Three types of inhibitory miniature potentials in frog spinal cord motoneurons: Possible GABA and glycine cotransmission

Miniature inhibitory postsynaptic potentials (mIPSP) of motoneurons in isolated frog spinal cord were recorded in conditions of blockade of the conduction of nerve spikes and ionotropic glutamate receptors (TTX, 1 μM, CNQX, 25 μM, D-AP5, 50 μM). Three types of mIPSP were identified: those with fast and slow time characteristics and mIPSP with two-component decays. Two-component mIPSP accounted for 8.7% of all selected responses, fast mIPSP for 64.5%, and slow mIPSP for 26.8%. Blockade of GABA_A receptors with bicuculline (20 μM) led to decreases in the numbers of slow and two-component mIPSP and an increase in the number of mIPSP with fast kinetics. Strychnine (1 μM), a blocker of glycine receptors, led to a reduction in the number of fast receptors and an increase in the number of slow potentials. These data suggest that frog spinal cord motoneurons have three types of inhibitory mIPSP, mediated by GABA, glycine, and simultaneous release of these two transmitters from the same presynaptic terminals. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 1, pp. 18–26, January, 2006.     

Mechanism of disturbance of inhibitory electrogenesis in spinal α-motoneurons in experimental local botulinus poisoning

The character of changes in postsynaptic inhibition in spinal -motoneurons of cats was studied in the course of experimental local botulinus poisoning. At the beginning of development of the local paralytic syndrome a marked decrease in the amplitude of the reciprocal, and a smaller decrease in amplitude of the polysynaptic IPSPs was observed. On the appearance of total paralysis of the muscles from botulinus poisoning the reciprocal and polysynaptic IPSPs were inhibited even more, but they never disappeared completely and were never converted into depolarization potentials. During the development of the IPSP the synaptic permeability of the motneurons as a rule was reduced.Department of Pathological Physiology, N. A. Semashko Moscow Medical Stomatological Institute. Department of Pathological Physiology, Saratov Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 6, pp. 651–654, June, 1977     

Location of the spinal nucleus of the accessory nerve in the human spinal cord

The segmental extent and topography of the spinal nucleus of the accessory nerve (SNAN) was investigated in the adult human spinal cord. Transverse sections of segments between the lower medulla and C6 were stained with cresyl violet and the motor cell columns identified according to the numerical locations defined by Elliott (1942). The segmental extent and topography of the cervical part of column 2 resembled that previously described for the SNAN of primates.     

Location of the phrenic nucleus in the human spinal cord

Eight normal human spinal cords were studied. Spinal segments were identified and embedded in paraffin wax. Serial cross sections were cut at 25 μm and stained by cresyl violet. Motor columns were reconstructed adapting Elliott's (1942) methods. Motor columns were classified into the medial and lateral divisions and were numbered sequentially from medial to lateral at the level of Cl. In the cervical cord, 8 motor columns were traced. Column 1, corresponding to the medial column, presented 3 subdivisions designated as 1a, 1b and 1c with ventral, dorsal and lateral positions respectively. Columns 1a and 1b extended throughout the cervical region while 1c was confined to 3rd, 4th and 5th cervical segments. At the level of C3, 1c was a discrete column situated lateral to 1a and 1b but at C4 and C5 it became displaced medially close to the medial margin of the ventral horn. In cross section, it presented smaller medial and large lateral part. With the help of clinical and developmental evidence an attempt was made to correlate column 1c with the phrenic nucleus.     

Mechanism of reinnervation of skeletal muscles injured by botulinus toxin

The course of reinnervation of a skeletal muscle, whose own myoneural apparatus has been damaged by botulinus toxin, by an implanted nerve was investigated in experiments on rats in order to determine the essential conditions for regeneration of nerve fibers in an area of paralysis due to botulism. Injection of a sublethal dose of the toxin into the limb was shown to hasten synaptogenesis of the implanted nerve. As a result, restoration of the normal weight of muscle tissue and the level of polarization of its fibers was promoted.Department of Pathological Physiology, N. A. Semashko Moscow Medical Stomatologic Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 12, pp. 651–653, December, 1979.     

