Kamikihito, a traditional Japanese Kampo medicine, increases the secretion of oxytocin in rats with acute stress

ETHNOPHARMACOLOGICAL RELEVANCE

Kamikihito (KKT) is a Kampo medicine that is prescribed in Japan for the treatment of anemia, insomnia and mental anxiety in Japan. However, its precise mechanism of action remains unclear.

AIM OF THE STUDY

This study aimed to evaluate the possible antistress effect of KKT in rats with acute stress and the contribution of oxytocin to the process.

MATERIALS AND METHODS

Acute immobilization stress (AIS; for 90 min) was used to assess the effect of KKT on acute stress. Male Wistar rats were orally treated with KKT. Parameters of stress were evaluated, and concentrations of oxytocin in plasma and cerebrospinal fluid (CSF) were measured.

RESULTS

AIS-induced defecation and fecal weight were significantly decreased because of treatment with KKT. The plasma levels of stress-related hormones following AIS were investigated. The pre-administration of KKT significantly increased adrenocorticotrophic hormone (ACTH) and corticosterone (CORT) levels following AIS. Conversely, there was no significant change in the plasma oxytocin level. Microdialysis and hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) were used to monitor the oxytocin secretion in CSF. Oxytocin level increased during AIS following the treatment of KKT. At 30 min after AIS, the level remained higher than before AIS. Furthermore, using an open field test, the locomotion (exploratory behavior) immediately after AIS was examined. The total traveled distance decreased after AIS; however, the decrease was significantly inhibited by the treatment of KKT. However, the effect of KKT was obstructed by the pre-administration of the oxytocin receptor antagonist.

CONCLUSIONS

These results suggest that KKT has antistress activity and increased oxytocin secretion may be a mechanism underlying this phenomenon.

LC-MS/MS measurement of endogenous oxytocin in the posterior pituitary and CSF of macaques: A pilot study

Oxytocin (OT) is a nanopeptide released into systemic circulation via the posterior pituitary (peripheral) and into the central nervous system via widespread OTergic pathways (central). Central OT plays a significant role in variety of functions from social and executive cognition to immune regulation. Many ongoing studies explore its therapeutic potential for variety of neuropsychiatric disorders. Measures of peripheral OT levels are most frequently used as an indicator of its concentration in the central nervous system in humans and animal models. In this study, LC-MS/MS was used to measure OT in pituitary samples collected from adult male macaque monkeys in order to explore the correlation between individual levels of OT in the CSF (central) and pituitary (peripheral). We quantified individual differences in the levels of OT in the pituitaries (44-151 ng/mg) and CSF (41-66 pg/mL) of these monkeys. A positive correlation between these two measures was identified. These preliminary results allow for future analyses to determine whether LC-MS/MS measures of peripheral OT can be used as markers of OT levels in the brain of nonhuman primates that serve as valuable models for many human neuropsychiatric disorders.

Transport of oxytocin to the brain after peripheral administration by membrane-bound or soluble forms of receptors for advanced glycation end-products

Oxytocin (OT) is a neuropeptide hormone. Single and repetitive administration of OT increases social interaction and maternal behaviour in humans and mammals. Recently, it was found that the receptor for advanced glycation end-products (RAGE) is an OT-binding protein and plays a critical role in the uptake of OT to the brain after peripheral OT administration. Here, we address some unanswered questions on RAGE-dependent OT transport. First, we found that, after intranasal OT administration, the OT concentration increased in the extracellular space of the medial prefrontal cortex (mPFC) of wild-type male mice, as measured by push-pull microperfusion. No increase of OT in the mPFC was observed in RAGE knockout male mice. Second, in a reconstituted in vitro blood-brain barrier system, inclusion of the soluble form of RAGE (endogenous secretory RAGE [esRAGE]), an alternative splicing variant, in the luminal (blood) side had no effect on the transport of OT to the abluminal (brain) chamber. Third, OT concentrations in the cerebrospinal fluid after i.p. OT injection were slightly higher in male mice overexpressing esRAGE (esRAGE transgenic) compared to those in wild-type male mice, although this did not reach statistical significance. Although more extensive confirmation is necessary because of the small number of experiments in the present study, the reported data support the hypothesis that RAGE may be involved in the transport of OT to the mPFC from the circulation. These results suggest that the soluble form of RAGE in the plasma does not function as a decoy in vitro.

Labeled oxytocin administered via the intranasal route reaches the brain in rhesus macaques

Oxytocin may have promise as a treatment for neuropsychiatric disorders. Its therapeutic effect may depend on its ability to enter the brain and bind to the oxytocin receptor. To date, the brain tissue penetrance of intranasal oxytocin has not been demonstrated. In this nonhuman primate study, we administer deuterated oxytocin intranasally and intravenously to rhesus macaques and measure, with mass spectrometry, concentrations of labeled (exogenously administered) and endogenous oxytocin in 12 brain regions two hours after oxytocin administration. Labeled oxytocin is quantified after intranasal (not intravenous) administration in brain regions (orbitofrontal cortex, striatum, brainstem, and thalamus) that lie in the trajectories of the olfactory and trigeminal nerves. These results suggest that intranasal administration bypasses the blood-brain barrier, delivering oxytocin to specific brain regions, such as the striatum, where oxytocin acts to impact motivated behaviors. Further, high concentrations of endogenous oxytocin are in regions that overlap with projection fields of oxytocinergic neurons.

Absence of a diurnal rhythm of oxytocin and arginine-vasopressin in human cerebrospinal fluid, blood and saliva

PURPOSE

The aims of our study were to determine first circadian influences on central concentrations of the neuropeptides oxytocin and arginine-vasopressin and second to investigate if these central concentrations are associated with those in the peripheral compartments blood and saliva in neurocritical care patients. We therefore included patients with external ventricular drain who attended a neurosurgical intensive care unit and were not exposed to painful or stressful stimuli during the sampling period. For this purpose, blood, cerebrospinal fluid and saliva were collected in a 24-hour-interval at the timepoints 06:00, 12:00, 18:00 and 24:00.

RESULTS

In none of the three body fluids examined, significant time-dependent fluctuations of oxytocin and arginine-vasopressin concentrations could be detected during the 24-hour sampling period. The only exception was the subgroup of postmenopausal women whose oxytocin concentrations in cerebrospinal fluid at 12:00 were significantly higher than at 18:00. Correlations of blood and cerebrospinal fluid and blood and saliva neuropeptide levels were very weak to weak at each timepoint. Cerebrospinal fluid and saliva oxytocin levels showed a moderate correlation at 06:00 but did correlate very weak at the other timepoints.

CONCLUSIONS

Central as well as peripheral oxytocin and arginine-vasopressin concentrations in neurocritical care patients did not show significant diurnal fluctuations. No strong correlations between central and peripheral neuropeptide concentrations could be detected under basal conditions. If investigators even though decide to use saliva concentrations as surrogate parameter for central neuropeptide activity, they have to consider that correlations of cerebrospinal fluid and saliva oxytocin seem to be highest in the early morning.

