The capillarity of the subendocardium of left ventricle in rats reared at a low temperature for many generations

The cardiac capillarity in adult rats reared at 5°C for 68 generations was studied with a double staining method for alkaline phosphatase and dipeptidylpeptidase IV. Capillary density. proportions of arteriolar. intermediate and venular capillary portions and capillary domain area were measured in the left ventricular wall. Compared with the control rats which had been brought back from the low temperature at the 12th generation and reared at 25°C since then. the heart and the cardiac cells were hypertrophied. total capillary density increased and the capillary domain areas were reduced along the capillary path from the arteriolar to venular capillary portions. The number of the venular capillary portions showed no significant change but the arteriolar and intermediate capillary portions significantly increased. All these changes suggest that the cardiac capillary network was better developed in the cold-reared rats than in control rats. In the cold-adapted rats the hypertrophic changes in cardiac cells are thus accompanied by improvements in the oxygen delivery capacity. This adaptation provides a basis for the maintenance of increased thermogenesis in many organs. The changes cannot be established by several weeks exposure to low temperature. but only after rats have been bred in a cold room for generations. Keywords capillarity. capillary     

Lasting effect of infantile cold experience on cold tolerance in adult rats.

The effect of short and repetitive exposure to cold (5 degrees C, 4 hr/day for 2 weeks) from the birth up to the 14th day of newborn rats onthe thermal regulation in adulthood and on the tolerance to cold was investigated. After being exposed to cold, they were transferred to a room at 25 degrees C (N-CA). The control rats were raised at 25 degrees C (N-WA). An acute cold exposure test was performed by placing the animals in a room at 5 degrees C under urethane anesthesia. Electrical activity of neck muscles as an index of shivering was recorded. The colonic temperature fell at a significantly slower rate in N-CA rats with less shivering than in N-WA ones. Nonshivering thermogenesis tested by norepinephrine was significantly greater in N-CA rats than in N-WA ones. These results suggest that N-CA rats developed improved cold tolerance accompanied by greater nonshivering thermogenesis. Such a phenomenon in N-CA lasted for 18 weeks after the termination of cold exposure. Adult rats subjected to the same scheme of cold exposure (A-CA) (5 degrees C, 4 hr/day, 2 weeks) showed essentially the same results as seen in N-CA, but its improved cold tolerance and elevated nonshivering thermogenesis disappeared 4 weeks after the termination of cold exposure. Extirpation of interscapular brown adipose tissue immediately before the cold test did not appreciably affect the cold tolerance in N-CA and A-CA rats. The colonic temperature at the onset of shivering was significantly lower in N-CA as well as A-CA rats than in each of the corresponding control rats, indicating a shift of the shivering threshold to lower temperature values in the animals exposed intermittently to cold. These results indicate that an infantile experience with cold results in a greater and longer sustained ability to tolerate cold in adulthood, characterized by enhanced nonshivering thermogenesis.     

Effect of exercise training on the disappearance of cold adaptability in rats

Summary Following the transfer of cold-adapted rats to a warm environment at 25‡ C, enhanced nonshivering thermogenesis and enlarged interscapular brown adipose tissue (BAT) decreased gradually and reached a steady state after 4 weeks of de-adaptation. Animals that were exercised in the process of de-adaptation, however, showed no decrease in enhanced nonshivering thermogenesis, but did show a decrease in BAT weight as compared with sedentarily de-adapted animals. Triiodothyronine (T₃), the physiologically most active thyroid hormone, was at a higher plasma level in cold-adapted rats than in de-adapted animals with or without exercise loads. Although the resting level of T₃ in running-trained rats was not higher than that in sedentary rats, some fluctuations of T₃ level were observed during running. The part of this work using radioisotopes was performed in the Central Institute of Isotope Science, Hokkaido University     

Capillary geometry in the soleus muscle of rats cold-acclimatized for 68 generations

The effects of chronic cold exposure on soleus muscle capillarity were examined, particularly in terms of the distribution of arteriolar and venular capillaries and their capillary domain area (CDA) in adult rats exposed to cold for 68 generations (CG; n = 6). These parameters were compared with those obtained from control rats (CON; n = 5) and deacclimatized rats (DCG; n = 4), reared in thermoneutral temperature after being reared for 11 generations in cold. Morphometric data were obtained from muscle cross sections exposed to a double-staining method that stained the arteriolar and venular portions of capillaries blue and red, respectively. In CG, the capillary densities of arteriolar and venular capillaries were significantly greater than that of both CON and DCG (P < 0.05). The CDA of arteriolar, intermediate and venular portions in CG was significantly smaller by 15, 14 and 13%, respectively, than those of respective portions in CON (P < 0.05). Although CDA of arteriolar and venular capillary portions was also smaller in DCG than in CON, the degree of reduction was less in DCG than in CG. The succinate dehydrogenase activity of soleus muscle was significantly greater in CG than in both CON and DCG (P < 0.05). These results suggest that adaptive changes in the oxygen transport system, identified as an increase in the number of arteriolar capillaries and a reduction in the diffusion distance for oxygen, were observed in the soleus muscle after chronic cold exposure. These changes may improve the effective oxygen supply to muscle tissues and enable muscle tissues to promote thermogenesis in the cold atmosphere.     

