Regional blood flow changes in response to thermal stimulation of the brain and spinal cord in the Pekin duck

Summary In conscious Pekin ducks, carotid and sciatic blood flows, respiratory rate, core and skin temperatures were measured during selective thermal stimulations of the spinal cord and rostral brain stem in thermoneutral (20 °C) and warm (32 °C) ambient conditions.At thermoneutral ambient temperature selective heating of the spinal cord by 2–3 °C (to 43–44 °C) increased the carotid blood flow by 138% and the sciatic blood flow by 46%. Increase in blood flows was correlated with increased breathing rate and beak and web skin temperatures.Selective cooling of the spinal cord at warm ambient temperatures and panting reduced the blood flow in both arteries and decreased the breathing rate.Heating or cooling of the brain stem showed generally very weak but otherwise similar responses as thermal stimulation of the spinal cord. In one duck out of six there was a marked effect on regional blood flow during brain stimulation.The results show that thermal stimulation of the spinal cord exerts a marked influence on regional blood flow important in thermoregulation, whereas the lower brain stem shows only a weak thermosensitivity, and stimulation caused only small cardiovascular changes of no major consequence in thermoregulation.     

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.     

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.     

Segmental inhibitory response in the frog spinal cord during orthodromic motoneuron activation

Different types of reflex discharges were produced in various preparations by stimulating the dorsal root of isolated frog spinal cord. These ranged from multiphasic low-amplitude waves to distinctly synchronized monosynaptic response. The discharges were followed by facilitation in the former and deep, protracted inhibition of response to test dorsal root stimulation in the latter. When interstimulus intervals measured 40–50 msec, inhibitory action was less pronounced than at shorter (15–30 msec) or longer (60–100 msec) intervals, thus indicating that at least two types of inhibition were at work, one at an earlier and the other at a later stage. Strychnine at a concentration of 10^–5 M effectively reinforced the former and blocked the latter, while 10^–4 M d-tubocurarine attenuated both types of inhibition substantially. It is concluded that inhibition of response occurs mainly as a result of recurrent activation of inhibitory systems via recurrent motoneuron axon collaterals when frog spinal cord afferents are excited. Intensity of the later (presynaptic) and earlier (postsynaptic) inhibition of reflex transmission is determined by the degree of synchrony in motoneuronal discharge in response to orthodromic stimulation.Institute of Medical Radiology, Academy of Medical Sciences of the USSR, Obninsk, Kaluga Oblast. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 343–350, May–June, 1987.     

Effects of hormones on axonal transport rate at the ventral root of the rat spinal cord

Male Wistar rats aged between 8 and 12 months were injected with 7–8 µl of aqueous L-leucine-¹⁴C (specific activity: 12543 megaBq/mM) in the region of the ventral horn at the level of segments L_5,6 of the spinal cord. Radioactivity was investigated in 3 mm segments of the ventral roots concerned within 1 h in all series of experiments. Estradiol dipropionate, testosterone propionate, insulin, and small doses of thyroxine were found to accelerate axonal transport of labeled material, while hydrocortisone, large doses of thyroxine, as well as castration and thyroidectomy delayed this process. It was thus concluded that axonal transport is under clear-cut hormonal control.Institute of Gerontology, Academy of Medical Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 459–464, July–August, 1990.     

Rate of axoplasmic transport of substances in spinal ventral roots of old rats and its dependence on energy metabolism

An aqueous solution of [¹⁴C]-L-leucine (specific activity 339 mCi/mmole) was injected in a dose of 7–8 µl into the region of the ventral horn of mature (8–12 months) and old (26–28 months) rats at the level of segments L5–L6 of the spinal cord. Radioactivity of different segments of the corresponding ventral roots was tested after 1–2.5 h. Labeled substances (including protein) were shown to migrate in mature rats in a rapid flow with a velocity of 408±10.9 and 380±22 mm/24 h, respectively, whereas in old rats the velocity was 217±11.3 and 200±40 mm/24 h. Slowing of the axoplasmic current in old rats increases with increasing distance from the neuron body. Uncoupling of oxidation and phosphorylation by injection of 2,4-dinitrophenol, inhibition of glycolysis by sodium fluoride, and hypoxic hypoxia all induce more marked slowing of the axoplasm flow in old rats. Small doses of sodium fluoride, on the other hand, accelerate the flow of axoplasm, and this correlates with elevation of the cAMP level in the ventral roots.Institute of Gerontology, Academy of Medical Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 189–194, March–April, 1984.     