Influence of perioperative stress on central and peripheral oxytocin and arginine-vasopressin concentrations

Perioperative stress provides not only physical, but also psychic and emotional aspects, which may influence the hypothalamic neuropeptide system. Studies investigating the perioperative course of central neuropeptide activity are missing. Therefore, the present study aimed to determine perioperative fluctuations in central and concomitant peripheral concentrations of the hypothalamic neuropeptides oxytocin (OXT) and arginine-vasopressin (AVP), as well as their impact on perioperative anxiety and depression. Cerebrospinal fluid (CSF), blood and saliva were collected from 12 patients who underwent elective endovascular aortic repair with a routinely inserted spinal catheter. AVP and OXT concentrations were analysed at four timepoints: (i) the evening before the operation; (ii) the operation day immediately before anaesthesia induction; (iii) intraoperatively after the stent was placed; and (iv) on day 1 after the operation. Patients completed the Hospital Anxiety and Depression Scale (HADS) at timepoints 1 and 4. For CSF OXT, the present study showed a significant intraoperative decline, accompanied by a decrease in saliva. OXT blood concentrations before anaesthesia induction were higher than at the evening before the operation. OXT concentrations in CSF and saliva correlated well at timepoints 2-4. AVP concentrations in CSF, blood and saliva did not show any significant changes perioperatively. However, postoperative AVP blood concentrations showed a significant negative correlation with anxiety and depression scores according to the HADS. This pilot study demonstrates perioperative fluctuations in central OXT concentrations, which are better reflected by saliva than by blood. Further studies are required to determine whether OXT and AVP can predict postoperative post-traumatic stress disorder.

Preference for novel faces in male infant monkeys predicts cerebrospinal fluid oxytocin concentrations later in life

The ability to recognize individuals is a critical skill acquired early in life for group living species. In primates, individual recognition occurs predominantly through face discrimination. Despite the essential adaptive value of this ability, robust individual differences in conspecific face recognition exist, yet its associated biology remains unknown. Although pharmacological administration of oxytocin has implicated this neuropeptide in face perception and social memory, no prior research has tested the relationship between individual differences in face recognition and endogenous oxytocin concentrations. Here we show in a male rhesus monkey cohort (N = 60) that infant performance in a task used to determine face recognition ability (specifically, the ability of animals to show a preference for a novel face) robustly predicts cerebrospinal fluid, but not blood, oxytocin concentrations up to five years after behavioural assessment. These results argue that central oxytocin biology may be related to individual face perceptual abilities necessary for group living, and that these differences are stable traits.

Effects of positive and negative human contacts and intranasal oxytocin on cerebrospinal fluid oxytocin

Despite the popularity of oxytocin (OT) research for its role in social behavior, the relationship between the social environment and endogenous central OT remains poorly understood. This study investigated the effects of positive and negative human contacts and intranasal OT administration on OT concentration in the cerebrospinal fluid (CSF). The pig was used as a model, with repeated CSF sampling through a spinal catheter using a within-subject design. Positive human contact led to sustained CSF OT elevation in pigs over 120min which outlasted the 15min interaction. Furthermore, the frequency of positive interactions was correlated with CSF OT increase. This provides a neurophysiological basis to positive human-animal relationships, with OT preserving bonds within but also between species through interactions. Conversely, CSF OT concentration did not vary during or after negative contact with an unfamiliar person, supporting CSF OT as a biomarker of positive valence in the human-animal relationship context. Intranasal OT administration resulted in peak CSF OT within 10min, with approximately 0.001% of the administered dose reaching the CSF. The sensitivity of the oxytocinergic system to variations in the social environment is a worthy area of investigation for its scientific and clinical implications. In particular, positive interactions result in outlasting central OT release.

CSF and blood oxytocin concentration changes following intranasal delivery in macaque

Oxytocin (OT) in the central nervous system (CNS) influences social cognition and behavior, making it a candidate for treating clinical disorders such as schizophrenia and autism. Intranasal administration has been proposed as a possible route of delivery to the CNS for molecules like OT. While intranasal administration of OT influences social cognition and behavior, it is not well established whether this is an effective means for delivering OT to CNS targets. We administered OT or its vehicle (saline) to 15 primates (Macaca mulatta), using either intranasal spray or a nebulizer, and measured OT concentration changes in the cerebral spinal fluid (CSF) and in blood. All subjects received both delivery methods and both drug conditions. Baseline samples of blood and CSF were taken immediately before drug administration. Blood was collected every 10 minutes after administration for 40 minutes and CSF was collected once post-delivery, at the 40 minutes time point. We found that intranasal administration of exogenous OT increased concentrations in both CSF and plasma compared to saline. Both delivery methods resulted in similar elevations of OT concentration in CSF, while the changes in plasma OT concentration were greater after nasal spray compared to nebulizer. In conclusion our study provides evidence that both nebulizer and nasal spray OT administration can elevate CSF OT levels.

Vasopressin and oxytocin in CSF and plasma of patients with aneurysmal subarachnoid haemorrhage

OBJECTIVE

Clinicopathological studies on patients succumbing to subarachnoid haemorrhage (SAH) demonstrated hypothalamic lesions. The implication of the hypothalamic neuropeptides arginine-vasopressin (AVP) and oxytocin (OXT) has not been linked to aneurysmal SAH yet. This study investigates AVP and OXT in CSF and plasma of patients with spontaneous aneurysmal SAH and their association with outcome.

METHODS

CSF and plasma samples of 12 patients with aneurysmal SAH were prospectively studied for 2weeks. AVP and OXT were measured by radioimmunoassay. Outcome was assessed on Glasgow-Outcome-Scale. Twenty-nine patients without neuropsychiatric disturbances served as controls. Differences in neuropeptide concentration time courses were assessed by regression models. Group comparisons were performed by Kruskal-Wallis and correlations by Spearman tests.

RESULTS

Regression of CSF levels between patients with poor and good outcome revealed significantly lower levels of AVP in patients with poor outcome (p=0.012) while OXT showed a trend towards lower levels (p=0.063). In plasma, no significant differences between outcome groups were found. Group comparisons between poor outcome patients and controls revealed significant differences in CSF for AVP (p=0.001) and OXT (p=0.015). In plasma, AVP yielded significantly different results while OXT did not. No differences were found between the good outcome group and controls. Plasma and CSF concentrations showed no significant correlation.

CONCLUSION

Patients with poor outcome after aneurysmal SAH have lower AVP and OXT levels in CSF than patients with good outcome while neuropeptide levels in plasma failed to reflect differences in outcome. The data indicate hypothalamic damage as an aetiologic factor for outcome after aneurysmal SAH.

