Interactive effects of parity and pup stress on the maternal behavior of Rattus norvegicus

Litters of primiparous and multiparous rat mothers received 0, 2, or 5 min of cold stress for the 1st 5 days postpartum. Primiparae showed increasing maternal responsiveness over the treatment period. Multiparae were initially maternally responsive to moderate stress cues from pups, but habituated to them over days. From Days 6 to 20, when pups were not stressed, lactation behavior of stressed groups declined in primiparous mothers but not in multiparous mothers.     

Interactive effects of genotype and early life undernutrition on the development of behavior in rats

Developing rats of 2 outbred stocks were either well-nourished or undernourished by underfeeding their mothers throughout pregnancy and lactation. All rats were well-fed from 25 days of age. Starting at 110 days male rats were observed first in an open field and then in a social situation; finally their motor performance was tested on a revolving drum. The social behavior test comprised pairing male rats of the same stock, 1 well-fed control with 1 previously undernourished rat. Analysis of variance of the results of the open-field and social behavior tests revealed main effects of Nutrition and of Stock for several measures of behavior in each test. There were also Nutrition X Stock interactions for 2 measures from the open field and 1 from the social situation. Motor performance was not impaired by early life undernutrition. The evidence of Nutrition X Stock interactions, together with that from analyses of the effects of nutrition performed separately for the 2 stocks, as if each stock had been investigated in a separate study, indicates that genotypic differences may be one of the reasons for the discordance often found between the conclusions of different early life malnutrition studies.     

Septal lesion, sex, and incentive shift effects on open field behavior of rats

Rats with lesions of the septum and control rats were placed in an open field for 5 min per day under three conditions: Habituation (3 days); Preshift (10 days), in which half of the animals were given access to 32% sucrose and half to 4% sucrose; and Postshift (4 days), in which all rats received 4% sucrose. Lesioned animals tended to spend less time in motion and engage in less rearing behavior than controls; showed a negative contrast in lick rate equivalent to the controls subsequent to the shift; showed an exaggerated increase in ambulatory behavior subsequent to the shift; and were more ‘conservative’ than controls in sampling from novel sources of sucrose present during the postshift period. Female rats engaged in more activity than males; were less affected by sucrose concentration differences during preshift; showed negative contrast effects equivalent to the males; but female rats with septal lesions showed the slowest rate of recovery from contrast and spent the most time in motion during postshift.     

Investigative behavior of rats differing in predisposition to stress in open field and chamber tests

Laboratory of Motivated Behavior and Learning, A. I. Karaev Institute of Physiology, Academy of Sciences of Azerbaijan, Baku. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 114, No. 8, pp. 130–132, August, 1992.     

Differential effect of acetyl-l-carnitine on open field behavior in young and old rats

Acetyl-l-carnitine (ALCAR) exerts antiaging effects with study we evaluated the effect of a chronic treatment with ALCAR (6 weeks, 50 mg/kg/day) on the open field behavior of 5-month-old and 26-month-old male Wistar rats. Old rats defecated more, made fewer crossings, and spent more time in the corner squares. However, it is difficult to interpret these findings in terms of an increase in emotional reactivity with age because locomotor performance generally has been found to be impaired in old rats. Consequently, treatment effects were analysed within age groups. ALCAR had no effect in young rats, but the old ALCAR-treated rats ambulated less and spent more time in the corner squares than the old control rats. We have interpreted this in terms of an enhanced emotional reactivity of old ALCAR-treated rats.     

