Behavioural conflict in two strains of rat: Home cage preference versus dark preference

When confronted with a novel situation rats show a tendency either to stay in a dark place or to retreat to a familiar place, if available. To produce a conflict between these two tendencies the rat's home cage was connected by a runway to a dark but unfamiliar compartment. Three groups of rats were tested in this apparatus with different levels of illumination in the home cage. Tryon Maze Bright rats showed a strong preference for the home cage which was independent of the illumination level. This preference was also found in Wistar rats. With a very high level of illumination in the home cage, however, Wistar rats showed a preference for the home cage only in the first few trials or a series of repeated trials. In later trials they spent more time in the dark part of the apparatus. The results were regarded as an indication that in a novel situation rats primarily search for a familiar place. When such a place is available they tolerate aversive stimulation present in this place.     

Effects of coprophagy on serum urea and the weight of the gastrointestinal tract of fed or fasted rats

Coprophagy can be minimized by fitting rat cages with metal grids which allow faecal pellets to pass through to the floor of the cage. When bedding was omitted overnight, the extent of coprophagy could be estimated from the weight of the droppings on the cage floor or the weight of the gastrointestinal (GI) tract removed from rats housed with or without grids. The effect of coprophagy was also demonstrated by the elevation of serum urea nitrogen in rats that consumed faeces. Therefore, precautions against coprophagy, or their absence, should be specified in all experimental protocols and reports.     

Short-term social memory in the laboratory rat: its susceptibility to disturbance

Adult rats presented with a juvenile conspecific for 5 min on two occasions, separated by a 15-min inter-exposure interval (IEI), investigated the reintroduced juvenile significantly less in the second encounter. It is suggested that this was because the adult rats remembered the identity of the juvenile, because when a novel juvenile was introduced for the second encounter, no such reduction in investigation was observed. When the rats were either handled, placed in a smaller, novel, cage, or introduced to a new juvenile midway through the IEI, investigation of the reintroduced juvenile did not decrease. This indicated that memory of that juvenile had been disrupted. However, a simple change of cage during the IEI had no disruptive effect on memory. These results suggest that routine husbandry procedures can disrupt short-term social memory, which may lead to an increase in aggression due to a failure of recognition. This has implications for the welfare of captive social animals.     

围堤式颅窗大鼠软脑膜微循环观察方法

本文介绍了本室建立的围堤式颅窗软脑膜微循环观察方法。大鼠暴露颅骨,顶骨钻孔后,固定一根４号头皮针于骨孔边缘,将牙托粉、牙托水调匀后于骨孔周围围一个环形堤,根据需要硬脑膜可以保持完整或剥去。经头皮针持续向颅窗内输恒温人工脑脊液（ａＣＳＦ）,并维持颅窗内ａＣＳＦ的ｐＨ值和Ｐｃｏ２于正常水平。颅窗内数毫米厚的ａＣＳＦ将外界隔开,使脑组织和软脑膜处于较好的生理环境。围堤式颅窗简便易行,并可达到与密闭颅窗相似的效果。     

Refining cage change routines: comparison of cardiovascular responses to three different ways of cage change in rats

Cage change is one of the unavoidable routines in laboratory rodent care. However, cage change disrupts the rodents' olfactory environment and can evoke stress reactions. In this study, the short-term cardiovascular responses to three different cage change procedures were compared with telemetric monitoring. These procedures were: placing the rats into a new, clean cage (NEW), transferring the old cage lid into the clean cage (LID) and transferring an enrichment object into the clean cage (ENR) with the animals. Seven outbred rats (four Hsd:Sprague-Dawley and three HsdBrlHan:WIST) were instrumented with telemetric transmitters. The reactions were recorded during the 24 h following the cage change procedures. All cage change procedures (and also simple handling) caused elevated heart rate and mean arterial pressure levels for up to 5 h after the procedure, with the largest effect seen during the first hour. The reactions observed after cage change were significantly (P < 0.05) greater than those observed after simple handling. The reactions after NEW were significantly higher than the reactions after ENR or LID, though the results were dependent on the stock. In Wistar rats the LID procedure resulted in smaller reactions than ENR. In Sprague-Dawley rats, the differences between ENR and LID were not so clear, but the transfer of scent-marked material into the new cage decreased the reactions compared with the NEW procedure also in this stock. Based on these results, using the old cage lid on the new cage could reduce the disturbance of cage change in rats.     

