Prolonged stationary colonic motility recording in seven patients with severe constipation secondary to antidepressants

The aim of this study was to determine whether the colonic motor profile of seven patients with constipation secondary to antidepressants differed from the motility of seven patients with idiopathic constipation and seven healthy volunteers. All constipated patients had very severe constipation. Colonic manometric recordings were performed for 24 h. The number of high amplitude propagating contractions (HAPC) was lower in the two groups of constipated patients than in controls. No HAPC were observed in 5/7 patients with constipation secondary to antidepressants and in 1/7 patients with idiopathic constipation. The overall area under the curve (AUC) in the left colon was lower in the two constipated patient groups than in controls. AUC increased after a 1000-kcal standard meal given at noon in controls but not in the two groups of constipated patients. In conclusion, in patients with constipation secondary to antidepressants, the overall AUC was as poor as in patients with idiopathic constipation, and no colonic response to eating was observed. Moreover, the number of HAPC was more markedly decreased in patients with constipation secondary to antidepressants than in patients with idiopathic constipation.     

Constipation and paradoxical puborectalis contraction in anismus and Parkinson's disease: a dystonic phenomenon?

Anismus, or constipation due to functional obstruction at the pelvic outlet by paradoxical contraction of the striated sphincter muscles during defaecation straining, is described in ten constipated patients and four patients with Parkinson's disease and constipation. The dysfunctional pattern of muscle recruitment resembled that characteristic of dystonia elsewhere in the body and was indistinguishable in patients with idiopathic anismus and those with extrapyramidal motor disturbance due to Parkinson's disease. These findings suggest that anismus may be a focal dystonic phenomenon.     

Studies of the inhibitory non-adrenergic neuromuscular transmission in the smooth muscle of the normal human intestine and from a case of Hirschsprung's disease

A modified sucrose-gap method was used to study both non-adrenergic inhibitory neuromuscular transmission and effects of adenosine 5'-triphosphate (ATP) on isolated smooth muscle preparations from the human intestine. It was found that non-adrenergic inhibition in the circular smooth muscle layer was of larger amplitude than in the longitudinal layer. Study of the ionic mechanisms underlying non-adrenergic inhibition indicated that an increase in K+ conductance was responsible for the generation of non-adrenergic inhibitory junction potentials (IJPs). The results suggest that the inhibitory actions of the endogenous neurotransmitter and exogenous ATP are due to increases in Ca2+-dependent K+ conductance. The K+-channel blockers tetraethylammonium and 4-aminopyridine had no effect on IJPs or ATP, while apamin slightly decreased both the amplitude of the IJP and the hyperpolarization of the circular smooth muscle caused by ATP. These results are consistent with the purinergic hypothesis of non-adrenergic inhibition. In addition to inhibitory purinoceptors, the existence of excitatory purinoceptors was identified in the longitudinal muscle, activation of which probably caused an increase in Na+-conductance. The excitatory purinoceptor-mediated contraction in the longitudinal muscle from the constricted region of large intestine from patients with Hirschsprung's disease was greater than that found in control specimens. It is possible that excitatory purinoceptors play a role in the pathophysiology of Hirschsprung's disease.     

Novel smooth muscle markers reveal abnormalities of the intestinal musculature in severe colorectal motility disorders

Histopathological studies of gastrointestinal motility disorders have mainly focused on enteric nerves and interstitial cells of Cajal, but rarely considered the enteric musculature. Here we used both classical and novel smooth muscle markers and transmission electron microscopy (TEM) to investigate muscular alterations in severe colorectal motility disorders. Full-thickness specimens from Hirschsprung's disease, idiopathic megacolon, slow-transit constipation and controls were stained with haematoxylin/eosin (HE) and Masson's trichrome (MT), incubated with antibodies against smooth muscle alpha-actin (alpha-SMA), smooth muscle myosin heavy chain (SMMHC), smoothelin (SM) and histone deacetylase 8 (HDAC8) and processed for TEM. Control specimens exhibited homogeneous immunoreactivity for all antibodies. Diseased specimens showed normal smooth muscle morphology by HE and MT. While anti-alpha-SMA staining was generally normal, immunoreactivity for SMMHC, HDAC8 and/or SM was either absent or focally lacking in Hirschsprung's disease (80%), idiopathic megacolon (75%) and slow-transit constipation (70%). Ultrastructurally, clusters of myocytes with noticeably decreased myofilaments were observed in all diseases. SMMHC and the novel smooth muscle markers SM and HDAC8 often display striking abnormalities linked to the smooth muscle contractile apparatus unnoticed by both routine stainings and alpha-SMA, suggesting specific defects of smooth muscle cells involved in the pathogenesis of gastrointestinal motility disorders.     

