A social environment influences the total RNA content of the brain cells of young laboratory rats

The paper describes the results of measurement of the total RNA content of single cells of the frontal pole of the cerebral cortex, the septum, the dorsal hippocampus and the medial hypothalamus of 35-day-old male laboratory (Wistar strain) rats. Two groups of ten animals each, reared in different ways, are compared: 1) young which lived from the age of 15 days with their mother, their siblings, other adult animals of both sexes and the young of other litters in a large, complex space, and 2) young which lived only with their mother and siblings in a small, simple space, as is usual under laboratory conditions. Nutrition and other environmental factors in the two groups were the same. The RNA content of cells from all the given parts of the brain was higher in community-reared rats, but the relative difference (related to the mean values for community-reared animals) in the various parts was not the same. It was smallest in the cerebral cortex and greatest in the dorsal hippocampus. Differences in the ventromedial hypothalamus and the septum were moderately large, with the hypothalamus rather resembling the cerebral cortex, while the septum differed statistically significantly from both the cortex and the hippocampus. The effect of social stimulation was thus strongest in the hippocampus.     

The active avoidance reaction of laboratory rats: differences between experiments carried out in the phase of motor activity and inactivity

The influence of two phases of the circadian cycle (motor activity and motor inactivity) on the rate of acquisition and extinction of an active avoidance reaction was studied in 35-day-old male laboratory rats reared in cages (with limited social contacts), in young reared from the age of 15 days in communities (with the broad social contacts typical of this species) and in adult males reared in cages. A difference was found between the results of experiments carried out in the morning (during the motor inactivity period) and in the early evening (at the outset of the motor activity period) in both young and adult animals. The factor deciding whether acquisition or extinction was influenced depended on the mode of life. In animals reared in cages, inhibition was influenced; extinction was elaborated faster in the evening in adult animals and juvenile young were capable of 100% extinction only in the evening (in the morning only 50%). Community young achieved 100% extinction in both cases. In young rats which lived in a community from the 15th day, acquisition was influenced (it was achieved faster in the evening). The correlation between the rate of acquisition and extinction in cage-bred adult and young rats was negative if the experiments were carried out in the morning and was positive in evening experiments on young animals. In community-bred young it was positive in both cases.     

Interaction between pre-weaning undernutrition and post-weaning environmental enrichment on somatic development and behaviour in male and female rats

Male and female rats were undernourished from birth to 30 days by restricting access to the lactating mother, and then fed ad libitum. At weaning, underfed and normally suckled controls were permanently housed either in pairs in standard cages or in groups of 10 in 1 m³ cages containing ladders, ropes etc. Severe undernutrition during suckling followed by 4 months of refeeding, produced some changes in sexual behaviour in adult males (increased ejaculation frequency) but had no effect on behaviour in open field, dark preference or passive avoidance. Differential post-weaning environment produced significant differences in behaviour, irrespective of previous feeding conditions. Enriched animals were more active and exploratory. Females differed from males in the same direction as enriched from standard, and were more responsive to social and housing conditions.     

Significance of the weaning period for natality and maternal behaviour of laboratory rats.

Normally weaned females (at 30 days) displayed seasonal cyclic changes in natality and the characteristics of the young. Natality in the spring and summer was high, the litters were large, the proportion of females and males in the litter was equal and deaths among the unweaned young were very few. Natality in the autumn and winter was low and the litters were small and consisted mainly of males. The death rate among the young was higher than in the spring and summer. Prematurely weaned females (at 15 days) displayed no seasonal cycle either in natality or in the characteristics of the young. The studied parameters corresponded to the values found in the spring and summer in normally weaned females. No differences were found in maternal retrieving, but there was a marked difference in nest-building. The normally weaned female tore up paper (building material) into small fragments 24 hours before giving birth and dropped the young into a soft nest of finely shredded paper. On leaving the nest it covered the young up. The prematurely weaned female scattered the paper about the cage 24 hours before giving birth and dropped the young into a depression stamped out among whole pieces of paper. It did not cover the young up on leaving the nest. The cause of the difference in building behaviour is evidently that prematurely weaned females failed to acquire early experience of this behaviour between the 15th and 30th day of life.     

