Exercise and sleep in aging: emphasis on serotonin.

Reductions in central serotonin activity with aging might be involved in sleep-related disorders in later life. Although the beneficial effects of aerobic exercise on sleep are not new, sleep represents a complex recurring state of unconsciousness involving many lines of transmitters which remains only partly clear despite intense ongoing research. It is known that serotonin released into diencephalon and cerebrum might play a key inhibitory role to help promote sleep, likely through an active inhibition of supraspinal neural networks. Several lines of evidence support the stimulatory effects of exercise on higher serotonergic pathways. Hence, exercise has proved to elicit acute elevations in forebrain serotonin concentrations, an effect that waned upon cessation of exercise. While adequate exercise training might lead to adaptations in higher serotonergic networks (desensitization of forebrain receptors), excessive training has been linked to serious brain serotonergic maladaptations accompanied by insomnia. Dietary supplementation of tryptophan (the only serotonin precursor) is known to stimulate serotonergic activity and promote sleep, whereas acute tryptophan depletion causes deleterious effects on sleep. Regarding sleep-wake regulation, exercise has proved to accelerate resynchronization of the biological clock to new light-dark cycles following imposition of phase shifts in laboratory animals. Noteworthy, the effect of increased serotonergic transmission on wake state appears to be biphasic, i.e. promote wake and thereafter drowsiness. Therefore, it might be possible that acute aerobic exercise would act on sleep by increasing activity of ascending brain serotonergic projections, though additional work is warranted to better understand the implication of serotonin in the exercise-sleep axis.

Kind attention and non-judgment in mindfulness-based cognitive therapy applied to the treatment of insomnia: state of knowledge.

Psychophysiological insomnia is characterized by acquired sleep difficulties and/or a state of hypervigilance when going to bed. This mental and physiological condition prevents sleep onset regardless of the presence of anxious or depressive disorders. Despite the fact that cognitive behavioural therapies have been shown to be effective for this disorder, some people are not responding to this treatment. It is therefore important to explore new ways of increasing the effectiveness of current treatments. Approaches based on mindfulness, which promote a non-judgemental acceptance of the living experience, are increasingly reported in the literature to be effective in the treatment of various physical and psychological health conditions, being particularly efficient in reducing the stress and discomfort associated with these problems. This article focuses on some cognitive factors associated with maintaining insomnia and suggests that approaches based on mindfulness, through certain action mechanisms, may help to improve sleep. A review of recent studies on the application of mindfulness-based approaches to treat insomnia is hereby presented. Avenues for future research to improve insomnia treatment protocols based on mindfulness are suggested.

Disturbance in uniformly 13C-labelled DHA metabolism in elderly human subjects carrying the apoE ε4 allele.

Carrying the apoE ε4 allele (E4+ ) is the most important genetic risk for Alzheimer's disease. Unlike non-carriers (E4- ), E4+ seem not to be protected against Alzheimer's disease when consuming fish. We hypothesised that this may be linked to a disturbance in n-3 DHA metabolism in E4+. The aim of the present study was to evaluate [13C]DHA metabolism over 28 d in E4+ v. E4-. A total of forty participants (twenty-six women and fourteen men) received a single oral dose of 40 mg [13C]DHA, and its metabolism was monitored in blood and breath over 28 d. Of the participants, six were E4+ and thirty-four were E4-. In E4+, mean plasma [13C]DHA was 31% lower than that in E4-, and cumulative b-oxidation of [13C]DHA was higher than that in E4- 1­28 d post-dose (P ≤0·05). A genotype x time interaction was detected for cumulative b-oxidation of [13C]DHA (P ≤ 0·01). The whole-body half-life of [13C]DHA was 77% lower in E4+ compared with E4- (P ≤0·01). In E4+ and E4-, the percentage dose of [13C]DHA recovered/h as 13CO2 correlated with [13C]DHA concentration in plasma, but the slope of linear regression was 117% steeper in E4+ compared with E4- (P ≤ 0·05). These results indicate that DHA metabolism is disturbed in E4+, and may help explain why there is no association between DHA levels in plasma and cognition in E4+. However, whether E4+ disturbs the metabolism of 13C-labelled fatty acids other than DHA cannot be deduced from the present study.

