Reflex In Spinal Rats Research Articles

Intramuscular Neurotrophin-3 normalizes low threshold spinal reflexes, reduces spasms and improves mobility after bilateral corticospinal tract injury in rats.

Brain and spinal injury reduce mobility and often impair sensorimotor processing in the spinal cord leading to spasticity. Here, we establish that complete transection of corticospinal pathways in the pyramids impairs locomotion and leads to increased spasms and excessive mono- and polysynaptic low threshold spinal reflexes in rats. Treatment of affected forelimb muscles with an adeno-associated viral vector (AAV) encoding human Neurotrophin-3 at a clinically-feasible time-point after injury reduced spasticity. Neurotrophin-3 normalized the short latency Hoffmann reflex to a treated hand muscle as well as low threshold polysynaptic spinal reflexes involving afferents from other treated muscles. Neurotrophin-3 also enhanced locomotor recovery. Furthermore, the balance of inhibitory and excitatory boutons in the spinal cord and the level of an ion co-transporter in motor neuron membranes required for normal reflexes were normalized. Our findings pave the way for Neurotrophin-3 as a therapy that treats the underlying causes of spasticity and not only its symptoms.

Involvement of Supraspinal Imidazoline Receptors and Descending Monoaminergic Pathways in Tizanidine-Induced Inhibition of Rat Spinal Reflexes

The neuronal pathways involved in the muscle relaxant effect of tizanidine were examined by measurement of spinal reflexes in rats. Tizanidine (i.v. and intra-4th ventricular injection) decreased the mono- and disynaptic (the fastest polysynaptic) reflexes (MSR and DSR, respectively) in non-spinalized rats. Depletion of central noradrenaline by 6-hydroxydopamine abolished the depressant effect of tizanidine on the MSR almost completely and attenuated the effect on the DSR. Co-depletion of serotonin by 5,6-dihydroxytryptamine and noradrenaline resulted in more prominent attenuation of tizanidine-induced inhibition of the DSR. Supraspinal receptors were then studied using yohimbineand some imidazoline-receptor ligands containing an imidazoline moiety. Idazoxan (I1, I2, I3, and α2), efaroxan (I1, I3, and α2), and RX821002 (I3 and α2), but not yohimbine, an α2-adrenergic receptor antagonist with no affinity for I receptors, antagonized the inhibitory effects of tizanidine. Thus, supraspinal I receptors (most likely I3) and descending monoaminergic influences are necessary for tizanidine-induced inhibition of spinal segmental reflexes.

GABAB Receptors Do Not Mediate the Inhibitory Actions of Gabapentin on the Spinal Reflex in Rats

The clinical effectiveness of gabapentin for the treatment of epilepsy, spasticity, and neuropathic pain has been established. The mechanisms responsible for those actions, however, are still not clearly understood. We have recently demonstrated that gabapentin reduces the spinal reflex in rats via mechanisms that do not involve γ-aminobutyric acid (GABA)A receptors. In the study, we attempted to explore the involvement of GABAB receptors in gabapentin-induced inhibition of the spinal reflexes in spinalized rats. Stimulation of the dorsal root at L5 elicited the segmental mono- (MSR) and polysynaptic reflex (PSR) in the ipsilateral ventral root. The microinjection of gabapentin (1.5 and 5 nmol) into the ventral horn reduced both MSR and PSR, whereas the injection into the dorsal horn only inhibited the PSR, indicating that systemic gabapentin inhibits the MSR at the ventral horn and it inhibits the PSR at both the ventral and dorsal horns. The GABAB-receptor antagonist CGP35348 (0.5 nmol) injected into the ventral horn antagonized the inhibition of the spinal reflexes by the GABAB-receptor agonist baclofen (i.v.) but not by gabapentin (i.v.). Thus, GABAB receptors do not appear to contribute to the gabapentin-induced inhibition of the spinal reflex.

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.

Study of 5-HT receptors involved in the effect of (R)-8-OH-DPAT on the monosynaptic spinal reflex in rats

Study of 5-HT receptors involved in the effect of (R)-8-OH-DPAT on the monosynaptic spinal reflex in rats

Differential effects of ( R)- and ( S)-8-hydroxy-2-(di- n-propylamino)tetralin on the monosynaptic spinal reflex in rats

