Sexual behavior and testis morphology in the BACHD rat model
Sexual behavior and testis morphology in the BACHD rat model
Arianna Novati 0 1
Libo Yu-Taeger 0 1
Irene Gonzalez Menendez 1
Leticia Quintanilla Martinez 1
Huu Phuc Nguyen 0 1
0 Institute of Medical Genetics and Applied Genomics, University of TuÈ bingen , T uÈbingen, Germany, 2 Centre for Rare Diseases , University of TuÈbingen, TuÈ bingen, Germany, 3 Institute of Pathology and Neuropathology and Comprehensive Cancer Center, University of TuÈ bingen, TuÈ bingen, Germany, 4 Department of Human Genetics, University of Bochum , Bochum , Germany
1 Editor: Xiao-Jiang Li, Emory University , UNITED STATES
Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene, which results in brain neurodegeneration and peripheral pathology affecting different organs including testis. Patients with HD suffer from motor and cognitive impairment, and multiple psychiatric symptoms. Among behavioral abnormalities in HD, sexual disturbances have often been reported, but scarcely investigated in animal models. The BACHD rat model of HD carries the human full-length mutated HTT (mHTT) genomic sequence with 97 CAG-CAA repeats and displays HD-like alterations at neuropathological and behavioral level. This study aims to phenotype the BACHD rats' sexual behavior and performance as well as testis morphology because alterations in these aspects have been associated to HD. Two rat cohorts at the age of 3 and 7 months were subjected to mating tests to assess different parameters of sexual behavior. Histological analyses for testis morphology were performed in different rat cohorts at 1.5, 7 and 12 months of age whereas immunohistochemical analyses were carried out at 7 and 12 months of age to visualize the presence of mHTT in testicular tissue. Furthermore, western blot analyses were used to assess HTT and mHTT expression levels in striatum and testis at three months of age.
Data Availability Statement: All relevant data are
within the paper.
Funding: This project was funded by the Marie
Curie Industry-Academia Partnerships and
Pathways (MC - IAPP) of the European
Commission's 7th Framework Program "Switch
HD" (FP7-PEOPLE-2012; grant agreement No.
324495) and the European Union's Horizon 2020
research and innovation programme under Grant
agreement No 643417 (ModelPolyQ) to HPN. The
funders had no role in study design, data collection
At 3 months, BACHD rats showed a decreased time exploring the female anogenital area
(AGA), decreased latency to mount, increased number of intromissions and ejaculations
and enhanced hit rate. At 7 months, all sexual parameters were comparable between
genotypes with the exception that BACHD rats explored the AGA less than wild type rats. Testis
analyses did not reveal any morphological alteration at any of the examined ages, but
and analysis, decision to publish, or preparation of
Competing interests: The authors have declared
that no competing interests exist.
showed presence of mHTT limited to Sertoli cells in transgenic rats at both 7 and 12 months.
BACHD rat HTT and mHTT expression levels in testis were lower than striatum at 3 months
The testis phenotype in the BACHD rat model does not mimic the changes observed in
human HD testis. The altered sexual behavior in BACHD rats at three months of age could
be to a certain extent representative of and share common underlying pathways with some
of the sexual disturbances in HD patients. Further investigating the biological causes of the
sexual phenotype in BACHD rats may therefore contribute to clarifying the mechanisms at
the base of sexual behavior changes in HD.
Huntington disease (HD) is an inherited neurodegenerative disorder caused by a
polyglutamine repeated expansion in the huntingtin (HTT) gene [
]. Mutant HTT (mHTT) is expressed
in most tissues examined in humans [
] and results in both widespread neurodegeneration
throughout the brain and peripheral abnormalities [
]. Patients with HD complain of motor
impairment, cognitive deficits and multiple psychiatric disturbances [4±6]. Sexual behavior
abnormalities have often been described in HD patients, among behavioral symptoms [7±15].
The typology of sexual disorders in HD is diverse with evidence for both hypersexuality
] and hyposexuality [
] as well as changes in sexual interest and paraphilia .
