Depolarizing effects of dopamine on motoneurons from a segment of spinal cord isolated from newborn rats

The effects on dorsal root potentials of applying dopamine to the perfusing fluid were investigated in experiments on a segment isolated from the spinal cord of 13- to 18-day-old rats. Dopamine induced slow, dose-dependent depolarization in motoneurons in 28 trials out of 32, retained in the solution blocking synaptic transmission. Threshold concentration of dopamine in the normal perfusing fluid measured 1·10^–6 M and 1·10^–5 M in a calcium-free perfusate containing magnesium or manganese ions. Depolarization was accompanied by an increased rate of motor discharges recorded from the ventral root. Segmental reflex response produced by dorsal root stimulation was depressed following depolarization. Hyperpolarization in response to dopamine was observed in 4 out of 32 experiments. Dopamine-induced electrotonic dorsal root potentials were suppressed by prior haloperidol application to the brain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 735–741, November–December, 1987.     

Depolarizing effects of dopamine on the primary afferent fibers of a segment isolated from the spinal cord of newborn rats

Effects of dopamine on dorsal root potentials were investigated during experiments on a segment of spinal cord isolated from 12- to 18-day-old rats. Applying dopamine to the brain was found to produce a slow, reversible, dose-dependent depolarization at primary afferent fiber terminals. This dopamine-induced depolarization was retained during complete blockade of synaptic transmission brought about by exchanging calcium ions in the perfusing fluid by magnesium or manganese ions. Minimum dopamine concentration required to produce this effect was 1·10^–10–1·10^–9 M. Peak amplitude of depolarization equaled 1.5 mV. Duration of this reaction ranged from 5.5 to 36.7 min, depending on the duration and concentration of dopamine application. Depolarizing response to dopamine differed considerably from GABA-induced dorsal root depolarization in amplitude and rate of rise. Haloperidol, a dopamine antagonist, reduced dopamine-induced dorsal root depolarization. Findings indicate that dopamine acts directly on the membrane of primary afferent fiber terminals, shifting membrane potential toward depolarization. This raises the possibility that dopaminergic brainstem-spinal pathways may exert an effect on sensory information transmission in segmental reflex arcs already traveling to the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 741–748, November–December, 1987.     

Effect of serotonin on neuronal background activity in a hemisegment isolated from the infant rat spinal cord

Neuronal background activity was investigated in a hemisegment of the lumbar section of the spinal cord before and after addition of serotonin (5-HT — 1 × 10^–8–10^–4 M) in 14- to 22-day-old rats. Reversible changes in background firing rate were recorded in 50% and 70.6% of dorsal and ventral horn interneurons respectively. Excitatory response predominated; in the dorsal horn, 62.4% of all cells responding to 5-HT showed an excitatory response, 8.4% an inhibitory reaction, and 29.2% a two-stage response. In the ventral horn, an excitatory and two-stage response were recorded in 91.6% and 8.4% of cells respectively. Application of 5-HT induced an increase in firing rate and depolarization in the ventral horn. Findings from this study would point to a primarily excitatory effect of 5-HT on background in segmental neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 335–343, May–June, 1989.     

Inhibitory effect of dopamine on the transmission of excitation in isolated rat spinal cord

The effects of dopamine on ventral root potential produced by a single supramaximal dorsal root stimulation of the dorsal root was investigated during experiments on isolated superfused spinal cord segments from 10–16-day old rats. A reciprocal dose-dependent inhibition of the mono- and polysynaptic components of reflex response was also observed. Minimum effective concentration was 1×10^–8 M dopamine. Extent of reflex response increased in step with dopamine concentration, so that the amplitude of the monosynaptic component of ventral root potential was decreased by 20% and 87% of baseline level by the action of 10^–4 and 10^–3 M dopamine respectively on the cord. The amplitude of the polysynaptic component was thereby decreased by an average of 18% and 87%. Findings indicate that dopaminergic brainstem-spinal pathways contribute to the governing of impulse transmission in the segmental reflex arcs. Inhibition of dopaminergic synaptic transmission probably underlies the increase in latency already described in the literature, as well as the increase observed in the threshold of reflex motor response to nociceptive action following either stimulation of the dopaminergic brainstem structures or intravenous administration of dopamine agonists.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 616–621, September–October, 1986.     

