Coeliac-superior Mesenteric Ganglion Research Articles

Neural Activity Between Ovaries and the Prevertebral Celiac–Superior Mesenteric Ganglia Varies During the Estrous Cycle of the Rat

The ovaries' innervation arrives via the superior ovarian nerve, which originates from the celiac ganglion. Using True Blue as an antidromic marker, the present study analyzed the changes in the anatomical relation between each ovary and the prevertebral celiac-superior mesenteric ganglia during the estrous cycle. The number of labeled neurons increased from the day of diestrus 1 to the day of proestrus. The largest number of labeled cells was observed when tracer was injected into the left ovary on proestrus. The number of labeled cells was significantly higher when the tracer was injected into the left ovary on proestrus than when it was done in the right one. When tracer was injected into the left ovary, the average labeled area of cells increased significantly from diestrus 1 to proestrus, and declined at estrus. In contrast, when True Blue was injected into the right ovary, the average labeled area was similar in diestrus 1 and diestrus 2, and the values increased in proestrus and estrus. The results indicate an apparent asymmetry in the activity of neural connections between ovaries and the prevertebral celiac-superior mesenteric ganglia, and that the number of active neurons of these connections varies during the estrous cycle.

Leptin receptors, NPY, and tyrosine hydroxylase in autonomic neurons supplying fat depots in a pig

The goal of this study was to determine the immunohistochemical characteristics of peripheral adrenergic OBR-immunoreactive (OBR-IR) neurons innervating adipose tissue in a pig. The retrograde tracer, Fast Blue (FB), was injected into either the subcutaneous, perirenal, or mesentery fat tissue depots of three male and three female pigs each with approximately 50 kg body weight. Sections containing FB + neurons were stained for OBR, tyrosine hydroxylase (TH) or neuropeptide Y (NPY) using a double labeling immunofluorescence method. OBR, TH, and NPY immunoreactivities were present in the thoracic (T) and lumbar (L) ganglia of the sympathetic chain, as well as in the coeliac superior mesenteric ganglion (CSMG), inferior mesenteric ganglion (IMG), intermesenteric ganglia (adrenal—ADG, aorticorenal—ARG, and ovarian—OG or testicular—TG ganglion). These results indicate that, in addition to neuroendocrine functions, leptin may affect peripheral tissues by acting on receptors located in sympathetic ganglion neurons.

Effect of splanchnectomy on jejunal motility and fos expression in brain stem after intestinal anaphylaxis in rat.

This study was to determine whether alterations in jejunal motility observed after antigen challenge of sensitized rats occurred after extirpation of the celiac-superior mesenteric ganglia. Hooded-Lister rats were prepared with an intact or extirpated celiac-superior mesenteric ganglion, an isolated Thiry-Vella loop of ileum for instillation of antigen, and jejunal electrodes for myoelectric recording. Animals were sensitized by injection of 10 microg egg albumin (EA, ip), and specific anti-EA IgE titers were determined to be >1:64. In both control and splanchnectomized rats, normal fasting migrating myoelectric complexes (MMC) were observed before challenge with EA. MMCs were disrupted, and diarrhea was observed immediately after EA challenge of control but not splanchnectomized animals. Brain stems were removed and processed for Fos immunoreactivity. The absence of perivascular neuropeptide Y immunoreactivity in the submucosa was used to confirm the success of splanchnectomy. The number of Fos-immunoreactive neuronal nuclei was significantly reduced in the brain stem after splanchnectomy. Thus the mesenteric sympathetic ganglia are an integral part of the extramural neuronal pathways required for altered motility in this model of intestinal anaphylaxis.

Identification of intestinofugal neurons projecting to the coeliac and superior mesenteric ganglia in the rat

Intestinofugal neurons are parts of the afferent limbs of inhibitory intestino-intestinal reflexes. These neurons have been mapped in guinea-pigs, where they have a gradient of increasing frequency of occurrence from oral to anal, but not in other species. In the present work in the rat, a species that is more amenable to physiological study than the guinea-pig, we have used retrograde tracing to map the distribution of the cell bodies of intestinofugal neurons projecting to the coeliac–superior mesenteric ganglion complex. Labelled nerve cells were found in the myenteric, but not the submucosal plexus. They were mono-axonal neurons, most with Dogiel type I morphology, and were immunoreactive for choline acetyltransferase, implying that they are cholinergic, which is consistent with functional studies. The cells increased in number per unit area from the stomach, through the small intestine, to the caecum. The results are consistent with physiological studies that reveal distal to proximal inhibitory reflexes that are more potent from distal compared to proximal sites.

