Hepatoprotective effect of Alchornea cordifolia leaf on liver damage in albino rats

Ethnopharmacological relevance: The dry leaf of Alchornea cordifolia (AC) is used, in traditional medicine in the S Nigeria, for the preparation of blood tonic, remedies for urinary, respiratory, liver and gas intestinal disorders. Aim of the study: This study investigated the protective property of AC leaf against liver damage in animals with a view to exploring its use for the treatment of hepatotoxicity in humans. Material and methods:  Ethanol extract of A. cordifolia was used to study the hepatoprotective activity in acetaminophen-induced Albino rats (150-200g). Animals in Group 1 served as vehicle control, Group 2 served as hepatotoxin (Acetaminophen 2g/kg treated) group, Groups 3 and 4 served as positive control (Vitamin E and Curcumin 100 mg/kg bw respectively) groups, and Groups 5-8 served as (200-500mg/kg bw) AC leaf extract treated groups while Group 9 served as normal group (AC extract only 300 mg/kg bw). Results: The hepatotoxic group showed hepatocytic necrosis, cellular infiltration and inflammation in the liver. The treatment group restored the liver cells to their normal lobular architecture in a dose dependent manner. The protection offered by the plant extract compared well with the standard antioxidant agents (Curcumin and Vitamin E). Tannins, flavonoids, alkaloids and saponins were detected in the phytochemical screening. Conclusion: Our findings suggest Alchornea cordifolia ethanol leaf extract as promising herpatoprotective herb and give credence to the folkloric use of this plant for the treatment of liver problems.DOI: http://dx.doi.org/10.3126/ijasbt.v2i2.10473Int J Appl Sci Biotechnol, Vol. 2(2): 217-221 

A low cost, safe, disposable, rapid and self-sustainable paper-based platform for diagnostic testing: lab-on-paper

There is a strong interest in the use of biopolymers in the electronic and biomedical industries, mainly towards low-cost applications. The possibility of developing entirely new kinds of products based on cellulose is of current interest, in order to enhance and to add new functionalities to conventional paper-based products. We present our results towards the development of paper-based microfluidics for molecular diagnostic testing. Paper properties were evaluated and compared to nitrocellulose, the most commonly used material in lateral flow and other rapid tests. Focusing on the use of paper as a substrate for microfluidic applications, through an eco-friendly wax-printing technology, we present three main and distinct colorimetric approaches: (i) enzymatic reactions (glucose detection); (ii) immunoassays (antibodies anti-Leishmania detection); (iii) nucleic acid sequence identification (Mycobacterium tuberculosis complex detection). Colorimetric glucose quantification was achieved through enzymatic reactions performed within specific zones of the paper-based device. The colouration achieved increased with growing glucose concentration and was highly homogeneous, covering all the surface of the paper reaction zones in a 3D sensor format. These devices showed a major advantage when compared to the 2D lateral flow glucose sensors, where some carryover of the coloured products usually occurs. The detection of anti-Leishmania antibodies in canine sera was conceptually achieved using a paper-based 96-well enzyme-linked immunosorbent assay format. However, optimization is still needed for this test, regarding the efficiency of the immobilization of antigens on the cellulose fibres. The detection of Mycobacterium tuberculosis nucleic acids integrated with a non-cross-linking gold nanoprobe detection scheme was also achieved in a wax-printed 384-well paper-based microplate, by the hybridization with a species-specific probe. The obtained results with the above-mentioned proof-of-concept sensors are thus promising towards the future development of simple and cost-effective paper-based diagnostic devices.

