Localization of intraspinal longitudinal systems participating in the spreading of viscerosomatic activity.

In experiments on the cats the relationship was studied of individual columns of the spinal cord to irradiation of the early (propriospinal) and late component of viscerosomatic reflex responses. It was found that the intraspinal systems involved in the descending spread of activity forming the early and the late component of the splanchnic response along the spinal cord were localized mainly in the anterolateral quadrants of the white matter. The descending systems are bilateral and cross at the segmental level. The pathways participating in the spread of the two-component somatomotor discharge evoked by intercostal nerve stimulation are localized in the same area. A bilateral lesion of the dorsal part of the lateral columns of segments C1 to C3 strongly inhibited the late component of the reflex responses. Inhibition was reversible, showing that systems modifying the development and course of the late component are localized in this region. Lesion-induced changes in viscerosomatic reflex responses were parallel with changes in somatomotor discharges. This finding supports the opinion that the pathways involved are localized close together and that their action is modified by similar factors.     

Long systems of the dorsolateral fascicle: influence of afferentation from the splanchnic region.

The influence of afferentation from the splanchnic region on the activity of long systems in the dorsolateral fascicle (DLF) was studied in chloralose-anaesthetized cats. Ascending axons (the dorsal spinocerebellar tract, DSCT and the spinocervical tract, SCT) did not respond to splanchnic stimuli. Conditioning from the splanchnic region modified their activity; the effect (mainly inhibitory) was strongest in the case of exteroceptive channels. The reaction of long propriospinal neurones depended on whether they belonged to ascending or descending pathways. No responses to splanchic stimuli were observed in the axons of ascending (proprioceptive, exteroceptive) units and conditioning from the splanchnic region only modified their activity. In decending axons, synaptic discharges with a long latent period (over 20 msec) were generated. The interaction of inputs from the visceral and somatosensory regions resulted in reciprocal inhibition of the tested activity. In axons descending from suprasegmental areas, splanchnic afferentation generated synaptic discharges with a time course comparable to spino-bulbo-spinal activity. Interaction with the responses from somatic nerves resulted inhibition of the tested activity. The results confirmed that the splanchnic region participates in modifying and evoking activity in the long DLF systems.     

Cortico- and rubrofugal activation of interneurons forming the propriospinal pathways of the dorsolateral funiculus of the cat spinal cord

Interneurons of the lumbar division of the cat spinal cord responding after a short latent period with intensive excitation to stimulation of the medullary pyramids and red nucleus but not responding (or excited after a long latent period) to stimulation of peripheral nerves were investigated by microelectrode recording. Most of these neurons, located in the lateral zones of Rexed's laminae IV–VII of the gray matter, were identified as propriospinal cells sending axons into the dorsolateral funiculus of the white matter (mean velocity of antidromic conduction in the group 34.6 m/sec). Marked convergence of corticofugal and rubrofugal excitatory influences was found on the overwhelming majority of neurons. Some neurons were activated monosynaptically by fast-conducting fibers of both descending systems. The minimal and mean values of the latent periods of the pyramidal EPSPs for the neurons tested were 4.5 and 6.28 msec, and for the rubral EPSPs 3.3 and 4.94 msec respectively. A distinguishing feature of the activation of these neurons is the intensive potentiation of their synaptic action on the arrival of a series of corticofugal and rubrofugal waves.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 489–500, September–October, 1972.     

Lumbar collaterals of neurons of the C6 segment projecting to sacral segments of the cat spinal cord

Electrophysiological investigations of neurons of the C6 segment of the spinal cord were made in α-chloralose anesthetized animals. It was established in the experiments that a part of long descending propriospinal neurons originating in the sixth cervical segment (C6) that projected to sacral segments (S1/S2) gave off collateral branches at the level of the fourth lumbar segment (L4). Several types of neurons were distinguished according to the ipsilateral, contralateral or bilateral course of axons at the thoracic level as well as their lumbar or sacral projections. The cell bodies of 58 identified neurons were distributed in Rexed's laminae VII and VIII of the gray matter. Axons descended in lateral funiculi and their conduction velocities varied from 50 to 85 m/s. The existence of collaterals to various segments of the lumbosacral enlargement indicates that the same information conveyed by long descending propriospinal neurons can reach separate motor centers controlling various muscles of the hindlimbs.     

