Ventral Root Responses Research Articles

The effect of folates on the reflex activity in the isolated hemisected frog spinal cord.

Folates may play a role in epileptic phenomena and may also be involved in synaptic events. Recently methyltetrahydrofolate was found to be a potent competitor for 3H-kainic acid binding sites in the cerebellum. The effects of 1 mM methyltetrahydrofolate (MTHF), 1 mM formyl-tetra-hydrofolate (FTHP) and 1 mM Na-folate (Na-F) were tested on the reflex activity of the isolated hemisected frog spinal cord. MTHF and FTHP were found to have an initial excitatory effect on the evoked ventral root responses. This was followed by a gradual decrease in the amplitudes of the ventral root responses. Sodium folate had only an inhibitory effect on these responses. When the evoked ventral root responses were totally inhibited by the folates the preparations did not respond to any of the following substances: (a) Kainic acid (KA), (b) L-glutamic acid (LG), (c) picrotoxin or (d) strychnine. All the folates had an inhibitory effect on the dorsal root responses. In most preparations neuronal activity was only partially restored by perfusion with normal Ringer solution. When the isolated spinal cords were bathed in either 0,5 mM KA or 1 mM LG similar results were obtained to that found with MTHF and FTHF. Glutamic acid diethyl ester (GDEE, 1 mM), however, yielded similar results to that seen with Na-F. It seems that the glutamates and related substances differ in their ability as neuroexcitants, but all share the common ability to inhibit synaptic activity when nervous tissue is exposed to the substances for long periods. Some of the folates share with KA some degree of neurotoxicity. These experiments could also not point out a separate kainic receptor in the frog spinal cord.

Convulsant and possible anticholinergic actions of dendrotoxin in the amphibian spinal cord.

1 Dendrotoxin (DTOX)6, 6a and 5,6-1, fractions of the venom isolated from the green mamba (Dendroaspis viridis) promoted both spontaneous and stimulus-coupled rhythmic activity and antagonized the cholinergically mediated ventral root-dorsal root potential (VR-DRP) of frog spinal cord. The different time course and reversibility of these two effects indicates that the toxin has two entirely separate sites of action on the frog spinal cord. 2 Since DTOX 6 neither blocked nor enhanced responses of ventral and dorsal roots to glutamate, gamma-aminobutyric acid (GABA), beta-alanine, glycine or aspartate, it is unlikely that its convulsant action resulted from an alteration of the postsynaptic actions of inhibitory or excitatory amino acids. 3 An alteration in the threshold for action potential generation could perhaps contribute to the convulsant action of DTOX 6, although other mechanisms such as blockade of the release of unspecified inhibitory substances cannot be excluded. 4 In addition to the lack of effect on amino acid responses, DTOX failed to block the polysynaptic DR-VRP or DR-DRP pathways, which are mediated at least in part by amino acid neurotransmitters. Although this would be consistent with a specific action of DTOX at the cholinergic synapse of the VR-DRP pathway, this site of action has not yet been demonstrated unequivocally. Other possible mechanisms whereby DTOX could block VR-DRP are discussed.

Disruption of vertebrate monosynaptic habituation by ethyl alcohol

The effects of ethyl alcohol on neuronal plasticity were examined using a model systems preparation of monosynaptic habituation: the lateral column to motoneuron pathway of the isolated frog spinal cord. Two fundamental effects of alcohol on this system were demonstrated. First, alcohol always depressed the ventral root responses to lateral column stimulation when stimulus intensity was held constant across conditions. This was accompanied by an increase in the amount of habituation produced as training progressed. Second, when stimulus intensity was increased in the alcohol condition so that responses were equated with pre-alcohol response amplitudes, the amount of habituation was markedly decreased. Results are discussed both in terms of proposed mechanisms of habituation and of possible pharmacological interactions with this simple example of response plasticity.

The effects of hyposmolality on spinal cord activity

The consequences of decreases in osmotic pressure were investigated using the isolated, hemisected frog spinal cord. The lateral column evoked ventral root response (LC-VRR) was depressed by a decrease in osmolality secondary to a decrease in the Na + concentration in the bathing medium. This depression resulted from neither a depression of motoneuronal excitability nor a depression of central axonal conduction but rather from an increased excitability of lateral column terminals. The depression of the LC-VRR and augmentation of the lateral column terminal excitability were reversed by picrotoxin (10- 4 M). Results are discussed in terms of the possible roles of endogenous gamma-aminobutyric acid (GABA) and extracellular K + in the effect produced by the hyposmotic (low Na +) media.

