Induction of copulatory behavior in sexually inactive rats by naloxine

New treatments for erectile impotence

The range of interventions available for the treatment of erectile failure has increased in the past ten years. A significant development is intracavernosal injection of vasoactive drugs, but this treatment is far from ideal. Other, less invasive, pharmacological interventions are being investigated; as yet, none of these appear effective enough to have any significant clinical impact. External vacuum devices are a viable option for some patients, and penile prostheses have become increasingly sophisticated, although research examining their benefits has not. The range of available treatment methods and the growing complexity of the assessment for erectile problems demands an eclecticism of approach which can best be provided by multidisciplinary clinics specialising in sexual dysfunctions.

Bilateral injections of a selective mu-receptor agonist (morphiceptin) into the medial preoptic nucleus produces a marked delay in the initiation of sexual behavior in the male rat

We examined the putative functional role of the medial preoptic nucleus mu-receptor population in the expression of male copulatory behavior in sexually vigorous Long-Evans rats. In the first experiment, three doses of morphiceptin (10, 500, and 1000 ng) a selective mu-receptor agonist injected bilaterally into the medial preoptic nucleus, produced a marked delay in the initiation of male copulatory behavior compared to saline injected controls. These injections significantly lengthened intromission and mount latencies while having no appreciable effect on any other parameter of male copulatory behavior. In a separate experiment, the transient inhibition of the expression of male copulatory behavior was completely abolished following pretreatment of naloxone 20 minutes prior to bilateral injections of morphiceptin (1000 ng) into the medial preoptic nucleus. Collectively, these results suggest that the delay in the initiation of copulation that is commonly observed following peripheral or central injections of opioids is mediated at least in part by mu receptors located within the medial preoptic nucleus.

Sexually dimorphic, androgen sensitive, enkephalinergic afferents to a lumbar motor nucleus of rats

In male rats, methionine-enkephalin immunoreactivity (enkephalin-ir) has been observed in the dorsal lateral nucleus (DLN), a longitudinal pool of motoneurons in the lumbar spinal cord. Within the DLN a mediodorsal crescent of intense enkephalin-ir staining surrounds the motoneurons innervating the ischiocavernosus muscle of the penis, which suggests a function of the enkephalinergic afferents in male copulatory activities. The present study attempted to determine the roles of gender and adult exposure to androgen in shaping the striking subnuclear distribution of enkephalin-ir. Transverse sections through L5-6 were obtained from mature male and female rats that were gonadally intact, gonadectomized, or gonadectomized and treated with testosterone, as well as from male rats genetically deficient in androgen receptors (Tfm). The sections were incubated with primary antiserum raised against methionine enkephalin and bound antibodies were visualized using the avidin-biotin-peroxidase technique. A microphotometer was used to compare the staining density in laminae I-II of the dorsal horn, ventral grey matter, and the DLN. In all groups the DLN stained more darkly than the ventral grey, demonstrating the presence of enkephalin-ir in the DLN regardless of gender or exposure to androgen. However, the mediodorsal crescent of dense staining in the DLN was obvious only in gonadally intact males, while the entire DLN stained darkly in both sexes of gonadectomized rats treated with androgen. Therefore, the preferential distribution of enkephalin-ir in the mediodorsal crescent of the DLN is sexually dimorphic though the overall content of enkephalin-ir within the DLN responds to androgen.

Yohimbine and naloxone: effects on male rat sexual behavior

We evaluated the effects of yohimbine (2 mg/kg) and naloxone (5 mg/kg), separately and in combination, on copulatory behavior in male rats. In Experiment 1, yohimbine evinced decrements in intromission frequency, ejaculation latency, and copulatory efficiency, whereas naloxone administration was followed by an increased ejaculation latency, and the combination of yohimbine plus naloxone was without effect. In Experiment 2, yohimbine evinced decreases in intromission frequency, ejaculation latency, copulatory efficiency in the first, but not subsequent, copulatory series, as well as a decreased latency to sexual exhaustion. Further, treatment with yohimbine alone, naloxone alone, or yohimbine plus naloxone was followed by a reduction in the number of ejaculation prior to sexual exhaustion. Thus, at the doses tested, no synergistic effects were observed for the combination of yohimbine plus naloxone.

Opioid modulation and sensitization of dopamine release elicited by sexually relevant stimuli: a high speed chronoamperometric study in freely behaving rats

High speed chronoamperometry was used to measure oxidation and reduction currents associated with monoamine release in the caudate putamen and nucleus accumbens of freely moving rats exposed to bedding from cages that housed other male, ovariectomized female, or estradiol-progesterone-primed female rats. Estrus female, but not male or ovariectomized female bedding potently increased the electrochemical signal from electrodes implanted within the nucleus accumbens, and less effectively from more dorsal sites. Naloxone pretreatment attenuated the increase in the electrochemical signal. Repeated exposure to estrus female bedding led to an increased, or sensitized, response within the nucleus accumbens that was also sensitive to naloxone pretreatment. The ratios of the reduction to oxidation currents indicated that dopamine was the principal contributor to the increase in the electrochemical signal, suggesting that activation of the mesolimbic dopamine system accompanies exposure to sexually relevant stimuli. These results suggest that the facilitation of sexual behaviors by dopamine may be due, at least in part, to the processing of incentive motivational cues, and not necessarily to effects on copulation, itself. The results of the present study also suggest that opioid peptides contribute to the activation of mesolimbic dopamine by sexually relevant olfactory stimuli.

Endogenous opioid-immunoreactive neurons of the ventromedial hypothalamic nucleus concentrate estrogen in male and female rats

Estrogen stimulates expression of proenkephalin mRNA in neurons of the hypothalamic ventromedial nucleus, and evidence is accumulating that synaptic release of one of the peptide end products, met-enkephalin, influences events that regulate reproductive behavior. To address the question of whether estrogen acts directly on neurons that synthesize met-enkephalin or indirectly through a separate neuronal population, we combined estrogen autoradiography with endogenous opioid peptide (EOP) immunohistochemistry. In agreement with previous studies, the ventrolateral subdivision of the hypothalamic ventromedial nucleus was densely packed with EOP-immunoreactive cells. In males, 48% of the estrogen-concentrating cells of the ventrolateral subdivision of the hypothalamic ventromedial nucleus contained EOP, and, in females, 27% of the estrogen-concentrating cells contained EOP. These findings indicate that estrogen acts directly on neurons that express EOP and suggest a mechanism that underlies sexually differentiated reproductive behavior.

