Spinal segmental sympathetic outflow to cervical sympathetic trunk, vertebral nerve, inferior cardiac nerve and sympathetic fibres in the thoracic vagus

The spinal segmental localization of preganglionic neurons which convey activity to the sympathetic nerves, i.e. vertebral nerve, right inferior cardiac nerve, sympathetic fibres in the thoracic vagus and cervical sympathetic trunk, was determined on the right side in chloralose anaesthetized cats. For that purpose the upper thoracic white rami were electrically stimulated with a single pulse, suprathreshold for B and C fibres, and the evoked responses were recorded in the sympathetic nerves. The relative preganglionic input from each segment of the spinal cord to the four sympathetic nerves was determined from the size of the evoked responses. It was found that each sympathetic nerve receives a maximum preganglionic input from one segment of the spinal cord (dominant segment) and that the preganglionic input gradually decreased from neighbouring segments. The spinal segmental preganglionic outflow to the cervical sympathetic trunk, thoracic vagus, right inferior cardiac nerve and vertebral nerve gradually shifted from the most rostral to the most caudal spinal cord segments. In some cases, a marked postganglionic component was found in the cervical sympathetic trunk. It was evoked by preganglionic input from the same spinal cord segments which transmitted activity to the vertebral nerve. These results indicate that there is a fixed relation between the spinal segmental localization of preganglionic neurons and the branch of the stellate ganglion receiving the input from these neurons.     

Properties of femoral venous afferent inputs and lumbosacral distribution of spinal evoked activity

The present studies were done to determine details of the anatomical and physiological characteristics of femoral-saphenous venous afferent input to the lumbar spinal cord. Gross anatomical examination revealed that afferent bundles could be seen coursing from the saphenous nerve to the femoral-saphenous vein. Compound action potentials elicited by femoral-saphenous venous afferent stimulation were recorded from the femoral nerve and in dorsal rootlets of the 6th lumbar cord segment. The compound action potentials included activity correlated with that of fibers conducting impulses at the rate of 31 to 61 m/s. Lumbar cord dorsum potentials elicited by femoral-saphenous venous afferent stimulation were abolished by rhizotomy of the most caudal rootlets of the 6th lumbar cord segment. L6 was also the cord segment from which the largest amplitude cord dorsum negative potentials were recorded, while action potentials with large late positive waves were recorded from more caudal cord segments. These observations suggested that the L6 segment contained the largest number of spinal neurons responding to primary femoral-saphenous venous afferent input, and that input reached the more caudal segments via intersegmental connections. A proposed physiological role of these afferents is briefly described.     

The human cervical and lumbo-sacral evoked electrospinogram. Data from intra-operative spinal cord surface recordings.

We have undertaken the analysis of the human 'evoked electrospinogram' during intra-dural surgical explorations in 20 patients. Averaged spinal cord surface evoked potentials to peripheral nerve electrical stimulation were obtained from various restricted loci on the pial surface of the cervical and lumbo-sacral spinal cord. The brachial plexus P9 potential and its lumbo-sacral counterpart P17 were recorded as ubiquitous initial far-field positivities. The pre-synaptic compound action potentials N11 and N21 dwelt on the ascending slope of N13 and N24 respectively. They were composed of 1-5 sharp peaks and collected from the dorsal and dorso-lateral positions mainly, on the cervical and lumbo-sacral cord respectively. They are thought to be generated in the proximal portion of the dorsal root, the dorsal funiculus and the afferent collaterals to the dorsal horn. Compound action potentials could also be gathered from the surface of the dorsal roots, the cervical N10 and lumbo-sacral N19 potentials. The large cervical N13 and lumbo-sacral N24 waves originate from a dorso-ventral post-synaptic dipole, generated in deep laminae of the dorsal horn during the activation of large diameter afferent fibers. These waves were maximal on the main entry cord segments of the stimulated nerves and fell off on the 1-4 more rostral and caudal segments. The N2 wave is the dorsal component of another post-synaptic dorso-ventral dipole generated in deep laminae of the dorsal horn but activated by medium diameter afferent fibers. The latest event was the N3 wave, also possibly part of a dorso-ventral post-synaptic dipole, and generated by cells in the dorsalmost and deep dorsal horn laminae during the activation of small diameter afferent fibers. The P wave was a prolonged positive deflection which carried the N2 and N3 waves. It is the manifestation of pre-synaptic inhibition on primary afferent fibers. A supra-segmental ascending spinal cord volley was also described, composed of a long succession of sharp and low voltage peaks.     

