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.     

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.     

Intersegmental connections and interactions of myelinated somatic and visceral afferents with sympathetic preganglionic neurons in the unanesthetized spinal cat

The aim of this study was to obtain a measure of the interactions through exclusively spinal circuits, of myelinated afferents with sympathetic preganglionic neurons. Experiments were performed on 16 unanesthetized cats rendered insensitive by bilateral vertebral and carotid occlusion, whose spinal cords had been transected at C1 6-12 h before recording. The evoked responses of 68 tonically active sympathetic preganglionic neurons were recorded from filaments dissected from the cervical sympathetic trunk. Excitation, inhibition and excitation-inhibition sequences were evoked by electrical stimulation of radial, femoral and pelvic nerve afferents. Inhibition was most often observed during pelvic nerve stimulation. Ninety percent of the sympathetic preganglionic neurons tested responded to radial, 77% to femoral and 85% to pelvic nerve stimulation. These differences in percentage of units responding to the three nerves were statistically insignificant. Thus, in the acute spinal cat, the fraction of tonically active sympathetic preganglionic neurons whose activity can be influenced by myelinated afferents is independent of the length of the intraspinal pathway which conveys the input. A main difference between the long pathway (mediating the responses to femoral or pelvic nerve) and the short pathway (mediating the responses to radial nerve) seems to be the efficacy of their connections. While single shocks reliably evoked responses from the radial nerve, trains (200 Hz, 20 msec) were usually necessary to elicit responses from femoral or pelvic nerve, indicating a requirement for summation in the long pathway.     

The sympathetic trunks of a hibernator, the bat Myotis lucifugus

The sympathetic trunks in Myotis lucifugus are each characterized by three unusually prominent ganglia: the superior cervical, the stellate and a “large lumbar” ganglion. The superior cervical appears to distribute only to the head region. The cervical sympathetic trunk connects with the vagus nerve but not to the cervical spinal nerves. The stellate is the largest of the trunk ganglia. A prominent nerve arising from it follows the vertebral artery. This vertebral nerve connects with the second to the seventh, and sometimes the eighth, cervical spinal nerves. Another prominent branch from this ganglion follows the cervical artery to ramify in the interscapular brown fat pad. The stellate ganglion supplies the brachial plexus directly and via the vertebral nerve. Its branches also supply thoracic viscera important for arousal from hibernation as well as for flight. The large lumbar ganglion contributes very few fibers to abdominal or pelvic viscera but, via the lumbosacral plexus, may affect vasoconstriction in the pelvic wall and posterior extremities. The prominent prevertebral ganglia in the abdomen and pelvis, which include an adrenal-;renal complex, are probably supplied by the tenth thoracic to second lumbar spinal nerves.     

Distribution of GABA-immunoreactive nerve fibers and cells in the cervical and thoracic paravertebral sympathetic trunk of adult rat: Evidence for an ascending feed-forward inhibition system

Neurochemical and immunohistochemical evidence suggests that the superior cervical ganglion (SCG) contains all components of a gamma-aminobutyric acid (GABA)ergic transmission system, which includes GABAergic axons of unknown origin. The number of nerve fibers with and without GABA-like immunoreactivity was determined in interganglionic connectives at all cervical and thoracic levels of the paravertebral sympathetic trunk. In addition, the distribution of GABA-immunoreactive (IR) neurons was established within the ganglion chain and compared with the relative frequency of principal neurons richly innervated by GABA-IR axon terminals. The following results were obtained: (1) the total number of nerve fibers in cross sections did not significantly vary between the cervical levels, but it increased steadily from upper to lower thoracic segments; (2) in contrast, the number of GABA-IR fibers decreased from the cervical sympathetic trunk below the SCG (～300 fibers) down to the seventh to tenth thoracic ganglion, below which no such fiber was seen; (3) GABA-IR nerve fibers originate from a subclass of GABA-IR cells; these are small, bipolar neurons with predominantly ascending, unmyelinated axon-like processes; (4) the number of principal neurons richly innervated by GABA-IR nerve fibers decreased from the SCG to the upper thoracic ganglia, and was very small below; and (5) apart from basket-like innervation, GABA-IR axons also formed diffuse networks around GABA-negative principal neurons predominantly in cervical and upper thoracic ganglia. These data suggest that the GABAergic innervation of paravertebral sympathetic ganglia is more complex than previously suspected. What appears as preganglionic afferents from several spinal segments (C8-Th7) innervate GABAergic neurons in the sympathetic trunk which have ascending axons and focus their inhibitory effects on the cervical sympathetic ganglia, predominantly the SCG. These data suggest that GABAergic small interganglionic neurons form a feed-forward inhibition system, which may be driven by multisegmental spinal input in the paravertebral sympathetic ganglion chain. © 1993 Wiley-Liss, Inc.     