Plasticity of recurrent inhibitory reflexes in cat spinal motoneurons following peripheral nerve injury

Summary Chronic axotomy of a peripheral motor nerve in cat causes a gradual reduction in the number of intramedullary axon collaterals originating from the axotomized motoneurons (Havton and Kellerth 1984, 1989). This axon collateral elimination would be expected to reduce the amount of recurrent inhibitory reflex actions mediated by these cells. The aim of the present study was to investigate the recurrent inhibition originating from axotomized motoneurons and, also, to see whether the elimination of axon collaterals from the axotomized neurons might induce secondary compensatory changes in the recurrent inhibitory pathways originating from synergistic non-lesioned motoneurons. The results, which were obtained by means of intracellular recordings and monosynaptic reflex testing, indicate that postoperative enhancement of reflex actions may take place in the recurrent inhibitory pathways persisting in the axotomized motoneurons as well as in those originating from synergistic nonlesioned motoneurons. It is suggested that the site of compensatory enhancement is at the synaptic reflex contacts between the motoraxon collaterals and the inhibitory Renshaw interneurons.     

Effect of developing insulin hypoglycemia on monosynaptic spinal reflexes in cats

Acute experiments on anesthetized and spinal cats showed that deepening insulin hypoglycemia causes inhibition of rhythmic monosynaptic EPSPs of motoneurons in the lumbar region of the spinal cord. In the initial period of hypoglycemia (a fall of the blood sugar to 50–60 mg%) the progressive decrease in the efficiency of trans-synaptic processes was not caused by pre-or postsynaptic inhibition or by depression and was due to exhaustion of the operative fraction of mediator. In deeper hypoglycemia the functions of the postsynaptic formation of the monosynaptic spinal reflex arc are disturbed.Laboratory of Physiology of the Autonomic Nervous System, I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. (Presented by Academician V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 4, pp. 305–308, April, 1979.     

Class A plexin expression in axotomized rubrospinal and facial motoneurons

The semaphorin family of guidance molecules plays a role in many aspects of neural development, and more recently semaphorins have been implicated to contribute to the failure of injured CNS neurons to regenerate. While semaphorin expression patterns after neural injury are partially understood, little is known about the expression of their signal transducing transmembrane receptors, the plexins. Therefore, in this study, we compared the expression patterns of all class A plexins (Plxn-A1, A2, A3, A4) in mouse CNS (rubrospinal) and peripheral nervous system (PNS)-projecting (facial) motoneurons for up to two weeks following axonal injury. Using in situ hybridization, immunohistochemistry, and Western blot analysis, in rubrospinal neurons, Plxn-A1 mRNA and protein and Plxn-A4 expression did not change as a result of injury while Plxn-A2 mRNA increased and Plxn-A3 mRNA was undetectable. In facial motoneurons, Plxn-A1, -A3 and -A4 mRNA expression increased, Plxn-A2 mRNA decreased while Plxn-A1 protein expression did not change following injury. We demonstrate that with the exception of the absence of Plxn-A3 mRNA in rubrospinal neurons, both injured rubrospinal (CNS) and facial (PNS) neurons maintain expression of all plexin A family members tested. Hence, there are distinct expression patterns of the individual plexin-A family members suggesting that regenerating rubrospinal and facial motoneurons have a differential ability to transduce semaphorin signals.     

Facilitation of transmission via inhibitory pathway 1a to spinal extensor motoneurons in response to stimulation of the forelimb nerves in cats

Activation of forelimb flexor reflex afferent in cats anesthetized with a mixture of Chloralose and Nembutal evoked temporospatial facilitation in the reciprocal inhibitory pathways to spinal extensor motoneurons. The amplitude of disynaptic reciprocal 1a inhibitory postsynaptic potentials (IPSP) evoked in the extensor motoneurons by activation of the most excitable fibers of the nerve supplying the antagonist muscle increased several-fold using conditioning stimulation of the forelimb nerve. Facilitation of 1a IPSP occurred on a background of IPSP evoked by descending inter-limb discharges. Facilitation of 1a IPSP had a latent period of 18–20 msec and could last to 60 msec. The possible role of inhibitory 1a interneurons in interlimb coordination is discussed. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 85, No. 3, pp. 430–435, March, 1999.     

