Stria terminalis lesions attenuate the effects of posttraining naloxone and beta-endorphin on retention.

These experiments examined the effect of posttraining administration of naloxone and β-endorphin in rats with lesions of the stria terminalis (ST). Rats with sham or bilateral ST lesions were trained either in an inhibitory avoidance task or in a Y-maze discrimination task and, immediately after training, received an ip injection of saline, naloxone (0.5, 2.0, or 5.0 mg/kg in the avoidance task; 3.0 mg/kg in the Y-maze task), or β-endorphin (10.0 μg/kg). Retention of each task was tested 24 hrs following training. In the Y-maze task, retention was assessed by training on a reversed discrimination. The ST lesions did not affect retention of either task in otherwise untreated animals. However, in both tasks, ST lesions attenuated the memory-enhancing effects of naloxone as well as the memory-impairing effects of β-endorphin. These findings are consistent with other recent evidence suggesting that the amygdala may be involved in posttraining memory modulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple-food-unit-incentive effect: Nonconservation of weight of food reward by rats.

A common assumption is that the incentive value of food is determined by weight independently of number of food units. In Experiments 1 and 2, rats trained in a T-maze with four 75-mg pellets in one alternative and a single 300-mg pellet in the other alternative developed a preference for the 75-mg pellet alternative, which did not diminish with extensive training. When the locations of the 75-mg and 300-mg pellets were reversed, rats reversed their choice of arm. Rats preferred a 300-mg pellet to four 45-mg pellets (Experiment 2) and four 75-mg pellets to four 45-mg pellets (Experiment 3). Thus, rats prefer multiple- to single-food units; this effect is permanent rather than temporary, and the incentive value of food is not determined by weight of food alone or number of food units alone. Rats may count food units, judging a given weight of food as greater the greater the number of units—a failure of conservation common, possibly, to a number of species from birds to humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Administered magazine training in 2 experiments to female albino Sprague-Dawley rats under 1 of 3 basic conditions: a 3,000-Hz tone followed by (a) 1 food pellet, (b) 10 food pellets, or (c) a quasi-random mixture of both 1 and 10 food pellets. Ss then learned to press a lever for either a 1-pellet or a 10-pellet reward. Results reveal significant and long-lasting negative-reinforcement contrast. When Ss pressed for 1 pellet after a mixed 1-and-10 pellet pattern during magazine training, they learned to lever-press more slowly than if they had been magazine trained with just the 1-pellet reward. Data do not show positive contrast, however. Results suggest that rats may form "abstractions" about patterns of reinforcing events to which a given reinforcer is compared when it is used to facilitate the acquisition of a new response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory discrimination of individual littermates in rats (Rattus norvegicus).

Tested the ability of 4 adult male Sprague-Dawley rats to use odors in discrimination among littermates living as a group. Ss were trained in a Y-maze to discriminate the presence of a littermate from its absence. Results from transfer of training in 3 subsequent testing periods indicated that the animals were capable of distinguishing among individuals when relatedness and familiarity were held constant, that this ability was not due to training, and that performance was based solely on odor cues. Results suggest that laboratory rats exhibit odor sensitivities conmensurate with very complex social processes. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbohydrate-conditioned odor preferences in rats.

The effectiveness of odor cues to support nutrient-conditioned flavor preferences in rats was studied. When the rats drank fluid, the CS+ odor was paired with intragastric (IG) infusions of Polycose, and the CS– odor with IG water. In Experiment 1, rats trained with almond and anise odors presented with plain drinking water failed to acquire a CS+ odor preference. In contrast, rats in Experiment 2 formed a strong aversion to anise (or almond) paired with lithium chloride, which indicated that the odors were distinguishable to the rats. Experiment 3 showed that providing unique tastes (bitter or sour) in combination with the odors during training potentiated odor conditioning. The rats displayed a strong preference for the odor?+?taste CS+ and for the odor component alone. Experiment 4 showed that with another pair of odors (peppermint and vanilla), CS+ preferences could be conditioned in the absence of taste cues during training. These results demonstrate that rats can acquire strong nutrient-conditioned odor preferences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Arousal of frustration following gradual reductions in reward magnitude in rats.