Localization of efferent sympathetic neurons and afferent neurons in dorsal root ganglia innervating the heart

The retrograde transport of horseradish peroxidase (HRP) has been used to study the localization and the number of neurons innervating the heart in the right stellate ganglion and accessory cervical ganglion, spinal cord and dorsal root ganglia of the cat. HRP was applied to the central cuts of anastomose of the stellate ganglion with the vagal nerve, of the vagosympathetic trunk caudal to anastomose and of the inferior cardiac nerve. HRP-labelled neurons were detected in the stellate ganglion in the regions which give off nerves, whereas in the accessory cervical ganglion labelled neurons were distributed throughout the whole ganglion. HRP-stained cells were found in the anastomose. In the spinal cord labelled neurons were detected in the lateral horn of T1-T5 segments. In the dorsal root ganglion the greatest number of neurons was observed in T2-T4 segments.     

Cells of origin of sympathetic pre- and postganglionic cardioacceleratory fibers in the pigeon

The pre- and postganglionic cardioacceleratory innervation is described in the pigeon. The peripheral course of the postganglionic cardiac nerves has been determined using microdissection and electrical stimulation. Using these techniques and retrograde degeneration methods, the distribution within the sympathetic ganglia of the cells of origin of these fibers has been localized to the three right caudal cervical ganglia (12, 13 and 14). It has also been shown on the basis of electrical stimulation combined with selective ablation of the right sympathetic chain that cardioaccelerator preganglionic fibers probably arise from the most caudal cervical segment of the spinal cord (14), always arise from the upper two thoracic segments (15 and 16), and occasionally arise from a mid-thoracic segment (17). The left sympathetic chain was shown to have an inconsistent influence on heart rate. On the basis of retrograde degeneration, the cells of origin of sympathetic preganglionic fibers have been localized to a welldefined cell column dorsal to the central canal (column of Terni).     

Embryonic spinal cord neurons develop preferential cholinergic projections to sympathetic ganglia explanted from appropriate levels of the neuraxis

To determine whether cholinergic spinal cord neurons can develop preferential projections in vitro within sympathetic ganglia (SGs) of appropriate levels of the neuraxis, organotypic explants of fetal mouse spinal cord (E13) from cervical, thoracic (upper and lower) and lumbar segments were co-cultured with either pairs of neonatal SGs: the rostral superior cervical ganglion (SCG) or a caudally located upper lumbar ganglion (LG). After 3.5-4 weeks of co-culture, levels of the enzyme, choline acetyltransferase (ChAT), were measured in individual spinal cord explants and SCGs or double LGs (to match the target mass of a single SCG). Interaction was assumed to occur primarily between an SCG or LG doublet and the adjacent ipsilateral half of the co-cultured cord segment. An index of cholinergic interaction was defined as the ganglion ChAT activity per unit ChAT activity in half co-cultured cord segment. The index of interaction with the SCG was highest with the T1/T2 (1.4) as compared with the T10/T11 (0.79), L1/L2 (0.38) and C2/C3 (0.11) segments. In contrast, the index of cholinergic interaction with double LGs was highest with the more caudally located T10/T11 (0.62) cord segment as compared with the rostral T1/T2 (0.33), cervical C2/C3 (0.2) and lumbar L1/L2 (0.17) segments. Ganglion compound action potentials evoked in LGs by stimulation of the ipsilateral portion of T10/T11 cord were blocked by the ganglionic antagonist, hexamethonium, as previously observed in co-cultures of SCGs with T1/T2 cord. These results indicate that pools of preganglionic neurons in thoracic cord segments can develop in vitro preferential cholinergic projections within SGs of appropriate position. Cervical and lumbar cord segments which contain a preponderance of somatic motoneurons over preganglionic neurons did not interact as effectively with either type of SG. The preferential cholinergic projections from rostral thoracic cord explants within co-cultured SCGs and from caudal thoracic cord explants within co-cultured SCGs and from caudal thoracic cord explants within LGs may reflect some degree of positional preference intrinsic to embryonic spinal cord neurons and/or their appropriate target SGs, consistent with the positional specificity expressed by preganglionic neurons and SGs in situ.     