Pharmacokinetic and pharmacodynamic characterization of an oral lysophosphatidic acid type 1 receptor-selective antagonist.

Lysophosphatidic acid (LPA) is a bioactive phospholipid that signals through a family of at least six G protein-coupled receptors designated LPA1₋6. LPA type 1 receptor (LPA1) exhibits widespread tissue distribution and regulates a variety of physiological and pathological cellular functions. Here, we evaluated the in vitro pharmacology, pharmacokinetic, and pharmacodynamic properties of the LPA1-selective antagonist AM095 (sodium, {4'-[3-methyl-4-((R)-1-phenyl-ethoxycarbonylamino)-isoxazol-5-yl]-biphenyl-4-yl}-acetate) and assessed the effects of AM095 in rodent models of lung and kidney fibrosis and dermal wound healing. In vitro, AM095 was a potent LPA1 receptor antagonist because it inhibited GTPγS binding to Chinese hamster ovary (CHO) cell membranes overexpressing recombinant human or mouse LPA1 with IC50 values of 0.98 and 0.73 µM, respectively, and exhibited no LPA1 agonism. In functional assays, AM095 inhibited LPA-driven chemotaxis of CHO cells overexpressing mouse LPA1 (IC50= 778 nM) and human A2058 melanoma cells (IC50 = 233 nM). In vivo, we demonstrated that AM095: 1) had high oral bioavailability and a moderate half-life and was well tolerated at the doses tested in rats and dogs after oral and intravenous dosing, 2) dose-dependently reduced LPA-stimulated histamine release, 3) attenuated bleomycin-induced increases in collagen, protein, and inflammatory cell infiltration in bronchalveolar lavage fluid, and 4) decreased kidney fibrosis in a mouse unilateral ureteral obstruction model. Despite its antifibrotic activity, AM095 had no effect on normal wound healing after incisional and excisional wounding in rats. These data demonstrate that AM095 is an LPA1 receptor antagonist with good oral exposure and antifibrotic activity in rodent models.

A novel, orally active LPA(1) receptor antagonist inhibits lung fibrosis in the mouse bleomycin model.

BACKGROUND AND PURPOSE: The aim of this study was to assess the potential of an antagonist selective for the lysophosphatidic acid receptor, LPA(1), in treating lung fibrosis We evaluated the in vitro and in vivo pharmacological properties of the high affinity, selective, oral LPA(1)-antagonist (4'-{4-[(R)-1-(2-chloro-phenyl)-ethoxycarbonylamino]-3-methyl-isoxazol-5-yl}-biphenyl-4-yl)-acetic acid (AM966). EXPERIMENTAL APPROACH: The potency and selectivity of AM966 for LPA(1) receptors was determined in vitro by calcium flux and cell chemotaxis assays using recombinant and native cell cultures. The in vivo efficacy of AM966 to reduce tissue injury, vascular leakage, inflammation and fibrosis was assessed at several time points in the mouse bleomycin model. KEY RESULTS: AM966 was a potent antagonist of LPA(1) receptors, with selectivity for this receptor over the other LPA receptors. In vitro, AM966 inhibited LPA-stimulated intracellular calcium release (IC(50)= 17 nM) from Chinese hamster ovary cells stably expressing human LPA(1) receptors and inhibited LPA-induced chemotaxis (IC(50)= 181 nM) of human IMR-90 lung fibroblasts expressing LPA(1) receptors. AM966 demonstrated a good pharmacokinetic profile following oral dosing in mice. In the mouse, AM966 reduced lung injury, vascular leakage, inflammation and fibrosis at multiple time points following intratracheal bleomycin instillation. AM966 also decreased lactate dehydrogenase activity and tissue inhibitor of metalloproteinase-1, transforming growth factor beta1, hyaluronan and matrix metalloproteinase-7, in bronchoalveolar lavage fluid. CONCLUSIONS AND IMPLICATIONS: These findings demonstrate that AM966 is a potent, selective, orally bioavailable LPA(1) receptor antagonist that may be beneficial in treating lung injury and fibrosis, as well as other diseases that are characterized by pathological inflammation, oedema and fibrosis.