We examined the effects of ( R)- and ( S)-8-hydroxy-2-(di- n-propylamino)tetralin hydrobromide (8-OH-DPAT) on the monosynaptic spinal reflex in rats. In intact rats, ( R)-8-OH-DPAT (10 μg/kg, i.v.) enhanced the amplitude of the monosynaptic reflex, whereas at 100 μg/kg, it reduced the amplitude. ( S)-8-OH-DPAT enhanced the monosynaptic reflex dose-dependently. In spinalized rats, ( R)-8-OH-DPAT produced dose-dependent inhibition, but the ( S)-enantiomer did not affect the monosynaptic reflex. Pretreatment with spiroxatrine or 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190) inhibited ( R)-8-OH-DPAT-induced monosynaptic reflex enhancement in intact rats, as did 5-hydroxytryptamine (5-HT) depletion. Ketanserin reduced the effect of ( R)-8-OH-DPAT. These pretreatment regimens had no effect on the monosynaptic reflex depression produced by the ( R)-enantiomer in intact and spinalized rats. Pretreatment with prazosin inhibited ( S)-8-OH-DPAT-induced monosynaptic reflex enhancement in intact rats, as did noradrenaline and 5-HT depletion. These results suggest that supraspinal 5-HT 1A receptors and the descending serotonergic system are involved in the stimulatory effect of ( R)-8-OH-DPAT on the monosynaptic reflex, while both the descending serotonergic and noradrenergic systems, the latter acting via α 1-adrenoceptors, are involved in the effect of the ( S)-enantiomer on this reflex.

The influence of 5-ht receptor antagonists to (R)- and (S)-8-OH-DPAT-induced effects on spinal reflexes in rats

The influence of 5-ht receptor antagonists to (R)- and (S)-8-OH-DPAT-induced effects on spinal reflexes in rats

250 The influence of 5-HT receptor antagonists to (R)- and (S)-8-OH-DPAT-induced effects on spinal reflexes in rats

250 The influence of 5-HT receptor antagonists to (R)- and (S)-8-OH-DPAT-induced effects on spinal reflexes in rats

N-Methyl- d-aspartate and α2-adrenergic mechanisms are involved in the depressent action of flupirtine on spinal reflexes in rats

In urethane-chloralose anesthetised rats the muscle relaxant activity of flupirtine was investigated on the monosynaptic Hoffmann reflex recorded from plantar foot muscles and on the polysynaptic flexor reflex recorded from tibialis muscle. Intraperitoneal (i.p.; 2.5–25 μmol/kg) and intrathecal (i.t.; 33–330 nmol) administration of flupirtine depressed the polysynaptic flexor reflex in anesthetised rats in a dose-dependent manner without affecting the monosynaptic Hoffmann reflex. Flupirtine produced a similar pattern on spinal reflexes as NMDA receptor antagonists, such as (−)-2-amino-7-phosphonoheptanoic acid (500 nmol i.t.) and memantine (125 μmol/kg i.p.), the benzodiazepines diazepam (18 μmol/kg i.p.) and midazolam (80 nmol i.t.), and the α 2-adrenoceptor agonist tizanidine (2 μmol/kg). In contrast, the GABA A receptor agonist muscimol (21 μmol/kg i.p.; 20 nmol i.t.) and the GABA B receptor agonist baclofen (47 μmol/kg i.p.; 2 nmol i.t.) reduced the magnitude of both the flexor and the Hoffmann reflex, whereas the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 nmol i.t.) depressed the Hoffmann reflex without affecting the flexor reflex. The effect of i.t. injection of flupirtine was prevented by coadministration of the mixed α 1 α 2- adrenoceptor antagonist yohimbine (10 nmol) and the excitatory amino acid N-methyl- d-aspartate (NMDA; 0.1 nmol), but neither by coadministration of the α 1-adrenoceptor antagonist prazosine (10 nmol), the GABA A receptor antagonist bicuculline (1 nmol), the GABA B receptor antagonist phaclofen (100 nmol), the non-NMDA receptor agonist α-amino-3-hydroxy-5-tertbutyl-4-isoxazolepropionic acid (ATPA; 0.1 pmol) nor by pre-treatment with the benzodiazepine receptor antagonist flumazenil (16 μmol/kg). These observations suggest that α 2-adrenoceptors and NMDA receptors might be involved in the mediation of the muscle relaxant activity of flupirtine. The presumed NMDA receptor antagonistic effect of flupirtine would be of particular clinical relevance, since flupirtine is free of typical side effects of NMDA receptor antagonists.

Effects of TA-0910, an orally active TRH analog, on the spinal reflex in spinal rats

Effects of TA-0910 (1-methyl-(S)-4,5-dihydroorotyl-L-histidyl-L-prolinamide), a new thyrotropin releasing hormone (TRH) analog, on spinal reflex potentials and flexor reflexes were compared with those of TRH in C1-spinal rats. Intravenously administered TA-0910 and TRH produced dose-dependent increases in the amplitudes of mono- and polysynaptic reflex potentials and withdrawal flexor reflexes. TA-0910 was more potent and more long-lasting than TRH. The stimulating actions of TA-0910 and TRH on the monosynaptic reflex potential were not antagonized by pretreatment with atropine, cyproheptadine, haloperidol or prazosin, suggesting no involvement of the cholinergic, serotonergic, dopaminergic or noradrenergic system. Intraduodenally administered TA-0910 also produced a lasting potentiation of the withdrawal flexor reflex, but intraduodenally administered TRH showed no effect. These results suggest that TA-0910 may be a more useful drug than TRH for spinal functional disorders.

