Neurotrophic control of 16S acetylcholinesterase at the vertebrate neuromuscular junction

Endplate 16S acetylcholinesterase (16S-AChE) from rat anterior gracilis muscle was assessed, 6 hr to 10 days after denervation, by velocity sedimentation analysis on linear sucrose gradients. The innervating obturator nerve was transected either close (1-2 mm, short stump) or far (35-40 mm, long stump) from the muscle. In both instances, the activity of 16S-AChE gradually decreased and reached approximately the same level (10%-20% of control) by 6 days after denervation. However, enzymatic decay started considerably earlier in short stump (12-24 hr) as compared to long stump (4-5 days) preparations, i.e., the time of onset of 16S-AChE loss depended on the length of nerve that remained attached to the muscle. Whether this result extended to other AChE molecular forms (10S, 4S) in muscle endplates could not be determined because, in contrast to 16S-AChE, these forms were also detected in red blood cells (4S) and plasma (10S). Only small amounts of 16S-AChE were found in intact obturator nerves (1/100 of that in gracilis endplate regions). Thus a faster depletion of enzyme from shorter nerve stumps after axotomy could not entirely account for the substantial effect of nerve stump length on 16S-AChE. Since muscle contraction ceases immediately following nerve transection, regardless of nerve stump length, the results can be ascribed to the lack of some neural influence other than nerve-evoked muscle activity. The present findings are consistent with the view that maintenance of 16S-AChE at neuromuscular junctions primarily depends on regulatory substances which are conveyed by axonal transport and released from nerve terminals.     

Bidirectional axonal transport of 16S acetylcholinesterase in rat sciatic nerve

Axonal transport of the 16S Molecular form of acetylcholinesterase (16S-AChE) in doubly ligated rat sciatic nerves was studied by means of velocity sedimentation analysis on sucrose gradients. This form of AChE was selectively confined to motor, and not to sensory, fibers in the sciatic nerve, where it represented 3--4% of total AChE. Its activity increased linearly with time (4--20 hr) in nerve segments (7 mm) proximal to the central ligature (4.5 mU/24hr) and distal to the peripheral ligature (2.0 mU/24 hr). From the linear rates of accumulation of 16S-AChE, we conclude that the enzyme is conveyed by anterograde and retrograde axonal transport at velocities close to those previously defined for the movement of total AChE (410 mm/day, anterograde; 220 mm/day, retrograde). The transport of AChE molecular forms, other than the 16S form, could not be resolved presumably due to their presence in blood as well as at extraaxonal sites. The present findings are consistent with the view that in rat sciatic nerve most, if not all, of the small portion of total AChE (approximately 3%) which is transported may be accounted for by 16S-AChE.     

Neurotrophic control of 16S acetylcholinesterase from mammalian skeletal muscle in organ culture

The effects of rat obturator nerve extracts on total and 16S acetylcholinesterase (AChE) activity were studied in endplate regions of denervated anterior gracilis muscles maintained in organ culture for 48 hr. The decrease of total AChE activity in cultured muscles was similar to that observed in denervated muscles in vivo. This decrease in activity was partly prevented by addition of either 100 or 200 μl nerve extract (2.7 mg/ml protein) to the nutrient medium. Nerve extract treatment also decreased the release of AChE activity from the muscle into the bathing medium. Conversely, rat serum (20 μl; 90 mg/ml protein) had no effect on total AChE activity in muscle endplates, nor on release of the enzyme by the muscle. The 16S form of AChE was confined to motor endplate muscle regions and its activity was drastically decreased by denervation in both organ culture and in vivo preparations in a comparable manner. Nerve-extract supplemented cultures contained a significantly (p ? 0.001) larger amount of endplate 16S AChE activity (140–145%) than the corresponding controls (100-). Our results suggest that some nerve soluble substance, other than serum contaminants or 16S AChE itself, affects the maintenance of 16S AChE at the neuromuscular junction.     