Pharmacodynamics and pharmacokinetics of AM103, a novel inhibitor of 5-lipoxygenase-activating protein (FLAP).

The 5-lipoxygenase-activating protein (FLAP) gene and an increase in leukotriene (LT) production are linked to the risk of asthma, myocardial infarction, and stroke. We evaluated the pharmacodynamics, pharmacokinetics, and tolerability of 3-[3-tert-butylsulfanyl-1-[4-(6-methoxy-pyridin-3-yl)-benzyl]-5-(pyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethyl-propionic acid (AM103), a novel FLAP inhibitor, in healthy subjects. Single and multiple doses of AM103 demonstrated dose-dependent inhibition of blood LTB(4) production and dose-related inhibition of urinary LTE(4). After a single oral dose (50-1,000 mg) of AM103, the maximum concentration (C(max)) and area under the curve (AUC) in plasma increased in a dose-dependent manner. After multiple-dose administration (50-1,000 mg once daily for 11 days), there were no significant differences in the pharmacokinetic parameters between the first and last days of treatment. AM103 was well tolerated at all doses in both the single- and multiple-dose cohorts. Further clinical trials with AM103 in inflammatory diseases are warranted.

Thyroid Function and Cognition during Aging.

We summarize here the studies examining the association between thyroid function and cognitive performance from an aging perspective. The available data suggest that there may be a continuum in which cognitive dysfunction can result from increased or decreased concentrations of thyroid hormones. Clinical and subclinical hypothyroidism as well as hyperthyroidism in middle-aged and elderly adults are both associated with decreased cognitive functioning, especially memory, visuospatial organization, attention, and reaction time. Mild variations of thyroid function, even within normal limits, can have significant consequences for cognitive function in the elderly. Different cognitive deficits possibly related to thyroid failure do not necessarily follow a consistent pattern, and L-thyroxine treatment may not always completely restore normal functioning in patients with hypothyroidism. There is little or no consensus in the literature regarding how thyroid function is associated with cognitive performance in the elderly.

Effects of ketamine and N-methyl-D-aspartate on glutamate and dopamine release in the rat prefrontal cortex: modulation by a group II selective metabotropic glutamate receptor agonist LY379268.

Previous studies have shown that the metabotropic glutamate receptor (mGluR)2/3 agonist LY354740 attenuated glutamate release in medial prefrontal cortex (mPFC) induced by the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine. In the present study we examined the effects of the more potent mGluR2/3 selective agonist LY379268 on ketamine-evoked glutamate and dopamine (DA) release in mPFC of male rats. Subjects were implanted with a unilateral microdialysis probe in the mPFC and were tested 12-24 h after implantation. Ketamine (18 mg/kg, s.c.) evoked a significant release of glutamate and DA, although the glutamate response was slower in onset compared with DA. Pretreatment with either systemic (3 mg/kg s.c.) or local (1 microM, in the probe) LY379268 blocked ketamine-evoked glutamate, but not DA, release. When applied directly to the mPFC via the dialysis probe, ketamine (1 mM in the probe) had no effect on glutamate release but did significantly enhance the release of DA. Application of NMDA (500 microM in the probe), on the other hand, decreased DA while increasing glutamate release. The effect of NMDA on evoking glutamate release was blocked by systemic but not local administration of LY379268. These findings indicate that systemic ketamine increases both glutamate and DA release in mPFC and that the effect on glutamate can be blocked by stimulating mPFC group II mGluR receptors. Local ketamine, on the other hand, does not increase glutamate but does increase DA release. This suggests that ketamine acts outside of the mPFC to enhance glutamate, but within the mPFC to enhance DA release. The origin of the ketamine effect on mPFC glutamate is currently not known.

Dopamine release in the medial preoptic area of female rats in response to hormonal manipulation and sexual activity.