Effects of changes in osmolality on spinal cord activity

The effects of change in the osmotic pressure of the bathing medium on central neural activity in the isolated, hemisected frog spinal cord were studied. The bathing medium was made hyperosmotic by either increasing all constituents (except NaHCO 3) proportionally or by adding a nonelectrolyte, mannitol; and hyposmotic by decreasing all constituents (except NaHCO 3) proportionally. Changes in osmotic pressure depressed the monosynaptic lateral column-evoked ventral root response (LC-VRR). Depression occurred with changes of only 25 mosmol/kg H 2O in bathing medium osmolality. This osmotic effect was fully expressed within the first 5 min of exposure. The osmotic effect was probably not due to a change in the excitability of the motoneurons as there was no change in the antidromic field potential recorded in the ventral horn following stimulation of the ventral root after exposure to the nonisosmotic bathing media that had depressed the LC-VRR. Exposure to nonisosmotic bathing media produced an increase in the excitability of the lateral column terminals as shown by an increase in the lateral column field potentials antidromically evoked by stimulation in the ventral horn. This increase mirrored the depression in the LC-VRR. The depression in the LC-VRR and the augmentation of the MN-LC are reversibly blocked by picrotoxin, a gamma-aminobutyric acid (GABA) antagonist. This suggests that the osmotic effect on isolated frog spinal cord may be due either to the release of endogenous GABA or perhaps to a change in extracellular K + concentration.

Actions of various gastrointestinal peptides on the isolated amphibian spinal cord.

The effects of a number of peptides which are found in the gastrointestinal tract have been ascertained on the direct current recorded dorsal and ventral root responses of the isolated hemisected toad spinal cord. Motilin, substance P, bombesin, neurotensin, and thyrotropin releasing hormone had potent depolarizing actions on dorsal root terminals and motoneurons. These substances evoked discernable effects at concentrations as low as 10--7 M, or even lower with motilin. The effects of motilin, neurotensin, and thyrotropin-releasing hormone were greatly reduced or abolished by perfusion of the preparation with tetrodotoxin. Adrenocorticotrophic hormone, secretin, and pancreozymin (cholecystokinin) also depolarized dorsal root terminals and motoneurons. The effects of secretin and cholecystokinin were not abolished by tetrodotoxin. Leu- and Met-enkephalin had weak hyperpolarizing actions on the dorsal and ventral root potentials of repetitively stimulated preparations. Gastrin, gastric inhibitory peptide, glucagon, and somatostatin had no apparent effects on the responses of the preparation. Angiotensin and vasopressin both had rather weak depolarizing effects on the dorsal and ventral roots.

Potentiation of the effects of GABA by pentobarbitone

Pentobarbitone (50 microM) has been shown to potentiate GABA-induced responses in rat isolated superior cervical ganglia and in dorsal or ventral root fibres of immature rat isolated spinal cords. Measurements of dose ratios for the antagonism of GABA-induced responses of dorsal root fibres by bicuculline showed that pentobarbitone (50 microM) did not significantly alter this antagonism. This result indicates that the antagonism of GABA by bucuculline at dorsal root fibres is not reversed by pentobarbitone. Ventral root responses to GABA (but not glycine) were also potentiated by pentobarbitone (+/-)-Nipecotic acid (300 microM) potentiated responses to GABA much more than those to 3-aminopropane-sulphonic acid.

Effect of Lissauer tract stimulation on activity in dorsal roots and in ventral roots

In decerebrate spinal cats, microelectrode stimulation of the lumbar lateral Lissauer tract (LLT), which does not spread to the dorsal roots, produces a volley in the tract that is conducted at 0.5 to 2.5 m/s. In 38 cats, such a volley in the LLT produced a negative dorsal root potential (DRP) beginning at 15 to 20 ms and lasting 30 to 40 ms, followed by a positive DRP lasting 90 to 140 ms. In seven cats, LLT stimulation produced a positive DRP alone beginning at 30 to 40 ms and lasting 80 to 110 ms. The LLT-evoked DRP was limited to the dorsal rootlets located within a few millimeters on either side of the stimulus point, unlike the dorsal root-evoked DRP. This local distribution parallels the limited spread of the LLT-evoked compound action potential. The LLT-evoked DRP occluded the dorsal root-evoked DRP. Conditioning stimuli applied to the LLT produced early facilitation and late inhibition of the monosynaptic ventral root reflex. The polysynaptic reflexes were inhibited for as long as 150 ms. With higher stimulus intensities, the polysynaptic reflexes were first inhibited and then facilitated for 150 to 1000 ms. Barbiturates first prolonged and then attenuated the LLT-evoked DRP. Picrotoxin reduced the LLT-evoked DRP but failed to have any effect on the facilitation or inhibition of the ventral root responses. Naloxone produced an enhancement of dorsal root-evoked polysynaptic reflexes. Although naloxone had no effect on the LLT facilitation of the monosynaptic reflex, it antagonized the LLT inhibition of the polysynaptic reflex.

