Does environmental exposure to the greenhouse gas,N2O,contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence

BackgroundNeurodevelopmental disorders are increasing in prevalence worldwide. Previous work suggests that exposure to the environmental air pollutant and greenhouse gas – nitrous oxide (N₂O) – may be an etiological factor in neurodevelopmental disorders through the targeting of several neural correlates.MethodologyWhile a number of recent systematic reviews have addressed the role of general anesthesia in the surgical setting and neurodevelopmental outcomes, a narrative mini-review was conducted to first define and characterize the relevant variables (i.e., N₂O, attention-deficit hyperactivity disorder [ADHD] and autism spectrum disorders [ASD]) and their potential interactions into a coherent, hypothesis-generating work. The narrative mini-review merges basic principles in environmental science, anesthesiology, and psychiatry to more fully develop the novel hypotheses that neurodevelopmental impairment found in conditions like ADHD and ASD may be due to exposure to the increasing air pollutant, N₂O.ResultsThe results of the present mini-review indicate that exposure to N₂O, even at non-toxic doses, may modulate central neurotransmission and target many neural substrates directly implicated in neurodevelopmental disorders, including the glutamatergic, opioidergic, cholinergic, and dopaminergic systems. Epidemiological studies also indicate that early and repeated exposure to general anesthesia, including N₂O, may contribute to later adverse neurodevelopmental outcomes in children.ConclusionsThe current evidence and subsequent hypotheses suggest that a renewed interest be taken in the toxicological assessment of environmental N₂O exposure using validated biomarkers and psychiatric endpoints. Given the relevance of N₂O as a greenhouse gas, societies may also wish to engage in a more robust monitoring and reporting of N₂O levels in the environment for climactic benefit as well.     

川芎嗪对体外循环心内直视手术患者血浆β-内啡肽、强啡肽A_(1-13)含量的影响

目的 观察川芎嗪(tetramethylpyrazine,TMP)对体外循环心内直视手术患者血浆β-内啡肽(β-EP)、强啡肽A_(1-13)(DynA_(1-13))含量的影响。方法 24例风湿性瓣膜病患者,随机分为对照组12例,用药组12例。检测了围手术期血浆β-EP,DynA_(1-13)含量。结果 用药组病人β-EP,DynA_(1-13)含量在术中及术后48h内显著低于对照组(P<0.05,P<0.01)。结论 TMP改善体外循环心内直视手术患者脑部微循环障碍,减少脑组织β-EP,DynA_(1-13)的合成和释放。     

鞘内注射前强啡肽基因修饰的骨髓干细胞对神经病理性痛大鼠的镇痛效应研究

目的 探讨前强啡肽(PDP)基因修饰的人骨髓间充质干细胞株(hBMSCs-PDP)对神经病理性疼痛模型大鼠的镇痛效应.方法 将雄性SD大鼠随机分为4组(n-10):A组为正常对照组,B、C、D组制备CCI模型.术后3d将hBMSCs-PDP移植入CCI模型大鼠髓鞘内,A组不做处理;B组鞘内注射生理盐水20 μl;C组鞘内注射hBMSCs-空载体悬液20 μl(约106/μl);D组鞘内注射hBMSCs-PDP悬液20 μl(约106/μl).分别于术前、术后3、5、7、9、11、13d测定大鼠足底的热痛阈值.术后13d取脊髓组织,用免疫组织化学法和Western Blot法测定脊髓强啡肽表达情况.结果 与A组比较,B、C及D组大鼠热痛阈降低;与B、C组相比,D组大鼠脊髓组织强啡肽表达增强,Western Blot法证实其强啡肽蛋白的分泌增加.注入hBMSCs-PDP细胞CCI模型大鼠的热痛阈值也比其它两组有所升高,差异有统计学意义(P＜0.05).结论 鞘内注射hBMSCs-PDP可提高脊髓组织强啡肽的表达,对CCI模型大鼠起到一定镇痛作用.     