Apoptotic phenomena are not a major cause of enteric neuronal loss in constipated patients with dementia

Chronic constipation is a frequent symptom in patients with dementia, especially in those institutionalized. However, few data are available on the neuropathological aspects of the colon in such patients. We investigated the enteric neuropathology of the colon in two patients with longstanding dementia and intractable constipation, requiring surgery to alleviate symptoms. The results were compared to those obtained in 10 controls. No abnormalities were found at conventional histological examination, except for the presence of melanosis coli. Immunohistochemical evaluation revealed no important difference between patients and controls, except for a decreased number of enteric neurons in patients. However, this neuronal decrease was not associated to apoptotic phenomena, as observed in patients with severe idiopathic constipation. We concluded that in severely constipated patients with dementia the neuropathological abnormalities might be reconducted to a physiological neuronal decrease as a result of aging, and that the pathophysiological aspects of constipation in these subjects differ from those found in idiopathic constipation.     

Paradoxical puborectalis contraction is a feature of constipation in patients with multiple sclerosis.

OBJECTIVE--To study the disturbed anorectal physiology associated with constipation in multiple sclerosis. METHODS--Anorectal function in 10 patients with clinically definite multiple sclerosis and constipation has been compared with 10 normal persons and 11 patients with idiopathic constipation, without multiple sclerosis. RESULTS--All 10 constipated patients with multiple sclerosis had difficulty evacuating barium paste during defaecography. In four of these there was complete failure of puborectalis relaxation when straining to defaecate, and in another four there was incomplete puborectalis relaxation. There was no evidence of lower motor neuron involvement of pelvic floor muscles in the multiple sclerosis group. CONCLUSIONS--Paradoxical puborectalis contraction is common in patients with multiple sclerosis in whom constipation is a symptom. This may be a feature of the disturbed voluntary sphincter control mechanism, analogous to detrusor sphincter dyssnergia in the bladder.     

Resealed fiber segments for the study of the pathophysiology of human skeletal muscle

The usefulness of long fiber segments for the study of the pathophysiology of human skeletal muscle was evaluated. Immediately after biopsy, the fiber segments were depolarized. Within 3 hours the cut ends resealed, and if the segments were greater than or equal to 2.5 cm long they regained normal resting membrane potentials (i.e., negative to -80 mV). Miniature endplate potentials, endplate potentials, action potentials, the current-voltage relationship, and the resting intracellular Ca2+ concentration of the resealed fiber segments were similar to those in fibers that were intact from tendon to tendon. In addition, specific properties of intact fibers obtained from patients with various neuromuscular diseases were preserved in the resealed fiber segments prepared from the same patients or patients with the same diseases. These segments are easily obtained as a routine muscle biopsy performed under local anesthesia; they provide valuable preparations for the study of the pathophysiology of human skeletal muscle as well as for in vitro pharmacological tests.     

Reduced capabilities of synaptic transmission in aged rats

Synaptic transmission at the neuromuscular junction of the rat phrenic nerve-diaphragm muscle was studied in aged and young, control rats; their ages were 24 to 26 and 12 to 13 months, respectively. The resting potential of the diaphragm muscle cells was found to be consistently lower in the old animals than in the controls. Membrane input resistance and capacitance were not significantly different. The rate of occurrence of miniature end-plate potentials (MEPPs) in old rats was 1.75 times higher than in the controls; the distribution of intervals between the times of occurrence of successive MEPPs was exponential in both cases, however. In Mg²⁺-blocked preparations, facilitation and posttetanic potentiation were observed; differences between data obtained from both age groups were not significant. In curare-blocked preparations, synaptic depression occurred during repetitive nerve stimulation. The depression was more severe in the aged animals; this difference was consistent and independent of the rate of stimulation. Repetitive nerve stimulation led to action potential conduction block in the presynaptic terminals of both age groups; however, failure occurred at lower frequencies and shorter times of stimulation in the aged animals. The block appeared to be associated with membrane depolarization. We conclude that the capability to sustain transmission is diminished at the neuromuscular junction of aged rats; this could underlie the deterioration of synaptic structures observed during senescence.     