Neurotransmitter, opiodergic system, steroid-hormone interaction and involvement in the replacement therapy of sexual disorders

Dopamine (DA) and serotonin (5-HT) are the neurotransmitters most directly involved in sexual activity. DA plays a stimulatory role while 5-HT has an inhibitory effect. The two monoaminergic systems modulate the secretion of many hormones (GnRH, LH, testosterone, prolactin and endorphins) involved in sexual functional capacity. Furthermore, hormones influence synthesis and storage of brain neurotransmitters. Impotence can often be associated to clinical depression and altered neurotransmitter function. Moreover, stress represents an unbalance between various neurotransmitter systems and can induce impotence especially when disorders of the endorphinic system are present. Replacement therapy is based upon the understanding of these basic concepts. Impotence due to an underlying depressive illness must be treated with dopaminergic antidepressant drugs; while in stressful conditions a good response to the naloxone test is the preliminary criterion to subsequent naltrexone treatment. When a hormonal deficiency has been proved, the hormone replacement therapy is of course highly effective (gonadotropins in hypogonadotropic syndromes, testosterone in aging, etc.). Finally, idiopathic impotence could be treated by DA agonist and/or 5-HT antagonist drugs either alone or better yet in association with psychotherapy.

Chronic pretreatment with naltrexone facilitates acquisition of intravenous cocaine self-administration in rats

Opioid systems may be involved in the reinforcing effects of drugs of abuse. It has been shown that the opioid antagonist naltrexone attenuates acquisition of intravenous cocaine self-administration behaviour in rats. Using a similar experimental set-up the effect of chronic blockade of opioid systems prior to cocaine exposure was examined. Rats were tested for acquisition of self-administration of one of 3 graded unit doses of cocaine (0.08, 0.16 and 0.32 mg.kg-1 per infusion) or saline. Chronic pretreatment with naltrexone (10 mg.kg-1 per day for 12 days) enhanced acquisition of intravenous cocaine self-administration but only in rats tested with the medium cocaine unit dose. It is concluded that chronic blockade of opioid systems facilitates acquisition of cocaine self-administration, probably by enhancing the reinforcing effect of cocaine.

Morphine and dynorphin(1-13) microinjected into the medial preoptic area and nucleus accumbens: effects on sexual behavior in male rats

The effects on sexual behavior of opiate receptor stimulation within A10 and A14 terminal areas were examined in the following experiments. Morphine (0.01-6 nmol) and dynorphin(1-13) (0.01-3 pmol) were microinjected into the medial preoptic area (MPOA). Morphine (10-100 pmol) and dynorphin (10-100 fmol) injected into the MPOA reduced both the latency to ejaculate and the number of intromissions triggering ejaculation. Morphine (6 nmol) produced a failure to resume copulating following the second ejaculation. Morphine (1-10 nmol) injected into the nucleus accumbens (ACC) shortened the latency to the first intromission and lengthened the second postejaculatory interval. Naloxone (3 mg/kg i.p.) reversed the effects of morphine on intromission latency and attenuated the lowering of ejaculatory threshold.

Central effect of yohimbine on sexual behavior in the rat

A large range of doses of yohimbine (Y) was administered intracerebroventricularly (ICV) (5-100 micrograms/rat) or intraperitoneally (IP) (0.35-10 mg/kg) to male rats and the effects on sexual, locomotor and general behavior were evaluated. For both routes there was a clear-cut inverted-U effect (stimulating/depressing), calculable as parabolic regressions on the log of administered doses. The maximal stimulating doses (15 micrograms/rat ICV and 1 mg/kg IP) significantly shortened mount, intromission and ejaculation latencies and the mean interintromission interval. These data indicate the importance of CNS mechanisms in the sexual effect of Y.

Naloxone disrupts the expression but not the acquisition by male rats of a conditioned place preference response for an oestrous female

Two experiments were conducted to investigate the possible role of endogenous opioid peptides in the regulation of masculine sexual reward. In experiment 1 sexually experienced male rats, which had recently been castrated or left gonadally intact, were allowed to mate with an oestrous female in an initially "non-preferred" chamber of a test apparatus. On alternate days these males were placed alone in the initially "preferred" chamber of the same apparatus. After eight such conditioning sessions both intact and castrated males had acquired a conditioned place preference (CPP) for the initially "non-preferred" chamber whereas control males, which were never given access to an oestrous female, showed no evidence of a significant shift in their preference for either chamber. Administration of the opioid receptor antagonist, naloxone (1 or 5 mg/kg, SC) prior to each conditioning session had no significant influence on the acquisition of a CPP for an oestrous female. By contrast, in experiment 2 naloxone treatment significantly attenuated the expression of a previously established CPP for an oestrous female in both gonadally intact and castrated males. The results suggest that opioid components of neural reward circuits are normally activated in the male rat by conditioned incentive stimuli, but not by the primary rewarding stimuli associated with access to and mating with an oestrous female.

Prodynorphin peptide distribution in the forebrain of the Syrian hamster and rat: a comparative study with antisera against dynorphin A, dynorphin B, and the C-terminus of the prodynorphin precursor molecule

The neuroanatomical distribution of the prodynorphin precursor molecule in the forebrain of the male Syrian hamster (Mesocricetus auratus) has been studied with a novel antiserum directed against the C-terminus of the leumorphin [dynorphin B (1-29)] peptide product. C-peptide staining in sections from colchicine-treated hamsters is compared to staining in sections from untreated animals. In addition, the pattern of C-peptide immunostaining in hamster brain is compared to that in the rat brain. Finally, the C-peptide immunolabeling patterns in hamsters and rats are compared to those obtained with antisera to dynorphin A (1-17) and dynorphin B (1-13). Areas of heaviest prodynorphin immunoreactivity in the hamster include the hippocampal formation, lateral septum, bed nucleus of the stria terminalis, medial preoptic area, medial and central amygdaloid nuclei, ventral pallidum, substantia nigra, and numerous hypothalamic nuclei. Although this C-peptide staining pattern is similar to dynorphin staining reported previously in the rat, several species differences are apparent. Whereas moderate dentate gyrus granule cell staining and no CA4 cell staining have been reported in the rat hippocampal formation, intense immunostaining in the dentate gyrus and CA4 cell labeling are observed in the hamster. In addition, the medial preoptic area, bed nucleus of the stria terminalis, and medial nucleus of the amygdala stain lightly for prodynorphin-containing fibers and cells in the rat, compared to heavy cell and fiber staining in the hamster in all three of these regions. In the rat there is no differential staining between tissues processed with the C-peptide, dynorphin A, and dynorphin B antisera, but numerous areas of the hamster brain show striking differences. In most hamster brain areas containing prodynorphin peptides, the C-peptide antiserum immunolabels more cells and fibers than the dynorphin B antiserum, which in turn labels more cells and fibers than dynorphin A antiserum. However, exceptions to this hierarchy of staining intensity are found in the lateral hypothalamus, substantia nigra, arcuate nucleus, and habenula. The differences in staining patterns between rat and hamster are greatest when C-peptide antiserum is used; apparent species differences are present, though less pronounced, in dynorphin B- and dynorphin A-immunostained material.

