Release Subtitle:Researchers from Okayama University in
Japan decode the mechanisms behind oxytocin controlled male sexual
functions and behaviors
Release Summary Text:
Hormones are the master regulators of sexual functions in mammals. The
hormone oxytocin has a well-established role in social bonding, sexual
function, maternal instinct, nursing, and lactation. Researchers from
Okayama University have now explored the roles of oxytocin in male
sexual function for the first time. Findings from the study suggest that
oxytocin-mediated control of male sexual function via the spinal cord
may in fact be instrumental in treating erectile dysfunction.
Full text of release:
Hormones are key players of the endocrine system and have a major
influence on our emotional and sexual wellbeing. The hormone oxytocin is
involved in a wide range of emotions from social bonding to maternal
behaviors like nursing and lactation. But the most popular and
well-known role of oxytocin, lending it its popular moniker of ‘love
hormone,’ is its role in romantic and sexual emotions.
The functional mechanism of oxytocin in male sexual function and
behavior is not clearly understood, but there is some evidence
supporting the role of oxytocin-specific nerve cells or neurons in the
brain that project to the lower spinal cord and control penile erection
and ejaculation in male rats. Now, in a brand new study published in
Current Biology, a group of researchers led by Professor Hirotaka
Sakamoto from Okayama University, Japan, has explored this potential
role of oxytocin and the underlying mechanisms in modulating male sexual
function using rats as a model system.
Oxytocin is transferred from the brain to various parts of the body by
the blood, and from neuron to neuron through structures called
“synapses.” However, the precise mechanisms by which sparsely dispersed
oxytocin fibers—structures responsible for responding to oxytocin in the
central nervous system—cause the activation of widely distributed
receptors remain unclear.
The researchers from Japan investigated a novel non-synaptic mode of
oxytocin transport across the central nervous system. When asked to
explain this process, Prof Sakamoto refers to an interesting analogy:
“Overall, the endocrine system, which acts on widespread distant organs
via the circulation, resembles a ‘broadcasting satellite’ communication,
whereas synaptic transmission resembles the hard-wired ‘ethernet.’
Accordingly, the localized volume transmission of peptides resembles
‘Wi-Fi’ communication, since it is a hybrid of both endocrine
(satellite) and synaptic (ethernet) systems, and may be the predominant
mechanism of oxytocinergic modulation of socio-sexual behavior and
cognition throughout the central nervous system.”
It is already known that spinal regions like the spinal ejaculation
generator (SEG) are known to control sexual functions in male rodents.
To assess the role of oxytocin in copulatory and ejaculatory responses,
the team injected oxytocin into the spine of male rats. The
gastrin-releasing peptide or GRP neurons are an important component of
the SEG, as they control the lower lumbar region connected to muscles at
the base of the penis, thereby controlling erection and ejaculation.
Oxytocin caused an increased sexual activity and neuronal activity in
injected animals. More specifically, oxytocin was found to directly
activate SEG/GRP neurons via oxytocin receptors, which detect oxytocin,
and influence male sexual function in the rat lumbar spinal cord. Using
an oxytocin receptor antagonist, which reduces the activity of oxytocin
receptors, resulted in a latency and decrease in number of sexual
activity and ejaculatory responses in majority of the animals,
confirming the importance of oxytocin.
The question remained about the transport of oxytocin, however. Electron
microscopy images acquired from slices of the lumbar region ruled out
the presence of synaptic vesicles or connections. Upon stimulation of
exocytosis ex-vivo, they were able to observe oxytocin transport
mediated by a more passive diffusion in extracellular spaces at
non-synaptic sites.
Highlighting the importance of the study, Prof Sakamoto remarks, “Now
that we have uncovered a novel neural mechanism–the ‘localized volume
transmission’ of oxytocin from axons–involved in controlling male sexual
function in the spinal cord, we can hope that this may lead to the
development of treatments for male sexual dysfunction.”
This study thus presents a completely unprecedented role for oxytocin in
male sexual function, in addition to its long-standing “female-centric”
role. Learning more about this “love hormone” may indeed help us foster
healthier and long-lasting loving relationships!
Release URL:
https://www.eurekalert.org/pub_releases/2020-11/ou-lbo111820.php
Reference:
Title of original paper: Oxytocin Influences Male Sexual Activity via Nonsynaptic
Axonal Release in the Spinal Cord
Journal: Current Biology
DOI: http://dx.doi.org/10.1016/j.cub.2020.09.089
Contact Person: SAKAMOTO Hirotaka
E-mail:hsakamo(a)okayama-u.ac.jp
For inquiries, please contact us by replacing (a) with the @ mark.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id118.html
https://sdgs.okayama-u.ac.jp/en/
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