Interaction of two electrical pacemakers in muscularis of canine proximal colon

Identification and classification of interstitial cells in the canine proximal colon by ultrastructure and immunocytochemistry

The ultrastructure and immunocytochemistry of interstitial cells (ICs) in the canine proximal colon were investigated. Three types of ICs were found within the tunica muscularis. (1) ICs were located along the submucosal surface of the circular muscle (IC-SM). These cells shared many features of smooth muscle cells, including myosin thick filaments and immunoreactivity to smooth muscle gamma actin, myosin light chain, and calponin antibodies. IC-SM were clearly different from smooth muscle cells in that contractile filaments were less abundant and intermediate filaments consisted of vimentin instead of desmin. (2) ICs in the region of the myenteric plexus (IC-MY) were similar to IC-SM, but these cells had no thick filaments or immunoreactivity to smooth muscle gamma actin or calponin antibodies. (3) The fine structures and immunoreactivity of ICs within the muscle layers (IC-BU) were similar to IC-MY, but IC-BU lacked a definite basal lamina and membrane caveolae. IC-BU and IC-MY were both immunopositive for vimentin. Since all ICs were immunopositive for vimentin, vimentin antibodies may be a useful tool for distinguishing between ICs and smooth muscle cells. Each class of ICs was closely associated with nerve fibers, made specialized contacts with smooth muscle cells, and formed multicellular networks. A combination of ultrastructural and immunocytochemical techniques helps the identification and classification of ICs by revealing the fine structures and determining the "chemical coding" of each class of ICs.

Cloning and expression of a Kv1.2 class delayed rectifier K+ channel from canine colonic smooth muscle

A cDNA (CSMK1) encoding a delayed rectifier K+ channel of the Kv1.2 class was cloned from canine colonic circular smooth muscle and expressed in Xenopus oocytes. These channels appear to be uniquely expressed in gastrointestinal muscles and may participate in the electrical slow wave activity. Functional expression of CSMK1 in Xenopus oocytes demonstrated a K+ current that activated in a voltage-dependent manner upon depolarization. This current was highly sensitive to 4-aminopyridine (IC50, 74 microM). A low-conductance K+ channel was identified in inside-out patches from oocytes injected with CSMK1. This channel displayed a linear current-voltage relation with a slope conductance of 14 pS. The channels were blocked in a concentration-dependent manner by 4-aminopyridine. Northern blot analysis demonstrated that CSMK1 is expressed in a wide variety of gastrointestinal smooth muscles. Portal vein, renal artery, and uterus do not express CSMK1, suggesting that, among smooth muscles, expression of this K+ channel may be restricted to gastrointestinal smooth muscles. CSMK1 is 91% homologous to RAK, a delayed rectifier K+ channel cloned from rat heart, but displays unique pharmacological properties and tissue distribution.

Electrical coupling of circular muscle to longitudinal muscle and interstitial cells of Cajal in canine colon