While a high percentage of patients suffer of sexual disturbances [
], the underlying
mechanisms are not known, nor it is clear to which extend these symptoms are specific for the disease
or secondary to other symptoms. More recent research also reported impaired sexual
performance and problems with erections in HD [
]. Thus, HD patients suffer a wide variety of
sexual dysfunctions of which the biological causes remain unclear.
HD has also been associated with physiological and morphological changes that could be
directly or indirectly related to sexual dysfunction. There are alterations of the hypothalamus
ÐpituitaryÐgonadal activity [
] and testis pathology which consists of changes in
seminiferous tubule morphology as well as decreased number of developing germ cells [
]. Mouse and
transgenic HD (TgHD) minipig boar models of HD mimic, to a certain extent, the testicular
pathology in humans [
] and additionally show testis atrophy and degeneration [17±19].
Whereas testicular pathology in YAC128 mice and TgHD minipig boar models was proposed
as a local effect of mutant HTT [
], testicular alterations in R6/2 mice were suggested to
derive from a decreased number of neurons secreting gonadotropinÐreleasingÐhormone
in the brain [
]. This indicates that the changes triggering testis pathology in HD could be
BACHD rats are an established model of HD carrying a construct which contains the
fulllength human HTT genomic sequence with 97 CAG/CAA repeats and all regulatory elements
]. These rats show neuropathological, metabolic and behavioral HD related alterations
[14,20±27]. The BACHD rat behavioral phenotype includes motor impairment [
cognitive deficits [
] and emotional changes [
]. In this study, we extend
the characterization of BACHD rats to new phenotypes related to sexual behavior and
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functionality as well as to testicular morphology, which have been little investigated in HD
Material and methods
Animals and housing
Experiments were performed in BACHD male rats and wild type (WT) littermates. Details on
the BACHD rat generation and construct were published previously [
]. Male experimental
rats in our study were bred on a Sprague Dawley background by pairing heterozygous BACHD
males of the TG5 line [
], born at our facility, with WT females (Charles River, Germany). At
postnatal day 21, rats were weaned, ear marked and genotyped following previous protocols
]. After weaning, experimental male rats were housed in social groups of 4 with same gender
littermates of mixed genotype and kept in type IV cages enriched with bedding, nesting material
and a wooden house. Ovariectomized Sprague Dawley WT females were purchased from
Charles River (Germany) and housed with the same cage conditions as males. Females were 8
weeks old when delivered and were left undisturbed for 3 weeks before starting the mating tests.
All experimental animals were kept in a room with constant temperature (22 ± 1 ÊC) and
humidity (55% ± 10%), under 12:12 hours light/ dark cycle (lights on at 4 am, lights off at 16.00 pm).
The experiments were approved by the local ethics committee (Regierungspraesidium
Tuebingen). All procedures were performed according to the German Animal Welfare Act and
the guidelines of the Federation of European Laboratory Animal Science Associations, based
on European Union legislation (Directive 2010/63/EU).
A total of 65 male rats were part of the behavioral experiments. Two cohorts of animals were
tested at the age of 3 and 7 months, respectively. The first cohort included 16 WT and 16
BACHD rats while in the second cohort there were 16 WT and 17 BACHD rats.
In order to score the test parameters in blind conditions, all animals were coded in advance.
Behavioral experiments were conducted in the dark phase under red light, starting one hour
after the beginning of the light phase. Tests were performed in a Plexiglas box (65X45X45 cm)
with bedding material. All animals were habituated to the testing box for 30 minutes, 8 days
preceding the experiments and later re-acclimatized to the room environment for 1 h before
being tested on each session. Testing protocols were adapted from earlier studies [
brief, each male rat was exposed to a stimulus female on four test series, applied at eight days
distance in order to be able to observe all parameters of interest. The box was cleaned and
bedding changed between animals tested on the same day. Rats housed together were not tested
on the same day to prevent that sequentially removing rats from the same cage, could affect
their behavior during the test. Different females interacted with the same male on different test
series and every female served as stimulus only once on each testing day. All stimulus females
received estradiol benzoate (10 μg/0.1 ml in sesame oil; Caelo, Germany) and progesterone
(500 μg/0.1 ml in sesame oil; Caelo, Germany), 48 and 4 hours before the test respectively to
induce receptivity. Before each mating test, each stimulus female was paired to a
nonÐexperimental male to prove the presence of lordosis.
