Motoneurone Depression by Norepinephrine

A NIR fluorescent probe tracing norepinephrine exocytosis and depression occurrence at the cellular level

A NIR fluorescent probe tracing norepinephrine exocytosis and depression occurrence at the cellular level revealed that norepinephrine exocytosis rather than the inherent intracellular concentration was related with depression.

Pharmacology of descending noradrenergic systems in relation to motor function

The function of descending noradrenergic systems in the spinal ventral horn has not been fully elucidated. We have reviewed our own findings and those of others relating to motor function of these noradrenergic systems. We studied the effects of adrenergic drugs on spinal reflexes, decerebrate rigidity, and noradrenaline release from the spinal cord in rats, and motoneuron activity in spinal cord slices isolated from adult rats. It was shown that the descending noradrenergic systems were facilitatory to the motor system, and that alpha 1-antagonistic action at the spinal cord and alpha 2-agonistic action at the brainstem inhibited spinal motor activity by blocking spinal alpha 1-receptors and by reducing the release of noradrenaline in the spinal cord, respectively.

Cholinergic modulation through biogenic amines during development of the chick spinal cord

Our previous analyses of the functional maturation of cholinergic neurotransmission in the chick embryo spinal cord showed that 12 days of development represents a crucial stage in the maturation of cholinergic neurotransmission. Since supraspinal inputs are essential for the modulation of motoneuron activity in the embryo, we studied, using a pharmacological approach, the regulatory effects of biogenic amines on the developing cholinergic neurotransmission. We show that, in spite of the early occurrence of serotonin and norepinephrine in the developing spinal cord, the modulatory influences of these biogenic amines on motoneurons can only be effective from 12 days of incubation onwards. It also appears that the inputs of biogenic amines on cholinergic activity is a sequential event. Whereas serotonin (5-HT) begins to stimulate cholinergic activity from 12 days of incubation, norepinephrine inputs are only observed at later stages (17 days of development). These observations underline the specific turning point in the functional maturation of motoneurons, we noted in our previous studies. At the end of embryonic life a specific interrelationship between the biogenic amines was noted, its effect on the cholinergic system may lead to a more precise motor control, preparing the chick embryo for hatching.

Immunocytochemical mapping of noradrenergic projections to the rat spinal cord with an antiserum against noradrenaline

The mapping of noradrenergic innervation was performed in transverse and longitudinal sections of the adult rat spinal cord using noradrenaline immunocytochemistry. Noradrenergic fibres and terminals were distributed in the dorsal horn (mainly in the superficial part), in the vicinity of the different groups of motoneurons, and concentrated in the intermediolateral cell column and around the central canal. The ultrastructural study showed principally axodendritic synapses in the ventral horn and in the intermediolateral cell column. Fewer axosomatic synapses were detected. In the dorsal horn, noradrenaline-innervation was predominantly non-synaptic. It is hypothesized that the noradrenergic modulation of nociception is not mediated through classical synapses. The concept of 'volume transmission' can explain such an influence. Conversely, noradrenaline may be involved in the control of locomotion and automatic functions through conventional synapses.

Norepinephrine effects on spinal motoneurons

Intracellular recordings from cat spinal motoneurons in situ demonstrated that microiontophoretic application of NE with low-intensity ejection currents produces a slowly developing, small-amplitude depolarization of the cells, in contrast to early reports of NE-induced hyperpolarization. This depolarization was associated with an increase in excitability of the cells and a decrease in membrane conductance. These observations are consistent with the hypothesis that NE reduces potassium conductance in spinal motoneurons as has been proposed for facial motoneurons (VanderMaelen and Aghajanian, 1980) and thalamic neurons (McCormick and Prince, 1988). The time course of the facilitatory effects of NE on cat motoneuron excitability recorded intracellularly agreed very closely with the time course of NE-induced facilitation of glutamate-evoked excitability in rat spinal motoneurons recorded extracellularly. The similarity of the observations in rats and cats suggests that NE functions generally to enhance mammalian motoneuron responsiveness to excitatory input.