CSF and plasma oxytocin levels in suicide attempters, the role of childhood trauma and revictimization

OBJECTIVE

Some studies have reported an inverse relationship between childhood adversity and oxytocin levels. The purpose of this study was to assess the relationship between CSF and plasma oxytocin levels and lifetime trauma history in suicide attempters. We hypothesised lower CSF and plasma oxytocin levels in suicide attempters with high exposure to interpersonal violence and negative childhood emotional climate.

METHODS

28 medication free suicide attempters participated in the study. CSF and plasma morning basal levels of oxytocin were assessed with specific radioimmunoassays. The Karolinska Interpersonal Violence Scale (KIVS) was used to elicit lifetime trauma history and revictimization status and the childhood emotional climate factor was derived from the socialization subscale of the Karolinska Scales of Personality.

RESULTS

Correlations between exposure to interpersonal violence as a child and as an adult and CSF and plasma oxytocin levels were not significant. Revictimized suicide attempters had significantly lower plasma oxytocin levels and more negative childhood emotional climate compared to non-revictimized suicide attempters.

CONCLUSIONS

Our results indicate a complex relationship between life time trauma and the oxytocin system.

The interaction between the oxytocin and pain modulation in headache patients

Oxytocin (OXT), a nonapeptide hormone of posterior pituitary, reaches the central nervous system from systemic blood circulation with a difficulty because of the blood-brain barrier (BBB). The interest has been expressed in the use of the nasal route for delivery of OXT to the brain directly, exploiting the olfactory pathway. Our previous study has demonstrated that OXT in the central nervous system rather than the blood circulation plays an important role in rat pain modulation. The communication tried to investigate the interaction between the OXT and pain modulation in Chinese patients with headache to understand the OXT effect on human pain modulation. The results showed that (1) intranasal OXT could relieve the human headache in a dose-dependent manner; (2) OXT concentration in both plasma and cerebrospinal fluid (CSF) increased significantly in headache patients in relation with the pain level; and (3) there was a positive relationship between plasma and CSF OXT concentration in headache patients. The data suggested that intranasal OXT, which was delivered to the central nervous system through olfactory region, could treat human headache and OXT might be a potential drug of headache relief by intranasal administration.

Negative correlation between cerebrospinal fluid oxytocin levels and negative symptoms of male patients with schizophrenia

BACKGROUND

Accumulating evidence indicates that oxytocin plays an important role in social interactions. Previous studies also suggest altered oxytocin function in patients with schizophrenia and depression. However, few studies have examined the central oxytocin levels in these disorders.

METHODS

Cerebrospinal fluid (CSF) oxytocin levels were measured by ELISA in male participants consisting of 27 patients with schizophrenia, 17 with major depressive disorder (MDD), and 21 healthy controls.

RESULTS

CSF oxytocin levels of patients with schizophrenia or MDD did not differ significantly with healthy controls. The antidepressant dose or the Hamilton depression rating scale score did not significantly correlate with the oxytocin levels in MDD patients. CSF oxytocin levels in schizophrenic patients significantly negatively correlated with second generation antipsychotic dose (r=-0.49, P=0.010) but not with first generation antipsychotic dose (r=-0.13, P=0.50). A significant correlation was observed between oxytocin levels and negative subscale of PANSS (r=-0.38, P=0.050). This correlation remained significant even after controlling for second generation antipsychotic dose (r=-0.47, P=0.016).

CONCLUSIONS

We obtained no evidence of altered CSF oxytocin levels in patients with schizophrenia or those with MDD. However, lower oxytocin levels may be related to higher second generation antipsychotic dose and more severe negative symptoms in schizophrenia.

Vasopressin and oxytocin release into CSF after sympathetic stimulation in rat

Vasopressin and oxytocin are neurohormones of the posterior pituitary lobe released not only into the blood, but also into cerebrospinal fluid (CSF). Posterior pituitary lobe has central and peripheral noradrenergic innervation; peripheral origins from superior cervical ganglia (SCG) (Alper et al. 1980; Saavedra 1986). It is known, that sympathetic nervous system is involved in vasopressin (AVP) and oxytocin (OXY) release from neurohypophysis into the blood (Romeo et al. 1991; Lipinska et al. 1996). The factors which stimulate neurohormones release into the blood do not always cause their release into CSF (Dogterom et al. 1977; Szczepanska-Sadowska et al. 1983). The aim of this study was to elucidate the question whether the stimulation of preganglionic fibers of the SCG could influence the release of AVP and OXY into CSF.

Effect of tooth pulp stimulation on oxytocin and vasopressin release into the cerebrospinal fluid and fluid perfusing the cerebral ventricles in rats

OBJECTIVE

Stress- and pain-related stimuli cause a release of vasopressin (AVP) and oxytocin (OT) into the cerebrospinal fluid (CSF) and extracellular fluid of the brain in various animal species. The aim of the study was to investigate the effect of stimulation of the nociceptive afferent terminals in the tooth pulp on the release of AVP and OT into CSF in rats under chloralose anesthesia.

METHODS

Cerebrospinal fluid was collected from the cerebellomedullary cistern and then 30-minute perfusions of the lateral cerebral ventricles with artificial cerebrospinal fluid (aCSF) were carried out. The perfusate was collected from the cerebellomedullary cistern at rest (control), during electric stimulation of the tooth pulp which induced nociceptive trigemino-hypoglossal reflex, and after stimulation. In the collected CSF and aCSF perfusates, AVP-like immunoreactivity (AVPLI) and OT-like immunoreactivity (OT-LI) were determined by radioimmunoassay (RIA).

RESULTS

The concentrations of AVP-LI and OT-LI in CSF were found to reach 21 pg/ml and 67 pg/ml, respectively. Electric tooth pulp stimulation exerted no effect on AVP and OT release into the fluid perfusing the cerebral ventricles during stimulation.

CONCLUSION

It was found that noxious stimulus from the tooth pulp is not a factor affecting significantly AVP and OT release into CSF.

Serial neurochemical measurement of cerebrospinal fluid during the human sexual response cycle

Recent studies examining the neuroendocrine response pattern underlying the human sexual response cycle revealed transient activation of the sympathoadrenal system and a substantial, long-lasting increase in plasma prolactin concentrations following orgasm in men and women. Prolactin has been discussed as being part of a feedback mechanism that signals centers in the central nervous system, such as the dopaminergic system controlling sexual arousal. To further elucidate the central role of neuropeptides, biogenic monoamines and neurotransmitters in human sexual behavior, a serial cerebrospinal fluid (CSF)-sampling technique was implemented using a previously established experimental paradigm for sexual activity in a laboratory setting. In parallel with peripheral endocrine measures, lumbar CSF was drawn via an indwelling spinal catheter during the sexual response cycle in 10 healthy males and 10 age-matched controls, and analysed for prolactin, oxytocin, biogenic monoamines and/or their metabolites as well as inhibitory and excitatory neurotransmitter concentrations. Parallel to raised peripheral sympathetic activity, norepinephrine also increased in CSF during audiovisual, masturbation-induced sexual arousal and orgasm, and remained elevated for the remainder of the session (F(4,72) = 8.79, P = 0.000). In contrast, none of the other measures, in particular prolactin and dopamine or its metabolites, reflected significant alteration. In conclusion, the human sexual response cycle is characterized by an increase in sympathetic activity in plasma and CSF, and by pronounced secretion of plasma prolactin after orgasm. However, alterations in dopaminergic or peptidergic activity are not found in lumbar CSF, possibly due to local and restricted release in diencephalic and mesencephalic brain regions.

