On the anatomical organization of the lumbosacral sympathetic chain and the lumbar splanchnic nerves of the cat--Langley revisited

Neurotrophins and target interactions in the development and regulation of sympathetic neuron electrical and synaptic properties

The electrical and synaptic properties of neurons are essential for determining the function of the nervous system. Thus, understanding the mechanisms that control the appropriate developmental acquisition and maintenance of these properties is a critical problem in neuroscience. A great deal of our understanding of these developmental mechanisms comes from studies of soluble growth factor signaling between cells in the peripheral nervous system. The sympathetic nervous system has provided a model for studying the role of these factors both in early development and in the establishment of mature properties. In particular, neurotrophins produced by the targets of sympathetic innervation regulate the synaptic and electrophysiological properties of postnatal sympathetic neurons. In this review we examine the role of neurotrophin signaling in the regulation of synaptic strength, neurotransmitter phenotype, voltage-gated currents and repetitive firing properties of sympathetic neurons. Together, these properties determine the level of sympathetic drive to target organs such as the heart. Changes in this sympathetic drive, which may be linked to dysfunctions in neurotrophin signaling, are associated with devastating diseases such as high blood pressure, arrhythmias and heart attack. Neurotrophins appear to play similar roles in modulating the synaptic and electrical properties of other peripheral and central neuronal systems, suggesting that information provided from studies in the sympathetic nervous system will be widely applicable for understanding the neurotrophic regulation of neuronal function in other systems.

Variations in the number and position of human lumbar sympathetic ganglia and rami communicantes

The purpose of this study is to provide precise anatomical and statistical information about the number and location of lumbar sympathetic ganglia and the number and length of the related rami communicantes, and to consider the neurological pathway for nociception from the low back. Three-hundred ninety-three ganglia and 719 rami communicantes from 50 human cadavers were identified by gross dissection. The number of ganglia in a single lumbar chain ranged from 2 to 6, the mean being 3.9. The mean lengths of rami connected to the 1st and 5th lumbar spinal nerves, respectively, were significantly longer and shorter than those connected to the 2nd, 3rd, and 4th nerves. The lumbar sympathetic ganglia and rami communicantes were not distributed segmentally. The present results may assist in understanding the nociceptive pathway from the low back.

Sympathetic efferent pathways projecting bilaterally to the vas deferens in the rat

BACKGROUND

The laterality of the signals passing through the splanchnic nerves to the vas deferens has not been well studied.

METHODS

The present study was designed to determine the bilateral distribution of sympathetic nerves to the rat vasa deferentia by measuring intravasal pressure (VP) responses to electrical stimulation of left lumbar splanchnic nerves (LSN) following consecutive transections of more distal nerves.

RESULTS

L2-L6 LSN stimulation increased VP bilaterally. Left VP responses decreased slightly (< 20%) after section of the right hypogastric nerve (HGN) and then were abolished by subsequent section of branches (B-M-APG) between the left major pelvic (MPG) and accessory pelvic ganglia (APG). Left VP responses were decreased by > 80% after section of left HGN, not changed further by subsequent section of commissural branches (CB-MPG) between the MPG, and completely eliminated by section of commissural branches between the APG (CB-APG). Right VP responses were decreased slightly (< 20%) by section of the left HGN and then abolished by section of the right B-M-APG. These responses were also decreased by > 70% by section of right HGN, not changed by section of CB-MPG, but then completely eliminated by section of CB-APG.

CONCLUSIONS

These results indicate that the left lumbar sympathetic pathway to the vas deferens is distributed bilaterally and exhibits two crossing points at the level of the inferior mesenteric ganglion and APG.