Altered periodic rectal motor activity: a mechanism for slow transit constipation

The pathophysiology of slow transit constipation is poorly understood. Both decreased and increased distal colonic motility have been reported. In healthy humans, a 3 cycles per minute (cpm), periodic rectal motor activity (PRMA) has been described. Our aim was to investigate the characteristics of PRMA and to assess its role in the pathogenesis of constipation. A six-sensor solid-state probe was placed with the tip sensor in the mid-transverse colon, without sedation, and prolonged colonic motility was recorded in nine patients with slow transit constipation (1M, 8F) and in 11 healthy subjects (3M, 8F). Subjects were free to ambulate. We examined the frequency, nocturnal vs. diurnal variation, and characteristics of PRMA, and its relationship to proximal colonic motility. All subjects showed PRMA. The rhythm was similar (2.5-4 cpm) in both groups. However, constipated patients exhibited a greater (P < 0.001) number of PRMA cycles than controls. The duration of each cycle and amplitude of pressure waves during PRMA were also greater (P < 0.05) at night in patients compared with controls. In patients, 40% of PRMA cycles were associated with a proximal colonic motor event compared with 81% in controls (P < 0.02). The area under the curve of all colonic pressure waves and incidence of specialized propagating pressure waves was lower (P < 0.05) in patients during daytime. When compared with controls, constipated patients exhibited reduced daytime colonic pressure waves and a higher frequency of PRMA. Most of the PRMA was unrelated to proximal colonic activity in constipated patients in contrast with findings in control patients. In addition to decreased colonic motility, this excessive and unco-ordinated phasic rectal activity may further impede stool transport and contribute to the pathogenesis of slow transit constipation.     

A digital technique for stimulus artifact reduction.

A method of recovering compound muscle action potentials which are overwhelm by a stimulus artifact is presented. In the specific example reported, such action potentials were recorded from the hamster diaphragm using an apposing platinum electrode for both stimulation and recording. To recover the artifact-free action potential, a combination of digital data acquisition and simple signal processing was employed. The recording of a stimulus artifact from a sub-threshold stimulus was used to subtract the artifact component from subsequent recordings and thus faithfully reveal the action potentials. The technique should find application in other preparations.     

Role for the skeletal muscle action potential in non-Hebbian long-term depression at the amphibian (Bufo marinus) neuromuscular junction

Retrograde signaling from skeletal muscle cells to motor nerve terminals is a recognized mechanism for modulating the strength of neuromuscular transmission. We recently described a form of long-term depression of transmitter release at the mature neuromuscular junction that is dependent on the production of nitric oxide, most likely by the muscle cell (Etherington and Everett 2004 J Physiol (Lond) 559:507-517). We now show that the depression is blocked by treating neuromuscular preparations with mu-conotoxin G111A, an antagonist of skeletal muscle voltage gated sodium channels, indicating that the depression requires postsynaptic action potential firing. Experiments on dually-innervated sartorius muscles revealed that propagation of action potentials generated by low-frequency stimulation of one nerve branch gives rise to nitric-oxide mediated depression at unstimulated nerve terminals located many millimetres away on the same muscle fiber. The non-Hebbian pattern of expression of the depression, as well as its reliance on postsynaptic action potential firing, distinguish it from forms of synaptic depression described at immature neuromuscular synapses and may provide a mechanism for coregulation of the strength of motoneurons innervating the same postsynaptic cell.     

Myasthenia gravis: Review of diagnosis and management

Although the cause of myasthenia gravis is still unknown, its pathogenesis appears clear: immunologic attack on synaptic receptors in muscle causes receptor deficiency, decreased miniature endplate potentials, and decrements in the compound action potentials evoked from muscles on repetitive stimulation of peripheral nerves. In addition to the involvement of skeletal muscle, some MG patients may manifest subtle alterations of the function of heart, lung, smooth muscle, and CNS, indicating that this is truly a systemic disorder. Modern therapy involves adjusting treatment to the needs of individual patients. Anticholinesterases, calcium, ephedrine, potassium, and germine partially correct the defect in neuromuscular transmission; prednisone, ACTH, cytotoxic drugs, antilymphocyte serums, gamma globulin, thoracic duct drainage, plasmapheresis, and thymectomy partially modify the abnormalities of the immune system.     