The number of mounts (no vaginal penetration), intromission (vaginal penetration),
ejaculations as well as latency to mount and post ejaculatory refractory period were scored during
thirty minutes male female interaction on each test session. The hit rate was then calculated as
the ratio between the total number of intromissions (I), including ejaculations, divided by the
sum of the number of mounts (M) and total number of intromissions (I): (I/M+I) and was
used as measure of copulatory efficiency [
]. The post ejaculatory refractory period was
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calculated as the time between the first ejaculation and the following mount. The time spent
sniffing the anogenital area (AGA) was scored in the first five minutes of test.
Histology and immunohistochemistry. Testis analyses were performed in different
animal cohorts at 1.5, 7 and 12 months of age (N = 3-5/group). Testicles were removed from rat
bodies directly after sacrifice and immediately fixed in 4,5% formalin. Following 24h, testicles
were cut into halves, and 24h later, the resulting testicle pieces were further cut in halves. Fixed
testis tissue was embedded in paraffin and cut in sections of 3±5 μm thickness. Paraffin
sections from all age cohorts were stained with hematoxylin and eosin (H&E) and used for
morphometric analyses and germinal epithelium cell counts.
The number of Sertoli cells and cells belonging to different maturation stages through the
germinal epithelium (spermatogonia, primary spermatocytes, spermatids, spermatozoa) was
manually counted in 3 animals per group in H&E sections. For each animal, 4 randomly
selected tubules were analyzed. Cells of different type were distinguished by morphology and
position within the tubules.
The cross-section area of the seminiferous tubules and the area of the germinal epithelium
were measured in 3±5 animals per group in H&E sections as previously described [
each animal 90±100 tubules were randomly selected for analysis. Tubules were then classified
as reduced (19x103±51x103 μm2), small (52x103±83x103 μm2), medium (84x103±115x103 μm2)
and large (116x103±147x103 μm2) based on their area [
] and the percentage of tubules
belonging to each size group was calculated. Additionally, the presence of degenerative
alterations including changes in the normal position of cell types in different maturation stages,
presence of cytoplasmic vacuoles in the tubular epithelium, multinucleated spermatids,
necrotic Leydig cells, desquamation of the germinal epithelium, congestion of blood vessels
and deformation of the interstitial tissue were investigated.
Moreover, the presence of mHTT protein was examined using immunohistochemistry. For
this purpose, paraffin sections obtained from testis of 7 and 12 months old animals (N = 4/
group/age), were immunostained with anti-HTT protein EM48 antibody (1: 50; MAB5374,
MerkÐMillipore) and secondary rabbit anti-mouse antibody (1:500, ab133469, Abcam) on an
automated Immunostainer (Ventana Medical Systems, Inc.) according to the company's
protocols for open procedures with slight modifications. Appropriate positive and negative
controls were used to confirm the specificity of the staining.
Western blot analyses. Western blot analyses were performed to assess WT HTT and
mHTT protein expression levels in striatum and testis of male BACHD rats and WT
littermates (N = 3) at 3 months of age. Testicular and striatal tissues were homogenized in modified
RIPA buffer (150 mM sodium chloride, 1.0% NP-40, 0.5% sodium deoxycholate, 0.1% SDS, 50
mM Tris, 5 mM EDTA pH8.0). The same amount of protein of each sample was separated
using 7% Tris-Acetate Gel (EA03585BOX of ThermoFische Scientific), and blots were probed
with monoclonal antibodies anti-huntingtin protein MAB2166 (1:1000, mouse,
MerkÐMillipore) and anti-huntingtin D7F7 (1:1000, rabbit, Cell Signaling), recognizing the amino acid
181±810 and residues surrounding Pro1220 of human huntingtin, respectively. Since actin,
GAPDH and beta-tubulin expression levels differ between tissues [
], we used Ponceau red
staining to confirm equal loading of proteins.
