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PubMed1982

Monosynaptic reflex depression in cats with organophosphorus neuropathy: effects of tri-o-cresyl phosphate.

The electrophysiology of organophosphorus induced delayed neurotoxicity was studied to determine the extent peripheral nerve changes affect monosynaptic reflex responses of the spinal cord. Cats were given a single dermal dose of 1500 mg/kg or two dermal doses of 500 mg/kg of tri-o-cresyl phosphate. Animals were observed for 60 days after which monosynaptic reflex (MSR) responses were recorded from L7 and S1 ventral roots after stimulation of the tibial or common peroneal nerves. Post-tetanic potentiated responses as well as ventral and dorsal root compound action potentials were also recorded. There was a significant decrease from control in the unconditioned MSR. The post-tetanic potentiated response was significantly decreased in the S1 ventral root, however, when expressed as a factor of potentiation of the unconditioned MSR, it was found to be increased, although not significantly. The dorsal and ventral root compound action potentials were also significantly decreased from control with their conduction velocities being no different from control The decrease in the unconditioned MSR as well as the dorsal and ventral root compound action potentials were attributed to peripheral nerve damage. The absence of any significant change in the post-tetanic potentiated response expressed as a factor of potentiation of the unconditioned MSR was attributed to a decrease in both the discharge zone as well as the subliminal fringe. The absence of any change in the conduction velocity indicates at least some of the large myelinated peripheral fibers were spared from significant damage.

Action Potentials↗
PubMed1993

Effects of afferent inputs from mechanical and nociceptive receptors in the footpads on the monosynaptic reflex in the spinalized cat.

We previously reported that the effects of footpad stimulation on the monosynaptic reflexes (MRs) in the cat's lumbar spinal cord depended on stimulated footpads. In this study, the effects of different types of stimulation (tonic pressure, phasic pressure, squeezing and radiant heating at 50 degrees C) on the MRs were studied in 12 adult cats spinalized at T11-12. The effects of tonic pressure were very weak or not detected. The pattern for the effects of phasic pressure was similar to that for squeezing, but the effects of squeezing was stronger than those of phasic pressure. These results indicate that effects of mechanical stimulation were mainly induced from phasic afferent inputs. Radiant heating was effective, and differential effects between mechanical stimulation and radiant heating were observed in some MRs. Our results suggest a difference in neuronal pathways from various types of receptors in the footpads.

Afferent Pathways↗
PubMed1981

[Effect of magnesium ions on presynaptic inhibition of monosynaptic reflexes].

In experiments on spinal narcotized cats perfusion of lumbosacral spinal cord through central canal with artificial cerebrospinal fluid containing high concentration (20-46 mM) of magnesium ions led to reversible depression of negative DRP as well as to depression of prolonged "presynaptic" inhibition of extensor monosynaptic reflexes produced by repetitive impulse volleys in group I flexor muscle afferents. Magnesium did not cause a depression of monosynaptic reflex discharges in spinal ventral roots.

Animals↗
PubMed1957

Monosynaptic reflex response of individual motoneurons as a function of frequency.

An assemblage of individual motoneurons constituting a synthetic motoneuron pool has been studied from the standpoint of relating monosynaptic reflex responses to frequency of afferent stimulation. Intensity of low frequency depression is not a simple function of transmitter potentiality. As frequency of stimulation increases from 3 per minute to 10 per second, low frequency depression increases in magnitude. Between 10 and approximately 60 per second low frequency depression apparently diminishes and subnormality becomes a factor in causing depression. At frequencies above 60 per second temporal summation occurs, but subnormality limits the degree of response attainable by summation. At low stimulation frequencies rhythm is determined by stimulation frequency. Interruptions of rhythmic firing depend solely upon temporal fluctuation of excitability. At high frequency of stimulation rhythm is determined by subnormality rather than inherent rhythmicity, and excitability fluctuation leads to instability of response rhythm. In short, whatever the stimulation frequency, random excitability fluctuation is the factor disrupting rhythmic response. Monosynaptic reflex response latency is stable during high frequency stimulation as it is in low frequency stimulation provided a significant extrinsic source of random bombardment is not present. In the presence of powerful random bombardment discharge may become random with respect to monosynaptic afferent excitation provided the latter is feeble. When this occurs it does so equally at low frequency and high frequency. Thus temporal summation is not a necessary factor. There is, then, no remaining evidence to suggest that the agency for temporal summation in the monosynaptic system becomes a transmitting agency in its own right.