Three electrophysiological classes of guinea pig sympathetic postganglionic neurone have distinct morphologies

Sympathetic postganglionic neurones can be differentiated electrophysiologically into three classes (phasic, Ph; tonic, T; and long-afterhyperpolarising, LAH) based on their potassium channel expression and consequent differences in excitability. We tested whether neuronal morphology differs between these classes. Neurones in coeliac, inferior mesenteric, and lower lumbar paravertebral ganglia of guinea pigs were filled with biocytin during in vitro experiments in which electrical properties were recorded. The dimensions of somata and dendrites were measured in approximately equal numbers of stained neurones of each class. The three electrophysiological classes were distinct in terms of soma shape, soma size (Ph < T = LAH), total dendritic length (LAH < Ph < T) and average length of dendrites (LAH < Ph < T) (P < 0.0001, multivariate analysis of variance). The mean number of primary dendrites also differed (LAH 13, Ph 16, T 20). The majority of dendrites did not branch, the ratios of terminations to primary dendrites being 1.36 (LAH), 1.63 (Ph) and 1.81 (T). Overall, LAH neurones, with medium-sized somata but the smallest dendritic trees, were more distinct morphologically than Ph and T neurones. The morphological differences between classes were not dependent on differences in location. Further, there was no apparent relation between morphology and the pattern of synaptic input each class receives. The results indicate that three distinct groups of sympathetic postganglionic neurone exist in adult guinea pigs, although more than three functions are subserved by these neurones.

Variation in the anatomy of the lumbar sympathetic chain in the rat

The rat is often used when the sympathetic nervous system contribution to various physiological and pathological processes is studied. These experiments require a detailed knowledge of the lumbar sympathetic chain anatomy since the macroscopic anatomy of the L2 and L3 levels of the sympathetic chain, which innervate a major portion of the hindleg, is highly variable. We have performed a detailed study of the anatomy of the lumbar sympathetic chain in 245 Sprague-Dawley rats. Through anatomical characterization of the L2 and L3 sympathetic ganglia white and gray ramus communicants, our study provides an anatomical guide for studies of the function of the lumbar sympathetic chain in the rat.

Peripheral administration of nerve growth factor in the adult rat produces a thermal hyperalgesia that requires the presence of sympathetic post-ganglionic neurones

Previous evidence suggests that, in adult animals, nerve growth factor (NGF) can induce hyperalgesia, and may be an endogenous mediator in some persistent pain states. Here we have studied the effects of single intradermal injections of 50-500 ng of human recombinant NGF into the plantar skin of adult rat hindpaws. We found that doses of 250 ng and more produced a prolonged and stable thermal hyperalgesia to radiant heat. NGF did not produce overt pain behaviour as judged by the absence of paw licking or guarding of the injected paw. In animals subjected to surgical or chemical sympathectomy, by repeated systemic guanethidine treatments, the hyperalgesic effects of NGF were markedly reduced. We also found that NGF produced plasma extravasation in rat skin, using the Evan's blue method, with a dose dependency similar to that determined for hyperalgesia. Together, these findings suggest that NGF can lead to a rapid activation and sensitization of cutaneous nociceptors. However, these actions appear at least partly indirect, requiring the presence of normal sympathetic post-ganglionic terminals.

Sympathetic and afferent neurones projecting into forelimb and trunk nerves and the anatomical organization of the thoracic sympathetic outflow of the rat

The anatomy of the cervicothoracic sympathetic nerves was studied in the rat. Details of the arrangements of white and grey rami communicantes and superior cervical, middle cervical and stellate ganglia are given. Dorsal root and sympathetic ganglion neurones projecting to skin and muscle of the forelimb and trunk were labelled retrogradely with horseradish peroxidase (HRP) in order to study their number, segmental distribution and location. HRP was applied to forelimb nerves supplying skeletal muscles (Ramus profundus of radial nerve, RP) or hairy skin (N. cutaneus brachii lateralis superior of axillary nerve, CB), to mixed nerves (median nerve, ME; ulnar nerve, UL; radial nerve, RA) and to segmental thoracic nerves supplying hairy skin of the back (dorsal cutaneous nerve, CD) and to mixed internal intercostal nerves (IC). All sensory and sympathetic neurones were located ipsilaterally. In the forelimb nerves sensory somata were commonly restricted to two or three adjacent dorsal root ganglia (usually C6-7 for CB; C7-8 for ME; C7-Th1 for RA and RP; C8-Th1 for UL). Nearly all of the sympathetic somata were located in the middle cervical and stellate ganglia (fusion of C6-Th3). Some 0-0.4% lay in Th4 and Th5, none in the superior cervical ganglia. In the trunk nerves sensory somata were strictly segmentally organized. Sympathetic somata were distributed more widely over 4-5 segments with 50-55% in the segmental ganglion and up to 41% in the next caudal segment. From the data, it is estimated that 400 sympathetic (28%) and 1050 afferent neurones project into CB, 1660 (29%) and 4050 into RA, 540 (42%) and 760 into RP, 1010 (22%) and 3670 into ME, 880 (22%) and 3040 into UL, 350 (25%) and 1040 into IC and 500 (27%) and 1370 into CD.

