Nepeta
cataria L. var. citriodora (Becker) increases
penile erection in rats.
Bernardi MM, Kirsten TB, Lago JH, Giovani
TM, Massoco CD.
Health Science Institute,
Paulista University; Department of Pathology,
School of Veterinary Medicine, University of
São Paulo, Brazil.
Abstract
Nepeta cataria (NC), catnip, induces
pleasure in cats and humans.
Because sexual behavior is involved in
pleasure, the effect of NC on sexual behavior
and penile erection was evaluated in male rats
that were acutely fed chow enriched with 10% NC
leaves. Further, yawning was monitored
because we previously demonstrated that NC
modifies dopaminergic-related behaviors and that
sexual behavior is closely linked with the
dopaminergic system. The general activity and
the motor coordination were examined to
investigate the possible motor and emotional
interferences of the sexual performance.
Male rats of the NC group received for a 4h
period the chow enriched with 10% NC leaves
while the control groups received regular chow.
Fifteen min after the end of the 4h period of NC
feeding the sexual behavior, apomorphine-induced
penile erection and motor coordination were
observed; the general activity in the open field
was assessed 0, 15, 30 and 60min after
treatment.
NC treatment increased male rat's penile
erection. A slightly facilitation on male rat
sexual behavior and a decreased in general
activity of NC treated rats were observed. No
effects on motor coordination and yawning
episodes were detected by the NC treatment.
It was suggested that NC increases penile
erection and slightly improves male rat sexual
behavior by an action on dopaminergic
systems.
1. Introduction
Nepeta cataria (NC), popularly called catnip
or catmint, is a perennial herb belonging to the
mint family (Lamiaceae). NC has long been used
in North American popular medicine and in teas,
dyes, and infusions. Nepeta species are widely
used because of their antispasmodic,
expectorant, diuretic, antiseptic, febrifuge,
antitussive, and antiasthmatic effects
(Smitherman et al., 2005). Also this plant that
has been used extensively in toys for pets
(Smitherman et al., 2005). Catnip alters
behavior and produces pleasurable sensations in
both wild and domestic cats as well as in other
mammals (Hatch, 1972). One study also associated
pleasurable experiences with catnip in humans.
The dried leaves or extract, when smoked,
produced symptoms similar to those of marijuana
and LSD (Jackson and Reed, 1969).
Because sexual behavior is involved with
pleasure, the aim of the present study was to
evaluate the sexual behavior and
apomorphine-induced penile erection in male rats
acutely fed chow enriched with 10% NC leaves.
The role of NC in sexual behavior has not yet
been elucidated.
It was also measured the apomorphine-induced
yawning episodes, because previously we
found that the ingestion of NC modifies
dopaminergic-related behaviors with an
amphetaminelike effect (Massoco et al., 1995).
Moreover, sexual behavior is closely linked to
the dopaminergic system. Among the central
neurotransmitters involved in the control of
sexual behavior, dopamine is one of the most
extensively studied. Several studies provide
neuropharmacological, biochemical,
electrophysiological and psychobiological
evidence that dopamine plays a pivotal role in
the control of different aspects of sexual
behavior (Hsieh et al., 2004; Dominguez and
Hull, 2005; Pfaus, 2009).
The general activity in the open field and
the motor coordination were also examined to
investigate the possible motor or emotional
effects on the sexual performance of male
rats.
4. Discussion
The results show that 4h of feeding of
experimental animal with 10% plant material (N.
cataria mixed with chow) was able to alter
sexual behavior, penile erection and general
activity of rats. Particularly, the locomotion
and rearing frequencies in the open field were
decreased after 15 min and first sessions,
respectively. Thus, the 15 min latency to NC
effects was chosen to perform the remained
experiments. In addition, previous results using
the same regimen dose reduced the depressive
signs observed in the learned helplessness model
of depression after 15 min after treatment
(Figueiredo et al., 2005).
Food consumption was not significantly
different between the control and NC groups;
thus, NC does not affect chow consumption and
indicates that each rat has equal access or
dosing within 4-h session. Therefore, the
behavioral changes found were not triggered by
nutritional differences by NC.
NC decreased the number of mounts prior to
the first ejaculation, without altering the
number of ejaculations. Consistent with previous
work, these data suggest that NC increases mount
efficiency (Bitran and Hull, 1987).
However, none of the other parameters of
sexual behavior examined were changed following
the ingestion of NC. Specifically, the lack of
differences between control and NC groups on
mount, intromission and ejaculation latencies
suggest that NC did not modify the motivational
aspects of sexual behavior. These aspects are
all considered parameters of sexual motivation
(Agmo, 1999; Pfaus, 2009). Thus, NC only
slightly improves male rat sexual behavior.
