Actions of guanidine hydrochloride on cat spinal monosynaptic reflex transmission

The effects of a single intravenous dose of guanidine hydrochloride were examined on the function of the lumbar dorsal-ventral root and triceps surae nerve-ventral root monosynaptic reflex (MSR) in unanesthetized acute spinal (C-1 sectioned) cats. Guanidine, in a dose of 25 mg/kg, consistently depressed the amplitude of the monosynaptic reflex response while a dose of 200 mg/kg always exerted a facilitatory action. Intermediate doses of 50 or 100 mg/kg produced variable actions on the amplitude of the monosynaptic reflex from one preparation to another. The differential effects of guanidine on the evoked monosynaptic reflex are postulated to represent the ability of the drug to enhance both excitatory and inhibitory transmission, the latter predominating at smaller doses and the former becoming apparent with an increasing dose of guanidine. The facilitatory and the depressant effects of guanidine on the function of spinal reflexes were slow to develop, suggesting an intracellular site of action. These results may have significance for an understanding of the possible efficacy of guanidine in motor neuron disease in man.     

Ventral root depolarization and spinal reflex augmentation by a TRH analog in rat spinal cord

The experiments were performed on spinal rats transected at the C 1 level. Intravenous administrations of TRH and its analog DN-1417 (gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide), which has less endocrine activity, produced a marked increase in the monosynaptic reflex (MSR) and depolarization of the ventral root, without affecting the dorsal root reflex (DRR) and the resting potential of the dorsal root. Excitation of the monosynaptic reflex was not antagonized by chlorpromazine, haloperidol, atropine or cyproheptadine, and was not influenced by pretreatment with reserpine. The depolarization of the ventral root persisted in the presence of baclofen or tetrodotoxin. These findings suggest that depolarization of the ventral root induced by TRH and DN-1417 is due to a direct action on motoneuronal membranes, and that an increase in the monosynaptic reflex is in part due to a depolarization of motoneurones. The effect of DN-1417 were longer lasting than those of TRH.     

Non-serotonergic depression of spinal monosynaptic reflex transmission by 5-hydroxytryptophan

Administration of a 50 mg/kg (i.v.) dose of either 1?, or the racemic D,L-mixture of 5-hydroxytryptophan (5-HTP) in acute unanesthetized spinal (C-1) cats produced a depression of the lumbar monosynaptic response (MSR) amplitude when the reflex was evoked by supramaximal triceps surae (TS) nerve stimulation. Neither pretreatment with the serotonin receptor antagonists cincanserin or cyproheptadine, nor the L-aromatic amino acid decarboxylase inhibitor methyldopa antagonized the depressant effect of 5-HTP on the MSR in TS-stimulated animals. Administration of amitriptyline, a selective serotonin reuptake inhibitor, reversed the depression in the MSR amplitude produced by 5-HTP and produced an increase in the MSR above the original pre-5-HTP control level. These data suggest that 5-HTP has a depressant action upon spinal monosynaptic reflex transmission that is unrelated to an increase in spinal serotonergic activity. The site of the depressant effect of 5-HTP within the MSR pathway is postulated to be the la afferent terminal. This non-serotonergic 5-HTP action should be considered when interpreting the results of neuropharmacologic studies employing 5-HTP as a serotonin precursor.     

Ptychodiscus brevis toxin enhances the frequency-dependent depression of the monosynaptic reflex in neonatal rat spinal cord in vitro