COX-2 inhibition prevents insulin-dependent diabetes in low-dose streptozotocin-treated mice

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease believed to be caused by an inflammatory process in the pancreas leading to selective destruction of the beta cells. Inducible cyclooxygenase (COX-2) is expressed under inflammatory conditions and its product prostaglandin E(2) (PGE(2)) is an important inflammation mediator. We report here that administration of the selective COX-2 inhibitor NS-398 prevents the onset of diabetes in mice brought on by multiple low-doses of streptozotocin (STZ). Histological observations indicated that STZ-mediated destruction of beta cells was prevented by NS-398 treatment. Delayed (day 3) administration of NS-398 was also protective in this model. No protective effect was observed when NS-398 was administered prior to a high, toxic dose of STZ. These results demonstrate the critical importance of COX-2 activity in autoimmune destruction of beta cells, and point to the fact that COX-2 inhibition can potentially develop into a preventive therapy against IDDM.

Novel method for the labeling of distant neuromuscular junctions

Essential to understanding the roles proteins and structural elements play at the synapse is to understand the development, remodeling and reinnervation of peripheral neuromuscular junctions. It has, however, been a challenging task to label and visualize neuromuscular junctions. In this paper we demonstrate how adenovirus technology can be combined with intraspinal microinjection techniques to follow both the development and the reinnervation of a distant peripheral neuromuscular junction in the rat. A recombinant adenovirus containing VAMP-2 (synaptobrevin-2) was fused to the green fluorescent protein (GFP) and microinjected into the region of the lumbar motor neurons. We were able to follow the neuronal incorporation, axonal transport and synaptic localization of the GFP-VAMP-2 using fluorescence microscopy. GFP-VAMP-2 was found in neuronal cell bodies, selected sciatic nerve axons and was concentrated in the presynaptic nerve terminal. During reinnervation of the neuromuscular junction, GFP-VAMP-2 allows us to follow the time course of junctional reinnervation. Thus, the microinjection of microliter amounts of labeled recombinant virus into locations far distant from target regions can be used to efficiently study the formation of neuromuscular junctions with a minimum of trauma to the animal.

The effect of age and injury on the expression of inducible nitric oxide synthase in facial motor neurons in F344 rats

Nitric oxide has been implicated in both normal neuronal aging as well as nerve repair events because of its known roles in synaptic plasticity, synaptogenesis and neuroplathologic processes. In this study, we have determined the effect of aging, by comparing brainstem facial motor neurons (FMNs) as well as blood vessels, from adult F344 rats to those in old animals. Inducible nitric oxide synthase (iNOS) expression was determined both by immunohistochemistry using an antibody to iNOS on tissue sections and slot blots. In adult rats, iNOS expression was detectable only in FMNs and not in blood vessels. In old rats, there were robust levels of iNOS protein in blood vessels, while iNOS protein was not detectable in FMNs from old rats. There was also a 12-fold increase in iNOS expression in isolated blood vessels from old rats compared to vessels from adult animals. To determine the effect of injury on iNOS expression, the facial nerve was transected and immunocytochemistry performed as above. After nerve transection in adult rats, iNOS was demonstrable only in blood vessels after 1 day, but by 7 days iNOS protein immunoreactivity was robust in FMNs. In old animals, iNOS protein expression was observed only in FMNs at 1 day, but by 7 days after injury, protein immunoreactivity was localized to the blood vessels. These data suggest that aging and injury differentially affect the expression of iNOS and that the up-regulation of iNOS may be important for the availability of nitric oxide in the aged or injured nervous system.

Lumbar motor neuron size and number is affected by age in male F344 rats

Motor neurons in the spinal cord of old rats appear similar in size but less numerous compared with those in mature rats; they also contain a large amount of lipofuscin, the lipid peroxidation by-product whose function is largely unknown. The object of this study was to morphometrically characterize motor neurons found in the L4/L5 lumbar spinal cord of mature (6-month) and old (22-month) rats. Paraformaldehyde-fixed, lumbar spinal cords from six rats at each age were embedded in paraffin, sectioned at 6 microm and stained with 0.1% toluidine blue. The nucleolar diameter and area from a minimum of 34 motor neurons per spinal cord were measured. Motor neuron number was calculated using Abercrombie's (Abercrombie, 1946) formula after correcting for tissue shrinkage. Motor neuron number was decreased with age while the neuronal area increased with age. Nucleolar diameter also increased in old rats. Frequency distributions of motor neuron area revealed unimodal distributions of motor neurons rats of both ages. We suggest that larger nucleolar diameter reflects more metabolically active neurons in old rats while larger neuron area is a reflection of the presence of lipofuscin in old motor neurons.

