an immunosuppressive drug. Five and 10 days after conditioning, an experimental group (Group CS) was reexposed to the saccharin drinking solution. Control Ss (Group CSo) were conditioned but were not reexposed to saccharin. On Days 10, 15, or 25 after conditioning, Ss were injected ip with sheep erythrocytes, and independent subgroups were sampled for hemagglutinating antibody titer 4, 6, or 8 days later. Antibody titers 4 days after immunization were lower than values observed 6 and 8 days after immunization, and CS Ss had an attenuated antibody response. There were no significant differences between Group CSo and a group of placebo-treated Ss, but CS Ss had lower antibody titers than placebo-treated animals 4, 6, and 8 days after antigenic stimulation. Results suggest that reexposure to a CS may have long-lasting effects, and provide further documentation of conditioned immunopharmacologic effects and the impact of behavioral factors in modifying immunologic reactivity. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned suppression with no CS-US contingency in the rat.

Presented CS to rats licking sucrose after 1 of several off-the-baseline Pavlovian defense conditioning procedures. 2 random procedures in which there was no CS-UCS contingency were constructed by programing CS and UCS on independent random schedules which had either a long or a short variable inter-CS interval (VITI). Ss were 48 naive male Sprague-Dawley rats in Exp. I and II and 20 rats from Exp. II in the 3rd experiment. Because the CS took up more of the session in the short VITI procedure, it contained more CS-UCS pairings and produced CS-elicited suppression of licking. Suppression occurred with neither the long VITI group nor with shock alone controls. Conditioning was all-or-none after both classical and random procedures. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned satiety in the rat.

In 3 experiments with a total of 72 male albino Wistar or Sprague-Dawley rats, liquid or solid diets differing in carbohydrate or triglyceride content were presented 1 at a time to each S once or twice a day. For a given S, each caloric density consistently had a particular odor and/or taste. Results show the size of the feeding bout on the dilute nutrient became larger than that on the more concentrated nutrient after several pairs of presentations. This differentiation was at least partly controlled by the oral cues which had been paired with nutrient differences. Results were attributable to acquired differences in the development of feeding inhibition during the meal, and not to original or acquired differences in initial rate of feeding or in the preference for 1 diet over the other in 2 stimulus tests. (33 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned aversion to distinct environmental stimuli resulting from gastrointestinal distress.

In Exp I, 40 male Sprague-Dawley-derived rats subjected to apomorphine-induced malaise following a 2-min placement in a black compartment avoided this black compartment significantly more than 10 controls in a choice situation. The degree of aversion, however, was substantially reduced when Ss were provided water (or saccharin) in the black compartment during conditioning and testing. Ss learned to suppress consumption of fluid in the black compartment. In Exp II, 10 Ss were made ill in the black compartment. Later, when drinking saccharin (or saline) preceded placement in the black compartment, Ss learned to suppress consumption of that fluid. The black compartment had become a conditioned reinforcer for taste aversion. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned suppression of distress calls in imprinted ducklings.

Exposed 20 Peking and 6 Khaki Campbell newly hatched ducklings to imprinting procedures. The subsequent filial reactions were studied using a classical conditioning paradigm. Exp. I revealed that a previously neutral stimulus can become a conditioned suppressor of distress calling as a consequence of pairing it with the imprinted stimulus. If the presentation of the imprinted stimulus was, however, omitted or delayed, or if it preceded rather than followed the presentation of the neutral stimulus, the effect was not obtained. Exp. II utilized a differential conditioning procedure to investigate the capacity of imprinted Ss to come under discriminative control. 2 differently colored lights were used as stimuli; 1 was consistently followed by presentation of the imprinted stimulus, while the other was never followed by its presentation. Only the former stimulus came to suppress distress calling. The importance of the apparent interaction between classical conditioning and imprinting is noted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned opioid activity in the rat fetus.

Classical conditioning in the rat fetus (Embryonic Day 20) was investigated in 4 experiments. Reexposure to a CS (sucrose), after 3 pairings with an unconditioned stimulus (UCS; milk), reduced fetal facial wiping in a bioassay of perioral cutaneous responsiveness. Reduced responsiveness was evident only in Ss that received paired presentations of the CS and UCS and cannot be attributed to habituation, sensitization to the CS, or protracted effects of UCS exposure during conditioning trials. Fetuses attended to the chemosensory, not the tactile, qualities of the sucrose infusion during CS reexposure. Changes in fetal responsiveness resulted from conditioned activity in the endogenous opioid system, specifically at mu opioid receptors. These data confirm that the rat fetus is capable of exhibiting a conditioned opioid response in utero. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the automatic nature of phobic fear: Conditioned electrodermal responses to masked fear-relevant stimuli.