N-methyl-D-aspartate effect on spontaneous activity of 16–20-day-old chick embryo spinal cord

The effects of N-methyl-D-aspartate (NMDA) and the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (2-APV), on spontaneous activity of dorsal and ventral roots (DR and VR, respectively) generated by isolated spinal cord from 16–20-day-old chick embryo were studied. This activity was synchronous oscillations of electrotonic potentials in DR and VR. There was no impulse activity in the VR. When NMDA was applied at 2–25 µM, the amplitudes of the oscillations increased, the impulse activities in VR and DR developed, and the tonic component of electrotonic potentials appeared. At 20 µM, 2-APV decreased both, the spontaneous and NMDA induced activity. After sectioning of the spinal cord, the neuronal network of the isolated dorsal arm conserved the capacity to generate spontaneous activity in the DR which increased after NMDA application. There was no rhythm in the ventral part of the spinal cord. The localization of the NMDA-sensitive neuronal network, generator of the rhythmic (motor) activity, in the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 205–213, March–April, 1991.     

Electrophysiological analysis of the organization of somatosensory thalamic inputs in the frog

Potentials produced in the frog thalamus by electrical stimulation of the peripheral nerves were investigated by sink and current source-density analysis. Sinks, which are viewed as potential generation sites, were located in three regions: the cell-free zone of the ventral thalamus adjoining the ventrolateral nucleus, the ventromedial and ventrolateral nuclei, and the caudal section of the dorsal thalamus. Evoked activity was recorded in individual neurons in the area of the second and third of these sinks. The first sink failed to form after section of the dorsal tracks of the spinal cord, while the remaining two only appeared after a considerably extended latency. It is suggested that nuclei of the ventral and caudal sections of the dorsal thalamus receive somatic impulses through the systems connected with the dorsal as well as the ventrolateral columns of the spinal cord. The direct projections of the primordial nuclei of dorsal columns may be involved in afferentation the ventral thalamus.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 687–695, September–October, 1986.     

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.     

Peculiarities of spinal hyperreflexia after combined synchronous transection of the sciatic nerve and chordotomy in rats

Parameters of the reflex discharges evoked by spinal dorsal root stimulation were measured in rats with the sciatic nerve and spinal cord (at low thorasic level) transected five days earlier. Monosynaptic discharges in the ventral roots were found to increase after the operation; the degree of increase was significantly higher as compared with that observed after isolated transections of the spinal cord or the nerve. The combined lesion of the nerve and spinal cord could result in the appearance of high-amplitude reflex discharge components, probably of a polysynaptic nature. We concluded, from the comparison of modifications of reflex discharges, that the mechanisms underlying spinal hyperreflexia after nerve or spinal cord lesions differ considerably from each other.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 197–202, May–June, 1994.     

Acetylcholinesterase distribution in chick spinal cord cultures

Summary Explants of 10–12 day chick embryo spinal cord were cultured by coverslip-roller tube method for 3–80 days. The cellular and subcellular localization of acetylcholinesterase activity in cultured neurons was studied by the thiocholine techniques of Karnovsky and Roots and Lewis and Shute.At the light microscopic level, acetylcholinesterase was demonstrated in the neurons of both ventral and dorsal horn regions. Occasionally neurons migrated in the outgrowth zone exhibited strong intracellular activity.At the electron microscopic level, acetylcholinesterase activity was found in the nuclear envelope, granular endoplasmic reticulum and the Golgi apparatus of the neurons. No enzyme reaction was detected in the glial cell cytoplasm.     