Diurnal rhythms in norepinephrine and acetylcholine synthesis of sympathetic ganglia, heart and adrenals of aging rats: Effect of melatonin

The effect of aging and melatonin on 24-h rhythms in tyrosine hydroxylase activity and 3 H−choline conversion into 3 H−acetylcholine were examined in cervical, stellate, coeliac-mesenteric and hypogastric ganglia, and in the adrenal medulla and heart of rats. Young (50 days old) and old (18 months old) rats received evening injections of 10 or 100 μg of melatonin or its vehicle for 17 days. In superior cervical, stellate and coeliac-superior mesenteric ganglia, as well as in the adrenal medulla, norepinephrine and acetylcholine synthesis attained maximal values at night (ca. 2030–0100 h). In the hypogastric ganglion, maximal tyrosine hydroxylase activity occurred at night at both studied ages. Two maxima in acetylcholine synthesis were detected in hypogastric ganglion of young rats (ca. 1300 h and 0100 h, respectively) while in old rats a single maximum was observed at noon. Cardiac tyrosine hydroxylase activity peaked at early night (ca. 2200–2300 h) while cardiac acetylcholine synthesis peaked at the afternoon (ca. 1700–1900 h). Old rats exhibited a significant decrease of rhythm amplitude and increase of mean values in tyrosine hydroxylase activity in autonomic ganglia and adrenal medulla, and abolition of tyrosine hydroxylase rhythm in the heart. Twenty-four hour rhythmicity in acetylcholine synthesis was impaired or abolished in aged rats. Treatment of old rats with 10 or 100 μg melatonin generally augmented amplitude of rhythms and reinduced the nocturnal peak of acetylcholine synthesis in the hypogastric ganglion. Only the high melatonin dose significantly augmented rhythm amplitude of tyrosine hydroxylase activity (superior cervical and coeliac-superior mesenteric ganglia) and acetylcholine synthesis (superior cervical, stellate and coeliac-superior mesenteric ganglia) in young rats. The results indicate that the activity of the central oscillator, driven to the organs in part via the autonomic nervous system, deteriorates significantly with aging and that melatonin may restore partially such a deterioration.

Denervation, but not decentralization, reduces nerve growth factor content of the mesenteric artery.

In the present study we applied an improved nerve growth factor (NGF) extraction method to examine the effects of denervation and sympathetic decentralization on NGF levels in vascular tissue. Adult male Wistar Kyoto rats underwent mesenteric arterial denervation or splanchnic nerve transection. Four days after operation, animals were killed, and the mesenteric artery and coeliac-superior mesenteric ganglia were removed. The arterial adventitia was stripped from the media to measure NGF levels in nerve and smooth muscle separately. A high concentration of NGF was detected in the normal artery, 90% of which was in the adventitial layer. Surgical denervation significantly reduced the NGF levels in the artery and ganglia by 78 and 71%, respectively. However, within the artery the level of NGF was reduced in the adventitia but not in the media. Thus, the large reduction of NGF content resulted from the loss of nerve plexus from the artery. In contrast, decentralization did not alter the NGF content in the artery, in either the adventitia or media. Our results are in marked contrast to previous studies reporting elevated levels of NGF following denervation. This discrepancy is explained by the ability of our new procedure to extract much greater amounts of NGF from the tissue.

Localization of choline acetyltransferase in rat peripheral sympathetic neurons and its coexistence with nitric oxide synthase and neuropeptides.

Indirect immunofluorescence methods using a mouse monoclonal antibody raised to rat choline acetyltransferase (ChAT) revealed dense networks of ChAT-immunoreactive fibers in the superior cervical ganglion, the stellate ganglion, and the celiac superior mesenteric ganglion of the rat. Numerous and single ChAT-immunoreactive cell bodies were observed in the stellate and superior cervical ganglia, respectively. The majority of ChAT-immunoreactive fibers in the stellate and superior cervical ganglia were nitric oxide synthase (NOS) positive. Some ChAT-immunoreactive fibers contained enkephalin-like immunoreactivity. Virtually all ChAT-positive cell bodies in the stellate ganglion were vasoactive intestinal polypeptide (VIP)-positive, and some were calcitonin gene-related peptide (CGRP)-positive. After transection of the cervical sympathetic trunk almost all ChAT- and NOS-positive fibers and most enkephalin- and CGRP-positive fibers disappeared in the superior cervical ganglion. The results suggest that most preganglionic fibers are cholinergic and that the majority of these in addition can release nitric oxide, some enkephalin, and a few CGRP. Acetylcholine, VIP, and CGRP are coexisting messenger molecules in some postganglionic sympathetic neurons.