Taste neophobia in individually and socially reared male rats

Individual housing of rats over a prolonged period of time results in attenuation of taste neophobia as evidenced by altered amount of novel fluid and food consumed.     

Adult-litter relations in rats reared in single and dual-chambered cages

BLU:(LE) rats were reared in cages which allowed movement of adults, but not pups, between 2 chambers. Some were reared in cages containing a virgin female (aunt) in addition to the mother. Although prenatal preferences for location and food and water consumption were for the side on which the litter was eventually delivered and reared, most postnatal food and water consumption occurred on the nonlitter side. Adult-litter contact decreased from 90% of Day 1 to 40% of Day 21, decreasing more rapidly during the dark hours. Presence of aunts increased activity of mothers, but did not affect adult-litter contact. Pups in the dual cages displayed higher rates of solid food consumption at age 17 days and lower brain weights at 21 days than pups in single cages.     

Auditory fear conditioning modulates prepulse inhibition in socially reared rats and isolation-reared rats

Prepulse inhibition (PPI) is the reduction of the startle reflex when the startling stimulus is shortly preceded by a non-startling stimulus. Previous studies have shown that PPI in rats can be enhanced by auditory fear conditioning (AFC) but weakened by isolation rearing. This study investigated whether isolation rearing affects the effect of AFC on PPI. The results show that PPI was lower in isolation-reared rats than that in socially reared rats, and it was markedly enhanced by AFC in socially reared rats. However, the AFC-induced PPI enhancement in isolation-reared rats was much lower than that in socially reared rats. Moreover, the AFC-induced PPI enhancement was blocked by intraperitoneal injection (1 mg/kg) of the selective antagonist of metabotropic glutamate receptor subtype 5 (mGluR5), 2-methyl-6-(phenylethynyl)-pyridine (MPEP), 30 minutes before AFC. The baseline startle was also enhanced by isolation rearing. Thus, isolation rearing impairs not only PPI but also the AFC-induced PPI enhancement, which depends on mGluR5 activity. This study advances the animal model for investigating both neural bases and cognitive features of schizophrenia.     

Olfactory sensitivity of rats reared in an odorous or deodorized environment

Male rats were exposed from the age of 1 or 14 days to the odor of cyclohexanone for two months. Four concentrations of cyclohexanone were used, ranging from near threshold to approximately 30,000 times this level. Other rats were reared in an environment of deodorized air or in a normal rat colony. The olfactory sensitivity of all rats for cyclohexanone was determined using an air dilution olfactometer and a two-choice (odor vs air) test procedure. There were no differences in the learning rates of groups reared in different environments for the detection task and the acuity of rats for cyclohexanone was not altered by exposure to it. Howerver, rats raised in the deodorized air environment were deficient in their ability to detect cyclohexanone. These results support the earlier proposal that rats do not lose sensitivity for an odor following prolonged exposure to it whilst deprivation can lead to a decrease in olfactory sensitivity.     

Acquisition and extinction of an operant response in differentially reared rats

Rats reared in either socially isolated or control environments were trained to bar press for food on a variable interval schedule of reinforcement, beginning at 125 days of age for 37 consecutive days. Following this phase the subjects were tested for response persistence during an extinction test. Next, the subjects were compared on measures of spontaneous recovery and the rate of response reacquisition when the reinforcement contingencies were once again reinstated. Though no differences were discerned between the groups on measures of acquisition, maintenance, and reacquisition, isolated rats emitted many more responses than the controls during extinction testing.     

Effect of methamphetamine exposure during prenatal and preweaning periods lasts for generations in rats

Our previous studies demonstrated that methamphetamine (MA) administration during gestation and/or lactation affects maternal behavior in rats and that birth weight and sensory-motor coordination of their pups are also influenced. The present study tested the hypothesis that the effect of MA induces long-term changes affecting second generation of rats that were not exposed to the drug. Adult females exposed during prenatal and preweaning periods to 5 mg/kg MA daily, were examined for regularity of estrous cycle and mated with stimulus, unexposed males. Dams (nontreated absolute control, saline- and MA-exposed) were observed with their pups in two tests of maternal behavior (observational and retrieval tests). Their pups were further tested throughout the preweaning period to examine their development. Our data demonstrate that MA-exposed mothers displayed more nursing, were more often in the nest and in contact with their pups, and were faster in retrieving their pups than saline-exposed and/or control mothers. There were no differences in litter characteristics, birth weight and weight gain of pups between groups. Interestingly, pups from mothers exposed to MA during prenatal and preweaning period had impaired sensory-motor coordination. They achieved righting reflex in mid-air later than both control groups. Additionally, they had more falls in rotarod and bar-holding tests than pups from both control and saline-exposed mothers. In homing performance, pups from MA- and saline-exposed dams learned slower to return to the home box than pups from control dams. Thus, the present study demonstrates that MA abused by mothers may affect two generations of their offspring.     