Normal Ss (n?=?64) were exposed either to pictures of snakes and spiders or to pictures of flowers and mushrooms in a differential conditioning paradigm in which one of the pictures signaled an electric shock. In a subsequent extinction series, these stimuli were presented backwardly masked by another stimulus for half of the Ss, whereas the other half received nonmasked extinction. In support of a hypothesis that suggests that nonconscious information-processing mechanisms are sufficient to activate responses to fear-relevant stimuli, differential skin conductance response to masked conditioning and control stimuli was obvious only for Ss conditioned to fear-relevant stimuli. These results were replicated in a 2nd experiment (n?=?32), which also demonstrated that the effect was unaffected by which visual half-field was used for stimulus presentation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Paradoxical autonomic responses to aversive stimuli in the developing rat.

The goals of this research were to determine (1) the change in heart rate elicited by aversive auditory stimuli in the laboratory rat at different ages and (2) the autonomic origins of those changes at each age. The results of the 1st 2 experiments showed that aversive white noise stimuli elicited cardiac deceleration in preweanling (16-day-old) rats and cardiac acceleration in weanling (23-day-old), periadolescent (30-day-old), and adult (60-day-old) rats. Subsequent experiments showed that (1) the decrease in heart rate elicited by the noise stimulus in preweanling rats was mediated by parasympathetic activation of the heart, (2) the stimulus-elicited increase in heart rate elicited by the noise in periadolescent rats was mediated by parasympathetic withdrawal of the heart, and (3) the noise-induced increase in heart rate in adult rats was primarily mediated by sympathetic activation of the heart. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned suppression of proboscis extension in Drosophila melanogaster..

Conducted a modified replication of J. Médioni and G. Vaysse's (1975) observations on conditioned inhibition of proboscis extension in the fruit fly. Médioni and Vaysse reported that the inhibition of the proboscis-extension response can be conditioned over trials if such proboscis extensions are punished by applying an aversive stimulus to the foreleg tarsi. In the present study, quinine was used as the aversive stimulus, and Ss were adult virgin female D. melanogaster of the Berlin wild-type strain. Ss in the experimental group showed a consistent decrement (62%) in the number of proboscis extensions over trials relative to the random control group, thus replicating Médioni and Vaysse's basic observations of conditioning, using a different strain of flies and a modified conditioning apparatus. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned hypoglycemia: A mechanism for saccharin-induced sensitivity to insulin in the rat.

Conducted 5 experiments with male Sprague-Dawley-derived rats (N = 123). Saccharin ingestion potentiated insulin-induced mortality, and this potentiating effect could be accounted for by the hypothesis that the taste of saccharin elicits hypoglycemia as a CR. Saccharin ingestion alone produced hypoglycemia in the same experiemtal context. As predicted by the conditioning hypothesis, long-term access to saccharin extinguished the hypoglycemic response. The hypoglycemic response could be elicited by stimuli, either gustatory or olfactory, which were paired with intragastric glucose administration. Results support the conditioning account of the potentiating effect of saccharin on insulin-induced mortality and suggest that hypoglycemia occurs as a CR in anticipation of feeding. (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 adrenocortical steroid elevations in the rat

An illness-induced taste aversion paradigm was used to condition an elevation in plasma corticosterone level. Rats were injected with cyclophosphamide 30 min after consuming a novel saccharin drinking solution. Plasma corticosterone levels were measured before conditioning to determine unconditioned steroid levels and 3 and 6 days after training when conditioned and nonconditioned animals were provided with the saccharin solution or plain water, or were left deprived. The pairing of saccharin and cyclophosphamide was effective in inducing a passive avoidance response. There were no differences between the steroid levels of conditioned and nonconditioned animals supplied with plain water or those that remained deprived, although deprivation increased corticosterone levels. Nonconditioned rats presented with saccharin had steroid levels that did not differ from control values. Conditioned animals presented with saccharin showed an elevation in steroid level which was significantly greater than that observed in any other group. Comparable results were obtained when LiCl was used as the unconditioned stimulus.     

Conditioned stimulus intensity and acquired alimentary aversions in the rat.

Studied 188 male Long-Evans hooded rats. Three groups were made ill following the ingestion of 1 of 3 intensities of salt taste and then were tested several times for aversions to each of the 3 intensities after this single training trial, yielding a 3 by 3 factorial design. ANOVA from this design revealed a significant positive effect on degree of aversion of both training intensity and testing intensity, and a significant interaction between these 2 intensity variables. The interaction was further analyzed into a component implying a multiplicative relationship between training intensity and testing intensity in determining strength of aversion, and into a component interpreted as indicating a decrement of the aversion when tested with intensities other than the training intensity. Results suggest a lawfulness of stimulus–response relationships comparable to those found in studies employing more typical conditioned responses. Previous conditioning studies, however, have demonstrated only the effect of conditioned stimulus intensity on "performance" (testing intensity effect), not on "learning" (training intensity effect). (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adrenalectomy reduces peripheral neural responses to gustatory stimuli in the rat.