Strain differences in avoidance reactions of septal laboratory rats

The effect of a lesion of the dorsal septum on active and passive type of avoidance reactions of adult male Wistar (W) and Long-Evans (LE) rats was studied. The rate of acquisition and extinction of the reaction was studied by 3 different testing methods. The animals were operated on when juvenile (30 days) or adult (90 days). The experiments were always started 50 days after the operation, when the "rage syndrome" was no longer present. In the three different tests we found a single common variable--the strain factor. It was this that determined whether the operation was effective, as well as the direction of deviations and the operation age which led to manifest changes. In W males the lesion did not impair either the acquisition or the extinction of an active avoidance reaction (AAR); the passive avoidance reaction (PAR) was acquired and extinguished more slowly after a lesion in adulthood. The spontaneous passive avoidance reaction (i.e. preference of a small, dark space) was likewise negatively affected by the operation. In intact LE animals the AAR was extinguished more slowly than in intact W males; after a lesion produced in juvenile or adult age extinction was speeded up, so that there were no differences compared either with intact or with septal W animals. Intact LE rats also acquired a PAR more slowly than W rats; a septal lesion led to faster acquisition, irrespective of the age at which the operation was performed, so that the rate for septal LE rats were the same as for intact W animals. The extinction of this reaction took longer after an operation at juvenile age and the rate for these septal LE rats were the same as for those of septal W individuals operated on at 90 days. The spontaneous PAR was qualitatively poorer in intact LE animals than in intact W rats, since only 40% of them preferred the small, dark space. A lesion was followed by improvement, which was especially marked after operation on the 30th day, when all the animals preferred this space, and in a very short time, so that they were equal to intact W males. Correlation of the acquisition and the extinction rate showed that there was imbalance of excitation and inhibition processes in the AAR of the W controls, that they were balanced in the PAR and that the lesion reversed these relationships. Both processes were balanced in the LE control and a septal lesion did not alter the situation.     

Diapause avoidance induced by low temperature in the yellow-spotted longicorn beetle, Psacothea hilaris

The diapause-averting effect of low temperature on pre-diapause larvae was examined in the yellow-spotted longicorn beetle, Psacothea hilaris. Larvae that had been reared under diapause-inducing conditions (25 °C , L12:D12) were temporarily exposed to 10 °C for various periods, and returned to the initial condition. Diapause was not averted by chilling for 15 days irrespective of the age of the larvae at chilling. After a 30-day chilling treatment, all of the 40- and 60-day-old larvae averted diapause, while diapause was averted in only one-third of the 10- and 20-day-old larvae. None of the pre-diapause larvae chilled for 60 days entered diapause irrespective of the age at chilling. With diapause avoidance, larvae that overwintered in earlier instars can start growing in earliest spring without any arrest; this phenomenon probably subserves the synchronization of larval development in a population.     

Sniffing behaviour, copulatory readiness, copulatory performance and reproductive morphology of adult male rats weaned prematurely

Sexual behaviour of adult male rats weaned prematurely--on day 15 after birth--and of males weaned at the optimal age--on day 28--was compared at two life periods: at the age of 90 days and when the males were one year old. Sexual behaviour was evaluated by means of three characteristics: a) sniffing behaviour, b) copulatory readiness, c) copulatory performance. The differences in sniffing behaviour between prematurely and normally weaned males were assessed in terms of their responsiveness to sccents of unrelated adult males or oestrous females and from the point of view of both housing conditions after weaning and the animals' sexual experience. No differences were found in copulatory readiness as well as in copulatory performance between the two groups of males tested in their interaction with a female exhibiting complete precopulatory pattern. The morphological examination revealed no differences in the weight of reproductive organs and in spermatozoa development. We conclude that the sexual behaviour as well as reproductive organs of male rats are very resistant to early separation of pups from the mother which contrasts with some earlier findings.     

Effect of neonatal hypoxia on the development of hepatic lipase in the rat

Increases in plasma lipids occur during hypoxia in suckling but not in weaned rats and may result from altered hepatic enzyme activity. We exposed rats to 7 days of hypoxia from birth to 7 days of age (suckling) or from 28 to 35 days of age (weaned at day 21). Hypoxia led to an increase in hepatic lipid content in the suckling rat only. Hepatic lipase was decreased to approximately 45% of control in 7-day-old rats exposed to hypoxia but not in hypoxic 35-day-old rats. Hypoxic suckling rats also had a 50% reduction in lactate dehydrogenase activity, whereas transaminase activity and CYP1A and CYP3A protein content were not different between hypoxic and normoxic groups. Additional rats were studied 7 and 14 days after recovery from hypoxic exposure from birth to 7 days of age; hepatic lipase activity had recovered to 85% by 7 days and to 100% by 14 days in the rats previously exposed to hypoxia. Administration of dexamethasone to neonatal rats to simulate the hyperglucocorticoid state found in hypoxic 7-day-old rats led to a moderate decrease ( approximately 75% of control) in hepatic lipases. Developmentally, in the normoxic state, hepatic lipases increased rapidly after birth and reached levels more than twofold that of the newborn by 7 days of age. Hypoxia delays the maturation of hepatic lipases. We suggest that the decrease in hepatic lipase activity contributes to hyperlipemia in the hypoxic newborn rats.     

