and Mice: In male rats, morphine significantly
reduces testosterone secretion, and "acts
... to impair noncontact erections and copulation."
Tanko et al reported "morphine
inhibited copulation" in both
male and female rats. Gessa et al found "naloxone
induce copulatory behavior in sexually inactive
& Olster found "naltrexone
administration enhanced both sexual receptivity
and proceptivity" in female rats,
"naltrexone injection increased
the display of sexual receptivity (lordosis quotient
p < 0.05) and also elicited proceptivity (PRO),
which was never observed after saline injection
(p < 0.01)." and that "Morphine
treatment blocked these effects of naltrexone
on sexual behaviors".
female rats, Vathy et al reported: "naloxone
infusion into the ventromedial hypothalamus 20
min before behavior testing reduced the inhibitory
effects of systemically administered morphine
on lordosis." Cicero et al reported:
"morphine exposure during
adolescence led to a pronounced inhibition of
a number of indices of sexual maturation (e.g.,
serum testosterone and luteinizing hormone levels
and reduced weights of the testes and seminal
male rats, Band & Hull reported: "Morphine
injections (to medial preoptic area and nucleus
both the latency to ejaculate and the number of
intromissions triggering ejaculation,... produced
a failure to resume copulating following the second
ejaculation,...shortened the latency to the first
intromission and lengthened the second postejaculatory
interval. Naloxone reversed the effects of morphine
on intromission latency and attenuated the lowering
of ejaculatory threshold." By
contrast, Mitchell & Stewart found with ventral
tegmental injections "morphine...
increased, in a dose-orderly manner, the number
of males that mounted, and the display of female-directed
behavior.", and also that "males
displayed more frequent female-directed behavior,
such as pursuit of the female, anogenital exploration,
and partial mounts" Leyton &
Stewart found "the stimulation
of central kappa opioid receptors inhibits sexual
behavior in the male rat" Gomez-Marrero
et al found morphine to decrease erection and
ejaculation frequency, and naloxone to reverse
this effect. Meyerson et al found "In
the female (rat), neonatal naltrexone treatment
enhanced copulatory (lordosis response) and exploratory
behavior." Agmo found naloxone
alone did not affect copulatory behaviour of male
rats, whereas morphine "reduced
the proportion of animals displaying sexual behavior"
with "a dose-dependent reduction
of mount, intromission and ejaculation percentages"
et al reported: "Female rats
treated neonatally with naltrexone displayed enhanced
copulatory behaviour as adults, and the morphine-induced
lordosis inhibitory effect was diminished."
In male rats, Meyerson also found "beta-endorphin
or morphine decreased exploratory activity and
socio-sexual approaches." Lieblich
et al found "naloxone...
significantly reduced ejaculation and mounting
in male rats in the weeks following castration.
A similar effect was obtained by injecting morphine
. In contrast, the same dosages of naloxone or
morphine did not affect the sexual performance
of gonadally intact males." The
sex differences in response were outlined by Vathy,
who concluded "prenatal morphine
treatment... disrupts the development of reproductive
function in females but has only minor effects
on male reproductive function."
Wiesenfield found "intrathecal
injection of morphine into female ovariectomized
rats pretreated with oestradiol benzoate and progesterone
inhibits sexual receptivity while injection of
the opiate receptor antagonist naloxone enhances
it. Similarly, intrathecal injection of morphine
increases while injection of naloxone decreases
the number of intromissions before ejaculation
in male rat." Misra, testing naloxone
implants in male rats, found these to produce
a side effect of "enhanced
sexual activity (e.g., spontaneous penile erections)"
et al found naloxone to decrease sexual activity
in sexually experienced rats, but increase it
in sexually naive rats, whereas morphine completely
abolished copulatory activity. Sachs et al, studying
penile reflexes and copulatory behaviour in male
rats reported "Naloxone resulted
in a small but reliable decrease in the number
of penile flips (and) significantly prolonged
the postejaculatory refractory period"
Saito et al concluded "opiate
antagonists play a role in the regulation of lordosis
behavior, but not proceptive behavior in female
rats." Meijs-Roelofs found Naltrexone
"advanced first ovulation
in about 55%-75% of (juvenile female) rats".
Wu and Noble concluded "opiate
antagonists alter male copulatory behavior by
enhancing the impact of stimuli occurring during
the sexual interaction.", whereas
Mandenoff et al found "Naltrexone
provoked an increase in the (frequency) of ejaculations"
Allen et al found that in female rats, naltrexone
"facilitated sexual receptivity".
Myers & Baum found naloxone and naltrexone
to facilitate sexual performance in male rats,
but Lieblich et al found "Naloxone...
impaired sexual performance in castrated male
rats, and in gonadally intact rats maintained
on sweet solutions."
female rats, Hulse et al reported "injection
of naloxone resulted in marked elevations in serum
FSH and LH, induced ovulation and increased the
frequency of lordosis behaviour.",
and Sirinathsinghji reported "the
facilitation of lordosis behaviour induced by
treatment with naloxone... may be due to enhanced
Gonadotrophin releasing hormone release",
and that "beta-Endorphin
regulates lordosis in female rats by modulating
LH-RH release." In male mice,
Landauer et al found "naloxone
reversed the decrease in female investigation
time observed with... morphine...
an animal model can be used to
study the disruption of socio-sexual behavior
produced by opiates." Schechtman
et al concluded "mating is
a biological stimulus for the release of endogenous
opoids, possibly to (a) prevent intense sexual
stimulation from becoming aversive, and (b) increase
its reward value."