The adrenalectomized rat, because of excessive body sodium loss, has been an important animal model for studying the physiological mechanisms underlying salt ingestion. To investigate the mediation by peripheral taste responsivity of changes in salt intake, multiunit responses of the chorda tympani nerve to various concentrations of NaCl, KCl, and LiCl, hydrochloric acid, and quinine hydrochloride were recorded from 18 adrenalectomized or intact male Sprague-Dawley rats. To control for a generalized decrease in sensory sensitivity, recordings from this auriculotemporal nerve to tactile stimulation of the pinna were also performed. There were no group differences in amplitude of the integrated neural responses to tactile stimulation. The largest decrease in gustatory responsivity occurred for suprathreshold concentrations of NaCl and LiCl. Data are discussed with reference to possible mechanisms underlying this neural alteration and the role that reductions in salt taste responsivity play in mediating increases in salt intake. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autonomic origins of cardiac responses to nonsignal stimuli in the rat.

Heart rate (HR) and blood pressure responses to nonsignal auditory stimuli were measured in rats after saline or pharmacological blockade of the sympathetic or vagal innervation of the heart. HR responses to the low-intensity stimulus were predominantly deceleratory, whereas responses to the high-intensity stimulus were more notably acceleratory. Both stimuli elicited a biphasic pressor–depressor response, although potential baroreflex influences accounted for only a small proportion of the HR response variance. Deceleratory responses to the low-intensity stimulus were eliminated by scopolamine and thus appeared to be predominantly of vagal origin. Acceleratory response to the high-intensity stimulus appeared to be mediated primarily by sympathetic activation because it was substantially attenuated by the β? antagonist atenolol. Furthermore, HR responses to the low-intensity stimulus appeared to reflect coactivation of both sympathetic and vagal systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversion and specific need states in the rat.

In 3 experiments, a total of 151 female Wistar rats were allowed to consume either sucrose or saline prior to being made ill by injection of either insulin or formalin, or by exposure to X rays. A 2-bottle preference test between sucrose and saline revealed that formalin was an effective agent in conditioned aversions to sucrose but not to saline. Similarly, injections of insulin were effective in producing conditioned aversions to saline but not to sucrose. X-irradiation produced strong aversions to either solution. Results are discussed with regard to the specific need states that insulin and formalin produce. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned suppression of medial forebrain bundle and septal intracranial self-stimulation in the rat: Evidence for a fear-relief mechanism of the septum.

In 3 experiments, a conditioned emotional response (CER) paradigm was presented to 2 groups of male albino Sprague-Dawley rats (N?=?20) during intracranial self-stimulation (ICSS). One group barpressed for medial forebrain bundle (MFB) stimulation reward; the other group barpressed for septal stimulation reward. The MFB ICSS was found to be suppressed by the CER procedure, but this procedure failed to suppress septal ICSS. The difference between the 2 sites was found only when both MFB and septal ICSS current intensities were available at their optimal levels. When ICSS current intensities were lowered to either threshold or medium level, both groups exhibited the CER suppression effect. Ss were also tested for a possible analgesic effect produced by the ICSS. MFB stimulation was found to produce some degree of analgesia, but septal stimulation failed to produce any analgesic effect. Thus, the possibility that the attenuation of the CER suppression effect in the septal group was due to analgesia was excluded. The difference in MFB and septal ICSS behavior during the presentation of the aversive stimulus suggests a possible qualitative distinction between the reward functions of the 2 sites, and a possible fear-reduction property of the septal area. (33 ref) (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)     

Conditioned suppression tests of the context-blocking hypothesis: Testing in the absence of the preconditioned context.

A conditioned-suppression procedure was used in 2 studies, with 96 male albino rats, to test the context-blocking hypothesis, the proposition that static apparatus cues, or conditioning contexts, can block conditioning to discrete CSs. Exp I tested for conditioning to the target CS in the same context that had been preconditioned and in which target conditioning had occurred. A context-blockinglike effect was demonstrated. Exp II tested for conditioning not only in the preconditioned context but also in a nonpreconditioned context. Exp II results are consistent with the idea that associative conditioning to a discrete target CS is not independent of the conditioned strength of the context in which target conditioning occurs. Evidence for context blocking was similar in the 2 studies, suggesting that conditioned contexts block the acquisition of associative strength by discrete CSs at the time of target conditioning and not through performance factors at the time of testing. (45 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)