Distribution and origin of peptide-containing nerve fibers in the celiac superior mesenteric ganglion of the guinea-pig

The origin of the peptidergic nerve fibers and terminals in the celiac superior mesenteric ganglion of the guinea-pig was studied. The distribution of immunoreactivity to enkephalin, substance P, calcitonin gene-related peptide, cholecystokinin, vasoactive intestinal polypeptide/peptide histidine isoleucine, bombesin and dynorphin was analysed in intact animals and in animals subjected to various denervation and ligation procedures. The present results show that each of the connected nerve trunks carries peptidergic pathways and contributes to the peptidergic networks in the celiac superior mesenteric ganglion. Thus, the thoracic splanchnic nerves contain enkephalin-, substance P- and calcitonin gene-related peptide-immunoreactivity of which substance P and calcitonin gene-related peptide coexist in the same nerve fibers. In addition, cholecystokinin-, vasoactive intestinal polypeptide/peptide histidine isoleucine- and dynorphin-immunoreactivity is present in some fibers. All of these immunoreactivities are present in sensory neurons except enkephalin which probably originates in the spinal cord. The mesenteric nerves carry enkephalin-, calcitonin gene-related peptide-, cholecystokinin-, vasoactive intestinal polypeptide/peptide histidine isoleucine-, bombesin- and dynorphin-immunoreactive fibers from the intestine and are the main source for cholecystokinin, vasoactive intestinal polypeptide/peptide histidine isoleucine, bombesin and dynorphin fibers. Double-staining experiments indicate that many of these peptides are synthesized in the same enteric neurons. Also the intermesenteric nerve contains peptide-immunoreactive fibers to the celiac superior mesenteric ganglion from different sources, probably including the distal colon as well as dorsal root ganglia and spinal cord at lower thoracic and lumbar levels. The results are discussed in relation to earlier morphological and physiological studies supporting the view of a role of the celiac superior mesenteric ganglion in local reflex mechanisms involved in regulation of gastrointestinal functions.     

Electrophysiological and morphological diversity of mouse sympathetic neurons

We have used multiple-labeling immunohistochemistry, intracellular dye-filling, and intracellular microelectrode recordings to characterize the morphological and electrical properties of sympathetic neurons in the superior cervical, thoracic, and celiac ganglia of mice. Neurochemical and morphological characteristics of neurons varied between ganglia. Thoracic sympathetic ganglia contained three main populations of neurons based on differential patterns of expression of immunoreactivity to tyrosine hydroxylase, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In the celiac ganglion, nearly all neurons contained immunoreactivity to both tyrosine hydroxylase and NPY. Both the overall size of the dendritic tree and the number of primary dendrites were greater in neurons from the thoracic and celiac ganglia compared with those from the superior cervical ganglion. The electrophysiological properties of sympathetic neurons depended more on their ganglion of origin rather than their probable targets. All neurons in the superior cervical ganglion had phasic firing properties and large afterhyperpolarizations (AHPs). In addition, 34% of these neurons displayed an afterdepolarization preceding the AHP. Superior cervical ganglion neurons had prominent I(M), I(A), and I(H) currents and a linear current-voltage relationship between -60 and -110 mV. Neurons from the thoracic ganglia had significantly smaller action potentials, AHPs, and apparent cell capacitance compared with superior cervical ganglion neurons, and only 18% showed an afterdepolarization. All neurons in superior cervical ganglia and most neurons in celiac ganglia received at least one strong preganglionic input. Nearly one-half the neurons in the celiac ganglion had tonic firing properties, and another 15% had firing properties intermediate between those of tonic and phasic neurons. Most celiac neurons showed significant inward rectification below -90 mV. They also expressed I(A), but with slower inactivation kinetics than that of superior cervical or thoracic neurons. Both phasic and tonic celiac ganglion neurons received synaptic inputs via the celiac nerves in addition to strong inputs via the splanchnic nerves. Multivariate statistical analysis revealed that the properties of the action potential, the AHP, and the apparent cell capacitance together were sufficient to correctly classify 80% of neurons according to their ganglion of origin. These results indicate that there is considerable heterogeneity in the morphological, neurochemical, and electrical properties of sympathetic neurons in mice. Although the morphological and neurochemical characteristics of the neurons are likely to be related to their peripheral projections, the expression of particular electrophysiological traits seems to be more closely related to the ganglia within which the neurons occur.     

