Physiology & Behavior, Vol. 16, pp. 431-438. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A.

Relationship of Wheel-Running Activity to Post-Wheel Running Plasma Testosterone and Corticosterone Levels: A Behavior-Genetic Analysis BASIL E. E L E F T H E R I O U

The Jackson Laboratory 2, Bar Harbor ME 04609 M E R R I L L F. ELIAS

Department o f Psychology and All-University Gerontology Center Syracuse N Y 13210 CHRIS C H E R R Y AND LINDA A. LUCAS

The Jackson Laboratory, Bar Harbor ME 04609 (Received 7 October 1974) ELEFTHERIOU, B. E., M. F. ELIAS, C. CHERRY AND L. A. LUCAS. Relationship of wheel-running activity to post-wheel running plasma testosterone and corticosterone levels: A behavior-genetic analysis. PHYSIOL. BEHAV. 16(4) 431-438, 1976. - Recombinant inbred (RI) strains of mice, their progenitor strains, and reciprocal F~ hybrids were compared with regard to wheel-running activity. The resulting strain distribution pattern (SDP), backcross data, and testing with congenic lines suggested a genetic model with a major locus for wheel-running. Correlations of the SDP for wheel-running and SDPs for testosterone and corticosterone levels determined immediately after testing were low and nonsignificant. Thus, all 3 phenotypic traits measured exhibited genetic variation, but variation in wheel-running was unrelated to variation in corticosterone and testosterone levels following a wheel-running experience. Descriptors RI strains

Wheel-running Congenic lines

Corticosterone

Testosterone

THE earliest studies of wheel-running in rodents revealed a relationship between genotype and activity level [ 1,9, 36]. More recent investigations have been concerned with the manner in which genetic factors exert their influence on wheel-running activity. Several studies indicate that wheelrunning activity is heterotic. A significant portion of the Ft hybrids formed by crossing of select strains [10] and the F t hybrids formed by a diallel cross [ 11 ] exhibited activity scores outside the range of scores observed for their parents. Recently, Oliverio et al. [30] performed a genetic analysis of avoidance leaming and wheel-running activity for 3 inbred mouse strains (C57BL/6J, DBA/2J, and SEC/1ReJ) and their F~, F 2 and F 3 progenies. Significant, negative, genetic correlations between performance mea-

Genetics

Behavior and Hormones

sures for the tasks provided evidence that both avoidance learning and wheel-running activity are related to many of the same genes. A negative correlation between avoidance and wheel-running activity was also evident in a 6 x 6 diallel cross [28]. The mode of inheritance (dominance or heterosis) depended on the F, hybrids and the particular strains under consideration. Characterization of the relationship between a single gene and behavioral phenotypes is a very important step in the tracing of pathways between genes and behavior. The f'trst systematic study of single gene effects on different patterns of activity and exploration was undertaken by van Abeelen [1]. More comprehensive investigations were conducted by Lindzey and Thiessen [25] and Thiessen et aL [42]. These experimenters obtained 11 behavioral

This investigation was supported by Research Grants HD-05523 and HD-08220 from the National Institute of Child Health and Human Developmefit. 2The Jackson Laboratory is fully accredited by the American Society for Accreditation of Laboratory Animal Care. 431

432 measures of different types of activity, exploration, and geotaxis for mice with different coat color alleles. Of the 14 genes examined, 10 exhibited an influence on behavior by either depressing or increasing open field and wheel-running activity, or by increasing the steepness of the geotaxic response. Oliverio and Messeri [31 ] made use of single gene mutant mice to examine 31 different alleles segregating on a C57BL/6J background. The wheel-running activity of 5 mutants was significantly different from that of normal mice with differences in the direction of both higher (1 mutant) and lower (4 mutants) activity scores. While studies o f single gene mutants are useful in the isolation of single locus effects, the relationship between the action of a single gene and activity often may be explained by obvious defects in peripheral and central nervous sytem mechanisms which may be expected to affect performance scores. Thus, it is important to develop and use genetic tools other than mutants. However, these techniques must ensure that only one gene is related to a behavioral or physiological phenotype rather than closely linked genes. The present investigation used a relatively new genetic tool which was provided by Bailey's [6] Recombinant Inbred (RI) strains and congenic lines. If a single gene influence is demonstrated, an important step is to determine the number and location of loci affecting differences in behavioral or physiological traits. Using Bailey's RI strains, the number and location of loci affecting differences in behavioral and physiological phenotypes for progenitor strains C57BL/6By and BALB/cBy may be evaluated by comparing a strain distribution pattern for predetermined histocompatibility loci [7] and followed by testing in the appropriate congenic line that represents the particular locus of interest. The RI strains were derived by prolonged brother-sister inbreeding from randomly selected pairs from the F~ generation of a cross between progenitor strains C57BL/6By and BALB/cBy. A schematic diagram of the breeding procedure has been published in this journal previously [17]. Inbreeding has been maintained for more than 40 generations. This procedure progressively fixes the chance recombination of genes as inbreeding continues and as full homozygosity is approached. The battery of strains resulting from this procedure may be considered a replicable recombinant population. The usefulness of RI strains for analyzing gene systems involved in endocrine, behavioral, and immunologic responses has been described previously [7, 16, 29, 41 ]. In addition to the RI strains, a battery of congenic lines was developed from the same initial crossing of C57BL/6By (B6) and BALB/cBy (C) by means of a regimen of skin graft testing and backcrossing to B6 for at least 12 generations. This procedure, explained more fully by Bailey [6] and by Bailey and Hoste [ 7 ] , resulted in congenic B6 lines which differed from B6 only by an introduced chromosomal segment carrying a C-strain allele at a distinctive histocompatibility (H) locus. There is a characteristic RI strain distribution pattern (SDP) for each locus. One purpose of the present investigation was to explore the number and the location of the genes related to wheel-running behavior in the mouse using the RI strains and congenic lines. Based on previous findings of a high genetic correlation between avoidance learning and wheelrunning activity scores [28,31], and the repeated demonstration of single gene control for avoidance learning [29,