Afferent and sympathetic neurons projecting into lumbar visceral nerves of the male rat

The cell bodies of thoracolumbar sensory and sympathetic pre- and postganglionic neurons that project to the colon and pelvic organs of the male rat were labeled retrogradely with horseradish peroxidase (HRP) in order to study numbers, segmental distribution, and location of the somata of these neurons quantitatively. HRP was applied to one hypogastric nerve (HGN), to the lumbar colonic nerves (LCN) and to the intermesenteric nerve (IMN). In order to estimate the significance of the branching of one axon into both hypogastric nerves a double-labeling technique with fluorogold and HRP was used. About 2640 neurons project into the two HGN added together (800 afferent, 1320 pre-, and 520 postganglionic), 4650 neurons into the LCN (360 afferent, 0 pre- and 4290 postganglionic), and 5990 into the IMN (1500 afferent, 1250 pre-, and 3240 postganglionic). About 4190 sympathetic postganglionic prevertebral neurons innervate the colon and pelvic organs, 1900 are located in the inferior mesenteric ganglion and 2290 in ganglia of the IMN. Considering the efferent component, the HGN mainly are preganglionic and the LCN exclusively postganglionic nerves. Branching of one axon into both HGN is a rare event and quantitatively negligible (less than 3%). Afferent neurons of all three nerves were found in the dorsal root ganglia (DRG) T12-L2 with the maximum in L1 and L2. The distribution of afferent neurons projecting into the LCN is shifted slightly more rostrally compared to neurons projecting into the HGN. The IMN distribution is located in a position in between. Preganglionic neurons projecting into the IMN are located in the spinal cord segments T12-L3 with the maximum in L1 and L2.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation of sympathetic neurones projecting in the hypogastric nerves in terms of their discharge patterns in cats

1. Sympathetic neurones that project in the hypogastric nerves (HGNs) were analysed for their discharge patterns in anaesthetized cats. The activity of these neurones was recorded from their axons. Afferents from the pelvic organs (urinary bladder, colon, anal canal), and arterial baro-and chemoreceptors were stimulated. 150 postganglionic and nine preganglionic neurones were analysed. 2. The postganglionic neurones exhibited reflex patterns that were typical of visceral vasoconstrictor neurones and various types of motility-regulating neurones. Most motility-regulating neurones and all visceral vasoconstrictor neurones had ongoing activity. 3. Postganglionic motility-regulating neurones were not influenced by stimulation of arterial baro-and chemoreceptors, but showed distinctive reflexes on stimulation of afferents from pelvic organs. Three subgroups of motility-regulating neurones were identified: type 1 neurones (34% of the sample of postganglionic neurones) were excited from the urinary bladder and inhibited or not influenced from the colon. Type 2 neurones (14%) exhibited a reflex pattern reciprocal to that of the type 1 neurones. Anal motility-regulating neurones (8%) were only influenced from the anal canal. The most powerful reflexes in these types of motility-regulating neurones were elicited by mechanical stimulation of the anal mucosa. 4. Postganglionic visceral vasoconstrictor neurones (16% of the sample) were under powerful inhibitory control from the arterial baroreceptors and weakly excited by stimulation of arterial chemoreceptors. Visceral stimuli had little or no effect on most of these neurones. Some visceral vasoconstrictor neurones exhibited some overlap in their functional properties with motility-regulating neurones. 5. Twenty-eight per cent of our sample of postganglionic neurones showed no reflexes to the afferent stimuli used. About half of these neurones had on-going activity. 6. Nine preganglionic neurones with on-going activity were identified. Most of these neurones behaved like visceral vasoconstrictor or motility-regulating neurones. 7. This study shows that the majority of postganglionic neurones that project in the HGNs can be divided into the same functional types as the lumbar preganglionic neurones that project to the inferior mesenteric ganglion. The proportions of the different types of neurones are similar at pre- and postganglionic levels. Thus the centrally generated patterns of activity are most likely faithfully transmitted from the spinal cord to the target organs in the pelvic cavity in functionally separate pathways.

