Elsevier

Behavioural Brain Research

Volume 144, Issues 1–2, 15 September 2003, Pages 143-156
Behavioural Brain Research

Research report
Fischer (F-344) rats have different morphology, sensorimotor and locomotor abilities compared to Lewis, Long–Evans, Sprague–Dawley and Wistar rats

https://doi.org/10.1016/S0166-4328(03)00076-7Get rights and content

Abstract

Locomotor and/or sensory behaviour is commonly evaluated in laboratory rats in the field of neuroscience. Many strains of rats, however, have been propagated through intensive breeding programs. With any breeding program, traits are selected purposefully or inadvertently. We set out to investigate whether differences in morphology, sensory or motor behaviours exist using five age-matched strains of laboratory rats. Personal observations of morphological differences between different strains of rats led us to hypothesize that Fischer rats were dissimilar to the other strains in each of the parameters investigated. Evaluation of morphology involved measuring long-bone lengths and body weights of each strain. Motor skills were evaluated by measuring paw preferences while rearing, abduction of the distal portion of hindlimbs during locomotion, footfalls through a horizontal ladder during locomotion, and ground reaction forces generated during trotting. Sensory ability was assessed by von Frey testing. Fischer rats had shorter long-bone lengths, weighed less, and had significantly abducted distal portion of their hindlimbs during locomotion compared to the other strains. Lewis and Sprague–Dawley rats were less sensitive to mechanical pedal stimulation compared to Fischer rats. While rearing, all strains of rats tended to use individual forelimbs 25% of the time for each right and left limbs, and both forelimbs together 50% of the time. There were no significant differences in the number of footfalls during the ladder task. Ground reaction force determination revealed that Fischer and Sprague–Dawley rats bore more weight on their hindlimbs compared to forelimbs during locomotion, Long–Evans and Lewis rats bore more weight on their forelimbs compared to their hindlimbs, while Wistar rats distributed weight evenly between forelimbs and hindlimbs during trotting. We conclude that morphologic, sensory and motor differences exist between the five strains of laboratory rats examined and several of these differences are most pronounced in the Fischer strain.

Introduction

Rats have been used for experimental purposes since at least the mid 1800’s [16]. Since these early experiments, and the domestication of the wild Norway rat (Rattus norvegicus), many strains of rats have been developed through intensive breeding programs throughout the world. Breeding and husbandry programs for the laboratory rat in North America were primarily brought about by the Wistar Institute of Philadelphia, USA [16]. Breeding programs have been developed based on the needs of various researchers and institutes.

Many strains of rats have been propagated using inbreeding or out-breeding strategies. A particular strain of animal is considered inbred if it was created following more than 20 generations of sibling or parent–offspring matings (inbred animals are considered homozygous but homozygosity may not be truly present until after 40 sibling matings; [8], [9]). Outbred strains, however, are strains that are maintained to have a considerable amount of genetic heterozygosity [12]. Confirmation of genetic heterozygosity within outbred strains can be verified using a variety of genetic screening tests [12]. Regardless, some of the more popular strains of rats originally developed in the early 1900’s are still in use today (for historical highlights of breeding practices see [16]).

Animal husbandry practices generally select and enhance particular traits of a given species of animal. There is no better example of this than the result of breeding practices of domesticated dogs. Purebred dogs have been bred for selected characteristics for hundreds of years [37]. Consequently, highly breed-specific morphological and sensorimotor characteristics have been developed. For example, dogs can range in size from 1 to 100 kg [34], and particular breeds appear to be more sensitive to painful stimuli than others [10]. Although the laboratory rat has been bred for a shorter period of time [16], these animals can propagate quickly and are intensely bred by many established institutes and animal suppliers. Like many domesticated species of animals, laboratory rats have developed many strain specific characteristics, although they may not be as obvious as in domestic dogs. Because the laboratory rat is a popular animal used for studying sensory and motor behaviours, and particular anatomical characteristics may contribute to these behaviours, we have set out to determine whether differences in morphology and sensory and/or motor behaviours exist between various strains of rats. We hypothesized that differences exist with regard to specific morphological, sensory, and motor abilities of different strains of rats. Specifically, based on grossly observing morphological differences between different strains of rats, we hypothesized that the Fischer strain is least similar amongst the strains of rats examined. By using morphologic, endpoint, kinematic and kinetic measurements, we have described the morphologic, sensory, and motor differences that exist between five strains of rats. We found that Fischer rats tend to be most dissimilar from the other strains we examined. These differences have implications for investigations involving sensorimotor behavioural manifestations of neurologic disease such as spinal cord injury. We discuss our findings in light of their significance for those studying sensory and motor behaviour in the neurosciences.

Section snippets

Subjects

Eleven female rats of each of five different age-matched strains were obtained from Charles River Laboratories, Canada (Quebec, Canada). Animals were approximately 4 months of age and considered to be mature. The strains used included: Fischer (CDF(F-344)/CrlBR); Lewis (LEW/CrlBR); Long–Evans (Crl:(LE)BR); Sprague–Dawley (Crl:CD (SD)IGS BR) and Wistar (Crl:(WI)BR). Fischer and Lewis are inbred albino strains; Long–Evans (pigmented), Sprague–Dawley (albino) and Wistar (albino) rats are outbred

Morphometric analysis

There were several differences noted between long-bone lengths of different strains of rats (Fig. 4). Wistar and Sprague–Dawley rats had longer femurs than Fischer (P<0.01), Lewis (P<0.01) and Long–Evans (P<0.01) rats. Wistar rats also had longer tibiae when compared to Fischer (P<0.001), Lewis (P<0.01) and Long–Evans (P<0.01); there were no statistical differences between the tibiae of Sprague–Dawley, Long–Evans, and Lewis rats. Fischer rats had significantly shorter tibiae than Sprague–Dawley

Discussion

Several recent papers have examined strain differences in rats specifically pertaining to visual acuity, reaching, and spatial performance [11], [24], [35]. This, however, is one of the first studies which describes simultaneously the morphologic, sensorimotor and locomotor differences between different age-matched strains of rats. We found that Fischer rats are much different in their morphology, sensory and locomotor abilities compared to the other four strains examined. Fischer rats are

Acknowledgements

The authors thank Dr. Valerie Verge and Tracy Wilson for providing the von Frey filaments and pedal withdrawal apparatus for this study. Funding was provided by a grant from Rick Hansen (Saskatchewan) Neurotrauma Fund to GDM and a WCVM Interprovincial Fellowship to AAW.

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