Supraspinal projections to the ventromedial lumbar spinal cord in adult male rats

In the present study, the fluorescent tract tracing compound Fluorogold was used to study the afferents of the SNB (spinal nucleus of the bulbocavernosus), which is found in the ventromedial spinal grey and innervates penile muscles of the male rat. Fluorogold was iontophoretically injected into the SNB, which was located by recording antidromic activation of the motoneurons after stimulating the bulbocavernosus muscle. Retrogradely labeled cells were found in laminae I, V-IX, and area X of the lumbar spinal cord, suggesting segmental input to the SNB. Supraspinally, the greatest number of labeled cells were in the medulla oblongata, particularly in the lateral vestibular nucleus, gigantocellular reticular nucleus, and ventral and alpha divisions of the gigantocellular reticular nucleus. Labeled cells were also observed in the medullary raphe nuclei, the ventral medullary nucleus, and the spinal vestibular nucleus. In the pons, labeled cells were observed in the nucleus locus coeruleus, nucleus subcoeruleus, and caudal pontine reticular nucleus. No labeled cells were present in the cerebellum, rostral pons, mesencephalon, and cerebral cortex. The most rostral occurrence of labeled cells was in the medial parvicellular division of the hypothalamic paraventricular nucleus. These potential afferents to the SNB identified in male rats imply that the inputs to motoneurons that innervate sex-specific muscles involved in male reproductive behavior may be similar to the inputs to lumbar motoneurons described in the female rat that innervate muscles involved in female sexual behavior.

Spinal alpha 1- and alpha 2-adrenoceptors mediate facilitation and inhibition of spinal motor transmission, respectively

The role of descending noradrenergic fibers in the spinal motor systems was investigated using spinal reflexes in acutely spinalized rats. In rats pretreated with the MAO inhibitor clorgyline-HCl (1 mg/kg, i.v.), L-3,4-dihydroxyphenylalanine (L-dopa) (5 mg/kg, i.v.), a precursor of dopamine and noradrenaline, markedly potentiated the mono- (MSR) and polysynaptic reflexes (PSR). Selective blockade of alpha 1-adrenoceptors by pretreatment with prazosin-HCl abolished these facilitatory effects on the MSR and the PSR and revealed the inhibitory effect of L-dopa on the PSR. The depression of PSR was antagonized by the alpha 2-antagonist piperoxan. Clonidine-HCl (0.05 mg/kg, i.v.), a so-called alpha 2-agonist, and tizanidine-HCl (0.1 mg/kg, i.v.) decreased the MSR and the PSR in rats pretreated with prazosin. These inhibitions were antagonized by piperoxan. These results suggest that alpha 1- and alpha 2-adrenoceptors mediate facilitation and attenuation of motor transmission in the rat spinal cord, respectively.

Epinephrine and norepinephrine modulate neuronal responses to excitatory amino acids and agonists in frog spinal cord

The interaction of the catecholamines epinephrine (E) and norepinephrine (NE) (1.0-100 microM) and excitatory amino acids on motoneurons of the isolated superfused frog spinal cord was investigated by sucrose gap recordings from ventral roots. Exposure of the cord to E or NE 30 sec prior to application of L-aspartate or L-glutamate reduced the motoneuron depolarizations produced by the amino acids. The reduction of responses to the mixed receptor agonists L-glutamate and L-aspartate may be the result of opposite actions of the catecholamines on the activation of specific excitatory receptors by the amino acids. Thus, E and NE facilitated depolarizations caused by application of N-methyl-D-aspartate (NMDA) and depressed those produced by quisqualate. The effect on NMDA responses appeared to be beta-adrenoceptor mediated because it was mimicked by the beta-agonist isoproterenol and blocked by propranolol. The effect on quisqualate depolarizations appeared to require activation of alpha 2-adrenoceptors; it was mimicked by the alpha 2-agonists clonidine and alpha-methylnorepinephrine and antagonized by yohimbine and piperoxan. These results are important in understanding the actions of catecholamines on reflex transmission in spinal pathways which use excitatory amino acids as transmitters.