Effects of progesterone on open field behavior of food deprived ovariectomized female rats

The effects of intraperitoneal progesterone administration on the open field behavior of ovariectomized female Wistar rats were studied in two experiments. Subjects were challenged with 5 different doses of progesterone (0, 10, 20, 40, 80 mg/kg body weight) during 5 successive days of open field testing (5 min a day) in the first experiment. Progesterone dose-dependently decreased rearing and object inspection, but did not affect total ambulation. In the second experiment food pellets were presented in the open field and subjects were repeatedly tested at regular intervals after progesterone administration on each of 5 consecutive testing days. Three doses of progesterone (0, 40, 80 mg/kg body weight) were administered during the final 3 days of the second experiment. Eighty mg/kg progesterone decreased rearing activity, but increased ambulation; motivation to retrieve food pellets was not affected. These effects of 80 mg/kg progesterone were observed at least as long as 2 hours after injection. Forty mg/kg progesterone did not produce such effects. These results, in conjunction with those of other experiments show that progesterone affects open field behavior in a way similar to central depressant drugs.     

Effects of intranasal zinc sulfate on open field and maternal behavior in female rats

Nulliparous white rats were injected intranasally (IN) or intraperitoneally (IP) with zinc sulfate (Zn) or were injected IN with saline or air, and were induced to show maternal behavior through continuous pup exposure begun 24 or 48 hr after treatment. ZnIN and ZnIP groups all showed declines in locomotor activity and rearing in an open field. ZnIN females sniffed less and groomed more often and for more total time than ZnIP or AIR females, effects attributed to nasal irritation and impaired olfaction. Declines in activity did not appear due to systemic absorption of zinc sulfate. Induction of maternal behavior was facilitated by ZnIN but not by ZnIP. Modifications of IN injection procedures were felt to have reduced post-treatment debilitation caused by accidental aspiration of zinc sulfate.     

Adolescent female rats are more resistant than males to the effects of early stress on prefrontal cortex and impulsive behavior

We tested the hypothesis that adolescent Sprague–Dawley females may be more resistant than males to display impulsive behavior and lower prefrontal cortex thickness after mother‐infant separation (MS). Starting at postnatal day 2 (P2), the MS group was separated 6 hr/day and the early handled (EH) group 15 min/day for 10 days, and another group was standard facility reared (SFR). Subjects were examined for novel open‐field activity (P28), light–dark apparatus (P29), familiar open‐field (P30) and frontal cortical thickness. This protocol resulted in impulsive behavior in MS rats relative to EH and SFR, but this effect was less pronounced in females than males. MS affected the two sexes differently in terms of decreased prefrontal cortex dorsoventral thickness, with this effect being significant in males but not females. Neuroanatomical and behavioral documentation that adolescent females are more resistant than males to ADHD‐like effects of maternal separation have not been previously reported. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 277–288, 2009     

Maternal stress and high-fat diet effect on maternal behavior, milk composition, and pup ingestive behavior

Chronic variable prenatal stress or maternal high-fat diet results in offspring that are significantly heavier by the end of the first postnatal week with increased adiposity by weaning. It is unclear, however, what role maternal care and diet play in the ontogenesis of this phenotype and what contributions come from differences already established in the rat pups. In the present studies, we examined maternal behavior and milk composition as well as offspring ingestive behavior. Our aim was to better understand the development of the obese phenotype in offspring from dams subjected to prenatal stress and/or fed a high-fat (HF) diet during gestation and lactation. We found that dams maintained on a HF diet through gestation and lactation spent significantly more time nursing their pups during the first postnatal week. In addition, offspring of prenatal stress dams consumed more milk at postnatal day (PND) 3 and offspring of HF dams consume more milk on PND 7 in an independent ingestion test. Milk from HF dams showed a significant increase in fat content from PND 10-21. Together these results suggest that gestational dietary or stress manipulations can alter the rat offspring's developmental environment, evidence of which is apparent by PND 3. Alterations in maternal care, milk composition, and pup consumption during the early postnatal period may contribute to long-term changes in body weight and adiposity induced by maternal prenatal stress or high-fat diet.     