The involvement of frequency-dependent depression (FDD) of synaptic transmission for the depressant action of the Ptychodiscus brevis toxin (PbTx) was investigated in neonatal rat spinal cord in vitro. The stimulation of a dorsal root by train of pulses (five stimuli) at different frequencies evoked potentials in the ventral root (monosynaptic reflex, MSR). Amplitude of the fifth response as percent of first response at 0.1, 0.2, 0.5, 1.0 and 2.0 Hz were 90, 80, 75, 70 and 50%, respectively. In Mg2+-free medium, PbTx depressed the MSR and also enhanced the FDD in a concentration-dependent manner. Further, the PbTx-induced depression can well be correlated with the enhancement of FDD (r=0.98). In the presence of Mg2+ (1.3 mM), the FDD was greater than that in the absence of Mg2+. But in the presence of Mg2+ PbTx did not alter FDD, even though there was 25% depression at 28 microM (significantly lesser than in Mg2+-free medium). The results indicate that the Mg2+-sensitive component of PbTx-induced depression of MSR is mediated via the neuronal systems involving FDD.     

Biphasic action of sarin on monosynaptic reflex in the neonatal rat spinal cord in vitro

The action of sarin, an organophosphorus (OP) compound, was examined in vitro for its effects on the spinal monosynaptic reflex (MSR) in neonatal rats. The effects of sarin were biphasic, i.e. facilitation at lower concentrations (2–20 nM) followed by depression of the MSR at concentrations above 30 nM. Facilitation of MSR was maximal (150% of control) at 20 nM sarin. The depression of MSR was maximal (70% of control) at 200 nM sarin, with half maximal inhibition occurring at 90 nM sarin. Atropine (200–500 nM) effectively reversed the depression caused by sarin, while pretreatment with low concentrations of atropine (10 nM) completely blocked the depression otherwise observed with sarin. Benactyzine was also effective in preventing sarin-induced depression, while pirenzepine was less effective. The nicotinic blocking agents tubocurarine and mecamylamine were, however, ineffective in preventing or reversing sarin-induced depression. The facilitation of MSR seen with lower concentrations (2–20 nM) correlated well with the blockade of late phase inhibition (between 30 and 50 ms conditioning-test interval) elicited in spinal cord by stimulating the adjacent dorsal root at various condition-test intervals, which has been shown elsewhere to be sensitive to bicuculline (Deshpande and Warnick 1988). Thus it is speculated that sarin at lower concentrations blocks GABA transmission, producing facilitation, and at higher concentrations activates the muscarinic receptors producing depression of MSR. The beneficial action of pretreatment with antimuscarinic agents may be attributed to the protection of the muscarinic receptors.     

Stimulation of spinal dopaminergic receptors: Differential effects on tail reflexes in rats

The tail-flick reflex to heat and tail-withdrawal reflex to touch were measured in spinal and intact rats given either apomorphine (0.02–1.75) μmol · kg^?1) or dopamine (0.02–1.76 μmol · kg^?1) in the lumbar subarachnoid space. In spinal rats both apomorphine and dopamine suppressed thermal tailflick reflex and enhanced tactile tail-withdrawal response in a dose-dependent way. The effect of apomorphine in spinal rats was counteracted by dopaminergic receptor antagonists (cis-flupenthixol and (+)-butaclamol), but not by their stereoisomers. Phenoxybenzamine, propranolol, methysergide and naloxone failed to counteract the effects of apomorphine on tail-reflex responses in spinal rats. (+)-Butaclamol also counteracted effects of dopamine in spinal rats. Neither apomorphine nor dopamine influenced tail reflexes in intact rats, which suggests that effects of spinal dopaminergic mechanisms on these reflexes are influenced by descending supraspinal pathways.     

Effects of apomorphine and methamphetamine on a quickly-learned conditioned-suppression response in rats