Functional properties of propriospinal pathways of the dorsolateral tract of the cat spinal cord

The characteristics of conduction of the excitation wave along propriospinal fibers of the dorsolateral tract of the spinal cord were studied in cats anesthetized with pentobarbital. At a preliminary operation, 10–18 days beforehand, lateral hemisection of the spinal cord was performed, cranially in the lumbar division and caudally and cranially in the cervical division to the segments to be studied, leading to degeneration of the long descending and ascending fibers. During stimulation, the dorsolateral tract developed a composite response consisting of a positive-negative wave recorded up to 60–65 mm (4 or 5 segments) from the point of stimulation. The mean conduction velocity of this wave in the lumbar division was 37.9 m/sec compared with 44.5 m/sec in the cervical division. From its properties as a whole this wave can be regarded as the result of excitation of relatively fast-conducting propriospinal fibers of the dorsolateral tract. If the strength of stimulation was increased, late components began to appear in the response. These were evidently connected with excitation of thinner propriospinal fibers and synaptic activation of other other groups of spinal neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 54–60, January–February, 1973.     

Responses of motor neurons of lumbar section of spinal cord elicited by the activity of the propriospinal pathways

We have carried out intracellular recording from the motor neurons of the lumbar section of the cat spinal cord with electrical stimulation of the propriospinal axons descending in the dorsolateral funiculus. To prevent activation of the long descending pathways of the lateral funiculus, ipsilateral hemisectioning of the spine was performed in the segments L₁-L₂ 10–14 days before the experiment. Stimulation of the dorsolateral funiculus in two segments cranial to the point of recording elicited in the flexor motor neurons essentially e.p.s.p. and in the extensor neurons i.p.s.p. with a latent period, on the average, of 1.97 and 1.93 msec, respectively. The amplitude of such p.s.p. considerably rose with rise in the frequency of stimulation of the funiculus to 50–100 a second. Activation of the segmental interneurons was observed only in a few cases. It is assumed that the synaptic processes elicited in the lumbar motor neurons are the result of the monosynaptic influences of the propriospinal neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 5–14, July–August, 1969.     

Study of neuronal structures of the brain stem which produce rapid reactions in reticulo-spinal pathways

The total electrical discharges of the ventral and ventrolateral funiculi of the 11th thoracic segment of the spinal cord in response to stimulation of different points of the pons varolii and the medulla oblongata between frontal planes P-2 and P-12 were investigated in decerebrated cats. Regions were found corresponding to the location of the oral and caudal reticular nuclei of the pons and the rostral section of the reticular giant cell nucleus whose stimulation caused a short-latent discharge in the ventral funiculus (latent period 1.6–1.9 msec) with maximum amplitude. It was concluded that such a discharge is due to the direct stimulation of a rather homogeneous group of fast-conducting reticulo-spinal fibers which terminate mainly in the ventral funiculus and which have an average rate of conduction of 131 m /sec. When the same regions were stimulated, the short-latet discharge of the ventro-lateral funiculus had a considerably lower amplitude and was accompanied by a powerful, late discharge with a latent period of about 3.3 msec. It was assumed that this funiculus consists mainly of fibers with a lower rate of conduction which originate in a broader region of the medial RF of the brain stem. Stimulation of contralateral regions of the reticular formation of the medulla oblongata evoked only a weak short-latent discharge in the ventral funiculus; the late component of the discharge in this case was considerably stronger.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 274–283, May–June, 1971.     

Descending neuronal projections to the lumbar segment of the spinal cord of cats

In the experiments, performed on cats by means of retrograde axonal horseradish peroxidase transport, localization of the sources of descending supra- and propriospinal projections to the area of the lumbar parts of the spinal cord, where the generator of locomotor movements is located. After local administration of horseradish peroxidase into the spinal cord, the greatest amount of the labelled neurons is observed in the ipsilateral reticular formation and in the Koelliker-Fuse nucleus. Comparison of the number of neurons, forming the descending projections from the I cervical up to the IV lumbar segments demonstrates an essential predominance of short propriospinal connections over the long, as well as over the supraspinal ones.     