Whole-cell and perforated patch recordings of four distinct K + currents in acutely dispersed coeliac-superior mesenteric ganglia neurons of adult rats

Properties and modulation of outward membrane currents in sympathetic neurons acutely dispersed from coeliac-superior mesenteric ganglia (C-SMG) of adult rats were examined using both the whole-cell variant of the patch-clamp technique and the perforated patch approach. Under voltage-clamp, four distinct outward currents were observed: a transient outward current (I A), a voltage-dependent sustained outward current consisting of a Ca 2+-dependent component (I KCa and a Ca 2+-insensitive component (I Kv), and a muscarinic agonist-sensitive outward current (I M). I A was isolated by digital subtraction, and characterized by very rapid activation at potentials more positive than −60 mV and by fast and complete voltage-dependent inactivation. Half inactivation potential (V h) and slope factor (K) were −76 mV and 8.3 mV, respectively. I A was not affected by removal of external Ca 2+, 1 mM tetraethyl ammonium ions, muscarinic agonists, or 8-bromo-cyclic AMP, but was suppressed by 4-aminopyridine (1 mM). Depolarizing pulses from of a holding potential of −50 or −60 mV to potentials more positive than −25 mV concomitantly activated two, independent sustained outward currents which decay slowly; one exhibited voltage-dependent activation similar to the delayed rectifier current (I KV) and the other being triggered by Ca 2+ influx into the cell (I KCa). The addition of tetraethylammonium ions (1 mM) strongly reduced the amplitude of the sustained outward currents. I M was characterized as a noninactivating time- and voltage-dependent outward current which activated at membrane potentials more positive than −60 mV and slowly turned off when the membrane was hyperpolarized back to −60 mV, and was suppressed by muscarinic agonists. The rank order of potency of the agonists tested was: oxotremorine > muscarine > bethanechol.

Nitric oxide synthase-containing neurons in rat parasympathetic, sympathetic and sensory ganglia: a comparative study

In rats, the distribution of nerve structures staining for NADPH-diaphorase, and showing immunoreactivities for nitric oxide synthase (NOS), tyrosine hydroxylase and various neuropeptides was studied in sensory ganglia (dorsal root, nodose and trigeminal ganglia), in sympathetic ganglia (superior cervical, stellate, coeliac-superior and inferior mesenteric ganglia), parasympathetic ganglia (sphenopalatine, submandibular, sublingual and otic ganglia), and in the mixed parasympathetic/sympathetic ganglia (major pelvic ganglia). The coincidence of neuronal cell bodies with strong NOS-immunoreactivity and strong NADPH diaphorase reactivity was almost total. The relative proportions of NOS-immunoreactive nerve cell bodies were largest in parasympathetic ganglia and major pelvic ganglia followed by sensory ganglia. In sympathetic ganglia no NOS-immunoreactive neuronal cell bodies could be detected. In parasympathetic and major pelvic ganglia, there was a very significant neuronal co-localization of immunoreactivities for NOS and vasoactive intestinal polypeptide (VIP). This was almost total in major pelvic ganglia, in which NOS-/VIP-immunoreactive nerve cell bodies were separate from sympathetic (tyrosine hydroxylase-/neuropeptide Y-immunoreactive), suggesting that NOS-/VIP-immuno-reactive neurons might also be parasympathetic.

Origins of nerve fibers containing nitric oxide synthase in the rat celiac-superior mesenteric ganglion.

The origin of nitric oxide synthase-containing nerve fibers in rat celiac-superior mesenteric ganglion was examined using retrograde tracing techniques combined with the immunofluorescence method. Fluoro-Gold was injected into the celiac-superior mesenteric ganglion. Neuronal cell bodies retrogradely labeled with Fluoro-Gold in the thoracic spinal cord, the dorsal root ganglia at the thoracic level, the nodose ganglion, and the intestine from the duodenum to the proximal colon were examined for nitric oxide synthase immunoreactivity. About 60% of sympathetic preganglionic neurons in the intermediolateral nucleus projecting to the celiac-superior mesenteric ganglion were immunoreactive for nitric oxide synthase, as were approximately 27% of nodose ganglion neurons and about 65% of dorsal root ganglion neurons projecting to the celiac-superior mesenteric ganglion. Neurons projecting to the celiac-superior mesenteric ganglion were found in the myenteric plexus of the small and large intestine. In the proximal colon, about 23% of such neurons were immunoreactive for nitric oxide synthase. However, in the small intestine, no immunoreactivity was found in these neurons.

