Contrast Effects In Rats Research Articles

Effect of preference conditioning in the anticipatory contrast effect in rats.

Effect of preference conditioning in the anticipatory contrast effect in rats.

A possible social relative reward effect: Influences of outcome inequity between rats during operant responding

Social interactions/situations have dramatic influences on motivation. Creating animal models examining these influences promotes a better understanding of the psychological and biological underpinnings of social motivation. Rodents are sensitive to social history/experience during associative conditioning and food-sharing tasks. Would reward-oriented operant behavior be sensitive to social influences by showing a negative contrast-like effect when another organism obtains a greater value outcome? We used a side-by-side arrangement of operant response chambers wherein one animal obtained consistently high reward signaled by a discrete cue. The neighboring, experimental rat experienced different combinations of high and low reward trial sequences. Control conditions included distraction from a conspecific in the neighboring chamber (rat distractor) or cue/food dispenser operating without a conspecific (program distractor) in addition to testing subjects alone. Results support an influence of the other animal actively performing the task on the experimental subject’s behavior. Primarily, responding was significantly slower for the low reward trials while the neighboring rat was receiving the higher magnitude reward. The lever-press and not food-cup retrieval latency was significantly slower during exposure to a conspecific neighbor performing the operant task. The effect was not obtained in all session sequences and was more pronounced using longer series of consecutive low reward trials. The slowing effect was also obtained with the program-distractor experience in a different trial sequence. These findings suggest a social-induced negative incentive contrast effect in rats possibly mediated by an outcome inequity process that could have key similarities to complex situational-affective effects on motivation involving frustration or jealously.

Psychopharmacological characterisation of the successive negative contrast effect in rats.

RationaleSuccessive negative contrast (SNC) describes a change in the behaviour of an animal following a downshift in the quantitative or qualitative value of an expected reward. This behavioural response has been hypothesised to be linked to affective state, with negative states associated with larger and/or prolonged shifts in behaviour.ObjectiveThis study has investigated whether different psychopharmacological treatments have dissociable actions on the SNC effect in rats and related these findings to their actions on different neurotransmitter systems and affective state.MethodsAnimals were trained to perform a nose-poke response to obtain a high-value food reward (four pellets). SNC was quantified during devalue sessions in which the reward was reduced to one pellet. Using a within-subject study design, the effects of acute treatment with anxiolytic, anxiogenic, antidepressant and dopaminergic drugs were investigated during both baseline (four pellets) or devalue sessions (one pellet).ResultsThe indirect dopamine agonist, amphetamine, attenuated the SNC effect whilst the D1/D2 antagonist, alpha-flupenthixol, potentiated it. The antidepressant citalopram, anxiolytic buspirone and anxiogenic FG7142 had no specific effects on SNC, although FG7142 induced general impairments at higher doses. The α2-adrenoceptor antagonist, yohimbine, increased premature responding but had no specific effect on SNC. Results for the anxiolytic diazepam were mixed with one group showing an attenuation of the SNC effect whilst the other showed no effect.ConclusionsThese data suggest that the SNC effect is mediated, at least in part, by dopamine signalling. The SNC effect may also be attenuated by benzodiazepine anxiolytics.

P.2.010 Carbon dioxide-induced anxiety and the successive negative contrast effect in rats

Dramatic increases in the issuance of political apologies over the last two decades mean that we now live in the “age of apology”. But what does this surge in frequency mean for the effectiveness of intergroup apologies in promoting forgiveness? In the current research we propose a paradoxical “normative dilution” effect whereby behavioral norms increase the perceived appropriateness of an action while at the same time reducing its symbolic value. We experimentally manipulated the salience of the age-of-apology norm prior to assessing participant (N = 128) reactions to past unjust treatment of ingroup POWs by the Japanese during WWII. The apologetic norm increased victim group members' desire for an apology in response to the harm. However, after reading the actual apology, the invocation of the norm decreased perceived apology sincerity and subsequent willingness to forgive. Thus, although apologetic trends may suggest greater contemporary interest in seeking reconciliation and harmony, their inflationary use risks devaluing apologies and undermining their effectiveness.

Lesions of the pontine parabrachial nuclei eliminate successive negative contrast effects in rats.

Rats shifted from a high to a low concentration of sucrose make fewer licks for the low concentration than rats that experience only the low concentration of sucrose. This phenomenon, referred to as successive negative contrast, is eliminated after bilateral electrolytic lesions of the amygdala. Because the amygdala receives direct projections from the gustatory zone of the parabrachial nuclei of the pons (PBN), this experiment was designed to examine this phenomenon in rats with electrophysiologically guided bilateral electrolytic lesions of the PBN. The results of this experiment showed that lesions of the PBN fully prevent contrast in rats shifted from the high to the low concentration of sucrose. Thus, an intact PBN is essential for the occurrence of successive negative contrast effects in rats.

