Components of early maternal environment affecting the predisposition to catalepsy

Reciprocal pup substitution (cross-fostering) in cataleptic GC (designated so by the initials of words "genetic" and "catalepsy") and control Wistar females resulted in attenuation of cataleptic predisposition in GC rats fostered by Wistar foster-mothers. The latter demonstrate a more intense maternal care than GC females. There was a significant negative correlation between the frequency of mother staying in nest and the duration of pinch-induced catalepsy in pups fostered by her. In the home-cage retrieval test, the females of the strains compared showed a significant dependence of the latencies of approach to, and retrieval of, pups on their own and the pups' genotype.     

Selection of Wistar rats for predisposition to catalepsy

Non-inbred Wistar rats were bred for predisposition to catalepsy for 14 generations. The percentage of cataleptic rats, beginning from the F1, was about 50%, while in the control population it was about 9%. This, together with the data obtained after comparison of the proportion of cataleptic animals in the progeny from homogeneous crossings between rats of normal and cataleptic phenotypes from the group selected for catalepsy (16 and 48%, respectively), makes one suppose predisposition to catalepsy to be an oligogenic character. The later onset of stereotype-like reactions to administrations of methylphenidate, and their longer persistence in cataleptic animals points to inertness of dopaminergic systems. At the same time, the increased frequency of "hyperactivity"-like reactions to methylphenidate, as well as higher arterial pressure and lower frequency of defecations seem to reflect an increased excitability of noradrenergic brain systems in rats predisposed to catalepsy.     

Influence of individual predisposition, maternal experience and lactation environment on the responses of pigs to weaning at two different ages

This study assessed the effect of predisposition to perform harmful social behaviour, maternal rearing environment, and lactation environment on the responses of pigs to weaning at 3 or 5 weeks of age. Predisposed and non-predisposed gilts were selected as dams for this study at 7 weeks of age. Selection was based on behaviour in a “tail chew” test and performance of harmful social behaviour towards penmates. The gilts were mated at puberty with boars of a similar predisposition, and farrowed at approximately 44 weeks of age. Half of the gilts of each predisposition were reared from the time of selection until farrowing in barren environments, and half in enriched environments. During lactation, gilts and litters were either housed in a similar environment to that which gilts had experienced during rearing, or in a different environment (i.e. in terms of being barren or enriched). Litters from each treatment group were weaned at either 3 weeks of age (early weaning), or 5 weeks of age. After weaning, piglets were regrouped and housed in slatted pens without access to substrates. Non-predisposition to perform harmful social behaviour was associated with reduced growth during the post-weaning period (P < 0.01), and increased belly nosing behaviour in response to early weaning (P < 0.05). These effects were not mitigated by maternal experience or lactation environment factors, and it is concluded that this type of selection may not be commercially viable. Rearing dams in barren rather than enriched environments led to reduced welfare in offspring. This was reflected in increased adrenocortical reactivity during the lactation period (P < 0.01), and increased belly nosing behaviour in response to early weaning (P < 0.05). The effect of barren maternal rearing environments on belly nosing behaviour by offspring was eliminated when pigs were housed in enriched lactation environments (P < 0.01). Enrichment during the lactation period also led to improved growth rates in the post-weaning period (P < 0.01). It is suggested that this effect was due to an enhanced ability to cope with the weaning process. Overall, the results show that both genetic and early environmental factors are important determinants of the responses of pigs to weaning. Adverse effects of barren maternal rearing environments may be overcome by housing pigs in enriched lactation environments.     

The wakefulness-sleep cycle in rats with a genetic predisposition to catalepsy

Neurophysiological studies on wakefulness-sleep cycle have been made in rats selected for hereditary inclination to catalepsy. It was shown that in these animals, the stage of delta-sleep is significantly reduced, whereas the duration of a superficial slow-wave sleep is increased. In a sleeping phase of the cycle, large amount of spindles in the range of alpha- and beta 1-oscillations was observed, especially significant in electrograms of n. caudatum and sensorimotor cortex. This activity is considered as a pathological manifestation of a transient hypnotic phase which includes the increase in immobilization of a cataleptic type.     

Selection for the predisposition to catalepsy enhances depressive-like traits in mice

Immobility reaction or catalepsy is a natural passive defensive (lurking) behavioral response to the appearance of a predator. Selection for high predisposition to catalepsy has been performed in a population of (CBA x (CBA x AKR)) backcrosses of the crossing between mouse lines sensitive and resistant to catalepsy (VBA and AKR, respectively). A rapid increase in the number of animals with catalepsy has been observed: from 23% in backcrosses to 71% in the S3 generation. Selection for catalepsy does not affect mouse anxiety in the open field and plus-maze tests. However, S8 and S9 mice are characterized by a decreased motor activity in the open-field test and an increased immobility in the forced swim and tail suspension tests, which is interpreted as an increase in "depressiveness." The results indicate that genetically determined catalepsy is related to depressive-like characteristics of defensive behavior.     