Synaptic links of propriospinal neurons of the lumbar section of the cat spinal cord

The distribution of propriospinal fiber terminals of the lateral funiculus in the lumbar segments of the cat spinal cord was examined by light and electron microscopy. For the selective demonstration of these terminals, preliminary hemisectioning of the brain at the boundary of the thoracic and lumbar segment, eliminating all the long descending pathways, and subsequent hemisectioning or sectioning of the lateral funiculus at the level of the third lumbar segment was carried out. It was established by staining the degenerating endings (by the Fink—Heimer method) that the terminals of the descending and ascending propriospinal fibers, which form part of the lateral and ventral funiculi, are located mainly in the lateral and medial parts of lamina VII and the dorsal section of lamina VIII, according to Rexed, as well as in the regions adjacent to the dorsolateral and ventromedial motor nuclei. A large number of these terminals is found in the corresponding regions of the gray matter on the contralateral side of the brain. Since, in the case of selective injury of the lateral funiculus the number of degenerating terminals in lamina VIII is noticeably decreased, it can be assumed that the propriospinal neuron terminals of the ventral funiculus are concentrated mainly in lamina VIII. The axons of the propriospinal neurons extend over several segments both in the ascending and in the descending directions. It was shown in an electron microscopic study of the regions in which most of the propriospinal terminals are located that these terminals are of an axo-dendritic nature and terminate in the dendrites of both inter- and motor neurons. Their degeneration can be of the "light" or "dark" type.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 401–407, July–August, 1971.     

Comparative dimensions of propriospinal neurons of different structural and functional groups in cats

A statistical comparison was made of geometric characteristics (area of cross section of the soma and proximal dendrites and d_con, the diameter of the circle of equivalent area to it) of propriospinal neurons of the cat spinal cord labeled with horseradish peroxidase. The linear dimensions of these cells differed by a factor of about seven. The mean d_con of propriospinal neurons in the cervical, thoracic, and lumbar divisions, whose axons reach level L6-7, was 39.9, 30.8, and 36.9 µm, respectively; direct correlation between the size of the neurons and the length of their axons was thus not observed. Characteristics of distribution of sizes of units in the cervical and thoracic divisions indicate the presence of two cell populations forming long propriospinal tracts; one consisting of a few, large neurons, concentrated in the cervical segments, the other consisting of small neurons, distributed among the cervical and thoracic segments. The mean d_con of neurons in the cervical division whose axons reach more caudal segments of the same cervical division was 44.2 µm (on account of a considerable number of large units in the ventral horn), evidence of the large relative size of the short-axon propriospinal neurons in this division of the spinal cord. Neurons located in the dorsal parts of the dorsal horn were the smallest in size, those located in the ventral horn were the largest. No significant differences were found in the dimensions of propriospinal neurons with uncrossed and crossed axons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 238–247, March–April, 1984.     

正常中国人中枢运动系统传导时间的测定

本文应用高电压、低输出阻抗刺激器,经皮给予大脑皮层和脊髓电刺激(BSPES),同时在上肢鱼际(Thenar)和下肢胫骨前肌(Muscle tibialis anterior)上记录诱发肌肉动作电位,测定了64名正常健康中国人(男:46;女:18)的中枢运动系统传导时间。受试者年龄为20—67岁,身高为156—185cm。刺激大脑皮层出现反应的潜伏期与刺激脊髓出现反应的潜伏期之差为中枢运动传导时间(CMCT)。实验测得鱼际的 CMCT 为6.69±1.48ms;胫骨前肌的 CMCT 为12.90±1.59ms。经统计学处理证明,CMCT 与左右侧肢体、性别、年龄及身高无关。说明 CMCT 是无损伤测定与评价中枢运动系统功能的较精确的一种客观指标。本文根据所测数据,计算出脊髓内运动传导速度为71.34±10.89 m/s,与文献报道的锥体束传导速度50—70 m/s 相近。因此,CMCT 反映了锥体束的传导时间。     

Functional differentiation of splanchnic A delta fibres in relation to viscerosomatic reflexes.

The splanchnic afferent signal in the myelinated fibre spectrum was analysed in cats and its relationship to viscerosomatic reflex activity was studied. In addition to Abeta and Adelta components, a further elevation was observed in the sympathetic chain neurogram. According to the conduction rate (15 plus or minus 4 m/sec), it was caused by myelinated fibres 2-3 mu in diameter. The presence of this component at thoracic dorsal root level, or in the sympathetic chain in stimulation of the postganglionic part of the nerve trunk, confirmed the afferent nature of the observed activity. The threshold stimulus for these fibres, which were termed group Adelta2, was four times higher than for Abeta fibres. Correlation of the neurogram with evoked activity in the intercostal nerves confirmed the different functional role of group Adelta2 fibres. Adelta2 fibre activity evokes the early component of the two-component viscerosomatic discharge and Adelta2 fibre activity its later component. The authors discuss the functional significance of Adelta2 fibres, which probably mediate nociceptive information from the viscera.     