Acceleration of axonal outgrowth in motor axons from mature and old F344 rats after a conditioning lesion

The conditioning lesion paradigm has proven to be a very useful model in which to examine the mechanisms of axonal outgrowth after injury. In the present study, we have used the conditioning lesion model to examine the ability of motor axons from mature (6-8 months) and old (22-24 months) Fischer 344 rats to form new axonal sprouts. We show that after a single lesion (sham-conditioned axons followed by a testing lesion), axonal outgrowth rates are slower at earlier vs longer postlesion times in mature rats: between 4 and 8 days postlesion, outgrowth rates are 2.4 +/- 0.4 mm/day, whereas between 8 and 11 days postlesion outgrowth rates are 4.6 +/- 0.7 mm/day. After a single lesion in the old rat, at early postlesion times, the axonal outgrowth rate is 1.9 +/- 0.4 mm/day but with increasing time after injury, outgrowth rates slow down to 1.1 +/- 0.8 mm/day. In conditioned motor axons from mature rats, outgrowth rates increase from 3.1 +/- 0.4 mm/day at early postlesion times to 5.2 +/- 0.6 mm/day at longer postlesion times. An even more dramatic increase in outgrowth rate is seen in conditioned axons from old rats: 2.4 +/- 0. 4 mm/day at early postlesion times to 6.3 +/- 1.0 mm/day at later times after lesion. There is no change in the initial delay before sprouting under any condition. These data support the hypothesis that axons from old animals can be stimulated to repair themselves at rates comparable to those seen in younger animals and suggest that there may be an absolute maximum outgrowth rate attainable by newly forming axon sprouts.

Spin trapping agent phenyl N-tert-butylnitrone protects against the onset of drug-induced insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus is an autoimmune disease believed to be caused by an inflammatory process in the pancreas leading to selective destruction of the beta-cells. Cytokines and nitric oxide (NO) have been shown to be involved in this destruction. Phenyl N-tert-butylnitrone (PBN) has demonstrated protective effects against several pathological conditions including ischemia-reperfusion injury and endotoxin-induced shock. We report here that PBN co-administration can prevent the onset of the STZ-induced diabetes in mice. PBN co-treatment inhibited the streptozotocin (STZ)-induced hyperglycemia, the elevation in the level of glycated hemoglobin and weight loss in the treated mice. Histological observations indicated destruction of B-cells in the STZ-treated animals and its prevention by PBN co-treatment. EPR spin trapping experiments in the pancreas indicated the in vivo formation of NO in STZ-treated animals and its attenuation by PBN treatment.

Timing-jitter reduction for a dispersion-managed soliton system: experimental evidence

We have measured the timing jitter for dispersion-managed solitons in a recirculating loop for distances up to 20,000 km. The data were obtained with modulated data, 2(7) - 1 and 2(23) - 1 pseudorandom binary sequence patterns, at 10-Gbit/s rates and with an unmodulated pulse train at 10 GHz. We have obtained good agreement with our data, using a filtered Gordon-Haus model for the timing jitter reduced by the energy enhancement of our solitons relative to solitons in a fiber with a constant dispersion equal to our map's path-average dispersion. We have also measured a bit-error rate of <10(-9) at a distance of 15,000 km.

Dispersion-managed solitons in a fiber loop with in-line filtering

We investigate both numerically and experimentally soliton propagation in a fiber loop with dispersion management, in-line filters, and frequency shifting. More than 90% of the fiber in the loop is in the normal-dispersion regime, but the net dispersion is anomalous. Stable pulses in the loop have an enhanced power relative to solitons in a fiber with uniform dispersion equal to the loop's path-averaged dispersion. Because the loop's path-averaged dispersion is small, the in-line filtering and the frequency shifting play an important role in pulse shaping. Recirculating loop experiments that demonstrate stable pulse propagation over 28,000 km are consistent with results from computer modeling.

