Ethological analysis of mother-pup interactions and other behavioral reactions in rats: effects of malnutrition and tactile stimulation of the pups

Mother-pup interaction, as well as other behavioral reactions were studied during the lactation period in 24 litters of Wistar rats and their dams fed either a 16 percent (control - C; 12 litters) or a 6 percent (malnourished - M; 12 litters) protein diet. The diets were isocaloric. Throughout lactation there was a 36.4 percent weight loss of M dams and a 63 percent body weight deficit in the M pups when compared to control pups. During this period, half of the litters were exposed daily to additional tactile stimulation (CS or MS), while the other half were submitted to normal rearing conditions (CN or MN). The tactile stimulation of pups (handling) consisted of holding the animal in one hand and gently touching the dorsal part of the animal's body with the fingers for 3 min. A special camera and a time-lapse video were used to record litter behavior in their home cages. Starting at 6 p.m. and ending at 6 a.m., on days 3, 6, 12, 15, 18 and 21 of lactation, photos were taken at 4-s intervals. An increase in the frequency (154.88 + or - 16.19) and duration (455.86 + or - 18.05 min) of suckling was observed throughout the lactation period in all groups compared to birth day (frequency 24.88 + or - 2.37 and duration 376.76 + or - 21.01 min), but the frequency was higher in the C (84.96 +- 8.52) than in the M group (43.13 + or - 4.37); however, the M group (470.2 + or - 11.87 min) spent more time suckling as compared with the C group (393.67 + or - 13.09 min). The M dams showed a decreased frequency of resting position throughout the lactation period (6.5 + or- 2.48) compared to birth day (25.42 + or - 7.74). Pups from the C group were more frequently observed separated (73.02 + or - 4.38) and interacting (258.99 + or - 20.61) more with their mothers than the M pups (separated 66.94 + or - 5.5 and interacting 165.72 + or - 12.05). Tactile stimulation did not interact with diet condition, showing that the kind of stimulation used in the present study did not lead to recovery from the changes induced by protein malnutrition. The changes in mother-pup interaction produced by protein malnutrition of both may represent retardation in neuromotor development and a higher dependence of the pups on their mothers. These changes may represent an important means of energy saving and heat maintenance in malnourished pups

Food intake and weight of lactating rats maintained on different protein-calorie diets, and pup growth

Studies on rats maintained on low-protein-calorie diets during the lactation period show that food intake decreases. This process results in weight loss and a delay in litter development. The purpose of the present study was to determine the alterations in food intake, maternal weight and litter growth during lactation when dams were exposed to diets with different levels os protein and carbohydrate. Female Wistar rats receiving one of 4 different diets, A (N = 14), B (N = 14), C (N = 9) and D (N = 9), were used. Diet A contained 16 per cent protein and 66 per cent carboydrate; diet B, 6 per cent protein and 77 per cent carboydrate; diet C, 6 per cent protein and 66 per cent carboydrate; diet D, 16 per cent protein and 56 per cent carboydrate. Thus, C and D diets were hypocaloric, while A and B were isocaloric. The intake of a low-protein diet in group B and C affected the weight of dams and litters during the last two weeks of lactation, while the low-calorie diets limited the growth of D litters at 21 days compared with A litters, but had no effect on the weight of D dams. Group B showed an increase in intake during the first five days of lactation, resulting in a behavioral calorie compensation due to the increase in carboydrate content, but the intake decreased during the last part of lactation. Food intake regulation predominantly involves the recruitment of a variety of peripheral satiety systems that attempt to decrease the central feeding command system.

Effect of zinc deficiency induced before and during pregnancy on the survival of female rats and their pups

The objective of the present study was to determine the consequences of Zn²+ deficiency on the gestational process. The study was conducted on adult Wistar virgin female rats fed isocaloric diets containing 16 percent protein and different Zn²+ concentrations, i.e., 2 ppm (severe restriction), 6 ppm (moderate restriction), and 20 ppm (control). Rats recived the diets and wather ad libitum for 7, 14 or 21 days before mating and throughout pregnancy. Survival of dams and pups decreased with increasing Zn²+ restriction and with time of exposure to the deficient diet. Mean survival rate for control dams and pups was 100 percent, whereas severe restriction (2 ppm for 21 days premating and during pregnancy) resulted in survival rates of 25 percent and 0 for dams and pus, respectively. Dam and pup survival rates for moderate restriction (6 ppm) for the same period were 83 percent and 72 percent, respectively. These results indicate the importance of Zn²+ before and during pregnancy and show that Zn²+ deficiency causes metabolic alterations which impair normal reproductive processes

Acquisition and extinction of jumping, two-way shuttle-box and bar press avoidance responses in malnourished rats: effects of shock intensity

1. In order to investigate the role of avoidance response and shock intensity in avoidance learning in malnourished rats, three avoidance responses (jumping, two-way shuttle-box and bar press) and three shock intensities (0.4, 0.6 and 1.0 mA) were used. Independent groups of 6 rats were used for each response topography and shock intensity. 2. Malnourished male Wistar rats were suckled by mothers fed a 12 percent casein diet during the lactation period (0-21 days of age) while the mothers of well-nourished controls received a 25//casein diet. After weaning (21 st day), all animals received a commercial lab chow diet until 70 days of age, when the avoidance training started. 3. Malnutrition did not affect the acquisiton of the avoidance response, but malnourisheed groups required more trials to extinguish jumping and two-way shuttle-box. During the acquisitiion phase all animals learned the jump response faster in comparison to bar press and shuttle-box avoidance responses. Both groups in the acquisition phase responded faster with 1.0 mA when compared to lower intensities (0.6 and 0.4 mA). The malnourished animals showed lower latency of avoidance in the jumping response when compared with well-nourished animals. During the extinction phase there was a significant effect of diet, response topography and shock intensity in the latency to respond and trials to criterion. The increased resistance to extinctio in malnourished rats was particularly evident with 1.0 mA in the two-way shuttle-box response. 4. These results suggest that contradictory data related to the acquisition of the avoidance response in malnourished animals cannot be attributed to response topography or variations in shock intensity. Furthermore, our results also indicate that resistance to extinction and latency to respond are appropriate for detecting differences between well-nourished and malnourished animals

Early malnutrition alters the effect of chlordiazepoxide on inhibitory avoidance

In order to study the functional consequences of brain changes caused by early malnutrition, rats were fed a protein-deficient diet from birth until 49 days of age and a balanced diet from day 50 to day 70. The animals were submitted to a step-down inhibitory avoidance task and to the flinch-jump nociceptive test at 49 and 70 days of age. Malnourished rats showed longer step-down latencies and lower flinch and junp theresholds than eutrophic animals. Chlordiazepoxide (5 mg/Kg, ip) shortened step-down latency of well-nourished rats, whereas it failed to do so in malnourished rats. Since well-nourished animals also became resistant to chlordiazepoxide when tested with a higher shock intensity, generating avoidance latencies comparable to those of malnourished animals, we conclude that the drug resistance induced by malnutrition may be secondary to enhanced pain sensitivity and/or reactivity