Circadian and light regulation of oxytocin and parvalbumin protein levels in the ciliated ependymal layer of the third ventricle in the C57 mouse

The walls of the third ventricle have been proposed to serve as a bidirectional conduit for exchanges between the neural parenchyma and the cerebrospinal fluid. In immunohistochemical studies of mice, we observed that light exposure and circadian phase affected peptide staining surrounding the third ventricle at the level of the suprachiasmatic nuclei. Under high magnification, we observed robust staining for the neurohormone oxytocin and the calcium-binding protein parvalbumin associated with cilia extending into the third ventricle from the surrounding ventricular wall; no similar staining was observed for vasopressin or calbindin. Retinal illumination had opposite effects on levels of parvalbumin and oxytocin in the cilia: light exposure during late subjective night increased oxytocin staining, but decreased parvalbumin staining in the cilia. Preventing cellular transport with colchicine eliminated immunohistochemical staining for oxytocin in the cilia. There was also a significant daily rhythm of oxytocin immunostaining in the third ventricle wall, and in magnocellular neurons in the anterior hypothalamus. The results suggest that environmental lighting and circadian rhythms regulate levels of oxytocin in the cerebrospinal fluid, possibly by regulating movement of oxytocin through the third ventricle wall.

Neuropeptides and non-human primate social deficits associated with pathogenic rearing experience

There is a persuasive evidence that autism is highly heritable and likely to be substantially determined by polygenic mechanisms. Nevertheless, some intriguing findings in children raised in conditions of extreme social deprivation suggest that an autistic-like syndrome may occur as a consequence of environmental conditions. A particularly close model of this human syndrome has been studied in rhesus monkeys for almost half a century. Monkeys reared in pathogenic rearing conditions manifest considerable deficits in social interaction and increased self-directed behaviors. We have been interested in the possibility that disruptions in normal social development in non-human primates might be expressed in neuropeptide systems which have emerged in rodent studies as important candidates for a unique social biology. In recent studies, we have described persistently reduced CSF OT levels in male rhesus monkeys with significant social deficits. We also found that OT levels were positively related to the expression of affiliative social behaviors. Alterations were also detected in both CRH and AVP receptor binding patterns in limbic structures likely to influence social and emotional development. Taken together, these data suggest that abnormal rearing influences the development of brain systems critical to normal social and emotional competence in rhesus monkeys and may contribute to the development of autistic-like symptomatology associated with pathogenic rearing histories.

Oxytocin levels in the plasma and cerebrospinal fluid of male rats: effects of circadian phase, light and stress

Oxytocin is involved in the regulation of reproductive and social behaviours, mood and stress responses. Previous work has indicated that oxytocin levels are regulated by circadian phase in brain tissue and plasma of both monkeys and rats, but in the cerebrospinal fluid (CSF) only of monkeys. We examined oxytocin levels in plasma and CSF of rats at two daily phases in darkness (mid subjective day and late subjective night) and after a 30 min exposure to light. We found that an apparent day-night difference in plasma oxytocin levels was eliminated by prior habituation to handling and injections. A previously reported daily oxytocin rhythm in rat plasma may instead reflect a rhythm of responsiveness to stressful experimental procedures. We also report for the first time that oxytocin levels in the CSF of rats are regulated by circadian phase and by prior exposure to light.

Changes in cerebrospinal fluid neurochemistry during pregnancy

BACKGROUND

Little is known about changes in brain function that may occur during pregnancy. Studies in rodents and sheep suggest that several brain neurotransmitter and neurohormonal systems known to modulate anxiety may be altered during pregnancy.

METHODS

Cerebrospinal fluid (CSF) and plasma samples were obtained from 21 women (during weeks 38-39 of pregnancy) who were undergoing elective cesarean section and from 22 healthy nonpregnant women.

RESULTS

The CSF levels of g-aminobutyric acid (GABA) and 3-methoxy-4-hydroxyphenylglycolwere reduced in pregnant women. There were no changes in CSF glutamate, 5-hydroxyindoleactic acid, and homovanillic acid. There was a large increase in CSF prolactin in pregnant women and also a trend toward an elevation in CSF oxytocin. Levels of prolactin, but not oxytocin, in CSF and plasma were correlated in pregnant women.

CONCLUSIONS

These results suggest that pregnancy alters regulation of brain GABA, norepinephrine, and prolactin, which may play a role in changes in vulnerability to anxiety and depression during pregnancy and postpartum. Prolactin circulating in the bloodstream seems to be the major source of CSF prolactin during pregnancy.

Vasopressin and oxytocin release within the brain: a dynamic concept of multiple and variable modes of neuropeptide communication

As exemplified particularly with vasopressin and oxytocin, release of neuropeptides within the brain occurs from dendrites, somata, and axons of neurosecretory neurons; mechanisms include activation of intracellular Ca2+ stores, changed strength of synaptic input and altered interaction between transcription factors and gene promoters. Upon demand, both diffuse spread of neuropeptides in the extracellular fluid following dendritic release and focal release from axonal terminals may contribute to regionally and temporally varying combinations of neuromodulator and neurotransmitter actions, thus providing a theoretically unlimited variability in interneuronal signaling. Thus, instead of favoring volume or synaptic transmission following central neuropeptide release, a more dynamic concept is presented with multiple and variable modes of release and communication. This concept considers neuropeptides in the extracellular fluid of the brain rather than those in the cerebrospinal fluid or plasma as primary signals, triggering a variety of receptor-mediated effects, including those underlying behavioral and neuroendocrine regulation and psychopathology.

Rearing effects on cerebrospinal fluid oxytocin concentration and social buffering in rhesus monkeys

Mother-reared (MR) and nursery-reared (NR) male rhesus monkeys exhibit profound and persistent differences in social and emotional behavior. Compared to MR animals, NR monkeys show reduced reciprocal social behaviors and increased agonistic behavior and high levels of stereotypy. Cerebrospinal fluid oxytocin (CSF OT) in NR monkeys was significantly reduced compared to MR monkeys measured at 18, 24, and 36 months of age. Correlations between OT and individual social behavioral profiles measured across rearing conditions also revealed a significant association between OT and the expression of affiliative social behaviors including allogrooming and reciprocal intermale mounting at each age examined. In contrast, CSF vasopressin levels did not differ according to rearing history, but did correlate with fearful behaviors independent of rearing history. Differential rearing was not associated with differences in basal or stress-related plasma cortisol, although these levels did progressively decline as monkeys matured. MR but not NR monkeys were able to use a social companion to buffer their response to a stressor, but OT levels did not appear to be sensitive to the presence of a social companion in either group. These results are consistent with earlier reports from studies of rodents suggesting an important role for central OT pathways in the development of social affiliation.