The sympathetic and sensory components of the caudal lumbar sympathetic trunk in the cat

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project in the caudal lumbar sympathetic trunk of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons. The application was made just proximal to the segmental ganglion that sends its gray rami to the L7 spinal nerve, and so identified the sympathetic outflow concerned primarily with the vasculature of the hindlimb and tail. The numbers, segmental distribution, location, and size of the labeled somata have been determined quantitatively. Labeled cell bodies were found ipsilaterally, but the segmental distributions of the different cell types were not matched. Afferent cell bodies lay in dorsal root ganglia L1-L5 (maximum L4), preganglionic cell bodies in spinal segments T10-L5 (maximum L2/3), and postganglionic cell bodies in ganglia L2-L5 (maximum L5). Both numbers and dimensions of labeled dorsal root ganglion cells were variable between experiments (maximum about 1,000); the majority were small relative to the entire population of sensory neurons. Labeled preganglionic cell bodies were located right across the intermediate region of the spinal cord, extending from the lateral part of the dorsolateral funiculus to the central canal. The highest density of labeled neurons lay at the border between the white and gray matter (corresponding to the intermediolateral cell column) with smaller proportions medially in L1-L2, and laterally in caudal L4-L5. Medial preganglionic neurons were generally larger than those lying in lateral positions. From the data, it is estimated that about 650 afferent, about 4,500 preganglionic, and some 2,500 postganglionic neurons project in each lumbar sympathetic trunk distal to the ganglion L5 in the cat.     

Tyrosine hydroxylase-immunoreactive fibers in the human vagus nerve

Sympathetic catecholaminergic fibers in the vagus nerve were immunohistochemically examined in formalin-fixed human cadavers using an antibody against the noradrenalin-synthetic enzyme tyrosine hydroxylase (TH). TH-positive fibers were extensively distributed in the vagal nerve components, including the superior and inferior ganglia, the main trunk and the branches (superior and recurrent laryngeal, superior and inferior cardiac, and pulmonary branches). The inferior ganglion and its continuous cervical main trunk contained numerous TH-positive fibers with focal or diffuse distribution patterns in each nerve bundle. From these findings, we conclude that sympathetic fibers are consistently included in the human vagus nerve, a main source of parasympathetic preganglionic fibers to the cervical, thoracic and abdominal visceral organs.     

The afferent and sympathetic components of the lumbar spinal outflow to the colon and pelvic organs in the cat. II. The lumbar splanchnic nerves

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project to the inferior mesenteric ganglion in the lumbar splanchnic nerves of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons near the inferior mesenteric ganglion. The numbers, segmental distribution, location, and size of these labeled somata have been determined quantitatively. After all the lumbar splanchnic nerves on one side of an animal were labeled, most labeled cell bodies were situated ipsilaterally in dorsal root ganglia, ganglia of the lumbar sympathetic trunk, and spinal cord segments L2-L5, with the maximum numbers in L3 and L4. A few labeled somata lay contralaterally or rostral to L2. After labeling of only one lumbar splanchnic nerve, the majority of cell bodies were found in the labeled segment, but a few were also present up to three segments rostral or caudal. These variations could always be attributed to extraspinal connections usually via the lumbar sympathetic trunk. Cross-sectional areas of labeled afferent somata were small relative to those of the entire population of dorsal root ganglion cells. Preganglionic cell bodies were labeled in the intermediate gray matter extending from its lateral border ventrolaterally across to the central canal. Two regions of high density were observed: one laterally just medial to the edge of the white matter and the other lateral to the central canal. The dorsolateral group lay somewhat medial and caudal to the usual limits of the intermediolateral column. Labeled preganglionic neurons were on the average larger than the unlabeled cells in the inferior mesenteric ganglion, with the group lying medially being larger than those that were laterally positioned. From the data, it is estimated that about 4,600 afferent axons, about 4,600 preganglionic axons, and about 2,800 postganglionic axons travel in the lumbar splanchnic nerves to the inferior mesenteric ganglion of the cat.     