5-Hydroxytryptamine-immunoreactive nerve fibers in the rat and porcine prevertebral sympathetic ganglia: effect of precursor loading and relation to catecholaminergic neurons

Localization of 5-hydroxytryptamine immunoreactivity was studied in the rat coeliac-superior mesenteric ganglion complex and in the porcine superior and inferior mesenteric ganglia by the indirect immunofluorescence technique. In normal rats, only 5-hydroxytryptamine immunoreactive SIF cells were seen in the coeliac-superior mesenteric ganglion complex. In the rats, pretreated with a 5-hydroxytryptamine precursor, l-tryptophan, and with a monoamine oxidase inhibitor, nialamide, a large number of 5-hydroxytryptamine-immunoreactive nerve fiber terminals were detected. In normal porcine superior and inferior mesenteric ganglia, intense 5-hydroxytryptamine immunoreactivity was found in numerous nerve fibers which were located around tyrosine hydroxylase-immunoreactive principal neurons. The origin and function of these fibers are discussed.

Origins of nerve fibers containing nitric oxide synthase in the rat celiac-superior mesenteric ganglion

Origins of nerve fibers containing nitric oxide synthase in the rat celiac-superior mesenteric ganglion

Ultrastructural study on NOS-immunoreactive nerve terminals in the rat coeliac ganglion.

Nerve terminals immunoreactive for nitric oxide synthase (NOS) were studied in the rat coeliac-superior mesenteric ganglion by electron microscopy using a pre-embedding immunostaining method. The immunoreactive material was distributed in the axoplasmic matrix and was not specifically associated with any subcellular organelle. In most NOS-immunoreactive axon terminals numerous small clear vesicles (35-50 nm) were seen, and in some terminals a small number of large granular vesicles (70-120 nm) were intermingled with small clear vesicles. Most NOS-immunoreactive axon terminals formed axodendritic as well as axo-somatic synapses with non-immunoreactive ganglion neurones, and axo-axonic contacts were very scarce. These results suggest that NO may be released at the synaptic sites from the axon terminals and may affect ganglion neurones.

Immunohistochemical demonstration of galanin-, and galanin message-associated peptide-like immunoreactivities in sympathetic ganglia and adrenal gland of the guinea pig.

Using the indirect immunofluorescence method, the distribution of galanin (GAL)- and galanin message-associated peptide (GMAP)-like immunoreactivities (LI) were studied in sympathetic ganglia and the adrenal gland of the guinea pig. A rather dense network of GAL-immunoreactive nerve fibers was found in the inferior mesenteric ganglion (IMG) and in the superior mesenteric pole of the celiac-superior mesenteric ganglion complex (C-SMG). The celiac pole of the C-SMG, the stellate ganglion, and the superior cervical ganglion contained fewer, mostly scattered fibers. SIF-cells in prevertebral and paravertebral ganglia contained GAL-LI, as did the adrenal medullary cells. The GAL fibers in the IMG surrounded mainly principal ganglion cells containing somatostatin-immunoreactivity (SOM-IR), whereas fewer fibers were seen around neuropeptide Y (NPY) cells and cells in which SOM and NPY coexisted. Application of colchicine or vinblastine onto the IMG did not result in the appearance of GAL-IR in the principal ganglion cells. In denervation experiments it was revealed that most of the GAL fibers reach the IMG via the lumbar splanchnic nerves. GAL-IR appears to be colocalized with substance P (SP) in fibers of the IMG, indicating an origin of the GAL-containing fibers in dorsal root ganglia (DRG). This conclusion was supported by the finding in lumbar DRGs of GAL-positive cell bodies that contained SP. The role of GAL in prevertebral ganglia is unclear. It may be suggested that GAL modulates the slow, long-lasting membrane depolarization of the principal ganglion cells caused by SP in the primary afferents related to the IMG. GMAP-LI was detected in SIF cells and adrenal medullary cells in which GMAP-LI parallels the immunoreactivity of GAL. GMAP-LI was not observed in neuronal cell bodies or nerve fibers of the ganglia.

Somatostatin inhibits pancreatic enzyme secretion at a central vagal site.

