Effects of neonatal oxytocin manipulations on male reproductive potential in prairie voles

Oxytocin (OT) modulates adult mammalian sexual behavior, sperm production and transport, and steroidogenesis; however, the consequences of developmental manipulations of oxytocin have received little attention. The purpose of this experiment was to determine whether neonatal exposure to OT, an oxytocin antagonist (OTA), saline (SAL), or handling (HAN)-only would have long-term effects on reproductive potential in male prairie voles (Microtus ochrogaster). Adult males were observed for 24 h with a sexually receptive female and sexual behavior was recorded. Females were subsequently lavaged and smears were examined for sperm. Reproductive parameters including motility of epididymal sperm, testis weight, and plasma androgen levels were in the normal range. OT-treated males that did not mate within the first 30 min did not mate at all, and in comparison to controls, a higher proportion of those OT-treated and OTA-treated males that did mate did not transfer sperm to the females. OTA-treated males also had significantly higher testicular sperm concentrations than HAN-only males, and significantly lower epididymal sperm concentrations. These differences suggest that in males, developmental manipulations of OT may have the potential to influence the subsequent expression of sexual behavior and sperm transport.     

Regulation of transmitter release by high-affinity group III mGluRs in the supraoptic nucleus of the rat hypothalamus

We analyzed the subtypes of group III metabotropic glutamate receptors (mGluRs) modulating inhibitory and excitatory transmission in the rat supraoptic nucleus. Bath application of the agonist l-AP4 at 200 microM, a concentration that activates all group III mGluR subtypes, inhibited the frequency but not the amplitude of miniature inhibitory and excitatory postsynaptic currents, indicating a presynaptic site of action. l-AP4 at low concentrations (10 microM), as well as ACPT-1 (50 microM), a specific mGluR III agonist, inhibited transmission at GABAergic and glutamatergic synapses to the same extent as 200 microM l-AP4. Because the potency of l-AP4 and ACPT-1 is much higher on mGluR4 and mGluR8 than on mGluR7, these results are consistent with the presence of high-affinity group III mGluRs regulating transmitter release in this nucleus. In agreement with these findings, DCPG (30 microM), a selective mGluR8 agonist, induced a significant depression of inhibitory and excitatory synaptic currents. Group III mGluRs such as mGluR8, because of their high affinity for glutamate, are particularly well suited to detect small changes in the concentration of this excitatory amino acid in the extracellular space. Their presence, therefore, may favor the negative feedback control exerted by glutamate on its own release as well as the intersynaptic crosstalk mediated by glutamate spillover on adjacent synapses.     

山莨菪碱促进经产妇产程的临床观察

目的 探讨山莨菪碱促进经产妇第一产程的临床观察。方法 60例进入正规产程的经产妇，30例用山莨菪碱＋缩宫素，30例用缩宫素，观察宫颈扩张时间，胎儿窘迫及新生儿窒息率，手术产率和产后出血情况。结果 治疗组宫颈扩张时间和手术产率明显低于对照组，差异有统计学意义（P〈0．05），两组胎儿窘迫和新生儿窒息率，产后出血率无明显差异（P〉0．05）。结论 山茛菪碱有促进经产妇产程进展作用，减少经产妇手术产率，是较安全有效的助产药。     

Maternal mean corpuscle volume and oxytocin augmentation during vaginal delivery

Objective: The aim of this study was to assess whether low maternal MCV values are associated with adverse course of vaginal delivery. Study design: A retrospective analysis of 92 consecutive vertex singleton vaginal deliveries in nulliparous women in a university tertiary health care facility. MCV was considered as major outcome variable. Results: 54.1% of Parturients with higher MCV needed oxytocin augmentation during labor as compared to 79.5% of parturients with lower MCV (P<0.05). The need for oxytocin for augmentation of labor was decreased with larger MCV (OR 0.90 per fL, 95% CI 0.82–0.98, P<0.05). No correlation was found between MCV and other parameters of labor course. Conclusion: Low maternal MCV values were associated with increased use of oxytocin augmentation during vaginal delivery.     