Polysynaptic components of the early somato-sympathetic reflex response in lumbar white rami

The second and third components of the somato-sympathetic reflex discharge in the lumbar white rami were investigated in anesthetized cats. Both components, under different experimental conditions, may undergo changes that are: parallel, not parallel, or actually opposite in direction to those in components of the propriospinal wave of the somato-somatic reflex. This suggests that the interneuronal apparatus of both types of reflexes may include common and separate components. It is postulated that the separate components of the somato-sympathetic reflex may be formed by discharges of sympathetic preganglionic neurons whose axons conduct at different velocities. On the basis of calculations of the central delay time it is concluded that the second component is formed by discharges of lateral horn neurons and the third component by neurons with axons conducting excitation at less than 1.5 m/sec, found in the lateral part of the intermediate zone.     

Interaction of visceral and somatic afferentation at the level of postsynaptic spinal cord elements.

The interaction of visceral and somatic afferentation at the level of postsynaptic spinal cord elements was studied in cats. The effect of conditioning stimuli on the propriospinal (PS) and suprasegmental (SS) component of the tested unit responses was compared. Afferentation from the splanchnic nerve completely inhibited the SS component of somatomotor motoneuronal responses; the PS component was only partly inhibited. Inhibition persisted even after the conditioning stimulus-induced changes in the membrane potential of the motoneurones had disappeared. The activity of the interneurones responsing synchronously with the SS component of the efferent discharges was also completely inhibited in the same intervals. The inhibitory effect of splanchnic afferentation on the PS component of interneuronal discharges evoked by the stimulation of somatic afferents was significantly less effective. The results of interaction for test responses from the cutaneous and muscular nerves was the same. When splanchnic responses were tested during conditioning from somatosensory areas, inhibitory control was found to be reciprocal. The authors discuss the question of the structures and mechanisms participating in functional relations between the autonomic and somatic nervous system in the spinal cord.     

Chemical activation of C1-C2 spinal neurons modulates intercostal and phrenic nerve activity in rats

Chemical activation of upper cervical spinal neurons modulates activity of thoracic respiratory interneurons in rats. The aim of the present study was to examine the effects of chemical activation of C(1)-C(2) spinal neurons on thoracic spinal respiratory motor outflows. Electroneurograms of left phrenic (n = 23) and intercostal nerves (ICNs, n = 93) between T(3) and T(8) spinal segments were recorded from 36 decerebrated, vagotomized, paralyzed, and ventilated male rats. To activate upper cervical spinal neurons, glutamate pledgets (1 M, 1 min) were placed on the dorsal surface of the C(1)-C(2) spinal cord. Glutamate on C(1)-C(2) increased ICN tonic activity in 56/59 (95%) ICNs. The average maximal tonic activity of ICN was increased by 174% (n = 59). After spinal transection at rostral C(1), glutamate on C(1)-C(2) still increased ICN tonic activity in 33/35 ICNs. However, the effects of C(1)-C(2) glutamate on ICN phasic activity were highly variable, with observations of augmentation or suppression of both inspiratory and expiratory discharge. C(1)-C(2) glutamate augmented the average amplitude of phrenic burst by 20%, whereas the increases in amplitude of ICN inspiratory activity, when they occurred, averaged 120%. The burst rate of phrenic nerve discharge was decreased from 34.2 +/- 1.6 to 26.3 +/- 2.0 (mean +/- SE) breaths/min during C(1)-C(2) glutamate. These data suggested that upper cervical propriospinal neurons might play a role in descending modulation of thoracic respiratory and nonrespiratory motor activity.     

c-Fos expression in rat brain stem and spinal cord in response to activation of cardiac ischemia-sensitive afferent neurons and electrostimulatory modulation