肾脏的交感神经支配

采用大体解剖学方法和肾内注射HRP逆行标记神经元的方法,研究了猫肾脏的交感神经支配。发现了下述的待点。1.猫左、右侧腹腔神经节相互融合,呈半环状包绕在肠系膜上(前)动脉的起始处,于其融合部,各发出左、右肾支。肠系膜上神经节与右侧腹腔神经节融合。2.肾交感神经节后神经元,分别位于腹腔神轻节,同侧主动脉肾神经节和T_(12)～L~4节段的交感干神经节内,並具有局部定位分布的关系。3.肾交感神经节后纤维主要来自腹腔神经节(82.08％),其次是主动脉肾神经节(12.76％),交感干神经节最少(5.16％)。4.肾交感神经节后神经元,多呈圆形或椭圆形,交感干神经节中有少量呈梭形。5.支配肾周腹膜的交感神经节后神经元与肾交感神经节后神经元存在部位、数量和在各种神经节内分布形式均不相同。     

Can intestinal innervation be preserved in pancreatoduodenectomy for cancer? Results of an anatomical study

Twenty dissections were carried out, in all of which the splanchnic nerves, celiac plexuses, capital pancreatic plexus and superior mesenteric plexus were identified and traced. The capital pancreatic plexus was formed from two bundles, the first taking its origin from the right celiac plexus, the second from the superior mesenteric plexus. These two bundles joined together just behind the head of the pancreas. Two preganglionic bundles, a ganglion and two postganglionic bundles composed the superior mesenteric plexus. Postganglionic bundles received fibers from both right and left celiac plexuses. In small cancers a thin layer of nervous tissue around the superior mesenteric artery might be spared in order to avoid diarrhea from intestinal denervation. This study has provided anatomical evidence that a part of the mesenteric plexus, which receives fibers from both left and right celiac plexuses, maintains a sufficient intestinal innervation.     

Constitution of the greater splanchnic nerve in the rat

The greater splanchnic nerve originating from the sympathetic ganglia between the 10th and 12th ribs on the dorsal thoracic wall passes through the diaphragm between its medial and lateral erura, to form the celiac plexus around the celiac trunk and superior mesenteric artery in the abdominal cavity. The nerve consists of about 10,000 of nerve fibers and of 25,000 of ganglion cells in its whole length of 2.5 cm; nerve fibers can be divided into myelinated fibers, accounting for less than 6% of total numbers, and unmyelinated fibers, which amount to more 90%. Special attention was not paid to the numerous ganglion cells in terms of their shapes, sizes, and cell organelles except for a small number of binucleate cells. However, the nerve contains remarkable synapses that connect between axon showing flat, elliptical, and cored vesicles and dendrite, between another type of axon having elliptical and cored vesicles and dendrite, and even between dendrite and cell body, in which synaptic vesicles are small spherical and elliptical. These facts can suggest that the greater splanchnic nerve contains more complex structure than has been hitherto described.     

Synaptology and sources of vasoactive intestinal polypeptide and substance p containing axons of the cat celiac ganglion. An experimental electron microscopic immunohistochemical study

We have examined the possible origin of vasoactive intestinal polypeptide (VIP) and substance P-containing axons and the synapses formed by these axons in the celiac ganglion of the cat, by means of ultrastructural immunohistochemistry combined with various surgical lesions.Axons containing VIP as well as those immunopositive for substance P, formed axo-dendritic and axosomatic synapses with principal ganglion cells. After transaction of the superior mesenteric nerve numerous degenerated axonal profiles could be found in the celiac ganglion. Some of these contained VIP immunoreactivity. By contrast in alternate sections stained with substance P antibody only intact axons were labelled.Bilateral vagotomy resulted in the appearance of degenerating axonal profiles in the celiac ganglion, some of which could be stained with substance P antiserum but not with VIP antiserum. Following removal of dorsal root ganglia (Th₆-Th₁₂) from both sides, a large number of degenerated axons were found, many of which were immunopositive for substance P but not for VIP.We conclude that the peripheral input to the celiac ganglion contains VIP fibers which form synapses with principal ganglion cells. Substance P-containing fibers reach the celiac ganglion via the vagal nerve as well as from the dorsal root ganglia, and they form synapses with the principal ganglion cells. It is proposed that the VIP and the substance P-containing axons are involved in two different peripheral reflex loops.     