The colocalization of substance P and prodynorphin immunoreactivity in neurons of the medial preoptic area, bed nucleus of the stria terminalis and medial nucleus of the amygdala of the Syrian hamster

To determine the extent of colocalization of substance P (SP) and prodynorphin peptides within neurons of the medial nucleus of the amygdala (AMe), medial bed nucleus of the stria terminalis (BNSTm) and medial preoptic area (MPOA), we incubated colchicine-treated Syrian hamster brain tissue in an antiserum mixture containing rat anti-SP antibody combined with 1 of 3 rabbit antibodies against prodynorphin peptides: anti-dynorphin A(1-17), anti-dynorphin B(1-13) or anti-C-peptide. This was followed by incubation in a secondary antiserum mixture containing fluorescein-labelled anti-rabbit and rhodamine-labelled anti-rat antibodies. Sections were viewed with an epifluorescence microscope using blue light excitation for fluorescein and green light excitation for rhodamine. Colocalization of SP and prodynorphin labelling was observed in neurons of the caudal parts of AMe, BNSTm and MPOA, areas which are essential for male mating behavior. The colocalization was most extensive in the dorsolateral part of the caudal MPOA, the caudodorsal part of the BNSTm, and in the posterodorsal subdivision of AMe. Although all 3 dynorphin peptides coexisted with SP in these areas, dynorphin B did so less than C-peptide, and dynorphin A less than dynorphin B.

Effects of the opiate antagonist naloxone upon hypothalamically elicited affective defense behavior in the cat

The opiate antagonist naloxone hydrochloride was employed in order to determine whether endogenous opioids play a role in the control of affective defense behavior elicited from the medial hypothalamus in the cat. The effects of naloxone upon quiet biting attack behavior elicited from the lateral hypothalamus were also assessed. A comparison of the differences in response latencies or thresholds before and after naloxone (i.p.) administration was made. Naloxone (1, 4 and 10 mg/kg) was found to significantly facilitate affective defense behavior in a dose- and time-dependent manner. The duration of facilitation ranged from 30 min after a 1 mg/kg injection to 180 min after a 10 mg/kg injection. The data also suggest that the effects of naloxone upon affective defense behavior are opposite to those seen with quiet biting attack. In two animals, quiet biting attack behavior was suppressed for 30 min following a 10 mg/kg injection of naloxone. Naloxone was also administered to cats in which hypothalamic stimulation elicited predatory responses coupled with components of affective defense behavior. In these cases, naloxone was ineffective in altering latencies for this 'mixed' response. These findings suggest that the opiate peptide system selectively inhibits affective defense behavior elicited from the medial hypothalamus of the cat.

Neuroendocrine control of male reproductive function. The opioid system as a model of control at multiple sites

It is known that the same peptide can be identified in different secretory tissues and in the central nervous system (CNS). We now provide evidence that the same peptides can be found in different organs related to the control of a single function, and speculate on the possibility that this reflects a common neuroendocrine programming. Endogenous opioid peptides (EOP) inhibit the reproductive function acting via the CNS. EOP inhibit gonadotropin secretion in rodents and humans via inhibition of GnRH release and have direct inhibitory actions at the pituitary level via specific binding sites on the gonadotrophs. However, EOP can also be synthesized in the testis and in different compartments of the male genital tract. Several findings indicate that EOP of the reproductive tract have a local, paracrine role. These include: (1) the detection of significant beta-endorphin (beta-EP) production by rat Leydig cells (Lc) in cultures; (2) the hormonal regulation of Lc beta-EP production by positive (gonadotropins) and negative (steroids, glucocorticoids, GnRH) factors; (3) the presence of opioid binding sites (Kd in the nanomolar range) in tubular homogenates and Sertoli cells (Sc) in culture of adult and immature rat testes; (4) the inhibition of basal and FSH-stimulated ABP production by Sc in culture when chronically exposed to beta-EP treatment; (5) the detection of high levels of beta-EP and met-enkephalin in human semen with values 6-12 times higher than in plasma; (6) the evidence for inhibitory functions of seminal opioids on sperm motility, vas deferens muscle contraction and partner immune system. Thus the same peptides, i.e. EOP, may control the reproductive function at multiple sites, operating as a multimessenger system in which the central and peripheral level are unified by the common chemical and inhibitory nature of the message.

Endorphins in male impotence: evidence for naltrexone stimulation of erectile activity in patient therapy

In the present study we evaluated whether naltrexone administration could stimulate sexual function in 30 male patients, ages 25 to 50 years, with idiopathic impotence of at least one year's duration and not of organic etiology. The patients received naltrexone (50 mg/day) or placebo, on a random basis for two weeks. Sexual performance, expressed as the number of full coitus/week, was assessed before (time 0) and during (on days 7 and 15) each treatment. The naltrexone therapy significantly increased the number of successful coitus compared to placebo after 7 and 15 days of treatment: improvement of sexual performance was evident in 11 out of the 15 treated patients. All the patients experienced a significant increase in morning and spontaneous full penile erections/week. No significant side effects were reported. Endocrine studies revealed no significant modification of plasma LH, FSH or testosterone by naltrexone, suggesting that the positive effect of the drug on sexual behavior was exerted at a central level. A two-month follow-up, at which time patients were off treatment, erectile capacity had returned to baseline in 10 patients, while five reported complete recovery of their sexual ability. We hypothesize that an alteration in central opioid tone is present in idiopathic impotence and is involved in the impairment of sexual behavior.