Assembly of microfilaments and microtubules from axonally transported actin and tubulin after axotomy

The slow component (SC) of axonal transport conveys structural proteins, regulatory proteins, and glycolytic enzymes toward the axon tip at 1-6 mm/day. Following axon interruption (axotomy), the rate of outgrowth corresponds to the rate of SCb-the fastest subcomponent of SC. Both axonal outgrowth and SCb accelerate 20-25% after axotomy. Tubulin and actin are the major proteins being carried by SCb. To further characterize the acceleration of SCb, we measured the equilibrium between subunits and polymers for both actin and tubulin. We radiolabeled newly synthesized proteins in rat motor neurons by microinjecting [35S]methionine into the spinal cord 7 days after crushing the sciatic nerve (85 mm from the spinal cord). Nerves were removed 7 days later for homogenization in polymer-stabilizing buffer (PSB) and centrifugation, followed by SDS-PAGE of supernatants (S) and pellets (P). We removed beta-tubulin, actin, and the medium-weight neurofilament protein (NF-M) from each gel by using the fluorogram as a template. After solubilizing gel segments for liquid scintillation spectrometry, we expressed counts as a polymerization ratio: P/[S+P]. In the nerve segments that contained radiolabeled Scb proteins, located 24-36 mm from the spinal cord, axotomy increased the polymerization ratio of SCb actin from 0.23 to 0.36 (P < 0.05) but had no effect on SCb beta-tubulin. In a separate experiment, we added 12 microM taxol to PSB to stabilize newly assembled microtubules. Adding taxol did not alter the polymerization ratio for SCb beta-tubulin in sham-axotomized nerves but aid increase the ratio in axotomized nerves, from 0.44 to 0.63 (P < 0.05); polymerization ratios for SCb actin were unaffected. We conclude that the assembly of microfilaments and microtubules increases to provide cytoskeletal elements for axon sprouts. The resulting loss of actin and tubulin subunits may play a role in the acceleration of SCb.

Acute treatment with pulsed electromagnetic fields and its effect on fast axonal transport in normal and regenerating nerve

The mechanism whereby low-frequency electromagnetic fields accelerate axonal regrowth and regeneration of peripheral nerve after crush lesion is not known. One candidate is an alteration in axonal transport. In this study we exposed unoperated rats for 15 min/day, and rats that had undergone a crush lesion of the sciatic nerve, for 1 hr/day for 2 days, to 2-Hz pulsed electromagnetic fields. To label fast transported proteins, [3H]-proline was microinjected into the spinal cord, and the sciatic nerves were removed 2, 3.5, and 5 hr later. The rates of fast axonal transport were obtained for animals in all groups by counting sequential 2-mm segments of nerves. The following transport rates were found: in unoperated normal sciatic nerve not exposed to PEMF, 373 +/- 14 mm/day; in unoperated normal nerve exposed to PEMF, 383 +/- 14 mm/day; in sham crush nerves not exposed to PEMF, 379 +/- 19 mm/day; in sham crush nerve exposed to PEMF, 385 +/- 17 mm/day; in crushed nerves not exposed to PEMF, 393 +/- 16 mm/day. and in crushed nerves exposed to PEMF, 392 +/- 15 mm/day. The results of these experiments indicate that 1) a crush injury to the sciatic nerve does not alter the rate of fast axonal transport, and 2) low-frequency pulsed electromagnetic fields do not alter fast axonal transport rates in operated (crush) or unoperated sciatic nerves.

Fast axonal transport rates are unchanged in 6- and 24-month F344 rats

The maximum rate of fast axonal transport in motor axons at 6 and 24 months was measured in F344 rats. Tritiated proline was injected near sciatic motoneurons and rats were killed after 2-5 h. Nerves were processed for liquid scintillation spectroscopy and fast transport rates calculated. The rates, in 6- and 24-month rats, were 373 +/- 12 mm/day and 368 +/- 10 mm/day, respectively. Thus, the maximum fast transport rate is unchanged with age in F344 rats.

