Food Approach Behaviors Research Articles

AMPA receptor antagonists reverse effects of extended habit training on signaled food approach responding in rats

Dopamine D1 receptor stimulation is critically involved in early appetitive phases of learning in various behavioral paradigms. However, extended habit training was previously shown to reduce the ability of dopamine D1 receptor antagonists such as R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) to disrupt behavioral performance. The present study aimed to evaluate whether coadministration of glutamate alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor antagonists restores sensitivity to acute blockade of D1 receptors. Adult male Wistar rats were presented with 45-mg food pellets delivered to the food tray, which was immediately preceded by a 400-ms tone (2.8 kHz, 78 dB). During each training and test session, there were 28 food-tone presentations with an average intertrial interval of 70 s, and each head entry into the food tray was recorded. Drug tests were conducted on either day 3 or 9 of the training using independent groups of animals. The main dependent variable was the number of trials during which no head-entry response was made during the 10-s period immediately after the food delivery. Longer training duration enhanced the resistance of the signaled food approach behavior to extinction and to disrupting effects of supplementary food ration. Similarly, acute administration of SCH-23390 (0.04-0.16 mg/kg) dose-dependently reduced the number of omitted trials when given before the test session on day 3 but much less so when injected on day 9. AMPA receptor antagonists, NBQX (10 mg/kg) or GYKI-52466 (3-10 mg/kg), had no effects on their own but significantly enhanced the disrupting effects of SCH-23390 (0.08 and 0.16 mg/kg) when given on day 9 but not on day 3 of the training. These results indicate that AMPA receptor blockade restores sensitivity to appetitive behavior-disrupting effects of SCH-23390 in subjects exposed to extended training protocol.

Food Entrainment to 4-h T Cycles in Rats Kept Under Constant Lighting Conditions

The effect of 4-h feeding cycles on the feeding pattern of rats kept under constant light and constant darkness, was analysed. In both cases, the scheduled pattern of food-approach behavior elicited dissociation of the feeding activity into several components associated to the feeding times (CAFT), which coexisted with the previous circadian free-running rhythms. In LL rats and in the rest phase of DD animals, the CAFT was characterized by an increased number of food approaches confined exclusively to the period of food availability, with poor anticipatory activity. However, in the active phase of some DD rats, CAFT included an additional anticipatory activity. The interaction between the CAFT and the free-running rhythms involved modulation of the CAFT, depending on the free-running periodicity. After termination of the feeding-restriction schedule, some DD and LL animals retained the CAFT for at least 3 days. However, when the access to food was blocked 10 days after ending the restricted schedule, rats did not show any feeding activity associated to the previous feeding times. A spontaneous feeding pattern similar to that imposed by the previous feeding schedule emerged immediately after food deprivation in two of the DD animals. Although these results are compatible with the existence of a food-entrainable pacemaker, the existence of a multioscillatory light-entrainable pacemaker with some oscillators entrained by food pulses and others free-running may explain our results.

STUDIES ON RIGIDITY AND CRYSTALIZATION OF BEHAV-IOR

Variability of food approach and shock avoidance behavior was studied using 12 rats in running and jumping situations. Following results were obtained. 1) Approach behavior was variable in the running situation; but it lost its variability in the jumping situation. 2) Avoidance behavior was fixated to direction both for running and for jumping. 3) There were at least two pieces of evidence for the apparent abnormal nature of fear motivated avoidance behavior. It was concluded that Maier's abnormal fixation might at least partly be due to an intrinsic nature of a fear motivated behavior. This tendency of a fear motivated behavior to fixate might have been enhanced in a situation in which S was forced jumping.