The mechanisms and site of action of somatostatin-induced inhibition of pancreatic enzyme secretion were investigated using different stimulants of pancreatic secretion acting on different sites in anesthetized rats. Administration of graded doses of somatostatin-14 resulted in a dose-related inhibition of pancreatic protein secretion evoked by 2-deoxy-D-glucose, a central vagal stimulant that acts by stimulating the dorsal vagal nuclei. The lowest effective dose of somatostatin-14 was 1.0 microgram.kg-1 x h-1; maximal effective dose was 25 micrograms.kg-1 x h-1, which resulted in complete inhibition of protein output. Similarly, somatostatin-14 at a dose of 25 micrograms.kg-1 x h-1 also completely inhibited pancreatic protein secretion in response to a physiological concentration of cholecystokinin octapeptide (CCK-8), which acts via a vagal afferent pathway. In contrast, pancreatic protein outputs evoked by bethanechol, which directly stimulates pancreatic muscarinic receptors, or electrical stimulation of the vagal trunk, which activates the vagal efferent pathway, were unaffected by somatostatin-14. In separate studies, we demonstrated that perivagal treatment with the sensory neurotoxin capsaicin impaired pancreatic responses to CCK-8 but had no effect on the inhibitory action of somatostatin-14 on pancreatic secretion evoked by 2-deoxy-D-glucose, ruling out an effect of somatostatin on the vagal afferent pathway. Similarly we also demonstrated that perineural capsaicin treatment of the celiac-superior mesenteric ganglia did not affect the inhibitory action of somatostatin. These findings indicate that somatostatin inhibits 2-deoxy-D-glucose- and CCK-8-evoked pancreatic enzyme secretion via a vagal pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Duodenal lipid inhibits gastric acid secretion by vagal, capsaicin-sensitive afferent pathways in rats.

Neural and endocrine pathways mediate the inhibitory effects of intestinal fat on gastric acid secretion. To study whether vagal and/or spinal afferent nerves contribute to the neural component of the enterogastric reflex, the sensory neurotoxin capsaicin was applied topically either to the vagus nerves bilaterally or to the celiac-superior mesenteric ganglia in rats with chronic gastric and duodenal fistulas. In lightly restrained, awake rats acid secretion was stimulated for 2 h by continuous intragastric perfusion with 8% peptone and was measured by extragastric titration to pH 5.5. Duodenal lipid perfusion (0-20%) during the 2nd h caused inhibition of peptone-stimulated acid output. Acid output was inhibited by 81% during 5% lipid perfusion of the duodenum and was restored after capsaicin treatment of the vagus nerves. In contrast, capsaicin treatment of the celiac ganglion did not alter the acid inhibitory response to any dose of intestinal lipid. Basal and maximum acid outputs were not significantly different among rats treated by either method with capsaicin. The neural component of the enterogastric reflex in awake rats is mediated in part by a capsaicin-sensitive, vagal-afferent neural reflex.

Distribution of NADPH-diaphorase activity in rat paravertebral, prevertebral and pelvic sympathetic ganglia.

Paravertebral (superior cervical and stellate), prevertebral (coeliac-superior mesenteric, inferior mesenteric) and pelvic (hypogastric) sympathetic ganglia of the rat were investigated by enzyme histochemistry to ascertain the distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity. In the paravertebral ganglia the majority of the sympathetic neuronal perikarya contained lightly and homogeneously distributed formazan reaction product but there was a range of staining intensities amongst the neuron population. In contrast, in the prevertebral ganglia, intense NADPH-diaphorase staining was present in certain neurons. Firstly, a population of neurons of the coeliac-superior mesenteric ganglion complex were surrounded by densely NADPH-diaphorase-positive 'baskets' of fibres and other stained fibres were seen in interstitial nerve bundles and in nerve trunks connected to the ganglion complex. Secondly, in both the inferior mesenteric ganglion and hypogastric ganglion there were many very intensely NADPH-diaphorase positive neurons. Stained dendritic and axonal processes emerged from these cell bodies. In both ganglia this population of neurons was smaller in size than the lightly stained ganglionic neurons and commonly had only one long (presumably axonal) process. The similarity of these highly NADPH-diaphorase-positive neurons with previously described postganglionic parasympathetic neurons in the hypogastric ganglion is discussed.