Analysis of the responses of frog motoneurons to epinephrine and norepinephrine

Epinephrine and norepinephrine were applied to the isolated superfused frog spinal cord hyperpolarized motoneurons. The hyperpolarization was related to both direct and indirect actions and the indirect effects were produced by activation of alpha 2-adrenoceptors. In about half of the spinal cords a slow depolarization caused by activation of beta-receptors was seen and was largely attributable to direct actions of the catecholamines on motoneuron membranes. In a small number of preparations an early alpha 1-mediated depolarization was noted. The results suggest that catecholamines released from terminals in the frog ventral horn could exert a modulatory action on the motoneuron output from the spinal cord.

The spinal monoaminergic systems relating to ejaculation ejaculation and monoamines after spinal cord transection

The authors investigated the relationship between ejaculation and spinal monoamine levels by transecting the dog spinal cord at the various levels. From the results obtained in this study it was concluded that the lumbar and upper sacral segments of the spinal cord are important for ejaculation, and that the suppression of ejaculation by lower lumbar to upper sacral transection may be induced by increase in serotonin in the 5th lumbar-1st sacral segments.

Effect of clonidine on motoneuron excitability in spinalized rats

In a dose of 0.1 mg/kg clonidine, an alpha-2 receptor agonist, depressed the spontaneous EMG activity of the biceps and quadriceps femoris in chronically-spinalized rats. It also antagonized in a dose-dependent manner the stimulating effect of 5-hydroxytryptophan (5-HTP, 100 mg/kg). Doses of more than 0.1 mg/kg were less potent in antagonizing the effect of 5-HTP. Clonidine reduced the tonic activity of the hindlimb muscles but allowed walking movements. The depressant effect of clonidine in animals pretreated with 5-HTP was prevented by yohimbine (1.25 mg/kg), while the depressant action of the serotonin antagonist, cyproheptadine was not. In chronically-spinalized rats, clonidine (0.1 mg/kg) increased the threshold of electrically-induced flexor and extensor reflexes and decreased their amplitude. No significant modification of reflexes was seen with this dose 24 hr after spinalization. Thus, clonidine in doses of 0.1 mg/kg or less reduced directly or indirectly the excitability of motoneurons. Clonidine may prove to be a useful therapeutic adjunct in the treatment of spasticity.

Characteristic distribution of noradrenergic terminals on the anterior horn motoneurons innervating the perineal striated muscles in the rat. An immuno-electromicroscopic study

Dopamine-beta-hydroxylase (DBH) immunohistochemistry was used to demonstrate the noradrenergic fibers and terminals in the anterior column of the rat lumbosacral spinal segments. PAP-positive varicose fibers were widely distributed in the gray matter with preferential accumulation in the nuclear regions containing motoneurons involved in the contraction of perineal striated muscles. Unmyelinated DBH fibers were composed of nodular enlargements (varicosities, 0.4-3.0 microns in diameter) and very fine, short intervals (intervaricose segments, 0.1-0.2 micron in diameter and 1.0-4.0 microns in length). DBH-positive dense products were electron microscopically often confined within small granular particles and less frequently within large granules. Additionally, in order to characterize the innervation pattern of noradrenergic fibers on dendritic bundles organized in the motoneuronal pools innervating the pelvic small muscles, semi-quantitative analysis was done in the area of the dorsolateral nucleus endowed with especially well-developed dendritic bundles. DBH terminals contacting with unreactive dendrites were more common (67.9%) than those with neuronal somata (15.1%), and the remainder (17%) had no contacts with surrounding neuronal elements. Furthermore, specialized synaptic formations were observed in only 20.1% of these nodules. The results suggest that bulbospinal descending noradrenergic neuron systems influence the functioning of pelvic muscles principally via the neuronal contacts with dendritic bundles in the spinal cord.

