Polysynaptic Reflex Potentials Research Articles

Bisphenol A depresses monosynaptic and polysynaptic reflexes in neonatal rat spinal cord in vitro involving estrogen receptor-dependent NO-mediated mechanisms

Bisphenol A (BPA), a toxic chemical from plastics, is known to produce locomotor abnormalities which may imply the alteration in synaptic activity at Ia-α motoneuron synapse also. However the effect of BPA on this synapse is not known. Therefore, this study was undertaken to examine the effect of BPA on reflexes originating at Ia-α motoneuron synapse in the spinal cord. The experiments were performed on isolated hemisected spinal cords from 4 to 6d rats. Stimulation of a dorsal root evoked segmental monosynaptic (MSR) and polysynaptic (PSR) reflex potentials in the corresponding ventral root. Nitrite content (indicator of NO activity) of cords was estimated in the presence of BPA with/without antagonists. Superfusion of BPA (3–100μM) depressed the reflexes in a concentration- and time-dependent manner. The depression was ∼20, ∼50 and ∼70% at 10, 30 and 100μM of BPA, respectively. The 50% depression occurred around 15min at 30μM of BPA. Pretreatment with estrogen receptor (ERα) antagonist, tamoxifen, blocked the BPA-induced depression of reflexes, whereas, 17β-estradiol, ER agonist, did not depress the reflexes even up to 10μM. Further, pretreatment with Nω-Nitro-l-arginine methyl ester hydrochloride (l-NAME) or hemoglobin (Hb) blocked the BPA-induced depression of spinal reflexes. Nitric oxide (NO) donor sodium-nitroprusside depressed the MSR and PSR in a concentration-dependent manner. The nitrite concentration of the cords exposed to BPA was 733μM/gm of tissue (three times the saline group). Pretreatment with tamoxifen/l-NAME/Hb blocked the BPA-induced increase of nitrite levels. The present observations indicate that BPA depressed spinal synaptic transmission through ERα-dependent NO-mediated mechanisms. The altered synaptic activity may implicate for neurobehavioral locomotor abnormalities after exposure to BPA.

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Bisphenol A (BPA), a toxic chemical from plastics, is known to produce locomotor abnormalities which may imply the alteration in synaptic activity at Ia-α motoneuron synapse also. However the effect of BPA on this synapse is not known. Therefore, this study was undertaken to examine the effect of BPA on reflexes originating at Ia-α motoneuron synapse in the spinal cord. The experiments were performed on isolated hemisected spinal cords from 4 to 6 d rats. Stimulation of a dorsal root evoked segmental monosynaptic (MSR) and polysynaptic (PSR) reflex potentials in the corresponding ventral root. Nitrite content (indicator of NO activity) of cords was estimated in the presence of BPA with/without antagonists. Superfusion of BPA (3–100 μM) depressed the reflexes in a concentration- and time-dependent manner. The depression was ∼20, ∼50 and ∼70% at 10, 30 and 100 μM of BPA, respectively. The 50% depression occurred around 15 min at 30 μM of BPA. Pretreatment with estrogen receptor (ERα) antagonist, tamoxifen, blocked the BPA-induced depression of reflexes, whereas, 17β-estradiol, ER agonist, did not depress the reflexes even up to 10 μM. Further, pretreatment with Nω-Nitro-l-arginine methyl ester hydrochloride (l-NAME) or hemoglobin (Hb) blocked the BPA-induced depression of spinal reflexes. Nitric oxide (NO) donor sodium-nitroprusside depressed the MSR and PSR in a concentration-dependent manner. The nitrite concentration of the cords exposed to BPA was 733 μM/gm of tissue (three times the saline group). Pretreatment with tamoxifen/l-NAME/Hb blocked the BPA-induced increase of nitrite levels. The present observations indicate that BPA depressed spinal synaptic transmission through ERα-dependent NO-mediated mechanisms. The altered synaptic activity may implicate for neurobehavioral locomotor abnormalities after exposure to BPA.

