Acquisition of avoidance reaction in rats with different social experience in youth

The acquisition of both active and passive avoidance response, the extinction of the former and the retention of the long-term memory trace of the latter were studied in 30- and 90-day-old male rats of the Wistar strain. The rats were in 3 groups which had had a different history between 15 and 30 days of age: (1) normally weaned rats lived from birth in a cage together with mother and siblings, i.e. under usual laboratory breeding conditions; (2) prematurely weaned rats lived under the same conditions for the first 15 days; after this period, their mother was removed from the cage; (3) community-reared rats had the same history up to 15 days of age; then they began to live in a community (5 connected cages) in contact with both young and adult rats from other cages. Ninety- day-old male rats acquired an active avoidance response at the same rate irrespective of their history in youth but 30-day-old rats were relatively slower if they had been prematurely weaned. Among both normally and prematurely weaned 30-day-old rats, the extinction was slower than in community-reared rats of the same age. Passive avoidance response was acquired by all rats at the same rate irrespective of their history and age. The long- term memory trace was always more stable in adult rats than in young ones.     

Faecal corticosterone and immunoglobulin A in young adult rats

Quantitative analyses of relevant molecules in faeces may have potential as future non-invasive measures of stress. This study examined levels of faecal corticosterone and immunoglubulin A (IgA) in young adult rats and how these levels varied according to age, gender and time of day. Faecal samples were collected from 40 young adult rats (7 weeks old, n = 20 and 10 weeks old, n = 20) of both sexes from two time windows: day and night. The concentrations of corticosterone and IgA were measured by ELISAs following organic solvent extraction and aqueous extraction, respectively, of the molecules from faecal pellets. The production of faeces per time unit was higher in males than in females, and linear correlations were found between the faecal concentrations of corticosterone and IgA and total amounts of the respective molecules excreted in faeces per kg body weight per hour. In all further analyses the levels of the two molecules were calculated as amounts secreted per kg of body weight per hour. There was no gender difference between females and males in the production of corticosterone and IgA, but 7-week-old animals excreted significantly higher amounts of both molecules than did 10-week-old rats. The levels of IgA excreted by female rats were higher in the evening than in the morning, and male rats excreted higher concentrations of corticosterone in the morning than in the evening.     

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.     

Pinealectomy blocks modulation of active avoidance by central vasopressin application in rats

The inter-relationship between central vasopressin and the pineal gland in the modulation of active avoidance behavior was investigated. In sham-operated (SO) rats, intracerebroventricular (i.c.v) application of 10 ng arginine vasopressin (AVP) after both the last acquisition and the first extinction trials prolonged the extinction of the active avoidance response; application of 50 ng of the V1 antagonist, d(CH2)5Tyr(Me)AVP (AAVP) was without effect in both experiments. In contrast to the SO in pinealectomized (PX) rats neither AVP nor AAVP influenced the extinction of the avoidance response. Intraseptal infusion of 200 pg AVP or 5 ng AAVP either after the last acquisition or the first extinction trial was without effect in both SO and PX rats. Comparison of the acquisition trials revealed no differences between SO and PX rats.     

Taste aversions in the ontogeny of the rat

The characteristics of acquisition and extinction of conditioned taste aversion (CTA) were studied in rats of both sexes and various ages by pairing of saccharin solution consumption with discomfort (LiCl intoxication, rotation). Pairing of saccharin consumption with LiCl in adult rats led to acquisition of CTA, more profound in male rats than in female ones. In rats of both sexes 30 days old, a profound CTA, comparable in intensity with CTA of adult male rats was acquired. In 2 months after acquisition of CTA in adult rats its magnitude did not change, while in rats of the junior group which by that time had reached puberty, CTA was reduced in females and did not change in males. Pairing of saccharin intake and rotation led to acquisition of CTA only in rats 30 days old. The role of external factors in duration of retention of CTA acquired by pairing of saccharin solution consumption with LiCl injection was studied in male and female rats 1 and 3.5 months old. In all cases CTA was extinguished much sooner in home cages than in experimental chambers, and in the elder group sex dimorphism was found: in both situations CTA disappeared sooner in female rats. The obtained data allow to suggest modulating influences of hormonal background and of contextual stimuli on CTA acquisition and retention.     

Social isolation improves working memory at reversal but not primary radial-arm maze learning in rats

Social isolation starting from the 21st day of birth affected neither a short-term nor a long-term memory in male rats at primary acquisition learning in an 8-arm radial maze. A number of the short-term and long-term memory errors were substantially decreased during primary learning but the difference between groups was not significant. Isolates were faster to start a search in an individual trial and took less time to finish offa trial. During the reversal learning, when baited and non-baited arms were reversed, the isolates outperformed of socially reared rats on working but not reference memory task. In overall they made twice less working memory errors than socially reared animals. During the reversal learning the isolates were also faster than non-isolates in initiation and completion of a trial. Maternal separation of rat's pups on the postnatal days 1-21 for 4 hr per day did not affect either working or reference memory on both primary and reversal learning. The data obtained are discussed on basis of influence of stress in early postnatal life on hypothalamo-pituitary axis and its effects on behavior of adult animals.     