Effects of early weaning and housing conditions on the development of stereotypies in farmed mink

Female mink pups were weaned at 6, 8 or 10 weeks of age and subjected to two different housing conditions. They were either kept together with a single male sibling in traditional mink cages (30x45x90 cm) or housed socially with all litter-mates in an alternative system consisting of three adjoining traditional cages (90x45x90 cm). All cages were supplied with nest boxes. At 5 months of age, the siblings were removed leaving the females socially isolated in the two different cage systems. Females' stereotypies were quantified by repeated scanning observations under the social housing conditions immediately before removal of the siblings, and again at the age of 7 and 9 months, when the animals had stayed solitary in the two systems for 2 and 4 months. Solitary females showed significantly more stereotypies than females under social housing conditions in both cage systems. Stereotypies were more frequent in the smaller traditional cages. Stereotypies declined from 7 to 9 months of age among solitary animals in traditional cages but not in alternative cages. Early-weaned solitary females in traditional cages showed more stereotypies than later-weaned animals, but only when measured at the age of 7 months. It is suggested that early weaning, individual housing and small cages promote the development of stereotypies in farmed mink. The influence of early weaning on stereotypies seems to decline with age, while effects related to individual housing and small cages appear to be more persistent.     

Role of early experience in social behaviour of laboratory-bred female rats

Social relationships among female laboratory-bred rats in a community are influenced by their early life history. When the rats were born and kept until adulthood under conventional breeding conditions, i.e. in single cages, and then used to form a community in which they gave birth, one female assumed the dominant role, with all others subordinate. The dominant female herded all young rats born in the community, irrespective of their age, in a single litter and suckled them. She accumulated food and wood shavings from other parts of the community near the nest and prevented access to the nest to all other community members including other females that had given birth. Subordinate females ceased to show maternal behaviour, including lactation, within 24 h (occasionally within 48 h). The mortality of the young until 15 days of age was high. This type of behaviour in a community was observed both with randomly chosen female rats and with rats selected as dominant and subordinate types in preceding experiments. Female rats born and reared in a community and rats living in a community from 15 to 30 days of age did not differentiate into dominant and subordinate types. All females retained their maternal behaviour, including lactation. Mortality of young rats was minimal. In most cases the females built one common nest; sometimes each female built her own nest. The results point to the decisive role of early experience in the development of maternal behaviour and in the occurrence of communal rearing of the young.     

The effect of cage size on reproductive performance and behavior of C57BL/6 mice

Scientific research has yet to conclusively determine the optimal cage size for mice. The authors examined the effect of cage size on mouse breeding performance and on offspring behavior, which can serve as indications of overall well-being. They housed breeding trios of C57BL/6Tac mice in standard or large individually ventilated cages and measured four reproductive parameters: litter size; litter survival to weaning age; average pup weight at 7, 14 and 21 days; and the number of days between litter births. They investigated the behavior of a subset of male and female pups from parents housed in cages of each size in the elevated plus maze test, the open field assay and the acoustic startle test. Cage size had no significant effect on any of the reproductive parameters measured and few or inconsistent effects on behavior in weaned pups.     

Onset of compensatory hypertrophy of interstitial tissue and Leydig cells in rats hemicastrated around the time of puberty

When rats were unilaterally castrated at 20, 30, and 40 days of age, only those rats hemicastrated at 40 days showed compensatory hypertrophy of the interstitial tissue and Leydig cells when killed 30 days after hemicastration. At the time of death, volume densities of interstitial tissue, Leydig cells, and vascular components were greater in 70-day-old hemicastrated rats than in intact rats of the same age. The total number of Leydig cells per testis in hemicastrated and intact rats was always the same at any age. Estimated Leydig cell volume in 70-day-old rats was twice that in intact rats. By contrast, the testes of 50- and 60-day-old rats at the time of death displayed essentially the same morphological features, regardless of whether animals were hemicastrated. The concentration of plasma testosterone was higher in 50-day-old controls than in hemicastrated rats. Seventy-day-old hemicastrated rats showed higher levels of plasma testosterone than controls. The level of plasma dihydrotestosterone in 60- and 70-day-old hemicastrated rats exceeded that in the controls. A significant increase in follicle-stimulating hormone was noted in 50- and 70-day-old hemicastrated rats compared to normal rats, while levels of luteinizing hormone were basically the same. The increase in Leydig cell volume, interstitial tissue volume, vascular component volume, and plasma testosterone level caused by hemicastration at 40 days of age differed from that at 20 and 30 days of age.     