Spinal segmental preganglionic outflow to cervical sympathetic trunk and postganglionic cardiac sympathetic nerves

The aim of this study was to verify in which spinal cord segments the preganglionic neurones projecting to the cervical sympathetic trunk or converging onto the somata of the postganglionic cardiac sympathetic neurones are located in cats. The thoracic white rami T1 to T5 were electrically stimulated and the evoked responses were recorded in the cervical sympathetic trunks and postganglionic cardiac nerves. The responses were mostly evoked by electrical stimulation of group B preganglionic fibres. The maximum amplitude of evoked responses in the cervical sympathetic trunk was obtained when the T2 white ramus was stimulated and decreased gradually when followed by the stimulation of T1, T3, T4 and T5 white rami. In most cases the maximum amplitude of evoked responses in the left inferior cardiac nerve, right inferior cardiac nerve and left middle cardiac nerve was obtained when the T3 white ramus was stimulated. The size of the responses decreased when more cranial and caudal white rami were stimulated. It was found that the somata of the postganglionic neurones of the right and left inferior cardiac nerves were placed in the right and left stellate ganglion, respectively. Somata of the postganglionic neurones with axons in the left middle cardiac nerve were mainly located in the left middle cervical ganglion and some in the left stellate ganglion.     

Analysis of reflex activity in cardiac sympathetic nerve induced by myelinated phrenic nerve afferents

Electrical stimulation of the phrenic nerve afferents evoked excitatory responses in the right inferior cardiac sympathetic nerve in chloralose-anaesthetized cats. The reflex was recorded in intact and spinal cats. The latency and threshold of the volley recorded from the phrenic nerve as well as of the cord dorsum potentials evoked by electrical stimulation of the phrenic nerve indicated that group III afferents were responsible for this reflex. The phrenicocardiac sympathetic reflex recorded in intact cats was followed by a silent period. The maximum amplitude of the reflex discharges was 800 microV, the latency was 83 ms and the central transmission time 53 ms. Duration of the silent period lasted up to 0.83 s. In spinal cats the reflex was recorded 5.5-8 h after spinalization. The maximum amplitude of the spinal reflex discharges ranged from 22 to 91 microV and the latency from 36 to 66 ms.     

Neural organization of the viscero-cardiac reflexes

The reflex responses evoked in the postganglionic nerves to the heart were tested in chloralose-anaesthetized cats. Electrical stimulation of the A delta afferent fibres from the left inferior cardiac nerve evoked spinal and supraspinal reflex responses with the onset latencies of 36 ms and 77 ms respectively. The most effective stimulus was a train of 3-4 electrical pulses with the intratrain frequency of 200-300 Hz. Electrical stimulation of the high threshold afferent fibres (C-fibres) from the left inferior cardiac nerve evoked the reflex response with the onset latency of 200 ms. The C-reflex was present in intact animals and disappeared after spinalization. The most effective stimulus to evoke this reflex was a train of electrical pulses delivered at a frequency of 1-2 Hz with an intratrain frequency of 20-30 Hz. The most prominent property of the C-reflex was its marked increase after prolonged repeated electrical stimulation. We conclude that: (1) viscero-cardiac sympathetic reflexes may be organized at the spinal and supraspinal level; (2) viscero-cardiac sympathetic reflexes evoked by stimulation of the A delta and C afferent fibres from the left inferior cardiac nerve have different central organization.     

Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves

(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord did not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.     

Three transverse dipolar generators in the human cervical and lumbo-sacral dorsal horn: evidence from direct intraoperative recordings on the spinal cord surface

In the context of the intraoperative study of spinal cord surface evoked potentials in patients operated upon for chronic pain and spasticity, we have undertaken an analysis of the dipolar dorso-ventral organization of surface spinal cord evoked potentials in man. Averaged evoked potentials to peripheral nerve electrical stimulations were obtained from the dorsal and ventral pial surface of the cervical and lumbo-sacral spinal cord (7 pairs from 5 patients), using a small silver ball macroelectrode, positioned during open neurosurgical approaches. We found that the dorsally recorded N13 and N24 waves reversed into ventral P13 and P24 waves respectively. A second negative potential, N2, and a late prolonged positivity, P, similarly reversed into a P2 and an N wave respectively. Our data add up to a collection of skin, oesophageal, epidural, pial and intramedullary recordings in man and animals to provide the evidence for a transverse dipolar organization of the human postsynaptic N13, N24 and N2 potentials, originating from deep layers of the cord dorsal horn, and for a similar organization of the P wave, which has been shown to correlate with presynaptic inhibition on primary afferent fibres.     