Statistical analyses were performed with Graph Pad Prism 7. Behavioral test parameters
measured over testing series were analyzed with Repeated Measure (RM) ANOVA followed by
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Tukey or Sidak post hoc test when appropriated. The entire sample size could not be used to
calculate all behavioral parameters. The number of animals included in the analysis of each
parameter is reported in the figure legends. Animals that did not display mounts and
intromissions in one or more of the testing series had to be excluded from the hit rate RM ANOVA
analyses. The post ejaculatory refractory period in each series could not be estimated for
animals that did not perform any ejaculation or ejaculated too late in a testing session. Because
this happened frequently in the first two series, RM ANOVA for post ejaculatory period could
not be applied through all testing series and genotypes were statistically compared only for the
fourth test series, when performance was the highest, using MannÐWhitney test at 3 months
and t-test at 7 months.
Germinal epithelium area and tubular area were compared between genotypes using t-test
for each age. The percentage of tubules belonging to each size group and the number of cells
counted through different stages of the germinal epithelium were analyzed with two-way
ANOVA for each age cohort. Significance level was set at p < 0,05 for all statistical tests
BACHD rats spent significantly less time than WT littermates exploring the female AGA over
all test series at 3 months (Fig 1A) and only in the first test series at 7 months of age (Fig 2A).
BACHD rats at 3 months showed also shorter mount latencies than WT rats, although this
effect was significant only in the first test series (Fig 1B). At seven months, WT and BACHD
rats displayed comparable latencies before performing the first mount (Fig 2B). While the
number of mounts was comparable between genotypes (Fig 1C), the number of intromissions
(Fig 1D) and ejaculations (Fig 1E) was significantly increased in three months old BACHD
rats through all test series. Accordingly, the hit rate was higher in BACHD relative to WT
rats (Fig 1F). There were instead no significant genotype differences in the length of the post
ejaculatory refractory period measured in test series 4 (Fig 1G). At seven months, none of
these parameters differed significantly between genotypes at any time point (Fig 2C, 2D, 2E,
2F and 2G).
Testis histological and immunohistochemical analyses
The number of cells counted in the germinal epithelium did not differ significantly between
WT and BACHD rats for any of the maturation stages at any age (Fig 3). There were no
genotype differences in tubular and germinal epithelium areas (Table 1) or in the percentage of
tubules belonging to each size group (Table 2) in any of the age cohorts. Furthermore, the
microscopic observation of the testicular tissue did not reveal any sign of degeneration. At
both 7 (Fig 4A and 4B) and 12 (Fig 4C and 4D) months of age, mHTT was present only in
BACHD rat testis and was localized at the level of Sertoli cells (Fig 4B and 4D) which were
recognized based on position in the germinal epithelium and morphology (pale oval-shape nuclei
and clear nucleolus). Of note, not all Sertoli cells were positive for mHTT.
Huntingtin protein expression in brain and testis
We assessed HTT expression in 3 months old BACHD rats and WT littermates using western
blot analyses. Both MAB2166 and D7F7 antibodies detected WT HTT in testis and striatum
of both genotypes and mHTT in testis and striatum of BACHD rats. Previous research in
YAC128 mice and HD humans showed higher relative HTT protein expression levels in brain
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Fig 1. Sexual behavior at 3 months of age. BACHD rats displayed shorter AGA exploration (A) and latency to mount
the female (B) compared to WT rats and showed increased number of intromissions (D) and ejaculations (E) and
enhanced hit rate (F). The number of mounts (C) and the post ejaculatory refractory period (G) were not significantly
different between genotypes. Values in the graphs indicate group mean and standard error for different test series.
Ttest and repeated measures ANOVA results are reported above the graphs. Results from post-hoc analysis are shown in
the graphs for series in which genotypes differed significantly. Series differences are not displayed on graphs.