Effects of catecholamines on spinal motoneurones and spinal reflex discharges in the isolated spinal cord of the newborn rat

The effects of catecholamines on spinal motoneurones and spinal reflex discharges were investigated in the isolated spinal cord of newborn rat. Noradrenaline (NA), adrenaline (Adr), dopamine (DA) and isoproterenol (Iso) caused depolarization of the motoneurones in a dose-dependent manner. The depolarizing action persisted in Ca2+-deficient Krebs solution. The order of potency was Adr greater than NA greater than DA much greater than Iso. The effects of NA and Adr on the monosynaptic reflex discharge varied; depression, potentiation or depression followed by potentiation. The polysynaptic reflex discharge was consistently depressed. DA depressed both the mono- and polysynaptic reflex discharges in all the preparations. Tyramine and adamantanamine induced a response similar to that to DA rather than to NA. Depolarization of the motoneurones and the effects on the spinal reflex discharges induced by all the catecholamines were decreased by phentolamine or phenoxybenzamine but not by propranolol or haloperidol. It is suggested that the endogenous catecholamines, mainly DA, depolarize the motoneurones and depress the mono- and polysynaptic reflex discharges through an alpha-adrenoceptor in the spinal cord of the newborn rat.

Catecholamine innervation of cervical dendrite bundles: possible phrenic nucleus innervation

The catecholaminergic innervation of three recently described dendrite bundles (midline, central and lateral) in the cervical spinal cord of the adult Long-Evans hooded rat [41] was examined using Golgi impregnation, fluorescence histochemistry for catecholamines, and cholinesterase histochemistry. The midline and lateral bundles were similar in appearance to those described by the Scheibel and Scheibel [50,51], while the central bundle, present in the region of the phrenic nucleus, has not been described previously. Analysis of Golgi-Cox impregnated horizontal sections demonstrated the presence of fine varicose fibers within all three bundles. These profiles entered the bundles at right angles, either singly or within small transverse dendritic subunits, then turned in a rostral or caudal direction, and coursed adjacent to dendrites of motoneurons in the bundles. Catecholamine histofluorescence in horizontal sections revealed abundant varicosities within all three bundles, similar in size and appearance to the varicose fibers seen in Golgi-Cox impregnated sections. Catecholamine fibers entered the dendrite bundles at right angles then turned rostrally or caudally and coursed horizontally within the bundles. Varicose fluorescent profiles formed pericellular rings around the motoneurons and linear profiles adjacent to the dendrites, sometimes outlining the entire proximal portion of primary dendrites. Catecholamine fibers entered the dendrite bundles at right angles then turned rostrally or caudally to course adjacent to the dendrites within the bundles. Cholinesterase histochemistry in alternate sections revealed staining of motoneurons and their dendrites, and confirmed the location of the catecholamine varicosities within the motoneuron dendrite bundles.(ABSTRACT TRUNCATED AT 250 WORDS)

The locus coeruleus and its possible role in ageing and degenerative disease of the human central nervous system

The central noradrenergic pathways with the mammalian brain are principally based on that group of nerve cells within the reticular substance of the upper pons known as the locus coeruleus. The physiological role of these nerve cells appears to be one of maintaining homeostasis within the central nervous system, whatever adverse conditions prevail in the rest of the body, through governing the flow of blood through, and degree of water permeability of, the capillary bed. The extensive ramifications of these noradrenergic terminals mean that the atrophy and loss of nerve cells from locus coeruleus that occurs in old age, and especially so in degenerative diseases of the central nervous system such as Alzheimer's disease and other conditions, will have widespread repercussions for brain function. The chain of physiological disturbances set up as a result of this cell loss may mean a progressive failure of homeostasis within the brain, which in the extreme may culminate in that pattern of mental breakdown which is usually termed dementia.