Sensitization and habituation of dorsal horn cells in cats.

1. Extracellular recordings were obtained from spinal dorsal horn cells in acutely spinalized cats anaesthetized with sodium pentobarbitone. The dorsal horn cells studied responded to ipsilateral tactile stimulation of the central pad of the hind foot. Eleven short latency dorsal horn cells driven by electrical stimulation of the foot pad were studied intensively; these short latency dorsal horn cells all discharged within 1.5 msec of the arrival of an afferent volley at the dorsal root entry zone. Electrode tip sites were histologically verified to lie near the medial border of the dorsal horn in the seventh lumbar segment, in Rexed's laminae III and IV. 2. Electrical stimulation of the foot pad not only activated the dorsal horn cells studied, but also produced a reflex discharge which was monitored by recording from the ipsilateral first sacral ventral root, which had been sectioned intradurally and mounted on bipolar recording electrodes. Repeated stimulation of the foot pad at moderate intensities and frequencies (e.g. three times threshold for the ventral root response at 5 Hz) typically produced a transitory increase in the magnitude of the reflex discharge (sensitization) followed by a marked waning of the reflex magnitude (habituation). Within a few minutes following cessation of stimulation, the reflex magnitude returned to its prestimulation value. During repeated bouts of five hundred stimuli each, at frequencies from 1.0 to 10.0 Hz, and intensities 1.5-10.0 times reflex threshold, the firing pattern of a short latency dorsal horn cell was monitored along with the magnitude of the ventral root response. Changes in response patterns of the dorsal horn cells were compared to those of the reflex discharges. 3. The short latency dorsal horn cells fell into two distinct patterns of response. The firing pattern of six dorsal horn cells paralleled the response pattern of the reflex discharge; when the reflex increased in magnitude, each of these dorsal horn cells increased in number of responses per stimulus; when the reflex discharge decreased in magnitude, each of these dorsal horn cells decreased the number of responses per stimulus. These dorsal horn cells were characterized by the following: intermediate thresholds to tactile stimulation, comparable to that of the reflex discharge itself; relatively low numbers of responses per stimulus (mean: 1.3/stimulus); low spontaneous activity rates (once per 10 sec or less). 4. The firing patterns of the other class of short latency dorsal horn cells did not parallel the response pattern of the reflex discharge; these showed only a rather rapid, though moderate, decrease in responses per stimulus over the entire range of intensities and frequencies tested. These five dorsal horn cells were characterized by the following: thresholds of tactile stimulation considerably below that of the reflex discharge itself; bursts of responses following each stimulation (mean: 7...

Complement‐dependent serum

In attempting to discover a relationship between the neurologic and immunologic abnormalities in multiple sclerosis, we found a serum factor that inhibits the ventral root response in isolated, perfused frog spinal cords. This effect is correlated with disease activity. Blocking activity of the serum was lost by heating to 56 degrees C, restored by adding complement, and was found in the serum IgG fraction. There was no correlation of neuroelectric blocking activity with measles complement-fixing antibody. An antibody other than that to measles virus may thus have a role in the pathogenesis of multiple sclerosis.

The actions of adenosine and various nucleosides and nucleotides on the isolated toad spinal cord