(p < 0.05), (p < 0.01), (p < 0.001), (p < 0.0001), ns (not significant). N differed among parameters as
explained in section 2.4. For the number of mounts, intromission and ejaculations as well as latency to mount N = 16
WT and 16 BACHD. For post ejaculatory refractory period N = 10 WT and 16 BACHD. For hit rate, N = 15 WT and
16 BACHD. AGA = anogenital area; S = series; WT = wild type.
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Fig 2. Sexual behavior at 7 months of age. The time spent exploring the AGA was lower in BACHD rats compared to WT rats in
the first test series (A) while latency to mount (B), number of mounts (C), intromissions (D) and ejaculations (E) as well as hit rate
(F) and post ejaculatory refractory period (G) were comparable between genotypes. Values in the graphs indicate group mean and
standard error for different test series. T-test and repeated measures ANOVA results are reported above the graphs. Results from
post-hoc analysis are shown in the graphs for series where genotypes differed significantly. Age differences are not displayed on
graphs. (p < 0.05) (p < 0.01) (p < 0.0001), ns (not significant). The group size (N) used in statistical analyses differed
among parameters, as explained in section 2.4. For number of mounts, intromission and ejaculations as well as latency to mount
N = 16 WT and 17 BACHD. For post ejaculatory refractory period N = 10 WT and 12 BACHD. For hit rate, N = 13 WT and 14
BACHD. AGA = anogenital area; S = series; WT = wild type.
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Fig 3. Number of cells in germinal epithelium. The representative image in (A) shows the germinal epithelium in a WT rat (200 x magnification) with Sertoli
cells and germinal cells in different maturation stages (Pink: Sertoli cells; Blue: spermatogonia; Green: spermatocytes; Yellow: spermatids; Red: spermatozoa). The
number of Sertoli cells and germinal cells in each stage of maturation were counted in testis of WT and BACHD animals at 1,5 (B), 7 (C) and 12 (D) months of age
in 4 randomly selected tubules per animal. There were no differences in the number of cells between genotypes. Values in the graphs indicate group mean and
standard error. Two-way ANOVA results are reported above the graphs. (p < 0.0001), ns (not significant). N = 3 WT and 3 BACHD. WT = wild type.
and testis compared to other organs [
]. Consistent with results in YAC128 mice , our
western blot results showed abundant WT HTT protein expression in both testis and striatum
(Fig 5). Differently than in YAC128 mice [
], in BACHD rats, the expression of both WT
HTT and mHTT were lower in testis than in striatum (Fig 5).
We examined sexual behavior and testis morphology in the BACHD rat model as sexual
disturbances and testis alterations have been associated with HD [7±15]. The main result in our
study is that sexual behavior is abnormal in BACHD relative to WT rats at three months of
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age. Our findings also show presence of mHTT in Sertoli cells at both 7 and 12 months and
normal testis morphology in different animal cohorts of various ages between 1.5 and 12
BACHD rats at three months of age spent less time exploring the female AGA as measured
in the first part of each test series and displayed shorter mount latencies in the first test series
suggesting an altered precopulatory behavior in these animals. Shorter AGA exploration may
also represent a decreased interest to interact with the female as shown earlier in R6/1 and R6/
2 HD mouse models [
] or reflect general changes in social behavior for which evidence
exists in BACHD rats . Measuring additional precopulatory behavior parameters, e.g.
ultrasonic vocalizations, in further experiments will help to understand better the
precopulatory phenotype in BACHD rats. Whereas precopulatory behavior was decreased, copulatory
behavior and efficiency were increased in 3 months old BACHD rats as suggested by the
increased number of intromissions and ejaculations and by the enhanced hit rate respectively.