Involvement of NO-guanylyl cyclase pathway for the depression of spinal monosynaptic reflex by Mesobuthus tamulus venom in neonatal rat in vitro

AimsThe present study was undertaken to evaluate the role of nitric oxide (NO) in Mesobuthus tamulus (MBT) venom-induced depression of spinal reflexes. Main methodsExperiments were performed on isolated hemisected spinal cords from 4 to 6day old rats. Stimulation of a dorsal root with supramaximal strength evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root. Key findingsSuperfusion of MBT venom (0.3μg/ml) depressed the spinal reflexes in a time-dependent manner and the maximum depression was seen at 10min (MSR by 63%; PSR by 79%). The time to produce 50% depression (T-50) of MSR and PSR was 7.7±1.3 and 5.7±0.5min, respectively. Pretreatment with bicuculline (1μM; GABAA receptor antagonist) or strychnine (1μM; glycineA receptor antagonist) did not block the venom-induced depression of spinal reflexes. However, Nω-nitro-L-arginine methyl ester (L-NAME, 100 or 300μM; NO synthase inhibitor) or hemoglobin (Hb, 100μM; NO scavenger) antagonized the venom-induced depression of MSR. Further, soluble guanylyl cylase inhibitors (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one, ODQ; 1μM or methylene blue, 100μM) also antagonized the venom-induced depression of MSR but not PSR. Nitrite concentration (indicator of NO activity) of the cords exposed to venom (0.3μg/ml) was not different from the control group. SignificanceThe results indicate that venom-induced depression of MSR is mediated via NO-guanylyl cyclase pathway without involving GABAergic or glycinergic system.

Involvement of 5-hydroxytryptaminergic transmission for the Mesobuthus tamulus venom-induced depression of spinal reflexes in neonatal rat in vitro

Mesobuthus tamulus (MBT) venom is shown to depress the spinal reflexes through a mechanism unrelated to the NMDA receptors. 5-Hydroxytryptamine (5-HT) is another excitatory transmitter in the spinal cord therefore, the present study was undertaken to examine the involvement of 5-HT in the venom-induced depression of reflexes. The experiments were performed on isolated hemisected spinal cords from 4 to 6-day-old rats. Stimulation of a dorsal root with supramaximal strength evoked monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root. MBT venom (0.3 μg/ml) depressed the spinal reflexes in a time-dependent manner and the maximal depression was seen at 10 min. The time to produce 50% depression (T-50) of MSR and PSR was 8.1 ± 1.41 and 6.8 ± 0.5 min, respectively. Pretreatment with pindolol (1 μM; 5-HT 1A/1B receptor antagonist) blocked the reflexes up to 15 min. On the other hand, ketanserin (10 μM; 5-HT 2A/2C receptor antagonist) or ondansetron (0.1 μM; 5-HT 3 receptor antagonist) blocked the venom-induced depression of MSR and PSR during entire exposure time (30 min). The 5-HT concentration of the cords exposed to venom (1.6 ± 0.04 μg/g tissue) was significantly greater than the control group (0.98 ± 0.08 μg/g tissue). The results indicate that venom-induced depression of spinal reflexes is mediated via 5-HTergic transmission involving 5-HT 1A/1B, 5-HT 2A/2C and 5-HT 3 receptors.

Indian red scorpion venom depresses spinal synaptic transmission without involving NMDA receptors

Stings of Indian red scorpion (Mesobuthus tamulus, MBT) produce neurological abnormalities such as convulsions and paralysis. These parameters indicate the activity at alpha-motoneuron. The present study was therefore, undertaken to evaluate the effect of MBT-venom on spinal reflexes and the involvement of N-methyl-d-aspartate (NMDA) receptors. The experiments were performed on isolated hemisected spinal cords from 4 to 6 days old rats. Stimulation of a dorsal root with supramaximal strength at 0.1Hz evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root. Superfusion of MBT-venom depressed the spinal reflexes in a time- and a concentration-dependent (0.1-1microg/ml) manner. MBT-venom at 0.1, 0.3 and 1.0microg/ml produced maximal depression of 55, 75 and 90% at 30, 10 and 7min, respectively. The time required to produce 50% depression (T-50) of MSR was 19.0, 8.0, and 3.6min and for PSR was 15.0, 5.6, and 2.9min at 0.1, 0.3 and 1microg/ml of venom, respectively. Pre-treatment with DL-alpha-2-amino-5-phosphonovaleric acid (APV) decreased MSR by 26% and abolished PSR. In the presence of APV, the MBT-venom-induced depression of MSR was not different from the venom only group. The results indicate that venom-induced depression of spinal reflexes did not involve NMDA receptors.