Pharmacological antagonism of facilitatory but not inhibitory effects of serotonin and norepinephrine on excitability of spinal motoneurons

Serotonin (5HT) and norepinephrine (NE) produced long-lasting facilitation of glutamate-evoked activity of spinal motoneurons when applied iontophoretically with small ejection currents into the ventral horn. The facilitation was usually preceded by a brief period of inhibition at the onset of current application to the monoamine-containing barrels. This inhibition did not outlast the current application. Ejection of hydrogen ions produced only inhibition of glutamate-evoked activity with no subsequent facilitation at current offset. The 5HT antagonists, methysergide and metergoline, blocked the facilitation, but not the inhibition of motoneuron excitability caused by 5HT. Similarly, the alpha-adrenergic antagonists, piperoxane and phentolamine, blocked the facilitatory, but not the inhibitory, effects of NE on excitability of motoneurons. Since the inhibitory effects of 5HT and NE could not be blocked with the antagonists used, and since ejection of hydrogen ions also produced inhibition, non-specific causes for the inhibitory effects of 5HT and NE could not be rejected. However, the facilitatory effects of 5HT and NE on excitability of motoneurons were readily blocked by antagonists and were, therefore, attributed to actions on separate 5HT and NE receptors in the ventral horn.

Development of beta-adrenergic receptors and the in vitro accumulation of cyclic AMP in the chick spinal cord

To clarify the functional development of the descending monoaminergic input to the chick spinal cord we have studied the ontogeny of beta-adrenergic receptors by measuring the specific binding the tritiated dihydroalprenolol (DHA). In addition, we examined the ability of isoproterenol to stimulate the accumulation of cyclic AMP in slices of developing chick spinal cord. Results show that the chick spinal cord contains a high density of beta-adrenergic receptors that are apparently linked to adenylate cyclase. During development, both the density of beta-receptors, as determined by the specific binding of DHA, and the response of tissue slices to isoproterenol underwent marked changes. beta-Adrenergic receptors (approximately 4 fmol/mg tissue) were first detected on the fourteenth day in ovo. Receptor density increased to approximately 20 fmol/mg by day 20. Between day 20 and the time of hatching, a sharp increase in receptor density, to approximately 50 fmol/mg, was seen. The density of receptors remained high until the second day after hatching, fell off to approximately 30 fmol/mg by the fourth day, and remained relatively unchanged through day 30. The response of spinal cord slices to isoproterenol showed a similar pattern of development with the peak response (7-fold increase in levels of cyclic AMP) occurring at or near the time of hatching. During the period between day 18 in ovo and the time of hatching, when both the response of tissue slices to isoproterenol and the density of beta-receptors increased markedly, the activity of phosphodiesterase did not change. Therefore, the pronounced changes in adrenergic responsiveness that occurred near the time of hatching appear to be related primarily to changes in the density of beta-adrenergic receptors coupled to adenylate cyclase. Such developmental changes in the density of beta-adrenergic receptors and adrenergic responsiveness may play an important role in determining the functional state of the descending monoaminergic systems in the chick spinal cord.

Facilitation of spinal motoneurone excitability by 5-hydroxytryptamine and noradrenaline

The effects of iontophoretic application of 5-hydroxytryptamine (5-HT) and noradrenaline (NA) on lumbar motoneurone excitability were examined. 5-HT and NA produced long-lasting changes in motoneurone excitability as revealed by decreased threshold for glutamate-evoked motoneurone action potentials, increased rate of motoneurone firing evoked by suprathreshold amounts of glutamate and increased amplitude of ventral root and dorsal root evoked motoneurone field potentials. Neither 5-HT nor NA directly evoked motoneurone action potentials in the absence of other excitatory input. The 5-HT antagonist, methergoline, reduced glutamate-evoked motoneurone activity and prevented 5-HT, but not NA, facilitation of glutamate-evoked activity. These results suggest that 5-HT and NA enhance the effects of excitatory inputs to spinal motoneurones by actions on separate receptors.