An intracellular study of the synaptic input to sympathetic preganglionic neurones of the third thoracic segment of the cat

In chloralose anaesthetized, paralyzed and artificially ventilated cats intracellular recordings were obtained from sympathetic preganglionic neurones (SPN) of the third thoracic segment of the spinal cord identified by antidromic stimulation of the white ramus T3. The synaptic input to SPNs was assessed, in cats with intact neuraxis or spinalized at C3, by electrical stimulation of segmental afferent fibres in intercostal nerves and white rami of adjacent thoracic segments and by stimulation of the ipsi- and contralateral dorsolateral funiculus and of the dorsal root entry zone of the cervical spinal cord. In both preparations SPNs showed on-going synaptic activity which predominantly consisted of excitatory post-synaptic potentials (EPSPs). Inhibitory post-synaptic potentials (IPSPs) were rarely observed. EPSPs were single step (5 mV) or, less frequently, large (up to 20 mV) summation EPSPs. The proportion of SPNs showing very low levels of on-going activity was markedly higher in spinal than in intact cats. Stimulation of somatic and sympathetic afferent fibres evoked early EPSPs (amplitude 3 mV, latency 5-22.3 ms), and late, summation EPSPs (amplitude up to 20 mV, latency 27-55 ms). Early and late EPSPs were evoked in nearly all SPNs in which this synaptic input was tested in the intact preparation (from 79-93% of the SPNs). In spinal cats, early EPSPs were evoked in 88% of the SPNs, whereas late EPSPs were recorded only in half of the neurones. No evidence for a monosynaptic pathway from these segmental afferent fibres to SPNs was obtained. In both intact and spinal cats, stimulation of the dorsolateral funiculus evoked early and late EPSPs in SPNs. Late EPSPs were recorded in 70% and 37% of the SPNs in intact and spinal cats, respectively. Early EPSPs, however, were evoked in all neurones. The early EPSPs evoked by stimulation of the dorsolateral funiculus had several components which are suggested to arise from stimulation of descending excitatory pathways with different conduction velocities. The following conduction velocities were calculated in intact (spinal) cats: 9.5-25 m/s (7.8-13.2 m/s), 5.7-9.5 m/s (5.5-7.8 m/s), 3.8-5.7 m/s (3.2-5.5 m/s), and 2.6-3.8 m/s (2.1-3.2 m/s). EPSPs of these various groups were elicited in a varying percentage in SPNs. EPSPs of the most rapidly conducting pathway were subthreshold for the generation of action potentials; some EPSPs of this group had a constant latency suggesting a monosynaptic pathway to SPNs. Stimulation of the dorsal root entry zone at the cervical level yielded essentially the same results as stimulation of the dorsolateral funiculus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Tonic descending inhibition of the spinal cardio-sympathetic reflex in the cat

Electrical stimulation of the left inferior cardiac nerve elicited a two-component reflex potential (spinal and supraspinal reflexes) in the ipsilateral white ramus T3 from which recordings were made in chloralose-anaesthetised cats. Reversible interruption of all spinal pathways achieved by cooling the spinal cord at C2/C3 produced an enhancement of the spinal reflex and abolished the supraspinal reflex, the latter usually being the more prominent reflex potential prior to spinal cord block. The spinal cord block-induced increase in the amplitude of the spinal reflex was, however, less than the increase observed during stimulation of the somatic intercostal nerve T4. Recordings of the afferent volley following cardiac nerve stimulation and analysis of the stimulus-reflex response relationship in neuraxis-blocked cats indicated that the spinal reflex as determined here was activated by A delta afferent fibres. However, if stimulus strength was raised above C-fibre threshold, spinal cord block revealed in addition a late spinal reflex response. In some cases, the appearance of this late potential was accompanied by a secondary decline of the earlier spinal reflex potential, possibly indicating C-fibre-mediated afferent inhibition. Neither baroreceptor activation nor denervation had any effect on spinal reflex amplitudes. Pharmacologically, clonidine given i.v. to cats with a blocked neuraxis reduced the spinal reflex amplitudes to pre-block values, an action which could be antagonised by the subsequent administration of the alpha 2-adrenoceptor antagonist rauwolscine. When given to non-pretreated cats with intact neuraxis, however, neither rauwolscine nor its analog yohimbine were capable of inducing a persistent release from tonic inhibition. The results suggest that both purely visceral and somato-visceral reflexes are subject to tonic descending inhibition, but they do not support the hypothesis that a catecholamine is the responsible transmitter mediating this inhibition.     