The Effects of Botulinum Toxin a on Ephaptic Transmission in Idiopathic Hemifacial Spasm

Objective: Lateral spreading and synkinetic responses of blink reflex are a sign of ephaptic transmission in idiopathic hemifacial spasm (HFS). The aim of this study was to evaluate the effect of botulinum toxin A (Btx A) on ephaptic transmission in idiopathic HFS. Methods: Thirty-three patients with idiopathic HFS were investigated. Btx A was injected only into the affected orbicularis oculi (OC) muscle. Electrophysiological studies were performed before and three weeks after the Btx A injection. Results: After Btx A, the latencies of motor response and blink reflexes elicited from the OC muscle were significantly increased. The lateral spreading was not obtained in the OC muscle, while the orbicularis oris muscle response was not changed. There were no significant differences in the synkinetic responses of blink reflex. During needle EMG examination, positive sharp waves and fibrilation potentials were observed due to chemodenervation only in the OC muscle. Conclusion: Btx A affects only the neuromuscular junctions of the injected muscle and has no effect upon ephaptic transmission.     

Altered electrical activity in colonic smooth muscle cells from dystrophic (mdx) mice

Because the colon from dystrophic (mdx) mice shows an altered motor pattern, probably due to neural disorders, our aim was to examine the electrophysiological properties of muscle cells and the functionality of nitrergic transmission in circular muscle from normal and mdx colon. Normal colonic cells (resting membrane potential [RMP] about -50 mV) showed spontaneous hyperpolarizations (inhibitory junction potentials; IJPs) and cyclic slow depolarizations were sometimes recorded. Mdx colon had a depolarized RMP (about -36 mV) and spontaneous IJPs, but the cyclic activity was never observed. In the normal colon, Nomega-nitro-L-arginine methyl ester (L-NAME) induced depolarization and abolished the cyclic activity. In the mdx colon, L-NAME caused a slight depolarization. Both preparations displayed the same value of RMP in the presence of L-NAME. In normals, neural stimulation induced nonadrenergic, noncholinergic IJPs composed of fast hyperpolarizations followed by a nitrergic slow hyperpolarization, selectively abolished by L-NAME. In the mdx colon the evoked IJPs were composed only of the initial fast hyperpolarization, the nitrergic component being absent. The hyperpolarization to sodium nitroprusside was not significantly different in both preparations. We conclude that the colon from animals lacking in dystrophin displays different electrophysiological features because of an impairment of nitric oxide function.     

Experimental myasthenia due to alpha-bungarotoxin.

Neuromuscular transmission was studied electrophysiologically in rabbits intoxicated by alpha-bungarotoxin, a specific inhibitor of acetylcholine receptor. The findings consisted of a slight reduction in amplitude of single evoked muscle action potentials, a decrement in amplitude of successive evoked muscle action potentials post-tetanic potentiation and exhaustion, edrophonium reversal, and no change of muscle action potentials evoked by direct stimulation of the muscle. These were similar to characteristic electrophysiologic phenomena seen in 40 patients with myasthenia gravis. The receptor abnormality may be responsible for the underlying defect of myasthenia.     

Passively transferred Lambert-Eaton syndrome in mice receiving purified IgG

Purified IgG antibodies were prepared by ion-exchange chromatography from the plasma of a patient with nonneoplastic form of the Lambert-Eaton myasthenic syndrome (LES). The antibodies were injected into mice with daily doses of 0.15-10 mg for 20-22 days, following which the integrity of neuromuscular transmission was assessed in vitro in phrenic nerve-diaphragm muscle preparations. The injected animals manifested electrophysiologic features of human LES, which were characterized by: dose-dependent reduction in the quantal content of nerve-evoked endplate potentials, an abnormally small increase in the frequency of spontaneous miniature endplate potentials (MEPPs) with elevated [K+]o, and normal MEPP amplitude with no evidence of postjunctional deficiency. Crude immunoglobulins (Igs) from the same patient and two LES patients with associated malignancy similarly transferred the defects in quantal transmitter release. In contrast, animals receiving Igs from control subjects or from a patient with small-cell carcinoma of the lung manifested no functional impairment of neuromuscular transmission. Instead, the evoked release in these animals was significantly enhanced relative to that found in normal untreated mice. These results suggest that an IgG antibody produces the presynaptic impairment that is characteristic of LES and support the concept that LES with and without cancer has an autoimmune pathogenesis.     