The response of feline spinal pial arterioles to norepinephrine

The effect of norepinephrine on the diameter of feline spinal pial arteries and arterioles was studied by microapplication of the drug to the perivascular environment. Vascular diameter was determined by the television image-splitting method. Application of norepinephrine over the range of 5 x 10(-8) M to 5 x 10(-3) M to spinal pial arterioles resulted in constriction of the vessels. The dose-response curve showed a tendency to plateau at concentrations above 5 x 10(-5) M, with a maximal constriction of 28.8 +/- 5.1% at 5 x 10(-3) M. The reduction in vessel diameter to microapplication of norepinephrine was prevented with the inclusion of an equimolar concentration of the alpha-adrenergic blocker, phentolamine, in the injectate. The data indicate the presence of alpha-adrenergic receptors on the smooth muscle of spinal pial arterioles, and it is suggested that the arguments pertaining to the sympathetic control of blood flow in the brain apply also to the spinal cord.

The role of locus coeruleus in decapitation convulsions of rats

The role of the central norepinephrine (NE) system, especially the locus coeruleus (LC), in the occurrence of decapitation convulsions was investigated in rats. Intraspinal injection of 6-hydroxydopamine (6-OHDA) caused a significant inhibition of decapitation convulsions as shown by prolongation of the latency and shortening of the convulsion's duration, as well as decreasing the NE content of the spinal cord to 35% of the control value without affecting the NE content of the various regions in the brain. Chemical lesion of the descending bundle from the LC by treatment with 6-OHDA significantly inhibited decapitation convulsions in a similar manner. Moreover, there was a decrease in the NE content of the spinal cord and hypothalamus to 24% and 47% of the control value, respectively. Bilateral electrolytic lesion of the LC also significantly inhibited decapitation convulsions and decreased the NE content of the cortex and spinal cord to 15% and 74% of the control value, respectively. However, lesions of the dorsal and ventral NE bundle by treatment with 6-OHDA, which caused a marked decrease in the NE content of the cortex and hypothalamus, respectively, did not affect the decapitation convulsion. Intraspinal injection of 5,6-dihydroxytryptamine resulted in a decrease in the 5-hydroxytryptamine content of the spinal cord only; moreover, it did not change the decapitation convulsion. These results suggest that coeruleospinal NE neurons play an important role in the occurrence of decapitation convulsions.

A comparison of extracellular and intracellular recording during extracellular microiontophoresis

A technique is described in which a central recording microelectrode can be moved independently of a concentrically arranged multibarrelled electrode prepared for microiontophoresis. Recordings were made from cat spinal motoneurones during microiontophoretic applications of excitatory amino acids and biogenic amines with the central electrode placed first extracellularly and then intracellularly. Recording were also made from one of the iontophoretic barrels. Both intra- and extracellular electrodes were used to record action potential firing, the ventral root field (VRF) evoked by antidromic ventral root stimulation and the membrane potential (EM). They were also used to record 'focal potentials' evoked by the extracellular application of drugs to nearby neurones. The firing pattern evoked by extracellular iontophoretic applications of DL-homocysteate and glutamate was not altered significantly following impalement of the cell by the recording microelectrode. Excitatory amino acids usually caused a reduction of the VRF negative wave and evoked an additional late positive wave. These VRF changes recovered at the same rate as the extracellularly recorded, negative 'focal potentials' (Flatman and Lambert, 1979). Iontophoretic applications of biogenic amines caused small increases, small decreases, or no change of the VRF negative wave. Variable responses were also seen during intracellular recording: hyperpolarization, no response and, occasionally, depolarizations were recorded. It is concluded that, during the drug action, VRF changes are difficult to interpret and are a poor index of drug-evoked changes in neuronal excitability or EM.