Properties of a spinal somatosensory evoked potential recorded in man.

Somatosensory evoked potentials were recorded from the skin overlying the cervical and lumbar spinal cord of man after stimulation of median and tibial nerves respectively. The early negative component (N11) of the cervical potential and the negative lumbar potential (N14) were studied. The spatial properties of N11 and N14 indicate a spinal cord origin. Evidence partly from threshold studies, shows that the low threshold cutaneous afferent fibres were responsible for activating the generators of the potentials. A conditioning test stimulation procedure supports a postsynaptic generator. It is concluded that N11 and N14 have properties similar to the cord dorsum potentials recorded in animals and probably have the same generator, the neurones of the dorsal horn.     

The effect of chronic undernourishment on the synaptic depression of cutaneous pathways in the rat spinal cord

The aim of this study was to determine the effect of chronic undernourishment on the amplitude depression of the first negative component in the cord dorsum potentials (N(1)-CDPs) caused by the conditioning stimulation of sensory cutaneous nerves in the rat spinal cord. Single electrical pulses (1Hz; 2 times threshold) applied to the sural (SU) nerve of control rats (n=14) produced CDPs with a first negative component (N(1)-CDPs) larger in amplitude (14.2±1.3%, p<0.01) than those recorded in chronically undernourished rats (n=14; 3 times threshold). The conditioning stimulation of the SP nerve (4 shocks at 300Hz, 3×T) in the control rats (n=5) evoked a long-lasting (～200ms) depression of the N(1)-CDP (60.2±7.2%). In contrast such depression was smaller in magnitude (42.5±5.7%, p<0.01) and time course (100-120ms) in undernourished rats (n=7). The systemic application of picrotoxin (PTX) reduced, but did not abolish the conditioned depression of the N(1)-CDPs and DRPs in both the control and undernourished rats. By assuming that the depression of the N(1)-CDPs is representative of presynaptic mechanisms, it is proposed that chronic undernourishment influence the activation of presynaptic neuronal pathways that regulate the transmitter release of cutaneous afferent fibers in the spinal cord and such effect could act as a compensatory mechanism that counterbalances the decreased activation of spinal neurons by the reduced afferent input in the rat.     

Characteristics of sympathetic reflexes evoked by electrical stimulation of phrenic nerve afferents.

In chloralose-anaesthetized cats, sympathetic reflex responses were recorded in left cardiac and renal nerve during stimulation of afferent fibres in the ipsilateral phrenic nerve. In cardiac nerve, a late reflex potential with a mean onset latency of 75.6 +/- 13.8 ms was regularly recorded which, in 20% of the experiments, was preceded by an early, very small reflex component (latency between 35 and 52 ms). In contrast, in renal nerve only a single reflex component after a mean latency of 122.1 +/- 13.1 ms was observed. Bilateral microinjections of the GABA-agonist muscimol into the rostral ventrolateral medulla oblongata resulted in a nearly complete abolition of sympathetic background activity and in an 88% reduction of the late reflex amplitude with only small effects on the latency of the evoked potentials. Under this condition, an early reflex component was never observed to appear. After subsequent high cervical spinalization, the residual small potentials which persisted after bilateral muscimol injections were completely abolished and in cardiac nerve an early reflex potential with a mean latency of 45 +/- 10 ms was observed in all but one experiment. The early reflex was therefore referred to as a spinal reflex component which, however, is suppressed in most animals with an intact neuraxis. In the renal nerve a spinal response was only observed in one experiment after spinalization. The results suggest that sympathetic reflexes evoked by stimulation of phrenic nerve afferent fibres possess similar spinal and supraspinal pathways as previously described for somato-sympathetic and viscero-sympathetic reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Control of the heart rate by sympathetic nerves in cats