Rats exhibited a marked suppression of motor activity when placed in the same chamber where they had been given electric shocks. Administration of apomorphine-HCl (0.1, 0.5 and 1.0 mg/kg, i.p.) attenuated the conditioned suppression, dose-dependently, but did not facilitate motor activity of control (i.e. non-shocked) rats. Methamphetamine-HCl (0.1, 0.5 and 1 mg/kg, i.p.) increased motor activity of both the shocked and non-shocked rats, in a dose-related manner. Haloperidol (0.3 and 1 mg/kg, i.p.), but not chlorpromazine-HCl (5 mg/kg, i.p.), enhanced the conditioned-suppression response. Atropine-sulfate (5 and 10 mg/kg, i.p.), p-chlorophenylalanine (300 mg/kg, i.p.) and alpha-methyl-p-tyrosine (100 mg/kg, i.p.) were slightly effective in reducing the conditioned-suppression response. Apomorphine- and methamphetamine-induced reduction of the conditioned-suppression response was inhibited by pretreatment with haloperidol. When catecholamine-synthesizing processes in rats were inhibited by pretreatment with alpha-methyl-p-tyrosine, or alpha-adrenergic receptor sites were blocked by pretreatment with phenoxybenzamine, the effect of methamphetamine, but not that of apomorphine, was reduced. Therefore, enhancement of dopaminergic neurotransmission may be responsible for attenuation of the conditioned-suppression response.     

Brain stem involvement in the effects of chlorpromazine on the monosynaptic reflex of the rat lumbar spinal cord

The brain stem areas involved in the inhibitory effect of chlorpromazine (CPZ) on the monosynaptic reflex (MSR) in the lumbar spinal cord of rats were investigated following brain stem transection and focal thermo-lesioning. Transection of the medulla oblongata markedly reduced the effect of CPZ, while transection in the mid-brain or more anterior level did not alter the effect of CPZ. With regard to focal lesions at various sites of the brain stem, lesioning of the medial portion of the medulla oblongata most effectively attenuated the MSR inhibition by CPZ and also attenuated the MSR inhibition induced by phenoxybenzamine. Bilateral lesioning of the locus coeruleus did not attenuate the MSR inhibition by CPZ. These results suggest that the pathway involved in the inhibitory effect of CPZ on the MSR originates in the pons and passes through the medial portion of the medulla oblongata, and that the coerulo-spinal pathway is not the major pathway involved in the effect of CPZ.     

5-HT-induced depression of the spinal monosynaptic reflex potential utilizes different types of 5-HT receptors depending on Mg2+ availability

Receptor subtypes involved in the 5-hydroxytryptamine (5-HT)-induced depression of synaptic transmission in neonatal rat spinal cords in vitro were evaluated in the absence or presence of Mg²⁺ in the medium. Stimulation of a dorsal root evoked monosynaptic reflex potential (MSP) and polysynaptic reflex potential (PSP) in the segmental ventral root in Mg²⁺-free medium where the voltage-dependent blockade of NMDAreceptors is absent. The 5-HT (0.3–50 μM) in the Mg²⁺-free medium depressed the MSPand PSP in a concentration-dependent manner. At 30 μM of 5-HT, the depression was 57% and 95% for MSP and PSP, respectively, and no further depression was seen at 50 μM. The 5-HT-induced depression of the reflexes in the Mg²⁺-free medium was blocked by ondansetron (5-HT₃ receptor antagonist), but not by spiperone (5-HT_2A/2C antagonist). In the Mg²⁺-free medium, phenylbiguanide (5-HT₃ agonist) also depressed the MSPand PSP in a concentration-dependent manner and was blocked by ondansetron. Addition of Mg²⁺ (1.3 mM) to the medium abolished the PSP and decreased the MSPby 30%. In the presence of Mg²⁺, 5-HT (1–50 μM) also depressed the MSP in a concentration-dependent manner. At 10 μM of 5-HT, there was approximately 20% depression and at 50 μM the depression was 100%. The 5-HT-induced depression of MSP in the Mg²⁺-containing medium was antagonized by spiperone (p < 0.05, two-way ANOVA), but not by ondansetron. The results indicate that the 5-HT-induced depression of MSPinvolves 5-HT₃ receptors in the Mg²⁺-free medium and 5-HT_2A/2C in the presence of Mg²⁺ when NMDA receptors are in the closed state.     

2-phenylethylamine and methamphetamine enhance the spinal monosynaptic reflex by releasing noradrenaline from the terminals of descending fibers.