Direct measurement of fast axonal transport rates in corticospinal axons of the adult rat

The bi-directional movement of proteins from the soma to the axon terminal is called axonal transport. Fast anterograde transport moves organelles and membrane-bound proteins distally. Fast transport rates were measured in corticospinal tract axons of male Sprague-Dawley rats by microinjection of tritiated proline into the sensorimotor cortex. Animals were killed after 3-5 h and the tract cut into 1 mm segments. A bimodal wave of radiolabeled proteins was evident, with the first peak at the spino-medullary junction and the second peak in cervical spinal segments. The fast transport rate was calculated at the leading edge of the distal wave, and found to be 303 +/- 44 mm/day.

Testosterone regulation of the regenerative properties of injured rat sciatic motor neurons

We have previously demonstrated that systemic administration of testosterone differentially regulates the regenerative properties of injured hamster facial motor neurons, which are androgen receptor-containing cranial motor neurons. In this investigation, the hypothesis that testosterone alters the regenerative properties of rat sciatic motor neurons, which are androgen receptor-containing spinal motor neurons, was tested using fast axonal transport of radioactively labeled proteins to assess sciatic nerve regeneration. Adult castrated male rats were subjected to crush axotomy of the sciatic nerve at the level of the gemelli tendons (mid-thigh). One-half of the axotomized animals received subcutaneous implants of testosterone propionate (TP), with the remainder of the animals sham implanted with blank capsules. The outgrowth distances of the leading axons were measured at 5, 6, 7, and 11 days postoperative. Linear regression analysis was accomplished, with the slope of the line representing the regeneration rate and the x-intercept the initial delay of sprout formation. Systemic administration of testosterone resulted in a 13% increase in the rate of regeneration, relative to the control, -TP group. Outgrowth distances were significantly increased in the +TP group only in the later stages of regeneration. However, TP did not shorten the delay in sprout formation in regenerating sciatic motor neurons, but instead produced a small prolongation in the delay time. This pattern of hormonal regulation of the regenerative properties of spinal motoneurons is similar to that previously found in cranial motoneurons. The prolongation of the initial delay may have been a factor in the lack of significant outgrowth distances during the early stages of regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Retardation of fast axonal transport in wobbler mice

To investigate axonal function in a model of early motor neuron disease, we examined fast and slow components of anterograde axonal transport in the less-affected hindlimb motor neurons of wobbler mice. To study the fast component (FC), we injected tritiated amino acids into the lumbar spinal cord and retrieved the sciatic nerve after 2 or 3 h. The transport distance was the extent of the plateau of labeling; regression analysis indicated that FC was 25% slower in wobbler mice than in unaffected littermates (P < 0.01). To study slow component (SC), [35S]methionine was injected. Transport distances were to the peaks of labeling for structural proteins after 2 or 3 weeks. Rates for each subcomponent (SCa and SCb) were unaffected by wobbler disease. Because the rate of retrograde FC is also unaffected (Mitsumoto et al., Muscle & Nerve 13:121-126, 1990), we conclude that wobbler disease specifically retards anterograde FC in less-affected hindlimb motor neurons, whereas all components of axonal transport are retarded in forelimb motor neurons.

