Study of pathways transmitting sympathetic-activating influences from hypothalamus to spinal cord

The properties of hypothalamic pathways activating sympathetic preganglionic neurons in the lateral horns of the spinal cord were studied in cats. This activation was shown to take place through reticulospinal sympathetic-activating neurons in the medulla. The possible zone of location of hypothalamic sympathetic-activating output neurons was shown by the scanning stimulation method to be in the posterolateral hypothalamus. Reticulospinal sympathetic-activating neurons in the medulla are probably excited monosynaptically by hypothalamo-sympathetic activating fibers projected on them.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 307–314, May–June, 1982.     

Escape behavior — brainstem and spinal cord circuitry and function

Recent work has demonstrated that the neural circuits mediating escape reactions in lower vertebrates and mammals have a common framework, with only two excitatory central synapses in the reflex arc. This relatively direct linkage from sense organs to muscles and the fact that segments of the network also transmit other motor commands help guarantee that escape always has priority over ongoing behaviors. Yet, modulation and plasticity contribute some variability to the expression of escape and, therefore, to the adequacy of its survival function.     

Recovery of supraspinal control of stepping via indirect propriospinal relay connections after spinal cord injury

Spinal cord injuries (SCIs) in humans and experimental animals are often associated with varying degrees of spontaneous functional recovery during the first months after injury. Such recovery is widely attributed to axons spared from injury that descend from the brain and bypass incomplete lesions, but its mechanisms are uncertain. To investigate the neural basis of spontaneous recovery, we used kinematic, physiological and anatomical analyses to evaluate mice with various combinations of spatially and temporally separated lateral hemisections with or without the excitotoxic ablation of intrinsic spinal cord neurons. We show that propriospinal relay connections that bypass one or more injury sites are able to mediate spontaneous functional recovery and supraspinal control of stepping, even when there has been essentially total and irreversible interruption of long descending supraspinal pathways in mice. Our findings show that pronounced functional recovery can occur after severe SCI without the maintenance or regeneration of direct projections from the brain past the lesion and can be mediated by the reorganization of descending and propriospinal connections. Targeting interventions toward augmenting the remodeling of relay connections may provide new therapeutic strategies to bypass lesions and restore function after SCI and in other conditions such as stroke and multiple sclerosis.     

Synaptic organization of supraspinal control over propriospinal ventral horn interneurons in cat and monkey spinal cord

Synaptic responses evoked in propriospinal neurons of the upper lumbar segments (L₃–L₄) by reticulo-, vestibulo-, and corticospinal impulses were studied in experiments on cats and monkeys. Propriospinal cells, identified by antidromic stimulation, were stained with Procion red, so that they could be localized in the different zones of the ventral horn. Monosynaptic reticular and vestibular excitatory influences were discovered in cats; convergence of these influences on the same neurons was demonstrated. In monkeys bulbospinal monosynaptic effects were supplemented by monosynaptic influences arriving from the motor cortex; convergence of monosynaptic excitatory influences from all supraspinal sources studied was found on some propriospinal neurons. The propriospinal neurons studied also had synaptic inputs from primary afferents.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 177–184, March–April, 1977.     

Extrapyramidal descending influences on neurons of the spinal cord in a superreflexia state

The spinal superreflexia state was modeled in experiments on rats using preliminary transection of the spinal cord and injection (in the course of the acute experiment) of 4-aminopyridine. An extremely high (reaching 15–20 mV) amplitude of monosynaptic reflex discharges (MRs) evoked by stimulation of the dorsal root and recorded from the ventral root (VR) L ₄ and the presence of an additional component in the above discharges were phenomena indicative of the development of the above state. Under such conditions, the amplitudes of the discharges evoked in the VR by electrical stimulation of the round window of the labyrinth (vestibular stimulation) and of the discharges elicited by stimulation of the motor cortex under conditions of bilateral transection of the pyramids increased several times. Thresholds of the VR responses to vestibular and cortical stimulations demonstrated an about threefold drop; latencies of the mass responses and responses of single spinal moto-and interneurons decreased about twofold, on average. The pattern of vestibular conditioning effects on the VR MRs changed: in intact animals vestibular stimulation induced inhibition of the VR MRs, while in animals with superreflexia such stimulation led to facilitation of the MRs. Cortical stimulation under conditions of pyramidotomy in both intact animals and animals with superreflexia resulted in facilitation of the VR MRs of a nearly the same intensity. The levels of convergence of the segmental and supraspinal effects on interneurons and motoneurons of the rat spinal cord dramatically increased under superreflexia conditions. The possible mechanisms of augmentation of the descending influences on spinal neuronal systems under the above conditions are discussed. Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 140–149, March–April, 2006.     