Opioids and sexual behavior in the male rat

Naloxone in the doses of 4 or 16 mg/kg failed to affect copulatory behavior of testosterone-treated castrated male rats. Morphine 10 mg/kg, administered 60 min before behavioral observation, reduced the proportion of animals displaying sexual behavior. Doses of 2.5 or 5 mg/kg reduced the latency to the second ejaculation, whereas the few animals still copulating after morphine 10 mg/kg showed a reduced latency to the first ejaculation. The same doses of morphine administered 5 min before behavioral observation produced a dose-dependent reduction of mount, intromission and ejaculation percentages. However, those animals that did copulate showed a normal copulatory behavior. D-Ala2-Met5 enkephalinamide (DALA) infused into the left cerebral ventricle in a dose of 5 micrograms 5 or 60 min before tests had no effect. When the peptide was infused 30 sec after the first intromission, the number of intromissions as well as the latency to ejaculation were reduced. Opioids may facilitate ejaculatory mechanisms, perhaps as a consequence of their rewarding properties. Moreover, in animals treated with DALA after the first intromission, the number of intromissions and the latency to ejaculation were similar for the first and second copulatory series, while these parameters were much reduced upon the second ejaculation for control animals. It is possible that liberation of endogenous opioids is the cause of ejaculation-induced facilitation of subsequent sexual behavior.

Effects of naloxone on penile erection in cats

Male cats were anesthetized with pentobarbital. A Foley catheter was placed in the urinary bladder and physiologic saline, under a head of pressure, was allowed to flow at a constant rate through the bladder. Naloxone, 0.2 mg, caused penile erection in 5 of 11 experiments. The onset of action was 0.5 to 4 minutes, and the duration of the erection was 5 to 36 minutes. In two of three experiments a second injection of naloxone caused a second erection. The erection caused by naloxone was not changed by pre- or posttreatment with morphine or by posttreatment with propranolol. It was suggested that the erection could be due either to altered levels of hormones released from the central nervous system or to removal of reflex inhibitory tone in the spinal cord or sacral parasympathetic ganglia.

Pharmacological analysis of male rat sexual behavior

Pharmacological influences on male rat sexual behavior are reviewed in an attempt to identify neurotransmitters and their respective receptor types that regulate various factors comprising the behavioral pattern. Evidence is presented that: (1) serotonergic influence is generally inhibitory to sexual behavior, although two receptor subtypes may lower ejaculation threshold; (2) dopaminergic agonists facilitate several aspects of copulatory behavior and ex copula genital responses; (3) noradrenergic activity appears to increase sexual arousal; (4) cholinergic agonists facilitate ejaculation, or in some cases, delay or prevent initiation of copulation; (5) GABA agonists inhibit sexual responses both in and ex copula; (6) opiate agonists appear to inhibit copulation and penile reflexes, although antagonists have mixed effects; (7) ACTH and MSH peptides promote copulatory behavior and genital responses; (8) oxytocin facilitates ex copula penile responses, but may contribute to postejaculatory refractoriness; and (9) long-term exposure to prolactin inhibits sexual behavior and penile responses. Although some progress has been made in identifying neurotransmitter-receptor effects on behavioral components, copulatory behavior is complex and no drug has been found to affect only a single component. Furthermore, drug specificity is only relative.

Selective effects of beta-endorphin infused into the hypothalamus, preoptic area and bed nucleus of the stria terminalis on the sexual and ingestive behaviour of male rats

beta-Endorphin was infused bilaterally into the medial preoptic area-anterior hypothalamic continuum at doses of 5, 10 and 40 pmol each side. The highest dose selectively abolished mounting, intromitting and ejaculating in sexually experienced male rats paired with an oestrous female. Males infused with 40 pmol beta-endorphin still followed the female, investigated her anogenital region and other parts of her body, but made abortive attempts to mount. A dose of 5 pmol beta-endorphin had no effect, but 10 pmol proved partially effective. The same males, in other tests, were allowed to ingest a highly preferred, sweet, non-calorific solution (acesulfame-K) in the absence of a female. beta-Endorphin infusions (up to 40 pmol) into the same area of the hypothalamus had no effect on this behaviour. Control males allowed simultaneous access both to an oestrous female and to the sweet solution copulated normally but reduced their ingestive behaviour, despite there being sufficient time during tests for both to occur. beta-Endorphin (40 pmol) infused into the preoptic area-anterior hypothalamic continuum under these conditions suppressed sexual interaction, but ingestion of acesulfame-K increased to values observed when the female was absent. beta-Endorphin infused into neighbouring areas of the brain had different behavioural effects. Sexual behaviour was not inhibited, and ingestion of acesulfame-K was unaltered, when beta-endorphin was infused either into the bed nucleus of the stria terminalis or the rostral ventromedial hypothalamus. However, infusions of cholecystokinin-8 into the ventromedial hypothalamus suppressed acesulfame-K ingestion in most animals, showing that the cannulae were placed in an area regulating ingestive behaviour. The inhibition of sexual behaviour after preoptic area-anterior hypothalamic continuum infusions of beta-endorphin was prevented by either pretreating rats with 1 mg/kg naloxone intraperitoneally, or by infusing a putative delta opiate receptor blocker (0.5 pmols ICI 174864) into the preoptic area-anterior hypothalamic continuum 5 min prior to beta-endorphin treatment. ICI 174864 administered alone significantly increased mount rate and reduced the post-ejaculatory refractory period in copulating males. These experiments suggest that there is both neurochemical and neuroanatomical specificity relating beta-endorphin to sexual behaviour in the male rat.

Inhibitory influence of corticotropin releasing factor on components of sexual behaviour in the male rat

Acute microinfusions of ovine corticotropin releasing factor (CRF) into the third cerebral ventricle (III vent.) of sexually experienced male rats produced a dose-dependent suppression of masculine sexual behaviour. This inhibition of male sexual performance induced by CRF could be reversed by simultaneous infusions of naloxone, the opiate receptor antagonist, which when infused without CRF facilitated copulatory performance. These findings suggest that CRF can exert drastic effects on male reproductive behaviour through mechanisms which involve the activation of opioid pathways within the central nervous system. This CRF-linked neurochemical signal may mediate some of the well-known deleterious effects of stressful and noxious stimuli on reproductive function.