1. Electrical communication between circular muscle, longitudinal muscle and interstitial cells of Cajal (ICC) was investigated; the hypothesis was tested that the resting membrane potential (RMP) gradient in the circular muscle of canine colon is caused by electrical coupling to neighbouring cells. 2. Isolated longitudinal muscle exhibited spike-like action potentials at a RMP of -45 mV with a frequency and amplitude of 20 cycles/min and 12 mV, respectively. 3. The circular muscle (CM), devoid of longitudinal muscle, myenteric plexus and submuscular ICC-smooth-muscle network, was electrically quiescent at a uniform RMP of -62 mV across the entire circular muscle layer. 4. Preparations consisting of only the submuscular ICC network and a few adjacent layers of circular muscle cells exhibited slow wave-type action potentials at a RMP of about -80 mV. 5. In ICC-CM preparations, consisting of the submuscular ICC network and circular muscle, a RMP gradient of 10 mV was observed near the submucosal border, whereas the RMP was constant at -62 mV in the myenteric half of the circular muscle. 6. In full thickness (FT) preparations, a RMP gradient of 23 mV was observed. The RMP decreased gradually from -71 mV at the submucosal border to -48 mV at the myenteric border of the circular muscle. 7. Coupling of longitudinal muscle to circular muscle caused circular muscle cells at the myenteric surface to depolarize by 14 mV and longitudinal muscle cells to hyperpolarize by 3 mV. 8. In the ICC-CM preparations, the slow wave amplitudes did not decay exponentially away from the ICC network indicating that slow waves propagated actively into the circular muscle; in the FT preparations there was an apparent exponential decay but this was due to the RMP gradient. 9. Spike-like action potentials (SLAPs) superimposed on the plateau phase of slow waves did not decay exponentially away from the myenteric border suggesting that SLAPs were generated within the circular muscle layer. 10. In summary, circular muscle cells possess a uniform intrinsic RMP of -62 mV. The RMP gradient in situ is caused by electrical coupling of circular muscle cells to longitudinal muscle cells and the submuscular network of ICC. In situ, slow wave-type action potentials propagate actively into the circular muscle layer, and, dependent on the level of excitation, circular muscle cells actively generate spikes.

Relaxation of distal colonic circular smooth muscle by nitric oxide derived from human leucocytes

The role of nitric oxide (NO) as a mediator of colonic circular smooth muscle relaxation by human leucocytes was investigated. Granulocytes and mononuclear cells were obtained by gradient centrifugation of venous blood from healthy volunteers. Both cell types relaxed precontracted distal colonic circular smooth muscle in a concentration dependent manner. Muscle relaxation was inhibited by preincubation of cells with NG-monomethyl-L-arginine (100 microM/l) but not by preincubation with NG-monomethyl-D-arginine (100 microM/l). Muscle relaxation by cells was reduced by 200 nM oxyhaemoglobin and 10 microM methylene blue but was increased by 60 units/ml superoxide dismutase. Non-viable cells did not produce muscle relaxation. Activation of mononuclear cells by incubation with 100 nM/l FMet-Leu-Phe increased muscle relaxation, whereas activation of granulocytes did not. Granulocytes and mononuclear cells relax precontracted distal colonic circular smooth muscle in vitro by the release of NO that may contribute to motility disorders of the gut associated with inflammation.

Nitric oxide affects mammalian distal colonic smooth muscle by tonic neural inhibition

1 The role of the L-arginine-nitric oxide (NO) pathway in tonic neural inhibition of spontaneous mechanical activity of distal colonic circular smooth muscle (DCCSM) was investigated in male Wistar rats. 2 Muscle strips were mounted in organ baths and spontaneous contractions recorded with isometric force transducers. They were characterized as low frequency (LFCs) 0.41 +/- 0.03 N cm-2 or high frequency contractions (HFCs) 0.22 +/- 0.04 N cm-2. The latter occurred intermittently to produce summation contractions (SCs) range 0.5-12 N cm-2. 3 Tetrodotoxin (100 nM) increased the forces of LFCs and SCs. Increase in force to tetrodotoxin did not occur after incubation of the muscle with NG-monomethyl-L-arginine (L-NMMA) 500 microM, an inhibitor of NO biosynthesis. 4 L-NMMA but not its enantiomer D-NMMA increased the force of LFCs (EC50: 200 microM) and SCS (EC50:175 microM) in a concentration-dependent manner which was reversed by L-arginine but not by D-arginine. 5 Muscle, precontracted by acetylcholine, relaxed to sodium nitroprusside (EC50:1.8 microM) NO gas (EV50:70 microliters) and NO solutions (EC50:4 microM) in a concentration-dependent manner. Guanosine 3':5'-cyclic monophosphate tissue concentrations (pmol mg-1 protein) were elevated in muscle after relaxation by sodium nitroprusside (500 microM) from 0.32 +/- 0.06 to 1.2 +/- 0.37 and by 1 ml of NO gas from 0.49 +/- 0.05 to 1.54 +/- 0.14. 6 These data suggest that DCCSM is under tonic neural inhibition mediated by NO biosynthesis.