Differing concentrations of corticotropin-releasing factor and oxytocin in the cerebrospinal fluid of bonnet and pigtail macaques

The two neuropeptides corticotropin-releasing-factor (CRF) and oxytocin (OT) may produce opposing behavioral effects - elevations of the former have been associated with anxiety and social vigilance and reductions of the latter with reduced social affiliation. We sought to test the hypothesis that, within the primate macaque genus, the more gregarious, affiliative, and affectively stable bonnet species (Macaca radiata) would exhibit lower cerebrospinal fluid (CSF) CRF and higher CSF OT concentrations in comparison to its close relative, the temperamentally volatile and socially distant pigtail (Macaca nemestrina). Cisternal CSF samples were obtained from young adult male and female pigtail and bonnet macaques, and CRF and OT concentrations were measured by radioimmunoassay. Pigtail macaques exhibited significantly higher concentrations of CSF CRF and significant lower concentrations of CSF OT than bonnet macaques. Results were not attributable to age or sex differences in group composition. When included together in a multiple regression, CRF and OT showed a multiple R of 0.76, accounting for more than half of the species variance. Although species differences in the bioeffectiveness of these peptides may possibly confound the observed biobehavioral relationships, in the absence of any existing data to that effect, the current findings appear in accordance with the hypothesis and consistent with previously reported species-typical behaviors observed in these macaques.

Physiological regulation of maternal behavior in heifers: roles of genital stimulation, intracerebral oxytocin release, and ovarian steroids

We tested the hypotheses that 1) epidural anesthesia at parturition would block both peripheral and central release of oxytocin and eliminate the development of maternal behavior in primiparous heifers and 2) estradiol priming, genital stimulation, and appropriate neonatal stimuli would induce maternal behavior in nulliparous heifers. In experiment 1, primiparous crossbred heifers (n = 13) with cannulas in the third cerebroventricle (IIIV) were assigned randomly to receive epidural treatments of saline (SAL; n = 6) or lidocaine HCl (EPI; n = 7) at the onset of labor induced between Days 270 and 280 of gestation. Epidural anesthesia blocked (P < 0.001) both central and peripheral release of oxytocin and markedly reduced (P < 0.05) or eliminated licking behaviors during a 3-h period following parturition as compared with SAL. Following approximately 1 wk of controlled daily suckling, during which calves were permitted access only to the inguinal region of their dams (three times daily for 10 min each time), a second maternal behavior test was performed. Although licking behavior remained markedly reduced (P < 0.001) in the EPI compared with the SAL groups, all heifers accepted their calf at the udder. In experiments 2-4, neither estradiol priming in ovariectomized heifers nor estradiol plus progesterone in intact heifers resulted in an induction of maternal behaviors following genital stimulation and presentation of a neonate wetted with amniotic fluid. Pelvic sensory deficits apparently block oxytocin release and disturb both short-latency and long-term maternal behaviors but do not result ultimately in rejection of the calf. Combinations of hormonal, sensory, olfactory, and visual cues observed previously to induce maternal behavior in nulliparous ewes do not appear adequate for induction of maternal behavior in nulliparous heifers.

Effect of centrally administered opioid receptor agonists on CSF and plasma oxytocin concentrations in dogs

OBJECTIVE

To measure oxytocin concentrations in blood and CSF following central administration of opioid agonists in dogs.

ANIMALS

5 male dogs.

PROCEDURE

In a crossover design, CSF and blood were collected immediately before and 15 and 30 minutes after cisternal administration of D-Ala2, MePhe4, Gly-ol-enkephalin (DAMGO, a mu-receptor agonist); D-Pen, pCl-Phe4, D-Pen5-enkephalin (a delta-receptor agonist); U50488H (a kappa-receptor agonist); morphine; and saline (0.9% NaCl) solution.

RESULTS

Plasma oxytocin concentration was significantly increased 15 minutes after administration of DAMGO and 30 minutes after administration of U50488H, compared with concentrations obtained after administration of saline solution. Concentration of oxytocin in CSF was significantly decreased 30 minutes after administration of U50488H, compared with concentration after administration of saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that in male dogs, activation of centrally located mu and kappa receptors elicits an overall excitatory effect on neurons that regulate peripheral release of oxytocin, whereas activation of centrally located kappa receptors elicits an overall inhibitory effect on neurons that regulate central release. These results are in contrast to those reported for other species, in which opioids have a pronounced inhibitory effect on release of oxytocin from the neurohypophysis.

CSF oxytocin and vasopressin levels after recovery from bulimia nervosa and anorexia nervosa, bulimic subtype

BACKGROUND

When ill, people with eating disorders have disturbances of the neuropeptides vasopressin and oxytocin.

METHODS

To avoid the confounding effects of the ill state, we studied women who were recovered (more than 1 year, normal weight, and regular menstrual cycles, no bingeing or purging) from bulimia nervosa (rBN) or binge eating/purging-type anorexia nervosa (rAN-BN), and matched healthy control women.

RESULTS

Vasopressin was elevated in rAN-BN and showed a trend towards elevation in rBN. In rBN, elevated cerebrospinal fluid vasopressin may be related to having a lifetime history of major depression. In comparison, cerebrospinal fluid oxytocin was normal in recovered subjects, but elevated levels in some rBN might be related to birth control pill use.

CONCLUSIONS

These data confirm and extend the possibility that elevated cerebrospinal fluid vasopressin may be related to the pathophysiology of eating disorders, and/or a lifetime history of major depression.

Normal CSF oxytocin and NPY levels in OCD

BACKGROUND

Attention has recently been focused on central nervous system neuropeptides as potential mediators of the symptom profile of obsessive-compulsive disorder (OCD). Increased CSF levels of the anxiolytic neuropeptide oxytocin have been reported in OCD. CSF levels of NPY, another anxiolytic neuropeptide, have not been studied.

METHODS

We measured CSF oxytocin and NPY in 14 OCD patients and 26 healthy normal volunteers.

RESULTS

There were no significant differences between the OCD patients and control subjects in CSF oxytocin or NPY levels. In both the OCD and control groups, women had significantly higher CSF oxytocin levels than men.

CONCLUSIONS

These results do not support a prior finding of elevated CSF oxytocin in OCD patients and do not provide any evidence for an abnormality of NPY regulation in OCD.