Opioids and sexual behavior

Opioids have long been known to inhibit sexual behavior. However, it is only within the last decade that the effects of opioids on sexual behavior have been studied extensively and a number of hormonal and neurochemical correlates established. In this review, the experimental literature on opioids and sexual behavior in humans and laboratory animals is examined. Clinical and anecdotal accounts of opioid use are also discussed, in addition to the pharmacology, neuroendocrinology, and biochemistry of opioid administration, to provide a synthesis of critical information. New research directions involving the study of endogenous opioid systems, opioid receptor subtypes, and the opioid modulation of neurotransmitter systems are outlined. Finally, a comprehensive bibliography of the human and animal literature is included.

Interactions between sucrose, pain and isolation distress

Two experiments were conducted that establish an opioid-based, functional-relationship between the taste of sucrose, pain threshold and distress vocalization in isolated 10-day-old albino rats. In the first experiment intraoral infusion of sucrose virtually doubled heat-withdrawal latencies. This elevation was naltrexone (0.5 mg/kg b.wt.) reversible. In the second experiment sucrose infusions caused a rapid and sustained diminution of distress vocalizations in rats totally isolated from dam and siblings. These are the first demonstrations of a causal relationship between a positive affective system and ones mediating pain and stress.

Progesterone and progestins modulate beta-endorphin concentrations in the hypothalamus and in the pituitary of castrated female rats

Hypothalamic and pituitary beta-endorphin (B-EP) concentrations are modified by ovariectomy and estrogen treatments, supporting a direct interaction between this peptidergic system and gonadal steroids. Because the use of progestins is becoming even more diffuse in clinical practice, we evaluated the effect of progesterone and of the synthetic progestins medroxyprogesterone acetate (MPA), norethisterone acetate (NET) and desogestrel on the concentration of B-EP in the medial-basal hypothalamus and the anterior and neurointermediate pituitary lobes in ovariectomized rats (OVX), treated or untreated with estradiol benzoate (EB). B-EP concentrations were significantly increased by desogestrel in the anterior lobe and by progesterone, desogestrel and medroxyprogesterone acetate in the neurointermediate lobe. Progesterone and progestins significantly reduced B-EP increase induced by estradiol benzoate in the anterior lobe. Estradiol benzoate treatment did not modify the effect of progesterone and desogestrel on B-EP in the neuro-intermediate pituitary lobe. Norethisterone acetate and progesterone increased B-EP concentrations in the medial-basal hypothalamus, while the other steroids were inactive. In contrast, in the hypothalamus all progestins attenuated the increase of B-EP induced by estradiol benzoate (p less than 0.01). These data indicate that progesterone and progestins modulate the hypothalamic and pituitary B-EP concentrations in concert with estrogens. The capacity of progestins to modify the hypothalamic contents of B-EP may represent one of the mechanisms of action of these steroids in influencing brain function.

Alpha-melanocyte-stimulating hormone infusions during pregnancy in the rat: effects on offspring weight, pain reactivity and sexual behavior

Pregnant rats treated during the last third of pregnancy with a continuous infusion of alpha-melanocyte-stimulating hormone (alpha-MSH) produced offspring that weighed less at birth and in adulthood. These offspring of the alpha-MSH treated mothers were less sensitive to pain and as adults showed a reduced analgesic response to morphine. Male offspring of alpha-MSH treated mothers and of control animals responded similarly in sexual performance tests, except that the treated animals significantly shifted their pattern of responding when they encountered a new testing arena or experienced defeat. The offspring of alpha-MSH treated mothers were influenced more by changes in their environment than were control offspring. These effects are similar to those reported following perinatal treatment with opiate drugs or peptides.

Oxytocin: an extremely potent inducer of penile erection and yawning in male rats

The intracerebroventricular (i.c.v.) injection of oxytocin, in doses ranging from 5 to 90 ng (5-90 pmol) induced penile erection and yawning in male rats. Such response was not induced by doses of the peptide higher than 100 ng, nor by equimolar doses of i.c.v. [Arg8]vasopressin, ACTH-(1-24), alpha-MSH, rat corticotropin-releasing factor (rCRF), delta sleep-inducing peptide, neurotensin or substance P. Oxytocin-induced penile erection and yawning were prevented by atropine and morphine, but not by methylatropine or the opiate antagonist naloxone. Haloperidol, a dopamine receptor antagonist, was ineffective at low doses; it partially prevented penile erection but not yawning at high doses. Since oxytocin is present not only in the neurohypophysis but also in other brain areas, our results suggest that oxytocin is implicated in the regulation of penile erection and yawning, and provide further evidence that oxytocin acts as a neuropeptide in the central nervous system.

Immunohistochemical distribution of substance P, serotonin, and methionine enkephalin in sexually dimorphic nuclei of the rat lumbar spinal cord

The purpose of the present study was to identify chemically some potential inputs to lumbar motoneurons of the rat in the spinal nucleus of the bulbocavernosus, ventral motor pool, dorsolateral nucleus, and retrodorsolateral nucleus. Substance P-like immunoreactivity and serotonin-like immunoreactivity were found in all four motor nuclei, with dense immunoreactive profiles surrounding motoneurons and their processes. Enkephalin-like immunoreactivity was restricted to the sexually dimorphic nuclei, the spinal nucleus of the bulbocavernosus, and the dorsolateral nucleus. Within the spinal nucleus of the bulbocavernosus, enkephalin-like immunoreactive profiles were apposed to the processes of motoneurons but not their somata. In contrast, enkephalin-like immunoreactivity surrounded motoneuron somata in the medial part but not the lateral part of the dorsolateral nucleus, in the location of motoneurons projecting to the ischiocavernosus muscle. Moreover, the density of serotonin-like immunoreactivity was also greater in the medial part of the dorsolateral nucleus. On the basis of the chemo-architecture and the connections of the dorsolateral nucleus, we suggest the division of this motor column into a medial part composed of ischiocavernosus motoneurons surrounded by enkephalin- and serotonin-like immunoreactivity and a lateral part that contains neurons that project to the sphincter urethrae muscle. Total spinal transection severely depleted both serotonin-like and substance P-like material in the lumbar ventral horn. No changes in the distribution of enkephalin-like immunoreactivity were observed following this lesion. It is therefore suggested that in the ventral horn, substance P- and serotonin-like material are derived from supraspinal tracts, whereas enkephalin-like material is derived from intrinsic nerve cell bodies of the spinal cord.