Pre- and postganglionic sympathetic nerves were electrically stimulated and heart rate was recorded in chloralose-anaesthetised cats. The vagal nerves and white rami were cut on both sides. Electrical stimulation was performed with a 15- or 30-s train of 0.2-ms pulses at a frequency of 30 Hz. The control heart rate was 150 beats/min. Heart rate was increased when the T3 white ramus on the left (52 beats/min above control) and T3, T4 white rami on the right side (100 beats/min above control) were stimulated electrically. The magnitude of the heart rate increase declined when the neighbouring thoracic white rami were stimulated. The increase of the heart rate was caused by group B preganglionic fibres. Electrical stimulation of the sympathetic fibres in the right vagus nerve and the right inferior cardiac nerve increased the heart rate by 92 beats/min and by 67 beats/min above the control level respectively. Electrical stimulation of the left inferior cardiac nerve, the left middle cardiac nerve and the sympathetic fibres in the left vagus nerve resulted in an increase of the heart rate of 43 beats/min, 30 beats/min and 49 beats/min from the control level respectively. This indicates that a majority of the preganglionic cardiac sympathetic fibres, whose activity influences the heart rate, originate from the T3 and T4 segments of the spinal cord. The majority of the postganglionic cardiac sympathetic fibres which affect the heart rate are located in the vagal nerves.     

Distribution of somatic and visceral primary afferent fibres within the thoracic spinal cord of the cat

Transport of horseradish peroxidase (HRP) through somatic and visceral nerve fibres was used to study the patterns of termination of somatic and visceral primary afferent fibres within the lower thoracic segments of the cat's spinal cord. A concentrated solution of HRP was applied for at least 5 hours to the central end of the righ greater splanchnic nerve and of the left T9 intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport times (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Somatic afferent fibres and varicosities (presumed terminals) were found in laminae I, II, III, IV, and V of the ipsilateral dorsal horn and in the ipsilateral Clarke's column. The density of the somatic projection was particularly high in the superficial dorsal horn. In parasagittal sections of the cord, bundles of somatic fibres were seen joining the dorsal horn from the dorsal roots via the dorsal columns and Lissauer's tract. A medio-lateral somatotopic arrangement of somatic afferent terminations was observed, with afferent fibres from the ventral parts of the dermatome ending in the medial dorsal horn and afferent fibres from the dorsal parts of the dermatome ending in the lateral dorsal horn. The total rostro-caudal extent of the somatic projection through a single spinal nerve was found to be of 2 and 2/3 segments, including the segment of entry, the entire segment rostral to it and two-thirds of the segment caudal to it. A lateral to medial shift in the position of the somatic projection was observed in the rostro-caudal axis of the cord. Visceral afferent fibres and varicosities (presumed terminals) were seen in laminae I and V of the ipsilateral dorsal horn. The density of the visceral projection to the dorsal horn was substantially lower than that of the somatic projection. Visceral afferent fibres reached the dorsal horn via Lissauer's tract and joined a lateral bundle of fine fibres that run along the lateral edge of the dorsal horn. The substantia gelatinosa (lamina II) appeared free of visceral afferent fibres. These results are discussed in relation to the mechanisms of viscero-somatic convergence onto sensory pathways in the thoracic spinal cord.     

Spinal evoked potential in man: a maturational study.

Summated evoked potentials to peroneal nerve stimulation which arise in the cauda equina and spinal cord afferent pathways were recorded from surface electrodes placed over the spine of 95 infants, children and adults. The conduction velocity of these potentials from lumbar to cervical recording sites was calculated. Additionally, segmental conduction velocities over peroneal nerve, caudal and rostral spinal cord were determined. In all age groups the speed of conduction up the spine was non-linear. It was slower over caudal spinal cord segments than over peripheral nerve or rostral cord. All these velocities were about half adult values in the newborn and progressively increased with age. The conduction velocity over peripheral nerve was within the adult range by 3 years of age. The speed of conduction over the spinal cord did not reach adult values until the 5th year. This suggests that spinal cord afferent pathways mature at a slower rate than peripheral nerve fibers.     

