Longitudinal study of rat volar fat pad fixation and ethanol storage: implications for the use of fluid‐preserved specimens in morphological studies

Abstract

Museum fluid collections preserve important biological specimens for study. Tissues are often fixed in 10% buffered formalin to halt metabolic activities and transferred to a solution of ethanol for long‐term storage. This process, however, forces water from the tissues and has been shown to alter the morphology of preserved specimens in ways that may influence the biological interpretation of results. The degree to which fluid preservation alters morphology is linked to multiple biological factors, such as tissue size and composition, and should therefore be examined prior to functional analysis. This study is undertaken as part of a more inclusive examination of mammalian volar morphology. A sample of five adult male and five adult female rats (Rattus norvegicus) was utilized to evaluate longitudinal changes in the dimensions of the volar pads across fixation in 10% buffered formalin and preservation in 70% ethanol for 1 year. No significant changes to the measured dimensions of the rat volar pads were present across stages of fixation and preservation, and no significant interactions of specimen size or sex were noted. These findings indicate that small mammalian volar pads that have been fixed in 10% buffered formalin and stored in 70% ethanol are appropriate for morphological study using the measurements described here without corrective algorithms. This finding is rare among preservation studies but highlights the variability of tissue behavior during chemical preservation and the necessity of preliminary investigations of preservation artifacts. Concurrence here between the preserved and unpreserved samples is likely related to the anhydrous nature of the volar pads and the supporting skeletal structure, and their confined position between major joints of the hands and feet.

Seasonal and sex-specific changes in the gastrointestinal tracts of Peromyscus maniculatus

“…Of a total of 2.3 million small mammal specimens stored in the 10 largest mammal archives in North America, only around 500,000 are fluid-preserved with GI tracts or organs ( Greiman et al 2018 ). Moreover, fluid preservation causes shrinkage that changes the morphology and leads to inaccurate measurements ( Kingston 2018 ). This occurs regardless of the solution used to preserve tissues, although different solutions and concentrations may result in different degrees of shrinkage ( Kingston 2018 ).…”

“…Moreover, fluid preservation causes shrinkage that changes the morphology and leads to inaccurate measurements ( Kingston 2018 ). This occurs regardless of the solution used to preserve tissues, although different solutions and concentrations may result in different degrees of shrinkage ( Kingston 2018 ).…”