Motor Neurons↗
PubMed1980

Monosynaptic reflexes during generalized spike and wave activity, provoked by intermittent photic stimulation.

Achilles tendon (T) and Hoffmann (H) reflexes were evoked during spike and wave activity (SWA) in 6 patients with generalized epilepsy, selected on the basis of their photosensitivity. SWA was provoked by intermittent photic stimulation (IPS). It was demonstrated that monosynaptic reflex amplitudes were larger during SWA than at rest. Although IPS caused by itself a slight increase in amplitudes, there was an obvious difference from the larger increase during SWA. T reflexes showed a more explicit increment than H reflexes. The activity changes in the spinal motor circuits were nearly always present in the absence of any clinical manifestation of motor activity. The possible mechanisms are discussed.

Adolescent↗
PubMed1983

Motor pool organization in monosynaptic reflexes: responses in three different muscles.

Recruitment order of motoneurons was measured as a function of their conduction velocities in the presence of monosynaptic reflexes evoked by dorsal root stimulation. Motoneurons were studied in three cat hindlimb muscles: medial gastrocnemius (MG), plantaris (Pl), and tibialis anterior (TA). A relationship between recruitment order and unit conduction velocity (CV) was clearly seen in all three muscles. The correlation between these two variables was lower than that found in previous studies. A CV-dependent recruitment order was most clearly sen in tibialis anterior motoneuron pool; the relationship was poorest in plantaris. Recruitment order of MG motoneurons was measured and related to their conduction velocities in response to monosynaptic reflexes evoked by L7 + S1 dorsal root stimulation. Recruitment order was then retested in the presence of rostral root stimulation (largely heteronymous) alone and again in the presence of caudal root stimulation (largely homonymous) alone. Changing the composition of the afferent input changed the critical firing levels (rank order) of some motoneurons by as much as 40% and that of others, not at all. Some motoneurons became harder to recruit and others easier; changes in recruitment order were not related to conduction velocities of the units. 1a-afferent inputs are not uniformly distributed to all the motoneurons of a pool. It appears that this nonuniformity is a determining factor in establishing a recruitment order. TA, which receives the most uniformly distributed monosynaptic input, also has the most nearly size-dependent recruitment order. Fractionation of input ca induce additional nonuniformity, and results in recruitment-order changes in some motor units that are independent of their conduction velocity. It is concluded that nonuniformity of afferent inputs, whether present or induced by experiment, can produce large recruitment-order changes among individual motoneurons in a pool and that these individual motoneurons need not share a common property such as conduction velocity or recruitment threshold in response to a control input. Therefore, arguments based on reversals in recruitment order of pairs of motor units or even changes in rank order of individual motor units do not present sufficient evidence for the presence of input specifically directed to motor units sharing a particular property.

Animals↗
PubMed1979

[Monosynaptic reflexes of the cat spinal cord during the development of insulin hypoglycemia].

Insulin-induced hypoglycemia caused depression of rhythmic monosynaptic EPSP motoneurons of the lumbar cord in acute experiments on narcotized and spinal cats. It was demonstrated that growing depression of monosynaptic transmission was associated with the exhaustion of mediator operative fraction and not with any pre- or postsynaptic delay or inhibition over a period of initial hypoglycemia when the sugar content in the blood fell to the level of 50--60 mg%. The function disturbance of postsynaptic formations of monosynaptic reflex arc of spinal cord occured in more advanced hypoglycemia.