Protein malnutrition in the rat: its effects on maternal behavior and pup development

Repeated time-lapse photographic observations were used to examine the maternal behavior and pup development of female Holtzman rats maintained on either a low-protein (12% casein by weight) or a high-protein (25% casein) diet throughout the period of lactation. Dams fed the low-protein diet were observed to spend more time in the nesting area with their pups than dams fed the high-protein diet. Locomotor activity of the dams did not differ between the 2 groups. The behavioral development of the pups suckling the dams receiving the low-protein diet was markedly depressed as compared with the controls. Included in this latter observation were pup behaviors such as movement from the nesting area, feeding and drinking from available supplies, and rearing and climbing activity. The results indicate that feeding a low-protein diet to a lactating dam results in behavioral changes in both the dam and pups that tend to minimize the exposure of the pups to the immediate environment.     

Systemic administration of endorphins selectively alters open field behavior of rats.

A single intraperitoneal injection of 100 μg of α, γ, and β-endorphin or their [D-Ala²] analog influenced the behaviors of male rats tested in the open field. Beta-endorphin significantly increased grooming behavior whereas [D-Ala²]-α-endorphin appeared to enhance sexual arousal. Both γ-endorphin and [D-Ala²]-γ-endorphin affected separate measures indicative of heightened emotionality. It appears that systemic injections of these fragments of β-LPH are capable of modulating behaviors unrelated to analgesia. Furthermore, the selective effects of these peptides suggest the possibility that each may be coded to act upon receptor sites in a differential manner resulting in separate and distinct patterns of behavioral alterations.     

Open field behavior and cardiovascular responses to stress in normal rats

Experiments were conducted in normal Wistar rats with different patterns of behavior to assess the effects of stress on cardiovascular reactivity. One week after weaning and one month later rats were tested in an open field. Animals that did not cross any square in both open fields were classified as HYPOACTIVE. Those crossing more than 43 squares in the first and any in the second open field were classified as HYPERACTIVE. No difference was found in the basal mean blood pressure (BP) or heart rate (HR) between both groups. After a stress (change of cage, electric shock or immobilization) BP and HR increased. The increase in BP was higher in HYPOACTIVE rats. The HR increase was similar in both groups. Therefore, the ambulatory activity in the open field allowed us to separate groups of rats with different cardiovascular reactivity to stress.     

The effects of early stress and undernutrition on the behavior of young adult rats and the correlations between behavioral and brain parameters.

Control and chronic undernourished newborn rat pups were exposed to cold stress for 3 min daily or left undisturbed on Days 2–11. On Days 25–29 (preweaning) and at 90 days of age, stressed and non-stressed pups in each group were tested in a cross-maze and a T-maze, and their preference for novel and social stimulation and activity levels were measured. At 90 days only, another group of such pups was trained to learn an active avoidance response to electric shock. The results on maze performance show that prior to weaning, stressed controls (SC) and nonstressed undernourished (NSU) pups exhibited shorter response latencies, and a greater preference for social stimulation than the non-stressed controls (NSC). At 90 days, SC and NSU again exhibited shorter latencies, and higher activity levels, and also a greater preference for novel stimulation than the NSC animals. In these parameters, there were no significant differences between stressed undernourished (SU) and NSU animals. In original avoidance learning, undernourished animals exhibited a slower rate of acquisition learning than controls. However, in reversal learning, NSU animals made significantly more errors than the SU animals. There were no significant differences between the two control groups and the SU group. These results show that early cold stress alone can have the same behavioral effects as early undernutrition alone and that early stress can have a significant reversing effect on the learning performance of previously undernourished adult animals. Statistical correlations between behavioral parameters (X- and T-maze behavior and active avoidance learning) and crude brain parameters (weight, cell number (DNA), cell density and protein) were investigated in the above animals. It was found that, in general, behavioral parameters whose high values appear to be of advantage for the animal (e.g. number of entries or social time in mazes and percent correct moves in the original and reversal learning) had significant positive correlations with weight, cell number (DNA), and protein content, at least in cerebral cortex and cerebellum, and negative correlations with cortical cell density. Conversely, parameters whose high values are of disadvantage (latency in mazes, or total trials to criterion and total errors in learning) generally had significant negative correlations with brain weight, cell number, and protein content, and positive with cortical cell density. Age, stress or undernutrition had no effect on these results. It is concluded that, statistically, even these crude brain parameters may be significantly correlated with behavior. That is, animals tend to perform better if their cortical cells are further apart and if their brain weight, cell number (DNA), and protein content are higher.     