The distribution and turnover of tryptamine in the brain and spinal cord

Tryptamine levels have been determined in mouse brain regions and spinal cord and in rat spinal cord. They were; caudate nucleus 2.5 ng·g^–1, hypothalamus <0.5 ng·g^–1, hippocampus <0.7 ng·g^–1, olfactory bulb <0.7 ng·g^–1, olfactory tubercles <0.6 ng·g^–1, brain stem <0.4 ng·g^–1, cerebellum <1.0 ng·g^–1, and the rest 0.9 ng·g^–1. The mouse whole brain was found to have 0.5 ng·g^–1, the mouse spinal cord 0.3 ng·g^–1, and the rat spinal cord 0.3 ng·g^–1. These concentrations increased rapidly to 22.8 ng·g^–1, 14.2 ng·g^–1, and 6.6 ng·g^–1 respectively at 1 hr after 200 mg·kg^–1 pargyline. The turnover rates and half lives of tryptamine in the mouse brain and spinal cord and rat spinal cord were estimated to be 0.14 nmol·g^–1·h^–1 and 0.9 min; 0.054 nmol·g^–1·h^–1 and 1.5 min and 0.04 nmol·g^–1·h^–1 and 1.6 min respectively. The aromaticl-aminoacid decarboxylase inhibitors NSD 1034 and NSD 1055 reduced synthesis of tryptamine in controls and pargyline pretreated animals. Tryptophan increased the concentrations of mouse striatal tryptamine and 5-hydroxytryptamine and brain stem 5-hydroxyindole acetic acid.p-Chlorophenylalanine reduced formation of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid but did not change that of tryptamine.     

Catecholamines in fetal pig plasma and the response to acute hypoxia and chronic fetal decapitation

Summary Dopamine, norepinephrine and epinephrine were measured by radioenzymatic assay in blood plasma samples drawn from the umbilical arteries of 30 anaesthetised Landrace pig fetuses. Just prior to term, the concentrations of dopamine (0.46±0.14 ng·ml^–1) and norepinephrine (1.74±0.60 ng·mg^–1) were lower than earlier in gestation, whereas epinephrine concentrations at term (0.80±0.31 ng·ml^–1) were similar to those at mid-gestation, intervening stages of gestation having higher levels of plasma epinephrine. Fetal hypoxia was induced by clamping the umbilical cord for 2 min and the catecholamines determined in arterial blood samples immediately thereafter, then again 3 min after removal of the clamp. Inconsistent effects of cord clamping on catecholamine levels were seen at 55 days, but thereafter, in all but one instance, the hormone levels were increased. Fetuses near term tended to respond less than fetuses at 75 and 96 days gestation (term=114±1 day). Catecholamines were also present in the circulation of fetuses decapitated at 42 days gestation and studied at 109±1 days. The average concentrations of dopamine (1.12±0.27 ng·ml^–1) and norepinephrine (8.23±3.04 ng·ml^–1) were greater than in intact fetuses, the plasma epinephrine levels being comparable to, or slightly higher than, those in intact fetuses. The results demonstrate that catecholamines are present in the circulation of the intact and decapitated pig fetus and that the actual concentrations and the type of response to umbilical cord clamping are dependent on gestation age.     

