Exp. Geront. Vol. 13, pp. 233-236.
0531-5565/78/0801-0233502.00/0
© Pergamon Press Ltd 1978. Printed in Great Britain.
N E A R N E S S TO DEATH A N D W H E E L R U N N I N G BEHAVIOR IN MICE TEENA M. WAX* and CHARLES L. GOODRICK Gerontology Research Center, NIA, Baltimore City Hospitals, Baltimore, MD 21224, U.S.A. (Received 12 October 1977)
SCATTERED studies have attempted to find systematic physical or psychological changes within an organism which could be related to the impending death of that organism. For example, LiebelTnan (1965) and Lieberman and Coplan (1970) indicated there were systematic changes in performance on certain personality and psychomotor tests as a function of nearness to death in a sample of institutionalized aged persons. Others noticed a "terminal d r o p " in intellectual or cognitive performance of older persons prior to death (Riegel and Riegel, 1972). Even terminally ill patients were said to show changes in certain psychological characteristics as a function of nearness to death (Verwoerdt and Elmore, 1967). Still others do not find convincing evidence of a specific relationship between death and changes in the organism (Kastenbaum, 1967; Siegler, 1975). There are few animal studies of the relationship between aging processes and nearness to death. Most aging studies concentrate on the demonstration of age differences as part of a developmental process and pay little attention to the variable of distance from death. Occasionally, however, results from animal research suggest a viable relationship between nearness to death and changes in certain aspects of the aging process. For example, Murakami (1972) alluded to unusual (e.g. unpredictable) changes in the water intake volume of two or three of his old rats which died during his experiment. Wax (1977; unpublished data) found that some internal desynchronization of several temporally related behavioral rhythms occurred more frequently in old mice than in young, suggesting the possibility that systematic changes in the rhythmic patterns of certain behavioral or other processes may be related to nearness to death, assuming that old animals are "nearer" to death than young. The present study is more directly concerned with possible changes in the wheelrunning patterns of mice as a function of nearness to death in an attempt to identify behavioral measures which can distinguish between moribundity and senescence p e r se. It was hypothesized that old mice, or at least mice closer to death, would show wheelrunning patterns more randomly distributed over 24 h periods (particularly between light and dark phases of the illumination cycle) than would young mice or mice luther away from death. METHOD Subjects
The 57 mice included in this study consisted of 18 C57BL/6J males, 16 C57BL/6J females, and 23 A/J males. The 26 young mice were 5 months of age at the beginning of the experiment, while the 31 old mice were 26 months for the male and female C57BL/6Js, and 23 months for the male A/Js. The ages of the old mice are those of the 50 ~ point of mortality for these populations of animals (Goodrick, 1975). Table 1 shows the distributions of the mice among the subgroups used in the study. * Reprint requests should be sent to Teena Wax, C/O Charles Goodrick, Gerontology Research Center, NIA, Baltimore City Hospitals, Baltimore, MD 21224, U.S.A. 233
234
TI~ENA M. WAX AND CHARLES L. GOODRICK
TABLE 1. SUBGROUPS OF OLD AND YOUNG, MALE AND FEMALE
A/J Male Young C57BL/6J Male C57BL/6J Female
C57BL/6J AND A/J
Death-near (DN) 0 0 0
A/J Male 5 C57BL/6J Male 1 C57BL/6J Female 4 Note: See Procedures for description of DN subgroups.
Old
MICE USED IN STUDY
Death-far (DF) 8 9 9 10 8 3 and DF
Procedures'
For at least 33 days, the mice were individually kept in Wahmann custom built stainless steel cage-wheel units. The wheels were 17.5 cm in diameter and the attached cages were 17.5 x 12.5 × 7-0 cm. Movable litter trays were maintained with San-i-cel litter while Purina Laboratory Chow pellets were always available to each mouse through mesh depressions in the cage tops, and water was always available through drinking tubes attached to the cage sides. Using a microswitch and a printout counter (Sodeeo PL 103) for each wheel, continuous half-hourly recordings of wheelrunning were obtained throughout the study. The mice were kept in a room with temperature, humidity, and noise held constant; the lights were on from 6 a.m. to 6 p.m. and off from 6 p.m. to 6 a.m. At the end of the experiment, old mice were subdivided into a "death-near (DN)" subgroup if they died during or within one week after the end of the study, or into a "death-far (DF)" subgroup if they did not die until later (see Table 1). Young mice did not die during the study and were not subdivided. All analyses were calculated using the first 33 days of wheelrunning, except for six mice in the DN subgroup which died before reaching 33 days. RESULTS W h e n a sex (male, female) × blocks o f hours (noon-6, 6-midnight, midnight-6, 6-noon) analysis o f variance (unweighted means, unequal-n) was calculated on mean wheelrunning measures for C57BL/6J mice, no sex effect or interaction was f o u n d ; therefore, data from male and female C57BL/6J mice were combined for subsequent analyses. Age [F(1,110)=49-15, p
0531-5565/78/0801-0233502.00/0
© Pergamon Press Ltd 1978. Printed in Great Britain.