Standardization of anal sphincter electromyography: effect of chronic constipation

Severe chronic constipation has been implicated as a cause of damage to the pelvic floor innervation. The aim of the present study was to examine the role of mild to moderate chronic constipation, a condition more relevant for clinical electromyographers, because this complaint is common in patients sent for evaluation of possible neurogenic dysfunction of lower sacral myotomes. A group of 59 subjects without major uroneurological dysfunction, proctological disorders, or neurological abnormalities participated in the study, which involved concentric needle electromyography of the external anal sphincter (EAS). Motor unit potentials (MUPs; sampled using multi-MUP analysis) and interference pattern (IP, sampled using turn/amplitude analysis) of chronically constipated and control subjects were compared. No effect of chronic constipation on MUP/IP parameters compatible with neurogenic injury was found. Our results suggest that mild chronic constipation does not cause damage to the EAS innervation, and that no separate reference values are needed for this group of subjects.     

Presynaptic and postsynaptic actions of procainamide on neuromuscular transmission

Procainamide (PA), a cardiac anti-arrhythmic agent, was applied in vitro to the rat neuromuscular junction and its effect on neuromuscular transmission was investigated using intracellular microelectrode recording techniques. Clinically relevant doses of PA produced a dosedependent decrease in the amplitude of spontaneous miniature endplate potentials (MEPPs) and a marked increase in the half-decay time without altering MEPP frequency or resting membrane potential. The amplitude of impulse-evoked end-plate potentials was also reduced in a similar dose-dependent manner, with a marked prolongation of the decaying phase. Direct quantal analysis using magnesium-blocked preparations showed that the drug also caused a reduction in the mean number of acetylcholine quanta released per nerve impulse. This presynaptic inhibitory effect of the drug, however, contributed less to the overall blocking action than did the postsynaptic effect. The junctional effects of the drug were completely reversible, with all affected parameters returning to the control levels after washout of PA with control solution. These direct inhibitory actions on neuromuscular transmission could account for the clinical exacerbations associated with the administration of PA to patients with myasthenia gravis and other neuromuscular diseases.     

Interactions between the duration of stimulation and noradrenaline on cholinergic transmission in the myenteric plexus-smooth muscle preparation

Output of acetylcholine (ACh), electromyogram (EMG) recordings and contractions of myenteric plexus-longitudinal muscle strip preparations from the guinea-pig ileum were studied during stimulation by single impulses or by trains (30 Hz; 2 to 128 impulses) under control conditions and in the presence of noradrenaline (NA). During supramaximal stimulation NA (2.5 microM) inhibited both contractions of the smooth muscle and the release of ACh evoked by single impulses more effectively than those evoked by train stimulation so that in a train of 4 impulses the output of ACh per impulse after the 2nd to 4th impulses was 69 to 104% higher than the output after the 1st impulse. During submaximal stimulation, contractions and ACh release evoked by single impulses were almost completely inhibited by NA. The neurogenic EMG, a direct consequence of the localized action of released transmitter (ACh), was recorded in the longitudinal muscle 4 and 10 mm aborally from the focal stimulation site. The incidence of the neurogenic response was much higher at the proximal (4 mm) than at the distal (10 mm) site and was proportional to the number of impulses in a train (100 Hz). NA inhibited propagation of the neurogenic response evoked by single impulses whereas its effect during train stimulation was less. It is concluded that in the course of train stimulation, sites of transmission more distant from the stimulation focus was recruited, and consequently the secretion of ACh in succeeding impulses was enhanced. NA could interfere with this process; it might inhibit the invasion by action potentials of cholinergic nerve terminal varicosities, thereby reducing the release of ACh.     

Repetitive action potentials induced in chloride-free solution: Effect of denervation

Isometric mechanical activity and action potentials registered with intracellular microelectrodes were studied in innervated and denervated fibers of the soleus muscle of the rat in normal and chloride-free solutions. The chloride-free solution promoted in both innervated and denervated fibers an increment in the resting membrane potential. The innervated muscles showed long mechanical relaxation and repetitive action potentials after a single depolarizing pulse. On the contrary, denervated muscles were resistant to show mechanical and electrical changes in the chloride-free medium. Spontaneous and evoked action potentials from innervated muscle fibers were abolished by tetrodotoxin. The evoked action potentials generated in denervated fibers had a slower time course and were resistant to tetrodotoxin. After 7 to 10 days of denervation the input resistance was increased by about 30%. Substitution of chloride with sulfate resulted in a 150% increase in input resistance of innervated muscle fibers and 80% in denervated preparations. Alterations in the ionic conductances, a decrease in the maximum rate of rise of the action potentials, and changes in the sodium current kinetics could be the main factors for the absence of repetitive action potentials in denervated fibers exposed to the chloride-free medium.