Dopamine in tissues of the hydrozoan jellyfishPolyorchis penicillatus as revealed by HPLC and GC/MS

Summary High performance liquid chromatography of alumina extracts of several tissues inPolyorchis penicillatus show the presence of dopamine and a catecholamine resembling norepinephrine. Dopamine is found in the highest concentrations in nerve-rich tissue (120 fmol·mg wet wt^–1), at intermediate concentrations in endoderm-rich tissue (30 fmol·mg^–1), and at the lowest concentrations in the mesoglea (10 fmol·mg^–1). The presence of dopamine was confirmed using gas chromatography/mass spectrometry with negative ion chemical ionization, but norepinephrine and epinephrine could not be detected in nerve-rich tissue.     

Effects of aspartate,substance P,and serotonin on neuronal activity in the central gray substance:In vitro experiments

Effects of aspartate (2 · 10^–5 M), substance P (10^–7–10^–8 M), and serotonin (5-hydroxytryptamine, 5-HT; 5 · 10^–5 M) on the background activity of neurons in the central gray substance (CGS) were studied on slices of the rat midbrain. Aspartate and substance P (transmitters of nociceptive signals), and 5-HT (modulator of transmission of nociceptive influences) were found either to facilitate or to depress the activity of CGS neurons. The predominant effect of substance P or 5-HT applications to neurons of the dorsal CGS part was facilitation, and to neurons of the ventral CGS part, inhibition. The effects of aspartate application on studied CGS neurons were of varying nature, but inhibitory effects were found to prevail.The findings support our earlier hypothesis that assigned the studied neurons to spontaneously discharging inhibitory CGS interneurons, which control the activity of efferent CGS neurons. The role of tested substances in the regulation of CGS neuronal activity and the antinociceptive CGS effects is discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 354–362, September–October, 1993.     

Effect of penicillin on synaptic activity of motoneurons in the lamprey isolated spinal cord

The effect of penicillin on the membrane potential (MP) and synaptic activity of motoneurons in the isolated spinal cord of the river lamprey was investigated. In cells with a low initial MP (58.7±5.2 mV, n=28), penicillin (2.5 mmole·liter^–1) caused a depolarization, and potentiated excitatory postsynaptic potentials (EPSPs) that were evoked by stimulating spinal tracts and dorsal roots. The EPSPs were potentiated by 80–220% relative to their initial amplitude. In motoneurons with a higher MP (72.0±5.7 mV, n=20), a depolarization did not develop, and the potentiation of EPSPs did not exceed 25–70%. The effects of penicillin were inhibited when antagonists of excitatory and inhibitory amino acids were added to the superfusate. The results obtained imply that the motoneuron membranes have two acceptor sites for penicillin.Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Saint Petersburg Institute of Biological Research, Belgrade, Yugoslavia. Translated from Neirofiziologiya, Vol. 24, No. 2, pp. 151–160, March–April, 1992.     

Synaptosomal degradation of substance P and some other neuropeptides

Synaptosomes purified from spinal cord and from different rat brain areas exhibit peptide hydrolase activity, cleaving substance P (SP), bradykinin, THRH, LHRH, and neurotensin. The lowest activity for all the peptides tested was found in spinal cord, while the region with the highest degrading activity depended on the substrate: for substance P, it was striatum and cortex; for bradykinin, hypothalamus, and medulla oblongata; for THRH, striatum; for LHRH, midbrain; and for neurotensin, hippocampus. Degradation of substance P takes place at the plasma membrane of synaptosomes. Synaptosome ghosts cleave substance P (pH optimum 7–9,K _m–2.5×10^–5 M,V _max–130 nmol·hr^–1·mg protein^–1 and also a number of its C-terminal fragments. Effects of the inhibitors show that several different classes of peptidases and proteases are involved in the degradation process. Peptide cleavage represents the probable pathway of synaptosomal inactivation of substance P.     

Effects of DL-α-aminoadipate on synaptic transmission in spinal interneurons of the lamprey

Summary In the giant interneurons of the spinal cord of the lamprey,Lampetra japonica, a primitive vertebrate, DL--aminoadipate, 3–5 mM, reversibly depressed both the monosynaptic EPSP and the depolarization produced by iontophoretic application of glutamate or aspartate. The monosynaptic EPSP was produced by intracellular stimulation of caudal giant interneurons. L-glutamate diethylester also depressed both the monosynaptic excitation and aspartate and glutamate potentials but 10–20mM was necessary. It seems likely that acidic amino acids or closely related substances may be serving the mutual excitation between giant interneurons of the lamprey spinal cord.     