Oxytocin decreases corticosterone and nociception and increases motor activity in OVX rats

OBJECTIVES: In the present study the effects of oxytocin administered subcutaneously (s.c.) or intravaginally (i.vag.) on spontaneous motor activity, nociceptive thresholds and plasma corticosterone levels were examined in female ovariectomized (OVX) rats. METHODS: Oxytocin (1 mg/kg s.c. or 100 microg i.vag.) was administered once a day for 10 days to OVX rats. Controls received saline s.c. or cellulose gel i.vag. Spontaneous motor activity was observed in an open-field arena, nociceptive thresholds were investigated by the tail-flick test, and corticosterone and oxytocin plasma levels were measured by radioimmunassay, 3, 4 and 5 days respectively, after the end of the treatment period. RESULTS: Both oxytocin administered s.c. and i.vag. increased forward locomotion (p<0.05) and nociceptive thresholds (p<0.05) significantly. In addition, oxytocin s.c. increased the amount of locomotor activity (p<0.05). Plasma corticosterone levels were decreased (p<0.05) and oxytocin levels were unchanged when measured 5 days after the last administration of oxytocin s.c. or i.vag. CONCLUSION: The present data indicate that oxytocin induces a spectrum of long-lasting effects in OVX rats, including an increase in spontaneous motor activity, elevation of nociceptive thresholds and decrease of corticosterone levels. Similar effects may be induced by estrogens. In addition, these data indicate that i.vag. administration of oxytocin may be used to induce oxytocin-mediated effects.     

Neural and anatomic characteristics of peripheral afferent fibers in the milk ejection reflex

Conduction velocities were measured and certain morphologic characteristics were examined of the abdominal mammary nerve in two- to ten-day postpartum rats. This nerve enters the spinal cord at the spinal segmental level T-12. Overall conduction velocity was (Mean +/- S.D.) 18.9 +/- 2.25 m/sec with a major peak at 9.7 +/- 0.72 m/sec. The distribution of conduction velocities in the nerve was similar to that of a typical spinal nerve. Nerve fiber diameters measured between about 1 and 25 microns with peaks at 4.9, 10.5, and 18.9 microns. Injection into the peripheral nerve of fluorescent dye, Lucifer yellow CH (LY), or wheat germ agglutinin-coupled horseradish peroxidase (WGA-HRP) after ventral root rhizotomy permitted study of the distribution of primary afferents in the spinal cord. The terminal field of these fibers centered around the dorsal cap of Clarke's column and the lateral spinal nucleus, bilaterally. The distribution of WGA-HRP was more restricted than that of LY. A large number of LY-staining fibers were also found ipsilaterally in the medial portion of the intermediomedial column. A smaller amount of LY-staining was present contralaterally in the area of the spinothalamic tract. It is concluded that afferent impulses resulting from mammary stimulation in the milk ejection reflex are probably carried in a mixed spinal nerve whose primary afferent field lies mainly in ipsilateral spinal structures, although there is some evidence for crossing fibers. The data suggest that considerable opportunity exists for interaction with major sensory afferent fiber systems as well as with autonomic fibers. Hence, the spinal path of afferent information relevant for the milk ejection reflex may well be diffuse and it may involve several sensory modalities.     

Acute Effects of Ethanol on Ingestive Behavior in Rats

The effects of acute ethanol administration on the ingestion of NaCl and food were assessed in adult rats subjected to 1-hr drinking and feeding tests 30 min after intraperitoneal administration of ethanol. Ethanol pretreatment did not induce spontaneous NaCl ingestion, but significantly potentiated angiotensin II-stimulated salt appetite, but not water intake, in a dose-dependent manner. Similarly, ethanol pretreatment significantly potentiated neuropeptide γ-stimulated food intake in nonfasted rats, but did not, by itself, cause spontaneous food ingestion. Ethanol pretreatment also significantly blunted pituitary secretion of oxytocin in response to multiple excitatory stimuli. Finally, administration of oxytocin intracerebroventricularly prevented the ethanol-induced potentiation of salt appetite elicited by angiotensin II. In view of our previous findings that central oxytocin secretion inhibits both NaCl and food intake, we propose that ethanol potentiates the ingestion of various solutes in rats, in part, by inhibiting brain-projecting oxytocinergic pathways concurrently with its well-known effects to inhibit pituitary oxytocin secretion.     