Dopamine (DA) is responsive to hormonal manipulations and has been implicated in the regulation of female rat sexual behavior. In the present studies, extracellular DA levels were assessed in the medial preoptic area (MPOA) of ovariectomized female rats in response to exogenous ovarian hormones and during sexual activity. In female rats primed with a low dose of estradiol benzoate (2 microg), but not with a higher dose (20 microg), a 500-microg progesterone injection increased extracellular DA and facilitated copulatory behavior. Extracellular DA levels in the MPOA were further augmented during sexual interactions with a male rat in a nonpacing copulatory chamber by either perineal or vaginal stimulation. However, in a pacing chamber, DA efflux did not increase, although the metabolites rose significantly during copulation. Together, these findings suggest that extracellular DA in the MPOA responds to the hormonal state of the female rat and may contribute to her expression of sexual behavior.

Previous exposure to amphetamine increases incentive to obtain the drug: long-lasting effects revealed by the progressive ratio schedule.

The present experiment tested whether previous exposure to amphetamine would enhance rats' predisposition to self-administer a high dose of the drug under fixed (FR) and progressive ratio (PR) schedules of reinforcement. Rats in different groups were given five injections of either amphetamine (1.5 mg/kg, i.p.) or saline (1.0 ml/kg, i.p.), one injection administered every third day and, starting 10 days later, given the opportunity to lever press for amphetamine (200 microg/kg/infusion, i.v.) on each of several 4 h sessions. When allowed to self-administer up to 10 infusions under first an FR-1 and then an FR-2 schedule, amphetamine and saline pre-exposed rats were indistinguishable and readily acquired the lever press response. However, when tested under the PR schedule of reinforcement, rats previously exposed to amphetamine achieved higher break points than saline pre-exposed rats across six consecutive PR sessions. This difference between groups was long lasting and durable. When compared to saline pre-exposed rats on three separate tests conducted 10, 14 and 21 days following the last PR session, rats pre-exposed to amphetamine also showed (i) greater nucleus accumbens dopamine reactivity to amphetamine (1.0 mg/kg, i.p.), (ii) higher break points when retested on the PR schedule, and (iii) a greater locomotor response to amphetamine (1.0 mg/kg, i.p.). On the last test, both groups showed higher levels of locomotion than no drug control animals that received amphetamine for the first time on this test. These findings suggest that previous exposure to amphetamine produces a long lasting enhancement in the incentive motivation animals will exhibit in their effort to obtain the drug. This enhancement appears to parallel sensitization of the drug's locomotor and nucleus accumbens dopamine activating effects. It may very well be exacerbated by continued exposure to self-administered amphetamine.

The effect of previous exposure to amphetamine on drug-induced locomotion and self-administration of a low dose of the drug.

RATIONALE AND OBJECTIVES: In order to assess directly the relationship between locomotor activity and drug self-administration, the present experiment simultaneously measured these two behaviors in rats with different histories of pre-exposure to amphetamine either following or in the absence of priming injections of the drug. METHODS: Different groups of rats were exposed to ten daily injections of either saline (1.0 ml/kg, i.p.) or amphetamine (1.5 mg/kg, i.p.) and, in each of 13 daily sessions starting 10 days later, were given the opportunity to lever press for a low dose of amphetamine (10 microg/kg per i.v. infusion) in a two-lever (active versus inactive) continuous reinforcement task. Animals were administered a priming injection of amphetamine (1.0 mg/kg, i.p.) immediately before testing on the first 8 days, a saline injection (1.0 ml/kg, i.p.) on the next 3 days and amphetamine on the final 2 days of testing. RESULTS: Consistent with previous reports, prior exposure to amphetamine led to an enhanced locomotor response to the priming injection of amphetamine on the first day of testing. Little pressing for drug was observed on this day. Following priming injections on the subsequent test days, evidence for enhanced locomotion by amphetamine-pre-exposed rats diminished and both groups showed comparable and progressive increases in active versus inactive lever pressing. When priming injections were not made, however, only animals previously exposed to amphetamine maintained lever pressing for the drug. Under these conditions, these animals emitted more active lever presses and time-out responses and exhibited higher levels of locomotor activation in proximity to the active drug administering lever than did saline-pre-exposed rats. CONCLUSIONS: These results are consistent with the view that previous exposure to amphetamine produces a long-lasting enhancement in the behavioral activation animals will direct toward stimuli associated with the drug. This enhancement was displayed initially as a sensitized locomotor response to amphetamine on the first day of testing and was subsequently observed on those test days when no priming injections were given when animals continued to self-administer a low dose of amphetamine under a simple schedule of reinforcement. The implications of these findings for our understanding of the excessive expression of drug-directed behaviors are discussed.