16 male Holtzman rats were assigned to each of 4 groups; Ss were given a 14-pellet reward for 60 runway acquisition trials. During a subsequent 18-trial shift phase, one group was shifted to a 1-pellet reward on Trial 1, a 2nd was shifted on Trial 13, and a 3rd was given 1 less pellet each trial and then 1 pellet for the last 6 trials. The speeds of all 3 groups decreased to a level below that of a control group given a 1-pellet reward throughout training. All Ss were then given hurdle-jump training to escape from the 1-pellet reward to a neutral box. All 3 shifted groups showed acquisition of the response, whereas the control group did not. Results indicate that both gradual and abrupt reward reductions arouse frustration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of cell migration in atrioventricular pads during chick early heart development: analysis of cushion tissue migration in vitro

Rats were trained by treadmill running after chemical sympathectomy with 6-hydroxy-dopamine or during chronic beta receptor blockade. Contrary to untreated trained animals, sympathectomized rats did not get a reduction of the intrinsic heart rate after training despite an increased heart weight. In contrast, no cardiac hypertrophy occurred after training during beta adrenergic blockade but the heart rate during exercise was reduced in these animals. It is concluded that the training-induced bradycardia contains a lowering of the intrinsic heart rate and that this is not dependent on the stimulation of cardiac beta receptors or the magnitude of heart rate increase during exercise. The results also indicate that there is not a causal relationship between the training-induced bradycardia and cardiac hypertrophy. The latter conclusion is supported by an echocardiographic study in humans where no correlation was found between IHR and cardiac dimensions.     

Effects of acute trimethyltin exposure on appetitive acquisition and extinction performance in the adult rat.

16 adult male Sprague-Dawley rats were given an intragastric infusion of 7 mg/kg of trimethyltin chloride (TMT), and 16 additional Ss (controls) received saline, to investigate TMT's effect on Ss' appetitive acquisition and extinction performance. Ss from each condition were divided into 2 equal groups and trained with either partial or continuous reinforcement (PRF or CRF) in a straight-alley maze 21 days after dosing. The acquisition training phase contained 40 trials (4 trials/day) and was followed by 20 trials of extinction training (4 trials/day). Analyses performed on total speed revealed that TMT Ss performed at lower levels during acquisition than controls, regardless of schedule condition. Also, the rate of resistance to extinction was significantly reduced for TMT Ss compared with that of controls, regardless of the training schedules used during acquisition. A PRF extinction effect was observed for both control and TMT Ss, independent of dose regimen. PRF training occasioned greater persistence during extinction than did CRF training. Findings are discussed in terms of issues relating to TMT-induced hippocampal lesions. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of training intertrial interval on acquisition of trace and long-delay fear conditioning in rats.

Many factors govern conditioning effectiveness, including the intertrial interval (ITI) used during training. The present study systematically varied the training ITI during both trace and long-delay fear conditioning. Rats were trained using one of six different ITIs and subsequently tested for conditioning to the white noise conditioned stimulus (CS) and the training context. After trace conditioning, percent freezing to the CS was positively correlated with training ITI, whereas percent freezing to the context was negatively correlated with training ITI. In contrast, when rats were trained using a long-delay paradigm, freezing during the CS test session did not vary as a function of training ITI; rats exhibited robust freezing at all ITIs. The long-delay conditioned rats exhibited relatively low levels of freezing during the context test. Thus, trace is more sensitive than long-delay fear conditioning to variations in the training ITI. These data suggest that training ITI is an important variable to consider when evaluating age or treatment effects, where the optimal ITI may vary with advancing age or pharmacological treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective memory impairments produced by transient lidocaine-induced lesions of the nucleus accumbens in rats.

Reversible lidocaine-induced lesions of the nucleus accumbens (NAC) impaired performance on the spatial win-stay, but not on the cued win-stay, radial arm maze task. Pretraining lesions on the former task did not affect foraging for 4 pellets during either the training or test phases. In contrast, lesions given prior to the test phase significantly disrupted retrieval of 4 pellets on the 8-arm maze. Comparable deficits also were observed in rats trained to forage for 4 pellets on an 8-arm maze without prior win-shift experience. State-dependent drug effects were ruled out by replicating the disruptive effects of lidocaine infusions into the NAC on spatial win-shift performance in rats receiving this treatment prior to both training and test phases. These results suggest that the NAC may interact with the hippocampus to guide foraging behavior requiring memory of previous spatial locations on a maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hippocampus is not necessary for a place response but may be necessary for pliancy.