ELEFTHERIOU, ELIAS, CHERRY AND LUCAS 35, 39], it seems reasonable to hypothesize a single gene model for wheel-running activity in the RI strains. A second purpose of this investigation was to explore the relationship between wheel-running activity for the RI strains and circulating plasma corticosterone and testosterone levies. High correlations among these variables and similar SDP patterns would suggest pleiotropic effects of the same gene or genes. At present, only meager and inconsistent evidence exists for a relationship between wheel-running activity and testosterone levels. Injections of testosterone failed to increase the activity level of castrated [21] and senile male rats [22], although minimal effects of testosterone implants on castrated male rats have been reported [5]. Few studies have been specifically concerned with correlations between corticosterone levels and wheelrunning activity p e r se. However, strain differences and changes in circulating levels of corticosterone and testosterone have been observed in response to a variety of stressors [18, 24, 34] including changes in corticosterone level induced by the mild stress of open field activity [5]. Thus, it seemed important to explore possible correlations between plasma testosterone level, corticosterone level and activity-wheel performance, and to determine whether the same loci are involved in these behavioral-endocrine interactions. METHOD Adult male mice of RI strains CXBD, CXBE, CXBG, CXBH, CXBI, CXBJ, and CXBK, their progenitor strains BALB/cBy (C) and C57BL/6By (B), and the reciprocal F1 hybrids B6CF~ and CB6F, were used in this experiment. All mice ranged in age from 45 to 50 days. On the day of testing, they were placed in an activity wheel (Fig. I) and supplied with food and water ad lib. The availability of 10 activity wheels permitted simultaneous testing of 10 mice selected randomly from the 11 stains. The wheels were placed in insulated compartments to avoid auditory reinforcement (temperature 72 _+ I ° F ; 12:12 hrs light:dark cycle), and counters for each of the activity wheels were placed in a room other than the testing room. Twenty mice for each of the 11 strains were tested for a total of 220 animals. The experiment was conducted during the months of July to October. During the experimental manipulation, continuous barometric recordings were made. Immediately following the termination of the 24 hr period in the activity wheel, mice were removed and heparinized blood was collected through the orbital sinus. Blood was centrifuged and the plasma obtained was frozen for later analyses of corticosterone and testosterone. Corticosterone was determined according to the technique used in our laboratory which has been adapted for the mouse [ 12]. Plasma testosterone levels were determined by a radioimmunoassay method used in our laboratory [3, 4, 26] and specifically adapted for the mouse using antitestosterone antiserum generously provided by Dr. Guy Abraham (Chief, Division of Reproductive Biology, Harbor General Hospital, Torrance, California, 90509). Differences among means were initially analyzed by 1-way analyses of variance. Multiple contrasts were made with the Student-Newman-Keuls test and Tukey's W estimate [43]. Covariance analyses were also carried out to determine the rote of body weight as a variable. A number

GENETICS OF WHEEL-RUNNING ACTIVITY

433

f

i ? i !i

FIG. 1. Activity wheel with accompanying cage. Letter code indicates mouse cage (A) with direct entry (B) into the activity wheel (C), position of microswitch (E) for detecting the number of revolutions attached directly to wiring (D) which leads to counter panels for recording. of correlation analyses were also run for the following variables: 1) total activity, 2) nighttime activity, 3) daytime activity, 4) plasma levels of testosterone: 5) plasma levels of corticosterone; 6) changes in barometric pressure, i.e., rising, falling, or steady during each 24 hr period. Subsequent to those analyses, a strain distribution pattern (SDP) was obtained and a number of congenic lines as well as mice produced by the backcross of B6CF, to BALB/cBy were tested. Following the testing of the congenic lines and backcrosses, statistical analyses were conducted to test whether congenic lines resembled either BALB/cBy or C57BL/6By progenitor strains and bimodality of the backcross was tested with the Kolmogoroff-Smimov test [38]. Based on the latter analysis, it was confirmed that the backcross data constituted two general groups of scores: low or BALB/cBy-like and high or C57BL/6By-like. In the initial analyses of the RI strains, there was no significant correlation between total wheel-running activity and either corticosterone or testosterone. Consequently, these latter hormones were n o t analyzed for the congenic lines or the lines formed by backcross. Also, since the congenic lines and backcross mice were tested subsequent

to the initial testing of the RI strains, additional mice of the 2 progenitor strains, BALB/cBy and C57BL/6By, were also tested in order to observe possible changes in activity. However, no significant differences were observed between the initial and subsequent testing of these progenitors. Thus, initial scores and subsequent scores for the progenitor strains were combined for presentations of the data comparing the progenitor strains and backcross. RESULTS Analysis of variance revealed a significant difference among means for activity scores obtained by the RI strains F(10,209) = 5.68, p

Relationship of wheel-running activity to post-wheel running plasma testosterone and corticosterone levels: a behavior-genetic analysis.

Physiology & Behavior, Vol. 16, pp. 431-438. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A. Relationship of Wheel-Running Activ...
889KB Sizes 0 Downloads 0 Views