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 (0.3–50μM) in the Mg2+-free medium depressed the MSPand PSP in a concentration-dependent manner. At 30μM of 5-HT, the depression was 57% and 95% for MSP and PSP, respectively, and no further depression was seen at 50μM. 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-HT2A/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+ (1.3mM) to the medium abolished the PSP and decreased the MSPby 30%. In the presence of Mg2+, 5-HT (1–50μM) also depressed the MSP in a concentration-dependent manner. At 10μM of 5-HT, there was approximately 20% depression and at 50μM 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-HT2A/2C in the presence of Mg2+ when NMDA receptors are in the closed state.

3-Nitropropionic acid-induced depression of spinal reflexes involves mechanisms different from ischemia-induced depression

Effect of 3-nitropropionic acid (3-NPA) and ischemia (glucose- and O 2-free solution) on synaptic transmission in hemisected spinal cord from 4 to 8 day old rats was examined in vitro. Stimulation of a dorsal root (L3-5 segments) evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the segmental ventral root. Superfusion of 3-NPA (0.17–3.4 mM) depressed the reflexes in a concentration- and time-dependent manner. At 3.4 mM of 3-NPA, the reflexes were abolished by 35 min. Time required to produce 50% depression (T-50) was around 170, 80, 40 and 17 min for MSR and 110, 70, 25 and 16 min for PSR at 0.17, 0.51, 1.7 and 3.4 mM of 3-NPA, respectively. Ischemia also produced a time-dependent depression of reflexes and abolished them by 35 min and the T-50 values were around 18 min. Presence of creatine phosphate (10 mM) in the superfusing medium did not alter the time course of 3-NPA-induced depression of reflexes but prolonged the ischemia-induced depression. dl-2-amino-5-phosphonovaleric acid (NMDA receptor antagonist; 10 μM) failed to block the 3-NPA (3.4 mM)-induced depression of reflexes, but blocked the ischemia-induced depression. The results indicate that 3-NPA-induced depression of spinal reflexes does not involve NMDA receptors and is different from ischemia-induced depression.

3-Nitropropionic acid depresses spinal reflexes involving GABAergic and glycinergic transmission in neonatal rat spinal cord in vitro

Aims 3-Nitropropionic acid (3-NPA) is a naturally occurring fungal toxin that leads to ATP-depletion by inhibiting mitochondrial succinate dehydrogenase and produces chemical anoxia. The present study was conducted to identify the involvement of inhibitory system in 3-NPA-induced depression of spinal reflexes. Methods The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials were recorded at ventral root by stimulating the corresponding dorsal root in hemisected (sagitally) spinal cord from 4–8 day old rats. Effect of 3-NPA in the absence and presence of antagonists was evaluated on the reflexes. Key findings Superfusion of 3-NPA (3.4 mM) depressed the reflexes in a time-dependent manner abolishing them by 35 min. The T-50 values were around 18 and 16 min for MSR and PSR, respectively. An NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (10 μM) failed to block the 3-NPA (3.4 mM)-induced depression of reflexes. Superfusion of bicuculline (GABA A receptor antagonist; 1 μM), or strychnine (glycine A receptor antagonist; 1 μM) antagonized the 3-NPA-induced depression of reflexes significantly. The T-50 values were 26 and 30 min in bicuculline and strychnine pretreated groups, respectively and were significantly greater than 3-NPA only group. Significance The results indicate that 3-NPA-induced depression of spinal reflexes is partially mediated by GABAergic and glycinergic inhibitory transmission.