Acceleration of axonal outgrowth in rat sciatic nerve at one week after axotomy

Following injury of sciatic motor axons in the rat, the rate of axonal outgrowth is faster if there has been a prior "conditioning" axotomy. The acceleration of outgrowth is due to an acceleration of SCb, the rate [slow (SC)] component of axonal transport that carries cytomatrix proteins; this occurs throughout the axon by 7 days after the conditioning axotomy (Jacob and McQuarrie, 1991a, J. Neurobiol. 22:570-583). To further characterize the conditioning lesion effect (CLE), it is important to know (1) the minimum effective conditioning interval (time between conditioning and testing lesions), (2) whether the cell body reaction is required, and (3) whether outgrowth accelerates after a single axotomy. Outgrowth distances were measured by radiolabeling all newly synthesized neuronal proteins and detecting those carried to growth cones by fast axonal transport. When the conditioning and testing lesions were made simultaneously (0 day conditioning interval), there was no CLE. With a conditioning interval of 3 days, there was a shortening of the initial delay (before the onset of outgrowth) without a change in outgrowth rate. With conditioning intervals of 7, 14, and 21 days, the rates of outgrowth were increased by 8%, 22%, and 11%, respectively. To determine whether the cell body reaction to axotomy is necessary for the CLE, a nonaxotomizing stimulus to axonal growth (partial denervation) was used in place of a conditioning axotomy. This had no effect on the rate of outgrowth from a testing lesion made 14 days later. Finally, we examined the possibility that outgrowth accelerates after a single lesion. Outgrowth was faster at 6-9 days after axotomy than at 3-6 days (p < 0.001), and accelerated further at 9-12 days (p < 0.001). We conclude that (1) the shortest effective conditioning interval is 3 days; (2) the cell body reaction is necessary for the CLE; (3) axonal outgrowth from a single axotomy accelerates in concert with the anabolic phase of the cell body reaction. The SCb motor is, in turn, upregulated by this reaction. This suggests that the SCb motor responds to a fast-transported signal that is a product of the cell body reaction.

Axotomy accelerates slow component b of axonal transport

Because the integrity of an axon depends on the supply of proteins synthesized in the cell body, we examined the effect of axotomy on the transport of structural proteins in rat motor axons, and the effect of altered transport on the rate of outgrowth after a subsequent testing axotomy. To examine the axonal transport of structural proteins, we labeled newly synthesized proteins with 35S-methionine 7 days after a "conditioning" lesion of the sciatic nerve, and removed the nerve 7-21 days later for SDS-PAGE. Tubulin, actin, calmodulin, and the 68-kD light neurofilament protein (NF-L) were identified by fluorography and removed for liquid scintillation counting. The fastest moving structural proteins were carried by slow component b (SCb) of axonal transport, which advanced 20% faster in conditioned axons: 4.2 versus 3.5 mm/day (p less than 0.01). NF-L was not accelerated, indicating that the motor for subcomponent a (SCa) of slow axonal transport was unaffected by axotomy. To measure outgrowth distances, the testing lesions was made 7 days after the conditioning lesion, and growth cones were located by the fast transport method 3 or 9 days later. The regression analysis of outgrowth distance on time showed that sprouts elongated 25% faster in conditioned axons: 4.0 versus 3.2 mm/day (p less than 0.001). These accelerated sprouts were formed too far from the spinal cord to contain SCb proteins that were synthesized after axotomy. Because the rate of outgrowth correlated closely with the rate of SCb in outgrowing sprouts (McQuarrie and Jacob, J. Comp. Neurol. 305:139-147, 1991), we conclude that SCb is accelerated throughout the length of the axon by 7 days after axotomy.

Conditioning nerve crush accelerates cytoskeletal protein transport in sprouts that form after a subsequent crush