Changes in the immunoreactivities of an opioid peptide leumorphin in the hypothalamus and anterior pituitary during the estrous cycle of the rat and their relation to sexual behavior

Leumorphin, an opioid peptide whose functions are unknown, is found in mammalian brain and pituitary and stimulates lordosis behavior in estrogen-treated female rats. To elucidate the role of leumorphin in the physiological control of female sexual behavior, the levels of immunoreactive (ir) leumorphin as well as ir dynorphin (dynorphin A) were measured in the rat brain and pituitary during the estrous cycle. There was a clear variation of ir leumorphin in the hypothalamus and anterior pituitary during the estrous cycle. The levels of ir leumorphin in the hypothalamus and anterior pituitary on the afternoon of proestrus were significantly higher (P less than 0.01) than those on the afternoons of estrus and metestrus. The rise in the hypothalamic levels of ir leumorphin on the afternoon of proestrus was correlated with the receptivity of lordosis during the estrous cycle. Furthermore, there was a close correlation with ir dynorphin levels. These findings are in agreement with studies demonstrating a common precursor for leumorphin and dynorphin. Ir leumorphin in the hippocampus and neurointermediate pituitary did not change significantly during the estrous cycle. Because the leumorphin antiserum used recognizes rimorphin (dynorphin B) 1.78 times more than porcine leumorphin on a molar basis, high performance-gel permeation chromatography was done on pooled extracts of hypothalamus taken at proestrus and estrus. The peak in the leumorphin-like substance in the activation of sexual behavior is discussed.

Behavioral specificity of beta-endorphin suppression of sexual behavior: differential receptor antagonism

Open field behavior was observed in conjunction with mating behavior to discern whether the effect of intraventricular (ICV) beta-endorphin (beta-END) on sexual behavior may be secondary to akinesia. Three groups of ovariectomized, estrogen-progesterone-primed rats each received counterbalanced treatments of saline ICV, 2 micrograms beta-END ICV, or 2 micrograms beta-END ICV in combination with a selective opioid receptor antagonist. Receptive behavior (lordosis) and proceptive behaviors (presentation and ear wiggling) were consistently suppressed by beta-END, while ambulation was unaffected. Rearing and grooming were generally decreased, although this effect was statistically significant in only one experiment. Pretreatment with the mu-1 antagonist naloxazone (50 mg/kg intravenously) reversed the effects of beta-END on all behaviors tested. The delta receptor antagonist ICI-154,129 (12.5 and 50 micrograms ICV) only partially reversed the sexual effects of beta-END but completely reversed the open field effects. It is concluded that the suppressive effect of beta-END on sexual behavior, while not behaviorally specific, is not secondary to opioid-induced akinesia.

Neurotransmitter specificity of cells and fibers in the medial preoptic nucleus: an immunohistochemical study in the rat

The medial preoptic nucleus (MPN) is a sexually dimorphic complex with three major subdivisions. The cell-dense central (MPNc) and medial (MPNm) subdivisions are larger in male rats, while the cell-sparse lateral subdivision (MPNl) occupies a majority of the nucleus in females. In the present study we evaluated the distribution of possible monoaminergic and peptidergic cells and fibers within the MPN, as well as in adjacent regions of the medial preoptic area of the adult male rat. For this, we used an indirect immunohistochemical method with antisera to serotonin (5HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (1-24; ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). The results suggest that cell bodies and/or fibers crossreacting with all of these putative neurotransmitters are differentially distributed within the MPN. Within the MPNm, the densest plexuses of fibers were stained with antisera to SP and NPY, while moderate densities of fibers were stained with anti-DBH, SS, CCK, CGRP, ACTH, and alpha-MSH, and only a few fibers were stained with anti-5HT, TH, NT, VAS, and L-ENK. Moderate numbers of SP- and L-ENK-immunoreactive cell bodies, and a few SS-, NT-, CRF-, and TRH-stained cell bodies were also found within the MPNm. The MPNc contained a dense plexus of CCK-immunoreactive fibers, as well as a few CRF-immunoreactive fibers. Both fiber types were localized almost exclusively to this subdivision, while most of the others studied here appeared to avoid it selectively. This suggests that there are relatively few inputs to the MPNc, and that they tend to avoid other parts of the nucleus, although moderate densities of DBH- and NPY-immunoreactive fibers were found in both the MPNm and MPNc. The MPNc contained several CCK-immunoreactive cell bodies as well as a moderate number of TRH-stained cell bodies. Both cell types were nearly completely localized to the MPNc. The major inputs to the MPNl studied here appear to be stained with antisera to 5HT and L-ENK, although moderate numbers of NT- and CRF- immunoreactive fibers were also found in this part of the nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

The endogenous opioid system in Gilles de la Tourette syndrome

The various neurotransmitter systems postulated to be involved in the pathogenesis of Gilles de la Tourette syndrome(GTS) are described with special reference to the endogenous opioid system(EOS). Malfunction of the opioid system is proposed as the underlying disturbance in this disease causing secondary dysfunction of the other systems. Furthermore, the various symptoms of the illness are examined also in terms of dysfunction of the endogenous opioid system.

The effects of naloxone and cage size on social play and activity in isolated young rats

The effects of large and small housing environments as well as naloxone on social play (as defined by pinning behavior) in isolated postweanling male rats were investigated. Animals housed in small cages played significantly more than those housed in larger cages. This effect was not observed when cage size was reversed. Administration of 0.5, 1.0, and 5.0 mg/kg of naloxone resulted in significant decreases in play behavior as compared to saline controls, both before housing environments were switched, and after. Animals in both isolation conditions were also compared to animals that were socially housed. Isolation was found to increase social play as well as the time spent in active social interaction, but had no effect on locomotor activity. While housing in a small cage increases play behavior, it had no effect on the amount of time spent in active social interaction or on activity. While administration of 0.5, 1.0, and 5.0 mg/kg naloxone to habituated animals differentially housed did not result in an overall decrease in activity, when compared with saline controls, only those animals housed in small cages and injected with the high dose of naloxone differed significantly from controls. In animals having no prior play experience, the activity of animals housed in the large and small cages differed significantly from each other only in the saline and 5.0 mg/kg naloxone conditions. Since naloxone's effect on play behavior was strong, but its effect on activity was not profound, our data suggest that naloxone primarily affects the affective component of play rather than altering activity levels.