Kappa-opioid receptor modulation of the release of substance P in the dorsal horn

Substance P (SP), a member of the tachykinin peptide family, has been found in high concentrations in the superficial laminae of the dorsal horn and it is thought to play a major role in the transmission of nociceptive information. Dynorphin(1–8), an opioid peptide with high selectivity for the κ-opioid receptor subtype, is also found in the dorsal horn of the spinal cord. The aim of this study was to determine the effect of dynorphin(1–8) on the release of SP-like-immunoreactivity (SPLI) in the dorsal horn before and during the activation of peripheral nociceptors by a thermal stimulus. A push-pull canula was used to perfuse the dorsal horn of non-anesthetized decerebrate/spinal transected rats and the collected perfusates were assayed for SPLI by using radioimmunoassay. Dynorphin(1–8) applied to the spinal cord at a concentration of 1 μM elicited a 27 ± 8% decrease in the basal release of SPLI and prevented the increase in the release of SPLI evoked by the application of a noxious thermal stimulus to the ipsilateral hind paw and lower limb. The effect of dynorphin(1–8) was reversed by 2 μM of nor-binaltorphimine (nor-BNI), a selective kappa opioid receptor antagonist. Application of nor-BNI alone to the perfusate resulted in a 62 ± 23% increase in the basal release of SPLI. In conclusion, dynorphin(1–8) reduces the basal release of SPLI and prevents the increase in the release of SPLI elicited by the application of a noxious cutaneous thermal stimulus. This effect is mediated through the κ-opioid receptor, which appears to tonically regulate the release of SPLI in the dorsal horn.     

Prolonged inflammatory pain modifies corticotropin-releasing factor-induced opioid peptide release in the hypothalamus

The influence of prolonged pain upon hypothalamic opioid peptide release in vitro was examined in rats subjected to Freund's adjuvant (FA)-induced unilateral inflammation of the hindlimb. Basal release of enkephalin (ENK) but not beta-endorphin (END) or dynorphin (DYN) was increased 10 days following FA treatment. Superfusion of corticotropin-releasing factor (CRF; 10(-8) M) stimulated the release of opioid peptides in control hypothalami. CRF, however, failed to modify beta-END and DYN release in hypothalami of FA-treated rats, whereas ENK release was markedly reduced. In contrast, KCl-stimulated opioid peptide release did not differ between FA and control hypothalami. These data demonstrate that prolonged inflammatory pain alters the responsiveness of hypothalamic opioid systems to CRF. It is suggested that this effect is mediated at the level of the CRF neuron or its receptor.     

Characterization of the High Affinity [H]Nociceptin Binding Site in Membrane Preparations of Rat Heart: Correlations with the Non-opioid Dynorphin Binding Site