The effect of norepinephrine on the spinal cord circulation and its possible implications in the pathogenesis of acute spinal trauma

The effect of intra-arterially administered norepinephrine (NE) upon spinal cord blood flow (SCBF), before and after disruption of the blood-cord barrier was studied in dogs. Barrier disruption was accomplished with an intra-arterial bolus injection of 2.5 M urea. Multiple ligations of branches of the posterior aorta and cannula placements ensured that the urea was directed to the lumbar and sacral segments of the cord. The SCBF was measured by the hydrogen clearance method. Intra-arterial urea by itself had no significant effect on SCBF. The intra-arterial infusion of NE (12 microgram/min and 30 microgram/min) was without overall effect on SCBF. However, if the blood-cord barrier had been previously disrupted with hypertonic urea, both concentrations of NE resulted in large reductions in SCBF. No such reductions in SCBF were seen with blood-cord barrier disruption and NE if the animals had been pre-treated with the alpha-blocker, phenoxybenzamine (1.5 mg/kg). Some aspects of the possible involvement of NE in the pathophysiology of acute spinal injury are discussed.

Analysis of the effects of p-methoxy-phenylethylamine on spinal cord neurones

1 Para-methoxyphenylethylamine (PMPEA) was applied microiontophoretically onto interneurones and motoneurones in the spinal cords of acute spinal cats anaesthetized with alpha-chloralose. Its effects were compared with those of noradrenaline (NA) and 5-hydroxytryptamine (5-HT). 2 PMPEA had effects on interneurones which were similar to those of NA and/or 5-HT; its action was predominantly depressant, and it rarely affected interneurones which could not be influenced by NA or 5-HT. 3 The actions of PMPEA on interneurones excited by electrical stimulation of leg nerves showed that the population of interneurones influenced by the drug coincides with the population affected by NA and 5-HT and by intravenously administered PMPEA. 4 Renshaw cells, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. 5 Alpha motoneurones, which are depolarized by intravenous PMPEA, were hyperpolarized by micoiontophoretically applied PMPEA. Antidromic firing of the cells could be blocked by PMPEA. 6 The differences between the effects of intravenous infusion and the iontophoretic application of PMPEA upon motoneurones is most easily explained by inhibition of interneurones and a concomitant disinhibition of motoneurones. A similar mechanism may also account for the different effects seen with intravenous and iontophoretic application of PMPEA on Renshaw cells.

The pathophysiological response to spinal cord injury

✓ In this review of spinal cord injury research, the author has selected contributions which in his opinion best represent modern experimental concepts regarding the mechanism and management of spinal cord injuries. He has placed special emphasis on the controversial issues appropriate to a new, stimulating, and competitive area of research.

Altered norepinephrine metabolism following experimental spinal cord injury. 1. Relationship to hemorrhagic necrosis and post-wounding neurological deficits

✓ Experimentally injured spinal cord tissues were chemically examined for changes in norepinephrine (NE), serotonin, and dopamine; remarkable NE metabolic alterations were found. The amine doubled in 30 minutes, quadrupled in 1 hour, and thereafter slowly declined to approach control values at 4 hours. Comparisons between injured tissue NE content and the presence of central gray hemorrhages and necrosis were consistently found, and profound increases in NE were universally associated with massive central hemorrhages. Within 2 hours of injection of minute quantities of pure NE into the spinal gray matter, large central hemorrhages appeared that closely resembled the lesions associated with severe spinal cord injury. We have hypothesized that toxic quantities of tissue NE induce intense vasospasm which impedes or arrests cord perfusion and causes the neuronal necrosis, vascular rupture, and parenchymal self-destruction manifest as central hemorrhagic necrosis. Thus, excess NE liberated within traumatized tissue may act to depress or halt electrical activity of adjacent fibers and neurons, producing the neuronal response of transient weakness or paralysis. Permanent loss of function ensues as the electrically depressed spinal cord tissue also undergoes hemorrhagic autodestruction.