Difference in the ability of neonatal and adult denervated muscle to accumulate acetylcholinesterase at the old sites of innervation

In adult rat sternocleidomastoid muscle, AChE is concentrated in the region rich in motor end-plates (MEP). All major AChE forms, "16 S," "10 S," and "4 S," are accumulated at high levels, and not only "16 S" AChE. After denervation, muscle AChE decreases; 2 weeks after denervation, low levels (20-40% of control) are reached for all forms. During the following weeks, a slow but steady increase in "10 S" and "16 S" AChE occurs in the denervated muscle. At this stage, all forms are again observed to be highly concentrated in the region containing the old sites of innervation. Thus, in adult rat muscle the structures able to accumulate "16 S," "10 S," and "4 S" AChE in the MEP-rich regions remain several months after denervation. In normal young rat sternocleidomastoid muscle at birth, all AChE forms are already accumulated in the MEP-rich region. After denervation at birth, the denervated muscle loses its ability to keep a high concentration of "4 S," "10 S," and "16 S" AChE in the old MEP-rich region. All AChE forms are still present 1 month after denervation, but they are decreased and diffusedly distributed over the whole length of the muscle. In particular, "16 S" AChE is detected in the same proportion (10-15%) all along the denervated muscle. Thus, the diffuse distribution of AChE, and especially "16 S" AChE, after neonatal denervation, contrasts with the maintained accumulation observed in adult denervated muscle. It seems that denervation of young muscle results in a specific loss of the muscle ability to concentrate high levels of all AChE forms at the old sites of innervation.     

Independence of changes in contraction properties and myofibrillar ATPase activity of denervated mammalian muscle on length of nerve stump.

1. Contractile properties of the fast extensor digitorum longus of one-month-old rats and of the fast peroneus longus muscles of adult rabbits were studied in vitro at 36 degrees C after nerve section close to the muscle. Changes in contraction properties (prolongation) are not observed until 48 hours after denervation in the rat and 14-30 days in the rabbit. 2. At no period after denervation are differences in twitch isometric contraction properties dependent on the length of the sectioned nerve stump. This lack of dependence of contractile behavior after denervation is in contrast to many metabolic changes which show a clear dependence on the length of the nerve stump. 3. It is concluded that the onset of denervation changes in contractile behavior are related to the loss of nerve-impulse activity, while the transient early metabolic changes are related to changes of fast axoplasmic flow, initiated after nerve section and therefore dependent on length of sectioned nerve stump.     

Rapid changes in levels of individual molecular forms of acetylcholinesterase after denervation of mouse sternocleidomastoid muscle

Experimental denervation of adult mouse sternocleidomastoid muscle results in a decrease in total AChE. The most rapid change essentially affects the tailed, asymmetric 16 S AChE, since one day after nerve section, “16S” AChE is already significantly decreased to about 70% of its control value. We found that both background and junctional “16S” AChE are affected by this rapid decrease. Later, a sharp fall in “10S” and “4S” AChE occurs about seven days after denervation when muscle atrophy develops with loss of weight and proteins. A gaussian analysis of the sedimentation profiles of AChE extracted from denervated muscle shows that there is not only an early rapid decrease in 16 S AChE but also a decrease in the monomeric 3.3S AChE. This result suggests that there is a very rapid turn-over of two molecular forms of AChE, the supposedly monomeric precursor and the complex asymmetric 16S AChE.     

Extrasynaptic accumulations of acetylcholinesterase in the rat sternocleidomastoid muscle after neonatal denervation. Light and electron microscopic localization and molecular forms

Denervated neonatal rat sternocleidomastoid muscle has decreased levels of total AChE when compared to control muscle. Denervated versus control values of total muscle AChE present a three-phase curve in function of time after denervation. There is a rapid initial fall 0-3 days after denervation, an increase during about 2 weeks, then again a decrease in total AChE. Thus, there is a transitory net accumulation of AChE after the initial fall of activity in denervated developing muscle. Extrasynaptic areas of high AChE activity develop between 1 and 2 weeks after denervation and remain visible up to 1 month after denervation before vanishing. An electron microscope study shows that these accumulations are internal to the muscle fiber, close to a limited number of muscle nuclei and associated to the sarcoplasmic reticulum and nuclear envelope, but not to the T-tubule system. As found in adult rat muscle, the initial fall in AChE affects first the 16 S AChE form, and soon after, the 4 S and 10 S AChE forms. A main difference with adult muscle is the sudden increase and predominance over other forms of 10 S AChE 2 weeks after denervation at birth. Later, the decrease in AChE affects 16 S and 4 S AChE before 10 S AChE. The regions rich in extrasynaptic sites of AChE accumulation possess a very high proportion of 10 S AChE. Thus, the mechanisms of biosynthesis, intracellular transport and/or secretion of AChE may be very different in young, developing muscle compared to adult muscle.     

