Pre- and/or postnatal protein restriction in rats impairs learning and motivation in male offspring

Abstract

Suboptimal developmental environments program offspring to lifelong health complications including affective and cognitive disorders. Little is known about the effects of suboptimal intra-uterine environments on associative learning and motivational behavior. We hypothesized that maternal isocaloric low protein diet during pregnancy and lactation would impair offspring associative learning and motivation as measured by operant conditioning and the progressive ratio task, respectively. Control mothers were fed 20% casein (C) and restricted mothers (R) 10% casein to provide four groups: CC, RR, CR, and RC (first letter pregnancy diet and second letter lactation diet), to evaluate effects of maternal diet on male offspring behavior. Impaired learning was observed during fixed ratio-1 operant conditioning in RC offspring that required more sessions to learn vs. the CC offspring (9.4±0.8 and 3.8±0.3 sessions, respectively, p<0.05). Performance in fixed ratio-5 conditioning showed the RR (5.4±1.1), CR (4.0±0.8), and RC (5.0±0.8) offspring required more sessions to reach performance criterion than CC offspring (2.5±0.5, p<0.05). Furthermore, motivational effects during the progressive ratio test revealed less responding in the RR (48.1±17), CR (74.7±8.4), and RC (65.9±11.2) for positive reinforcement vs. the CC offspring (131.5±7.5, p<0.05). These findings demonstrate negative developmental programming effects due to perinatal isocaloric low protein diet on learning and motivation behavior with the nutritional challenge in the prenatal period showing more vulnerability in offspring behavior.

Figure 1. Operant Conditioning

A) Comparison of FR-1 conditioning shows the number of sessions to reach performance criterion. B) Comparison of FR-5 conditioning shows the number of sessions to reach performance criterion. Offspring of rats fed with control (C = 20% casein) or restricted (R = 10% casein) diet during pregnancy (first letter) and lactation (second letter). Mean ± SEM, n = 8 offspring from different litters. Groups not sharing a letter are statistically different, p<0.05.

Figure 2. Progressive ratio

A) Average number of responses made during 10 sessions. B) Average number of reinforcements earned during 10 sessions. Offspring of rats fed with control (C = 20% casein) or restricted (R = 10% casein) diet during pregnancy (first letter) and lactation (second letter). Mean ± SEM, n = 5 offspring from different litters. Groups not sharing a letter are statistically different, p<0.05.