Macro- and microstructural organization of the rabbit''s celiac-mesenteric ganglion complex (Oryctolagus cuniculus)

The macro- and microstructures of the rabbit celiac-mesenteric ganglion complex are described in 20 young animals. We found ten celiac ganglia, twenty-seven cranial mesenteric ganglia and eleven celiac-mesenteric ganglia. The celiac ganglia had a rectangular shape in nine cases (90%) and a circular one in one case (10%). The cranial mesenteric ganglia presented triangular (66.7%), rectangular (11.1%), L-shape (18.5%) and semi-lunar (3.7%) arrangements. The celiac-mesenteric ganglia were organized in three patterns: a single left celiac-mesenteric ganglion having a caudal portion (72.7%); celiac-mesenteric ganglia without a caudal portion (18.2%) and a single celiac-mesenteric ganglion with two portions: left and right (9.1%). The microstructure was investigated in nine celiac-mesenteric ganglia. The results showed that the celiac-mesenteric ganglion is actually a ganglion complex constituted of an agglomerate of ganglionic units separated by nerve fibers, capillaries and septa of connective tissue. Using the semi-thin section method we described the cellular organization of the celiac-mesenteric ganglion complex. Inside of each ganglionic unit, there were various cell types: principal ganglion neurons (PGN), glial cells (satellite cells) and SIF cells (small intensely fluorescent cells or small granular cells), which are the cytologic basis for each ganglionic unit of the rabbit's celiac-mesenteric ganglion complex.     

Effect of substance P on colonic mechanoreceptors, motility, and sympathetic neurons

Intracellular recording techniques were used in vitro to analyze the effects of substance P (SP) on synaptic transmission and electrical properties of sympathetic neurons in the inferior mesenteric ganglion (IMG) of the guinea pig. Intraluminal pressure-recording techniques were used to study the effects of SP on colonic motility. Superfusion of the ganglia with SP (10(-7) to 10(-6) M) depolarized the cell soma (2--12 mV) and increased cell input resistance (8--11 M omega). These effects converted synchronous excitatory postsynaptic potentials, in response to electrical stimulation of preganglionic nerves, and asynchronous excitatory postsynaptic potentials, in response to activation of colonic mechanoreceptors, to action potentials. Administration of SP to only the colon increased basal intraluminal pressure and the frequency and amplitude of phasic changes in intraluminal pressure. These changes increased mechanoreceptor synaptic input to neurons in the IMG. We conclude that SP facilitates synaptic transmission along noradrenergic pathways and increases colonic motility.     

猫肠系膜下神经节神经元与肠壁内传入神经元的突触联系

采用神经纤维和突触溃变的光镜和电镜结合方法，探讨肠系膜下神经节与来自肠神经丛内的传入神经元间的突触联系。切断肠系膜下神经节发出的分支，光镜下见节内存在溃变神经纤维；电镜下见有突触溃变，溃变轴突终末的大小多为１μｍ左右，主要含有球形透明囊泡，线粒体多少不等，与肠系膜下神经节神经元的树突或胞体形成轴－树型或轴－体型突触；溃变突触见有三种类型：电子致密型，电子透明型和神经丝型。确切证明了来自肠壁内的传入     

Origin of sympathetic efferent axons in the renal nerves of the cat

The origin of efferent axons in the renal nerves of the cat was examined using retrograde transport of horseradish peroxidase (HRP). Nerves on the surface of the left renal blood vessels were dissected 5-7 horseradish mm proximal to the medial margin of the kidney, transected and the central cut ends exposed to HRP. Labeled neurons were typically identified in three locations: (1) centrally along the renal nerve, (2) in the superior mesenteric ganglion, and (3) in the ipsilateral sympathetic chain ganglia (T12-L3). HRP was not detected in preganglionic neurons in the thoracolumbar spinal cord. Labeled cells ranged in size from 15 to 50 micrometers, with those in the renal nerve at the smaller end of the spectrum and those in the superior mesenteric ganglion at the larger end. In the superior mesenteric ganglion labeled cells were typically localized to a small region in the caudal pole of the ganglion around the origin of the renal nerve. The results show that the sympathetic efferent innervation of the kidney is derived from both paravertebral and prevertebral ganglia. In the latter (superior mesenteric ganglion), renal efferent neurons exhibited a topographic distribution.     