Junctional form of acetylcholinesterase restored at nerve-free endplates.

Rat soleus muscles were ectopically innervated by implanting a foreign nerve in an endplate-free region of muscle and, 2–3 weeks later, cutting the original nerve. The junctional, 16 S form of acetylcholinesterase (AChE) and focal staining for AChE disappeared from the old endplate region within a few days after denervation. In muscles with an ectopic nerve, but not in paired control muscles, 16 S AChE and focal staining were restored in the old endplate region 1–2 weeks after denervation even though nerve fibers could not be detected in that region. These results suggest that the nerve exerts a local effect, specifying the site at which junctional AChE appears, and a nonlocal effect, perhaps mediated by muscle activity, regulating the amount of junctional AChE.     

Effects of Acute and Chronic Denervation on Release of Acetylcholinesterase and Its Molecular Forms in Rat Diaphragms

Abstract: Hemidiaphragms were removed from rats at various times after intrathoracic transection of the left phrenic nerve and were incubated in organ baths containing 1.5 ml of oxygenated, buffered physiologic saline solution, with added glucose and bovine serum albumin. After incubation, the acetylcholinesterase (AChE; EC 3.1.1.7) activities of the bath fluid and of the muscle were determined. Innervated left hemidiaphragms were found to release 107 units of AChE over a 3-h period, corresponding to 1.9% of their total AChE activity. Denervation led to a rapid loss of AChE from the muscle coincident with a transient increase in the outpouring of enzyme activity into the bath fluid. Thus, 1 day after nerve transection the left hemidiaphragm contained only 68% of the control amount of AChE activity, but released 140% as much as control. After 3 or 4 days of denervation, the AChE activity of the diaphragm stabilized at 35% of the control value. Release also fell below control by this time, but not as far. One week after denervation the release, 69 units per 3 hr, corresponded to 3.3% of the reduced content of AChE activity in the muscle, indicating that denervation caused an increase in the proportion of AChE released. Sucrose density gradient ultracentrifugation showed that 10S AChE accounted for more than 80% of the released enzyme activity at all times. The results did not rule out the possibility, however, that the released enzyme originally stemmed from 4S or 16S AChE in the diaphragm.     

Neurovascular free-muscle transfer for the treatment of established facial paralysis following ablative surgery in the parotid region

Neurovascular free-muscle transfer for facial reanimation was performed as a secondary reconstructive procedure for 45 patients with facial paralysis resulting from ablative surgery in the parotid region. This intervention differs from neurovascular free-muscle transfer for treatment of established facial paralysis resulting from conditions such as congenital dysfunction, unresolved Bell palsy, Hunt syndrome, or intracranial morbidity, with difficulties including selection of recipient vessels and nerves, and requirements for soft-tissue augmentation. This article describes the authors' operative procedure for neurovascular free-muscle transfer after ablative surgery in the parotid region. Gracilis muscle (n = 24) or latissimus dorsi muscle (n = 21) was used for transfer. With gracilis transfer, recipient vessels comprised the superficial temporal vessels in 12 patients and the facial vessels in 12. For latissimus dorsi transfer, recipient vessels comprised the facial vessels in 16 patients and the superior thyroid artery and superior thyroid or internal jugular vein in four. Facial vessels on the contralateral side were used with interpositional graft of radial vessels in the remaining patient with latissimus dorsi transfer. Cross-face nerve grafting was performed before muscle transfer in 22 patients undergoing gracilis transfer. In the remaining two gracilis patients, the ipsilateral facial nerve stump was used as the primary recipient nerve. Dermal fat flap overlying the gracilis muscle was used for cheek augmentation in one patient. In the other 23 patients, only the gracilis muscle was used. With latissimus dorsi transfer, the ipsilateral facial nerve stump was used as the recipient nerve in three patients, and a cross-face nerve graft was selected as the recipient nerve in six. The contralateral facial nerve was selected as the recipient nerve in 12 patients, and a thoracodorsal nerve from the latissimus dorsi muscle segment was crossed through the upper lip to the primary recipient branches. A soft-tissue flap was transferred simultaneously with the latissimus muscle segment in three patients. Contraction of grafted muscle was not observed in two patients with gracilis transfer and in three patients with latissimus dorsi transfer. In one patient with gracilis transfer and one patient with latissimus dorsi transfer, acquired muscle contraction was excessive, resulting in unnatural smile animation. The recipient nerves for both of these patients were the ipsilateral facial nerve stumps, which were dissected by opening the facial nerve canal in the mastoid process. From the standpoint of operative technique, the one-stage transfer for latissimus dorsi muscle appears superior. Namely, a combined soft-tissue flap can provide sufficient augmentation for depression of the parotid region following wide resection. A long vascular stalk of thoracodorsal vessels is also useful for anastomosis, with recipient vessels available after extensive ablation and neck dissection.     