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)     

The tonic activity of single nerve fibers of the rabbit cervical sympathetic nerve

Spontaneous sympathetic activity was recorded in single fibres dissected from the cervical sympathetic nerve trunk (CSNT) of rabbit. Conduction velocities and action potential amplitudes for B-fibres were measured in the whole nerve trunk. Results of the spectral analysis suggested that activity of unmyelinated fibres depended on baroreceptor activity to a greater extent than that of myelinated fibres and that the 2-3 Hz rhythm was present in animals with intact baroreceptors simultaneously with the cardiac rhythm. That rhythm was a usual feature of activity of both B- and C-fibres. Cross-correlation analysis of the single fibre activity was estimated in 24 fibre pairs. It was found that in five fibre pairs there was a correlation associated with the presence of a common physiological rhythm, in one fibre pair there was a correlation derived from the existence of a strong common input to both distinct preganglionic neurons.     

Spinal cord representation of the micturition reflex

The spinal cord origin and peripheral pathways of the sensory and motor nerves to the urinary bladder were delineated in the cat by stimulating the appropriate nerves near the urinary bladder and recording from the dorsal and ventral rootlets near the spinal cord. The parasympathetic preganglionic neurons originated in the sacral segments of the spinal cord and reached the bladder by way of the pelvic nerve. The preganglionic parasympathetic perikarya to the urinary bladder were distributed over a length of approximately 1.5 segments, centered near the junction of segments S-2 and S-3 in cats with a median arrangement of the lumbosacral plexus. Conduction velocities in preganglionic parasympathetic fibers to the bladder ranged from 46 to 2 M/sec with a mean maximal velocity of 18.2 M/sec. The major sympathetic pathway to the bladder was in the hypogastric nerve. Preganglionic sympathetic fibers originated in the lumbar spinal cord and traveled through the caudal mesenteric ganglion and hypogastric nerve to the urinary bladder. There were both ipsilateral and contralateral preganglionic and afferent fibers in this pathway. The preganglionic sympathetic neurons originated in segments L-2 and L-5. They were usually distributed over approximately 2 full segments centered near the junction of L-3 and L-4 in cats with a median arrangement of the lumbosacral plexus. Neurons involved in the micturition reflex may extend from the rostral end of the L-2 segment to the caudal end of the S-3 segment. The sympathetic preganglionic neurons were usually separated from the somatic and parasympathetic columns by segments L-5 to L-7.     

Spinal origins of preganglionic B and C neurons that innervate paravertebral sympathetic ganglia nine and ten of the bullfrog

These experiments were designed to characterize the distribution, morphology, and number of spinal preganglionic neurons that selectively innervate the B- and C-type sympathetic neurons in paravertebral ganglia 9 and 10 of the bullfrog. For this purpose, horseradish peroxidase (HRP) was applied to the anterior end of the sectioned sympathetic chain between ganglia 8 and 9. Subsequent retrograde axonal transport of the HRP labeled ipsilateral spinal neurons whose cell bodies form a column having rostral and caudal boundaries that are, respectively, just caudal to the level of spinal nerve 4 and midway between the entry zones of spinal nerves 7 and 8. In all segments, the labeled preganglionic somata were found in the lateral half of the spinal gray and slightly dorsal to the central canal; a position analogous to that of the intermediolateral cell column in mammals. Most labeled preganglionic neurons were multipolar in shape, and the cell bodies lying between spinal nerves 4 and 5 were, on average, larger than those found between spinal nerves 7 and 8. In transverse sections that were cut near spinal nerve 5, the axons of preganglionic neurons could be seen to exit the cord through ventral roots. Counts of labeled preganglionic neurons indicate that an average +/- S.D. of 338 +/- 89 cells innervate ganglia 9 and 10. Selective labeling of preganglionic B neurons, by cutting spinal nerves 7 and 8 central to their rami communicantes at the time of HRP application, revealed an average +/- S.D. of 137 +/- 31 cells that lie exclusively between spinal nerves 4 and 6. By contrast, selective labeling of preganglionic C neurons, by cutting the sympathetic chain rostral to ganglion 7 at the time of HRP application, revealed an average +/- S.D. of 187 +/- 77 cells in an adjacent portion of the preganglionic column that is bounded by spinal nerve 6 and by a point midway between spinal nerves 7 and 8. These results thus demonstrate a clear segmental segregation between the preganglionic B and C neurons that innervate ganglia 9 and 10.     