These effects may indicate an increased copulatory performance in BACHD rats. Increased
sexual performance has only been described in a few animal models and different studies
using these models defined sexual behavior on the base of different parameters [35±37]
making it difficult to compare our results to previous findings and understand the underlying
mechanisms. Brain lesioning studies suggest the involvement of septal and hypothalamic areas
in increasing sexual behavior [
]. Hypothalamic changes in HD are known in patients and
animal models  and may affect also systems such as oxytocinergic transmission and sexual
hormones in turn modulating sexual behavior and functionality [
]. Evidence from
pharmacological studies administering methamphetamine and chlorophenylalanine in rats [
further indicate a possible role of the dopaminergic and serotonergic systems in enhancing
Tubules per size group (%)
79.0 (± 2.8) 10.6 (± 4.1)
81.0 (± 2.3) 6.7 (± 2.9)
75.6 (± 6) 20.9 (± 6.2)
67.1 (± 8.1) 26.2 (± 6.5)
70.2 (± 7.4)
83.6 (± 3.9)
24.6 (± 9.9)
13.3 (± 1.9)
Fig 4. Mutant huntingtin in testis. The figure shows representative images (400 x magnification) of mutant
huntingtin staining in WT and BACHD rats at 7 (A and B) and 12 (C and D) months of age. Note that WT rats are
negative for mutant huntingtin (A, C) while scattered Sertoli cells in BACHD rat testis show positive nuclear staining
(brown; B, D). No apparent differences are visible between 7 and 12 months of age. WT = wild type.
Fig 5. Wild type and mutant huntingtin protein expression in testis and striatum. Western blot analyses for
huntingtin expression were performed in 3 months old BACHD rats and WT littermates. In order to validate the
results, the blot was probed with anti HTT antibodies MAB2166 (mouse) and D7F7 (rabbit), recognizing distinct
epitopes. Both antibodies detected both WT and mutant huntingtin. Ponceau red staining served to confirm equal
loading of proteins. Note that WT HTT and mHTT expression levels were lower in testis than in striatum of BACHD
rats. N = 3; fl-mhtt: full length mutant huntingtin; fl-wthtt: full length wild type huntingtin.
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sexual behavior. Changes in dopaminergic receptors have been already shown in the BACHD
rat model at the striatal level [
] and investigating the dopaminergic system in other sexually
relevant areas [
] may help to understand the bases of the sexual phenotype in BACHD rats.
Increased sexual behavior in rats has been also defined as hypersexual behavior in some of
the previous research [
]. The enhanced performance in our rats though is not directly
translatable to hypersexuality in HD patients as hypersexuality may not be directly comparable in
rats and humans. Yet, it is noteworthy that common brain areas are responsible for
hypersexuality in humans and hypersexuality-like behavior in rats [
] and it is therefore possible that
the sexual phenotype in BACHD rats shares some common biological bases with
hypersexuality in HD subjects. One should keep in mind that sexual abnormalities in BACHD rats may
also derive from or at least be influenced by other behavioral phenotypes. The decreased
latency to mount the female in the first test series could be the result of an impulsivity-like
phenotype which is known in BACHD rats at three months of age [
]. This is supported by a
previous study showing that neurobiological changes causing impulsivity affect also male sexual
behavior in rats [
]. Moreover, a shortened mount latency may be in part related to decreased
anxiety levels in BACHD rats [
] and common mechanisms have even been proposed as
modulators of both sexual and anxious phenotypes [
The lack of difference in sexual performance between genotypes at 7 months could have
different explanations. One could expect that the progression of the disease at later ages results in
a worsening of behavioral alterations e.g. motor impairment [
] that would prevent the
expression of an increased sexual performance. On the other hand, unknown developmental
deficits in the control of sexual behavior may play a role as well. It could be that BACHD
rats go first through a phase of deficient precopulatory behavior and enhanced copulatory
behavior before developing the normal sexual behavior patterns. Regrettably, it is not known
how sexual disturbances evolve longitudinally in HD patients and therefore we cannot
compare the changes in our model with those in humans. In order to prove the reasons at the base
of the discrepancy in sexual performance at different ages in BACHD rats, it will be necessary
to examine how the sexual phenotype develops in older animals and how sexual performance
relates to key regulatory factors at brain and hormonal level. In this study we did not measure
plasma testosterone, whose metabolites play an important role in male rat sexual behavior
. The absence of alterations observed in Leydig cells that are responsible for testosterone
], doesn't support the view of an impaired testosterone production in BACHD
rats. Accordingly, earlier research in our lab failed to show changes in plasma testosterone
levels in three months old BACHD rats (Yu-Taeger, unpublished results). For a better
understanding of the sexual phenotype in the BACHD rat model, new studies will follow up the
relation between sexual performance and hormonal levels by measuring both parameters in
the same animals and taking into account the hormonal response to female exposure.