Involvement of cyclic GMP in non-adrenergic, non-cholinergic inhibitory neurotransmission in dog proximal colon

1. Nitric oxide (NO) may serve as a non-adrenergic, non-cholinergic (NANC) neurotransmitter released from enteric inhibitory nerves in the gastrointestinal tract. We tested whether guanosine 3':5'-cyclic monophosphate (cyclic GMP) may serve as a second messenger in transducing the NO signal into inhibitory junction potentials (i.j.ps) and relaxation in the canine proximal colon. 2. The membrane permeable analogue of cyclic GMP, 8-bromo cyclic GMP (8-Br-cyclic GMP) mimicked the effects of NO by hyperpolarizing cells near the myenteric border of the circular muscle layer and shortening slow waves in cells near the submucosal surface of the circular muscle layer. 8-Br-cGMP also inhibited spontaneous phasic contractions. 3. The specific cyclic GMP phosphodiesterase inhibitor, M&B 22948, hyperpolarized cells near the myenteric border and prolonged the duration of i.j.ps. M&B 22948 also inhibited phasic contractile activity. 4. Methylene blue failed to reduce significantly the amplitude and duration of i.j.ps and had variable effects on contractions. 5. Cyclic GMP levels were assayed in unstimulated muscles and in muscles exposed to exogenous NO and electrical field stimulation. Both stimuli hyperpolarized membrane potential, inhibited contractions, and elevated cyclic GMP levels. 6. Treatment of muscles with L-NG-nitroarginine methyl ester (L-NAME) increased spontaneous contractile activity and lowered cyclic GMP levels. The inhibitory effect of M&B 22948 on contractions was greatly reduced after muscles were treated with L-NAME. 7. These data support the concept that the effects of NANC nerve stimulation and NO (which may be one of the enteric inhibitory transmitters) may be mediated by cyclic GMP.

The cellular network of interstitial cells associated with the deep muscular plexus of the guinea pig small intestine

Systematic examination using electron microscopic montages and serial sections has demonstrated that three types of interstitial cell, namely gap junction-rich cells, glycogen-rich cells and fibroblast-like cells, are densely located along the whole extent of the deep muscular plexus of the guinea pig small intestine. They tend to be distributed in an alternating fashion in the cellular network, connected with muscle cells of the outer, circular layer by means of gap junctions. These three types of interstitial cell show close relations to two types of nerve varicosity: one type is characterized by clear round vesicles with diameters of about 50 nm, and the other by flattened vesicles measuring about 35 nm by 70 nm. Electron-dense patches have been observed at the cytoplasmic side of the axonal membranes. Muscle cells of both inner and outer circular layers also show close relations to these two types of nerve varicosity. These morphological features are discussed with the implication that they may have some regulatory role in intestinal movement.

Interstitial cells associated with the deep muscular plexus of the guinea-pig small intestine, with special reference to the interstitial cells of Cajal

Interstitial cells associated with the deep muscular plexus of the guinea-pig small intestine were studied by electron microscopy, and three-dimensional cell models were reconstructed from serial ultrathin sections with a computer graphic system. Three types of cells were recognized. The first type was similar in shape to smooth muscle cells, but did not contain an organized contractile apparatus. Many large gap junctions comprising about 4% of the cell surface were present; they connected cells of the first type to each other, to the second type of cell and to smooth muscle cells of the outer circular layer. The second type of cell had a well-demarcated cell body with long slender processes and was characterized by a large amount of glycogen comprising about 9% of the cell volume. The third type of cell was similar to fibroblasts, and contained well-developed Golgi apparatus and rough endoplasmic reticulum. Some of these fibroblast-like cells (a possible subtype) formed small gap junctions. All three types of cells showed close relationships with nerve varicosities. This cellular network consisting of gap-junction-rich cells, glycogen-rich cells and smooth muscle cells may be involved in the pacemaking activity of intestinal movement.