Effects of under- and overcrowding on exploratory behavior in the elevated plus-maze

The present work investigated whether the number of rats housed in a cage affects exploration of an elevated plus-maze. Male Wistar-derived rats were kept 1, 2, 3, 4, 6, 8, 12, 16, or 24 to same size cages either for 1 or 14 days and tested in the elevated plus-maze. Rats kept 6 to a cage were arbitrarily considered controls because this is the housing condition adopted in many laboratories, ours included. In comparison to controls, 1-day housed rats kept 1, 2, 16, and 24 to a cage decreased the percentage of entries into the open arms. Similar decreases were also found in the time spent in the open arms, the only exception being the group with rats kept 16 to a cage which failed to show significant differences from the control group. Fourteen-day housed rats kept 1, 2, 16, or 24 to a cage decreased the percentage of entries and time spent in the open arms. We found plus-maze exploration to be similar in groups in which rats were kept from 4 to 12 to a cage. The present data indicate that anxiogenic effects resulting from under- and overcrowding should be taken into consideration in behavioral studies.     

Test of an antifouling treatment on tuna fish-cages in Boston Bay, Port Lincoln, South Australia

A test of the antifouling properties of Wattyl NetClear was conducted on fish farms containing southern bluefin tuna (Thunnus maccoyii) during a 6-month period (February-July 2002). Wattyl NetClear is a water-based synthetic latex-based coating where the active antifouling agent is a mixture of two isothiazolinones likely to affect both biochemical conditioning and bacterial colonisation. The development of fouling was monitored using underwater stereo-photogrammetry on 3 treated and 3 untreated net cages with the main factors treatment, depth and cage nested within treatment. A significant treatment and depth effect was found but variable through time and in some instances with significant cage effects. By the end of the study, the difference in fouling load between treated and untreated nets was 14.7%. In total 72% of all free-space data points were on treated nets. The dominating fouling organisms were Enteromorpha sp. and sponges with low settlement of blue mussel and paper oysters. Passive deposition of tuna faeces contributed significantly to the cover. The largest cover of fouling was observed in April-May with a dominance of sponges in June-July. Enteromorpha sp. dominated shallow depths while sponges dominated at deeper levels. Tuna faeces were distributed independent of depth but varied with time. The results showed that fouling of fish cages consisted of both active settlement and passive deposition, the latter independent on antifouling treatment.     

A simple method for 14CO2 measurement in metabolic experiments]

The determination of the fate of a compound following administration can be performed using the disposition method with 14C-labeled substances, which also allow the measurement of metabolism with CO2 as an expired end product. To substitute the laborious CO2-collection in washing bottles as carbonate a simple instrumentation was built for continuous 14CO2-measurement. The air from the metabolic cage is led in thin layer through a chamber fitted to a foot-monitor, the output of which is online for computation. The instrument is sensitive and calibration is easy.     

Effects of water dilution, housing, and food on rat urine collected from the metabolism cage

The objective of the study reported here was to investigate three factors that may affect the amounts of water consumed and urine excreted by a rat in the metabolism cage: water dilution, housing, and food. Young F344/N rats (eight per group) were used for all experiments. Food was withheld from rats before each 16-h urine collection, then rats were transferred into a metabolism cage. For trial A (water dilution), urine was collected from rats supplied with dyed water (0.05%, vol/vol). This was repeated three times over a 2-week period. Dye in water or urine was quantified, using a spectrophotometer. For trial B (housing), rats were individually housed in wire cages for 3 weeks before the first urine collection. Then they were group housed in the solid-bottom cage (four per cage). After 2 weeks of acclimation, urine collection was repeated. For trial C (food), one group of rats was provided with food, the other was not, during urine collection. About 8% of urine samples of small volume (< or = 3 ml) from trial A were contaminated with drinking water up to 13% of volume. The average urine volume associated with individual housing was approximately twice as large as that associated with group housing. When food was provided during urine collection, rats consumed similar amounts of water but excreted significantly smaller amounts of urine than did rats without food. It was concluded that water dilution of a urine sample from a sipper bottle is relatively small; rats individually housed in wire caging before urine collection can consume and excrete a larger quantity of water, compared with rats group housed in solid-bottom cages; and highly variable urine volumes are, in part, associated with lack of access to food during urine collection.     