Rats with kainate-colchicine hippocampal lesions (HL) and controls (C) were initially trained in the Morris water maze with procedures that deterred their prepotent thigmotaxic response. Training began with an escape platform that occupied nearly the entire pool. The area to which the rats could escape was made smaller by substituting smaller platforms as training progressed. In contrast to standard procedures, HL rats and C rats showed comparable performance during acquisition and preferentially searched the goal quadrant on probe trials during which the platform was removed. In a follow-up experiment, the platform was moved to a random position along the wall, which required a switch to a thigmotaxic response for most effective escape. HL rats that were thigmotaxic before place training did not switch to a thigmotaxic response as readily as did controls, behavior consistent with the view that hippocampal damage reduces pliancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of tantalum markers of longitudinal bone growth

The influence of Actinomycin D (AMD) applied intrahippocampally at doses of 1-6 mug/animal, on the acquisition and retention of a shock-motivated brightness discrimination was studied on rats in a semiautomatic Y-maze. The injection of AMD 4 hr prior to training did not influence the acquisition, but causes, dose-dependent, a retention loss in relearning 24 hr after training. Twenty-eight hr after AMD application, naive rats exhibited a deterioration of acquisition performance increasing equally with the dose. At the same time, both circumscribed necroses in the hippocampus and signs of a general intoxication were observed. Considering the described pro- and retroactive effects, it is concluded that the use of the inhibitor AMD in learning experiments is not suitable to provide reliable evidence of the specific importance of the cerebral RNA synthesis for memory consolidation.     

Influence of stress and stress-protecting factors on rat tolerance to cold and efficiency of rat adaptation to cold]

The adaptive characteristics of the body, including the specific features of increased cold resistance upon repeated exposures to cold, are determined not only by the properties of thermogenic structures themselves, but largely depend on the contribution of the central mechanisms which control the processes of habituation and mobilization of functions. The experiments revealed an increase in cold resistance in rats after preexposure to cold. Immobilization stress prior to training cold significantly decreased rapid cold resistance in the animals, but increased the training effect of the first cooling. On the contrary, chlordiazepoxide increased cold resistance during the first cooling. Testing of the untreated animal showed no effect of training. No adaptive changes in cold resistance occurred in rats with impaired amygdaloid complex. Analyzing adrenal catecholamines revealed a significant elevation of dopamine concentrations in the rats exposed to cold. Hypothalamic catecholamines did not change with cold and serotonin in intact rats and 5-hydroxyindoleacetic acid in amygdalectomized rats substantially increased.     

Preweanling rats solve the Morris water task via directional navigation.

Adult rats show a preference for directional navigation over place navigation in the Morris water task. Here, the authors investigated whether preweanling rats with a newly developed ability to perform the water task also solve the task via directional navigation. After 24-day-old rats were trained to find a hidden platform in a fixed spatial location, a no-platform probe trial was conducted with the pool either in the same position as that used during training (no shift group) or shifted to a new position in the room (shift group). The authors found that rats in the shift group did not search for the platform at its absolute spatial location but rather navigated in the same direction that the platform was located during training and searched at the correct distance from the pool wall, resulting in a search at a location that was never trained. This pattern of results suggests that young rats learn to solve the water task by navigating in a particular direction rather than navigating to a precise place--a finding that may have implications for understanding hippocampal development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intact selective attention in rats with lesions of the dorsal noradrenergic bundle.

Tested S. T. Mason's hypothesis (1980) that lesions of the dorsal noradrenergic bundle (DNB), which induce depletion of forebrain noradrenaline, alter performance of discrimination tasks because they retard habituation to naturally attractive, but instrumentally irrelevant, stimuli. Exp I used 100 male Wistar rats in groups with either vehicle or 6-hydroxydopamine injections into the DNB. Groups were assigned to 5 discrimination tasks in a cross-maze. Lesions of the DNB did not alter performance of any of the tasks. In Exp II, control and noradrenaline-depleted Ss were trained in a task of light–dark discrimination followed by shift to position discrimination in a Y-maze. At the onset of training, Ss of both groups reliably avoided the bright goal arm and responded to the dark arm, thus demonstrating predominant attention for the relevant brightness stimuli rather than the irrelevant position stimuli. DNB lesions impaired acquisition of brightness discrimination only when the positive stimulus was the illuminated goal arm, and they did not alter shift performance. These results do not support Mason's hypothesis; but on the other hand they do indicate that DNB lesions in the rat can impair habituation of light avoidance. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fatigue contributes to the strength training stimulus