Animals↗
PubMed1986

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.

Animals↗
PubMed1985

Changes with age in monosynaptic reflexes elicited by mechanical and electrical stimulation.

Absence of the achilles tendon reflex (T) has been reported to increase with age. Other investigators have reported no age relationship. Age changes in the Hoffmann reflex (H) have been examined in only one recent investigation. It was our purpose to compare the T and H reflexes of healthy, active old (n = 20) against young (n = 20) subjects using methods which provide stimulus-response data for both T and H. We also compared the age differences of H against T to estimate fusimotor involvement in age changes. No significant age difference were found in the response:stimulus ratio for T. Amplitude of H responses were 32.7 percent smaller in the old (P less than 0.04) and M waves were smaller by 24 percent (P less than 0.025). No significant age difference was found between mechanically and electrically elicited reflexes; and, therefore, our data do not support fusimotor involvement in the age changes of monosynaptic reflexes.

Achilles Tendon↗
PubMed1995

Reproducibility of a heteronymous monosynaptic reflex in biceps brachii.

The present study provides normal data for a new technique to assess conduction across the C5/C6 segments by recording a heteronymous monosynaptic reflex response from the contracting biceps brachii in response to stimulation of the median nerve in the cubital fossa. The reflex responses were reproducible and symmetrical, with a mean latency of 14.8 msec (S.D. 1.4 msec) and an absolute side-to-side differences of 0.5 msec (S.D. 0.29 msec). Latency was significantly correlated with both age and height, and multiple regression analysis provided the following equation: latency (msec) = 0.091 x height (in cm) + 0.036 x age (years) - 1.988. Amplitudes had wide scatter (22-365 microV on the right side) and positive skew. An amplitude less than 40% of that for the other side would be outside the 90th percentile. Five cases are described to illustrate the potential clinical utility of this test. However, whether this reflex is of diagnostic value can be answered only by a prospective study comparing it with other routine investigations.

Adult↗
PubMed1975

Neurochemical aspects of post-tetanic potentiation of monosynaptic reflexes in the cat spinal cord. III. Analysis of amino acids after long-term potentiation.

Following 30-min intermittent post-tetanic potentiation of monosynaptic reflexes in the ventral horn of the spinal cord of 10 cats, the amino acid composition was analyzed after reacting with 14C-dansylchloride and by two-dimensional chromatography. The amino acids in comparable segments of the spinal cord from eight animals after ether anesthesia and from five animals who were operated on but not stimulated were also analyzed. In the latter the operation itself influenced the amino acid composition as compared to those animals who were anesthetized. Comparison between the different control groups showed that the operated animals can be used as a control for calculation of the changes caused by potentiation. The amino acids glycine, glutamic acid and aspartic acid, which act as either inhibitory or excitatory neurotransmitters, increased significantly after potentiation, as did the amino acids lysine, histidine, leucine, isoleucine, and proline.

Amino Acids↗
PubMed1981

Effects of fusaric (5-butylpicolinic) acid on the monosynaptic reflex neural activity of cat spinal cord.

It has been demonstrated that most hypertensive drugs which cause increases in levels of norepinephrine influence the stimulation of monosynaptic reflex (MSR) neural activity. However this report discusses the effects of a hypotensive drug, which causes decreases in levels of norepinephrine, on the MSR amplitude of acute spinal cats. This drug is 5-butylpicolinic acid (fusaric acid: FA) which is an effective hypotensive agent and a potent inhibitor of dopamine beta-hydroxylase (approximately 10 times more potent than disurfiram). Intravenous injections of FA increased MSR neural activity in a dose-dependent manner. The FA-induced neural activity was gradually depressed by treatment with haloperidol, a dopamine and/or a alpha receptor blocker and methysergide, a serotonin receptor blocker, respectively. In addition, this neural activity was potentiated by the sequential administration of L-dopa. FA did not cause increases in the blood pressure but inhibit the synthesis of norepinephrine from dopamine. These results suggest that not only hypertensive but also hypotensive drugs can affect the increase of MSR neural activity, and dopamine plays an important role in FA-induced neural activity.