腹腔-肠系膜上神经节内腹部内脏器官的代表区

目的 探讨支配腹部内脏器官的交感节后神经元在腹腔－肠系膜上神经节内的代表区。方法 用ＨＲＰ逆行标记法，显微镜描图仪做连续切片描图记录，计数标记细胞的面数密度，并经统计学处理。结果 猫脾、胰、肾、十二指肠和空间肠交感节后神经元在腹腔－肠系膜上神经节内具有各自的集中分布区和分散分布区，亦即各自的局部定位区。支配脾的交感节后神经元集中区位于该节的左侧上部，支配胰的交感节后神经元集中区位于该节两侧的上中后     

Receptor binding sites for cholecystokinin, galanin, somatostatin, substance P and vasoactive intestinal polypeptide in sympathetic ganglia.

Sympathetic ganglia are innervated by neuropeptide-containing fibers originating from pre- and postganglionic sympathetic neurons, dorsal root ganglion neurons, and in some cases, myenteric neurons. In the present report receptor autoradiography was used to determine whether sympathetic ganglia express receptor binding sites for several of these neuropeptides including bombesin, calcitonin gene-related peptide-alpha, cholecystokinin, galanin, neurokinin A, somatostatin, substance P, and vasoactive intestinal polypeptide. The sympathetic ganglia examined included the rat and rabbit superior cervical ganglia and the rabbit superior mesenteric ganglion. High levels of receptor binding sites for cholecystokinin, galanin, somatostatin, substance P, and vasoactive intestinal polypeptide were observed in all sympathetic ganglia examined, although only discrete neuronal populations within each ganglion appeared to express receptor binding sites for any particular neuropeptide. These data suggest that discrete populations of postganglionic sympathetic neurons may be regulated by neuropeptides released from pre- and postganglionic sympathetic neurons, dorsal root ganglion neurons, and myenteric neurons.     

A study of peripheral input to and its control by post-ganglionic neurones of the inferior mesenteric ganglion.

1. Intracellular recordings were made, in vitro, from neurones of guinea-pig inferior mesenteric ganglia (IMG) attached, via the lumbar colonic nerves, to segments of distal colon. 2. 'Spontaneous' synaptic input from colonic afferent fibres was observed in 79% of the neurones tested. In any given preparation, the level and pattern of this synaptic input to different neurones varied considerably. 3. Superfusion of colonic segments with drugs (papaverine, isoprenaline, and adenosine triphosphate) which reduce colonic motility decreased colonic afferent input to IMG neurones. 4. Superfusion of colonic segments with acetylcholine or stimulation of pelvic nerves, both of which increase colonic motility, increased colonic afferent input to IMG neurones. 5. Superfusion of colonic segments with either atropine or tubocurarine reduced the level of 'spontaneous', colonic afferent input. However, distension of these relaxed segments increased the colonic afferent input. 6. Repetitive stimulation of preganglionic inputs to the IMG inhibited afferent input from drug relaxed segments of colon that were moderately distended by the injection of air into the lumen. Superfusion of the colon with phentolamine blocked this inhibition. 7. The results of this study suggest that IMG neurones receive afferent input from mechanoreceptors located in the distal colon and that the mechanosensitivity of this afferent pathway is in part controlled by efferent noradrenergic neurones of the IMG. The IMG-colon neural circuitry can therefore be considered to form a feed-back control system which participates in the regulation of colonic motility.     

Regeneration of the abdominal postganglionic sympathetic system

The abdominal sympathetic system is unique in that its postganglionic axons do not directly innervate gastrointestinal smooth muscle layers but exert their effects through the enteric nervous system. The purpose of the present study was to examine the ability of neurons in abdominal sympathetic ganglia to regenerate after axonal injury and to determine whether reinnervation occurs after the removal of ganglia. Axons from the celiac ganglion and superior mesenteric ganglion complex (CG/SMG) of adult female BALB/c mice were crushed or the ganglion complex was removed. Immunohistochemistry, western blotting and in situ hybridization were performed to examine the changes in tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP-43) in the duodenum and the sympathetic ganglia. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and injection of the tracer dye, fluorogold were also performed. After crushing the nerve, TH in the duodenum disappeared and reappeared within 90 days. In the CG/SMG, TH decreased and increased as in the duodenum, while the expression of GAP-43 changed in the opposite direction. Nerve crushing caused cell death to limited number of neurons in the CG/SMG. The removal of CG/SMG decreased TH in the duodenum and stomach, but 180 days later TH-positive innervation was recovered. Fluorogold injection revealed that the inferior mesenteric ganglion reinnervated the stomach. Therefore, postganglionic sympathetic nerves in the abdomen are able to regenerate and reinnervation occurs even after the removal of sympathetic ganglia.     