Characteristics of postsynaptic potentials produced in single human motoneurons by homonymous group 1 volleys

Summary Changes in the firing probability of voluntarily activated human tibialis anterior motor units occurred when the muscle nerve was stimulated below the threshold of motoneuron axons. A prominent period of increased firing probability was considered to result from the group 1 composite EPSP. The rise time of this composite EPSP, estimated from the duration of the period of increased firing probability, was between 2 and 5 ms. One estimate of the relative amplitude of the EPSP was derived from the cross-correlation and tested by inserting synthetic EPSPs into a computer simulation of a rhythmically discharging neuron. A second estimate of the amplitude was obtained by delivering stimuli with various delays within the interspike interval to determine the position (as a percentage of the mean interspike interval) at which the postsynaptic potential was capable of bringing the membrane potential to threshold. The two estimates were in reasonable agreement. The largest of these EPSPs could bring the motoneuron to threshold after 39% of the elapsed interspike interval. The falling phase of the postsynaptic potential was explored by delivering double stimuli within the interspike interval to produce temporal summation. The duration of the falling phase, so tested, was between 5 and 20 ms. An attempt was made to deduce the general form of the trajectory representing the effective distance of an EPSP from threshold during the interspike interval from the alterations in the cross-correlation profile that occurred when motoneuron firing rate was voluntarily altered.     

The action of ammonium on postsynaptic inhibition of cat spinal motoneurons

Summary Potential changes were investigated which follow the intra- and extracellular electrophoretic injection of NH₄ ⁺ and also the intravenous application of neutral ammonium salts. The common effect found in all kinds of application is a depolarizing shift of the IPSP-equilibrium potential (E_IPSP) towards the resting potential. Inhibitory transmission is preserved but produces considerably reduced hyperpolarizing potential changes at normal resting potentials. In addition, ammonium ions produce short term shifts of resting and overshoot potentials with intracellular application. The latter changes can be explained under the assumption that NH₄ ⁺ partly substitutes for Na⁺ as for the action potential generation.The observed reversible reduction of E_IPSP has high sensitivity towards extracellular and systemic NH₄ ⁺ application as compared to intracellular injection. The time course of the depolarizing shift of E_IPSP, especially its restitution, was shortest in extracellular application. It is suggested that ammonium release from the internal site produces the long term effects observed on the IPSP after intracellular injection. The externally effective dosages correspond to intracerebral NH₄ ⁺-concentrations which are reported for preconvulsive states of various kinds of metabolically induced epilepsies.We thank Miss C. Lueg for careful technical assistance.     

GABA- and glycine-immunoreactive terminals contacting motoneurons in lamprey spinal cord

Double postembedding GABA- and glycine-immunostaining was performed on the lamprey (Lampetra fluviatilis) spinal cord after previous HRP labeling of motoneurons. Immunopositive boutons contacting motoneurons were counted and distinguished as GABA (39%), glycine (30%) and both GABA+glycine-immunopositive (31%). Densely-packed, flattened synaptic vesicles were only observed in glycine-immunopositive boutons while GABA-immunoreactive and GABA+glycine-immunoreactive boutons contained rounded or oval synaptic vesicles. Dense-core vesicles of different diameters were associated with conventional synaptic vesicles in 74% of GABA-only-immunopositive boutons, 50% of double GABA+glycine-immunopositive boutons, but were only observed in 9% of glycine-only-immunopositive boutons. The presence of terminals immunoreactive to either GABA or glycine contacting the motoneurons suggests that there is a morphological substrate for both GABAergic and glycinergic postsynaptic inhibition of motoneurons in the lamprey spinal cord.     

