Tatiana Manrique

Patterns of Ethanol Intake in Preadolescent, Adolescent, and Adult Wistar Rats Under Acquisition, Maintenance, and Relapse‐Like Conditions

BACKGROUND Animal behavioral models of voluntary ethanol consumption represent a valuable tool to investigate the relationship between age and propensity to consume alcohol using an experimental methodology. Although adolescence has been considered as a critical age, few are the studies that consider the preadolescence age. This study examines the ethanol consumption/preference and the propensity to show an alcohol deprivation effect (ADE) after a short voluntary ethanol exposure from a developmental perspective. METHODS Three groups of heterogeneous Wistar rats of both sexes with ad libitum food and water were exposed for 10 days to 3 ethanol solutions at 3 different ontogenetic periods: preadolescence (PN19), adolescence (PN28), and adulthood (PN90). Ethanol intake (including circadian rhythm), ethanol preference, water and food consumption, and ADE were measured. RESULTS During the exposure, the 3 groups differed in their ethanol intake; the greatest amount of alcohol (g/kg) was consumed by the preadolescent rats while the adolescents showed a progressive decrease in alcohol consumption as they approached the lowest adult levels by the end of the assessed period. The pattern of ethanol consumption was not fully explained in terms of hyperphagia and/or hyperdipsia at early ages, and showed a wholly circadian rhythm in adolescent rats. After an abstinence period of 7 days, adult rats showed an ADE measured both as an increment in ethanol consumption and preference, whereas adolescent rats only showed an increment in ethanol preference. Preadolescent rats decreased their consumption and their preference remained unchanged. CONCLUSIONS In summary, using a short period of ethanol exposure and a brief deprivation period the results revealed a direct relationship between chronological age and propensity to consume alcohol, being the adolescence a transition period from the infant to the adult pattern of alcohol consumption. Preadolescent animals showed the highest ethanol consumption level. The ADE was only found in adult animals for both alcohol consumption and preference, whereas adolescents showed an ADE only for preference. No effect of sex was detected in any phase of the experiment.

Hippocampus, aging, and segregating memories.

Rats use time‐of‐day cues to modulate learned taste aversion memories. If adult rats are accustomed to drinking saline in the evening and they receive a lithium chloride injection after drinking saline in the morning, they form a stronger aversion to saline than rats that were conditioned after drinking saline at the familiar time. The difference indicated that the rats formed segregated representations of saline taste and the time of day the saline was consumed. This was inferred because the modulation of learning by time of day was observed when the aversions were tested at the familiar evening drinking time. If the rats had formed a compound representation of saline taste and the time of day it was consumed, the opposite pattern of differences would be expected. We used this modulation of learning by time of day to assay whether aged rats have an impaired ability to form segregated representations of experience. We find that aged rats had similar saline aversions if they were conditioned at either the familiar or the unfamiliar time of day. Furthermore, dorsal hippocampal lesions affecting also the overlying parietal cortex in the aged rats caused greater saline aversions if the rats were conditioned after drinking saline at the familiar time of day. This indicated that aged rats are aware of the time of day but after the lesion, they act as if they do not segregate saline taste from the time of day it was consumed. The results suggest that the ability to form segregated representations of a complex experience is impaired in aging and abolished by hippocampal lesions.

Peculiar modulation of taste aversion learning by the time of day in developing rats.

The ontogeny of the temporal context modulation of conditioned taste aversion was studied in male Wistar rats using a palatable 1% NaCl solution. A procedure that included two saline preexposures, a single pairing saline-lithium chloride (0.15 M; 1% b.w.) either at the same or a different time of day of preexposures and a one-bottle test at the same time than preexposure was applied. Four age groups (PN32, PN48, PN64, and PN100) covering the complete range from adolescence to the adult period were tested. The results showed no effect of a temporal context shift in PN32. A peculiar enhancement of temporal context-specific saline aversions was exhibited by PN48 and PN64 rats, while the adult typical temporal context specificity of latent inhibition was only evident in PN100 rats. The results are discussed in terms of the peculiar brain functional organization during a protracted adolescence period.