Swimming immobility of REM sleep deprived rats reared in different environments

This study tested the hypothesis that environmental rearing treatments which alter the REM sleep levels of rats affect swimming immobility, an adaptive, REM sleep sensitive behavior. At weaning, 72 female Sprague-Dawley rats were maintained in either an enriched, an impoverished, or a social control environment for 32–33 days. They were then placed in either a REM sleep depriving platform-in-water condition or in one of two control conditions (large platform or dry control) for 4 days before being scored for swimming immobility during a 10-min swimming test. A 3 (environments) × 3 (platforms) ANOVA revealed a main effect for environments, F(2,63)=5.20, p<0.01. Enriched rats exhibited a behavioral advantage over impoverished rats under the large platform control condition, F(1,63)=6.58, p<0.025, and under the dry control condition, F(1,63)=6.14, p<0.025. However, under the REM depriving condition, their behavioral advantage was virtually eliminated, F(1,63), p<1. The conclusion that the REM sleep levels of the rat groups probably determined their swimming immobility scores is discussed.     

Differential reinforcement effects in rats reared in enriched and impoverished environments

Comparison of the effects of environmental enrichment (EC) and impoverishment (IC) on learning in the rat is hindered by difficulty in distinguishing, experimentally, EC/IC differences in learning capacity per se from differences in performance-related variables such as sensory or motor ability, activity and motivation. Experiments are described which analyse EC/IC performance differences in a simple lever-press training procedure. In particular the hypothesis that EC and IC rats may be differentially reinforced by the same response-contingent events is examined. The data firmly support this hypothesis and possible explanations of the differential reinforcement effect are examined.     

Exploration, distraction, and habituation in rats reared in isolation

Rats reared in isolation have been reported to show increased motor activity; the purpose of the present experiment was to establish whether they also show enhanced exploratory and orienting responses. Rats were reared in isolation or in social groups from Day 20 to Day 45. Subgroups of each rearing condition were either left undisturbed, received daily handling, or received daily handling and were given objects in their cages. From Day 45 all the rats were rehoused in groups of 6, and testing began at Day 73. In a 1st test exploration was measured by the number of contacts with objects placed in the home cage; and a 2nd test exploration was measured by responses to a holeboard; and in a 3rd test orienting was measured by the distraction produced by the presentation of a tone. When tested in novel situations, in contrast to their enhanced motor activity, isolates showed reduced exploration and orienting. This may have been due to a discrepancy between their adaptation level (established during rearing) and their current level of sensory input. In all the tests the isolates showed normal habituation, both within sessions and between sessions. An inability to habituate is not, as has been claimed, a general characteristic of isolates.     

Structure of renal glomeruli in hypertensive NISAG rats reared by normotensive females

Morphometry of ultrastructural components of renal glomeruli in 3-week- and 6-month-old rats with hereditary stress-induced arterial hypertension (NISAG rats) reared by normotensive Wistar females showed deceleration of the development of arterial hypertension in NISAG rats and attenuated its negative consequences for kidneys as the target organs.     

Motor competence in rats of different stocks reared in large and small litters

The effects of sex and stock on a task of motor competence (balancing on a rod) were studied in Long-Evans, Sprague-Dawley and Wistar rats reared in large and small litters. The data indicated significant sex and stock effects but no effects of rearing condition. Although no nutritional effect was found on this task, the data suggest that stock differences should receive greater attention particularly with regard to the possibilities that such differences provide for the identification and analysis of a broad spectrum of effects.     

Is swimming exercise or cold exposure for rats?

Rats were trained by daily swimming sessions (up to 3 h per day) for at least 6 weeks in water at 30, 36 and 38 degrees C. After this training, the adaptive changes obtained were compared with those typical of cold-acclimated (cold-specific changes) and running-trained (training-specific changes) rats. The most typical training-specific change, an increased activity of oxidative muscle enzymes was negligible for swimming-trained rats, while the lowered activity of muscle lactate dehydrogenase was evident for all trained groups. Cold-specific changes, such as increased food intake, increased calorigenic response to injected noradrenaline, an increase both in mass and metabolic capacity of brown adipose tissue, and maintenance of the stores of ascorbic acid and muscle glycogen during cold exposure, were observed for rats trained at 36 and 30 degrees C. The cold tolerance test in cold air did not make any distinct difference between the rats trained at different water temperatures, while in cool water the 30 degrees C -swimmers were clearly superior to other groups, that is, their cooling rate was slowest. Other adaptive changes were found, to a variable extent, for all trained groups. These included loss of body fat, cardiac hypertrophy, reduced urinary catecholamine excretion after test swimmings either in cold or warm water, increased tail-skin temperature response to isoprenaline, and a higher tail-skin temperature in response to cold. Generally, however, the adaptive changes observed for 30- and 36 degrees C-swimmers were similar, while the changes observed for 38 degrees C-swimmers were different. The latter group neither displayed any cardiac enlargement nor any cold-specific changes.(ABSTRACT TRUNCATED AT 250 WORDS)