To investigate the role of fatigue in strength training, strength increases produced by a training protocol in which subjects rested between contractions were compared with those produced when subjects did not rest. Forty-two healthy subjects were randomly allocated to either a no-rest group, a rest group, or a control group. Subjects in the two training groups trained their elbow flexor muscles by lifting a 6RM weight 6-10 times on 3 d each week for 6 wk. Subjects in the no-rest group performed repeated lifts without resting, whereas subjects in the rest group rested for 30 s between lifts. Both training groups performed the same number of lifts at the same relative intensity. The control group did not train. Subjects who trained without rests experienced significantly greater mean increases in dynamic strength (56.3% +/- 6.8% (SD)) than subjects who trained with rests (41.2% +/- 6.6%), and both training groups experienced significantly greater mean increases in dynamic strength than the control group (19.7% +/- 6.6%). It was concluded that greater short-term strength increases are achieved when subjects are required to lift training weights without resting. These findings suggest that processes associated with fatigue contribute to the strength training stimulus.     

Xenobiotic-enhanced expression of cytochromes P450 2E1 and 2B in primary cultured rat hepatocytes

The purpose of this investigation was to determine whether long-term, heavy resistance training would cause adaptations in rat skeletal muscle structure and function. Ten male Wistar rats (3 weeks old) were trained to climb a 40-cm vertical ladder (4 days/week) while carrying progressively heavier loads secured to their tails. After 26 weeks of training the rats were capable of lifting up to 800 g or 140% of their individual body mass for four sets of 12-15 repetitions per session. No difference in body mass was observed between the trained rats and age-matched sedentary control rats. Absolute and relative heart mass were greater in trained rats than control rats. When expressed relative to body mass, the mass of the extensor digitorum longus (EDL) and soleus muscles was greater in trained rats than control rats. No difference in absolute muscle mass or maximum force-producing capacity was evident in either the EDL or soleus muscles after training, although both muscles exhibited an increased resistance to fatigue. Individual fibre hypertrophy was evident in all four skeletal muscles investigated, i.e. EDL, soleus, plantaris and rectus femoris muscles of trained rats, but muscle fibre type proportions within each of the muscles tested remained unchanged. Despite an increased ability of the rats to lift progressively heavier loads, this heavy resistance training model did not induce gross muscle hypertrophy nor did it increase the force-producing capacity of the EDL or soleus muscles.     

Effect of endurance exercise training on muscle glycogen supercompensation in rats

The purpose of this study was to test the hypothesis that the rate and extent of glycogen supercompensation in skeletal muscle are increased by endurance exercise training. Rats were trained by using a 5-wk-long swimming program in which the duration of swimming was gradually increased to 6 h/day over 3 wk and then maintained at 6 h/day for an additional 2 wk. Glycogen repletion was measured in trained and untrained rats after a glycogen-depleting bout of exercise. The rats were given a rodent chow diet plus 5% sucrose in their drinking water and libitum during the recovery period. There were remarkable differences in both the rates of glycogen accumulation and the glycogen concentrations attained in the two groups. The concentration of glycogen in epitrochlearis muscle averaged 13.1 +/- 0.9 mg/g wet wt in the untrained group and 31.7 +/- 2.7 mg/g in the trained group (P < 0.001) 24 h after the exercise. This difference could not be explained by a training effect on glycogen synthase. The training induced approximately 50% increases in muscle GLUT-4 glucose transporter protein and in hexokinase activity in epitrochlearis muscles. We conclude that endurance exercise training results in increases in both the rate and magnitude of muscle glycogen supercompensation in rats.     

Differential outcome effects in Pavlovian biconditional and ambiguous occasion setting tasks.

Three experiments with rats explored the differential outcome effect (DOE) using a Pavloian magazine approach conditioning preparation. Experiment 1 compared groups trained on a biconditional discrimination (AX+, AY?, BX?, BY+) with differential or nondifferential outcomes, and Experiment 2 examined this using an ambiguous occasion setting task (e.g., AX+, X?, Y+, AY?). In both experiments, subjects trained with differential outcomes learned the tasks better than subjects trained with nondifferential outcomes. Furthermore, subjects given differential outcome training learned the positive occasion setting component of the ambiguous task more efficiently than the negative occasion setting component, although both were enhanced by differential outcome training. Experiment 3 demonstrated that the ambiguous occasion setting task was reversed more readily when the target–outcome relations (as opposed to the modulator–outcome relations) were maintained during the reversal phase. These data suggest that an acquired distinctiveness effect may be responsible for the DOE in Pavlovian learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)