Spatial and temporal patterns of intracellular calcium in colonic smooth muscle

Intracellular calcium [Ca2+]i measurements in cell suspension of gastrointestinal myocytes have suggested a single [Ca2+]i transient followed by a steady-state increase as the characteristic [Ca2+]i response of these cells. In the present study, we used digital video imaging techniques in freshly dispersed myocytes from the rabbit colon, to characterize the spatiotemporal pattern of the [Ca2+]i signal in single cells. The distribution of [Ca2+]i in resting and stimulated cells was nonhomogeneous, with gradients of high [Ca2+]i present in the subplasmalemmal space and in one cell pole. [Ca2+]i gradients within these regions were not constant but showed temporal changes in the form of [Ca2+]i oscillations and spatial changes in the form of [Ca2+]i waves. [Ca2+]i oscillations in unstimulated cells (n = 60) were independent of extracellular [Ca2+] and had a mean frequency of 12.6 +/- 1.1 oscillations per min. The baseline [Ca2+]i was 171 +/- 13 nM and the mean oscillation amplitude was 194 +/- 12 nM. Generation of [Ca2+]i waves was also independent of influx of extracellular Ca2+. [Ca2+]i waves originated in one cell pole and were visualized as propagation mostly along the subplasmalemmal space or occasionally throughout the cytoplasm. The mean velocity was 23 +/- 3 microns per sec (n = 6). Increases of [Ca2+]i induced by different agonists were encoded into changes of baseline [Ca2+]i and the amplitude of oscillations, but not into their frequency. The observed spatiotemporal pattern of [Ca2+]i regulation may be the underlying mechanism for slow wave generation and propagation in this tissue. These findings are consistent with a [Ca2+]i regulation whereby cell regulators modulate the spatiotemporal pattern of intracellularly generated [Ca2+]i oscillations.

Distributions of interstitial cells of Cajal in stomach and colon of cat, dog, ferret, opossum, rat, guinea pig and rabbit

Electrical slow waves vary in prominence from one location to another in stomach and colon. If interstitial cells of Cajal are involved in generation of the slow waves, they might be more abundant in regions where slow waves are prominent than in regions where slow waves are small or absent. We calculated the density of distribution of interstitial cells of Cajal in colon and stomach of cat, dog, ferret, guinea pig, opossum, rabbit, and rat, using the zinc iodide-osmic acid reaction for light microscopy. The cells in the stomach were concentrated in the myenteric plexus and in the circular muscle layer. Along the greater curvature, cells were relatively sparse in the fundus, more frequent in the corpus and densest in the antrum. Along the lesser curvature, they were denser distally than proximally in all species except guinea pig. In the colon most cells lay with an axonal network at the circular muscle-submucosal interface. The axons were sparse in the cecum but uniformly conspicuous from the ileocolonic junction to the internal and sphincter. The density of the interstitial cells of Cajal in cat, dog, opossum, and rabbit rose from a relatively low level in the cecum to a maximum in the mid-colon, declining toward the rectum. In guinea pig, rat, and ferret, the levels throughout the most proximal colon were high. Since gastric slow waves are absent from the fundus, diminutive in the body, and prominent in the antrum, the density of interstitial cells of Cajal in the stomach roughly parallels the prominence of slow waves. Colonic slow waves are most prominent in the right colon and mid-colon, and so the density distribution of interstitial cells of Cajal in the colon also roughly parallels the prominence of slow waves.