Microclimate in two types of rat cages

The microclimate in two types of rat cages (a Makrolon type IV with a solid floor and a stainless steel cage with a wire mesh floor (five rats per cage)) placed in the same macro-environment was compared. The temperature, relative humidity and ammonia concentration in the cages were measured twice a day for 8 days. The cages were cleaned every 4 days. The greatest difference between the cage types was in the ammonia build-up. In Makrolon cages the ammonia concentration never reached 5 ppm, whereas in steel cages it showed a constant increase and already exceeded the threshold limit for man (25 ppm for 8 h per day) on the third day after cleaning.     

Behavioural responses of rats to early housing conditions and to protein-energy malnutrition

Lactating rats were fed either the commercial diet (CO) or the low protein diet which induced symptoms of protein - energy deprivation (PD). They were housed in cages either individually (IH) together with eight offspring or in a large community cage (COM) shared by six dams and 48 youngs. After weaning all rats lived in cages by 4-5 animals. The PD terminated at the age of 49 days. Behaviour was tested on the 10th, 42nd and 150 th days of life. Body weight was recorded during nursing period both in dams and pups, after weaning in male rats. The low protein diet affected both body weight and maternal behaviour of the dams. In PD + IH pups growth as well as behavioural development was retarded. Behavioural alterations persisted even after the PD had been treated. The COM housing improved the body weight in the PD + COM dams, behaviour of both the PD + COM dams ond the pups was less affected than of the PD + IH group. The effect of the early housing was long lasting, manifested itself in elevated exploratory activity and in the decreased emotional responses in both the PD + COM and the CO + COM groups at the age of 42 and 150 days.     

Influence of age and caging upon protein metabolism,hypopharyngeal glands and trophallactic behavior in the honey bee (Apis mellifera L.)

Summary Different-aged honey bees were either kept in a cage together with young sisters for eight days or lived in their colony. Following an injection of¹⁴C-phenylalanine (Phe) we measured incorporation of¹⁴C-Phe into head protein and total protein, as well as the size of the hypopharyngeal glands. While confined in a cage for four hours, injected bees (from colony or cage) dispensed the¹⁴C-labelled protein-rich products of their hypopharyngeal glands to recipients. Eight-day-old colony bees had well developed hypopharyngeal glands, whereas at the age of sixteen days the glands had already decreased in size. Young caged bees had smaller hypopharyngeal glands. Colony bees had higher incorporation rates into total protein and head protein than bees living in a cage. Bees of different age classes, irrespective of caging, fed the same number of recipients; but the amount of¹⁴C-labelled protein-rich jelly distributed by caged bees was significantly smaller than that distributed by colony bees. Our results indicate that trophallaxis between young donor workers and newly emerged recipient worker bees is not the key factor for regular development and activity of the hypopharyngeal glands.Dedicated to Achim Lass's daughter Katrin.     

The relationship between protein retention and energy requirements in rats of different ages

Male Wistar rats aged 30, 75 and 150 days were fed for 14 days ad libitum on diets with an optimum protein content (15% for 30-day-old, 12.5% for 75-day-old and 10% for 150-day-old animals) and a mounting fat content (from 5 to 40%), supplemented by saccharides (from 76 to 41%). Net protein utilization was determined for each of the diets from the body nitrogen and protein intake values. Protein retention values were determined from protein intake on the basis of net protein utilization (NPU). Energy intake was computed from fat and saccharide intake, using energy coefficients. The optimum fat content of the diet, evaluated from the maximum protein retention value per day and the minimum amount of energy needed for the retention of 1 g protein, is 30% at 30 days, 15% at 75 days and 10% at 150 days. Protein retention per kg body weight falls with advancing age--mildly at 75 days compared with 30 days, but markedly at 150 days. From their smaller weight increments and NPU values and also from their lower protein retention, 150-day-old animals are characterized by slower growth and higher protein requirements for maintenance of their organism likewise demonstrated by the growth parameter net protein ratio (NPR). Energy requirements for total protein retention/day per kg body weight diminish with age. In old age a small amount of energy is needed only for the maintenance of body functions. This study contributes to the expression of the interrelationship of energy requirements and protein retention.     