Glutamatergic innervation of rat skeletal muscle by supraspinal neurons: a new paradigm in spinal cord injury repair

Acetylcholine is the specific chemical code of spinal nerve terminal transmission at the mammalian neuromuscular junction (NMJ), whereas nicotinic acetylcholine receptors inserted into the membrane of muscle fibres mediate signalling for the muscle response. Glutamate has a primary role in neuromuscular transmission of organisms that are phylogenetically distant from mammals, the invertebrates, including insect and molluscs. Recent research has shown that diverting descending glutamatergic fibres in the spinal cord to rat skeletal muscle by means of a peripheral nerve graft causes the cholinergic synapse to switch to the glutamatergic type. These data demonstrate that under appropriate surgical manipulation supraspinal neurons can directly target muscle fibres and specify the postsynaptic receptors to achieve a functional glutamatergic NMJ.     

Reticulofugal influences of interneurons in the lateral region of gray matter of the cat spinal cord

Responses of lumbar interneurons located in the most lateral regions of Rexed's laminae IV–VII to stimulation of the medial longitudinal bundle and gigantocellular reticular nucleus of medullary pyramids, red nucleus, and peripheral nerves were investigated in cats anesthetized with pentobarbital. Stimulation of the reticulospinal fibers evoked monosynaptic excitation of many interneurons specialized for transmitting activity of the lateral descending systems, but not of peripheral afferents. Convergence of excitatory influences of all three descending systems (cortico-, rubro-, and reticulospinal) was observed on some cells of this group. In addition, monosynaptic "reticular" E PSPs appeared in interneurons transmitting activity of group Ia muscle fibers and in some interneurons of the flexor reflex afferent system. Stimulation of reticulospinal fibers evoked IPSPs in some neurons of this last group. Neurons not exposed to reticulofugal influences (both specialized neurons and interneurons of segmental reflex arcs) were located chiefly in the dorsal zones of the region studied. Recordings were also obtained from single fibers of the lateral reticulospinal tracts (conduction velocity from 26 to 81 m/sec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 525–536, September–October, 1973.     

Response of human motor units to spinal and supraspinal inhibition

High-selectivity surface electrodes were used to record the activity of single motor units of the human flexor pollicis brevis muscle and their involvement in the "silent period" and the inhibitory phase of the startle response was compared. In both these situations the degree of inhibition was greater for motor units whose action potential had a smaller amplitude. In cases of spinal inhibition, an independent direct relationship also was discovered between the intensity of the inhibitory response and the mean duration of the prestimulus interspike interval, which was completely absent during supraspinal inhibition. Correlation between the parameters of the inhibitory response of the single motor unit to influences of both types was significantly weaker than correlation between the effects of the spinal rebound phenomenon after both responses. The results suggest that involvement of spinal motoneurons in the inhibitory response is determined by interaction between several relatively independent factors.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 298–306, May–June, 1973.     

A growth factor from spinal cord.

Mitogenic activity is present at a variety of sites in the central nervous system. A growth factor was purified from neonatal bovine spinal cord. It has a pI of 9.5-9.8 and a molecular weight of about 11,000 daltons. Spinal cord growth factor is a basic polypeptide that is inactivated by extremely acid or basic conditions. Its mobility on SDS polyacrylamide gels suggests that this factor is different from pituitary FGF and brain FGF-1.     

Characteristics of the potential of the dorsal surface of the spinal cord in a chronic deficit of afferent influences

The changes of spinal cord dorsal potential (SCDP) has been studied on white rats to the posterior root stimulation at different intervals after sciatic nerve cutting. The increase of threshold, the decrease of amplitude, the growth of duration in some components of SCDP have been revealed on the site of the cutting. These changes were manifested at a less degree on the contralateral cutting site. A conclusion concerning the relative resistance of the spinal cord afferent system to the prolonged absence of peripheral afferent influence has been drawn.