Bioassay of nitric oxide released upon stimulation of non-adrenergic non-cholinergic nerves in the canine ileocolonic junction

1. The release and the nature of the inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitter was studied in the canine ileocolonic junction. A circular muscle strip of the canine ileocolonic junction served as donor tissue in a superfusion bioassay in which rings of rabbit aorta with the endothelium removed served as detector tissue. 2. The ileocolonic junction released a labile factor with vasodilator activity upon stimulation of non-adrenergic non-cholinergic (NANC) nerves in response to electrical impulses and the nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP). This release was respectively frequency- and concentration-dependent. 3. The release was reduced by the blocker of neuronal conductance, tetrodotoxin, and by the inhibitor of the nitric oxide (NO) biosynthesis NG-nitro-L-arginine. The biological activity was enhanced by superoxide dismutase and eliminated by haemoglobin. Hexamethonium abolished only the release in response to DMPP. 4. Injection of adenosine 5'-triphosphate (ATP) or vasoactive intestinal polypeptide (VIP) onto the cascade induced relaxations of the rabbit aorta but they were different from those induced by NO or the transferable factor. 5. Based on organ bath experiments in which the reactivity of different parts of the circular smooth muscle layer of the ileocolonic junction was investigated, a muscle strip of superficial circular muscle with submucosa was chosen as the detector strip in the bioassay cascade. 6. The ileocolonic junction dose-dependently relaxed in response to nitroglycerin and NO. NO was much more potent in the rabbit aorta than in the canine ileocolonic junction. 7. In conclusion, our results demonstrate the release of a transferable vasorelaxant factor in response to NANC nerve stimulation which behaves pharmacologically like NO but not like ATP or VIP. Therefore, we suggest that NO or a NO releasing substance is the inhibitory NANC neurotransmitter in the canine ileocolonic junction.

Sodium pump isozymes are differentially expressed in electrically dissimilar regions of colonic circular smooth muscle

Molecular analyses of Na,K-ATPase abundance and alpha-subunit isoform distribution were performed to determine whether pump expression varies at different points through the thickness of the circular layer of colonic smooth muscle. The mRNA and polypeptides of Na,K-ATPase alpha 1 and beta subunits were twice as abundant in the submucosal region of the circular layer, which has previously been shown to generate large pump potentials. Sodium pump activity directly correlated with the relative abundance of the alpha 1 polypeptide. These data show that sodium pump expression varies in electrically dissimilar regions of the circular layer.

Simultaneous measurement of electrical activity from two colonic smooth muscle layers using a dual sucrose gap apparatus

An apparatus using the sucrose gap technique is presented. With this apparatus simultaneous measurements of contractile and intracellular electrical activity from the two smooth muscle layers of the colon are made. An "L-shaped" muscle preparation consisting of a leg from the circular muscle layer and a leg from the longitudinal muscle layer is used. A theoretical discussion of the device's operation is presented. Finally, experimental results that validate the theory are included.

Origin of slow waves in the isolated proximal colon of the cat

Slow oscillations of the membrane potential difference of circular smooth muscle cells of the colon, slow waves, arise at the interface between the submucosa and muscularis externa of the colon. These studies test the hypothesis that the generation of slow waves in the circular muscle layer of the colon of the cat is dependent upon an intact interface between the submucosa and muscularis externa. Electrical recordings were made from 3 types of tissue preparations from the proximal colon: (a) submucosa and muscularis externa intact, (b) submucosa isolated from the circular muscle, and (c) muscularis externa isolated from the submucosa. The cellular make-up of each tissue was determined by the osmic acid-zinc iodide method (Champy-Maillet), and the Masson's trichrome stain. Continuous slow waves were recorded from intact tissues. Removal of the submucosa abolished slow waves from the underlying muscularis externa. Either irregular electrical transients or waxing and waning slow wave-like activity were recorded from the isolated submucosa. Submucosal tissues removed from the muscularis externa contained no circular smooth muscle, but did contain elements of the plexus submucosus extremus.