N-methyl-D-aspartate (NMDA)-mediated muscle relaxant action of dextromethorphan in rats

The present study examined whether the antitussive agent dextromethorphan, which is an antagonist at the N-methyl-D-aspartate (NMDA) receptor, depresses spinal reflexes in rats. Injection of both the specific NMDA antagonist (-)-2-amino-7-phosphonoheptanoate and of dextromethorphan dose-dependently reduced the magnitude of the polysynaptic flexor reflex without affecting the monosynaptic H-reflex. In contrast, the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione depressed the H-reflex in a dose-dependent manner without affecting the flexor reflex. The depressant effect of dextromethorphan on the flexor reflex was prevented by co-administration with NMDA but not with the non-NMDA agonist alpha-amino-3-hydroxy-5-terthyl-4-isoxazole-propionic acid. These data suggest that dextromethorphan exerts a muscle relaxant action via the NMDA receptor.

Pentamidine, an inhibitor of spinal flexor reflexes in rats, is a potent [formula omitted] (NMDA) antagonist in vivo

The present study examined whether the antimicrobial agent pentamidine exerts an antagonistic action at the N- methyl- d-aspartate (NMDA) receptor as tested on spinal reflexes in rats in vivo. After intrathecal injection both the specific NMDA antagonist (-)-2-amino-7-phosphonoheptanoate and pentamidine dose-dependently reduced the magnitude of the polysynaptic flexor reflex without affecting the monosynaptic H-reflex. In contrast, the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione depressed the H-reflex in a dose-dependent manner without affecting the flexor reflex. The depressant effect of pentamidine on the flexor reflex was prevented by coadministration with NMDA but not with the non-NMDA agonist α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid. These data suggest that pentamidine exerts an antagonistic action at the NMDA receptor in vivo.

Pharmacological Effects of Zotepine and other Antipsychotics on the Central 5-HT2Receptors

The effects of the atypical neuroleptic zotepine in comparison with clozapine, risperidone and haloperidol were examined in tests related to the central 5-HT2 activity. Zotepine, as well as clozapine and risperidone, were very potent inhibitors of the 5-HTP-induced head twitches (the behavior mediated by 5-HT2 receptors) in mice, with rank order of potency risperidone > zotepine > clozapine; haloperidol used in high doses only slightly reduced the effect of 5-HTP. Zotepine, clozapine, risperidone and haloperidol antagonized the stimulatory effects of mCPP on the hind limb flexor reflex in spinal rats. As the mCPP-induced stimulation is considered to be mediated by 5-HT2 receptors, the above results provide further evidence for the 5-HT2 antagonistic activity of the drugs studied. Te rank order of potency in that test was the same as in the 5-HTP-induced head twitches (risperidone > zotepine > clozapine). The effect of haloperidol was somewhat unspecific, since its active doses were very high. In the model of hind limb flexor reflex of spinal rats, the anti-alpha 2-adrenergic effect was also tested. Clonidine-induced stimulation of the hind limb flexor reflex (an alpha 2-adrenergic effect) was antagonized by zotepine, clozapine, risperidone and haloperidol. It may be concluded that zotepine, clozapine and risperidone show an alpha 2-adrenergic antagonistic activity (order of potency: zotepine = risperidone > clozapine). The effect of haloperidol may be considered unspecific, since it is observed at high (cataleptic) doses only. In conclusion, it appears that zotepine, as well as clozapine and risperidone, are strong 5-HT2 antagonists, while haloperidol is not.

Potentiation of spinal reflexes in rats after cerebellectomy

Potentiation of spinal reflexes in rats after cerebellectomy

Presynaptic dopaminergic inhibition of the spinal reflex in rats

Dopaminergic influence on spinal monosynaptic transmission was examined in rats. Monosynaptic mass reflex (MMR) was recorded from the ventral root L6 following supramaximal stimulation (0.2 Hz; 0.1 ms) to the ipsilateral dorsal root L6 in spinalized rat under pentobarbitone sodium (40 mg/kg i.p.) anaesthesia. MMR was inhibited by intravenous administration of the dopaminergic agonist, apomorphine (50–200 ug/kg) in a dose-dependent manner. The attenuatory effect of apomorphine (200 ug/kg i.v.) on the reflex could be reversed by the dopaminergic antagonist haloperidol (0.5 mg/kg i.v.). Under tetanic stimulation (200 Hz; 15s), the pretetanic relative inhibition induced by apomorphine (200 ug/kg i.v.) was increased only for a short period immediately after the cessation of tetanic stimulation. The results indicate existence of presynaptic dopamine receptors on the afferent terminals converging on the motoneurone which may functionally modulate the spinal motor output.