Hormone-neurotransmitter interactions in the control of sexual behavior.

The stimuli from a receptive female and/or copulation itself leads to the release of dopamine (DA) in at least three integrative hubs. The nigrostriatal system promotes somatomotor activity; the mesolimbic system subserves numerous types of motivation; and the medial preoptic area (MPOA) focuses the motivation onto specifically sexual targets, increases copulatory rate and efficiency, and coordinates genital reflexes. The previous (but not necessarily concurrent) presence of testosterone is permissive for DA release in the MPOA, both during basal conditions and in response to a female. One means by which testosterone may increase DA release is by upregulating nitric oxide synthase, which produces nitric oxide, which in turn increases DA release. Hormonal priming in females may also increase DA release in the MPOA, and copulatory activity may further increase DA levels in females. One of the intracellular effects of stimulation of DA D1 receptors in the MPOA of male rats may be increased expression of the immediate-early gene c-fos, which may mediate longer term responses to copulation. Furthermore, increased sexual experience led to increased immunoreactivity to Fos, the protein product of c-fos, following copulation to one ejaculation. Another intracellular mediator of DA's effects, particularly in castrates, may be the phosphorylation of steroid receptors. Finally, while DA is facilitative to copulation, 5-HT is generally inhibitory. 5-HT is released in the LHA, but not in the MPOA, at the time of ejaculation. Increasing 5-HT in the LHA by microinjection of a selective serotonin reuptake inhibitor (SSRI) increased the latency to begin copulating and also the latency to the first ejaculation, measured from the time the male first intromitted. These data may at least partially explain the decrease in libido and the anorgasmia of people taking SSRI antidepressants. One means by which LHA 5-HT decreases sexual motivation (i.e. increases the latency to begin copulating) may be by decreasing DA release in the NAcc, a major terminal of the mesolimbic system. Thus, reciprocal changes in DA and 5-HT release in different areas of the brain may promote copulation and sexual satiety, respectively.

Lateral hypothalamic serotonin inhibits nucleus accumbens dopamine: implications for sexual satiety.

Dopamine (DA) is released in several brain areas, including the nucleus accumbens (NAcc), before and during copulation in male rats. DA agonists administered into this area facilitate, and DA antagonists inhibit, numerous motivated behaviors, including male sexual behavior. Serotonin (5-HT) is generally inhibitory to male sexual behavior. We reported previously that 5-HT is released in the anterior lateral hypothalamic area (LHA(A)) and that a selective serotonin reuptake inhibitor microinjected into that area delayed and slowed copulation. Our present results, using high temporal resolution microdialysis, (1) confirm previous electrochemical evidence that extracellular levels of DA increase in the NAcc during copulation and decrease during the postejaculatory interval (PEI) and (2) reveal that LHA(A) 5-HT can inhibit both basal and female-elicited DA release in the NAcc. These findings suggest that the neural circuit promoting sexual quiescence during the PEI includes serotonergic input to the LHA(A), which in turn inhibits DA release in the NAcc. These findings may also provide insights concerning the inhibitory control of other motivated behaviors activated by the NAcc and may have relevance for understanding the sexual side effects common to antidepressant medications.

Partial antagonism of 8-OH-DPAT'S effects on male rat sexual behavior with a D2, but not a 5-HT1A, antagonist.