Spontaneous electrical activity of interstitial cells of Cajal isolated from canine proximal colon

Interstitial cells of Cajal (ICC) have been suggested as pacemaker cells in the gastrointestinal tract. A method was developed to isolate ICC from the slow-wave pacemaker region of the canine proximal colon. These cells were identified under phase-contrast microscopy, and their identity was verified by comparing their ultrastructure with the morphology of ICC in situ. Patch-clamp experiments demonstrated that these cells are excitable; voltage-dependent inward and outward currents were elicited by depolarization. Inward current transients were identified as calcium currents. A portion of the outward current appears to be due to Ca2+-activated K channels commonly expressed in these cells. ICC were also spontaneously active, generating electrical depolarizations similar in waveform to slow-wave events of intact colonic muscles. These findings are consistent with the hypothesis that ICC initiate rhythmicity in the colon.

Spontaneous junction potentials and slow waves in the circular muscle of isolated segments of guinea-pig ileum

Spontaneous electrical activity was recorded with intracellular microelectrodes from cells within the circular muscle of isolated, 2 cm long, intact segments of guinea-pig ileum that were unstretched, and in segments that had been slit open along the entire length of either their mesenteric or antimesenteric border and pinned flat under a minimum of tension. Intact segments usually exhibited fast spontaneous irregular oscillations in membrane potential (mean 1.6 Hz) which were unaffected by hyoscine (0.5 microM), the substance P antagonist D-Arg1, D-Pro2, D-Trp7.9, Leu11-substance P (10 microM), hexamethonium (100 microM), propranolol (1 microM) or phentolamine (1 microM) but were blocked by tetrodotoxin (0.4 microM) or apamin (0.4 microM). This irregular spontaneous activity is deduced to be due to ongoing firing of inhibitory motor neurons. After blockade with apamin or tetrodotoxin, a slow wave-like activity with a mean frequency of 16.4 cycles/min and maximum amplitude 2-14 mV was observed in 47% of intact segments. The amplitude of slow waves waxed and waned with a mean frequency of 0.9 cycles/min. Spontaneous cholinergic (hyoscine-sensitive) excitatory junction potentials were observed in some preparations. In contrast, in the majority of opened segments the resting membrane potential was quite stable, although slow waves that were similar to those in intact segments were observed in 14% of preparations. These studies indicate that spontaneous inhibitory junction potentials and slow waves can be recorded in intact segments of guinea-pig ileum. Their relative absence in opened segments suggests their normal expression is facilitated by the circumferential integrity of the intestine.

In vitro motor activity of intestinal segments of streptozotocin diabetic rats

The spontaneous motor activity of the isolated segments of the gut of streptozotocin-diabetic rats was studied in vitro. In normal preparations, the frequency of intraluminal pressure changes was little influenced by raising the intraluminal pressure. In contrast, in diabetic preparations, the frequency tended to increase with a rise of the intraluminal pressure, and the pressure waves were more irregular than in controls. The motor frequency with a pressure load of 3 cm H2O in the duodenum was 33/min in control rats and 21/min in diabetic rats. The motor frequencies in the other intestinal segments were also higher in normal preparations than in diabetic ones, although these differences were statistically not significant. The amplitude of intraluminal pressure changes increased according to the increase of pressure load, both in normal and diabetic preparations. These amplitudes were higher in normal than in diabetic preparations; however, the differences were statistically significant only in the jejunum. Insulin treatment (5 U/day) for one month, one to two months after streptozotocin injection, lowered the plasma glucose level to nearly normal and increased the body weight up to 80% of the normal but did not re-establish the normal motor frequency in the duodenum. Moreover, treatment of diabetic rats with aldose reductase inhibitor, ONO-2235 (per os, 50 mg/kg b.w./day for one month, one to two months after streptozotocin injection) did not re-establish the normal rhythms in duodenum. The pacemaker activity as well as mechanical properties in the intestinal tract may be disturbed in diabetic preparations.

