Anabolic Response to Testosterone in Transgenic Mice with Knocked-down Androgen Receptor in
Skeletal Muscle Fibers
Cindy D. Knaff, Douglas A. Monks, Ph.D., Cynthia L. Jordan, Ph.D.
Neuroscience Program and Department of Psychology, Michigan State University
STATISTICAL ANALYSES
INTRODUCTION
Testosterone is an anabolic steroid hormone which increases muscle mass
and regulates both size and number of levator ani (LA) muscle fibers
RESULTS
 Paired t-tests were used to examine mean differences in LA muscle
fiber diameter and number of wild type and transgenic mice.
The LA muscle skeletal muscle is sexually dimorphic, very sensitive to
the androgen testosterone and provides a useful model for understanding how
anabolic steroids affect skeletal muscle
Although, no significant differences were found, the number of muscle fibers
between animal groups borders on significance.
Graph 1.
LA Muscle Fiber Size
14.5
Previous research has shown that testosterone acts on androgen receptors
(AR) in skeletal muscle to regulate size and number of muscle fibers
A larger sample size is needed in order to clarify and extend the results from
the current study
 This study determines whether the AR in LA muscle fibers themselves regulate
LA muscle fiber size and number by studying a line of transgenic mice whose AR
expression has been lowered in skeletal muscle fibers.
Size (Diameter in Micrometers)
14
LA muscle fiber, fibroblasts and endothelial cells express AR
OBJECTIVE
13.5
13
CONCLUSIONS
12.5
The results suggest that AR in LA muscle fibers may regulate LA
muscle fiber number.
12
11.5
Androgens can increase the number of LA muscle fibers in
development and not in adulthood.
11
1
To determine whether the AR in LA muscle fibers regulates LA muscle size
and number
No significant differences in mean diameter of muscle fibers and number were
observed between animal groups
2
3
Graph 2.
Thus, the present results suggest that lowering the number
of androgen receptors in developing LA muscle fibers will
interfere with the effect of androgen on fiber number.
LA Muscle Fiber Number
METHODS
3000
LA muscle was harvested from three transgenic and three wild type mice
2500
Fiber Number
Muscles were sectioned in twelve micron sections with a cryostat, two slides
per animal, six LA muscle sections per slide
An H+E stain was performed on all slides
 Cross sectional area of LA muscles were measured in micrometers using images
captured at 4x and imageJ public domain software
2000
1500
FUTURE DIRECTIONS
1000
500
Cross sectional area of individual LA muscle fibers were measured in micrometers using
images captured at 40x and the minor axis of a fitted ellipse is used as a measure of
muscle fiber diameter
0
1
2
Transgenic
Mean=1821
3
Wildtype
Mean=2394
Examine the spinal cords from these same wild type and transgenic
mice because the motoneurons that innervate the LA are also sensitive
to androgen
Increase our sample size for all measures
Muscle fiber number was estimated by multiplying cross sectional area by counts of
individual muscle fibers sampled from three 40x images
Figure A. Low magnification view of a cross section of a LA Muscle
Table 1.
LA Muscle Fiber Number
Mean
Transgenic
1821
Wildtype
2394
SD
223
207
Hypothesized Mean Difference
P(T<=t) one-tail
P(T<=t) two-tail
Alpha=0 .05
SEM
74.4
68.9
Variance
49903
42652
Obervations
3
3
0
0.068
0.134
REFERENCES
Breedlove, S.M., and A. P. Arnold (1983) Hormonal Control of a developing
neuromuscular system. I. Complete demasculinazation of the male rat spinal
nucleus of the bulbocavernosus using the anti-androgen flutamide. J.
Neurosci. 3: 417-423.
Breedlove, S.M., and A. P. Arnold (1983) Hormonal Control of a developing
neuromuscular system. II. Sensitive periods for the androgen-induced
masculinization of the rat spinal nucleus of the bulbocavernosus. J.
Neurosci. 3: 424-432.
Table 2.
LA Muscle Fiber Size
Mean
Transgenic
12.87
Wildtype
13.39
SD
0.525
0.897
SEM
0.175
0.299
Variance
0.276
0.812
Obervations
3
3
Christensen, S. E., S. M. Breedlove, and C. L. Jordan (2000) Sexual
Differentiation of a Neuromuscular System. Sexual Differentiation of the
Brain: 149-169.
ACKNOWLEDGEMENTS
The Breedlove Jordan Lab - Michigan State University - Neuroscience Program
Hypothesized Mean Difference
P(T<=t) one-tail
P(T<=t) two-tail
Alpha= 0.05
Figure B. High magnification view of cross sectioned LA Muscle
0
0.263
0.526