Distinct localization and target specificity of galanin-immunoreactive sympathetic preganglionic neurons of a teleost, the filefish Stephanolepis cirrhifer

Immunoreactivity for galanin was examined in the sympathetic preganglionic neurons in the spinal cord, adrenal glands, sympathetic ganglia, and some sensory ganglia of the filefish Stephanolepis cirrhifer. Galanin-immunoreactive neurons were found only in the rostral part, but not in the caudal part of the central autonomic nucleus (a column of sympathetic preganglionic neurons of teleosts). Many galanin-immunoreactive nerve terminals were found in contact with neurons in the celiac ganglia and the cranial sympathetic ganglia on both sides of the body. Most neurons encircled by galanin-immunoreactive nerve fibers were negative for tyrosine hydroxylase. Galanin-immunoreactive nerve fibers were very sparse in the spinal sympathetic paravertebral ganglia. No galanin-immunoreactive nerve fibers were found in the adrenal glands. No sensory neurons of the trigeminal, vagal, or spinal dorsal root ganglia were positive for galanin-immunoreactivity. These results suggest that galanin-immunoreactive sympathetic preganglionic neurons have distinct segmental localization and might project specifically to a population of non-adrenergic sympathetic postganglionic neurons in the celiac and cranial sympathetic ganglia.     

Death of preganglionic sympathetic neurons after surgical or immunologic lesion of peripheral processes

Three months after systemic injection of antibody to acetylcholinesterase (AChE), there is a 60% decrease in the population of preganglionic sympathetic neurons expressing choline acetyltransferase (ChAT) in the intermediolateral (IML) nucleus of the rat spinal cord. In principle, the disappearance of identifiable cholinergic neurons might reflect either outright cell death or severe atrophy with downregulation of cholinergic markers. To distinguish between these possibilities, preganglionic neurons were labeled with the retrograde tracer dye, Fast Blue, 1 week before antibody injection or surgical transection of the cervical sympathetic trunk. Three months after either treatment, the thoracic IML contained 40-60% fewer Fast Blue-labeled neurons than in controls. Therefore, preganglionic sympathetic neurons do degenerate after antibody injection or axotomy. To clarify the role of axonal damage in this process, the effects of three different mechanical lesions were examined. A lumbar ganglionectomy designed to interrupt most sympathetic axons emanating from L2 IML caused 92% loss of ChAT-positive cells observed 10 weeks later at that site. In comparison, transection of the cervical sympathetic trunk, which spared some distally directed axonal branches from the thoracic IML, caused only a 46% loss of ChAT-positive neurons at T1. Still smaller effects were seen after the same nerve was crushed, a lesion that is less destructive. Thus, the ability of central sympathetic neurons to survive a peripheral lesion may be related to the degree of axonal damage and to the opportunity for axonal regrowth.     

Vagal and gastric connections to the central nervous system determined by the transport of horseradish peroxidase