Malate dehydrogenase and glucose-6-phosphate dehydrogenase activity in livers of Ni-deficient rats.

In experiments using rats it was shown that inadequate dietary supply of Ni reduces growth and lowers the erythrocyte count, hematocrit and hemoglobin level in blood, that the Ni supply affects the trace element content of iron, copper and zinc in various body organs, and that the absorption of iron is greatly impaired by Ni deficiency. For further biochemical criteria on the essentiality of nickel, the activities of two dehydrogenases, malate dehydrogenase and glucose-6-phosphate dehydrogenase, were measured in liver homogenates from two generations of rats at 30 and 50 days of age. In the 30-day-old rats of both the F1 and F2 generation, the activity of the malate dehydrogenase fell to about two-thirds the level of control animals. In the liver of the 50-day-old rats the activity of this enzyme was about the same in deficient animals as in the controls. The activity of glucose-6-phosphate dehydrogenase of Ni-deficient rats was reduced by 85% in the F1 generation and by 56% in the F2 generation at 30 days of age as compared with control levels. In 50-day-old rats the activity had fallen to half the level of control animals at 30 days of age. At the age of 50 days, there was no significant difference between the deficient and the control groups of either generation.     

Effects of early malnutrition on Swiss white mice: avoidance learning after rearing in large litters

Mice were undernourished by rearing in litters of 20 pups per mother, weaned onto stock diet and their shuttle-box avoidance performance measured at 2 months of age. The mice from these large litters learned the avoidance response more slowly than controls (mice reared in litters of 5). In a second experiment, avoidance performance was measured after nutritional rehabilitation until 2, 4 or 6 months old. No significant improvement was observed in the previously malnourished mice. In the controls, performance was high at 2 and 4 months but by 6 months had fallen almost to the same level as the test group.     

Presence of mother and unfamiliar female alters levels of testosterone,progesterone, cortisol,adrenocorticotropin, and behavior in maturing Guinea pigs

Although the guinea pig is characterized by precocial physical development and minimal active maternal care, studies suggest the presence of the mother can influence neuroendocrine and behavioral activity of offspring even well beyond weaning. Previous results may have been influenced by the procedure of housing weaned subjects with the mother to within 2 days of testing. The present study examined approximately 40-day-old guinea pigs housed apart from the mother for 0 (not rehoused), 2, or 10 days. Rehousing without the mother led to elevations in plasma testosterone (measured in males), progesterone (measured in females), cortisol, and adrenocorticotropin (ACTH) (both measured in males and females). Offspring housed without the mother for 10 days had the highest progesterone, cortisol, and ACTH levels. Testosterone elevations were observed in 2-day-, but not 10-day-, rehoused animals. Regardless of rehousing condition, 60 min isolation in a novel test cage elevated progesterone, cortisol, and ACTH, and reduced testosterone. These effects were all moderated if the subject was tested with the mother or another female. Sexual behavior toward the mother was observed frequently, but only in males housed apart from her prior to testing. Overall, males and females that had been housed apart from the mother interacted with her as they would an unfamiliar female. Our results corroborate previous findings, suggest the effect of housing apart from the mother on male testosterone is transitory, and indicate that continuous housing with the mother past weaning suppresses circulating progesterone in females and cortisol and ACTH in both sexes.     

Effect of sexual steroids and androgen sterilization on avoidance and exploratory behaviour in the rat

The effect on avoidance and exploratory behavior of large doses of sexual steroids or of changes in ovarian steroid secretion induced by gonadotropin treatment or androgen sterilization was studied in female R-Amsterdam rats. Estrogen, progesterone, testosterone, androgen sterilization, and human chorionic gonadotropin (HCG) effects were tested and evaluated. Estrogen in castrated female rats delayed extinction of the conditioned avoidance response from Day 8 of extinction and increased intertrial activity during extinction. Estrogen treatment applied from extinction was ineffective. Progesterone treatment of castrated female rats applied from the first days of conditioning delayed extinction from Day 12. If the treatment was begun at extinction, this was delayed after Day 8. Intertrial activity was also higher between Day 8 and Day 15 of extinction. Testosterone treatment of castrated male rats increased intertrial activity during acquisition. In the animals treated from extinction, a delay was observed from Day 9, and intertrial activity was increased simultaneously. In androgen-sterilized female rats, extinction was facilitated. HCG treatment of intact female rats delayed the extinction. The steroids used failed to affect the exploratory activity of castrated rats, indicating that, under the conditions tested, general activity and exploratory activity are not motivated by the same mechanism.