Cage size preference in rats in the laboratory

The size of an enclosure is an integral part of how well it accommodates a nonhuman animal's welfare; however, most enrichment studies concentrate on modifying the area inside the enclosure rather than enlarging it. It has been suggested that rats have little need for more cage space, but there is no empirical evidence about rats' need for space. This experiment provides preliminary evidence for the preferences of 5 male and 5 female albino rats using T-maze choices followed by 5 min dwelling times. The rats showed a moderate but significant preference for the larger of 2 cages [540 cm2 vs. 1,620 cm2; binomial z, p <.05]. When the rats shared the chosen cage with 4 familiar cage mates, their preference for the larger cage did not become any stronger [paired t[9] = -.820, p >.05]. The results suggest that rats should be given a somewhat larger space allowance but could share it with up to 4 other rats.     

Genotoxic potential of 1.6 GHz wireless communication signal: in vivo two-year bioassay

Timed-pregnant Fischer 344 rats (from nineteenth day of gestation) and their nursing offspring (until weaning) were exposed to a far-field 1.6 GHz Iridium wireless communication signal for 2 h/day, 7 days/week. Far-field whole-body exposures were conducted with a field intensity of 0.43 mW/cm(2) and whole-body average specific absorption rate (SAR) of 0.036 to 0.077 W/kg (0.10 to 0.22 W/kg in the brain). This was followed by chronic, head-only exposures of male and female offspring to a near-field 1.6 GHz signal for 2 h/day, 5 days/week, over 2 years. Near-field exposures were conducted at an SAR of 0.16 or 1.6 W/kg in the brain. Concurrent sham-exposed and cage control rats were also included in the study. At the end of 2 years, all rats were necropsied. Bone marrow smears were examined for the extent of genotoxicity, assessed from the presence of micronuclei in polychromatic erythrocytes. The results indicated that the incidence of micronuclei/2000 polychromatic erythrocytes were not significantly different between 1.6 GHz-exposed, sham-exposed and cage control rats. The group mean frequencies were 5.6 +/- 1.8 (130 rats exposed to 1.6 GHz at 0.16 W/kg SAR), 5.4 +/- 1.5 (135 rats exposed to 1.6 GHz at 1.6 W/kg SAR), 5.6 +/- 1.7 (119 sham-exposed rats), and 5.8 +/- 1.8 (100 cage control rats). In contrast, positive control rats treated with mitomycin C exhibited significantly elevated incidence of micronuclei/2000 polychromatic erythrocytes in bone marrow cells; the mean frequency was 38.2 +/- 7.0 (five rats). Thus there was no evidence for excess genotoxicity in rats that were chronically exposed to 1.6 GHz compared to sham-exposed and cage controls.     

The cage preferences of laboratory rats

Preference tests were used to assess a range of enrichment options for rats kept under standard New Zealand (and similar) caging conditions. The rats did not show significant preferences for most of the options, over an empty cage. The exceptions were shredded paper, a nesting box and a semi-enriched condition incorporating a range of modifications. These cage modifications are recommended for the enrichment of laboratory rats.     

Behavioural differentiation of rats confronted to a complex diving-for-food situation

Previous studies have shown that a behavioural differentiation appeared in groups of rats subjected to an experimental design in which access to the feeder was made difficult. Some rats brought back food pellets to the cage (divers) while the others (non-divers) stayed in the sole home cage and obtained food only by stealing it from divers. In this study, we elaborated a more complex diving-for-food device which allowed divers to consume the food in a second cage away from non-divers. As a result, the expected lack of suppliers should not allow the emergence of the non-diver status. Unexpectedly, our results showed the apparition of non-divers and the persistence of divers (divers c1) bringing food back to the initial cage. Two new categories of rats appear: individuals which consume the food in the second cage where they stay once they have reached it (divers c2), or occasionally go back to the initial cage throughout the experiment (divers c1c2). Our results show the influence of spatial environment on social organization of rats and suggest that social pressure strongly determines the emergence of specialized roles in a group.     

Effects of housing density on Long Evans and Fischer 344 rats

At many breeding facilities, rats are housed at relatively high densities until they are 5 weeks old, at which point they are either shipped for research or rehoused at standard cage densities according to weight. The authors carried out a pilot study in Long Evans and in Fischer 344 rats to investigate whether continuing to house rats at high densities (24 in(2) floor space per rat) past the age of 5 weeks, through puberty and into adulthood would alter behavioral or physiological parameters compared with raising rats at standard densities (about 72 in(2) floor space per rat). After rats reached puberty, the authors rehoused them with unfamiliar cagemates. The researchers evaluated clinical and behavioral signs of stress, weight, blood glucose concentration, white blood cell count and serum corticosterone concentration. Overall, cage density had little effect on the parameters measured, though gender seemed to affect stress in Long Evans rats. The results suggest that rats of these strains can be raised at the higher densities tested until any age and regrouped with unfamiliar cagemates without compromising rats' welfare or subsequent experimental data.     