The binding parameters of [³H]nociceptin were examined in membrane preparations of rat heart and compared with those of [³H]dynorphin A-(1-13) ([³H]Dyn A-(1-13)). Scatchard analysis of [³H]nociceptin binding revealed the presence of two distinct sites: a high affinity (K_d: 583 nm) low capacity (B_max: 132 pmol/mg protein) site and a low affinity (K_d: 10 316 nm) high capacity (1552 pmol/mg protein) site. Dyn A and related peptides were potent competitors of the binding to the high affinity site with the following rank order of potencyα-neo-endorphin>Dyn A-(2-13)=Dyn A-(3-13)>Dyn A-(5-13)>Dyn A-(1-13)>Dyn A>Dyn B>Dyn A-(6-10)>>Dyn A-(1-8). Nociceptin was 6.7 times less potent than Dyn A with a K_iof 4.8μmas compared with 0.72μmfor Dyn A. The order of potency of the various peptides in inhibiting [³H]nociceptin binding correlated well (r=0.93) with their ability to compete with the binding of [³H]Dyn A-(1-13) (Dumont and Lemaire, 1993). In addition, the high affinity [³H]nociceptin and non-opioid [³H]Dyn A-(1-13) sites were both sensitive to NaCl (120 mm) and the phospholipase C (PLC) inhibitors, U-73122 and neomycin (100μm). The binding activities were less affected by the weak PLC inhibitor, U-73343, and no effect was observed with the non-hydrolysable GTP analogs, Gpp(NH)p and GTP-γ-S. Nociceptin (1–50μm) was also shown to inhibit the uptake of [³H]noradrenaline ( [³H]NA) by cardiac synaptosomal preparations. In spontaneously hypertensive rats (SHR), the potency of nociceptin in inhibiting [³H]NA uptake was increased by 1.6-fold as compared with Wistar Kyoto (WKY) control rats and such effect was accompanied by comparable increased levels of cardiac ORL₁mRNA and [³H]nociceptin high affinity sites. These changes correlated well with the previously observed increased levels of non-opioid cardiac [³H]Dyn A-(1-13) sites in SHR (1.3 times as compared with WKY) and increased potency of Dyn A-(1-13) in inhibiting [³H]NA uptake by cardiac synaptosomes in SHR (2.2-fold as compared with WKY) (Dumont and Lemaire, 1995). The results demonstrate that in rat heart the characteristics of the high affinity, low capacity [³H]nociceptin binding site are similar to those of the non-opioid Dyn binding site. The stimulation of this site by nociceptin, Dyn A or related peptides is more likely to produce a modulation of PLC activity and [³H]NA uptake and may participate to the pathophysiology of hypertension.     

Effect of dynorphin A(1–13) on cardiomyocytes in culture: modulation of the response to increased extracellular calcium,but no effect on intrinsic cardiac contractile frequency or the response to isoproterenol or increased extracellular potassium

Summary The purpose of this study was to determine whether the endogenous opioid peptide dynorphin A(1–13) has a direct effect on the heart or acts to modulate the cardiac chronotropic response to calcium, potassium, or -adrenergic receptor stimulation. Spontaneously contracting myocardial cell aggregates were prepared from 7-day-old chick embryos and were maintained in culture for 72 h before study. Dynorphin A(1–13), 10^–8 to 10^–6 M, did not alter spontaneous contractile frequency. Increases in [Ca²⁺]₀ spontaneously suppressed cardiac contractile frequency, and dynorphin A(1–13) significantly (p<0.05) enhanced this response. Nifedipine, 10^–8 M, antagonized the effect of increased [Ca²⁺]₀ on cardiac contractile frequency, but did not block the action of dynorphin A(1–13) to accentuate the effect of increasing [Ca²⁺]₀. Dynorphin A(1–13) did not alter the significant (p<0.05) increase in contractile frequency produced by beta-adrenergic receptor stimulation by isoproterenol, or the suppression in contractile frequency produced by increases in extracellular potassium ([K⁺]₀). These data indicate that dynorphin A(1–13) does not act directly on the cardiac myocyte to alter cardiac contractile frequency or alter the response to increases in [K⁺]₀ or to isoproterenol, but that dynorphin A(1–13) does modulate the response to increases in extracellular calcium.Funded in part by a grant from the Medical Research Council of Canada     

Morphine-like discriminative stimulus effects of opioid peptides: possible modulatory role ofd-Ala2-d-Leu5-enkephalin (DADL) and dynorphin A(1-13)