3-Nitropropionic acid-induced depression of spinal reflexes does not involve 5-hydroxytryptaminergic system in contrast to ischemia-induced depression in neonatal rat spinal cord in vitro

The involvement of 5-hydroxytryptaminergic (5-HTergic) system for the 3-nitropropionic acid (3-NPA)-induced depression of spinal reflexes was evaluated and compared with other energy deficiency condition (ischemia; glucose-free and O 2-free). The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials were recorded at ventral root by stimulating the corresponding dorsal root in neonatal rat spinal cord in vitro. Superfusion of 3-NPA (3.4 mM) or ischemic solution depressed the reflexes in a time-dependent manner abolishing them by 35 min. Pretreatment with pindolol (1 μM), ketanserin (10 μM) or ondansetron (0.1 μM); 5-HT 1, 5-HT 2, or 5-HT 3 receptor antagonist, respectively, did not block the 3-NPA-induced depression of reflexes whereas, ischemia-induced depression was blocked by ondansetron. 5-HT content of the spinal cords incubated with 3-NPA (3.4 mM) for 30 min was decreased significantly (33 ng/g tissue) while increased (286 ng/g) in cords exposed to ischemic solution as compared to saline-treated cords (161 ng/g). Thus, 3-NPA-induced depression of spinal reflexes does not involve 5-HTergic pathway unlike ischemia-induced depression.

Zinc modulates primary afferent fiber-evoked responses of ventral roots in neonatal rat spinal cord in vitro

Zinc ions (Zn 2+) are known to modulate the functions of a variety of channels, receptors and transporters. We examined the effects of Zn 2+ on the reflex potentials evoked by electrical stimulation and responses to depolarizing agents in the isolated spinal cord of the neonatal rat in vitro. Zn 2+ at low concentrations (0.5–2μM) inhibited, but at high concentrations (5 and 10μM) augmented, a slow depolarizing component (slow ventral root potential). Zn 2+ had no effect on fast components (monosynaptic reflex potential; fast polysynaptic reflex potential). Unlike Zn 2+, strychnine (5μM), a glycine receptor antagonist, and ( S),9( R)-(−)-bicuculline methobromide (10μM), a GABA A receptor antagonist, potentiated both fast polysynaptic reflex potential and slow ventral root potential. Zn 2+ (5μM) did not affect depolarizing responses to glutamate and N-methyl- d-aspartate. Zn 2+ enhanced the substance P-evoked depolarization in the absence of tetrodotoxin (0.3μM) but not in its presence. The dorsal root potential was inhibited by ( S),9( R)-(−)-bicuculline methobromide (10μM) but not by Zn 2+ (5μM). The Zn 2+-potentiated slow ventral root potential was inhibited by the N-methyl- d-aspartate receptor antagonists, ketamine (10μM) and dl-2-amino-5-phosphaonovaleric acid (50μM) but not by P2X receptor antagonists, pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid (30μM) and 2′,3′- O-(2,4,6-trinitrophenyl)ATP (10μM). Ketamine (10μM) and dl-2-amino-5-phosphaonovaleric acid (50μM) almost abolished spontaneous activities increased by Zn 2+. It is concluded that Zn 2+ potentiated slow ventral root potential induced by primary afferent stimulation, which was mediated by the activation of N-methyl- d-aspartate receptors but not by activation of P2X receptors or blockade of glycinergic and GABAergic inhibition. Zn 2+ does not seem to directly affect N-methyl- d-aspartate receptors. The release of glutamate from interneurons may play an important role in Zn 2+-induced potentiation of slow ventral root potential in the spinal cord of the neonatal rat.

Aglycemia and ischemia depress monosynaptic and polysynaptic reflexes in neonatal rat spinal cord in vitro by involving different types of 5-hydroxytryptamine receptors

Involvement of 5-hydroxytryptaminergic (5-HT) system for aglycemia- and ischemia-induced depression of the spinal reflexes was evaluated. The monosynaptic (MSR) and polysynaptic (PSR) reflex potentials were elicited in the ventral root by stimulating the corresponding dorsal root in an isolated spinal cord from neonatal rat. Superfusion of aglycemic (glucose-free) or ischemic (glucose- and O 2-free) solution produced a time-dependent depression of the spinal reflexes and abolished them within 35 min. The time required to produce 50% depression of the reflexes (T-50) was around 19 and 13 min for aglycemia and ischemia, respectively. Spiperone (5-HT 2A antagonist) and ketanserin, (5-HT 2A/2C antagonist) blocked the aglycemia-induced depression of the reflexes completely while ondansetron (5-HT 3 antagonist) attenuated it partially (as abolition times were around 50 min). Ischemia-induced depression was blocked up to 50 min by ketanserin or ondansetron but not by spiperone. In the presence of ketanserin or ondansetron, the reflexes were abolished by 60 min while in spiperone the reflexes were abolished by 30 min. In 5,7-dihydroxytryptamine treated rats, aglycemia depressed the reflexes by 45 min (greater than control, P < 0.05) while the time for ischemia-induced depression was not different from the control response. The results indicate that aglycemia involves mainly 5-HT 2 receptors while ischemia involves 5-HT 3 receptors.