Features of the behavior of the rat with hereditarily determined arterial hypertension

The behaviour of spontaneously hypertensive rats (SHR strain), rats with inherited stress induced arterial hypertension (ISIAH, a new developed strain), and of their normotensive Wistar progenitors was studied. The open-field arena and a device for measuring the total activity in the home cage were used in the behavioural studies. The SHR were much more active in the open--field and home cage tests than the Wistar and ISIAH rats. The basal locomotor activity of the ISIAH strain was lower than that of the Wistar rats, but the ISIAH strain had an index of behavioural reactivity 2.7 fold higher than the Wistar or SHR strains. These behavioural characteristics corresponded to the hypertension patterns of the strains compared. Enhanced spontaneous locomotion of the SHR rats was associated with spontaneous increase in arterial blood pressure. The ISIAH rats showed low spontaneous locomotor activity, but high behavioural and blood pressure reactivity under conditions of mild emotional stress.     

A forced-air ventilation system for rodent cages

A novel forced-air ventilation system for rodent cages was developed. The apparatus was operated at an air flow rate of 56 L/min when used with a 230 mm wide X 450 mm long X 165 mm deep cage. Air velocity measurements in the cage did not exceed 8 m/min at animal (rat) height. The average NH3 concentration in a cage which housed two 250 g rats was less than 0.3 ppm at the end of the third day, whereas the concentration measured in a cage without the forced-air ventilation system was 150 ppm after 3 days. Tests of the water content of soiled bedding showed the forced-air ventilation system to provide a much drier environment for the rodents.     

Telemetered heart rate responses of the rat during free and learned behavior

To assess the effect of recording on the heart rate and on the behavior of the free moving rat, the electrocardiogram was recorded with the aid of radiotelemetry or through wire leads attached to the animal in different behavioral situations. Adaptation of heart rate both within and across sessions in the home cage and in a novel environment (open-field) was observed in rats bearing a transmitter. No adaptation occurred in rats attached to wire leads. The pattern of heart rate changes appeared to be independent of the mode of recording during passive avoidance behavior and when the rats displayed various motor activities like walking, sniffing, rearing or grooming in the open-field. The heart rate of rats attached to wire leads, however, was always higher. These data indicate that radiotelemetry is preferable to the use of wire connections for recording cardiac activity during behavioral studies in the rat.     

Incremental Changes in Extracellular Noradrenaline Availability in the Frontal Cortex Induced by Naturalistic Environmental Stimuli: A Microdialysis Study in the Freely Moving Rat

Abstract: Changes in levels of extracellular noradrenaline (NA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindole-3-acetic acid (5-HIAA) in the frontal cortex, induced by exposure of unrestrained, conscious rats to novel environments, were compared using in vivo microdialysis. NA efflux increased when rats were transferred to a novel cage, but this was not significant when compared with either basal efflux or with changes after equivalent handling in their home cage. Increasing the intensity of illumination of the novel cage by fivefold significantly increased NA efflux with respect to basal efflux but not handled controls. However, a sustained and significant increase in NA efflux (cf. basal efflux or handled controls) was found when an unfamiliar conspecific was also present in the novel cage. In all cases, basal efflux was restored within 1 h of returning rats to their home cage. Neither handling nor environmental stimuli described above affected DOPAC efflux. 5-HIAA efflux was increased (cf. basal) in the presence of an unfamiliar conspecific, but this increase was no greater than that in handled rats. It is concluded that different naturalistic stimuli cause incremental changes in the levels of extracellular NA in the frontal cortex; these changes affect both phasic and tonic components of the response.     

Improvements of Hagmann's Method for Injecting Insect Tracheae

A simple technic for holding and releasing the specimen cage under vacuum by means of paraffin and heat is described. The technic is very easy to follow and greatly facilitates the handling of large numbers of specimens. The specimen cage used is illustrated and the use of a household detergent, Tide, in substitution of Santomerse for preparing Hagmann's solution A is mentioned.