The serotonin agonist 8-hydroxy-di-propylaminotetralin (8-OH-DPAT), injected systemically or directly into the medial preoptic area (MPOA), reduces the ejaculatory threshold in male rats. While 8-OH-DPAT has been characterized as an agonist at the 5-HT1A receptor, it also acts at other receptor sites including the dopamine D2 receptor. The current experiments investigated whether 8-OH-DPAT injected into the MPOA facilitates male sexual behavior through stimulation of the 5-HT1A receptor or the dopamine D2 receptor. Experiment 1 co-administered 8-OH-DPAT (6 microgram) with either the 5-HT1A antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-ben zamide hydrochloride (MPPI) (10 microgram) or the D2 antagonist raclopride (10 microgram). Raclopride blocked 8-OH-DPAT's facilitative effects on ejaculation frequency and latency, while the 5-HT1A antagonist was ineffective. In Experiment 2, 8-OH-DPAT (500 microM), retrodialyzed into the MPOA through a microdialysis probe, enhanced male copulatory behavior similarly to the microinjection, increasing ejaculation frequency and decreasing ejaculation latency, postejaculatory interval and mount frequency. Retrodialyzing 8-OH-DPAT through a microdialysis probe in the MPOA had been previously shown to increase extracellular levels of dopamine and serotonin. The data from the present studies suggest that the effects of 8-OH-DPAT in the MPOA on male rat copulatory behavior may be mediated, at least in part, either directly through 8-OH-DPAT's activity at D2 receptors or indirectly through 8-OH-DPAT's ability to increase extracellular dopamine.

Sleep position and sleep stages: evidence of their independence.

Recently we conducted a first ontogenetic study of sleep positions in the human, which involved five groups of 10 subjects (5 males, 5 females) from each of the following age categories: 3-5 years, 8-12 years, 18-24 years, 35-45 years, 65-80 years. They slept for 4 consecutive nights in the laboratory. Sleep positions were recorded during 2 nights with super-8 time-lapse photography. In a first report we presented results showing developmental trends in sleep position shifts, position durations and in the use of prone, supine and side positions. In the current report we present results showing that there was no significant relationship between sleep stages and sleep positions in any group. Furthermore, time-series analyses revealed no consistent pattern of position sequences in any of the age groups. It is concluded that, while there are ontogenetic trends in sleep position preferences, sleep positions are independent of sleep stages and do not show consistent rhythmicity.

8-OH-DPAT influences extracellular levels of serotonin and dopamine in the medial preoptic area of male rats.

Serotonin (5-HT) is generally inhibitory to male rat sexual behavior. However, the 5-HT1A agonist 8-hydroxy-di-propylaminotetralin (8-OH-DPAT), injected either systemically or into the medial preoptic area (MPOA), facilitates ejaculation. Three experiments were conducted to test the effects of 8-OH-DPAT on 5-HT and dopamine (DA) neurotransmission in the MPOA, a very important site for the control of male sexual behavior. In Experiment 1, systemically injected 8-OH-DPAT (0.4 mg/kg) decreased extracellular 5-HT levels in the MPOA as measured by in vivo microdialysis. In Experiment 2, 8-OH-DPAT (500 microM) administered directly into the MPOA via reverse dialysis increased extracellular levels of both DA and 5-HT; pretreatment with the selective 5-HT1A antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-ben benzamide hydrochloride (p-MPPI) failed to prevent 8-OH-DPAT's stimulatory effects on DA and 5-HT levels in the MPOA. In Experiment 3, 8-OH-DPAT (8 microg) co-injected with 5,7-dihydroxytryptamine (5,7-DHT; 6 microg) prevented neurotoxic depletion of 5-HT in the site of injection (MPOA). Because systemic and MPOA injections of 8-OH-DPAT resulted in opposite effects on extracellular 5-HT in the MPOA, yet both can facilitate ejaculation, these data suggest that moderate changes in 5-HT in the MPOA may have relatively little influence on male copulatory behavior. Instead, the facilitative effects of 8-OH-DPAT in the MPOA on male copulatory behavior may result, at least in part, from stimulatory effects of 8-OH-DPAT on DA transmission. Facilitative effects of systemic injections of 8-OH-DPAT may result from decreased 5-HT release in several sites.

Castration decreases extracellular, but increases intracellular, dopamine in medial preoptic area of male rats.