Origin of sympathetic innervation of the knee joint in the cat: a retrograde tracing study with horseradish peroxidase

In the cat the origin of sympathetic nerve fibers in the medial and posterior articular nerve (MAN and PAN) of the knee joint was studied using retrograde labeling with horseradish peroxidase (HRP). Three to 5 days after uptake of HRP by MAN per cat 404 +/- 136 labeled somata (mean +/- S.D., n = 4 cats) were found mainly in the paravertebral ganglia L4 and L5 of the ipsilateral sympathetic trunk, and uptake of HRP by PAN labeled per animal 532 +/- 155 cell bodies (mean +/- S.D., n = 4 cats) mainly in the paravertebral ganglia L5 and L6. The cross-sectional areas of the labeled somata ranged from 200 to 1300 microns 2 with a mean of about 620 microns 2.

Lumbar sympathetic ganglia in man: an electrophysiological study in vitro

A method has been developed for the removal, preservation and electrophysiological study 'in vitro' of sympathetic lumbar chains (L1-L3) from subjects undergoing lumbar ganglionectomy in the treatment of peripheral vascular diseases. Extracellular recordings from interganglionic trunks, and intracellular recordings from single sympathetic neurons, were performed. The extracellular experiments substantiated the concept, hitherto deduced from animal experiments, that the preganglionic fibres in the sympathetic lumbar chain are mainly of a descending nature. In fact, stimulation of the interganglionic trunk cranial to ganglia is always much more effective in driving ganglion neurons to fire than stimulation of the interganglionic trunk caudal to ganglia. The intracellular experiments produced a good definition of the main electrical characteristics of human sympathetic neurons. The results can be summarized as follows: the resting membrane potential ranged from 50 to 75 mV (63.4 +/- 9.2 mV; 21 neurons); action potential amplitude from 62 to 93 mV (74.3 +/- 8.1 mV; 27 neurons); membrane input resistance was 42.3 +/- 12.6 m omega (8 neurons) and total membrane capacitance 83.7 +/- 15.3 pF (8 neurons).

False-positive artifacts of tracer strategies distort autonomic connectivity maps

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

Sympathetic and afferent somata projecting in hindlimb nerves and the anatomical organization of the lumbar sympathetic nervous system of the rat

The anatomy of the sympathetic pathways from the spinal cord to the lumbar sympathetic trunk and the inferior mesenteric ganglion was studied systematically in the rat. Details of the arrangements of white and gray rami communicantes, sympathetic trunk ganglia, the intermesenteric nerve, and the lumbar splanchnic nerves are summarized. A modified nomenclature for the segmental ganglia of the paravertebral sympathetic chain is proposed. Cell bodies of sensory and sympathetic axons projecting to the skin and skeletal muscle of the rat hindlimb were labeled retrogradely with horseradish peroxidase (HRP) in order to study numbers, segmental distribution, and location of the somata of these neurons quantitatively. HRP was applied to the nerves supplying skeletal muscle (gastrocnemius-soleus, GS), hairy skin (sural, SU; saphenous, SA) and to a mixed nerve (tibial, TI). All sensory somata and 96.4% of the sympathetic cell bodies were located ipsilaterally. Sensory somata were commonly restricted to two adjacent dorsal root ganglia (usually L3-4 for SA; L4-5 for GS, TI; L5-6 for SU). Although the sympathetic somata were more widely distributed rostrocaudally (four to six segments), their maximum was always located one or two segments more cranially than the sensory outflow, i.e., corresponding to the rami communicantes grisei. From the data, it is estimated that 420 sympathetic and 530 afferent neurons project into GS, 590 and 3,610 into SU, 920 and 3,750 into SA, and 1,070 and 5,760 into TI. These absolute neuron numbers are compared with electron microscopic fiber counts from the literature.