Effect of chronic exposure to alcohol on the circulation of rats of different ages

Two groups each of young and old animals were fed nutritonally adequate liquid diet. One group of each served for control, while in the other one 36% of the total caloric intake was supplied by ethanol in place of part of the fat and carbohydrate. The young animals became rapidly adapted to the alcohol containing diet, while the aged animals refused to eat it even at the expense of transient hunger and thirst. Alcohol treatment resulted in body weight loss and the appearance of slight ST segment abnormalities in the ECG. Histological study of the myocardium revealed no pathological finding. Alcohol reduced the blood pressure, TPR, gut and skin fractions of the cardiac output, myocardial nutritive blood flow, and vascular resistance of the carcass in both groups, whereas it increased the relative weight of the heart. There was a greater decrease of blood pressure and a greater increase in the relative weight of the heart in the old than in young alcohol treated animals. Chronic exposure to alcohol results in a redistribution of circulation which is detrimental to cardiac function. This alcohol induced redistribution affects the cardiovascular system of old animals more severely.     

Importance of genetic predisposition and maternal environment for the occurrence of congenital malformations in offspring of diabetic rats

Previous experimental studies have implicated a genetic component in the induction of malformations in the offspring of diabetic rats. We have compared the outcome of diabetic pregnancy in two outbred (sub)strains of Sprague-Dawley rats (with low incidence [H] and high incidence [U] of skeletal malformations in the offspring) and hybrids between them. The fetuses of diabetic H mothers had no skeletal malformations and the lowest frequency of resorptions (8-9%), regardless of embryo type (H/H or H/U). When the diabetic mother was U or from the hybrid strain (H/U) and the offspring were of the mixed H/U type, we found increased resorption (16-21%) and skeletal malformation (3-5%) rates. If instead the embryos contained a major U genome [either U/U or U/(H/U)], further increased resorptions (23-30%) and skeletal malformations (17-19%) resulted. The H/H and U/U embryonic susceptibility to defined teratogens (3-6 mg/ml D-glucose, 4-8 mM B-hydroxy-butyrate) were compared in whole embryo culture and found to be similar, suggesting that the malformations occurring in vivo may have a different etiology than those found in vitro. In the rat model studied, diabetes in the mother appears to cause a disturbance of early stages of embryogenesis in genetically predisposed embryos. This early disturbance results in skeletal malformations and seems to require inducing factor(s) in addition to increased levels of D-glucose and B-hydroxybutyrate. The findings are in concert with the notion of a mixed genetic-environmental etiology of malformations in (diabetic) pregnancy.     

Tissue changes in the intervertebral disk following hypokinesia in rats of different ages

Effect of various duration of hypokinesia on structural-metabolic characteristics of the lumbar vertebral segment has been studied in Wistar rats. Hypokinesia results in certain morphological changes of the spongy bone and tissues of the intervertebral disk, demonstrating as delayed processes of ossification, disturbed course of organization into bundles of collagenous fibers of the fibrous ring, widening of the nucleus pulposus zone. Polarization-optical investigations reveal some disturbances in the macro-molecular organization of collagen, expressed as decreasing degree of its refraction and as redistribution of glycosaminoglycans towards increasing sulfated keratan sulfates.     

The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague-Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60-100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague–Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60–100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen (Bridges, R.S., 1984. A quantitative analysis of the roles of dosage, sequence, and duration of estradiol and progesterone exposure in the regulation of maternal behavior in the rat. Endocrinology 114, 930–940) or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

Mitotic activity changes in the corneal epithelium of rats of different ages following exposure to pain]

A study was made of pain stimulus (amputation of 1/3 of the tail) on the mitotic activity in the corneal epithelium of 21-day fetuses, 1-, 3-, 4-, 5-, 7-, 10-, 15-, 20- and 25-day rats. In 45 minutes after the infliction of trauma no significant change was seen in the cornea of the fetuses and of the one-day-old ratlings. A gradual establishment of the reactive inhibition of mitoses in response to pain occurred between the 3rd and the 10th day of postnatal development. This reaction became more intense after the 10th day, reaching the maximum by the 25th day. Reactive inhibition of the mitotic activity was connected with the inhibition of the entrance of cells into mitosis.     

Effect of salt loading on the body water compartments in rats of different ages

In acute experiments on anaesthetized rats from three age groups (15-20, 25-30 days of postnatal life, adult ones), studies have been made on water basins of the organism after peroral injection of hypertonic (2.5-5%) solutions of NaCl (5 and 10 ml per 100 g of the body weight). It was demonstrated that during ontogenesis, total content of water decreases mainly at the expense of extracellular fluid. Infusion of saline solutions into the stomach of rats decreases fluid content in all water basins, especially in the interstitial one. The level of changes depends on the volume of the injected solution and, to a greater extent, on the concentration of the latter and the age of animals. The described response is due to osmotic transport of water into the alimentary tract, as suggested by the decrease of water content in this tract. The role of the digestive tract in osmotic and volume regulation during peroral salt loading is discussed.     