Mating produced analgesia in the Syrian hamster

A series of experiments examined the hypothesis that mating produced analgesia in the Syrian hamster can be blocked by opiate antagonists. The first experiment established a dose response relation to painful footshock. Females were more responsive to footshock than males (p less than 0.001). The second experiment demonstrated that ten minutes of mating reduced responsiveness of both males and females to a moderate intensity of footshock. The third experiment replicated the effect of mating on the responsiveness of males to footshock, but did not demonstrate any effect of the opiate antagonist naltrexone on mating induced analgesia. The fourth experiment demonstrated that limited mating stimulation (five intromissions) has little effect on the responsiveness of sexually inexperienced males to footshock. The fifth experiment replicated the fourth experiment using sexually experienced males and obtained comparable results. Apparently mating induced analgesia in male hamsters is not blocked by opiate antagonists and which raises questions about biological activity of reported changes in endorphin activity during mating.

Opiate antagonists and copulatory behavior of male hamsters

A possible role of endogenous opioids in male copulatory behavior was examined in six experiments which studied the effects of opiate antagonists on the copulatory behavior of male hamsters (Mesocricetus auratus). In Experiment 1, the acute administration of naloxone hydrochloride (4 mg/kg, SC) ten minutes before testing significantly decreased mount frequency, intromission frequency, and ejaculation latency. In Experiment 2 males were tested weekly for three weeks. Half of the males were injected with naloxone ten minutes before each test and half with physiological saline. Naloxone administration reduced mount frequency, and intromission frequency while increasing the postejaculatory interval and the proportion of males displaying behavioral signs of satiety. In Experiment 3 similar effects were obtained following daily administration of naltrexone hydrochloride (10 mg/kg/day SC). In Experiment 4 males were allowed to mate to satiety. Naloxone treated males were more likely to display behavioral signs of satiety during the first ten minutes of these tests. In Experiment 5 it was demonstrated that naloxone administration did not alter the duration of insertion during either intromissions or ejaculations. In Experiment 6 the administration of naloxone did not facilitate the display of copulatory behavior by sexually inactive males. Overall the results are consistent with the hypothesis that opiate antagonists alter male copulatory behavior by enhancing the impact of stimuli occurring during the sexual interaction.

The sex hormone-dependent development of opiate receptors in the rat medial preoptic area

The opiate receptor content of the sexually dimorphic medial preoptic area (MPOA) was examined in newborn and 5-day old (D6) male and female rats. A significant increase of [3H]naloxone binding was observed in and around the sexually dimorphic nucleus of the preoptic area (SDN-POA) in D6 female rats, relative to newborn females. Opiate receptor labeling did not increase over this period in males, nor was labeling different between males and females at birth. This dramatic alteration of MPOA opiate receptor content was observed to occur in either sex in the absence of testosterone postnatally; that is, neonatally-castrated males exhibited the same increase of labeling by D6 as did normal females. Conversely, daily postnatal testosterone treatment of females from birth to D6 resulted in the development of male-like MPOA opiate receptor pattern. The sex hormone-dependence of MPOA opiate receptor development is discussed in relation to the sex hormone-dependent ontogeny of SDN-POA structure. The overlap of critical periods for the development of these structural and chemical sexual dimorphisms suggests a role for endogenous opioids in modulating MPOA development.

Changes in the processing of beta-endorphin in the hypothalamus and pituitary gland of female rats during sexual maturation

Puberty in the female rat is accompanied by a marked attenuation of the opioid inhibition of luteinizing hormone secretion. One factor which may contribute to this altered role is a change in the metabolism of opioid peptides during sexual maturation. beta-Endorphin undergoes a considerable degree of metabolism through both C-terminal proteolysis and N-acetylation, and these metabolites do not possess opioid activity. The processing of beta-endorphin in the hypothalamus and in the anterior and neurointermediate lobes of the pituitary gland in prepubertal and adult female rats was studied using gel filtration and high performance liquid chromatography coupled with radioimmunoassay. In the anterior lobe, high molecular weight precursors of beta-endorphin (pro-opiomelanocortin and beta-lipotropin) were present in prepubertal (28 days old) rats, but little authentic beta-endorphin was detected. In contrast, only beta-lipotropin and beta-endorphin were present in mature (70 days old) animals. Only beta-endorphin-sized peptides were present in the neurointermediate lobes of both prepubertal and adult rats. However, the proportion of N-acetylated metabolites was higher in sexually mature animals. In the hypothalamus, only beta-endorphin-sized peptides were present in both juvenile and adult animals. However, C-terminal proteolysis increased with age (no acetylated metabolites were detectable in this tissue). The proportion of the total beta-endorphin-like immunoreactivity attributable to beta-endorphin was lower in young adult (first dioestrus after vaginal opening) (55%) and mature (dioestrus, 61-64 days old) rats (56%) compared to prepubertal (30 days old) animals (75%) and the proportions of non-acetylated metabolites [beta-endorphin-(1-27) in young adults and beta-endorphin-(1-26) in adults] were increased concomitantly. These changes were correlated with a reduced luteinizing hormone response to the opiate antagonist naloxone in adult compared to prepubertal rats. beta-Endorphin is processed differently in the two lobes of the pituitary gland and in the hypothalamus and the degree of metabolism increases as the rat reaches sexual maturity. The increased metabolism of beta-endorphin in the hypothalamus, the site most likely to be involved in the control of luteinizing hormone secretion, results in a reduction in the relative proportion of the opioid active parent peptide. Thus, increased inactivation of beta-endorphin may contribute to the attenuation of the opioid inhibition of luteinizing hormone secretion observed during puberty.

Inhibition of mating by naloxone or morphine in recently castrated, but not intact male rats

Administration of naloxone (SC 5 mg/kg) significantly reduced ejaculation and mounting in male rats in the weeks following castration. A similar effect was obtained by injecting morphine (SC 1 or 5 mg/kg). In contrast, the same dosages of naloxone or morphine did not affect the sexual performance of gonadally intact males. Opioid peptides may contribute to the temporary persistence of sexual behavior in testosterone-deficient male mammals, in which incentive qualities of the female partner are an important determinant of sexual arousal.