Endogenous GABA Does Not Mediate the Inhibitory Effects of Gabapentin on Spinal Reflexes in Rats

The novel antiepileptic drug gabapentin was designed as a structural analog of γ-aminobutyric acid (GABA). However, its mechanism of action remains unclear. In the present study, we investigated the effect of gabapentin on spinal reflexes in anesthetized rats. The mono- and polysynaptic reflex potentials were recorded from the ipsilateral L5 ventral root after stimulation of the L5 dorsal root. The dorsal root reflex potential, an index of presynaptic inhibition, was recorded from the ipsilateral L4 dorsal root. In non-spinalized (intact) and spinalized rats, intravenously administered gabapentin reduced the mono- and polysynaptic reflex potentials in a dose-dependent manner. These inhibitory effects of gabapentin were not suppressed by the GABAA antagonist picrotoxin. Moreover, gabapentin also decreased spinal reflexes in spinalized rats depleted of spinal GABA with semicarbazide, an inhibitor of the GABA-synthesizing enzyme. The dorsal root reflex potentials were not affected by gabapentin. These results suggest that endogenous GABA does not mediate the inhibitory effects of gabapentin on spinal reflexes.

Deprenyl blocks the aglycemia-induced depression of the synaptic transmission but not the ischemia-induced depression in neonatal rat spinal cord in vitro

The protective action of R-(−)-deprenyl against the aglycemia (glucose-free) and the ischemia (glucose-free and O 2-free)-induced changes in the synaptic transmission was investigated. The in vitro “glucose-free and O 2-free” condition mimics in vivo ischemia where there is a deficiency of O 2 and energy substrate, hence the term ischemia was used. The monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials were elicited in the ventral root by stimulating the corresponding dorsal root in an isolated spinal cord from the neonatal rat. Aglycemia and ischemia depressed the spinal reflexes in a time-dependent manner and abolished them within 30 min. The 50% depression of the reflexes (T-50) occurred around 25 min for aglycemia and 15 min for ischemia. Creatine phosphate, an energy supplement, attenuated the aglycemia- and ischemia-induced depression of the reflexes. The T-50 values for both the reflexes were around 40 and 25 min for aglycemia and ischemia, respectively. Deprenyl (10 μM) blocked the aglycemia-induced depression completely but failed to block the ischemia-induced depression. The present results indicate that aglycemia and ischemia abolished the synaptic transmission simultaneously and energy supplementation partially attenuated the depression. The protective effects of deprenyl against aglycemia may not be due to its MAO-B action and suggest for the involvement of non-MAO-B mechanisms.

Involvement of the GABAergic system for Ptychodiscus brevis toxin-induced depression of synaptic transmission elicited in isolated spinal cord from neonatal rats

The involvement of inhibitory transmitters for Ptychodiscus brevis toxin (PbTx)-induced depression of spinal synaptic transmission in neonatal rats was investigated. Stimulation of a dorsal root evoked monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials in the segmental ventral root. The PbTx depressed the reflexes in a concentration-dependent manner and the depression was blocked by GABA A antagonist, bicuculline (1 μM). GABA also produced depression of the reflexes in a concentration-dependent manner. Simultaneous application of submaximal concentrations of PbTx (28 μM) and GABA (30 μM) enhanced the depression (>75%). In contrast, PbTx alone (28 μM) depressed the MSR and the PSR by 33 and 47%, respectively, and GABA (30 μM) alone depressed the reflexes by 30%. The N-methyl- d-aspartate receptor antagonist, dl-2-amino-5-phosphono-pentanoic acid (10 μM), blocked the PbTx-induced depression of MSR and also the enhancement of GABA response by PbTx. A glycine receptor antagonist, strychnine (1 μM), failed to block the depression by the toxin up to 28 μM; however, the depression was attenuated significantly at 84 μM of the toxin. The results indicate that PbTx depressed the spinal reflexes via GABA A receptors. Furthermore, the potentiation of GABAergic action by PbTx requires the N-methyl- d-aspartate dependent mechanism.