1. 1. The effects of nucleosides and nucleotides of several purines and pyrimidines have been ascertained on the a.c. and d.c. recorded dorsal and ventral root responses of isolated, hemisected, perfused toad spinal cords. 2. 2. On preparations subjected to repetitive dorsal root stimulation, adenosine and adenosine 5′-monophosphate, 5′-diphosphate and 5′-triphosphate (2 × 10 −4−10 −2 M) hyperpolarized both dorsal and ventral roots. Dorsal root-evoked dorsal and ventral root potentials were reduced in duration but not amplitude. These effects were antagonized by theophylline and caffeine. 3. 3. Adenosine 5′-triphosphate and, to a lesser extent, adenosine 5′-diphosphate, at concentrations of 10 −3 M or higher frequently depolarized one or both roots. This effect was potentiated by caffeine and theophylline. 4. 4. Guanosine 5′-monophosphate, 5′-diphosphate and 5′-triphosphate (10 −3−10 −2 M) hyperpolarized both roots and reduced both the amplitude and duration of dorsal and ventral root potentials evoked by dorsal root stimulation. These effects were only weakly antagonized by caffeine and theophylline. Depolarizations of the roots were sometimes observed with guanosine and its 5′-di- and triphosphates. 5. 5. Adenosine 3′,5′-cyclic monophosphate and guanosine 3′,5′-cyclic monophosphate had no effect at concentrations of up to 10 −2 M on the responses and polarization levels of the dorsal and ventral roots. 6. 6. Inosine 5′-monophosphate at high concentrations (10 −3−10 −2 M) had a weak hyperpolarizing action on the ventral root potential. Cytidine, thymidine, uridine and xanthosine and their 5′-monophosphates had no effect at concentrations of up to 10 −2 M. The 5′-triphosphates of these substances all depolarized dorsal and ventral roots. 7. 7. After perfusion with magnesium-containing solutions, adenine nucleotides and uridine 5′-triphosphate depolarized the dorsal roots but had no consistent effect on ventral root polarization levels. 8. 8. The sodium and dicalcium salts of adenosine 5′-triphosphate had equipotent depolarizing actions. The excitant actions of the nucleotides are therefore unlikely to be due to calcium chelation. 9. 9. In conclusion, it appears that adenosine and the adenine nucleotides can have depressant and hyperpolarizing actions on dorsal root terminals and motoneurons of repetitively stimulated preparations. It is suggested that these effects result from a reduction in the release of excitatory transmitter. The 5′-polyphosphates of all the purines and pyrimidines tested can have an excitatory action, the nature of which is currently uncertain.

The effect of myelin basic protein (MBP) on the bioelectric activity of spinal cord and cerebellar neurones

The effects of myelin basic protein (MBP) on the ventral root response in rat spinal cord in situ and on the spontaneous bioelectric activity of cultured rat Purkinje cells were investigated. Injection of 2 or 4 μl MBP (10 −4 M/l) into the motoneurone pool reduced the ventral root response to dorsal root stimulation. The depression was long-lasting (30–50 min) and partially reversible. At 5 × 10 −6 M/l MBP abolished the spontaneous activity of most cultured Purkinje cells, an effect which was not blocked by haloperidol, propranolol, phenoxybenzamine and bicuculline. The EC 50 for the depression was 4 ± 1 × 10 −6 M/l.

Effect of Multiple Sclerosis Serum on Ventral Root Responses in Isolated Frog Spinal Cord

Serum from patients with multiple sclerosis (MS) and other diseases was added to the medium perfusing isolated hemisected frog spinal cord, and the effect on ventral root responses (VRR) tested. As control, a standardized commercial human serum (Moni-trol I) was used. In 25 out of 40 spinal cord preparations Moni-trol gave inhibition of VRR ranging from 2.8 to 23.1%. 76% of the tests with confirmed MS sera showed inhibition of VRR, after deduction of the control serum effect, while 53% of the tests with sera from other diseases were inhibitory. Sera from cases of suspected but clinically unconfirmed MS gave strong inhibition (above 20%).

Neuroelectric blocking factors in human and animal sera evaluated using the isolated frog spinal cord.

The effects of sera from guinea-pigs with experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS) patients were evaluated and compared with the activity of control sera using the isolated frog spinal cord. Ventral root responses (VRR) were recorded during supramaximal ipsilateral dorsal root stimulation in the presence and absence of 25% serum. In control experiments with normal human and guinea-pig sera we observed a consistent, reversible increase in VRR averaging 20% and 17% respectively, and in no case was any significant decrease produced. In contrast, sera from EAE guinea-pigs 12 to 19 days after injection produced an equally rapid, reversible decrease in VRR. The decrease averaged 36% and was highly significant (P less than 0.0001) relative to controls. Similarly, sera from MS patients on the average decreased the VRR by 26%, and this again was significant compared with controls (P less than 10(-6).

Low level potentiation of the brain stem laryngeal reflex

Trains of electrical stimuli were applied to the superior laryngeal nerve (SLN) innervating the upper respiratory tract while evoked potentials were recorded from the recurrent nerve (RN) which innervates the intrinsic laryngeal muscles. Responses of this brain stem reflex (central delay 3.5–5.0 msec) were compared to the post-tetanic potentiation (PTP) of the polysynaptic ventral root response (L 6-S 1) with trains of stimuli applied to the dorsal root of adult cats. Stimulation of the SLN with a train of pulses varying from 10–450/sec evokes an initial depression of the polysynaptic potential from the RN followed by a low but sustained increase in the amplitude of the integrated signal (1.2–1.6 x) lasting 45–130 msec and lacking the early maximum amplitude as seen in the PTP of the polysynaptic spinal reflex. Both the early and late components of the superior laryngeal-recurrent nerve reflex (SLN-RN) demonstrate potentiation whereas the shortest latency components of the spinal reflex account for most of the PTP. Systemic administration of strychnine sulfate (dosage: 0.03–0.45 mg/kg) does not alter the normalized PTP of the SLN-RN reflex despite enhancement of both early and late components of the reflex following control stimuli at 1/sec.