N E A R N E S S TO DEATH A N D W H E E L R U N N I N G BEHAVIOR IN MICE TEENA M. WAX* and CHARLES L. GOODRICK Gerontology Research Center, NIA, Baltimore City Hospitals, Baltimore, MD 21224, U.S.A. (Received 12 October 1977)
SCATTERED studies have attempted to find systematic physical or psychological changes within an organism which could be related to the impending death of that organism. For example, LiebelTnan (1965) and Lieberman and Coplan (1970) indicated there were systematic changes in performance on certain personality and psychomotor tests as a function of nearness to death in a sample of institutionalized aged persons. Others noticed a "terminal d r o p " in intellectual or cognitive performance of older persons prior to death (Riegel and Riegel, 1972). Even terminally ill patients were said to show changes in certain psychological characteristics as a function of nearness to death (Verwoerdt and Elmore, 1967). Still others do not find convincing evidence of a specific relationship between death and changes in the organism (Kastenbaum, 1967; Siegler, 1975). There are few animal studies of the relationship between aging processes and nearness to death. Most aging studies concentrate on the demonstration of age differences as part of a developmental process and pay little attention to the variable of distance from death. Occasionally, however, results from animal research suggest a viable relationship between nearness to death and changes in certain aspects of the aging process. For example, Murakami (1972) alluded to unusual (e.g. unpredictable) changes in the water intake volume of two or three of his old rats which died during his experiment. Wax (1977; unpublished data) found that some internal desynchronization of several temporally related behavioral rhythms occurred more frequently in old mice than in young, suggesting the possibility that systematic changes in the rhythmic patterns of certain behavioral or other processes may be related to nearness to death, assuming that old animals are "nearer" to death than young. The present study is more directly concerned with possible changes in the wheelrunning patterns of mice as a function of nearness to death in an attempt to identify behavioral measures which can distinguish between moribundity and senescence p e r se. It was hypothesized that old mice, or at least mice closer to death, would show wheelrunning patterns more randomly distributed over 24 h periods (particularly between light and dark phases of the illumination cycle) than would young mice or mice luther away from death. METHOD Subjects
The 57 mice included in this study consisted of 18 C57BL/6J males, 16 C57BL/6J females, and 23 A/J males. The 26 young mice were 5 months of age at the beginning of the experiment, while the 31 old mice were 26 months for the male and female C57BL/6Js, and 23 months for the male A/Js. The ages of the old mice are those of the 50 ~ point of mortality for these populations of animals (Goodrick, 1975). Table 1 shows the distributions of the mice among the subgroups used in the study. * Reprint requests should be sent to Teena Wax, C/O Charles Goodrick, Gerontology Research Center, NIA, Baltimore City Hospitals, Baltimore, MD 21224, U.S.A. 233
234
TI~ENA M. WAX AND CHARLES L. GOODRICK
TABLE 1. SUBGROUPS OF OLD AND YOUNG, MALE AND FEMALE
A/J Male Young C57BL/6J Male C57BL/6J Female
C57BL/6J AND A/J
Death-near (DN) 0 0 0
A/J Male 5 C57BL/6J Male 1 C57BL/6J Female 4 Note: See Procedures for description of DN subgroups.
Old
MICE USED IN STUDY
Death-far (DF) 8 9 9 10 8 3 and DF
Procedures'
For at least 33 days, the mice were individually kept in Wahmann custom built stainless steel cage-wheel units. The wheels were 17.5 cm in diameter and the attached cages were 17.5 x 12.5 × 7-0 cm. Movable litter trays were maintained with San-i-cel litter while Purina Laboratory Chow pellets were always available to each mouse through mesh depressions in the cage tops, and water was always available through drinking tubes attached to the cage sides. Using a microswitch and a printout counter (Sodeeo PL 103) for each wheel, continuous half-hourly recordings of wheelrunning were obtained throughout the study. The mice were kept in a room with temperature, humidity, and noise held constant; the lights were on from 6 a.m. to 6 p.m. and off from 6 p.m. to 6 a.m. At the end of the experiment, old mice were subdivided into a "death-near (DN)" subgroup if they died during or within one week after the end of the study, or into a "death-far (DF)" subgroup if they did not die until later (see Table 1). Young mice did not die during the study and were not subdivided. All analyses were calculated using the first 33 days of wheelrunning, except for six mice in the DN subgroup which died before reaching 33 days. RESULTS W h e n a sex (male, female) × blocks o f hours (noon-6, 6-midnight, midnight-6, 6-noon) analysis o f variance (unweighted means, unequal-n) was calculated on mean wheelrunning measures for C57BL/6J mice, no sex effect or interaction was f o u n d ; therefore, data from male and female C57BL/6J mice were combined for subsequent analyses. Age [F(1,110)=49-15, p