The number of mounts also may reflects an
increase in sexual motivation, but it may be
confounded by other factors, such as motor
interferences and should be interpreted with
caution (Agmo, 1997). Data from motor
coordination studies indicate that NC does not
affect the fine motor performance involved in
sexual behavior (Agmo, 1999).
The most interesting result of this study is
the penile erection data. In addition to the
slight effects of NC on sexual behavior, the
penile erection was increased in these rats.
Thus, the increased penile erection represents
an improvement in sexual performance.
Presently, penile erection was induced by
apomorphine, a potent nonselective DA receptor
agonist that activates all of the DA receptor
subtypes (Missale et al., 1998). High
apomorphine doses induce stereotyped behavior
and low doses penile erection and yawning
behavior (Andersson, 2001). In relation to
penile erection, the paraventricular nucleus
(PVN) of the hypothalamus is an integration
center between the central and peripheral
autonomic nervous systems (Argiolas and Melis,
2005). Apomorphine has PVN selective action at
low doses to induce penile erection. Moreover,
activation of these areas by excitatory amino
acids (N-methylD-aspartic acid), oxytocin,
dopamine or its agonists, or electrical
stimulation leads to penile erection (Giuliano
and Rampin, 2004). In this respect, previous
results from our group suggest that NC exposure
has an amphetamine-like effect (Massoco et al.,
1995), suggesting that NC active principles has
dopaminergic activity. The present findings also
suggest a dopaminergic activity of NC active
principles, since NC treatment potentates the
penile erection induced by a low dose of the
dopaminergic agonist. This effect seems to be
specific because no stereotypy or stimulation
was observed. However, apomorphine also
activates oxytocinergic neurons in the PVN
(Melis et al., 1992). Dopamine-containing nerve
endings impinge on oxytocinergic cell bodies in
the PVN, which project, in turn, to
extra-hypothalamic brain areas such as the
hippocampus, the ventral medulla and the spinal
cord. In addition, apomorphine indirectly
activates septo-hippocampal cholinergic neurons,
which have a modulatory role in penile erection
(Heaton, 2000). Finally, dopaminergic
stimulation activates serotonergic neurons in
the median raphe, thus placing DA neurons
upstream of raphe hippocampal 5-HT neurons in
this segment of the erectile pathway (Heaton,
2000). Thus, it is possible that NC increased
penile erection not only by dopaminergic
activity but also by interference with other
neurotransmitters.
In this study, apomorphine administration
not only induced penile erection but also
yawning behavior. Yawning is a
stereotyped behavior, which can occur alone or
in combination with stretching and/or penile
erection in humans and animals (Argiolas and
Melis, 1998). The present data show that
apomorphine induced both yawning and
penile erection, but only penile erection was
increased by NC exposure, reinforcing the
specificity of the plant on penile erection
mechanisms.
Consistent with previous studies, we also
found that chow enriched with NC has
antidepressant properties in mice (Bernardi et
al., 2010). Clinically, this finding could be
very interesting because most antidepressant
drugs induce sexual dysfunction and reduce the
human and laboratory animals' libido (Baldwin,
2004; Habr et al., 2009). However, in the
present study, NC improved sexual behavior and
performance.
Because we previously detected an
amphetamine-like effect of this plant in mice,
increasing motor or emotional behaviors (Massoco
et al., 1995), which could interfere with sexual
behavior, we performed the open field general
activity and motor coordination studies.
The different behavioral parameters
evaluated in the open field are related to
emotional, exploratory and motor behavior.
Particularly, the first exposure of the animal
to the device has mainly a strong emotional
component (Moniz et al., 1994; Batatinha et al.,
1995; Massoco et al., 1995). Moreover,
locomotion in an open field is inversely
associated with anxiety ratings. This
association depends upon whether the locomotion
appears purposeful or whether the animal
exhibits other exploratory behaviors or
exhibiting anxiety-related behaviors (Dishman et
al., 1996).
Thus, despite a decrease in locomotion and
rearing behavior in the NC group during the
15-min and first sessions, respectively, no
differences were detected during the other
observation sessions. Likewise, immobility and
motor coordination were not modified by NC.
These results suggest that fine (motor
coordination) and gross (general activity)
motor, emotional and anxiety interferences are
not induced by NC. Therefore, the general
activity and motor coordination negative results
reinforce our present findings that NC improves
sexual behavior and performance.