Discharge properties of mechanosensitive afferents supplying the retroperitoneal space

Functional properties of lumbar mechanosensitive afferent fibres in the white rami L3 to L4 and the lumbar splanchnic nerves, which supply the retroperitoneal space were investigated. The receptive fields of these afferents, consisting of 1 to 3 mechanosensitive sites, were found on large vessels (aorta, inferior mesenteric artery, segmental arteries), on nerves, on the peritoneum, in fat lobules, on lymph nodes and on the vertebral column. Most afferent units were associated with small vessels. About 50% of the afferents had ongoing activity (about 0.1 to 2 imp/s). Two thirds of the afferents conducted at less than 2 m/s, the rest at 2 to 16 m/s. About 60% of the units were excited by local application of bradykinin and 75 to 90% by local application of hypertonic NaCl solution (4.5 and 9%) or KCl solution (60 and 155 mmol/l). About 50% of the afferent units with receptive fields on large arteries were activated by an increase in the arterial blood pressure. The function of these afferent fibres is unclear. However, it is conceivable that they are involved in nociception.

The effect of a transient outward current (IA) on synaptic potentials in sympathetic ganglion cells of the guinea-pig

The responses to stimulation of preganglionic fibres have been studied in sympathetic neurones in ganglia of the caudal lumbar sympathetic chain (l.s.c.) and in the distal lobes of inferior mesenteric ganglia (i.m.g.) isolated from guinea-pigs. Most l.s.c. neurones were classified as 'phasic' and i.m.g. neurones as 'tonic' (see Cassell, Clark & McLachlan, 1986). The types of preganglionic inputs received by l.s.c. and i.m.g. neurones differed: l.s.c. cells almost invariably received at least one suprathreshold ('strong') input, in addition to several subthreshold ones; i.m.g. neurones more commonly received only subthreshold inputs via the lumbar splanchnic nerves. Prolonged discharges were evoked in some i.m.g. cells by stimulation of lumbar splanchnic nerves at strengths just supramaximal for the conventional fast synaptic responses. These appeared to arise from repetitive discharges evoked in other neurones intrinsic to the i.m.g. The time constants of decay of subthreshold synaptic currents recorded under voltage clamp in l.s.c. neurones (4.9 +/- 0.2 ms) were significantly shorter on average than those recorded in tonic i.m.g. cells (7.1 +/- 0.3 ms), although the values of time constant for the two populations overlapped. In phasic neurones, excitatory synaptic potentials (e.s.p.s) evoked at resting membrane potential by stimulation of preganglionic axons decayed with the same exponential time course as an electrotonic potential. In tonic neurones, the time course of decay of the e.s.p. was briefer, but always followed an exponential with the same time constant as the cell input time constant over the final part of the response. If tonic neurones were hyperpolarized by the passage of current through the recording micro-electrode, the time course of decay of the e.s.p. was prolonged and became the same as that of the electrotonic potential. The shape of e.s.p.s in phasic and tonic neurons could be mimicked in a computer model of the neurones incorporating the different activation/inactivation characteristics of the A current (IA) (Cassell et al. 1986) for each neurone type. It is concluded that, in addition to the contribution of IA to the rhythmic firing properties of tonic sympathetic neurones, this current also markedly inhibits the effects of excitatory synaptic conductance changes in this type of ganglion cell.

Identification of distinct topographical distributions of lumbar sympathetic and sensory neurons projecting to end organs with different functions in the cat

A comparison has been made between the lumbar sensory and sympathetic pre- and postganglionic neurons that project in the lumbar splanchnic nerves and those that project in the caudal lumbar sympathetic trunk of the cat. The neuron cell bodies have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons near the inferior mesenteric ganglion on one side, and the results have been compared with those obtained after labeling the contralateral lumbar sympathetic trunk of the same animal (Jänig and McLachlan, '86). The numbers, segmental distribution, location, and size of the labeled somata have been determined quantitatively. The data for individual animals confirm in every way those previously reported for separate experiments in different groups of animals. In addition, similar experiments were performed in which the neurons projecting in the white rami of either L4 or L5 were labeled. This procedure labeled populations of neurons that overlapped both splanchnic and paravertebral populations. Consideration of the spatial distributions and numbers of sensory and preganglionic neurons with destinations in somatic and visceral domains has enabled us to describe the different topography of these neuron populations with respect to function.