Identifiable neurons controlling penile eversion in the leech.

1. This paper describes the neuroanatomy and electrophysiology of motor neurons causing penile eversion in the leech. 2. The male organ is innervated by ganglia 5 and 6 of the 34 ganglia in the leech brain through special sex nerves deriving from anterior roots. These sex ganglia have at least 200 more neurons than the other midbody ganglia. Many of the extra neurons are involved in reproductive behavior. 3. Two pairs of motor neurons on the ventral side of ganglion 6, named rostral and lateral neurons, are the only ones that elicit full penile eversion. Evidence that the lateral and rostral neurons are, in fact, motor neurons comes from HRP and electrophysiological studies. HRP injections reveal that each neuron's single primary axon grows into the sex nerve. Electrophysiological evidence is twofold: a) action potentials of lateral and rostral cells can still contract the genitalia after the neurons are deafferented from chemical synaptic input in the ganglion by high Mg2+, b) their action potentials are followed by junction potentials in male organ muscle fibers.     

猫空回肠交感节后神经元和副交感节前神经元的局部定位

本文应用ＨＲＰ逆行标记法研究猫空回肠的植物神经支配，发现猫空回肠交感节后神经纤维来自腹腔节和肠系膜前节以及双侧Ｔ９～Ｌ５交感于神经节，但大多数来自椎前节。交感节神经元大多数呈簇状集中分布在右侧腹腔节的前下部和肠系膜前节，而在左侧腹腔节和右侧腹腔节后上部仅有少数散在分布的标记细胞，具有明显的局部定位分布的特征。猫空回肠的交感节后神经元在双侧交感于神经节具有基本相同的分布范围，即Ｔ９～Ｌ５节段。其集中分布节段是Ｔ１１～Ｌ３，符合“既分散又集中的分布模式”。腹腔节和肠系膜前节内的标记细胞呈椭圆形、圆形或不规则形。交感干神经节内的标记细胞呈椭圆形和梭形。猫空回肠的副交感书前神经元主要分布在双侧迷走神经前核的闩以上４ｍｍ到闩以下２ｍｍ的范围内．但多数分布在此核的背外侧部靠近闩的水平上，细胞呈椭圆形。     

Excitatory input from the distal colon to the inferior mesenteric ganglion in the guinea-pig

1. Intracellular recordings were obtained from ganglion cells in the guinea-pig inferior mesenteric ganglion (IMG) with a segment of the distal colon attached to the lumbar colonic nerves.2. Continuous electrical activity consisting of excitatory synaptic potentials and action potentials was recorded from ganglion cells in all regions of the IMG.3. The ;spontaneous' synaptic potentials were indistinguishable from those elicited by submaximal stimulation of any of the nerve trunks connected to the IMG.4. The excitatory activity was irreversibly abolished when the lumbar colonic nerves were cut and reversibly abolished when tetrodotoxin (5 x 10(-7) g/ml.) was added to the colon side of a two-compartment organ bath.5. Addition of dihydro-beta-erythroidine (5 x 10(-6) g/ml.) to the ganglion side of the bath abolished the synaptic activity of colonic origin and the synaptic responses to stimulation of any of the nerve trunks connected to the IMG.6. Addition of dihydro-beta-erythroidine (1 x 10(-5) g/ml.) to the colon side of the bath markedly depressed the synaptic input of colonic origin but had no effect on synaptic responses produced by preganglionic nerve stimulation.7. Distension of the colonic segment and the application of 5-HT (1 x 10(-5) g/ml.) to the mucosal surface of the colon increased the frequency of synaptic input.8. The synaptic input from the colon was transiently blocked following repetitive stimulation of any of the nerve trunks connected to the IMG. The discharge of miniature synaptic potentials was unaffected.9. Addition of noradrenaline (1 x 10(-7) to 1 x 10(-6) g/ml.) to the colon side of the bath reduced, and in some cases completely abolished, the synaptic input to the IMG. Phentolamine (1 x 10(-6) g/ml.), when added to the colon side of the bath, blocked the effect of noradrenaline and the transient inhibition following repetitive nerve stimulation.10. Addition of noradrenaline (1 x 10(-4) g/ml.) to the ganglion side of the bath reduced but never abolished the amplitude of the synaptic potentials of colonic origin.11. It was concluded that in the guinea-pig, the IMG is involved in a peripheral reflex whose afferent limit of this reflex consists of the axons of cholinergic neurones within the wall of the colon. Many of these neurones are driven either directly or indirectly by cholinergic synapses. The efferent noradrenergic neurones of the IMG function as a group of inhibitory neurones which depress the activity of the excitatory neurones of the colon which are driving them.     

