Metabolic and thermoregulatory responses of the rat maintained in acrylic or wire-screen cages: Implications for pharmacological studies

Abstract

Because of differences in thermal conductivity, it is likely that a rodent's thermoregulatory requirements and their response to drugs and other stimuli will vary in metal and acrylic cages. To address these issues, thermoregulatory responses were measured in rats housed in an envirommental chamber with a floor made of either solid metal (aluminum) or acrylic materials (Plexiglas). Metabolic rate ( M), evaporative water loss ( E), thermal conductance ( C), and tail skin ( T sk) and core temperature ( T c) were measured at ambient temperatures ( T a) of 10, 20, 28, 30, 32, and 34°C. These thermoregulatory variables were essentially unaffected by floor type at T as of 20 and 28°C. The acrylic floor showed greater increases in M, E, T c, and T sk, but a smaller elevation in C as T a increased from 28 to 34°C. At a T a of 10°C, rats on the acrylic floor had a smaller M compared to that measured on the metal floor. Rats were then injected with saline or 30 mg/kg (SC) of 3,4-methylenedioxymethamphetamine (MDMA) and placed in an acrylic cage with wood chip bedding or a wire-screen cage at a T a of 20°C. The MDMA caused T c to increase > 2.0°C in rats in the acrylic cage but had no effect on T c of rats in the wire-screen cage. The marked effect of cage type on basal thermoregulatory processes and thermogenic response to MDMA should be useful in the design and interpretation of many pharmacological studies.