Cerebrospinal fluid levels of oxytocin in Prader-Willi syndrome: a preliminary report

BACKGROUND

Prader-Willi syndrome (PWS) is a genetic disorder characterized by mental retardation, appetite dysregulation, and a high risk for obsessive-compulsive disorder (OCD). Microscopic abnormalities of the hypothalamus have been described in PWS, and oxytocin has been implicated in both appetite regulation and OCD.

METHODS

Oxytocin and arginine vasopressin (AVP) were measured in the cerebrospinal fluid of 5 subjects with PWS (2 male, 3 female) and in 6 normal control subjects (all female).

RESULTS

CSF oxytocin was elevated in PWS (9.2 +/- 3.9 pmol/L) as compared to normal control subjects (5.1 +/- 0.9 pmol/L, p = 0.045), a finding that was more significant when excluding male subjects from analysis (p = 0.02). AVP was not significantly different between the groups as a whole.

CONCLUSIONS

These data provide further evidence for hypothalamic and oxytocinergic dysfunction in PWS. The associations between oxytocin, appetite regulation, and obsessive compulsive symptomatology in PWS warrant further investigation.

Oxytocin content of the cerebrospinal fluid of dogs and its relationship to pain induced by spinal cord compression

OBJECTIVES

To determine whether oxytocin exists in the cerebrospinal fluid (CSF) of dogs and whether the amount of oxytocin in the CSF of dogs with neck or back pain caused by spinal cord compression is significantly different than that in the CSF of clinically normal dogs.

STUDY DESIGN

Prospective controlled study.

ANIMAL POPULATION

A total of 15 purpose-bred beagles and 17 client-owned dogs.

METHODS

CSF was collected by needle puncture of the cerebellar medullary cistern after induction of general anesthesia. Oxytocin levels within the samples were determined through radioimmunoassay.

RESULTS

Dogs with spinal cord compression had significantly more oxytocin in their CSF than the clinically normal dogs (13.76 +/- 2.0 pg/mL and 3.61 +/- 0.63 pg/mL, respectively; P < .0001). Dogs with chronic signs (>7 days) had significantly more oxytocin in their CSF than dogs with acute signs (<7 days) (21.60 +/- 0.86 pg/mL and 6.80 +/- 0.81 pg/mL, respectively; P < .0001). Both acutely and chronically affected dogs had significantly more oxytocin in their CSF than the controls (P < .005 and P < .0001 respectively).

CONCLUSIONS

Dogs with neck and back pain caused by spinal cord compression have significantly more oxytocin in their CSF than clinically normal dogs. Dogs with chronic clinical signs have significantly more oxytocin in their CSF than dogs with acute clinical signs.

CLINICAL RELEVANCE

In humans, intrathecal injection of oxytocin is effective in treating low back pain for up to 5 hours. Intrathecal oxytocin may be a logical choice for perioperative analgesia in dogs undergoing myelography because the intrathecal space is accessed for injection of contrast agent.

Effect of central administration of the kappa-opiate receptor agonist U 69.593 on neurohypophyseal hormone levels in blood and cerebrospinal fluid

Intracerebroventricular (i.c.v.) administration of the kappa-opiate receptor agonist U 69.593 induces a rapid and short lasting suppression of oxytocin (OXT) levels in plasma of water deprived rats, whereas only a tendency towards a suppression of vasopressin (AVP) levels in plasma is observed. No change in neurohypophyseal hormone levels in CSF occurs following i.c.v. administration of U 69.593 at the various times points studied. It is concluded that, upon i.c.v. administration, the suppressive influence of U 69.593 is much weaker than that of the dynorphins and that neurophypophyseal hormone levels in CSF behave differently from those in the peripheral circulation.

Compression of the pituitary stalk elicits chronic increases in CSF vasopressin, oxytocin as well as in social investigation and aggressiveness

The neurochemical and behavioural effects of a novel stereotaxic surgical method developed for interrupting the nerve fibres running through the rat pituitary stalk to the posterior pituitary gland was studied. The cerebrospinal fluid (CSF) vasopressin (AVP) and oxytocin (OT) content as well as changes in aggressiveness were measured in rats one week and one month after the surgical intervention. The main results are as follows: (1) the compression of the pituitary stalk elicits a chronic increase in water consumption, as well as in CSF vasopressin and oxytocin content; (2) the surgical intervention increased the frequency of clinch fighting after one week. The increase in aggressiveness accentuated after one month and, in addition, operated animals showed reduced scores of resting while exploratory and social behaviours increased; (3) there was a strong positive correlation between water consumption, vasopressin, and aggressiveness; (4) oxytocin changes showed a positive correlation with variation in social behaviour. The surgical intervention may serve as a model for lesions of the pituitary stalk and formation of ectopic neurohypophyses in humans.

Effect of chronic hyponatremia on central and peripheral oxytocin and vasopressin secretion in rats

Previous studies have shown that many treatments that stimulate the peripheral secretion of oxytocin (OT) and vasopressin (AVP) from the pituitary simultaneously increase the levels of these peptides in the cerebrospinal fluid (CSF). Since osmotically and nonosmotically stimulated pituitary secretion of OT and AVP is markedly blunted in hyponatremic rats, the present studies evaluated whether central OT and AVP secretion into the CSF is similarly inhibited during sustained hyponatremia. Adult male rats with indwelling cisterna magna cannulae were rendered hyponatremic (plasma [Na+] < 110 mmol/l) by s.c. infusion of desmopressin (dDAVP; 10 ng/h) in combination with ingestion of a liquid diet for 3 days, then subjected to osmotic (i.v. or i.p. injection of 2 M NaCl; HS) or nonosmotic (6 mmol/kg of 0.15 M LiCl i.p.) stimulation. In normonatremic rats both i.v. and i.p. HS caused marked increases in plasma OT and AVP levels 30 min after treatment. Significant elevations of OT, but not AVP, were also present in CSF. Despite similar increases in plasma Na+ concentrations, plasma OT responses in the hyponatremic rats were absent after HS i.v. and were significantly blunted after HS i.p., but neither group had increased plasma AVP. In parallel with the plasma results, CSF OT responses were absent in hyponatremic rats given HS i.v. and significantly blunted in hyponatremic rats given HS i.p., but neither group had increased CSF AVP. Nonosmotic stimulation with isotonic LiCl increased OT levels both in plasma and CSF in normonatremic rats 20 min after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated cerebrospinal fluid levels of oxytocin in obsessive-compulsive disorder. Comparison with Tourette's syndrome and healthy controls

BACKGROUND

Limited neurobiological data have implicated central arginine vasopressin in the pathobiology of obsessive-compulsive disorder (OCD). Based on twin, family genetic, and pharmacological studies, some forms of OCD are etiologically related to Tourette's syndrome. The role of arginine vasopressin and related compounds such as oxytocin in Tourette's syndrome has not been previously explored.

METHODS

To compare cerebrospinal fluid (CSF) levels of arginine vasopressin and oxytocin, we collected CSF at midday in a standardized fashion from a total of 83 individuals (29 patients with OCD, 23 patients with Tourette's syndrome, and 31 normal controls). We also collected family study data on each subject to determine which subjects had a family history positive for Tourette's syndrome, OCD, or related syndromes.