成人腹腔神经节的形态观察

目的观察成人腹腔神经节的位置及形态结构,为揭示其功能提供形态学资料。方法取死后24～48h的18具成人尸体的18个腹腔神经节,经石蜡包埋切片,苏木精-伊红、Nissl及Masson染色,观察该神经节的细胞构筑。结果腹腔神经节多位于从腹主动脉发出的腹腔干的两侧,其形态不规则,但轮廓清楚,质地坚实,易与其它结构区别;镜下观察到,该神经节被单层扁平细胞构成的被膜包裹,节内的神经元为多极形,尼氏体丰富,核大圆亮;卫星细胞的形态结构也完整;在节内的细胞间质中含有丰富的胶原纤维。神经节的所有细胞均无溶解现象。结论若能在成年病人死亡后24～48h及时固定,既可确保其腹腔神经节的形态结构完整,又可为神经生物学的教学和科研制作成良好的组织切片标本。     

Origin of peptide-containing fibers in the inferior mesenteric ganglion of the guinea-pig: Immunohistochemical studies with antisera to substance P,enkephalin, vasoactive intestinal polypeptide,cholecystokinin and bombesin

After different denervation procedures the guinea-pig inferior mesenteric ganglion was analysed by immunohistochemistry using antisera to substance P, enkephalin, vasoactive intestinal polypeptide, cholecystokinin and bombesin. The results demonstrate that each of the nerve trunks connected to the ganglion carries specific peptidergic pathways. Thus, the lumbar splachnic nerves contain substance P-immunoreactive primary afferent neurons, which to a large extent traverse the ganglion, and enkephalin-immunoreactive preganglionic neurons; the colonie nerves carry vasoactive intestinal polypeptide-, cholecystokinin- and bombesin-immunoreactive fibers from the distal colon to the ganglion; the hypogastric nerves contain vasoactive intestinal polypeptide-positive fibers from the pelvic plexus; and the intermesenteric nerve contains vasoactive intestinal polypeptide, cholecystokinin, substance P and enkephalin from divergent sources. By studying accumulations of peptides in ligated lumbar splanchnic, intermesenteric, hypogastric and colonic nerves the existence of these major peptidergic pathways was confirmed and evidence was obtained for additional, not so prominent, peptidergic projections. The results are discussed in view of earlier morphological and physiological studies.     

An electrophysiological study of inferior mesenteric ganglion of the dog

Intracellular recordings were made in vitro from 430 sympathetic neurons in the inferior mesenteric ganglion (IMG) of the dog. Ganglion cells had resting membrane potentials between -35 and -70 mV; input resistance (Rin) was approximately 22 M omega. Cell rheobase to depolarizing current was 0.3 nA, and the action potential elicited was 80-100 mV in amplitude followed by an afterhyperpolarization of up to 15 mV in size, which decayed to the resting membrane potential over a range of 50-500 ms. Neurons were classified as either phasic (188 of 280) or tonic (92 of 280) firing cells, depending on their discharge pattern in response to depolarizing current. Two hundred eight of 430 neurons showed continuous electrical activity in the form of spontaneous excitatory postsynaptic potentials, 2-5 mV in amplitude. Continuous electrical activity was unaffected by tetrodotoxin (3 X 10(-6) M) but abolished by hexamethonium (10(-4) M). A small number of cells (21 of 430) adopted a repetitive firing pattern not associated with injury discharge. These cells may have been pacemaking neurons. Stimulation of peripheral and central nerves resulted in multiple synaptic input to ganglion cells. There was marked convergence of excitatory fibers to any one cell. Evoked synaptic potentials were abolished by hexamethonium (10(-4) M). Synaptic input from peripheral and central nerves could not be correlated with location of postganglionic neurons in the IMG. The possibility of neuronal intercommunication and dissemination of central and peripheral commands is discussed.