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting.In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.     

Diurnal variations in the catecholamine content in rat tissues. Effects of exogenous noradrenaline

Endogenous noradrenaline (NA) content of the interscapular brown adipose tissue (IBAT), and of the hypothalamus, as well as adrenaline (A) and NA content of the adrenals were measured in the morning and in the evening in rats treated with saline (controls) or with NA (1.6 mg kg-1 pp). NA content in IBAT and in hypothalamus of control animals varies diurnally. NA content in IBAT was significantly higher in the evening than in the morning. In the hypothalamus, these variations were different of those found in the IBAT. Exogenous NA applied both in the morning and in the evening increases significantly NA content in IBAT both in the morning and in the evening, but more in the evening. Unlike IBAT, NA content of the hypothalamus after NA administration does not change essentially. In the adrenal gland of control rats, A content only is changed during the day, being markedly lower in the evening. After NA injection both A and NA are not changed significantly.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Effects of post-weaning environment on learning in the rat

Rats were reared in three different kinds of post-weaning environment: (1) with litter-mates and a variety of playthings (objects/social), (2) without either litter-mates or playthings (no-objects/isolates), (3) with litter-mates, but without playthings (no-objects/social). The animals were subsequently tested on a variety of learning tasks. In one task, the rats had to remove an obstacle from an alley in order to enter a food compartment; subsequently they were required to remove the obstacle in a different way from the one they had learned. Another task was to open a door leading to a food compartment; when the rats and learned this, the floor of the apparatus was lowered so they had to reach the door by climbing a ladder. Object-deprived/isolates were slower than the objects/social group in the transfer phase of the above tasks, though not in original acquisition. Object-deprived/social animals were not inferior to an objects/social group. Isolates had a higher free feeding weight than social animals, were more active in an open field, and ran faster for food reward when deprived.     

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.     

Savings and extinction of conditioned eyeblink responses in fragile X syndrome

The fragile X syndrome (FRAXA) is the most widespread heritable form of mental retardation caused by the lack of expression of the fragile X mental retardation protein (FMRP). This lack has been related to deficits in cerebellum-mediated acquisition of conditioned eyelid responses in individuals with FRAXA. In the present behavioral study, long-term effects of deficiency of FMRP were investigated by examining the acquisition, savings and extinction of delay eyeblink conditioning in male individuals with FRAXA. In the acquisition experiment, subjects with FRAXA displayed a significantly poor performance compared with controls. In the savings experiment performed at least 6 months later, subjects with FRAXA and controls showed similar levels of savings of conditioned responses. Subsequently, extinction was faster in subjects with FRAXA than in controls. These findings confirm that absence of the FMRP affects cerebellar motor learning. The normal performance in the savings experiment and aberrant performance in the acquisition and extinction experiments of individuals with FRAXA suggest that different mechanisms underlie acquisition, savings and extinction of cerebellar motor learning.     

Functional inactivation of the hippocampus by controlled neuroimmunization

The method of immunization with hippocampal tissue cytosol was employed for functional disturbance of hippocampus in newborn and mature rats. This influence resulted in behavioral disorders resembling the hippocampectomy consequences. There were ++non-decremental motor activity and rearing in "open field" test and an improvement in acquisition of active avoidance response in adult rats (250-300 g). In young animals the decreased levels of motor and exploratory activity in "open field" and difficulties in active avoidance learning (in 40 days) were the main features of hippocampal disturbance. In case of immunization with neocortical cytosol no significant alterations in behavior were revealed.     

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.     

Effects of cholecystokinin octapeptide sulphate ester and unsulphated cholecystokinin octapeptide on active avoidance behaviour in rats

The effects of peripherally administered cholecystokinin octapeptide sulphate ester and its unsulphated form on the active avoidance behaviour of rats were studied. The acquisition of avoidance behaviour was impaired, while extinction was facilitated, following cholecystokinin octapeptide sulphate ester or unsulphated cholecystokinin octapeptide treatment. These peptides had no action on open-field activity. It is concluded that peripherally administered cholecystokinin octapeptide influences acquisition and extinction of active avoidance behaviour and this effect is unrelated to general motor activity of the animals.     