Experiments were performed on spinalized rats transected at C1. Intravenous administration of 2-phenylethylamine-HCl (PEA-HCl) (0.3 and 1 mg/kg, i.v.) and methamphetamine-HCl (MAP-HCl) (0.1 and 0.3 mg/kg, i.v.) increased the amplitude of the monosynaptic reflex (MSR). The increase of the MSR caused by PEA and MAP was antagonized by prazosin-HCl and abolished by the pretreatment with reserpine (i.p.) and 6-hydroxydopamine (intracisternally, 14 days previously). A dopamine D1 antagonist, SK&F 83566-HBr (0.01 mg/kg, i.v.), and a D2 antagonist. YM-09151-2 (0.3 mg/kg, i.v.), did not antagonize the increasing effects produced by PEA and MAP. An inhibitor of type-B monoamine oxidase, (-)deprenyl-HCl (1 mg/kg, i.v.), prolonged the effect of PEA but not that of MAP, suggesting that PEA alone, and not its metabolites, enhanced the MSR. These results suggest that PEA and MAP increase the amplitude of the MSR by releasing noradrenaline from the terminals of descending noradrenergic fibers, and that PEA, an endogenous trace amine, has a mechanism of action similar to that of MAP.     

钙敏感受体和钙蛋白酶在大鼠脊髓的表达及其定位

目的 探讨钙敏感受体(CaSR)和钙蛋白酶在大鼠脊髓缺血-再灌注损伤(SCII)中的作用.方法 采用Western blot法检测CaSR在5只健康SD大鼠脊髓中的表达,免疫组化法观察CaSR及钙蛋白酶在脊髓表达的定位.结果 CaSR和钙蛋白酶在大鼠脊髓白质和灰质的前角、侧角及后角均有广泛表达.CaSR在脊髓神经元及神经胶质细胞的胞膜、胞浆和突起部均有表达,而钙蛋白酶仅在神经元的胞浆、胞膜和突起部表达.结论 大鼠脊髓神经元细胞的细胞膜、胞浆及突起部是CaSR和钙蛋白酶的共表达部位,可能参与SCII的发生发展.     

A novel metabotropic glutamate receptor agonist: marked depression of monosynaptic excitation in the newborn rat isolated spinal cord.

1. Neuropharmacological actions of a novel metabotropic glutamate receptor agonist, (2S,1'R,2'R,3'R)-2(2,3-dicarboxycyclopropyl)glycine (DCG-IV), were examined in the isolated spinal cord of the newborn rat, and compared with those of the established agonists of (2S,1'S,2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3R)-ACPD). 2. At concentrations higher than 10 microM, DCG-IV caused a depolarization which was completely blocked by selective N-methyl-D-aspartate (NMDA) antagonists. The depolarization was pharmacologically quite different from that caused by L-CCG-I and (1S,3R)-ACPD. 3. DCG-IV reduced the monosynaptic excitation of motoneurones rather than polysynaptic discharges in the nanomolar range without causing postsynaptic depolarization of motoneurones. DCG-IV was more effective than L-CCG-I, (1S,3R)-ACPD or L-2-amino-4-phosphonobutanoic acid (L-AP4) in reducing the monosynaptic excitation of motoneurones. 4. DCG-IV (30 nM-1 microM) did not depress the depolarization induced by known excitatory amino acids in the newborn rat motoneurones, but depressed the baseline fluctuation of the potential derived from ventral roots. Therefore, DCG-IV seems to reduce preferentially transmitter release from primary afferent nerve terminals. 5. Depression of monosynaptic excitation caused by DCG-IV was not affected by any known pharmacological agents, including 2-amino-3-phosphonopropanoic acid (AP3), diazepam, 2-hydroxysaclofen, picrotoxin and strychnine. 6. DCG-IV has the potential of providing further useful information on the physiological function of metabotropic glutamate receptors.     