Characteristics of phasic and tonic sympathetic ganglion cells of the guinea-pig

Intracellular recording techniques have been used to determine the electrophysiological properties of sympathetic neurones in ganglia of the caudal lumbar sympathetic chain (l.s.c.) and in the distal lobes of inferior mesenteric ganglia (i.m.g.) isolated from guinea-pigs. Passage of suprathreshold depolarizing current initiated transient bursts of action potentials in 97% of l.s.c. neurones, but only 13% of i.m.g. cells ('phasic' neurones). Most i.m.g. neurones fired continuously during prolonged depolarizing pulses ('tonic' neurones). Passive membrane properties varied; mean cell input resistance was similar between groups, but phasic neurones had smaller major input time constants on average than had tonic cells. Current-voltage relations determined under both current clamp and voltage clamp were linear around resting membrane potential (approximately 60 mV), where membrane conductance was lowest. Instantaneous and time-dependent rectification varied in the different neurone types. The current underlying the after-hyperpolarization following the action potential was significantly larger on average in tonic i.m.g. cells than in phasic neurones, although its time course (tau = 100 ms) was similar. Phasic neurones fired tonically when depolarized after adding the muscarinic agonist, bethanechol (10(-5) M to 10(-4) M), to the bathing solution. Bethanechol blocked a proportion of the maintained outward current (presumably the M-current, IM, Adams, Brown & Constanti, 1982) in phasic neurones; this current was small or absent in tonic neurones. Transient outward currents resembling the A-current (IA, Connor & Stevens, 1971 a) were evoked in tonic but not in phasic neurones by depolarization from resting membrane potential. IA could only be demonstrated in phasic neurones after a period of conditioning hyperpolarization. After a step depolarization to approximately --50 mV, IA reached peak amplitude at about 7 ms and then decayed with a time constant of about 25 ms in both neurone types. Activation characteristics of IA were similar for phasic and tonic neurones, but inactivation curves, although having the same shape, were shifted to more depolarized voltages in tonic neurones. That is, IA was largely inactivated at resting membrane potential in phasic, but not tonic neurones. It is concluded that the discharge patterns of the two populations of sympathetic neurones result from differences in the voltage-dependent potassium channels present in their membranes. The anatomical occurrence of the different cell types suggests that phasic neurones are vasoconstrictor and tonic neurones are involved with visceral motility.

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.

Functional characterization of preganglionic neurons projecting in the lumbar splanchnic nerves: neurons regulating motility

Lumbar preganglionic neurons, which projected in the lumbar splanchnic nerves and were probably involved in regulating motility of colon and pelvic organs (motility-regulating, MR neurons), were analyzed for their discharge patterns. The responses of the neurons to the following stimuli were tested: stimulation of arterial baro- and chemoreceptors and of afferents from the urinary bladder, colon, mucosal skin of the anus and perianal hairy skin. The following findings were made: a total of 131 preganglionic neurons were classified as MR neurons; these reacted to natural stimulation of at least one of the afferent inputs from the urinary bladder, colon and anal and perianal skin. The ongoing activity of these neurons did not correlate with the cardiac cycle or the cycle of the artificial ventilation. Most of them did not respond to an increase of blood pressure produced by i.v. injection of adrenaline or noradrenaline; some showed a weak depression or weak excitation which, in the time course, was untypical for visceral vasoconstrictor neurons. Stimulation of arterial chemoreceptors either did not influence MR neurons or produced only a secondary response owing to contraction of the urinary bladder. Ninety-seven preganglionic MR neurons could be subclassified: MR1 neurons were excited by distension and contraction of the urinary bladder and/or inhibited by distension and contraction of the colon (n = 61), a few were excited from both organs (n = 4); MR2 neurons were inhibited by distension and contraction of the urinary bladder and/or excited by distension and contraction of the colon (n = 32). Ninety-five out of 121 MR neurons (78.5%) were excited, 10 (8%) were inhibited and 16 (13%) not influenced by mechanical shearing stimuli applied to the mucosal skin of the anus. Most neurons which were excited by anal stimulation were not influenced by mechanical stimulation of the perianal (perigenital) skin. Twenty-eight per cent of the MR neurons (18 out of 64) were excited or inhibited upon stimulation of perianal skin. A few of these (7 out of 64 neurons, 11%) were involved in reflex responses which were different from those elicited from anal skin. At present no further consistent subclassification of MR1 and MR2 neurons appears possible on the basis of the excitatory and inhibitory anal and perianal reflexes. The results show that the population of visceral preganglionic neurons, which are probably involved in regulation of motility of colon and pelvic organs, is not homogeneous and probably consists of several subpopulations.