Animals↗
PubMed1993

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.

Animals↗
PubMed1983

Influence of different barbiturate anesthetics on delta-9-tetrahydrocannabinol effects on spinal monosynaptic reflexes.

Two barbiturates, pentobarbital and methohexital, were used as general anesthetics to evaluate their interactions with the effects of delta-9-tetrahydrocannabinol (delta-9-THC) on spinal monosynaptic reflexes in cats with transected spinal cords and ischemically destroyed brains. In animals initially anesthetized with pentobarbital, delta-9-THC over a wide dosage range produced only an enhancement of the reflex, whereas in methohexital-treated animals only depression was elicited. Because delta-9-THC is known to produce both excitatory and depressant effects in conscious animals, the results of the present study demonstrate that the choice of anesthetic may determine which effects manifest themselves. Therefore, if anesthesia is used in the investigation of any cannabinoid, the possibility of such interactions must be considered when interpreting the results.

Anesthetics↗
PubMed1993

Thyrotropin releasing hormone-induced potentiation of spinal monosynaptic reflex in rats in vitro.

Superfusion of thyrotropin-releasing hormone (TRH) in neonatal rat spinal cord in vitro produced dose (0.01-1.00 microM) dependent potentiation of monosynaptic reflex (MSR) which was maximum (44% of control) at 1 microM of TRH. But no ventral root depolarization was observed with TRH (1 microM) although potassium concentration out side ([K+]0) when increased produced a depolarization at the magnitude of 0.2 mV/mM of [K+]0. TRH-induced potentiation of MSR was not altered in spinal cords, obtained from the animals pretreated with 5,7-dihydroxytryptamine or 6-hydroxydopamine. Neither serotonin antagonists (spiperone, ketanserin, cyproheptadine or 3-troponyl-indole-3-carboxylate) nor adrenergic antagonists (phentolamine or haloperidol) could attenuate TRH-induced potentiation. Inhibition of MSR observed in the spinal cord elicited by stimulating the adjacent dorsal root was unaffected by TRH. The results suggest that, TRH potentiates MSR by directly acting on the motoneurons, without involving presynaptic serotonergic or catecholaminergic neuronal systems or the disinhibition of pre- or post-synaptic inhibition in the spinal cord.

Animals↗
PubMed1989

Enhancement of spinal monosynaptic reflexes with phenylethylamine and related drugs through descending noradrenergic neurons.

The effects of phenylethylamine (PEA) and related drugs, such as methamphetamine, phenelzine, methylphenidate, nomifensine and mazindol on the spinal monosynaptic reflex (MSR) were investigated in rats treated with 6-hydroxydopamine (6-OHDA) or 5,6-dihydroxytryptamine (5,6-DHT). PEA (1 x 10(-5) mol/kg, i.v.) increased the amplitude of MSR in control rats, but decreased the amplitude in rats treated with 6-OHDA. Although PEA-related drugs increased the amplitude of MSR, they did not change the MSR amplitude in 6-OHDA-treated rats. In 5,6-DHT-treated rats, PEA-related drugs increased the amplitude of MSR, whereas PEA produced a decrease. These results support our previous suggestion that the enhancement of MSR by these drugs might be mediated through release of noradrenaline or inhibition of noradrenaline uptake at the noradrenergic synapses.

5,6-Dihydroxytryptamine↗
PubMed1983

Effect of tetanus toxin on the monosynaptic reflex.

Tetanus toxin was injected at various doses (0.1-10,000 mouse MLD/kg) into the gastrocnemius muscle of the left hind leg of the cat. The relative excitability of the monosynaptic reflex (MSR) was increased in the very early period of the intoxication decreased in the later period, during which the MSR of the gastrocnemius was either partially or totally depressed at doses as low as 10 mouse MLD/kg.

Animals↗