Heterogeneity in spontaneous and tetraethylammonium induced intracellular electrical activity in colonic circular muscle

Marked differences were observed in the intracellular electrical activities (spontaneous and TEA-induced) comparing the submucosal and myenteric plexus surfaces of the circular muscle of the dog colon. Distinct characteristics of the cells at the myenteric plexus surface were: a less (10 mV) polarized membrane, a lower amplitude slow wave, and the occurrence of burst type spiking activity. However, slow waves with a high upstroke amplitude (approximately 2.5 times higher than the plateau) were observed in 40% of the preparations. This high upstroke amplitude was dependent on the occurrence of a regenerative membrane potential change (a spike) during the slow wave propagation into the myenteric plexus surface. Such a spike was mediated by Ca2+-influx and could be evoked or enhanced by electrical pulses or by blocking a TEA-sensitive potassium conductance. In the presence of TEA, spikes occurred in bursts. Both slow waves and spiking activities generated contraction. In conclusion, at least two types of cells exist in the circular muscle layer with marked differences in electrophysiological properties. Slow waves are generated at the submucosal surface, passively propagated to the outermost circular muscle where they induce regenerative membrane potential changes.

Effects of blood pressure change upon brain-stem pO2 in rabbits with surgically removed baroreceptor nerve. Possible mechanisms for vertigo due to autonomic nerve dysfunction

The effect of denervation of carotid sinus nerve (CSD) on the brain-stem tissue pO2 tension was studied in the awake rabbit. Tissue pO2 around the vestibular nuclei was measured in two groups of rabbits, normal and CSD, under two experimental conditions, viz. blood pressure (BP) modulation and tilt stimulation. BP was either depressed by hemorrhage (up to 50 mmHg) or elevated by intravenous injection of phenylephrine (up to 160 mmHg). In the normal rabbit, tissue pO2 showed minimum change during BP modulation (ranging between 70 and 160 mmHg. In contrast, CSD surgery resulted in the failure to maintain pO2 at a constant level when BP was elevated. However, tissue pO2 did not change when BP decreased. Head-up tilt stimulation (up to 40 degrees) also induced a transient decrease in BP and pO2 in the CSD rabbit; however, these were maintained at a constant level in the normal rabbit. These conditions were assumed to be due to the decrease in autoregulation of cerebral blood flow (CBF), which resulted in CSD. In these experiments, tissue pO2 recovered first, even when BP still remained low. Therefore, it can be proposed that the carotid baroreceptor reflex works for CBF autoregulation of brain stem primarily during an early phase of BP change. Therefore a disturbed carotid sinus reflex, as shown in the present experiment, may be a possible explanation for the mechanism of stress-related vertigo and/or orthostatic vertigo.

Intrinsic nerves in the mammalian colon: confirmation of a plexus at the circular muscle-submucosal interface

Slow waves in the small intestine seem to arise in plexuses of neurites with interstitial cells of Cajal. In the colon, slow waves appear to arise at the circular muscle - submucosal interface. We therefore sought a plexus at this surface in the colon in the cat, dog, ferret, opossum, rabbit, rat, guinea-pig and man. Segments from all levels of the colon were stained by the Champy-Maillet osmic acid-zinc iodide method and cut into serial 25 micron sections in the plane of the muscle layers. A dense network of neurites with abundant interstitial cells of Cajal was found at the circular muscle - submucosal interface in all species except rabbit. Neurites in this plexus appeared to arise from the deep plexus of the submucosa (Schabadasch's or Henle's plexus). It was not found in the small intestine and stomach. A similar plexus was found in the interstices of the myenteric plexus in the colon. Interstitial cells of Cajal in both plexuses were positive for the NADH-diaphorase stain, but not for silver impregnation. The possible roles of the plexuses of neurites and interstitial cells of Cajal at the circular muscle - submucosal interface and at the plane of the myenteric plexus in the generation of rhythmic activity in the colon are discussed.