经腹主动脉灌注瑞芬太尼聚己内酯对脊髓缺血再灌注损伤中脊髓能量代谢的影响

目的:观察腹主动脉内灌注Mu阿片受体激动剂REM-PCL对兔脊髓缺血再灌注损伤(SCIRI)中脊髓能量代谢的影响。方法:30只健康新西兰大白兔随机分为对照组(C组)、REM-PCL组(RP组,0.1 mg·kg^-1)和REM-PCL+ GSK1521498组(RG组,0.1 mg·kg^-1 REM-PCL+1 mg·kg^-1 GSK1521498),每组10只。采用肾下腹主动脉阻断法,建立SCIRI模型。分别于缺血前、缺血45 min及再灌注60 min时,取脊髓测定腺苷酸(ADP、AMP、ATP、TAN、EC)、Mu阿片受体表达、活性氧(ROS)、丙二醛(MDA)含量、线粒体肿胀度(MSD)、总抗氧化能力(T-AOC) 并观察其病理学改变。分别于缺血前、缺血45 min、再灌注30 min及再灌注60 min监测血清神经特异性烯醇化酶(NSE)浓度变化。结果:与缺血前比较,缺血45 min及再灌注60 min时C组和RG组ATP、EC、TAN、T-AOC及Mu阿片受体表达均降低(P<0.01),ROS、MDA和MSD均升高(P<0.01);RP组在缺血45 min时和再灌注60 min时ATP、T-AOC、TAN、EC及Mu阿片受体表达均显著高于C组和RG组(P<0.01),ROS、MDA和MSD含量均显著低于C组和RG组(P<0.01),RP组脊髓灰质的病理损害程度明显轻于C和RG组(P<0.01)。缺血45 min、再灌注30 min及再灌注60minRP组血清NSE浓度明显低于C组和RG组(P<0.01)。结论:腹主动脉内灌注REM-PCL通过激活Mu阿片受体能够明显改善SCIRI中脊髓能量代谢,保护脊髓线粒体的结构,从而减轻SCIRI。     

Diisopropylfluorophosphate-induced depression of segmental monosynaptic transmission in neonatal rat spinal cord is also mediated by increased axonal activity

Involvement of dorsal and ventral root activity for the depressant action of diisopropylfluorophosphate (DFP) on synaptic transmission was examined using in vitro spinal cord/root preparations. Superfusion of DFP produced a dose-dependent depression of monosynaptic reflex (MSR) and maximal depression of about 80% occurred at 1000 μM. The concentration to produce 50% of the maximal inhibition was about 100 μM of DFP. The DFP (100 μM)-induced depression of MSR was reversed by atropine (0.5 μM) but not by mecamylamine (0.5 μM). Contrary to the action on MSR, DFP potentiated the ventral root potential and 1st peak of dorsal root potential. The maximal potentiation was about 25% of control in both the root potentials at 100 μM of DFP. However, the second peak of dorsal root potential was slightly depressed (10–20% of control) by DFP (1–1000 μM). Further, the cords treated with DFP (100 μM) showed significant decrease in the cholinesterase (ChE) activity (27% of control). Results suggest that the DFP-induced depression was mediated at least by two different mechanisms, one through the inhibition of ChE activity and the other through the activation axonal activity having inhibitory inputs to the segmental synaptic transmission. These inputs mediate their action through muscarinic receptors.     