Effects of unusually early visual stimulation on the development of homing behavior in the rat pup

Two studies examined the theory that early limitations on sensory functioning contribute to the organization of a structure for perceptual development and intersensory functioning. Rat pups' eyelids were surgically opened on Day 7, following which the development of homing to their nest site was investigated, with each animal alone in its living cage. Control pups increased homing until Day 14, and then decreased. Experimental pups showed no such decline, with the highest rate of homing evident on the last day of testing. The importance of visual cues for this altered development of homing was examined. Visual cues for the home were reduced by removing all shavings during testing, while leaving an odorous substrate in place. Under these conditions, both groups showed the characteristic increase and decline in homing, suggesting that premature eyelid opening results in a modification of the distribution of attention to visual and olfactory characteristics of the nest.     

Effect of substance P on behavior in the open field forced swimming tests in rats with various types of behavior

It was found that substance P administered to rats with active and passive types of behavior reversed their behavioral type but dit not affect the behavioral parameters of rats comprising an intermediate group. The “pure” effect of substance P (discounting the influence of repeat testing) was significant only for the number of rearings and the time of passive floating. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N ^o 3, pp. 244–247, March, 1996 Presented by P. V. Simonov, Member of the Russian Academy of Sciences     

The effects of prenatal psychological stress on the sexual behavior and reactivity of male rats

Male offspring of prenatally stressed rats showed low levels of copulatory behavior during a series of brief tests with estrous females but successfully impregnated female cagemates during long term tests of breeding effectiveness. Sexual performance on the short term tests was inversely related to open field activity with the offspring of prenatally handled mothers exhibiting more sexual behavior and less open field activity. These results support the notion that prenatal stress influences both the sexual behavior and emotional reactivity of male offspring. Deficits observed during short term tests of breeding effectiveness appear to be reversible under optimal conditions.     

Maternal behavior priming in virgin and caesarean-delivered Long-Evans rats: effects of brief contact or continuous exteroceptive pup stimulation

The effects of 8 days of prior exposure to pups (Priming) in the form of continuous exteroceptive (smell, sight and sound), or 15 min/day physical access (taste and touch possible) stimulation on the subsequent latency to become maternal during cohabitation with pups (concaveation) was studied in Long-Evans female rats. Brief daily access was effective in hastening the onset of maternal behavior only in those virgins which engaged in pup licking during Priming and in maintaining short-latency maternal responsiveness only in those day 21 pregnancy-terminated, thelectomized rats which initiated maternal behavior during Priming. Exteroceptive stimulation was ineffective in both virgins and caesarean-sectioned rats. These findings stress the importance of physical interactions with pups (unrelated to nipple stimulation) for the development of nurturance.     

Sensory regulation of maternal behavior in rats: Effects of pup age

Maternal behavior (retrieving, crouching, and licking) was induced in Sprague-Dawley virgin female rats by constant exposure to pups aged 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, 13-14, or 15-16 days. The incidence of spontaneous components of maternal behavior, notably retrieving, was geater towards pups 1-8 days of age than towards older pups, whereas the occurrence of cannibalism did not differ as a function of pup age. With pups 1-2 through 13-14 days, the latency to onset of full maternal behavior was shortest with 1-2-day-old pups (2-day median) and longest with 13-14-day-old pups (7-day median). Females exposed to pups aged 3-4 through 11-12 days did not differ significantly in their latencies, the medians of which ranged from 4.0 to 5.5 days. Only 1 female out of 8 exposed to pups aged 15-16 days became fully maternal, but 5 more displayed components of maternal responsiveness. The optimal nature of neonates and the general attractiveness of a wider range of pup ages as stimuli for the elicitation of maternal behavior in rats, as well as comparisons to mice and hamsters, were discussed.