Our study did not aim to link sexual performance with testis morphology directly and the
results do not support any relation between these two aspects in BACHD rats, although testis
analyses were not examined at 3 months of age, when changes in sexual behavior where found.
Testis features in our rats do not mimic the testicular pathology in HD patients and are not in
line with findings in other animal models showing testicular degeneration and decreased
number of germ cells [
]. BACHD rat testis were however, as expected, positive for mHTT
when stained with EM48 antibody. The presence of mHTT in BACHD rat Sertoli cells does
not seem to have affected their function in regulating spermatogenesis  as the number
of developing cells in BACHD rats was comparable to those in WT rats. Why mHTT was
detected selectively in Sertoli cells and only in a part of them, remains an interesting question,
which will be considered in future research. Although EM48 stained areas in BACHD rat
testis did not seem to consist of aggregates, we can not exclude the presence of small mHTT
11 / 15
aggregates. Previous research in both YAC128 mice and HD patients failed to demonstrate
mHTT aggregation in testis, but showed high levels of expression of WT and mutant HTT in
brain and testis relatively to other organs [
]. Results in Hdh knockout mouse models
suggested also an essential function of HTT in regulating spermatogenesis [
]. If changes in
maturing cells in the germinal epithelium and testis pathology are associated with mHTT and
HTT expression in testis, one would expect that the lack of changes in germinative cell number
and testis morphology in BACHD rats, is paralleled by a low expression of mHTT in testis or
at least a lower expression of mHTT in testis than in brain where pathological alterations are
known in this model already at three months of age . In line with this and in contrast with
earlier results in YAC128 mice and HD humans [
], we observed lower mHTT expression
levels in testis than in striatum in BACHD rats. A lower mHTT expression may have
contributed to the lack of major pathological changes in BACHD rat testis and may partly explain the
different testis phenotype between BACHD rats and YAC128 mice.
In conclusion, the results of this study expand the knowledge on the BACHD rat model
phenotype to sexual behavior, which is altered in HD patients, but still scarcely investigated in
animal models. While the intact testis morphology in BACHD rats does not resemble the
testicular pathology in humans and other animal models, the presence of mHTT in Sertoli cells is
an interesting finding which deserve deeper examination. The increased sexual performance
in BACHD rats at young age may be in line with hypersexuality in HD patients or at least have
common underlying pathways. Further research aimed to clarify the biological causes of sexual
abnormalities in BACHD rats may contribute to understand the mechanisms at the base of the
sexual disturbances reported in HD subjects.
We thank Tina Roenisch, Patrycja Bambynek-Dziuk and Celina Tomczak for their help with
Conceptualization: Arianna Novati, Huu Phuc Nguyen.
Data curation: Arianna Novati, Huu Phuc Nguyen.
Formal analysis: Arianna Novati.
Funding acquisition: Huu Phuc Nguyen.
Investigation: Arianna Novati, Irene Gonzalez Menendez.
Methodology: Huu Phuc Nguyen.
Project administration: Arianna Novati, Huu Phuc Nguyen.
Resources: Huu Phuc Nguyen.
Software: Arianna Novati, Huu Phuc Nguyen.
Supervision: Leticia Quintanilla Martinez, Huu Phuc Nguyen.
Validation: Arianna Novati, Huu Phuc Nguyen.
Visualization: Arianna Novati, Libo Yu-Taeger, Irene Gonzalez Menendez.
Writing ± original draft: Arianna Novati.
Writing ± review & editing: Arianna Novati, Libo Yu-Taeger, Irene Gonzalez Menendez,
Leticia Quintanilla Martinez, Huu Phuc Nguyen.
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