Lesions of the pontine parabrachial nuclei eliminate successive negative contrast effects in rats.

Lesions of the pontine parabrachial nuclei eliminate successive negative contrast effects in rats.

Nmr contrast enhancement of brain tumours: comparison of the blood brain barrier tracer GdDTPA and the tumour-selective contrast agent MnTPPS

Contrast enhancement of two different NMR contrast agents, GdDTPA and MnTPPS, was compared. Sequential recording ofT1-weighted images at 50s intervals allowed the observation of the temporal and spatial evolution of the contrast effect in rats with glioma implanted into the right brain hemisphere. The maximum signal intensity ratio of tumour over contralateral striatum was 1.80±0.10 for GdDTPA and 1.61±0.15 for MnTPPS. The enhancement was maximal 3min after application of GdDTPA and fell rapidly to reach half maximum after 24 min. MnTPPS led to maximum tumour enhancement within 11 min and did not return to control level within the observation period (150 min). In the peritumoural edema, an enhancement effect was absent for MnTPPS, but GdDTPA spread out from the tumour resulting in a delayed but strong enhancement outside the tumour. Thus, GdDTPA, as a blood-brain-barrier tracer, led only to a transient contrast enhancement between tumour and surrounding tissue and no unambiguous demarcation of the tumour against peritumoural edema. Application of MnTPPS resulted in a long-lasting strong tumour enhancement and reliable delineation from peritumoural edema.

Evidence for a calorically costly negative consummatory contrast effect in rats

For 2 h prior to their daily meal of Purina Chow, rats (which were 14% below ad-lib weight levels) had access to a sucrose solution. For half (Group 16-4), the solution was alternated daily between 18% and 4%; for the other half (Group 4-4), the solution was always 4%. On 18% days, Group 16-4 consumed significantly more calories and gained significantly more weight than did Group 4-4, because of a greater consumption of sucrose calories (Purina intake was similar for the two groups). On 4% days, however, Group 16-4 consumed both significantly fewer sucrose calories and significantly fewer Purina calories than did Group 4-4. These two contrast effects resulted in a 17% shortfall in total caloric intake for Group 16-4 on 4% days. As a consequence, Group 16-4 showed a significant drop in body weight, compared to Group 4-4, on 4% days. A second experiment was carried out to investigate whether the contrast-induced reduction in Purina intake shown by Group 16-4 on 4% days would be eliminated if (1) a 30-min interval separated sucrose ingestion from Purina ingestion, or (2) a 25-min interval plus 5-mmn exposure to 16% sucrose separated ingestion of 4% sucrose from Purina ingestion. Purina intake was still suppressed in Group 16-4 under both conditions.

Effects of magnitude of reward increment on positive incentive contrast effects in the rat

An increase from.01% to 1% in the concentration of saccharine solution in an operant conditioning box with rats produced positive contrast, while an increment from.05% to 1% failed to result in positive contrast effects. These findings are in agreement with the few studies that have examined the effects of magnitude of reinforcement change on the magnitude of incentive contrast with human and infrahuman organisms. It would appear that amount of reward increment is a variable that controls the occurrence of positive incentive contrast effects in rats.

Within-subjects positive and negative contrast effects in rats.

Rats were given alternating 1-min. access periods to 2 tubes containing either 32% or 4% sucrose solutions for daily 6-min. test sessions. Lick rate for 32% was higher under comparison (32 vs. 4) than noncomparison (32 vs. 32) conditions; and lick rate for 4% was lower under comparison conditions (4 vs. 32) than under noncomparison conditions (4 vs. 4). All sucrose conditions were varied within subjects and both positive and negative contrast were obtained with a small n. In addition to lick rate, intake and latency measures also revealed contrast effects. Deprivation conditions altered latency but not lick rate measures of contrast. Reducing the test session to 3 min. (alternating 30-sec. access periods) did not greatly affect contrast. Additional experiments provided evidence for distinct within-days and between-days contrast effects, as well as a between-groups contrast effect.

Effects of varied preshift reward magnitude on successive negative contrast effects in rats.

Effects of varied preshift reward magnitude on successive negative contrast effects in rats.

Percentage body weight and the successive negative contrast effect in rats

In two runway experiments employing rats the successive negative contrast effect was evaluated for animals maintained at high or low body weights. In both experiments the effects on performance of shifting reward magnitude were independent of body weight. These results contrast with those of previous studies in which the successive negative contrast effect occurred only under low body weight. It was suggested that when conditions are maximal or near maximal for production of the successive negative contrast effect, as they were here but not in previous investigations, body weight will not influence the size of this effect.

Reinforcement contrast effects in rats following experimental definition of a dimension of reinforcement magnitude.

Reinforcement contrast effects in rats following experimental definition of a dimension of reinforcement magnitude.

Differential conditioning and contrast effects in rats.

Differential conditioning and contrast effects in rats.