Reflex gastric motor inhibition caused by intraperitoneal bradykinin: Antagonism by Hoe 140, a bradykinin antagonist

Bradykinin (BK) has been reported to have mixed excitatory/inhibitory effects on gastrointestinal motility. The present study examined the mechanism responsible for the inhibition of gastric motor activity caused by intraperitoneal administration of BK. Gastric motor activity was measured by recording the intragastric pressure (IGP) of phenobarbital-anesthetized rats via a transesophageal catheter. To facilitate the study of inhibitory influences, gastric motility was stimulated by neurokinin A (NKA), which on intravenous injection evoked reproducible gastric contractions as measured by a rise of IGP. Intraperitoneal injection of BK (0.1–10 nmol) inhibited the NKA-induced increase in IGP in a dose-dependent manner, and the effect of epigastric administration of BK was not significantly different from that of intraperitoneal administration. The inhibitory effect of intraperitoneal BK on gastric motility was due to an effect on BK 2 receptors because it was blocked by prior intraperitoneal injection of the BK 2 antagonist Hoe 140. The specificity of this BK antagonist was demonstrated by its inability to antagonize the effect of intraperitoneal hydrochloric acid (HCl), which, like BK, inhibited the NKA-induced gastric contractions. Because the BK- and HCl-induced inhibition of the NKA-induced rise of IGP was abolished by acute removal of the celiac-superior mesenteric ganglion complex, but left unaltered by acute bilateral subdiaphragmatic vagotomy, it is inferred that intraperitoneal BK inhibits gastric motor activity via activation of an autonomic reflex that involves prevertebral ganglia.

An after-depolarization following action potentials and its modulation by substance P in rat sympathetic neurons

Sympathetic neurons in rat coeliac-superior mesenteric ganglia (C-SMG) displayed an after-depolarization (ADP) following action potentials and after-hyperpolarization. The ADP had amplitudes of 3–10 mV and lasted for 2–6 s, during which membrane resistance and excitability of C-SMG neurons increased. The reversal potential of ADP was dependent on external K + concentrations. The ADP was suppressed in a solution containing Cd 2+ or zero Ca 2+. The ADP thus appears to be produced by inhibition of certain K + channels via a Ca 2+-dependent process. Substance P (SP) depolarized ganglion cells and increased the ADP, leading to a long-lasting increase in membrane excitability of rat C-SMG neurons.

Fast and slow depolarizations produced by substance P and other tachykinins in sympathetic neurons of rat prevertebral ganglia

Using intracellular recording, we examined the effects of three mammalian tachykinins, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), on sympathetic neurons of isolated rat coeliac-superior mesenteric ganglia (C-SMG). The 3 tachykinins elicited two distinct depolarizing responses in ganglion cells: fast depolarization with time-to-peak of 1–2 sec and duration of 5–10 sec, and slow depolarization with time-to-peak of about 20 sec and duration of 120–140 sec. Both fast and slow responses persisted in a solution containing low Ca 2+ and high Mg 2+ or tetrodotoxin, which indicates that the tachykinins directly act on ganglion cells to produce fast and slow depolarizations. The two types of tachykinin-induced responses exhibited clearly distinguishable properties. The membrane conductance was increased during the fast response, but not significantly changed, slightly decreased or sometimes increased during the slow response. Within certain range of membrane potential, the amplitude of fast response increased upon membrane hyperpolarization and decreased upon depolarization of ganglion cells. In contrast, the amplitude of slow response associated with membrane conductance decrease was increased with membrane depolarization and decreased with hyperpolarization. The fast response was markedly suppressed in a Na +-deficient solution, a solution containing nominally zero Ca 2+ (plus 0.1 mM EGTA in some cases), and in a solution containing Cd 2+ or Mn 2+, whereas the slow response was not affected in these solutions and was augmented in some cells in K +-free solution. Thus it seems that the increase in Ca 2+-dependent cationic conductance underlies the fast response and that the slow response is produced at least in part by suppression of certain K + channels. The fast response progressively decreased in amplitude upon repeated application of the peptides with short intervals, whereas the slow response was rather augmented by repeated application. Lowering the temperature markedly depressed the slow response, while the fast response remained almost unaffected. It is therefore likely that the fast and slow depolarizations are mediated by two different subtypes of tachykinin receptors or a single class of receptors linked with two different intracellular mechanisms. Measurement of tachykinins in several sympathetic ganglia by combined use of HPLC and radioimmunoassay revealed that the highest amount of SP occurs in the C-SMG where the content of SP (136.0 pmol/g protein) was higher than those of NKA (44.3) and NKB (18.7). SP thus appears to function as a major tachykinin in rat C-SMG.