Dopamine (DA) is released in the medial preoptic area (MPOA) of male rats in the presence of a female, and it facilities male sexual behavior. Castration blocks the DA response to a female and the male's ability to copulate. The present experiments examined the effects of castration on (1) basal levels of extracellular DA in the MPOA, using the no net flux microdialysis technique, (2) the response of extracellular DA to amphetamine, and (3) tissue levels of DA. Castrated rats had lower basal levels of extracellular DA in the MPOA, compared with gonadally intact rats; in vivo recovery, a measure of uptake, was not different. This suggests that castration decreases DA release in basal conditions, as well as in response to a female. However, systemic amphetamine injections, which induce DA release, resulted in greater DA release in castrates. Finally, tissue levels of DA were higher in the MPOA, the caudate-putamen and the bed nucleus of stria terminalis of castrates. These data suggest that DA synthesis and storage in the MPOA are normal, or even enhanced, in castrates, and uptake is not altered. The deficit in extracellular levels appears to be related to release, perhaps due to decreased nitric oxide.

Extracellular serotonin in the lateral hypothalamic area is increased during the postejaculatory interval and impairs copulation in male rats.

Serotonin (5-HT) is generally inhibitory to masculine sexual behavior. It has been suggested that 5-HT released after ejaculation may promote the sexual quiescence of the postejaculatory interval (PEI). The following experiments were conducted to test (1) whether extracellular 5-HT increases in either the anterior lateral hypothalamic area (LHAA) or the medial preoptic area (MPOA) of male rats after ejaculation; (2) whether increasing 5-HT in these sites, by microinjecting the selective serotonin reuptake inhibitor alaproclate, could inhibit copulatory abilities; and (3) whether copulation deficits produced by alaproclate were attributable to locomotor impairments. The effects of local application of alaproclate on extracellular 5-HT levels in the LHAA and the MPOA were also tested. Extracellular serotonin was measured in all experiments using in vivo microdialysis. Ejaculation was correlated with enhanced 5-HT release from the LHAA; no 5-HT increases were observed before ejaculation, and levels were decreased toward basal values during a subsequent copulatory series. Elevating 5-HT in the LHAA by microinjecting alaproclate inhibited copulation by increasing the latency to mount, intromit, and ejaculate. This inhibition did not result from nonspecific locomotor impairments. In the MPOA, 5-HT release remained stable throughout copulation, and microinjecting alaproclate into this site did not significantly alter sexual behavior. These data support the large body of evidence suggesting that 5-HT is inhibitory to masculine sexual behavior. Furthermore, the LHAA, but not the MPOA, may be one site responsible for serotonergic inhibition of copulation during the PEI.

Testosterone, preoptic dopamine, and copulation in male rats.

Steroid hormones prime neural circuits for sexual behavior, in part by regulating enzymes, receptors, or other proteins affecting neurotransmitter function. Dopamine facilitates male sexual behavior in numerous species and is released before and/or during copulation in three integrative neural systems. The nigrostriatal system enhances readiness to respond; the mesolimbic system promotes many appetitive behaviors; the medial preoptic area (MPOA) contributes to sexual motivation, genital reflexes, and copulation. We have reported a consistent relationship between precopulatory dopamine release in the MPOA, when an estrous female was behind a perforated barrier, and the ability to copulate after the barrier was removed. Recent, but not concurrent, testosterone was necessary for the precopulatory dopamine response and copulation. The deficit in MPOA dopamine release in castrates was observed in basal conditions as well as the sexual context. However, dopamine in tissue punches from castrates was higher than in intact males. Because tissue levels represent primarily stored neurotransmitter, dopamine appeared to have been synthesized normally, but was not being released. Amphetamine induced greater dopamine release in castrates, again suggesting excessive dopamine storage. The decreased release may result from decreased activity of nitric oxide synthase in the MPOA of castrates. A marker for this enzyme showed lower activity in castrates than in intact males. Finally, blocking nitric oxide synthase in intact males blocked the copulation-induced release of dopamine in the MPOA. Therefore, one means by which testosterone may promote copulation is by upregulating nitric oxide synthesis in the MPOA, which in turn enhances dopamine release.