Characteristics of L-proline and sodium transport in renal brush border membranes isolated from 7-day-old and adult rats

To explore the nature of differences in uptake by renal brush border vesicles from animals of different ages, vesicles were isolated from 7-day old and adult rats by a Mg-aggregation method. A number of criteria were compared in vesicles from the young and mature animals. The vesicles isolated from animals of both ages appear similar on electron microscopy, in response to osmotic changes, and in uptake kinetics for L-glucose. Despite these parameters which indicate no basic differences between the membranes of young and mature kidney, differences in proline and sodium handling are seen. When compared to the uptake pattern seen in vesicles from adult animals, the height of the sodium gradient-stimulated proline overshoot is diminished and sodium entry is faster in vesicles of the 7-day old rats. These are the same differences which were found in vesicles prepared by differential centrifugation from 7-day old animals. In addition, although sodium efflux was faster from vesicles of immature kidney and mirrored the faster sodium entry, proline efflux was slower. The data indicate a dissociation of proline and sodium fluxes in brush borders of the young rat kidney.     

Development of rodent macrovibrissae: Effects of neonatal whisker denervation and bilateral neonatal enucleation

In this paper we describe the effects of manipulating two kinds of sensory input in neonatal rats upon the development of the macrovibrissae—that movable subset of the rodent mystacial vibrissae. In an initial study of normal whisker development, data on whisker size were obtained from neonatal, perinatal, and adult rats. Data on whisker size were also obtained from rats sustaining either neonatal sensory or motor denervation of the whiskers and from both rats and mice bilaterally enucleated as neonates (BEN). In normally reared rats, most whiskers attain their final size over the first three postnatal weeks but development of rows 6 and 7 are not completed until after the first month. In normal animals we found a significant correlation both between body weight and whisker size and between the size of a whisker and the size of its corresponding cortical barrel. Rats sustaining neonatal denervation of the whiskers have shorter and thinner whiskers as adults than normally reared animals. In both rats and mice bilaterally enucleated as neonates a subset of the macrovibrissae are significantly larger than those of normal controls but no such effect is seen if the enucleation is carried out in adults. Moreover, BEN rats exposed to a novel stimulus environment whisk at a significantly higher frequency than normally reared animals. Mechanisms which might mediate these effects are discussed.     

Development of rodent macrovibrissae: effects of neonatal whisker denervation and bilateral neonatal enucleation

In this paper we describe the effects of manipulating two kinds of sensory input in neonatal rats upon the development of the macrovibrissae--that movable subset of the rodent mystacial vibrissae. In an initial study of normal whisker development, data on whisker size were obtained from neonatal, perinatal, and adult rats. Data on whisker size were also obtained from rats sustaining either neonatal sensory or motor denervation of the whiskers and from both rats and mice bilaterally enucleated as neonates (BEN). In normally reared rats, most whiskers attain their final size over the first three postnatal weeks but development of rows 6 and 7 are not completed until after the first month. In normal animals we found a significant correlation both between body weight and whisker size and between the size of a whisker and the size of its corresponding cortical barrel. Rats sustaining neonatal denervation of the whiskers have shorter and thinner whiskers as adults than normally reared animals. In both rats and mice bilaterally enucleated as neonates a subset of the macrovibrissae are significantly larger than those of normal controls but no such effect is seen if the enucleation is carried out in adults. Moreover, BEN rats exposed to a novel stimulus environment whisk at a significantly higher frequency than normally reared animals. Mechanisms which might mediate these effects are discussed.     

Aging alters properties of the circadian pacemaker controlling the locomotor activity rhythm in males of Drosophila nasuta

Effects of aging on the circadian rhythm of locomotor activity in males of Drosophila nasuta were investigated. The adult life of males was divided in 1-3 stages according to spontaneous changes in free-running period x in constant darkness (DD): stage 1, days 1-19; stage 2, days 20-36; stage 3, days 37-43. Stage 1 was characterized by a bimodal activity pattern with a short light-induced morning peak and a prolonged evening peak when the flies were entrained to light-dark cycles of 12 hours of light, 12 hours of darkness (LD 12:12). The morning peak had a phase angle difference Ψ_m (Ψ, the time from lights on in LD 12:12 cycles to the onset of morning peak) of about 0.1h, while Ψ_e (Ψ of evening peak) was about 9h at stage 1. The transient morning peak was curtailed at the end of stage 1. At stage 2, the Ψ_e was about 10h, and the activity end was delayed by an addition of about 3h of activity in the scotophase. The changes in W during DD free runs were determined in two groups of flies: flies reared in LD 12:12 and flies reared in DD. In both groups, W increased from about 23h at stage 1 to about 25h at stage 2. Stage 3 was characterized by arrhythmicity associated with highest mean activity level (total number of passes/fly/day) in the entrained and both free-running groups. The mean activity level increased significantly from stage 1 to stage 3 in all three groups of flies.     

Protein synthesis in the critical periods of early postnatal ontogeny: its role in the development of the interspecific aggressive behavior of rats

Chronic administration of cycloheximide to young rats from 15-th to 30-th postnatal day before daily 3-hour seances of their contacts, disturbed the formation of animals intraspecies aggressivity. In adults it was manifested by hyperaggressivity and by changes of proportions of different reactions in the integral act of aggressive behaviour. By their character these disturbances were close to those observed in the young rats completely deprived of social contacts in this period of ontogenesis.