To examine the relationship between axonal outgrowth and the delivery of cytoskeletal proteins to the growing axon tip, outgrowth was accelerated by using a conditioning nerve crush. Because slow component b (SCb) of axonal transport is the most rapid vehicle for carrying cytoskeletal proteins to the axon tip, the rate of SCb was measured in conditioned vs. sham-conditioned sprouts. In young Sprague-Dawley rats, the conditioning crush was made to sciatic nerve branches at the knee; 14 days later, the test crush was made where the L4 and L5 spinal nerves join to form the sciatic nerve in the flank. Newly synthesized proteins were labeled in motor neurons by injecting 35S-methionine into the lumbar spinal cord 7 days before the test crush. The wave of pulse-labeled SCb proteins reached the crush by the time it was made and subsequently entered sprouts. The nerve was removed and sectioned for SDS-PAGE and fluorography 4-12 days after the crush. Tubulins, neurofilament proteins, and representative "cytomatrix" proteins (actin, calmodulin, and putative microtubule-associated proteins) were removed from gels for liquid scintillation counting. Labeled SCb proteins entered sprouts without first accumulating in parent axon stumps, presumably because sprouts begin to grow within hours after axotomy. The peak of SCb moved 11% faster in conditioned than in sham-conditioned sprouts: 3.0 vs. 2.7 mm/d (p less than 0.05). To confirm that sprouts elongate more rapidly when a test crush is preceded by a conditioning crush, outgrowth distances were measured in a separate group of rats by labeling fast axonal transport with 3H-proline 24 hours before nerve retrieval.(ABSTRACT TRUNCATED AT 250 WORDS)

Age differences in morphology of reinnervation of partially denervated mouse muscle

The effect of age on the ability of motor neurons to develop and maintain an enlarged total axonal and synaptic volume was compared in soleus muscles of 5-8-month and 25-30-month mice, 30-120 d after partial denervation. Before and after partial denervation (transection of the L5 root), the total number of muscle fibers was the same in all muscles. However, in young animals, there was only some transient atrophy and hypertrophy mostly receded by 120 d, whereas in old muscle, a more prominent early atrophy was followed by persistent hypertrophy. Ectopic endplates were not found. In zinc-iodide-osmium (ZIO) stained preparations, muscle fibers with small nerve terminals were present at 60 d and were still present in old muscle at 120 d. Fluorescent staining of nerve terminals and acetylcholine receptors revealed that in young muscle, postsynaptic sites were nearly or completely reoccupied by 60 d. In old muscle, about 22% of former junctions were denervated, with the remainder minimally to fully reinnervated. At 60 d and thereafter, collateral sprouts originated from nodes of Ranvier in both young and old muscle and were remyelinated in young but mainly unmyelinated and remarkably tortuous in old animals. These results, confirmed with immunofluorescent strains for myelin basic protein and neurofilaments, account for many of the physiological findings (Jacob and Robbins, 1990). Motor unit size expanded 2.5 times in young and 2 times in old muscle at 60 d after partial denervation. However, the increment in total quantal output and nerve terminal volume per motor neuron was 60-100% greater than control in young but only 20-25% greater in old muscle, with little further recovery. This inability of the motor neuron in old mice to expand the field of innervation may reflect a limitation imposed by reduced axonal transport. The present findings may elucidate the muscle weakness in postpolio syndrome and amyotrophic lateral sclerosis.

Differential effects of age on neuromuscular transmission in partially denervated mouse muscle

The response of the neuromuscular junction to expansion of the motor unit after partial denervation (section of L5 root) was compared in soleus muscles from young (5-8 month) and old (25-30 month) mice. The object was to determine the relative capacity of young and old motor neurons to adapt to an enlarged functional field of innervation, and to delineate physiological parameters that are compromised under these conditions. Neuromuscular function was studied at 30, 60, and 120 d after partial denervation. The initial (18-23) and postoperative number (5-8) of motor units was the same in both age groups. Twitch strength declined in proportion to loss of motor units at 30 d but returned completely (young) or nearly completely (old) by 60 d. In old but not young muscle, the safety factor (assayed by twitch depression in low calcium) was decreased even before functional sprouting had occurred, indicating a reduced safety factor in nondenervated junctions. The proportion of fibers with "long" latencies (delay between stimulation and endplate potential) increased transiently (at 30 d) in young muscle but persisted without recovery at 120 d in regenerated junctions in old muscle. After partial denervation, decline in miniature endplate potential (mepp) amplitude, in mepp frequency, and in estimated quantal content of evoked release was relatively more pronounced in old than in young mice, and in the case of mepp amplitude and frequency, more persistent. Mepp amplitude was also decreased in presumed nondenervated junctions of old muscles.(ABSTRACT TRUNCATED AT 250 WORDS)