Presynaptic inhibition of segmental interneurons

In experiments on spinal cats changes in the second negative postsynaptic component (N₂) of the dorsal surface potential (DSP) of the spinal cord recorded in the region of segment L7 was used as the index of inhibition of segmental dorsal horn interneurons. Conditioning and testing stimuli were applied at increasing time intervals to the popliteal and superficial peroneal nerves respectively. Changes in the N₂ component were compared with changes in the N₁ component of the DSP, reflecting mainly activity of nonsegmental ascending dorsal horn interneurons. After an initial short facilitation a conditioning volley of pulses evokes prolonged (over 500 msec) inhibition of the N₂ component, characterized by the presence of two maxima (on the average at the 16th and 80th milliseconds) which indicate that two systems with different latent periods play a role in this inhibition. In its shape and temporal characteristics the curve of inhibition of the N₂ component corresponds to the two-component dorsal root potential (DRP) recorded in spinal animals in response to stimulation of flexor afferents (FRA) [8, 19]. Together with other features, this similarity is evidence of the presynaptic nature of this inhibition. Intravenous injection of hexobarbital has a stronger action on inhibition of the N₂ component, leading to a marked increase in its depth and duration. Suggestions are made regarding the functional organization of systems responsible for presynaptic inhibition of segmental dorsal horn interneurons.Deceased.Dnepropetrovsk State University. Translated from Neirofiziolgiya, Vol. 4, No. 1, pp. 75–82, January–February, 1972.     

Blood-brain glucose transfer in the mouse

The intracarotid injection method has been utilized to examine blood-brain barrier (BBB) glucose transport in normal mice, and after a 2-day fast. In anesthetized mice, cerebral blood flow (CBF) rates were reduced from 0.86 ml·min^–1·gm^–1 in control to 0.80 ml·min^–1·gm^–1 in fasted animals (p>0.05). Brain Uptake Indices were significantly (p<0.05) higher in fasted (plasma glucose =4.7 mM) than control (plasma glucose = 6.5 mM) mice, while plasma glucose was significantly lower. The maximal velocity (V_max) for glucose transport was 1562±303 nmoles·min^–1·g^–1, and the half-saturation constant (Km =) 6.67±1.46 mM in normally fed mice. In fasted mice the Vmax was 2053±393 nmoles·min^–1·g^–1 (p>0.05), and the half-saturation constant (Km =) 7.30±1.60 mM (not significant, P>0.05). A rabbit polyclonal antiserum to a synthetic peptide encoding the 13 C-terminal amino acids of the human erythrocyte glucose transporter (GLUT-1) immunocytochemically confirmed that the mouse brain capillary endothelial glucose transporter is a GLUT-1 transporter, and immunoreactivity was similar in brain endothelia from fed and fasted animals. In conclusion, after a 2-day fast in the mouse, we saw significant reductions in forebrain weight (7%), and plasma glucose levels (27%). Increased brain glucose extraction (25%, p<0.05), and a 22% increase in the unsaturatedpermeability-surface area product (p<0.05) was also observed.     

Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4

Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h^–1) nitrate and nitrite reductase activities of 200 nmol · mg^–1 protein · min^–1 and 250 nmol · mg^–1 protein · min^–1 were measured, respectively. At a high growth rate (0.55 h^–1) both enzyme activities were considerably lower (25 and 12 nmol mg^–1 · protein · min^–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.     