The sexually dimorphic region of the preoptic area in rats contains denser opiate receptor binding sites in females

Quantitative autoradiographic analysis of opiate receptor binding using [3H]naloxone shows higher levels in the sexually dimorphic region of the medial preoptic area in female rats than in males. Opiate receptor density varies across the estrous cycle being densest in diestrous females. The sexually dimorphic nucleus of the preoptic area lies within the opiate receptor-rich region. Endogenous opiates in the medial preoptic region acting at opiate receptors which are of differential density in males and females could influence sex-specific behavior mediated by the region.

Effects of trichloroethylene exposure on male reproductive function in rats

The present study was designed to evaluate the influences of trichloroethylene (TCE) on the reproductive system of male rats. In addition, information was obtained on the distribution and metabolism of TCE. At 100 days of age, male rats were allowed to copulate with ovariectomized, hormonally primed females and copulatory behaviors scored. Fifteen minutes post-ejaculation, females were sacrificed and ejaculate and semen plug recovered from the uterus and vagina for evaluation. These data served as a pre-exposure baseline for each animal. TCE exposure was then initiated with animals intubated with either 0, 10, 100, or 1000 mg/kg of TCE (10 males/group) for 5 days/week for 6 weeks. Copulatory behaviors and semen evaluations were conducted at Weeks 1 and 5 as well as 4 weeks post-exposure. Three males/group were sacrificed at the end of the sixth week of exposure and levels of TCE and its metabolites measured in various organs and blood. The remaining animals were sacrificed at the end of Week 10. TCE-related effects were seen primarily in the 1000 mg/kg group as reduced body weight gain, elevated liver/body weight ratios, and impaired copulatory behavior. However, the copulatory performance of the "affected" males had returned to normal by the fifth week of exposure. Although TCE and its metabolites concentrated to a significant extent in the male reproductive organs, semen evaluations failed to reveal any indices of spermatotoxicity. The initial alterations in copulatory behavior may be attributed to the narcotic properties of TCE. Tolerance to this pharmacological effect may explain the absence of these effects by the fifth week of exposure.

Immunoreactive-beta-endorphin and LHRH levels in the brains of aged male rats with impaired sex behavior

Levels of immunoreactive beta-endorphin and luteinizing hormone releasing hormone (LHRH) were measured in brain tissue of aged male Long-Evans rats. The animals were tested for sex behavior twice in one week at bimonthly intervals between the 7th and 27th month of life and were sacrificed along with a group of young (5-month old) sexually active rats. Thirty-one of the 89 rats which began the study remained healthy and tumor-free. By month 27, 21 of these had completely ceased to mate and 10 continued to show adequate sexual behavior. Diminished levels of beta-endorphin-like immunoreactivity were measured in the hypothalami and hindbrain of the old animals grouped together as compared to young animals and this reduction was shown to be significantly greater in hypothalamic tissue from the behaviorally inactive subgroup. Hypothalamic LHRH levels were not significantly altered by age in these animals. However, a marked reduction of LHRH content in the septal and midbrain regions of the aged-behaviorally inactive subgroup was evident when compared with the behaviorally active group. The data suggest that altered function of beta-endorphin and LHRH neurons of the aged brain may be involved in the behavioral deterioration observed in aged animals.

Beta-endorphin suppression of lordosis behavior in female rats; lack of effect of peripherally-administered naloxone

Endogenous opioid peptides have been implicated in the control of copulatory behavior of the male rat. In order to assess the possible role of opioids in modulation of sexual receptivity in the female rat, lordosis behavior of ovariectomized (OVX) steroid-primed rats was tested after administration of beta-endorphin (B-END) or naloxone (NAL). Lordosis-to-mount ratio (L/M) of estrogen (E) - and progesterone (P) -primed rats was suppressed 15 and 45 minutes after intraventricular infusion of 100 ng B-END. This suppressive effect was blocked by subcutaneous injections of NAL (2 mg/kg). NAL alone, however, failed to enhance L/M in E-primed rats when administered in subcutaneous doses of 2 or 40 mg/kg. Thus, B-END is capable of suppressing lordotic responsiveness, but endogenous B-END does not appear to tonically suppress responsiveness in the E-primed rat.

Effects of opiate antagonists on hormones and behavior of male and female rhesus monkeys

Opiate antagonists, naloxone (100 micrograms/kg) and naltrexone (1 mg/kg) were given to singly housed adult male or female rhesus prior to a 20-minute behavioral test with an oppositely sexed stimulus monkey. Four of the intact adult males were socially and sexually experienced. The remaining two intact males and two castrated males had been reared in socially restricted conditions and were psychosexually deficient. Adult females were ovariectomized, and the effects of opiate antagonists were examined with or without concurrent estradiol treatment. Both antagonists inhibited sexual behavior of the socially reared, sexually active, intact males. No stimulatory effects on sexual behavior were observed for sexually deficient males, whether intact or castrated. Females showed little change in sexual behavior following opiate antagonist treatment, regardless of endocrine status. The proportion of approaches of the female to the male was increased when naloxone, but not naltrexone, was given. Specific endocrine effects of the opiate antagonists were only found in intact males. Naltrexone significantly increased LH concentrations in the two males tested, while the increase in LH in the four males receiving naloxone was not significant. In all intact males, increases in LH were accompanied by statistically significant increases in circulating concentrations of testosterone following naloxone and naltrexone. The gonadotropic stimulating effect of the opiate antagonists was specific to LH, and no changes were observed in circulating concentrations of FSH in either sex.

Effect of phosphoramidon - a selective enkephalinase inhibitor - on nociception and behaviour

Phosphoramidon (100-350 micrograms i.c.v.), a selective enkephalinase inhibitor, induced in the rat a decrease of nociception to pressure stimulation without evident respiratory depression. In addition, intensive behavioural changes such as grooming (licking the fur, face washing and scratching), mounting behaviour and wet dog shakes were observed. Naltrexone pretreatment (1 mg/kg i.p.) caused a significant decrease in the phosphoramidon-induced nociception and behavioural changes. Puromycin (30 micrograms i.c.v. or 7.5 mg/kg i.p.) caused no changes in nociception or behaviour.

Raised plasma metenkephalin in patients who habitually mutilate themselves

Mean plasma metenkephalin concentration was significantly higher in ten patients who habitually mutilated themselves than in matched, healthy controls. No differences were found in corticotropin, N-lipotropin or C-lipotropin (beta-endorphin). Plasma metenkephalin was raised only in the five patients receiving hospital treatment because of their behaviour disorder. It was not raised in those patients sufficiently well to have been discharged from hospital.