Horseradish peroxidase (HRP, Sigma Type VI) crystals were encased in a parafilm envelope and applied to the transected central ends of the left and right cervical vagus nerves and the anterior and posterior esophageal vagus nerves of adult male hooded rats. Injections of 30% HRP were made into the muscle wall of the fundus and antrum regions of the stomach. After 48 hr survival time, animals were perfused intracardially with a phosphate buffer plus sucrose wash followed by glutaraldehyde and paraformaldehyde fixative. The brain stem, spinal cord and corresponding dorsal root ganglia, superior cervical sympathetic ganglion, and the nodose ganglion were removed and cut into 50 micron sections. All tissue was processed with tetramethylbenzidine (TMB) for the blue reaction according to Mesulum and counterstained with neutral red. Sequential sections were examined under a microscope. Labeled neurons and nerve terminals were identified using bright and dark field condensers and polarized light. In tissue from animals that had HRP applied to the cervical vagus nerves, retrogradely labeled neurons were identified ipsilaterally in the medulla located in the dorsal motor nucleus of the vagus (DMN) and the nucleus ambiguus (NA). Labeled cells extended from the DMN into the spinal cord in ventral-medial and laminae X regions C1 and C2 of cervical segments. Many neurons were labeled in the nodose ganglion. Anterogradely labeled terminals were observed throughout and adjacent to the solitary nucleus (NTS) dorsal to the DMN and intermixed among labeled neurons located in the DMN. In tissue from animals that had HRP applied to the esophageal vagus nerves, similar labeling was observed. However, fewer neurons were identified in the NA, the nodose ganglion, and only in laminae X of the cervical spinal cord segments C1 and C2. Also, very little terminal labeling was observed in and adjacent to the NTS. Labeled neurons in tissue from animals that had HRP injected into the stomach wall were observed bilaterally in the DMN, nodose ganglion, and only in laminae X at the C1 and C2 levels of the spinal cord. Labeled neurons also were observed in the dorsal root ganglia of the thoracic cord. These data indicate that cervical cord and NA neurons are important in the supradiaphragmatic motor innervation by the vagus. Also, many afferents to the NTS originate above the diaphragm. In addition, some afferents from the stomach enter the central nervous system via the thoracic spinal cord.     

Categories of axons in the inferior cardiac nerve of the cat

Myelinated and unmyelinated axons in the inferior cardiac nerve of the cat were examined to determine how many axons were (1) sensory, (2) preganglionic sympathetic, and (3) postganglionic sympathetic. In one group of cats, a segment was removed from the middle of the inferior cardiac nerve as a control, and the proximal and distal stumps of the nerve were examined one week later. In another group of cats, the control segment of nerve was removed and the first thoracic white ramus communicans and sympathetic trunk were cut proximal to the stellate ganglion, followed in one week by examination of the proximal and distal stumps of the inferior cardiac nerve. In still another group of cats, the first five thoracic spinal nerves were cut just distal to the dorsal root ganglion. The counts of myelinated and unmyelinated axons after these surgical procedures indicated that, in the cat inferior cardiac nerve, all or almost all of the approximately 30,000 unmyelinated axons and 10 percent of the myelinated axons are postganglionic sympathetic fibers, and that approximately 90 percent of the myelinated axons are sensory.     

Serotonin inputs to rabbit sympathetic preganglionic neurons projecting to the superior cervical ganglion or adrenal medulla

The input from serotonin-containing nerve fibres to rabbit sympathetic preganglionic neurons projecting to either the superior cervical ganglion or the adrenal medulla was investigated by combining retrograde tracing with the B subunit of cholera toxin and immunocytochemistry for serotonin. There were pronounced rostrocaudal variations in the density of serotonin fibres in the rabbit intermediolateral cell column from T1 to L4; maximum numbers of fibres were found in T3-6 and L3–4 and minimum numbers in T1 and T10–12. By light microscopy, retrogradely labelled sympathetic preganglionic neurons projecting to the superior cervical ganglion or the adrenal medulla received variable densities of close appositions from serotonin-immunoreactive fibres. Some neurons from each population received many close appositions, whereas others received moderate numbers or few appositions. Appositions occurred on the cell bodies, dendrites, and occasionally axons of sympathetic preganglionic neurons. Rare neurons in both groups of retrogradely labelled cells received no appositions from serotonin-containing nerve fibres. At the ultrastructural level, synapses were found between serotonin-positive boutons and sympathetic preganglionic neurons projecting either to the superior cervical ganglion or to the adrenal medulla. These results indicate that, through direct synaptic contacts, serotonin-immunoreactive, presumably bulbospinal, nerve fibres affect the activity of the vast majority of sympathetic preganglionic neurons that send axons either to the superior cervical ganglion or to the adrenal medulla. This serotonin input may be sympathoexcitatory and could mediate increases in sympathetic nerve activity and in the release of catecholamines from the adrenal medulla. © 1995 Wiley-Liss, Inc.