Tricyclic analogs cyclobenzaprine, amitriptyline and cyproheptadine inhibit the spinal reflex transmission through 5-HT 2 receptors

The centrally acting muscle relaxant cyclobenzaprine decreases the amplitude of monosynaptic reflex potentials by inhibiting the facilitatory descending serotonergic influences in the spinal cord. Interestingly, the structure of cyclobenzaprine is much similar to those of amitriptyline and cyproheptadine. In the present study, we attempted to elucidate the relationship between 5-HT 2 receptor antagonistic and inhibitory effects of cyclobenzaprine, amitriptyline, cyproheptadine and ketanserin on the spinal reflexes. Cyclobenzaprine, amitriptyline, cyproheptadine, and ketanserin significantly inhibited facilitatory effects of 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on flexor reflexes and mono- and polysynaptic spinal reflex potentials in spinalized rats. In intact rats, these drugs significantly reduced the mono- and polysynaptic reflex potentials. 5-HT depletion significantly prevented the depression of the spinal reflex potentials induced by these drugs. These results suggest that the inhibitory effects of cyclobenzaprine, amitriptyline, and cyproheptadine on mono- and polysynaptic reflex potentials are due to the inhibition of descending serotonergic systems through 5-HT 2 receptors in the spinal cord.

Involvement of N-methyl- D-aspartate receptors for the Ptychodiscus brevis toxin-induced depression of monosynaptic and polysynaptic reflexes in neonatal rat spinal cord in vitro

The effects of Ptychodiscus brevis toxin (PbTx) on the Ia-α motoneuron synaptic transmission in neonatal rat spinal cord in vitro was examined. The stimulation of a dorsal root evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the segmental ventral root in Mg 2+-free medium. Superfusion with PbTx (2.8–84 μM) depressed the MSR and the PSR in a concentration-dependent manner. At 2.8 μM of PbTx, the depression of MSR and PSR was 24±8.3% and 37±9.7%, respectively. The maximal depression was seen at 84 μM of the toxin (78% for MSR and 96% for PSR). The concentration of toxin required to produce 50% depression was 28.3±6.4 μM for MSR and 5.5±1.1 μM for PSR. The PbTx (28 μM) did not alter the magnitude of the dorsal root or the ventral root potentials. Addition of MgSO 4 (1.3 mM) or DL-2-amino-5-phosphonovaleric acid (APV; 10 μM) to the physiological solution abolished the PSR totally and decreased the MSR by about 30%. In both the conditions, the PbTx-induced depression of the MSR was attenuated significantly. The PbTx-induced depression was blocked completely in the presence of APV+6-cyano-7-nitroquinoxaline-2,3-dione (0.1 μM). NMDA (1 μM) by itself did not alter the magnitude of MSR or PSR but enhanced the PbTx-induced depression (28 μM) of PSR significantly. 7-Chlorokynurenic acid (3 μM; glycine B antagonist) did not block the PbTx-induced depression of MSR. D-serine (glycine B agonist) did not reverse the PbTx-induced depression of reflexes although it reversed the 7-chlorokynurenic acid-induced depression of PSR. The results indicate that the PbTx depressed the spinal reflexes without altering the magnitude of dorsal root or ventral root activity. The depression of the PSR involved NMDA receptors while that of the MSR involved NMDA and non-NMDA receptors. The PbTx actions did not involve the glycine B site of the NMDA receptor.

Method for Recording Spinal Reflexes in Mice: Effects of Thyrotropin-Releasing Hormone, DOI, Tolperisone and Baclofen on Monosynaptic Spinal Reflex Potentials

Mice were used to record the spinal reflex potentials and to examine the effects of some drugs upon them. In anesthetized mice, laminectomy was performed in the lumbo-sacral region, and monosynaptic reflex potential (MSR) and polysynaptic reflex potential were recorded from the L5 ventral root after stimulation of the L5 dorsal root. Thyrotropin-releasing hormone (TRH) and 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI) produced transient and long-lasting increases in the MSR amplitude, respectively. Tolperisone hydrochloride and baclofen produced transient and long-lasting MSR depressions, respectively. These results show that mice can be used to record spinal reflex potentials, and that it may be possible to study the spinal cord function of mutant and knockout mice using this method.