Selective Increase of Tetrameric (G4) Acetylcholinesterase Activity in Rat Hindlimb Skeletal Muscle Term Denervation

Acetylcholinesterase (AChE; EC 3.1.1.7) isoenzymes in gracilis muscles from adult Sprague-Dawley rats were studied 24-96 h after obturator nerve transection. Results show a selective denervation-induced increase in the globular G4 isoform, which is predominantly associated with the plasmalemma. This enzymatic increase was (a) transient (occurring between 24 and 60 h) and accompanied by declines in all other identifiable AChE isoforms; (b) observed after concurrent denervation and inactivation of the enzyme with diisopropylfluorophosphate, but not following treatment with cycloheximide; and (c) more prominent in the extracellular compartment of muscle endplate regions. Aside from this transient change, G4 activity did not fall below control levels, indicating that at least the short-term maintenance of G4 AChE (i.e., at both normal and temporarily elevated levels) does not critically depend on the presence of the motor nerve. In addition, this isoform's activity increases in response to perturbations of the neuromuscular system that are known to produce elevated levels of acetylcholine (ACh), such as short-term denervation and exercise-induced enhancement of motor activity. The present study is consistent with the hypothesis that individual AChE isoforms in gracilis muscle are subject to distinct modes of neural regulation and suggests a role for ACh in modulating the activity of G4 AChE at the motor endplate.     

Long-term changes in neurotrophic factor expression in distal nerve stump following denervation and reinnervation with motor or sensory nerve

Several factors have been proposed to account for poor motor recovery after prolonged denervation, including motor neuron cell death and incomplete or poor regeneration of motor fibers into the muscle. Both may result from failure of the muscle and the distal motor nerve stump to continue expression of neurotrophic factors following delayed muscle reinnervation. This study investigated whether regenerating motor or sensory axons modulate distal nerve neurotrophic factor expression. We found that transected distal tibial nerve up-regulated brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) mRNA, down-regulated neurotrophin-3 and ciliary neurotrophic factor mRNA, and that although these levels returned to normal with regeneration, the chronically denervated distal nerve stump continued to express these neurotrophic factors for at least 6 months following injury. A sensory nerve (the cutaneous saphenous nerve) sutured to distal tibial nerve lowered injury-induced BDNF and GDNF mRNA levels in distal stump, but repair with a mixed nerve (peroneal, containing muscle and cutaneous axons) was more effective. Repair with sensory or mixed nerves did not affect nerve growth factor or neurotrophin-3 expression. Thus, distal nerve contributed to a neurotrophic environment for nerve regeneration for at least 6 months, and sensory nerve repair helped normalize distal nerve neurotrophic factor mRNA expression following denervation. Furthermore, as BDNF and GDNF levels in distal stump increased following denervation and returned to control levels following reinnervation, their levels serve as markers for the status of regeneration by either motor or sensory nerve.     

Can surface electromyography improve surgery planning? Electromyographic assessment and intraoperative verification of the nerve bundle entry point location of the gracilis muscle

Purpose: To verify the precision of surface electromyography (sEMG) in locating the innervation zone of the gracilis muscle, by comparing the location of the IZ estimated by means of sEMG with in vivo location of the nerve bundle entry point in patients before graciloplasty procedure due to fecal incontinence. Methods: Nine patients who qualified for the graciloplasty procedure underwent sEMG on both gracilis muscle before their operations. During surgery the nerve bundle was identified by means of electrical stimulation. The distance between the proximal attachment and the nerve entry point into the muscle’s body was measured. Both measurements (sEMG and in vivo identification) were compared for each subject. Results: On average, the IZ was located 65.5 mm from the proximal attachment. The mean difference in location of the innervation zones in each individual was 10 ± 9.7 mm, maximal – 30 mm, the difference being statistically significant (p = 0.017). It was intraoperatively confirmed, that the nerve entered the muscle an average of 62 mm from the proximal attachment. The largest difference between the EMG IZ estimation and nerve bundle entry point was 5 mm (mean difference 2.8 mm, p = 0.767). Conclusion: Preoperative surface electromyography of both gracilis muscles is a safe, precise and reliable method of assessing the location of the innervation zones of the gracilis muscles. The asymmetry of the IZ location in left and right muscles may be important in context of technical aspects of the graciloplasty procedure.     