腹腔与侧脑室注射八肽胆囊收缩素对大鼠中枢催产素含量的影响

采用放射免疫测定法比较腹腔注射和侧脑室注射八肽胆囊收缩素(CCK-8)后中枢各脑区及脊髓内催产素含量的变化.结果表明,腹腔注射CCK-8可使垂体、下丘脑、桥脑及脊髓内催产素含量明显增加(P<0.05,P<0.01);侧脑室注射CCK-8后,仅垂体内催产素含量增加(10min后P<0.05,20min后P<0.01),其他脑区及脊髓内催产素(OXT)含量未见有统计学意义的变化(P>0.05).提示CCK-8对中枢脑区及脊髓内OXT含量增加的影响以外周性传入机制为主.     

Steroid priming promotes oxytocin-induced norepinephrine release in the ventromedial hypothalamus of female rats

In vivo microdialysis was used to detect norepinephrine (NE) release in the ventromedial hypothalamus of estradiol (E₂)- or E₂ plus progesterone (P)-treated female rats injected with 1.0 IU of oxytocin (OXY). Dialysates were collected before and after OXY administration on 3 consecutive days and analyzed for NE content by high performance liquid chromatography with electrochemical detection. After the last sample was collected on day 1, animals were injected with 3 μg E₂ benzoate or oil. On day 3, E₂-primed animals received 200 μg of P and control females received oil prior to OXY administration. OXY administration did not induce NE release on day 1. When OXY was administered to animals that received E₂ approximately 20 h earlier, increased release of NE was not consistently seen. In contrast, E₂-primed animals that received P on day 3 displayed significant increases in the release of NE after OXY administration compared to their own basal levels and to NE levels in control animals. To distinguish whether E₂ priming is sufficient to promote OXY-induced release of NE without the addition of P, NE content of VMH dialysates in a second group of animals was examined following exposure to vehicle or E₂ alone. When OXY was administered 24 or 48 h after estrogen priming, only 1 of 4 E₂-primed females had modestly elevated dialysate NE levels. To evaluate the interactions between OXY and NE in the regulation of reproductive behavior, lordosis responses were observed in hormone-primed female rats receiving systemic injections of OXY, the ₁-adrenoceptor antagonist prazosin, or both OXY and prazosin. OXY enhanced lordosis behavior in females primed with subthreshold doses of E₂ and P. Prazosin abolished lordosis behavior in rats primed with behaviorally effective doses of E₂ and P and significantly inhibited lordosis in steroid-primed females given OXY. These data suggest that after priming with both E₂ and P together, but not with E₂ alone, OXY may facilitate lordosis behavior through activation of NE transmission.     

Oxytocin but not vasopressin facilities social recognition following injection into the medial preoptic area of the rat brain

Social recognition of juvenile rats by adult male residents has been shown to be modulated by peripheral administration of neurohypophyseal hormones vasopressin and oxytocin. In the present study, the effects of these peptides on social recognition were investigated after local injection into the medial preoptic area of the hypothalamus. It was found that oxytocin given in a wide range of doses (0.3–1000 pg) facilitated social recognition. This effect was not blocked by pretreatment with oxytocin receptor antagonist desGly(NH₂)⁹-d(CH₂)₅[Tyr(Me)²Thr⁴]OVT. Oxytocin injected into the septum in doses of 0.03–3 pg was not effective. Administration of vasopressin (100 or 1000 pg), [pGlu⁴,Cyt⁶]AVP-(4-8) (200 pg) or [pGlu⁴,Cyt⁶]AVP-(4-9) (200 pg) into the medial preoptic area did not influence social recognition. It is concluded that the medial preoptic area is a sensitive brain site for the oxytocin-induced facilitation of social recognition in rats.