RESULTS

In contrast to previous reports, we report similar concentrations of arginine vasopressin for all three groups but increased oxytocin levels in patients with OCD. Remarkably, this increase was observed only in a subset of patients with OCD (n = 22) independently identified as being without a personal or family history of tic disorders (P = .0003). In this subgroup of patients, the CSF oxytocin level was correlated with current severity of OCD (n = 19, r = .47, P < .05).

CONCLUSIONS

A possible role for oxytocin in the neurobiology of a subtype of OCD is suggested by the elevated CSF levels of oxytocin and by the correlation between CSF oxytocin levels and OCD severity. These findings reinforce the value of family genetic data in identifying biologically homogeneous (and perhaps more etiologically homogeneous) groups of patients with OCD. Together with emerging pharmacological data showing differential responsiveness to treatment of tic-related OCD vs non-tic-related OCD, these data also argue strongly for the incorporation of tic-relatedness as a variable in biological and behavioral studies of patients with OCD.

Oxytocin administered centrally facilitates formation of a partner preference in female prairie voles (Microtus ochrogaster)

Prairie voles (Microtus ochrogaster) are monogamous mammals that form male-female pair bonds. Partner preference formation, one component of the pair bond in prairie voles, occurs following male-female cohabitation and is facilitated by mating. The peptide hormone oxytocin is released during physical contact and particularly following vaginal stimulation. Oxytocin has been implicated in mother-infant bond formation. The present study tested the hypothesis that oxytocin participates in the partner preference component of pair bond formation in adult prairie voles. Ovariectomized female prairie voles were implanted with osmotic mini-pumps releasing oxytocin (1-100 ng/h) or artificial cerebrospinal fluid (CSF). Pumps were implanted intracerebroventricularly or subcutaneously and females then were housed for 6 h with a male partner, followed by a preference test in which females could elect to spend time with either the partner or an unfamiliar male. Females in groups that received centrally-administered oxytocin (10 or 100 ng/h), but not CSF, exhibited a significant preference for the partner present during infusion. The induction of a partner preference after oxytocin administration appeared specific for central oxytocin pathways as peripheral oxytocin administration was ineffective. Moreover, central administration of a selective oxytocin receptor antagonist inhibited the behavioral effect of exogenous oxytocin. These results suggest that oxytocin may be one factor contributing to the development of partner preferences in this monogamous rodent.

Maternal behaviour in sheep and its neuroendocrine regulation

Non-parturient sheep, hormonally primed and presented with newborn lambs are, at best, indifferent to them and if approached by the lamb may show violent rejection. However, non-gestant ewes primed with oestrogen and progesterone, but given vaginocervical stimulation, do show a rapid onset in maternal behaviour. This stimulation is ineffective in promoting maternal behaviour with epidural anaesthesia. Vaginocervical stimulation increases the release of oxytocin into cerebrospinal fluid and in-vivo microdialysis has revealed high levels of oxytocin release in limbic brain areas known to be important for maternal behaviour. Oxytocin, when given intraventricularly, produces the full complement of acceptance and suckling behaviour in non-gestant ewes. Although ineffective when given alone, opioids potentiate the release of oxytocin in the limbic brain and increase the intensity of maternal responding, while the opioid receptor blocker, naltrexone, prevents both maternal induction and oxytocin release. This neural basis for maternally motivated behaviour may be equally relevant to human behaviour, although the mechanisms available for addressing these peptidergic systems have clear differences.

Cerebrospinal fluid oxytocin concentration in schizophrenic patients does not differ from control subjects and is not changed by neuroleptic medication

Cerebrospinal fluid (CSF) oxytocin concentrations in 20 neuroleptic-treated schizophrenic patients, 31 neuroleptic-withdrawn schizophrenic patients, and 15 normal control subjects were compared. Neither within-subject comparisons of CSF oxytocin concentration measurements made during neuroleptic treatment and withdrawal (n = 11), nor comparison of the combined neuroleptic-withdrawn and neuroleptic-treated patient group (n = 40) with control subjects (n = 15) differed significantly, suggesting that CSF oxytocin concentration is not altered in schizophrenia.

The antinociceptive effect of non-noxious sensory stimulation is mediated partly through oxytocinergic mechanisms

The objective of the present study was to investigate whether oxytocinergic mechanisms may contribute to the antinociceptive effect of non-noxious, sensory stimulation. To test this hypothesis, oxytocin levels in plasma and cerebrospinal fluid (CSF) were measured in control rats as well as in rats exposed for 30 min to electro-acupuncture (2 Hz), thermal stimulation (40 degrees C) or vibration (100 Hz). All modes of stimulation induced significant elevations of oxytocin levels in plasma and/or in CSF, 30 or 90 min after the end of stimulation. Secondly, the antinociceptive effects of these treatments were investigated in the tail-flick test with and without prior administration of the oxytocin antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin (1 mg kg-1 i.p.). All three modes of stimulation caused a significant delay of the tail-flick latency to the same degree as that caused by injection of oxytocin 1 mg kg-1 i.p. (electro-acupuncture P < 0.01, thermal stimulation and vibration P < 0.05). In all cases, the delay was reversed by administration of the oxytocin antagonist (1 mg kg-1 i.p.). These findings suggest that analgesic effects induced by non-noxious sensory stimulation may, in part, be mediated through activation of oxytocinergic mechanisms.

An evaluation of human neurophysin production in Alzheimer's disease: preliminary observations

The concentrations of human neurophysins in the cerebrospinal fluid (CSF) of nine patients with Alzheimer's disease: Preliminary observations. (AD), and one patients with Pick's disease, were determined using specific radioimmunoassays (RIAs). Concentrations of vasopressin and oxytocin were also measured. Values were compared with those from 20 age-matched mentally normal individuals who were being treated for back pain. CSF levels of vasopressin-associated human neurophysin (VP-HNP) and oxytocin-associated human neurophysin (OT-HNP) in patients with AD (22 +/- 4 fmol/ml and 104 +/- 17 fmol/ml) were only 42% and 58% of those in the control subjects (p less than 0.0001, p less than 0.0004). Vasopressin levels for these patients (3.6 +/- 0.4 fmol/ml) were also significantly reduced to 51% of controls (p less than 0.007) and oxytocin levels were marginally (p = 0.092) reduced to 70% of controls. Because neurophysins and neuropeptides are gene-related products of vasopressin-neurons and oxytocin-neurons, the data indicate that these neurons are functionally impaired in patients with AD. Plasma neurophysin values suggest this impairment is confined to neurons with centrally-directed axons. Data from the one patient with Pick's disease demonstrates that reduced CSF levels of neurophysins and hormones is not confined to Alzheimer-type dementia.