Properties of 16S acetylcholinesterase from rat motor nerve and skeletal muscle

Rat obturator nerve 16S acetylcholinesterase (16S AChE) was separated by sucrose gradient velocity sedimentation and compared to the 16S form of AChE similarly derived from endplate regions of anterior gracilis muscles. The 16S AChE from both tissues could only be extracted in high ionic strength buffer; as it aggregated under low ionic strength conditions. Treatment of nerve and muscle 16S AChE with purified collagenase, in the presence of calcium, caused an identical shift in the enzyme's sedimentation coefficient to 17.5S. Other properties which were also equivalent for 16S AChE from both tissue sources included: an excess substrate inhibition above 2×10^–3 M acetylcholine andK _m of 1.6×10^–4 M, relative sensitivity to the specific inhibitors BW284C51 (I₅₀ of 5×10^–8 M) and Iso-OMPA (I₅₀ of 5×10^–4 M), and a half maximal thermal inactivation at 62.5°C. These and additional results indicate that the 16S forms of AChE in both tissues are analogous molecules, which have a highly asymmetric conformation probably containing a collagen-like domain. The present findings are also consistent with the view that motor neurons provide at least a fraction of the 16S AChE present at the neuromuscular junction.     

Neural Regulation of Muscle Glucose 6-Phosphate Dehydrogenase: Effect of Batrachotoxin and Tetrodotoxin

Abstract: We tested the hypothesis that glucose 6-phosphate dehydrogenase (G6PD) activity in the rat skeletal muscle is regulated by putative axonally derived neurotrophic factors. This was accomplished by comparing the effects of nerve section and subperineural injection of batrachotoxin (BTX) or tetrodotoxin (TTX) on G6PD in rat extensor digitorum longus (EDL) muscle. BTX, an agent known to block nerve impulse conduction and axonal transport, increased G6PD activity to 155% and 163% of control by days 2 and 4 after injection. Denervation of the EDL muscle by section of the peroneal nerve 10–20 mm from its entrance to the muscle caused G6PD activity to increase to 170% of control by day 1 and to 200% and 180% of control by days 2 and 4, respectively. The increase in enzyme activity after denervation and after subperineural injection of BTX was due in part to muscle inactivity resulting from blockade of nerve impulses. This conclusion is based upon the observation that subperineural injection of TTX at an identical site in the peroneal nerve caused a small but significant (30%) increase in G6PD activity after 4 days. Choline acetyltransferase (CAT) activity was assessed as a measure of the efficacy of blockade of slow axonal transport. Decreases in CAT activity following denervation or injection of BTX or TTX were parallel to increases in G6PD activity observed under these conditions. These results argue for a role of axonal transport in neural regulation of muscle G6PD, with a small contribution by neuromuscular activity.     

Regulation of turnover and number of acetylcholine receptors at neuromuscular junctions

The number and metabolic stability of acetylcholine receptors (AChRs) at neuromuscular junctions of rat tibialis anterior (TA) and soleus (SOL) muscles were examined after denervation, paralysis by continuous application of tetrodotoxin to the nerve, or denervation and direct stimulation of the muscle through implanted electrodes. After 18 days of denervation AChR half-life declined from about 10 days to 2.3 days (TA) or 3.6 days (SOL) and after 18 days of nerve conduction block to 3.1 days (TA). In contrast, the total number of AChRs per endplate was unaffected by these treatments. Denervation for 33 days had no further effect on AChR half-life but reduced the total number of AChRs to about 54% (SOL) or 38% (TA) of normal. Direct stimulation of the 33-day denervated SOL from day 18 restored normal AChR stability and counteracted muscle atrophy but had no effect on the decline in AChR number. The results indicate that motoneurons control the stability of junctional AChRs through evoked muscle activity and the number of junctional AChRs through trophic factors.     