牛脊髓前角匀浆皮下注射损伤豚鼠脊髓运动神经元

目的探讨牛脊髓前角匀浆对豚鼠脊髓、前根及坐骨神经的影响。方法采用新鲜牛脊髓前角匀浆免疫豚鼠。观察脊髓、前根、坐骨神经光镜及超微结构的变化。结果豚鼠体重在第4次免疫后明显下降。脊髓前角运动神经元变性和丢失,有卫星、噬节及墓穴现象形成。电镜下最主要的表现是线粒体异常;其次神经元核周质内异常神经丝聚集,形成包涵体;轴突内异常神经丝聚集形成轴索球。前根及坐骨神经的变化,表现为轴索变性及继发的髓鞘改变。结论牛脊髓前角匀浆可以作为抗原引起豚鼠脊髓、前根及坐骨神经免疫所介导的损伤,为进一步研究运动神经元病的发病机制提供了可靠的方法。     

Intracellular recording from spinal cord motoneurons in the chronic cat

This report describes chronic intracellular techniques for identifying spinal cord motoneurons and recording from them for prolonged periods of time. The preparation is the intact, unanesthetized, undrugged, normally respiring cat. Comparisons are made between data obtained in the chronic state with that reported in the “acute” preparation, and standards are suggested for intracellular recording in the chronic preparation. Various traditionally used tests of neuronal functioning are outlined in the context of determining basic electrophysiological properties of motoneurons as a function of state-dependent influences.     

Duration of action potentials of motor units after spinal cord trauma

The duration of action potentials of motor units (MU) of the gastrocnemius and tibialis muscles was studied in patients with spinal cord trauma by the method of local electromyography. The duration of action potentials of gastrocnemius MU was found to be reduced on average by 27%, and of tibialis MU by 38% of the age norm. The degree of shortening of the action potentials of the gastrocnemius and tibialis MU was not directly dependent on the level of spinal cord injury, the length of time after trauma, or the severity of the spastic syndrome. Changes in the duration of action potentials of MU are evidently due to differences in the degree of atrophy developing as a result of prolonged adynamia.Department of Spinal Cord Trauma, A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR M. I. Kuzin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 9, pp. 267–270, September, 1978.     

Induced auxotonic muscle contractions in animals with lateral spinal cord hemisection under various cooling regimens

We studied the effects of long-term moderate hypothermia on induced auxotonic contractions of dog hindlimb extensor muscle after lateral hemisection of the spinal cord at the thoracolumbar region (T_XII-L_I–II) during the early and late postoperative periods (1–2 and 3–5 weeks, respectively). The mechanisms of antispastic effects of moderate hypothermia are different: the immediate effect was due to cold blockade of spinal neurons, while delayed effects resulted from activation of descending bilateral oversegmental motor apparatus. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 9, pp. 270–273, September, 1999     

Nontumor lesions of spinal cord and spine

Nontumor lesions of the spinal cord and spine include developmental disorders, cystic tumor-like lesions, vascular disorders, infective diseases, demyelinating diseases, degenerative diseases, metabolic and toxic disorders, and spinal cord injury. In addition, diseases of the spine and extradural spaces secondarily cause spinal cord injury. Aside from tumors, these include developmental abnormalities, inflammatory diseases, nontumor space-occupying lesions, and tumor-like lesions such as lipomas, vascular malformations, and cysts. Awareness is required of hemostatic agents used during surgery and subsequently presenting as space-occupying lesions, which have to be differentiated from recurrent lesions. On the therapeutic front, stem cell transplantation into spinal cord for treatment of neurodegenerative disorders, spinal cord injury, and multiple sclerosis is a challenging prospect.     

Wiring diagrams of functional connectivity in monosynaptic reflex arcs of the spinal cord

The direct functional connections between Ia and group II spindle afferent fibers from the cat medial gastrocnemius muscle and their homonymous motoneurons were examined in 10 acute experiments. Trains of stretch-evoked impulses from as many as 20 undivided sensory fibers were recorded simultaneously from 5 dorsal root filaments, as well as the corresponding excitatory postsynaptic potentials (EPSPs) they elicited in 10-20 motoneurons. Spike-triggered averaging [13] of these tape-recorded signals revealed the functional connections (or non-connections) between each Ia or group II afferent fiber and each motoneuron. Wiring diagrams constructed from these data indicate that the probability of a functional connection between an afferent fiber and a motoneuron decreases with the size of either and with the distance between the entry point of the afferent fiber and the motoneuron.