Presynaptic mechanisms of changes in segmental responses accompanying the formation of a spinal locomotor generator in the cat

Using unanesthetized and decorticated (or decerebrated at level A 13) cats, it was found that spinalization leads to depolarization of the central terminals of primary afferents and an increase in the N₁ component of dorsal surface potential and dorsal root potential (DRP) produced by stimulating the low-threshold cutaneous and muscle afferents. Other effects include an increase in early polysynaptic responses and DRP produced by stimulation of high-threshold muscle afferents, a reduction in the intensity of interneuron activation in the nucleus interpositus mono- and polysynaptically connected with primary afferents, and a rise in the activity of n. interpositus interneurons di- and oligo-synaptically connected with afferent terminals. Changes in the opposite direction were produced by injecting DOPA into spinal animals. The connection between changes in the state of the segmental neuronal apparatus of the lumbosacral spinal cord and the level of spinal locomotor generator activity is discussed in the light of the findings obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 669–678, September–October, 1986.     

Cholinergic modulation of the synaptic transmission in the frog spinal cord

It was found during experiments on isolated frog spinal cord involving extracellular recording from the dorsal roots (sucrose bridging) and intracellular recording from motoneurons by microelectrodes that 10 mM of the M-cholinomimetic arecoline produces motoneuronal depolarization which is matched by depolarizing electronic ventral root potentials and a rise in motoneuronal input resistance. Arecoline changes synaptic transmission by increasing the amplitude of postsynaptic potentials during intracellular recording and that of motoneuronal reflex discharges in the ventral roots but reduces the duration of dorsal root potentials. In the presence of arecoline, L-glutamate-induced motoneuronal response increases. Facilitation of synaptic transmission produced by arecoline in the spinal cord is bound up with cholinergic M₂- activation, since it is suppressed by atropine but not by low concentrations of pirenzipine; it is also coupled with a reduction in adenylcyclase activity. When motoneuronal postsynaptic response has been suppressed, as in the case of surplus calcium or theophylline, arecoline produces an inhibitory effect on the amplitude of motoneuronal monosynaptic reflex discharges which is suppressed by pirenzipine at a concentration of 1×10^–7 M. This would indicate the presence at the primary afferent terminals of presynaptic cholinergic M₁ receptors which mediate its inhibition of impulses of transmitter release. This effect is independent of changes in cyclic nucleotide concentration.A. M. Gorkii Medical Institute, Donetsk. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 399–405, May–June, 1987.     

Prostatic Acid Phosphatase Is Expressed in Peptidergic and Nonpeptidergic Nociceptive Neurons of Mice and Rats

Thiamine monophosphatase (TMPase, also known as Fluoride-resistant acid phosphatase or FRAP) is a classic histochemical marker of small- to medium-diameter dorsal root ganglia (DRG) neurons and has primarily been studied in the rat. Previously, we found that TMPase was molecularly identical to Prostatic acid phosphatase (PAP) using mice. In addition, PAP was expressed in a majority of nonpeptidergic, isolectin B4-binding (IB4⁺) nociceptive neurons and a subset of peptidergic, calcitonin gene-related peptide-containing (CGRP⁺) nociceptive neurons. At the time, we were unable to determine if PAP was present in rat DRG neurons because the antibody we used did not cross-react with PAP in rat tissues. In our present study, we generated a chicken polyclonal antibody against the secretory isoform of mouse PAP. This antibody detects mouse, rat and human PAP protein on western blots. Additionally, this antibody detects PAP in mouse and rat small- to medium-diameter DRG neurons and axon terminals in lamina II of spinal cord. In the rat, 92.5% of all PAP⁺ cells bind the nonpeptidergic marker IB4 and 31.8% of all PAP⁺ cells contain the peptidergic marker CGRP. Although PAP is found in peptidergic and nonpeptidergic neurons of mice and rats, the percentage of PAP⁺ neurons that express these markers differs between species. Moreover, PAP⁺ axon terminals in the rat partially overlap with Protein kinase Cγ (PKCγ⁺) interneurons in dorsal spinal cord whereas PAP⁺ axon terminals in the mouse terminate dorsal to PKCγ⁺ interneurons. Collectively, our studies highlight similarities and differences in PAP localization within nociceptive neurons of mice and rats.     

