The Effect Of Beta-Endorphin In Taste Preference Learning

Conditioned taste preference (CTP) or taste preference learning is an important paradigm to research the mechanism of learning and memory, which has a profound biological significance to acquire nourishment and keep nutrition balance when animals are hunger or nutrient deficiency. The pleasantness induced by palatability is closely related to Beta-Endorphin (β -EP). It will help us to elucidate the CTP's mechanism of neurochemistry by observing the expression of P -EP in brain after establishing CTP. Therefore, this research discusses the effect of β -EP in CTP through three related experiments .Experiment 1, let rats acquire taste preference to quinine solution, and take account of β -EP-immunoreactive neurons in different nucleuses of hypothalamic areas, separately adopted taste preference learning training and immunohistochemistry; Experiment 2, Added banana essence into quinine solution to discuss the connection between flavor preference learning and the expression of β -EP; Experiment 3, To research endogenous opiate like substances contribute to the establishment of CTP and influence the behavior of taste preference by naloxone was i.p. injected into rats.Results and analysis:1 Rats ingested both 0.04mmol/L quinine solution and then 0.2mol/L sucrose for 20 min, the preference ratio to quinine solution enhanced markedly after 5 days training, but the preference ratio of most animals couldn't reach 50%. It shows that the preference to quinine solution is still lower to water.2 Quinine solution was delivered directly into rats' mouths with an intraoral catheter, which changed the expression level of β -EP in hypothalamus, but the influence of related nucleus was different. The number of β-EP -immunoreactive neurons in SO (supraoptic nucleus), Pa (paraventricular hypothalamic nucleus) and Arc (arcuate hypothalamic nucleus) decreased, and those in CMC (caudal magnocellular nucleus) increased. Which suggest that different nucleus have different functions to modulate taste preference.3 The expression of β -EP induced by quinine solution reversed after CTP. The number ofP -EP -immunoreactive neurons in SCK Pa and Arc exceeded those of control group. The result illuminates the preference of taste is one of the factor to modulate β -EP's expression; but the expression level of β -EP is not incompletely paralleled with the behavior of taste preference, which suggests that the expression of β -EP induced by CTP may participate in other nerve process (such as the variety of emotion, the rewarding...