The purpose of this study was to identify central neuronal sites activated by stimulation of cardiac ischemia-sensitive afferent neurons and determine whether electrical stimulation of left vagal afferent fibers modified the pattern of neuronal activation. Fos-like immunoreactivity (Fos-LI) was used as an index of neuronal activation in selected levels of cervical and thoracic spinal cord and brain stem. Adult Sprague-Dawley rats were anesthetized with urethane and underwent intrapericardial infusion of an "inflammatory exudate solution" (IES) containing algogenic substances that are released during ischemia (10 mM adenosine, bradykinin, prostaglandin E2, and 5-hydroxytryptamine) or occlusion of the left anterior descending coronary artery (CoAO) to activate cardiac ischemia-sensitive (nociceptive) afferent fibers. IES and CoAO increased Fos-LI above resting levels in dorsal horns in laminae I-V at C2 and T4 and in the caudal nucleus tractus solitarius. Dorsal rhizotomy virtually eliminated Fos-LI in the spinal cord as well as the brain stem. Neuromodulation of the ischemic signal by electrical stimulation of the central end of the left thoracic vagus excited neurons at the cervical and brain stem level but inhibited neurons at the thoracic spinal cord during IES or CoAO. These results suggest that stimulation of the left thoracic vagus excites descending inhibitory pathways. Inhibition at the thoracic spinal level that suppresses the ischemic (nociceptive) input signal may occur by a short-loop descending pathway via signals from cervical propriospinal circuits and/or a longer-loop descending pathway via signals from the nucleus tractus solitarius.     

Activation of slowly conducting medullary raphe-spinal neurons, including serotonergic neurons, increases cutaneous sympathetic vasomotor discharge in rabbit

Neurons in the rostral medullary raphe/parapyramidal region regulate cutaneous sympathetic nerve discharge. Using focal electrical stimulation at different dorsoventral raphe/parapyramidal sites in anesthetized rabbits, we have now demonstrated that increases in ear pinna cutaneous sympathetic nerve discharge can be elicited only from sites within 1 mm of the ventral surface of the medulla. By comparing the latency to sympathetic discharge following stimulation at the ventral raphe site with the corresponding latency following stimulation of the spinal cord [third thoracic (T3) dorsolateral funiculus] we determined that the axonal conduction velocity of raphe-spinal neurons exciting ear pinna sympathetic vasomotor nerves is 0.8 +/- 0.1 m/s (n = 6, range 0.6-1.1 m/s). Applications of the 5-hydroxytryptamine (HT)(2A) antagonist trans-4-((3Z)3-[(2-dimethylaminoethyl)oxyimino]-3-(2-fluorophenyl)propen-1-yl)-phenol, hemifumarate (SR-46349B, 80 microg/kg in 0.8 ml) to the cerebrospinal fluid above thoracic spinal cord (T1-T7), but not the lumbar spinal cord (L2-L4), reduced raphe-evoked increases in ear pinna sympathetic vasomotor discharge from 43 +/- 9 to 16 +/- 6% (P < 0.01, n = 8). Subsequent application of the excitatory amino acid (EAA) antagonist kynurenic acid (25 micromol in 0.5 ml) substantially reduced the remaining evoked discharge (22 +/- 8 to 6 +/- 6%, P < 0.05, n = 5). Our conduction velocity data demonstrate that only slowly conducting raphe-spinal axons, in the unmyelinated range, contribute to sympathetic cutaneous vasomotor discharge evoked by electrical stimulation of the medullary raphe/parapyramidal region. Our pharmacological data provide evidence that raphe-spinal neurons using 5-HT as a neurotransmitter contribute to excitation of sympathetic preganglionic neurons regulating cutaneous vasomotor discharge. Raphe-spinal neurons using an EAA, perhaps glutamate, make a substantial contribution to the ear sympathetic nerve discharge evoked by raphe stimulation.     

Localization and distribution patterns of nicotinamide adenine dinucleotide phosphate diaphorase exhibiting axons in the white matter of the spinal cord of the rabbit