Denervated muscle fibers explain the deficit in specific force following reinnervation of the rat extensor digitorum longus muscle

The authors tested the hypothesis that, after denervation and reinnervation of skeletal muscle, observed deficits in specific force can be completely attributed to the presence of denervated muscle fibers. The peroneal nerve innervating the extensor digitorum longus muscle in rats was sectioned and the distal stump was coapted to the proximal stump, allowing either a large number of motor axons (nonreduced, n = 12) or a drastically reduced number of axons access to the distal nerve stump (drastically reduced, n = 18). A control group of rats underwent exposure of the peroneal nerve, without transection, followed by wound closure (control, n = 9). Four months after the operation, the maximum tetanic isometric force (Fo) of the extensor digitorum longus muscle was measured in situ and the specific force (sFo) was calculated. Cross-sections of the muscles were labeled for neural cell adhesion molecule (NCAM) protein to distinguish between innervated and denervated muscle fibers. Compared with extensor digitorum longus muscles from rats in the control (295 +/- 11 kN/m2) and nonreduced (276 +/- 12 kN/m2) groups, sFo of the extensor digitorum longus muscles from animals in the drastically reduced group was decreased (227 +/- 15 kN/m2, p < 0.05). The percentage of denervated muscle fibers in the extensor digitorum longus muscles from animals in the drastically reduced group (18 +/- 3 percent) was significantly higher than in the control (3 +/- 1 percent) group, but not compared with the nonreduced (9 +/- 2 percent) group. After exclusion of the denervated fibers, sFo did not differ between extensor digitorum longus muscles from animals in the drastically reduced (270 +/- 20 kN/m2), nonreduced (301 +/- 13 kN/m2), or control (303 +/- 10 kN/m2) groups. The authors conclude that, under circumstances of denervation and rapid reinnervation, the decrease in sFo of muscle can be attributed to the presence of denervated muscle fibers.     

The innervated gracilis musculocutaneous flap for total tongue reconstruction

A functional neotongue following total glossectomy requires both soft-tissue bulk and reconstruction of muscle function. We used innervated transverse gracilis musculocutaneous flaps to reconstruct total glossectomy defects in eight patients. The obturator nerve to the gracilis muscle was approximated to the hypoglossal nerve to reinnervate the gracilis muscle by using microsurgical technique. The cutaneous paddle of the gracilis flap easily supplies sufficient bulk to replace the total glossectomy defect. Follow-up of patients ranged from 3 to 47 months. All patients were able to resume oral feeding. Electromyographic studies performed on one patient showed reinnervation of the flap with active elevation of the posterior pharynx. Ultimately, seven patients died because of recurrence of their disease. The innervated gracilis musculocutaneous flap may benefit patients who have a total glossectomy by allowing them to achieve a more functional recovery.     

Has nonquantal acetylcholine secretion from motor nerve endings a role in neurotrophic control of resting membrane potential in rat muscle fibers?

The resting membrane potential of fibers of the rat diaphragm was measured by a microelectrode technique 3 h after division of the phrenic nerve and incubation in culture medium for 5 days after denervation. The membrane potential was recorded in synaptic regions of fibers close to (2–3 mm) and distant from (9–11 mm) the site of nerve division. The membrane potential of the synaptic region of the close fibers 3 h after denervation became smaller, whereas that of the synaptic region of distant fibers did not change relative to the control. Placing the muscle 3 h after denervation into medium with carbamylcholine (1·10^–8 M), cGMP (1·10^–4 M), or dibutyryl-cGMP (1·10^–6 M) led to hyperpolarization of the synaptic region of the close fibers but did not change the resting potential in the synaptic region of the distant fibers, and abolished differences between them. Five days after division of the nerve, incubation of the muscle in a solution with the above-mentioned substances did not affect the resting membrane potential. Nonquantal release of acetylcholine from motor nerve endings, assessed by the amplitude of hyperpolarization of the postsynaptic membrane, induced by application of curarine against the background of acetylcholine esterase inhibition, 3 h after denervation was identical in the synaptic region of the close and distant fibers and did not differ from the control. It is postulated that the postdenervation fall of membrane potential of rat muscle fibers is not due to disturbance of nonquantal secretion of acetylcholine from motor nerve endings.S. V. Kurashov Kazan' Medical Institute, Ministry of Health of the USSR. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 358–365, May–June, 1985.