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[[Image:Lab_rat.jpg|200px|thumb|right|'''Lab Rat''' Source: WikiMedia Commons Author: Jean-Etienne Poirrier (2007)]]

[[Image:Lab_rat.jpg|200px|thumb|right|'''Lab Rat''' Source: WikiMedia Commons Author: Jean-Etienne Poirrier (2007)]]

==Introduction==

==Introduction==

<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, when 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, when 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.

===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.

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.

====Transgenic rats====

====Transgenic rats====

Most of the techniques used for genetic manipulation depend upon the culture and manipulation of embryonic stem cells (eES).  eES techniques are relatively difficult in rats compared to mice and for this reason, transgenic rats are not commonly used in scientific research.  However, in 2003 researchers succeeded in cloning two laboratory rats by nuclear transfer <ref>Zhou Q ''et al.'' (2003) "Generation of fertile cloned rats by regulating oocyte activation". ''Science'', 302, pp. 1179</ref>. and the rat genome is now available <ref>Rat Genome Sequencing Project Consortium (2004) "Genome sequence of the Brown Norway rat yields insights into mammalian evolution". ''Nature''. 428, pp. 493-521</ref>.  For these reasons, usage of transgenic rats may increase in the near future, as rats are more appropriate models than mice in specific situations.  These are the most common types of genetic modification:

Most of the techniques used for genetic manipulation depend upon the culture and manipulation of embryonic stem cells (eES).  eES techniques are relatively difficult in rats compared to mice and for this reason, transgenic rats are not commonly used in scientific research.  However, in 2003 researchers succeeded in cloning two laboratory rats by nuclear transfer <ref>Zhou Q ''et al.'' (2003) "Generation of fertile cloned rats by regulating oocyte activation". ''Science'', 302, pp. 1179</ref>. and the rat genome is now available <ref>Rat Genome Sequencing Project Consortium (2004) "Genome sequence of the Brown Norway rat yields insights into mammalian evolution". ''Nature''. 428, pp. 493-521</ref>.  For these reasons, usage of transgenic rats may increase in the near future, as rats are more appropriate models than mice in specific situations.  These are the most common types of genetic modification:

:* '''''Knock-out '''''animals have a single gene turned off through a targeted mutation (gene trapping).  They are mostly used as human disease models, for the study of gene function and for drug discovery and development.  The technology for production of knock out rats has evolved significantly during the last years and rat models for the study Parkinson\’s, Alzheimer\’s, hypertension, and diabetes are now available commercially [http://www.knockoutrat.org/].

:* '''''Knock-out '''''animals have a single gene turned off through a targeted mutation (gene trapping).  They are mostly used as human disease models, for the study of gene function and for drug discovery and development.  The technology for production of knock out rats has evolved significantly during the last years and rat models for the study Parkinson\’s, Alzheimer\’s, hypertension, and diabetes are now available commercially.

:* '''''Knock-in '''''animals have a single gene insertion in a specific locus (it is targeted too).  This is currently done in mice.

:* '''''Knock-in '''''animals have a single gene insertion in a specific locus (it is targeted too).  This is currently done in mice.

:* '''''Conditional Knock-out/in '''''animals have modified genes that can be knocked-out or knocked-in by manipulation of the environment or administration of a drug.  This provides researchers with added flexibility in experimental design.  Also in this case these manipulations are mostly conducted in mice.

:* '''''Conditional Knock-out/in '''''animals have modified genes that can be knocked-out or knocked-in by manipulation of the environment or administration of a drug.  This provides researchers with added flexibility in experimental design.  Also in this case these manipulations are mostly conducted in mice.

==References==

==References==

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