Effects of change of maternal environment during early postnatal development on behaviour in cataleptic rats

Pinch-induced catalepsy was compared at an age of 2 weeks and at weaning in cataleptic GC and control Wistar rats reared by their biological mothers or subjected to reciprocal in-or cross-fostering. Besides, some open-field parameters were studied in the same groups of rats at an age of 2 months. Significant interstrain differences in all the behavioural parameters studied were found. Reciprocal cross-fostering tended to diminish interstrain differences in most parameters. It brought about a decrease of duration of pinch-induced catalepsy at 2 weeks and at weaning in GC rats, and an increase of duration of catalepsy at weaning in Wistar females. Besides, cross-fostering decreased the duration of freezing in the open-field test in GC rats at 2 months.     

Learning and extinction of passive avoidance in mice with high predisposition to catalepsy

The passive avoidance learning and extinction in mice strain ASC with high predisposition to catalepsy as compared with mice of CBA and AKR strains were analyzed. Impairment of fear extinction as a major symptom of depression was revealed in ASC mice, whereas a delay of extinction in CBA mice and fast formation of new inhibitory learning in AKR mice were found. It is suggested that the long persistence of fear in ASC mice results from increased anxiety during the repeated presentation of a context in the absent of aversive stimulus. Defect of fear inhibition in ASC mice makes it possible to use this strain of mice as genetic model of depression.     

Effect of insulin on lipolysis in adipose tissue of rats of different ages

Several authors have not been able to find any antilipolytic effect of insulin in adipose tissue "in vitro". We investigated the possible role of cell size and/or age of donors on this phenomenon. The lipolytic rates (glycerol release per cell) were lower in the small cells of the 4-6 weeks old rats than in the larger cells of the 25-30 weeks old animals; however, the difference disappeared when the data were expressed per unit of cell surface area. Insulin (0.5-50 ng/ml) failed to inhibit both maximally and submaximally noradrenaline stimulated lipolysis in the adipocytes of the young rats, but its antilipolytic action was fully restored by using glucose-free medium. Therefore, at our experimental conditions, a glucose dependent factor, possibly involving the preferential hydrolysis of newly synthetized triglycerides, seems to blunt or to mask the insulin induced inhibition of glycerol release. Relatively higher rates of glucose metabolism and a lower lipolysis in small fat cells might explain the difference in the action of insulin on glycerol release in the adipose tissue of young rats as compared to the older ones.     

Effect of emotional stressing on organization of the waking-sleep cycle in rats of different ages

In chronic experiments on 27 late, postnatal, pubertate, and adult rats, organization of the waking-sleep cycle was studied after long-lasting emotional stressing. The pattern of disturbances in the limbico-neocortical mechanisms, responsible for organization of the above cycle, is shown to be age-dependent. In late postnatal and pubertate rats, stressing decreased the duration of the waking phase and prolonged the stage of slow-wave deep sleep. In adult rats, the waking phase became longer, while the stage of deep slow-wave sleep was stabilized Changes in the paradoxical sleep phase were insignificant.     

Tissue reaction of rats of different ages to xerophagia

Studies have been made on the ionic and osmotic indices of the blood, as well as on the content of water and electrolytes in different tissues of rats from 2 age groups (adult animals over 90 days and 18-24 days old ones) in the course of water deprivation within 7 days. It was demonstrated that concentration of sodium in and osmolarity of the blood plasma increased earlier and to a greater extent in young animals as compared to adult ones. In most of the tissues investigated, these changes were accompanied by the increase in the content of electrolytes and water. In the subcutaneous tissue, accumulation of cations and dehydration were observed. Adult rats exhibited mainly ion-accumulating processes in all the tissues investigated, whereas young animals showed mainly shifts in water content of the tissues.     

Effect of acetylcholine on cyclic guanosine monophosphate levels in the hearts of rats of different ages

The effect of various doses of acetylcholine on the content of myocardial cGMP was studied in rats of different age. The degree of changes was shown to depend on acetylcholine dosage and animals' age. Low doses produced more potent effect in adult rats. It is suggested that these features of alteration of cGMP content may be a reason for increased myocardial sensitivity to acetylcholine in old age.     

Effect of altitude hypoxia on ATPase activity in the brain of rats of different ages.

In experiments on 5-day-old and adult rats of both sexes, the authors investigated Na+--K+-stimulated and Mg2+-dependent ATPase activity in the cerebral cortex, subcortical formations and the medulla oblongata. They studied the effect of 20 min acute altitude hypoxia corresponding to either 7,000 or 9,000 m, in a thermostable chamber (30 degrees C). ATPase activity was found to increase during ontogenesis -- this being the greatest in cortical tissue and the least in the medulla oblongata. Hypoxia corresponding to 7,000 m altitude significantly depressed total ATPase activity in 5-day-old rats, but significantly stimulated it in adult animals. Changes in Na+--K+-stimulated ATPase activity played the major role in these changes. Hypoxia corresponding to 9,000 m altitude likewise depressed total ATPase activity in 5-day-old rats and to practically the same extent as moderate hypoxia (7,000 m). In adult rats, marked hypoxia (9,000 m) significantly reduced only Mg2+-dependent ATPase activity. Mg2+ activity rose during ontogenesis to a lesser degree than Na+--K+-stimulated ATPase and the reciprocal ratio of these ATPase and the reciprocal ratio of these ATPase activities, in the given parts of the brain, fell progressively in adult animals to values close to 1.