The role of the different opioid receptors was studied in rats trained to discriminate SC injections of 3.0 mg/kg morphine from saline by tests for generalization to graded doses of morphine and receptor-selective peptides administered into the lateral cerebral ventricle. Dose-dependent morphine-like stimulus effects were produced over a wide range of doses (0.001–30 g), depending upon ligand and animal, by morphine, by themu-selective peptides DAGO[d-Ala²-NMePhe⁴-Gly(ol)-enkephalin] and FK33824[d-Ala²,NMePhe⁴-Met(O)⁵-(ol)-enkephalin], and by thedelta-selective peptide, DADL[d-Ala²,d-Leu⁵enkephalin]. The order of relative potency of these substances was: FK33824>DAGO>morphine>DADL. In contrast, DPLPE[d-Pen²,l-Pen⁵)enkephalin], which has much greaterdelta receptor selectivity than does DADL, and dynorphin A(1-13) (0.1–10 g), akappa-receptor agonist, engendered choice responding appropriate for saline. When 1.0 g DADL, a dose lacking morphine-like discriminative effects, was administered concurrently with SC morphine, the stimulus effects of morphine were potentiated. Concurrent administration of 10 g dynorphin A(1-13) and morphine attenuated the stimulus effects of morphine inconsistently. These results support previous findings thatmu-opioid receptors are of primary importance in mediating the morphine-like discriminative effects of opioid peptides. They also suggest that morphine-like discriminative effects can be modulated by other types of opioid receptors.     

BDNF heterozygous mice demonstrate age-related changes in striatal and nigral gene expression

TrkB receptors mediate the effects of BDNF on striatal medium spiny neurons and mesencephalic dopamine neurons. The effect of partial BDNF gene deletion on locomotor activity and the gene expression of these neurons was evaluated at 3, 12, and 24 months of age in BDNF heterozygous (BDNF(LacZ/neo+)) and wildtype mice. BDNF(LacZ/neo+) mice displayed less spontaneous horizontal activity than wildtypes at 3 and 24 months of age. Whereas striatal preproenkephalin and preprodynorphin mRNA and mesencephalic tyrosine hydroxylase mRNA levels were significantly lower at all ages in BDNF(LacZ/neo+) mice, GAD67 mRNA was only lower at 24 months. In contrast, BDNF(LacZ/neo+) mice expressed more trkB mRNA in the striatum at 3 months and less at 24 months of age than wildtypes. Total striatal cell number in the two genotypes was not different at 12 months of age, whereas Golgi staining revealed that the spine density on distal dendrites of medium spiny neurons was less in BDNF(LacZ/neo+) mice than in wildtypes at 24 months of age. These data indicate that endogenous BDNF is required to maintain the normal phenotype and functioning of striatal projection neurons and mesencephalic dopamine neurons and that exaggerated dysfunction of these neurons and a concomitant decline in locomotor behavior occurs during aging.     

Dynorphin-mediated antinociceptive effects of L-arginine and SIN-1 (an NO donor) in mice

The antinociceptive response of mice to the amino acid L-arginine (L-ARG) has been attributed to either an opioid mechanism or a non-opioid but nitric oxide (NO)-dependent mechanism. Earlier it was reported that the mechanism of nitrous oxide-induced antinociception involved opioid components and was also dependent on brain NO. This study was designed to determine whether the antinociceptive effects of L-ARG and the NO donor 3-morpholinosydnoimine (SIN-1) might be mediated by brain mechanisms similar to those that are responsible for nitrous oxide (N(2)O) antinociception. L-ARG and SIN-1 were administered to mice intracerebroventricularly (i.c.v.), and antinociception was assessed using the acetic acid abdominal constriction test. Both L-ARG and SIN-1 caused dose-related antinociceptive effects that were blocked by naloxone and norbinaltorphimine. The antinociceptive effects of both SIN-1 and L-ARG were also blocked to a greater extent by i.c.v. administration of a rabbit antiserum against rat dynorphin 1-13 than an antiserum against methionine-enkephalin, suggesting that the SIN-1 and L-ARG effects may be related to stimulated release of dynorphin. The antinociceptive effect of L-ARG was antagonized by an inhibitor of neuoronal NO synthase enzyme, indicating that L-ARG had to be converted to NO for its antinociceptive action. These findings indicate that the mechanisms of antinociceptive action of L-ARG and SIN-1 are both mediated by dynorphin and dependent on NO.