Effects of a new centrally acting muscle relaxant, NK433 (lanperisone hydrochloride) on spinal reflexes

(−)-( R)-2-methyl-3-(1-pyrrolidinyl)-4′-trifluoromethylpropiophenone monohydrochloride, lanperisone hydrochloride (NK433) administered intravenously or orally depressed the mono- and polysynaptic reflex potential, dorsal root reflex potential, flexor reflex mediated by group II afferent fibers, patellar and flexor reflexes. These effects were reduced by spinal transection. NK433 inhibited the facilitation of the flexor reflex mediated by group II afferent fibers that was induced by intrathecal administration of noradrenaline–HCl. (+)-(1 R,2 R)-2-methyl-3-(1-pyrrolidinyl)-1-(4-trifluoromethylphenyl)-1-propanol (LPS-9)–HCl, a metabolite of NK433, also inhibited the spinal reflexes. Given orally, NK433 had effects more than three times stronger and tending to be longer-lasting than those of eperisone–HCl. These results suggest that NK433 exerts a non-selective inhibition on spinal reflexes and that inhibition of the descending noradrenergic tonic facilitation within the spinal cord is involved in the mechanism of spinal reflex depression by NK433. LPS-9 could contribute to the potent activity of NK433 after oral administration.

Inhibition of nitric oxide synthesis accelerates the recovery of polysynaptic reflex potentials after transient spinal cord ischemia in cats.

Nitric Oxide (NO) has been implicated as a mediator of neuronal injury in vascular stroke. On the other hand, NO is suggested to play a neuroprotective role by increasing blood flow during cerebral ischemia. In order to evaluate the role of NO in the spinal cord ischemia, effects of nitric oxide synthase (NOS) inhibition on the recovery of reflex potentials after a transient spinal cord ischemia were examined in urethane-chloralose anesthetized spinal cats. Spinal cord ischemia was produced by occlusion of the thoracic aorta and the both internal mammary arteries for 10 min. Regional blood flow (RBF) in the spinal cord was continuously measured with a laser-Doppler flow meter. The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials elicited by electrical stimulation of the tibial nerve, were recorded from the L7 or S1 ventral root. The recovery process of spinal reflex potentials was reproducible when the oclusion was repeated twice at an interval of 120 min. Pretreatment with N(G)-monomethyl-L-arginine (L-NMMA, 10 mg/kg), a NOS inhibitor significantly accelerated the recovery of PSR potentials after spinal cord ischemia. The accelerating effect of L-NMMA on the recovery of PSR potentials was abolished by co-administration of L-arginine (1 mg/kg/min) but not by that of D-arginine (1 mg/kg/min). L-NMMA failed to improve RBF in the spinal cord during ischemia and reperfusion. Nitroprusside (10 microg/kg/min), a NO donor, retarded the recovery of PSR potentials after spinal cord ischemia. These results suggest that NO production has a significant influence on the functional recovery after transient spinal cord ischemia.

Effects of central nervous stimulants on spino-bulbo-spinal reflex potentials in cats.

Effects of central nervous stimulants on the spino-bulbo-spinal reflex potential were evaluated in anesthetized intact cats, and compared with those on segmental spinal reflex potentials in anesthetized spinal cats. In spinal cats, strychnine augmented polysynaptic reflex potential, picrotoxin inhibited dorsal root reflex potential, aminopyrine potentiated mono- and poly-synaptic reflex potentials but inhibited dorsal root reflex potential, and 4-aminopyridine potentiated all the three types of segmental reflex potentials. A combination of fenbufen, a non-steroidal antiinflammatory agent, and enoxacin, a new quinolone antimicrobial, inhibited all the three types of segmental reflex potentials. In contrast, all these drugs consistently produced an augmentation of the spino-bulbo-spinal reflex potential in anesthetized intact cats. From these findings, we suggest that the spino-bulbo-spinal reflex potential may be used as an electrophysiological parameter for the evaluation of central nervous stimulants.