. It is possible that MPH treatment
has impaired gametogenesis and changes were still present even after
40 days recovery period, probably by affecting germ cells [68]. Also, it
is known that the progression of type A spermatogonia until the stage
of pachytene spermatocyte phase is a FSH dependent process [69]
playing an important regulatory role on the proliferation and renewal
of spermatogonia type A at the initial stages of spermatogenesis
[70,71]. Although in the present study the FSH was not measured, the
results could also suggest an action of MPH on the release of GnRH,
and consequently, altering FSH, since dopaminergic pathways work in
the modulation of GnRH release [53]. Despite changes in spermatogenesis
which has been demonstrated in several studies [19–21], to date,
there is no basis in the literature that reinforces this hypothesis,
correlating MPH on the release of gonadotropins in male rats.
Regarding sexual behavior, there is evidence supporting the role of
medial preoptic area projections interacting with the mesolimbic DA
system to promote the appetitive and consummatory aspects of sexual
behavior [72]. Indeed, the neurobehavioral functioning in adult life
could be influenced by environmental, emotional and drug experiences
during development [73–76]. Despite the MPH capacity to change DA
levels during development of the organism and that this neurotransmitter
is involved in the establishment of reproductive behavior, no influences
in sexual behavior were observed in this study. Impairment in
sexual behavior was seen in rats after treatment with 4 mg/kg/day
(i.p.) [17], even six weeks after the last MPH injection. It is known that
intraperitoneal administration of MPH, when compared to the same
oral dose has greater central bioavailability to induce locomotor response
[77]. It is suggested that the divergent results found between
our study and from Bolaños' group [17] might be related to the bioavailability
inherent to the administration route used.
The present study shows that repeated treatment with MPH during
late infancy until early adulthood may impact the reproductive function
of adult male rats. Data from the literature reinforce the possibility of a
direct action of MPH on spermatogenesis. These results underscore the need for further research aimed at understanding the mechanisms
involved.