头孢曲松对甲基苯丙胺致大鼠行为及纹状体氨基酸等递质含量改变的影响

目的观察甲基苯丙胺(METH)急性处理时致神经损伤情况,以及纹状体中氨基酸类神经递质谷氨酸(glutamate,Glu)、单胺类神经递质多巴胺(dopamine,DA)及其代谢产物DOPAC的变化。方法建立METH急性毒性模型,同时利用药物头孢曲松进行干预,利用清醒动物脑微透析技术检测神经递质含量的变化。结果 METH急性给药组与盐水对照组相比,刻板行为明显增加(P<0.01);急性给予METH后,胞外Glu浓度持续增加,在本试验检测时间(0～6 h)范围内,与基础平衡值相比,在给药5.5 h时Glu浓度已增加450%。胞外DA水平在1 h达峰值,与基础平衡值相比,浓度增加1248.6%。与METH组相比,头孢曲松预防给药可明显降低大鼠纹状体胞外Glu浓度(P<0.05)。结论 METH急性处理能引起纹状体中胞外谷氨酸的含量明显增加,导致神经损伤;METH的神经毒性与兴奋性氨基酸的过度释放密切相关。     

A GABAergic component in homosynaptic depression in the spinal monosynaptic pathway. A requirement for action of benzodiazepines

Spinal monosynaptic responses, evoked by repetitive stimulation, undergo homosynaptic depression the pattern of which is altered by 0.5 mg/kg of clonazepam. The dependence of this effect of clonazepam on the GABAergic system was examined in spinal unanaesthetized cats. Topical application of bicuculline to the spinal cord did not change any feature of the homosynaptic depression in the biceps-semitendinosus (BST) or triceps surae (TS) monosynaptic pathway but antagonized the action of clonazepam. Semicarbazide (200 mg/kg, i.v.) also prevented the effect of the benzodiazepine but alone had actions of its own. Evidence is presented that clonazepam influenced homosynaptic depression of the biceps-semitendinosus pathway by lengthening the primary afferent depolarization (PAD). This prolongation of the primary afferent depolarization did not last for the entire duration of the train as primary afferent depolarization also underwent depression. Therefore later responses in the train were unaffected by clonazepam. Homosynaptic depression of the triceps surae pathway was not similarly affected because activation of triceps surae afferents does not cause significant depolarization of its own afferents. It is suggested that the enhancement of GABAergic transmission at least partially underlies the effect of clonazepam on homosynaptic depression.     

5-HT receptor-mediated regulation of thyrotropin-releasing hormone release in rat spinal cord.

5-Hydroxytryptamine (5-HT, 10 microM) increased the veratridine-evoked release of thyrotropin-releasing hormone (TRH) from spinal cord slices. This effect of 5-HT was reduced by pre-exposure of the tissue to 10 microM ketanserin and methysergide, which both have 5-HT2 antagonistic activity. A 5-HT1 agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (10 microM), reduced the release of TRH. These results imply that 5-HT released from the terminals of descending fibers modulates the release of TRH, a cotransmitter contained in 5-HT fibers.     

Stereospecific binding of 3H-haloperidol in rat dorsal spinal cord

[³H]Haloperidol as dopaminergic ligand used on pooled microdiscs punched from the rat dorsal spinal cord allowed detection of a stereospecific binding. Characteristics of such a binding: dissociation constant, Hill's slope and IC₅₀ of different specific drugs were nearly the same as those found in the striatum, which suggests the presence of individualized dopaminergic receptor sites in the rat dorsal horn. Their density (B_max) is about three time lower than in the whole striatum.     

NMDA receptor activation modulates evoked release of substance P from rat spinal cord

The possible modulation exerted by glutamate on substance P (SP) release from the rat spinal cord has been investigated. The N-methyl-D-aspartate (NMDA) receptor agonist, NMDA (1 μM), increased SP basal outflow by 46.5±10.9% (n=3, P<0.01) without changing the evoked release of the peptide. Conversely, NMDA antagonists but not 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) inhibited both electrically-evoked and capsaicin-induced release of SP. In particular, D-2-amino-5-phosphonopentanoate (D-AP5; 50 μM) inhibited electrically-evoked and capsaicin-induced release of SP by 93±2.4% and 93.2±3.8% (n=12, P<0.01), respectively. Functional pharmacological evidence is provided for glutamate exerting a positive feedback on SP release evoked by C fibre stimulation via NMDA receptor activation.