Furth found naloxone to reduce the effect of smell
on anticipatory sexual behaviour in male rats,
whereas deCatanazaro, studying male mice suggested
"the influences of prior
social condition on male sexual activity are robust
in the face of naloxone administration."
In male rats, Pfaus & Wilkins found "Naloxone...
facilitated the display of mounts and intromissions",
Clark & Smith reported "naloxone
... evinced a facilitation of ejaculatory behavior",
Hughes et al reported naloxone "markedly
facilitated copulatory responses"
et al reported both naloxone and naltrexone to
"exert a dose-based biphasic
effect on the proportion of sexually exhausted
rats displaying copulation.",
higher doses "facilitated
copulation reflected as a shortening of the ejaculation
latency and the interintromission interval and
an increase in the copulatory rate"
and "decreased the spontaneous
ambulatory behaviour of sexually satiated rats
without impairing sexual behaviour execution."
The differences in behavioural effects of opiates,
endorphins and antagonists are attributed by Torii
et al to the time of administration in relation
to steroid hormone secretion, concluding "opioidergic
systems modulate an initial phase of estrogen
action to induce lordosis and play a part in neural
input from the forebrain structures to regulate
female sexual receptivity."
et al found naloxone to induce sexual receptivity
in female rats immediately following coitus, and
also during lactation. Lindblom et al found there
to be differences in the effect of naloxone on
already receptive or partially receptive female
rats, having little effect in the former but "facilitated
sexual behavior" in the latter,
finding the site of injection also to cause differences
in response. Wiesner & Mossfound beta-endorphin
to suppress "Receptive behavior
(lordosis) and proceptive behaviors (presentation
and ear wiggling)... the mu-1 antagonist naloxazone...
reversed the effects of beta-END on all behaviors
Rodents: In guinea-pigs, Olster found that
naloxone injections to the medial preoptic area/anterior
hypothalamus reliably elicited female sexual display
(lordosis - 87% positive response vs 12% for saline),
and found naloxone to produce a dose-related increase
in lordosis behaviour, noting "the
facilitatory effect of naloxone on sexual receptivity
was completely blocked by concomitant injection
male rabbits, Agmo et al found "Morphine
was found to inhibit sex behavior in a dose dependent
way. ... Naloxone also inhibited sexual behavior."
but added "The effects of
morphine were reduced but not completely antagonized
by several doses of naloxone"
Agmo also concluded "peripheral
opioid receptors are responsible for at least
some of the inhibitory actions of morphine on
male sexual behavior.", and that
"Perhaps compulsive sexual
activity obeys the same mechanisms as compulsive
drug use in opiate addicts."
hamsters, Ostrowski et al found "administration
of morphine to female hamsters reliably decreases
lateral displacement, a sensitive index of female
sexual responsitivity... Large doses of naltrexone
produced no reliable effects on sexual behavior
during estrus in unmated females, nor did it attenuate
the mating-induced decreases in sexual responding,
regardless of the time of day of mating."
They also found "Large doses
of morphine consistently produced sedation and
behavioral depression of responses to nociceptive
stimuli. Smaller doses of morphine suppressed
a measure of female sexual responding. The suppressive
effects on sexual behavior were reversed by naloxone."
although there was no effect of naloxone alone
in opioid-naive animals. Murphy reported "The
debilitating effect of methadone was judged to
be highly selective for sexual behavior since,
for example, at 16 mg/kg of methadone, sexual
behavior was eliminated but ambulatory activity
was unaffected. Pretreatment with naltrexone blocked
the effects of methadone and posttreatment reversed
the effects, thereby indicating that the methadone
was inhibiting sexual behavior by acting on specific
opiate receptors." Donham et al
found naloxone to advance puberty in female hamsters
by enhancing LH release.
Animals In rams, morphine decreased ejuaculation
frequency, whereas naloxone increased courship
behaviour and ejaculatron frequency in sexually
active animals, and in female sheep naloxone increased
the frequency of pulse-secretion of luteinising
(sex) hormone, and was involved in the onset of
oestrus, Fuentes reporting "naloxone
facilitates the expression of oestrus in the ewe
during anoestrus and lactation.",
and in male goats."naloxone
enhances libido... during anoestrus"
Primates: Studying rhesus monkeys, Abbott
et al reported "The proportion
of approaches of the female to the male was increased
when naloxone, but not naltrexone, was given."
In male Talapoin monkeys, Meller et al reported
reduced sexual behaviour in previously active
males", whereas Martensz et al
found differences in response depending on the
monkeys level in the social hierarchy, concluding
"Altered opiate neural activity
may be responsible for the depressed levels of
sexual behaviour and gonadal function observed
in monkeys at the bottom of the hierarchy."
In male rhesus monkeys, Gilbeau & Smith found
naloxone to reverse stress-related reproductive
effects including resoration of LH secretion to
pre-stress levels, however Glick et al found that
"Despite the positive behavioral
cues of the females, the males failed to initiate
heterosexual interactions at any level of naloxone
vertebrates: The influence of endogenous opiates
on sexual behaviour appears relatively early in
vertebrate evolution, in newts, "bremazocine,
a kappa-receptor opiate agonist, can markedly
reduce sexual activity and that an ip injection
of naloxone can reverse this inhibition in a dose-dependent
fashion.", effects on sex hormones
and/or sexual behaviour have also been demonstrated
in lizards, and birds, where "compared
to controls a greater number of naloxone-treated
birds copulated in the test arena on the first
day" and "Naloxone
treatment showed a significant increase in the
frequency of several aggressive actions and the
effect was dose dependent."