Cerebrospinal Fluid Neurochemistry in Children and Adolescents With Obsessive-Compulsive Disorder

Cerebrospinal fluid hormones, monoaminergic metabolites, and dynorphin A (1-8 sequence) were examined in 43 children with severe, primary obsessive-compulsive disorder. Cerebrospinal fluid levels of 5-hydroxyindoleacetic acid were positively correlated with one of eight obsessive-compulsive disorder severity ratings and three of seven measures of improvement following 5 weeks of treatment with clomipramine hydrochloride. Arginine vasopressin concentration was significantly and negatively correlated with several ratings of obsessive-compulsive disorder symptom severity, while oxytocin concentration was positively correlated with depressive symptoms. The ratio of arginine vasopressin to oxytocin was also negatively correlated with obsessive-compulsive disorder and depressive symptoms. Comorbid affective disorder was associated with decreased arginine vasopressin concentrations, while concomitant anxiety disorder was associated with increased oxytocin. Dynorphin A (1-8 sequence), homovanillic acid, corticotropin, 3-methoxy-4-hydroxyphenylglycol, and corticotropin releasing hormone were not significantly related to obsessive-compulsive disorder symptoms. These results seem to indicate that arginine vasopressin may be related to obsessive-compulsive disorder symptom severity, while 5-hydroxyindoleacetic acid might be associated with drug response.

Amperozide and clozapine but not haloperidol or raclopride increase the secretion of oxytocin in rats

The aim of the present study was to investigate whether amperozide, an antipsychotic drug which possesses anti-aggressive and anxiolytic-like properties, stimulates the secretion of oxytocin and if so, by which receptor mechanism. For this purpose, female or male Sprague Dawley rats were given amperozide (0.5, 2.5 and 5.0 mg/kg IP), ritanserin (5.0 mg/kg), raclopride (2.0 mg/kg) and prazosin (1.0 mg/kg) and were subsequently decapitated for collection of blood (30 and 120 min) after injection. Oxytocin levels were measured with radioimmunoassay. Amperozide 2.5 and 5 mg/kg increased plasma levels of oxytocin significantly (P < 0.05 and < 0.001). The effect appeared maximal about 30 min after injection of the drug and oxytocin levels were almost back to basal within 120 min. Similar effects were obtained in female and male rats as well as in animals that were freely fed or food deprived for 24 h. CSF levels of oxytocin were also increased. Ritanserin, a 5-HT2-receptor antagonist but not the D2 receptor antagonist raclopride or the alpha 1-adrenoceptor antagonist prazosin stimulated oxytocin release. In addition, clozapine, a neuroleptic with potent HT2-antagonistic properties, was a potent releaser of oxytocin, whereas haloperidol was without effect. A possible role for oxytocin in the behavioural effects of amperozide and clozapine remains to be explored.

Pulses of oxytocin in the cerebrospinal fluid of rhesus monkeys

Cerebrospinal fluid (CSF) samples were collected at frequent intervals (every 10-15 min) to determine if oxytocin pulses were present in the CSF of monkeys. Temporary indwelling subarachnoid catheters, with the tip of the catheter at the T12-L1 subarachnoid space, were placed in 4 nonlactating and 3 lactating (4 months post partum) female monkeys. Monkeys were maintained on jacket/tether/swivel systems in a constant photoperiod (07.00-19.00 h). CSF was continuously withdrawn at a rate of 1.2 ml/h by peristaltic pump, and CSF was collected in 15-min fractions (from 3 lactating monkeys and 1 nonlactating monkey) or in 10-min fractions (from the other 3 nonlactating monkeys) using a fraction collector. CSF oxytocin was measured by radioimmunoassay. Pulses of oxytocin were analyzed using the computerized Pulsar pulse detection algorithm. A pulsatile pattern of oxytocin concentrations was found in the CSF of lactating and nonlactating monkeys. The ultradian pulses of oxytocin were superimposed upon the diurnal rhythm of oxytocin in CSF. We conclude that frequent sampling of CSF provides a way to monitor moment-to-moment changes in central nervous system concentrations of oxytocin in primates.

Effect of naloxone administration upon the diurnal concentrations of oxytocin in the cerebrospinal fluid of rhesus and cynomolgus monkeys

A diurnal pattern in oxytocin concentrations is present in cerebrospinal fluid (CSF) removed from the spinal subarachnoid space of monkeys, with elevated levels occurring in the early light hours. In order to investigate the possible role of endogenous opioid peptides in the generation of this oxytocin rhythm, we administered naloxone (0.4 mg/kg/h x 48 h) to rhesus and cynomolgus monkeys and examined the effects on the diurnal pattern of oxytocin in CSF collected from the lumbar subarachnoid spinal space. Monkeys maintained on jacket/tether/swivel systems and in a 12 h light: 12 h dark cycle (lights on 07.00-19.00 h) were implanted with temporary spinal subarachnoid catheters. CSF was continuously collected from the lumbar subarachnoid space and assayed for oxytocin. Oxytocin concentrations in CSF showed a diurnal variation with peak and nadir concentrations during light and dark hours, respectively. The lumbar CSF concentrations of oxytocin were not significantly different during naloxone vs. saline infusion. Plasma oxytocin concentrations, measured in the same animals, displayed no diurnal variation and were not significantly different during naloxone vs. saline infusion. We conclude that naloxone administration for 48 h does not perturb the diurnal variation in oxytocin concentrations in the CSF of monkeys. Mu opioid receptors are unlikely to be involved in modulating the diurnal rhythm of oxytocin in the CSF of monkeys.

Cerebrospinal fluid and plasma concentrations of oxytocin and vasopressin during parturition and vaginocervical stimulation in the sheep

Simultaneous blood and cerebrospinal fluid (CSF) samples were taken from conscious sheep before, during and after parturition. Concentrations of plasma and CSF oxytocin were significantly elevated during contractions and particularly at birth. Mean prepartum CSF concentrations of oxytocin were around 55% of those found in plasma but postpartum they were up to 2-fold higher than those in plasma. Plasma concentrations of oxytocin were only significantly elevated, compared to prepartum levels, for 15 min postpartum whereas those in CSF were increased for the whole of the 120 min postpartum sampling period. Plasma, but not CSF, concentrations of arginine-vasopressin (AVP) were significantly raised during contractions and birth, and for 15 min postpartum. During the prepartum period CSF AVP concentrations were 67% of those found in plasma whereas at birth plasma levels were 10-fold higher than in CSF. In a separate experiment it was shown that 5 min of mechanical vaginocervical stimulation also stimulated significant increases in CSF and plasma oxytocin concentrations and in plasma vasopressin. Results support previous work suggesting an important role for central oxytocin release in the postpartum induction of maternal behavior and demonstrate that elevated concentrations of oxytocin in the CSF are present for a greater period than in blood. Elevated plasma AVP concentrations during contractions, birth or vaginocervical stimulation may be stimulated by stress associated with these stimuli.