Food reward

Lepore M, Vorel SR, Lowinson J, et al Conditioned place preference induced by delta-9-tetrahydrocannabinol comparison with cocaine, morphine, and food reward. LifeSci 56 2073-2080, 1995... 

A study that examined the interaction between exposure concentration and time of exposure on nervous system function found that concentration, rather than time of exposure, was more important in determining effects (Bushnell 1997). Rats were trained to press two levers for food reward one lever when a light flashed, the second lever produced food when there was no signal. The trained rats were exposed to 0,400, 800, 1,200, 1,600,2,000, or 2,400 ppm trichloroethylene for 0.33, 0.67, or 1 hour. Response times were signiflcantly increased only at 2,400 ppm at 0.67 and 1 hour. Sensitivity was significantly decreased at 2,400 ppm at all exposure times. At 0.33 hour, sensitivity was not affected at the other concentrations. At 0.67 hour, sensitivity was significantly decreased at 2,000, and 1,200 ppm, and at 1 hour, sensitivity was... 

The tests generally involve some form of maze but the simplest is the passive avoidance test. In this the animal learns that in a certain environment it will be punished with an electric shock for some particular action, like stepping onto a special part of the floor of the test chamber. The test of memory is how long the rat avoids (remains passive to) making the movement that will initiate the shock. Of course, drugs that reduce the animal s anxiety also modify the response. Using a maze in its simplest T shape, the animal is placed at the base of the vertical arm and a food reward at the end of one of the horizontal arms. Clearly the animal has to learn which arm contains the reward. Memory is assessed by the time taken for a food-deprived animal to reach the reward and the number of false arm entries. This simple system can be made more complex by introducing many more arms and branches but the principle is the same. 

Kovacic, B., and Domino, E. F. (1976) Tolerance and limited cross-tolerance to the effects of N,N-dimethyltryptamine (DMT) and lysergic acid diethylamide-25 (LSD) on food-rewarded bar pressing in the rat. J. Pharmacol. Exp. Then, 197 495-502. 

In the operant performance test (Ritchie et al. 2001), groups of four rats were exposed separately for four successive test sessions to each test concentration. Performance was measured by the number of food rewards earned in a specific time. The exposures to HFC-134a were for approximately 15 min and were either preceded or followed by a 15-min exposure to room air. Atmospheres were measured with infrared spectrometry. Compared with the air exposures, there were no significant differences in any performance measures during exposures at 40,000 to 100,000 ppm. At 140,000 ppm, food rewards earned were significantly reduced, although the error-to-reward ratios were significantly increased. 

Cognitive enhancing effects of 5-HT3 receptor antagonists have been observed in several animal models, using both normal animals and animals in which a cognitive deficit has been induced by the administration of the muscarinic antagonist scopolamine [41]. An example is the Wisconsin test, in which marmosets learn to discriminate which of two objects conceal a food reward and, after learning this, the task is reversed such that the food is hidden beneath the other object. Treatment with ondansetron has been shown to enhance the ability of marmosets to learn the reversal task. 

Wyvell CL, Berridge KC (2000) Intra-accumbens amphetamine increases the pure incentive salience of a Pavlovian cue for food reward enhancement of wanting without either liking or reinforcement, J Neurosci 20 8122-8130... 

More rarely, navigation of a T-maze has been used for drug discrimination studies. Early studies used a T-maze procedure where rats were trained to select one of the two arms when nicotine was administered, whereas entries into the opposite arm were punished by foot-shock (Romano et al. 1981 Schechter and Rosecrans 1971a, b Overton 1982). Nicotine proved to have moderate relative discriminability, as measured by the sessions to criterion performance (20 sessions at 0.55 mg kg Overton 1982). More recently, a food-rewarded discrimination procedure using a T-maze has been described, but no studies involving nicotine have been identified (Colombo et al. 1996). 

Hernandez, Luis, and Bartley G. Hoebel. 1988. "Food Reward and Cocaine Increase Extracellular Dopamine in the Nucleus Accumbens as Measured by Microdialysis." Life Sciences 42 1705-12. 

Defense is a further category in which plants employ food rewards to acquire protection by arthropod mutualists. The provision of food sources allows plants to recruit or sustain predators or parasitoids, which, in turn, can provide protection against herbivory. The plant-derived food structures involved in indirect defensive interaction can be divided in two main groups food bodies and extrafloral nectaries. 

Coyle and Singer (ref. 107) found that vitamin A treatment (100 000 i.u./kg) applied to pregnant rats on gestational days 8-10 decreased performance of their offspring in a water maze and in a food rewarded Henderson type maze. This was observed only vhen the animals were reared in an enriched environment. These results parallel those obtained with imlpramine. 

Barbiturates have been shown to affect spontaneous alternation and radial maze performance in mice (ref. 150). Rats treated prenatally with aluminum showed a deficit in radial maze acquisition (ref. 151). Neonatal clonidine treatment delayed choice of a water rewarded arm in a T-maze by water deprived rats which had been pretrained in this maze vith food reward (ref. 33). 

Another aspect of radial maze performance is the use of positive motivation (food reward), in contrast to the aversive motivations maintaining the passive avoidance and Morris maze procedures. Data suggesting drug-induced cognitive impairment are more convincing if the impairments span the different motivational systems maintaining the behaviors. 

The technique also lends itself readily to the study of memory function, in particular by use of delayed responding procedures. In delayed responding, the animal is required to retain information over a short period (usually seconds) and then to show, by pressing an appropriate lever, whether it has correctly remembered the information (Dunnett et al. 1988). In the procedure described below, a rat in a Skinner Box is presented with a lever, either on the left or the right side of the food dispenser. The rat presses the lever and the lever is withdrawn. Five seconds later, two levers are presented and the rat has to press the lever which was not presented previously to obtain a food reward (delayed alternation or delayed non-matching to sample). If the rat presses the same lever as that previously presented, the lever is withdrawn but no food is given. In this fashion, the animal can be trained to retain a piece of information (position of a lever), and thereby demonstrate its short-term memory capacity. 

A training session consists of 36 successive trials separated by 10 seconds. Each trial starts by presenting the animal with one lever (left or right). When the animal presses on the lever, it is given a food pellet, the lever is retracted and 5 seconds later two levers are presented. The animal has to learn to press on the lever not previously presented in order to gain a food reward (delayed alternation). If the animal does not lever-press within 20 seconds of a one- or two-lever presentation, the lever(s) are withdrawn and the next trial commences 10 seconds later. 

Thurlby and Samanin (1981) studied the effect of anorectic drugs on food-rewarded runway behaviour. 

In a shortcut experiment by Chapuis and Varlet (1987), dogs were led from Point D to a food reward at Point A and from Point D to a food reward at Point B. Shortcut behavior was shown when a dog ran directly from A to B. 

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