Effect of hypertonic solutions on electrical activity of the isolated frog muscle spindle

Changes in electrical activity of the isolated frog muscle spindle were investigated in hypertonic solutions obtained by adding 400 mM sucrose, glucose, or glycerol to Ringer's solution. The spontaneous firing rate in hypertonic sucrose and glucose solutions increased at first (for 3–5 min) and then fell rapidly to zero; the receptor potential and evoked spike activity diminished under these conditions and disappeared. In the hypertonic solution with glycerol a similar effect was observed but, unlike in the first two media, in this case spike activity returned after its initial increase to the normal level; a second rise in the firing rate was then observed up to a steady value which was higher than normal. After rinsing out the hypertonic sucrose and glucose solutions with ordinary Ringer's solution the spontaneous and evoked activity gradually returned to normal with a small overshoot. During the rinsing out of the hypertonic glycerol solution a sharp and considerable rise in spontaneous activity was first observed, while the changes in frequency of the evoked activity were negligible. The spike activity then returned to normal. The observed changes in electrical activity of the muscle spindle in hypertonic media are attributed to deformation of the sensory terminals and intrafusal muscle fibers (in the glycerol medium), leading to depolarization of the receptor membrane.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 291–299, May–June, 1976.     

Effects of tractotomy on reflex activity in the lumbar segment of the rat spinal cord previously disrupted by severing the sciatic nerve

Evoked electrical discharges in the spinal cord roots and dorsal surface ipsilateral to the previously severed sciatic nerve (as well as on the contralateral side) were investigated in rats one, three, seven, and 14 days after tractotomy. Monosynaptic reflex discharges in the ventral roots were found to return to 20–40% of the level of this parameter as measured on the contralateral side within seven and 14 days after tractotomy. Mean amplitude of antidromic dorsal root discharges, afferent peak, and the N₁ component of potential(s) at the dorsal surface ipsilateral to the severed nerve barely altered, remaining significantly lower than on the contralateral side. Mechanisms are suggested for the increase in monosynaptic reflex ventral root discharges ipsilateral to the severed nerve following tractotomy — thought to be largely due to raised sensitivity to transmitter at the motoneuronal membrane resulting from degeneration of synapses of descending pathways.Medical Institute of the Ukrainian Ministry of Health, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 366–371, May–June, 1989.     

Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Reflex discharges in intercostal nerves and activity of reticulospinal fibers of the ventral and lateral funiculi, evoked by stimulation of the reticular formation and of the splanchnic and intercostal nerves were investigated in cats anesthetized with chloralose (50 mg/kg). Brain-stem neuronal structures participating in the "relaying" of spino-bulbo-spinal activity were shown to lie both in the medial zones of the medullary and pontine reticular formation and in its more lateral regions; they include reticulospinal neurons and also neurons with no projection into the spinal cord. Structures whose stimulation led to prolonged (300–800 msec) inhibition of reflex spino-bulbo-spinal activity were widely represented in the brain stem, especially in the pons. Analogous inhibition of this activity was observed during conditioning stimulation of the nerves. Reticulospinal fibers of the ventral (conduction velocity 16–120 m/sec) and lateral (17–100 m/sec) funiculi were shown to be able to participate in the conduction of spino-bulbo-spinal activity to spinal neurons. In the first case fibers with conduction velocities of 40–120 m/sec were evidently most effective. Evidence was obtained that prolonged inhibition of this activity can take place at the supraspinal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 373–383, July–August, 1976.     

Distribution of myelinated and nonmyelinated nerve fibers of a cat cutaneous nerve in the spinal roots

The distribution of myelinated and nonmyelinated nerve fibers of the saphenous nerve of cats in the ventral and dorsal roots of the spinal cord was investigated by methods improving the signal—noise ratio in records of evoked responses from the nerve. The fibers of this nerve enter the spinal cord through roots of segments L_4–6. Nerve fibers with conduction velocities of between 80 and 0.38 m/sec were distributed in the dorsal roots of these segments. Four groups of nerve fibers with conduction velocities of 80–60, 40–30, 12.0–3.0, and 1.1–0.51 m/sec, possibly afferent in nature, were found in the ventral roots. The conditions of origin and detection of low-amplitude potentials in the roots of the spinal cord and the probable functional role of the nerve fibers in the ventral roots are discussed.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 647–654, November–December, 1975.     