The components of the hypogastric nerve in male and female guinea pigs

A quantitative study has been made of the neural components of the hypogastric nerves of male and female guinea pigs using retrograde transport of horseradish peroxidase (HRP) to identify the population of neurones projecting in the nerve trunk, and electronmicroscopic analysis of the myelinated and unmyelinated axons present. Application of HRP to the transected axons of the hypogastric nerve labelled the cell bodies of sensory neurones in lumbar and sacral dorsal root ganglia, preganglionic neurones in the lumbar and sacral spinal cord, and postganglionic neurones in the inferior mesenteric ganglion and in the lumbar paravertebral chain; some ganglion cells of the pelvic plexus were also labelled. The number and distribution of each type of neurone with axons in the hypogastric nerve differed between the sexes: in particular, about twice as many preganglionic axons were present in the male as in the female.

Degeneration patterns of postganglionic fibers following sympathectomy

In cats the time course of degeneration following lumbal sympathectomy was studied in the ramus communicans griseus (rcg) and in the nerves to the triceps surae muscle using light and electron microscopic methods. The left lumbar sympathetic trunk including its rami communicantes was removed from L2 to S1 using a lateral approach. The animals were sacrificed between 2 and 48 days after the sympathectomy. Tissue samples were taken (a) one cm proximal to the entrance of the rcg into the spinal nerve, and (b) one cm proximal to the entrance of the nerve into the muscle belly. In the rcg signs of degeneration can already be recognized in the myelinated as well as in the unmyelinated axons 48 h after sympathectomy. The degenerative processes in the axons reach their peak activity at about 4 days p.o. They end a week later. Signs of the reactions of the Schwann cells and of the endoneural cells can first be seen 2 days p.o. They are most pronounced around the 8th day p.o., and last at least up to the third week. Thereafter the cicatrization processes settled to a rather steady state (total observation period 7 weeks). In the muscle nerves the first signs of an axonal degeneration of the sympathetic fibers can be recognized 4 days after surgery. The signs of axonal degeneration are most striking about 8 days p.o. They have more or less disappeared another week later. The reactions of the Schwann cells also start on the fourth day but outlast the degenerative processes by some 8 days. Thus the degenerative and reactive processes in the rcg precede those in the muscle nerves by 2 days early after surgery and by 6 days 3 weeks later. Seven weeks after surgery, fragments of folded basement lamella and Remak bundles with condensed cytoplasm and numerous flat processes are persisting signs of the degeneration. In addition to the differences in time course between the proximal and the distal site of observation, it was also noted that both the axonal degeneration and the reactions of the Schwann cells are more pronounced in the rcg than in the muscle nerve. For example there was abundant mitotic activity in the central endoneural and Schwann cells whereas we could not detect such activity in the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of hindlimb vasomotor neurones in the lumbar spinal cord of the guinea pig

After retrograde labelling with horseradish peroxidase, sympathetic preganglionic neurones projecting to paravertebral ganglion cells with destinations primarily in the hindlimb were found to lie laterally in the intermediate region of the lumbar spinal cord. The majority of the labelled cell bodies were located near the edge of the grey matter or lateral to it within the white matter. In the most caudal segments (L3-L4) neurons extended right across the lateral funiculi. This distribution of neurones with predominantly vasoconstrictor functions differs markedly from that observed after labelling preganglionic fibres that project in the hypogastric nerve to the pelvic viscera.