Moderate drinking? Alcohol consumption significantly decreases neurogenesis in the adult hippocampus

Abstract

Drinking alcohol in moderation is often considered a health-conscious behavior, associated with improved cardiovascular and brain health. However, "moderate" amounts of alcohol include drinking 3-4 alcohol beverages in a day, which is closer to binge drinking and may do more harm than good. Here we examined how daily drinking of moderate-high alcohol alters the production of new neurons in the adult hippocampus. Male and female adult Sprague-Dawley rats were provided free access to a liquid replacement diet that was supplemented with either 4% ethanol or Maltodextrin for a period of 2 weeks. Proliferating cells were labeled with 5-bromo-2-deoxyuridine (BrdU) and the number of BrdU-positive cells in the hippocampus was assessed after the final day of drinking. A subset of rats was also exposed to a motor skill or associative learning task to examine the functional effects of alcohol consumption. The drinking regime resulted in an average blood alcohol concentration of approximately 0.08%, which is comparable to the human legal driving limit in many countries. This level of intoxication did not impair motor skill learning or function in either sex, nor did the alcohol consumption disrupt associative learning 2 days after drinking. Therefore, moderate alcohol consumption did not disrupt basic sensory, motor or learning processes. However, the number of cells produced in the dentate gyrus of the hippocampus was reduced by nearly 40%. Thus, even moderate consumption of alcohol for a relatively short period of time can have profound effects on structural plasticity in the adult brain.

Figure 1. Liquid diet regime produces moderate blood alcohol levels

(A) Animals that received a liquid diet with alcohol drank less than with the alcohol but this difference dissipated by the second week. Females tended to drink more of the diet than males, regardless of the alcohol content. (B) After the two week period, blood alcohol levels were measured from trunk blood. Concentrations ranged from 54.2 -147.6 mg/dl with a mean of 86.4 mg/dl (0.0864 %) for males and 87.6 mg/dl (0.0876 %) for females.

Figure 2. Daily moderate alcohol consumption reduces the number of new cells made in the dentate gyrus

(A) Males that drank alcohol produced and retained fewer new cells than those that did not drink alcohol. (B) Similar effects were observed in females. (C) The number of BrdU-positive cells per unit volume was calculated to assess and account for sex differences in volume, but there were none. (D) Representative photomicrographs of BrdU-positive cells at 1000×.

Figure 3. Moderate drinking does not impair motor performance or associative learning

(A) Consumption was similar to females in experiment 1. Initially, animals that were given diets that contained alcohol drank less than animals not given alcohol. However, daily consumption was similar by the end of the two-week drinking period. (B) Females that drank alcohol performed similarly compared to females that did not drink alcohol when motor performance was tested on a rotarod on day 6 of the drinking regime. (C) Females that consumed alcohol emitted similar numbers of CRs during training as those that did not drink alcohol. Therefore, there was no persistent effect of alcohol consumption on this type of associative learning.