VENTRAL ROOT RESPONSES OF THE HEMISECTED AMPHIBIAN SPINAL CORD TO PERFUSED AMINO ACIDS IN THE PRESENCE OF PROCAINE

The use of the procaine-blocked hemisected spinal cord preparation to identify the primary action of amino acids and their antagonists on amphibian mononeurones is described. 2 Apart from an anomalous effect of glycine, the responses of frog spinal motoneurones to amino acids were shown to be similar to those of mammalian spinal neurones. 3 In the presence of procaine, gamma-aminobutyrate (GABA), taurine and beta-alanine caused a hyperpolarizing response, measured in ventral roots, whereas L-glutamate and, to a lesser extent, glycine caused depolarization. 4 Picrotoxin and bicuculline specifically blocked ventral root responses to GABA; strychnine blocked responses to taurine and beta-alanine but not responses to L-glutamate, glycine or GABA.

The effect of reserpine and DOPA on reflex activity in the rat spinal cord

The effect was studied of reserpine and DOPA on ventral and dorsal root responses evoked by stimulation of dorsal roots, gastrocnemius-soleus and sural nerves in intact and spinal rats. Both drugs increased ventral and dorsal root responses, apart from the flexor reflex evoked by sural nerve stimulation which was depressed by reserpine in the intact rat. DOPA, injected after the administration of reserpine, antagonized the effects of the latter drug.

Bicuculline and the frog spinal cord.

1 The effects of bicuculline on dorsal and ventral root activity and upon the depressant effect of gamma-aminobutyric acid (GABA) and glycine on ventral root responses have been studied on the isolated spinal cord of the frog.2 In the absence of stimulation, the alkaloid induced a variety of activity of which the most notable was phasic simultaneous slow wave depolarization in the dorsal and ventral roots which could be reduced or suppressed by magnesium.3 With low concentrations of bicuculline, the adjacent dorsal root response evoked by a single stimulus was depressed maximally before an increase in the ventral root response could be discerned.4 The bicuculline-induced dorsal root activity (in the absence of stimulation) was still apparent at times when the evoked dorsal root response was reduced.5 Bicuculline did not differentiate between the depressant effects of GABA and glycine on the evoked ventral root responses.6 The excitant effects of bicuculline reported here did not appear to be attributable to specific antagonism of the postsynaptic depressant action of GABA.

Depression of frog isolated spinal cord by morphine and antagonism by tetracosactin.

The purpose of these experiments was to determine if tetracosactin (ACTH1-24) will antagonize the actions of morphine (MS) on neural tissue isolated from other body systems. The monosynaptic ventral root response (MVR) of frog isolated spinal cord in vitro was used to test this question. In this preparation MS produces a depression of MVR which is antagonized by naloxone, by CaCl2, and by decreased temperature. ACTH1-24 did not alter MVR, but did antagonize the actions of MS.

The action of general anaesthetic agents on root responses of the frog isolated spinal cord.

1. The action of volatile and barbiturate general anaesthetic agents on synaptic transmission in the frog isolated spinal cord has been studied by recording ventral root synaptic potentials and spike discharges evoked by volleys in a dorsal root and in the lateral column fibres.2. Some observations on the distribution of the lateral column fibres and the characteristics of the dorsal root potentials have been presented.3. Volatile agents depressed and eventually abolished all components of the ventral root responses. Failure of motoneurone discharge was the result of two factors, a decrease in the slope of the synaptic potential and an elevation of the critical depolarization required to trigger propagated impulses.4. Barbiturate compounds, in contrast, readily abolished polysynaptic components of the ventral root responses, but the short latency discharge produced by lateral column stimulation was potentiated, and was accompanied by a lowering of the firing threshold of motoneurones. The mechanism of this potentiation by barbiturate compounds is discussed.5. It is concluded that volatile agents act predominantly on the initial segment and subsynaptic elements of the motoneurone, whereas barbiturate compounds depress the presynaptic or postsynaptic components of interneuronal synapses.