The funicular distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-exhibiting axons was examined in the white matter of the rabbit spinal cord by using horizontal, parasaggital, and transverse sections. Four morphologically distinct kinds of NADPHd-exhibiting axons (2.5–3.5 m in diameter) were identified in the sulcomarginal fasciculus as a part of the ventral column in the cervical and upper thoracic segments and in the long propriospinal bundle of the ventral column in Th3–L3 segments. Varicose NADPHd-exhibiting axons of the sympathetic preganglionic neurons, characterized by widely spaced varicosities, were found in the ventral column of Th2–L3 segments. A third kind of NADPHd-positive ultrafine axons, 0.3–0.5 m in diameter with numerous varicosities mostly spherical in shape, was identified in large number within Lissauer's tract. The last group of NADPHd-exhibiting axons (1.0–1.5 m in diameter) occurred in the Lissauer tract. Most of these axons were traceable for considerable distances and generated varicosities varying in shape from spherical to elliptical forms. The majority of NADPHd-exhibiting axons identified in the cuneate and gracile fascicles were concentrated in the deep portion of the dorsal column. An extremely reduced number of NADPHd-exhibiting axons, confirmed by a computer-assisted image-processing system, was found in the dorsal half of the gracile fascicle. Axonal NADPHd positivity could not be detected in a wide area of the lateral column consistent with the location of the dorsal spinocerebellar tract. Numerous, mostly thin NADPHd-positive axonal profiles were detected in the dorsolateral funiculus in all the segments studied and in a juxtagriseal portion of the lateral column as far as the cervical and lumbar enlargements. A massive occurrence of axonal NADPHd positivity was detected in the juxtagriseal layer of the ventral column all along the rostrocaudal axis of the spinal cord. The prominent NADPHd-exhibiting bundles containing thick, smooth, nonvaricose axons were identified in the mediobasal and central portion of the ventral column. First, the sulcomarginal fasciculus was found in the basal and medial portion of the ventral column in all cervical and upper thoracic segments. Second, more caudally, a long propriospinal bundle displaying prominent NADPHd positivity was localized in the central portion of the ventral column throughout the Th3–L3 segments.     

Weight-Bearing Locomotion in the Developing Opossum,Monodelphis domestica following Spinal Transection: Remodeling of Neuronal Circuits Caudal to Lesion

Complete spinal transection in the mature nervous system is typically followed by minimal axonal repair, extensive motor paralysis and loss of sensory functions caudal to the injury. In contrast, the immature nervous system has greater capacity for repair, a phenomenon sometimes called the infant lesion effect. This study investigates spinal injuries early in development using the marsupial opossum Monodelphis domestica whose young are born very immature, allowing access to developmental stages only accessible in utero in eutherian mammals. Spinal cords of Monodelphis pups were completely transected in the lower thoracic region, T10, on postnatal-day (P)7 or P28 and the animals grew to adulthood. In P7-injured animals regrown supraspinal and propriospinal axons through the injury site were demonstrated using retrograde axonal labelling. These animals recovered near-normal coordinated overground locomotion, but with altered gait characteristics including foot placement phase lags. In P28-injured animals no axonal regrowth through the injury site could be demonstrated yet they were able to perform weight-supporting hindlimb stepping overground and on the treadmill. When placed in an environment of reduced sensory feedback (swimming) P7-injured animals swam using their hindlimbs, suggesting that the axons that grew across the lesion made functional connections; P28-injured animals swam using their forelimbs only, suggesting that their overground hindlimb movements were reflex-dependent and thus likely to be generated locally in the lumbar spinal cord. Modifications to propriospinal circuitry in P7- and P28-injured opossums were demonstrated by changes in the number of fluorescently labelled neurons detected in the lumbar cord following tracer studies and changes in the balance of excitatory, inhibitory and neuromodulatory neurotransmitter receptors’ gene expression shown by qRT-PCR. These results are discussed in the context of studies indicating that although following injury the isolated segment of the spinal cord retains some capability of rhythmic movement the mechanisms involved in weight-bearing locomotion are distinct.     

Effect of epicortical stimulation on depolarization of primary afferents in rats during early postnatal ontogenesis

Studies have been made on the parameters cord dorsum potentials (CDP) during stimulation of sensorimotor cortex in rats during first month of their postnatal life. First CDP were recorded from the 10th day, their latency being equal to about 80 msec, amplitude--65-70 microV, duration--more than 200 msec. During postnatal life of rats, the latent period decreases twice, the amplitude increases more than 3-fold, whereas the duration remains almost unchanged. These data indicate maturation of the descending pathways to the spinal cord, the increase in the propagation rate along these pathways and formation of segmentary mechanisms responsible for the generation of CDP. The effect of stimulation of the sensorimotor cortex on depolarization of primary afferent was also investigated. It was found that from the 2nd week of postnatal, life, formation of supraspinal control of afferent impulsation takes place.