Pharmacological properties of EXP 561, a potential antidepressant drug.

The compound EXP 561 (1-amino-4-phenylbicyclo-[2,2,2]-octane), an inhibitor of the noradrenaline (NA), 5-hydroxytryptamine (5-HT) and dopamine (DA) uptake, a potential antidepressant agent, was studied in tests for evaluation of antidepressant drugs (AD). In most experiments (the apomorphine and reserpine hypothermia, the behavioural despair test, the blood pressure increases induced by NA and 5-HT) EXP 561 revealed similar activities as tricyclic AD. EXP 561 evoked stimulation of the hind limb flexor reflex in spinal rats, blocked by prazosin, metergoline and clomipramine. EXP 561 administered repeatedly in mice (twice daily for 14 days) did not evoke the adaptive changes induced by AD inhibiting the amine uptake, i.e. it did not enhance the amphetamine locomotor hyperactivity, did not potentiate the clonidine aggressiveness (at a lower dose, while at a higher one it acted less potently than when given acutely) or did not change the reserpine effect on the locomotor activity. EXP 561 showed a poor affinity to alpha 1-adrenoceptor (IC50 was 135,000 nM). The results indicate that the inability to induce adaptive changes is a feature which differentiates EXP 561 from tricyclic AD.

Involvement of noradrenergic systems in the effects of conditioning stimulation of the lower brain stem on the lumbar spinal reflex in rats

1. 1. The effects of conditioning stimulation at various positions in the pons and the medulla on the lumbar spinal monosynaptic reflex (MSR) were examined in rats. 2. 2. The conditioning stimulation facilitated the MSR. Facilitation with long latency was completely blocked by phenoxybenzamine, chlorpromazine or haloperidol. 3. 3. Phenoxybenzamine and chlorpromazine inhibited the MSR. Haloperidol, on the other hand, augmented the MSR, and this effect became more potent after the brain stem had been transected at the upper part of the medulla oblongata. 4. 4. These results suggest that pontine noradrenergic systems have a facilitatory influence on the MSR via α-adrenoceptors, and that α-blockers exert an inhibitory effect on the MSR by blocking these receptors.

O-22 - Spinal α-adrenoceptor-mediated modulation of spinal reflexes in rats

O-22 - Spinal α-adrenoceptor-mediated modulation of spinal reflexes in rats

LSD but not methysergide reduces the inhibitory effect of the medullary raphe stimulation on the spinal reflex in rats

1. 1. Conditioning stimulation of the nucleus raphe in the rat medulla enhanced the monosynaptic reflex (MSR) and depressed the polysynaptic reflex (PSR) in separate time courses. 2. 2. The PSR decreasing effect was reduced in preparations pretreated with reserpine, PCPA, or 5,6-DHT. The MSR increasing effect was not altered by these three pretreatments. 3. 3. Intravenously administered LSD but not methysergide reduced the PSR decreasing effect with no influence on the MSR increasing effect. These two drugs had similar effects on the unconditioned responses; the MSR was decreased and the PSR was increased. 4. 4. Thus, the PSR decreasing effect seems to be mediated via a serotonergic pathway probably descending from the nucleus raphe.

Central action of amitriptyline N-oxide.

The central action of amitriptyline N-oxide (AMINO) has been compared with amitriptyline (AMI) in biochemical and pharmacological studies in rats and mice. It has been found in rats that both drugs prevent 6-OH-dopamine-induced depletion of brain noradrenaline (NA). At the same time AMINO increases and AMI lowers the NA level, both being without effect on 3-methoxy-4-hydroxyphenylglycol concentrations in the brain. AMINO and AMI potentiate the depletion of 5-hydroxytryptamine (5-HT) induced by p-chloroamphetamine in the rat brain and it may be considered as evidence that both drugs do not inhibit 5-HT uptake in vivo. Neither AMINO nor AMI affects the rat brain level of 5-HT but at higher doses they elevate the 5-hydroxy-indoleacetic acid concentrations. AMINO antagonizes the head twitch reaction induced by 5-hydroxytryptophan in mice and tryptamine convulsions in rats. The hyperthermia induced by fenfluramine (in rats at a high ambient temperature) as well as the stimulation of the hind limb flexor reflex in spinal rats, induced by fenfluramine or LSD, are also inhibited. AMINO antagonizes the 5-HT-induced increase in blood pressure in pithed rats. All the above effects are similar to those induced by AMI, only the active doses of AMINO are higher. The results presented indicate that AMINO, like AMI, inhibits NA uptake and is a 5-HT antagonist.