Bedding Material Affects Mechanical Thresholds, Heat Thresholds, and Texture Preference - PubMed (original) (raw)

Bedding Material Affects Mechanical Thresholds, Heat Thresholds, and Texture Preference

Francie Moehring et al. J Pain. 2016 Jan.

Abstract

It has long been known that the bedding type on which animals are housed can affect breeding behavior and cage environment, yet little is known about its effects on evoked behavior responses or nonreflexive behaviors. C57BL/6 mice were housed for 2 weeks on 1 of 5 bedding types: aspen Sani-Chips (standard bedding for our institute), ALPHA-Dri, Cellu-Dri, Pure-o'Cel, or TEK-Fresh. Mice housed on aspen exhibited the lowest (most sensitive) mechanical thresholds and those on TEK-Fresh exhibited 3-fold higher thresholds. Although bedding type had no effect on responses to punctate or dynamic light touch stimuli, TEK-Fresh-housed animals exhibited greater responsiveness in a noxious needle assay than did those housed on the other bedding types. Heat sensitivity was also affected by bedding because animals housed on aspen exhibited the shortest (most sensitive) latencies to withdrawal, whereas those housed on TEK-Fresh had the longest (least sensitive) latencies to response. Slight differences between bedding types were also seen in a moderate cold temperature preference assay. A modified tactile conditioned place preference chamber assay revealed that animals preferred TEK-Fresh to aspen bedding. Bedding type had no effect in a nonreflexive wheel running assay. In both acute (2 day) and chronic (5 week) inflammation induced by injection of complete Freund's adjuvant in the hindpaw, mechanical thresholds were reduced in all groups regardless of bedding type, but TEK-Fresh and Pure-o'Cel groups exhibited a greater dynamic range between controls and inflamed cohorts than aspen-housed mice.

Perspective: These findings indicate that the bedding type routinely used to house animals can markedly affect the dynamic range of mechanical and heat behavior assays under normal and tissue injury conditions. Among beddings tested, TEK-Fresh bedding resulted in the least sensitive baseline thresholds for mechanical and thermal stimuli and the greatest dynamic range after tissue injury. Therefore, selection of routine cage bedding material should be carefully considered for animals that will be tested in behavioral somatosensory assays.

Keywords: Mechanical behavior; acute inflammation; bedding; chronic inflammation; cold behavior; mechanotransduction; tactile place preference; wheel running.

Copyright © 2016 American Pain Society. Published by Elsevier Inc. All rights reserved.

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Figures

Figure 1

Figure 1

Bedding materials used for housing mice two weeks prior to behavioral testing. A Aspen Sani Chips® B TEK-Fresh C Pure-o’Cel™ D Cellu-Dri™ Soft E ALPHA-Dri® F Mice housed on Aspen Sani Chips® build small nests out of Enviro-dri®. G Mice housed on TEK-Fresh bedding mix the Enviro-dri® with their bedding to build larger nests. H Mice housed on Pure-o’Cel™ push bedding material away from Enviro-dri® nest to the other side of the cage.

Figure 2

Figure 2

Bedding material affects mechanical thresholds and noxious responses but not light touch responses. A Mice housed on TEK-Fresh bedding were significantly less sensitive to the von Frey stimulus (P < 0.001). Also Pure-o’Cel™ and ALPHA-Dri® beddings were significantly different from the mice housed on Aspen bedding (P < 0.05). Cellu-Dri™ was not different (p = 0.0764). **B** Mouse hindpaws were stimulated with a spinal needle. Only mice housed on TEK-Fresh bedding displayed significantly different moderate and noxious responses when compared back to the Aspen-bedding mice (P < 0.01). **C** The bedding type had no significant effect on the % response when the hindpaw was probed five times using a 0.68mN Filament (P>0.5). D There was also no significant difference in the cotton swab light touch assay between the bedding types (P>0.5). n=8 per group.

Figure 3

Figure 3

Bedding types affect thermal behavior assays. A Thermal paw withdrawal threshold latencies are longer for mice housed on TEK-Fresh, Pure-o’Cel™ and ALPHA-Dri® bedding than Aspen bedding (P < 0.001). There was no significant difference between mice housed on Cellu-Dri™ and Aspen bedding (P>0.5). B All bedding types show no preference between the sides of the thermal preference plate when both sides are 30°C (“baseline”) as the temperature on one side was decreased to 23°C animals spent an equal amount of time on each side (P>0.5). C Animals crossed the two plates an equal amount of time, there was no significant difference between bedding types (P>0.5). D Animals housed on the three different bedding types spent about 50% on each plate at baseline. Lowering the temperature to 20°C on one p late caused mice housed on Aspen and Pure-o’Cel™ bedding to avoid the colder side (P < 0.01), whereas there was no significant difference between the time that TEK-Fresh animals spent on the colder side versus their baseline (P>0.5). E The bedding type did not affect the number of crosses between different temperature plates (P>0.5). n = 8 per group.

