title: Environmental housing affects the duration of mechanical allodynia and the spinal astroglial activation in a rat model of chronic inflammatory pain.
abstract: In this study, we aimed at investigating the effect of an enriched environment (EE) on the recovery from chronic inflammatory pain. Inflammatory pain was induced by the injection of 2 mg of carrageenan (CAR) into the right knee of male Sprague-Dawley rats (n=34). Rats were housed either singly (S-housed) or in an EE (EE-housed). The EE consisted of a large cage (L x W x H=2.0 x 1.0 x 0.8 m) containing various attributes (e.g. running wheels, shelter house, climbing frame). Withdrawal response to von Frey filament was used to assess mechanical allodynia at days post-operative (DPO) -1, 1, 7, 14, 21 and 28. S-housed animals showed a marked tactile sensitivity in the ipsilateral paw from DPO1 to DPO21. Four weeks after the CAR injection, S-housed rats were no longer allodynic. In contrast, EE-housed rats showed a significantly faster recovery: already at DPO21, they were no longer allodynic. In a first attempt to analyse the possible role of astroglial cells in the EE-induced effect, histological analysis at DPO21 was performed. Immunohistochemical staining of the spinal dorsal horn at L3-L5 indeed showed that spinal levels of astroglial activation are different between the two housing groups and therefore may play a role in the EE-induced effect on the duration of mechanical allodynia. In conclusion, our results showed that EE-housing results in a reduced duration of mechanical allodynia in chronic inflammatory pain in rats. Astroglial activation is suggested to be involved in this housing effect.
authors.affiliation: Department of Anesthesiology, Academic Hospital Maastricht, 6202 AZ Maastricht, The Netherlands. a.gabriel@np.unimaas.nl
authors.forename: Anne F
authors.initials: AF
authors.lastname: Gabriel
authors.forename: Marco A E
authors.initials: MA
authors.lastname: Marcus
authors.forename: Wiel M M
authors.initials: WM
authors.lastname: Honig
authors.forename: Nicole
authors.initials: N
authors.lastname: Helgers
authors.forename: Elbert A J
authors.initials: EA
authors.lastname: Joosten
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D002351:Carrageenan; D002908:Chronic Disease; D004195:Disease Models, Animal; D004777:Environment; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006799:Housing, Animal; D007150:Immunohistochemistry; D008297:Male; D010146:Pain / Q000139:chemically induced / Q000503:physiopathology* / Q000523:psychology*; D010147:Pain Measurement; D010812:Physical Stimulation; D020671:Posterior Horn Cells / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000503:physiopathology*
chemical_list: D005904:Glial Fibrillary Acidic Protein; D002351:Carrageenan