Primary afferent depolarization distribution of the γ-aminobutyric acid system in frog spinal cord

In the frog spinal cord primary afferent depolarization (PAD) constitutes a powerful inhibitory control mechanism. It has been suggested that -aminobutyric acid (GABA) is the transmitter substance involved in the genesis of PAD. In these studies we show that maximal glutamic acid decarboxylase activity is localized roughly 400–600 m from the dorsal surface, and that correlates well with the intraspinal distribution of field potentials associated with PAD. Measurement of GABA in serial spinal cord sections cut in a dorsal-ventral direction shows that high levels of GABA are seen at 400–600 m, with a peak at 800 m from the dorsal surface. Stimulation at frequencies shown to produce PAD augments the release of endogenous GABA from a superfused frog hemicord preparation.     

Assessment of spinal temperature sensitivity in conscious goats by feedback signals

Summary In two conscious goats with chronically implanted spinal thermodes, fifty-six experiments were carried out at two environmental conditions of + 5 °C DB and 30 °C DB. The temperature of the spinal cord was altered by perfusing the thermodes with water whose temperature, as measured at the inlet of the thermodes, varied between 30 °C and 43 °C. Heat production, respiratory evaporative heat loss, rectal and oesophageal temperatures were measured. At the lower air temperature, spinal cord cooling resulted in an elevation of rectal temperature, while spinal cord heating caused a fall in rectal temperature. At the higher air temperature, spinal cord cooling did not result in an increase of rectal temperature. As in the lower air temperature, spinal cord heating caused a fall hi rectal temperature. The experiments suggest that the generation of spinal warm signals is independent of air temperature between +5 °C and 30 °C, while spinal cold signals are not generated in the absence of skin cold signals.     

Influence of Temocapril on Cultured Ventral Spinal Cord Neurons

Temocapril, a angiotensin-converting enzyme (ACE) inhibitor, was tested for neurotrophic activity in primary explant cultures of ventral spinal cord of fetal rats (VSCC). Temocapril had a remarkable effect on neurite outgrowth with a 4.2- to 5.1-fold increased over that of control VSCC at their effective concentrations. In temocapril-treated VSCC, choline acetyltransferase (ChAT) activity was also increased 2.4–3.2 times over that of control at 10^–9 and 10^–8 M, respectively. Our data suggest that temocapril is a candidate for neurotrophic factors on spinal motor neurons in vitro. A possible therapeutic role for temocapril in damaged motor neurons, such as in motor neuropathy and amyotrophic lateral sclerosis, remains to be defined.     

Changes in electrical activity of spinal cord neurons in adrenalectomized rats under the effects of corticosteroid hormones

The effects of glucocorticoid (dexamethasone) and mineralocorticoid (deoxycorticosterone) hormones on electrical excitability of nerve cells belonging to the dorsal and ventral horns of the spinal cord induced by stimulating the sciatic nerve, as well as background and evoked activity in single dorsal horn cells were investigated during experiments on adrenalectomized spinal rats using intracellular techniques for recording potential. Both hormones were found to produce mainly facilitatory effects in adrenalectomized animals, manifesting in increased background activity rates in single cells and higher amplitude of field potentials in nerve cells of the dorsal half of the spinal cord. It was shown that neuronal response followed different patterns in the ventral half of the spinal cord gray matter under the action of gluco- and mineralocorticoids: dexamethasone and deoxycorticosterone respectively increased and reduced the amplitude of field potentials in the motoneuronal region. Findings indicate the modulatory influence of adrenal cortical hormones on the electrical activity of spinal cord neurons.Institute of Experimental Biology, Academy of Sciences of the Armenian SSR, Erevan. I. A. Orbeli Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 233–238, March–April, 1989.     

Effect of adequate stimulation on the discharge pattern of an isolated frog muscle spindle

Discharges from an isolated frog muscle spindle during mechanical stimulation of varied amplitude, velocity, and shape were investigated. The firing rate during a linear increase in strength of the stimulus is determined by its amplitude, whereas the change in firing rate is determined by the rate of increase of amplitude. With sinusoidal stimulation the firing rate apparently reproduces stimulus shape, i.e., the muscle spindle is sensitive not only to amplitude and velocity, but also to acceleration of the stimulus. Sensitivity to acceleration is most probably due to the change in threshold of appearance of action potentials observed during variation of the speed of stretching.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 426–433, July–August, 1976.