Figure 4

Figure 4

Animals prefer softer bedding materials over wood chips, but general activity levels are unaffected by bedding type. A A modified place preference chamber was used and showed that animals spent an equal time in the white and black chamber (P>0.5) but preferred the small grey middle chamber. B Bedding material was added on top of the plexi glass and animals spent significantly more time in the chamber with the TEK-Fresh bedding than the Aspen bedding (P < 0.01)**. C** The number of wheel revolutions in a cage with a running wheel was recorded for animals housed on either Aspen or TEK-Fresh bedding for 4 days. Total wheel revolution counts per day did not differ between the two bedding types (P>0.5). D The average wheel revolutions per minute did not differ between bedding types (P>0.5). n = 9–10 per group.

Figure 5

Figure 5

Bedding types affect the dynamic range in von Frey mechanical thresholds after acute inflammation. A The dynamic range significantly increased by using a softer bedding Type (TEK-Fresh). Comparing TEK-Fresh and Pure-o’Cel™ PBS animals to CFA animals shows that CFA animals are significantly more sensitive to the von Frey Up-Down threshold test (P < 0.001). Mice housed on Aspen bedding showed a significant difference, however due to the dynamic range decrease the significance was less: P < 0.01 **B** The paw withdrawal latencies of the Hargreaves test revealed that all animals were equally significantly more sensitive after CFA injections than their PBS-injected controls (P < 0.001) **C** All animals treated with CFA responded with a higher number of noxious responses to the needle stimulus than animals treated with CFA: Aspen bedding P < 0.001, TEK-Fresh P < 0.01, and Pure-o’Cel™ P < 0.01. CFA treated animals housed on TEK-Fresh responded with a significant increase in their percent responses than Pure-o’Cel™ CFA animals (P < 0.01). **D** Both treatment types and all three bedding types show no preference for sides of the thermal preference plate at baseline (P>0.5). When the temperature on the test plate was reduced to 20°C, mice of all treatments and bedding types spend less time on the colder side. Aspen PBS, Aspen CFA, and TEK-Fresh PBS were less significantly different (P < 0.05) than Pure-o’Cel™ CFA (P < 0.01). TEK-Fresh CFA and Pure-o’Cel™ PBS differed the most between baseline at 30°C and the reduced temperature 20°C P < 0.001. n = 8–9 per group.

Figure 6

Figure 6

Effect of bedding type on chronic inflammation. A Aspen versus TEK-Fresh PBS treated animals were significantly more sensitive to the von Frey stimulus (P < 0.001). CFA treated animals housed on Aspen were significantly more sensitive than their PBS controls (P < 0.05). TEK-Fresh animals injected with PBS had significantly higher thresholds than TEK-Fresh animals that received CFA 5 week’s prior (P < 0.001). **B** Heat withdrawal latencies differed between Aspen PBS and Aspen CFA animals (P < 0.01), however TEK-Fresh animals housed on PBS versus CFA were not different (P > 0.5). C At baseline animals spent about equal times on either plate (P > 0.5). Lowering the temperature of one of the plates to 20°C, revealed that Aspen and TEK-Fresh animals that received CFA injections 5 weeks prior spent significantly less time on the colder plate (P < 0.01). Whereas animals housed on either Aspen or TEK-Fresh bedding that received PBS were not significantly different from baseline (P > 0.5). D The number of crosses between the two plates of the cold temperature preference assay (20°C/30°C test temperature) was not significantly different between bedding types (Aspen or TEK-Fresh) and the treatment type (PBS or CFA) (P > 0.5). (Aspen PBS n=8; Aspen CFA n=9; TEK-Fresh PBS n=8; TEK-Fresh CFA n=9)

Figure 7

Figure 7

Just two weeks of housing on a new bedding material is long enough to affect mechanical and thermal sensitivities. A Paw withdrawal thresholds do not differ between being housed on a bedding first or second (P > 0.5), but thresholds significantly differ between TEK-Fresh versus Aspen Bedding (P < 0.001) **B** Heat withdrawal latencies do not differ within the bedding type groups (P > 0.5), but they do significantly differ between Aspen and TEK-Fresh bedding (P < 0.001) **C** Animals spent about 50% of time on each plate at baseline (P > 0.5). When one plate was lowered to 20°C no difference within the bedding type groups was observed (P > 0.5). D Animals housed secondly on TEK-Fresh exhibited significantly lower number of crosses between the 20°C and the 30°C plate, as compared to Aspen First and TEK-Fresh first (P < 0.05). Aspen first numbers of crosses versus Aspen second number of crosses were not significantly different (P > 0.5). n = 8 per group.

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