Controlling caloric consumption: protocols for rodents and rhesus monkeys☆

doi:10.1016/S0197-4580(99)00043-3

Neurobiology of Aging

Volume 20, Issue 2, March–April 1999, Pages 157-165

https://doi.org/10.1016/S0197-4580(99)00043-3 Get rights and content

Abstract

One approach for investigating biological aging is to compare control-fed animals with others restricted in calorie intake by 20% or more. Caloric restriction (CR) is the only intervention shown to extend the maximum lifespan of several invertebrates and vertebrates including spiders, fish, rats and mice. The capacity of CR to retard aging in nonhuman primates is now being explored. The rodent studies show that CR opposes the development of many age–associated pathophysiological changes, including changes to the brain and changes in learning and behavior. One goal of studying CR in rodents is to determine the mechanisms by which it retards aging to design interventions that duplicate those effects. The methods that we use for conducting CR studies on mice and rhesus monkeys are described. We employ procedures designed to achieve a high degree of caloric control for all animals in the study. As used in our studies, this control includes the following features: 1) animals are individually housed, and 2) all individuals in the control group eat the same number of calories (i.e., they are not fed ad lib). Although this method results in strict caloric control for all animals, there seems to be considerable procedural flexibility for the successful conduct of CR studies.

Introduction

The use of caloric restriction (CR) in gerontological [11], [43], [48], toxicological [15], [19], and oncological [1], [43], [47] research is widespread. This interest stems from the fact that a reduction of caloric intake by 20 to 50% in laboratory mice and rats, if unaccompanied by malnutrition, retards the appearance of a broad set of age–associated pathophysiological changes and extends the maximum lifespan. This manuscript is intended be a resource for investigators in the field of neurobiology who may wish to conduct controlled feeding studies to evaluate the effects of caloric intake and aging on neurobiological parameters. There is evidence that certain aspects of neurobiological aging in rodents are sensitive to CR including the loss of striatal dopamine receptors [24], [36], striatally mediated behavioral responses [18], maze learning [5], [13], [17] and motor function [8], and the increase with age in transcription of glial fibrillary acidic protein [29].

Surprisingly, with the exception of a recent publication [6], protocols supplying practical details on how to conduct CR studies have, to our knowledge, not been published. Although essential descriptions are provided in most manuscripts, certain aspects of the methodologies have not been fully described, usually owing to space considerations. As a result, methodological questions asked of us by investigators contemplating or conducting CR studies have resulted in a large volume of private communication. Accordingly, investigators embarking on CR studies may benefit from a resource providing detailed methodological descriptions.

This article first considers some background information about CR studies and provides a historical overview of the evolution of CR methods. We then describe in greater detail those protocols that we have either recently used or now employ in studies of mice, rats and monkeys subjected to CR. It is not our intent to imply that the methods used by other investigators, including the use of ad lib feeding, cannot be used with success; however, we do seek to point out the advantages that may be associated with controlled feeding of all animals in CR studies.

Section snippets

Terminology

Terms (and acronyms) used to describe these lifespan extending diets include “food restriction,” “dietary restriction (DR),” “caloric restriction (CR, which is used herein),” “chronic energy intake restriction (CEIR)” [9], “undernutrition without malnutrition” [41], and “every other day (EOD) feeding” (i.e., giving animals free access to food but only every other day) [14]. Although these terms vary in meaning and in use because specific details of the restriction may differ, all are used to

1935–1955

McCay et al. provided the first clear demonstration that CR can increase species-specific maximum lifespan in 1935 [27]. Although his methods are no longer used, they were sufficient to yield life extension. Control groups received a diet ad lib from weaning, while rats were started on CR either at the time of weaning or two weeks later. It is not stated whether the animals were housed and fed individually or in groups. In some respects, the diets resembled modern SPDs as they contained casein,

Protocols for rodents

Our rodents are housed in the Shared Aging Rodent Facility at Madison’s VA Hospital that provides a specific pathogen free environment. Temperature and humidity are held constant; lights are on from 0600 to 1800 h. Animals are housed in shoebox type plastic cages of appropriate size with wood shavings bedding and acidified water changed weekly.

Here we discuss our use of two types of diets for feeding laboratory rodents. The first type, SPDs in powdered form, are combined with agar to form a

Rationale for use

We recently initiated a collaboration with Dr. Stephan Spindler of the University of California (Riverside) to study, in male C57Bl/6× C3HF₁ mice, the influences of selected dietary supplementation on the rate of aging. The experimental design involves 12 groups of 100 mice subjected to the intervention at 14 months of age. Sixty mice per group are being studied for longevity and disease patterns, whereas the other 40 per group will be sacrificed for study of selected biochemical measures. Nine

Aging studies at the Wisconsin Regional Primate Research Center

Aging is being actively explored at the Wisconsin Regional Primate Research Center in studies of rhesus monkeys (Macaca mulatta, maximum lifespan of ∼40 years). Our research is facilitated by having, to our knowledge, the world’s largest colony of well-characterized, middle-age or older rhesus monkeys with a current census of 117 animals over 20 years of age. These animals, as members of the general colony, are fed in a conventional fashion. They eat Purina Monkey Chow on an ad lib basis.

Summary

The use of CR for studies in tumor development, gerontology, and toxicology is now long established and in widespread use. Protocols for CR studies contain certain basic elements.

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Control animals may be fed ad lib or less than ad lib (controlled feeding)
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Controlled feeding permits accurate measures of caloric intake and of the degree of restriction between groups
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Restrictions of 15 to 40% of caloric intakes are usually accomplished with diets supplemented with vitamins, minerals, and sometimes

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^☆: ☆ Supported in part by grants from the National Institute on Aging (K01 AG00650 [T.D.P] and P01 AG11915 [R.W.]); and the Life Extension Foundation (R.W.). This is Publication #99-02 of the Madison VA Geriatric Research, Education and Clinical Center and #39-018 of the Wisconsin Regional Primate Center.

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Original ArticlesControlling caloric consumption: protocols for rodents and rhesus monkeys☆☆

Abstract

Introduction

Section snippets

Terminology

1935–1955

Protocols for rodents

Rationale for use

Aging studies at the Wisconsin Regional Primate Research Center

Summary

Neurobiol Aging

J Nutr

Neurobiol Aging

J Nutr

Exp Gerontol

Free Radic Biol Med

J Nutr

J Nutr

J Nutr

J Nutr

Mech Ageing Dev

J Nutr

Hematol Oncol Clin North Am

Total calories, body weight, and tumor incidence in mice

Cancer Res

Caloric restriction reduces fiber loss and mitochondrial abnormalities in aged rat muscle

FASEB J

Dietary restriction

Longevity, body weight, and neoplasia in ad lib-fed and diet restricted C57Bl/6 mice fed NIH-31 open formula diet

Toxicol Pathol

Rate of aging and dietary restrictionsensory and motor function in the Fischer 344 rat

J Gerontol

Caloric restriction in rhesus monkeys reduces low density lipoprotein interaction with arterial proteoglycans

J Gerontol Biol Sci

Biological effects of dietary restriction

Nutritional deficiency, immunological function, and disease

Am J Pathol

Original Articles
Controlling caloric consumption: protocols for rodents and rhesus monkeys☆☆