Changes

==Introduction==

==Introduction==

[[Image:Wistar rat.jpg|thumb|A Wistar rat. © Charles River Laboratories]]

[[Image:Wistar rat.jpg|thumb|A Wistar rat. © Charles River Laboratories]]

<ref>Krinke, George J. (2000). "History, Strains and Models". ''The Laboratory Rat (Handbook of Experimental Animals)''. Bullock, G.R., Bunton, T. (Eds.). Academic Press. pp. 3–16.</ref> Laboratory rats belong to the species ''Rattus norvegicus'' and are bred and kept for scientific research.  They are and have been used in experimental studies that have added to our understanding of genetics, disease, pharmacology, psychology and other fields.

<ref>Krinke, George J. (2000). "History, Strains and Models". ''The Laboratory Rat (Handbook of Experimental Animals)''. Bullock, G.R., Bunton, T. (Eds.). Academic Press. pp. 3–16.</ref> Laboratory rats belong to the species ''Rattus norvegicus'' and are bred and kept for scientific research.  They are and have been used in experimental studies that have added to our understanding of genetics, disease, pharmacology, psychology and other fields.

They originate from wild brown rats.  The process of domestication started in Europe during the 18^th century, during which wild rats were caught for food and rat-baiting.  Occasionally, albino rats were trapped and these were kept as pets or show animals.  The first time one of these albino mutants was brought into a laboratory for a study was in 1828, in an experiment on fasting.

They originate from wild brown rats.  The process of domestication started in Europe during the 18^th century, during which wild rats were caught for food and rat-baiting.  Occasionally, albino rats were trapped and these were kept as pets or show animals.  The first time one of these albino mutants was brought into a laboratory for a study was in 1828, in an experiment on fasting.

Domestic rats differ from wild rats in that they are calmer, less likely to bite, can tolerate greater crowding, breed earlier and are more prolific.  Also, their brains, livers, kidneys, adrenal glands and hearts are smaller.

Domestic rats differ from wild rats in that they are calmer, less likely to bite, can tolerate greater crowding, breed earlier and are more prolific.  Also, their brains, livers, kidneys, adrenal glands and hearts are smaller.

===Strains, Stocks and Transgenics===

===Strains, Stocks and Transgenics===

All rat populations used in research can be included in one of these three groups. Figure 1 is based on a PubMed search of the number of papers using the designated strain or stock for the years 2001-2005 [http://www.isogenic.info/html/rat_strains.html-http://www.isogenic.info/html/rat_strains.html].

All rat populations used in research can be included in one of these three groups. Figure 1 is based on a PubMed search of the number of papers using the designated strain or stock for the years 2001-2005 [http://www.isogenic.info/html/rat_strains.html-http://www.isogenic.info/html/rat_strains.html].

The vast majority of work (76%) was done using outbred Sprague-Dawley or Wistar rats.  Inbred strains were used on only 12% of occasions.  Of the inbred strains, the most widely used was F344 (32.1%), followed by LEW (22.5%).  Mutants (=transgenic) were used only in 1% of the studies, reflecting the circumstances explained below.

The vast majority of work (76%) was done using outbred Sprague-Dawley or Wistar rats.  Inbred strains were used on only 12% of occasions.  Of the inbred strains, the most widely used was F344 (32.1%), followed by LEW (22.5%).  Mutants (=transgenic) were used only in 1% of the studies, reflecting the circumstances explained below.

====Stocks (~outbred strains)====

====Stocks (~outbred strains)====