Evoked activity of spinal neurons in the early period after sciatic nerve division

The character of dorsal horn motoneurons and interneurons evoked by stimulation of the dorsal root, and activity of Renshaw cells in response to stimulation of the ventral root were studied in albino rats in the lower lumbar segments of the spinal cord 5 days after sciatic nerve division. A significant increase in the mean amplitude of excitatory postsynaptic potentials of motoneurons was observed on the side of division of the nerve. No significant change in membrane potential and in the threshold of appearance of the action potential of these motoneurons took place. The mean number of action potentials and the duration of discharge of the Renshaw cells and dorsal horn interneurons likewise were not significantly changed.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 306–314, May–June, 1992.     

Signal role for activation of caspase-3-like protease and burst of superoxide anions during Ce<Superscript>4+</Superscript>-induced apoptosis of cultured <Emphasis Type="Italic">Taxus cuspidata</Emphasis> cells

The signal events of 1 mM Ce⁴⁺ (Ce(NH₄)₂(NO₃)₆)-induced apoptosis of cultured Taxus cuspidata cells were investigated. The percentage of apoptotic cells increased from 0.82% to 51.32% within 6 days. Caspase-3-like protease activity became notable during the second day of Ce⁴⁺-treatment, and the maximum activity was 5-fold higher than that of control cells at the fourth day. When the experiment system was pretreated with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) at 100 M, caspase-3-like activity resulted in distinct inhibition by 70% and 77.3% after 3 and 4 days of induction. Furthermore, 100 M Ac-DEVD-CHO partially reduced the apoptotic cells by 58.6% and 60.8% at day 4 and 5 respectively. Ce⁴⁺ induced superoxide anions (O₂·–) transient burst, and the first peak appeared at around 3.7–4 h, the second appeared at about 7 h. Both O₂·– burst and cell apoptosis were effectively suppressed by application of diphenyl iodonium (NADPH oxidase inhibitor). Inhibition of O₂·– production attenuated caspase-3-like activation by 49% and 53.6% during day 3 and 4 respectively. In addition, a total of 15 protein spots changed in response to caspase-3-like protease activation were identified by two-dimensional gel electrophoresis. These results suggest that Ce⁴⁺ of 1 mM induces apoptosis in suspension cultures of T. cuspidata through O₂·– burst as well as caspase-3-like protease activation. The burst of O₂·– exerts its activity as an upstream of caspase-3-like activation. Our results also implicate that other signal pathways independent of an O₂·– burst possibly participate in mediating caspase-3-like protease activation.     

Spinal and spino-bulbo-spinal neuronal mechanisms of transmission of somatomotor and visceromotor reflexes in the thoracic spinal cord

Early (spinal) and late (spino-bulbo-spinal) responses of interneurons in segments T9–10 to stimulation of the splanchnic and intercostal nerves and the dorso-lateral and ventral funiculi of the spinal cord (at the C3 level) were investigated in experiments on cats anesthetized with chloralose. The experiments showed that interneurons activated by spinal and spino-bulbo-spinal mechanisms differ in their distribution in the dorso-ventral plane of the spinal cord. Cells of layers I–V were excited by spinal pathways only, but those of layers VII and VIII by both spinal and spino-bulbo-spinal or only by the latter. Spino-bulbo-spinal effects were evoked in interneurons by both somatic and visceral afferent waves. A conditioning spino-bulbo-spinal wave evoked deep and prolonged inhibition of late activity induced by somatic or visceral afferent impulses. Early (spinal) activity was inhibited only partially under these circumstances. This inhibition was shown to take place with the participation of supraspinal structures. The possible types of spinal and supraspinal mechanisms of inhibition of early and late activity in spinal neurons are discussed.Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev, USSR. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 392–400, July–August, 1973.