Lumbar cord potentials evoked by stimulation of the nerves of the lower limb in man

Lumbar cord potentials evoked by electrical stimulation of the posterior tibial and sural nerves at the ankle were recorded with monopolar epidural electrodes, at T11-T12 level in 20 subjects and were compared with surface recorded potentials. Two quadriplegic patients with spinal section were included in this group. Curare was given in two cases. Xylocaine block of peripheral nerve was carried out in 4 cases. Double shock study was done in 5 cases. The lumbar cord evoked potentials show two successive components: a 'primary' negative-positive spike response with a latency of 19-35 msec, and the 'secondary' waves with latencies up to 200 msec. The 'primary' response is mainly produced by the afferent volley in the fibres of the dorsal roots and of their intramedullary prolongations. There is no evidence which suggests that it is correlated with presynaptic inhibition. The secondary components may be divided into the early and the late waves. The early waves (40-90 msec) are related to the polysynaptic activities from the afferent fibres of small diameters. The late waves are under the influence of supraspinal mechanism and may be related to long-loop reflexes. The clinical implications of these evoked potentials are discussed.     

STUDIES ON THE HUMAN EVOKED ELECTROSPINOGRAM

The propagation velocity of the ascending volleys along the dorsal funiculus of the human spinal cord was studied in 31 normal volunteers. Intrathecal recordings from lower cervical and lower thoracic intervertebral levels were made after the supramaximal stimulation of the posterior tibial nerves. When the electrode tip was behind the cord dorsum at the cervical level, it was easily possible to obtain very clear triphasic compound action potential on stimulation of the posterior tibial nerve of one leg or both legs. This "Tractus Potential" was found to originate mainly from the dorsal funiculus fibres, i.e. Fasciculus gracilis. The maximal conduction velocity of the ascending afferent volley from the leg was then calculated to be, on average, 37 meters/sec between lumbar and cervical spinal enlargements. Intrathecal stimulation and recording of the spinal cord gave the distinct triphasic wave with low threshold. This was also found to be related to dorsal funiculus activity. In these intraspinal stimulations and recordings, very early small and some late long-lasting deflections appeared, especially in the lateral position of the intrathecal electrode.     

Afferent pathways and responses of T3-T4 spinal neurons to cervical and thoracic esophageal distensions in rats

The purposes of this study were to (1) compare responses of T(3)-T(4) spinal neurons to thoracic and cervical esophageal distension (TED, CED) and (2) determine afferent pathways for esophageal input to these neurons. Extracellular potentials of single superficial and deeper T(3)-T(4) neurons were recorded in pentobarbital anesthetized male rats. Graded TED or CED was produced by water inflation (0.1-0.5 ml) of a latex balloon. TED changed activity of 121/432 (28%) neurons (114 were excited); CED activated 69/269 (26%) neurons (56 were excited). Of 151 neurons that were tested for responses to both TED and CED, 40 (26%) neurons responded to both TED and CED. Mean duration of excitatory responses in convergent neurons to TED was significantly longer than the duration of responses to CED (31.4+/-2.8 vs. 25.4+/-1.0 s, n=34, P<0.05). A total of 105 out of 121 (87%) and 66 out of 69 (96%) neurons responsive to TED and CED had somatic fields. Spinal transection at rostral C(1) and at C(7)-C(8) indicated that excitatory responses to TED resulted from activation of afferent input that entered thoracic spinal segments; whereas, excitatory responses to CED resulted from afferent inputs entering cervical or thoracic spinal segments. These data showed that the upper thoracic spinal cord received sensory information from the esophagus through cervical and/or thoracic spinal visceral afferent pathways.     

The spinal cord processing of input from the superior sagittal sinus: pathway and modulation by ergot alkaloids

The effects of ergot alkaloids on field potentials and unit responses produced in the upper cervical spinal cord by stimulation of the superior sagittal sinus (SSS) were examined in 57 anesthetized cats. Electrical stimulation of the SSS produced field potentials and single-unit responses at latencies of 5–20 ms. Field potentials were abolished by section of the first division of the trigeminal nerve but were unaffected or increased by section of the upper cervical nerves. Field potentials were reduced or abolished by intravenous injection of ergotamine or dihydroergotamine (DHE). The evoked response of 41 units (34.4%) were suppressed by either i.v. or iontophoretic administration of ergotamine, DHE or ergometrine. The results suggest that ergot alkaloids exert an effect at a spinal cord relay centre which receives trigeminally mediated input from cranial blood vessels.