Histomorphology of rabbit thigh muscles: establishment of standard control values

Autonomic Nerve Fibers Aberrantly Reinnervate Denervated Facial Muscles and Alter Muscle Fiber Population

The surgical redirection of efferent neural input to a denervated muscle via a nerve transfer can reestablish neuromuscular control after nerve injuries. The role of autonomic nerve fibers during the process of muscular reinnervation remains largely unknown. Here, we investigated the neurobiological mechanisms behind the spontaneous functional recovery of denervated facial muscles in male rodents. Recovered facial muscles demonstrated an abundance of cholinergic axonal endings establishing functional neuromuscular junctions. The parasympathetic source of the neuronal input was confirmed to be in the pterygopalatine ganglion. Furthermore, the autonomically reinnervated facial muscles underwent a muscle fiber change to a purely intermediate muscle fiber population myosin heavy chain type IIa. Finally, electrophysiological tests revealed that the postganglionic parasympathetic fibers travel to the facial muscles via the sensory infraorbital nerve. Our findings demonstrated expanded neuromuscular plasticity of denervated striated muscles enabling functional recovery via alien autonomic fibers. These findings may further explain the underlying mechanisms of sensory protection implemented to prevent atrophy of a denervated muscle.SIGNIFICANCE STATEMENT Nerve injuries represent significant morbidity and disability for patients. Rewiring motor nerve fibers to other target muscles has shown to be a successful approach in the restoration of motor function. This demonstrates the remarkable capacity of the CNS to adapt to the needs of the neuromuscular system. Yet, the capability of skeletal muscles being reinnervated by nonmotor axons remains largely unknown. Here, we show that under deprivation of original efferent input, the neuromuscular system can undergo functional and morphologic remodeling via autonomic nerve fibers. This may explain neurobiological mechanisms of the sensory protection phenomenon, which is because of parasympathetic reinnervation.

Histomorphological and functional contralateral symmetry in the gastrocnemius muscles of the laboratory rat

It is usual in anatomical and physiological research to assess the effects of some intervention on extremities (e.g., training programmes or injury recovery protocols) using one muscle for the intervention and its contralateral as control. However, the existence of laterality (left‐handedness or right‐handedness) in athletes of different specialities is widely recognized. In rats, gastrocnemius is one of the muscles most widely used because of its importance in locomotion and high relative limb mass. Since we have not found studies reporting laterality assessment on the morphology and function in rat gastrocnemius, our study aimed to evaluate the fibre histochemical, morphometrical and muscle force contractile properties between right and left gastrocnemius of the laboratory rat. Fibre‐type proportion, fibre morphometrical measurements, muscle capillarization and muscle force properties were analysed in the right and left gastrocnemius of six male rats. No statistically significant differences (p = 0.265) were found in gastrocnemius to body weight ratio (‰) between right (6.55 ± 0.40) and left (6.49 ± 0.40) muscles. The muscles analysed showed a great degree of heterogeneity in fibre type distribution, having three clearly distinguished regions named red, mixed and white. In the three regions, there were no statistical differences in fibre type proportions between right and left gastrocnemius, as is indicated by the p‐values (from 0.203 to 0.941) obtained after running t‐Student paired tests for each fibre type. When analysing fibre cross‐sectional area, individual fibre capillarization and fibre circularity, no significant differences between right and left gastrocnemius in any of these morphometrical parameters were found in any muscle region or fibre type. Most of the p‐values (70%) resulting from running t‐Student paired tests were higher than 0.400, and the lowest p‐value was 0.115. Seemingly, global capillary and fibre densities were not statistically different between right and left sides in all muscle regions with p‐values ranging from 0.337 to 0.812. Force parameters normalized to gastrocnemius mass (mN g⁻¹) did not show any significant difference between right (PF = 74.0 ± 13.4, TF = 219.4 ± 13.0) and left (PF = 70.9 ± 10.7, TF = 213.0 ± 18.0) muscles with p = 0.623 (PF) and p = 0.514 (TF). Twitch time parameters (ms) also lacked significant differences between the two sides (CT: 43.4 ± 8.6 vs. 45.0 ± 14.3, p = 0.639; HRT: 77.6 ± 15.0 vs. 82.3 ± 25.3, p = 0.475). Finally, both muscles also showed similar (p = 0.718) fatigue properties. We did find an absence of laterality at the morphological and functional levels, which raises the possibility of using right and left gastrocnemius muscles interchangeably for experimental designs where one muscle is used to analyse data after a physiological intervention and its contralateral muscle plays the control role, thus allowing unbiased paired comparisons to derive accurate conclusions.

Fiber Composition of the Grasscutter (Thryonomys swinderianus, Temminck 1827) Thigh Muscle: An Enzyme-histochemical Study

The aim of this study was to describe de fiber composition in the thigh muscles of grass cutter (Thryonomys swinderianus, Temminck 1827). Ten 4 to 6-month-old (3 to 4 kg) male grasscutter were used in this study. Eleven skeletal muscles of the thigh [M. biceps femoris (BF), M. rectus femoris (RF), M. vastus lateralis (VL), M. vastus medialis (VM), M. tensor fasciae latae (TFL), M. semitendinosus (ST), M. semimembranosus (SM), M. semimembranosus accessorius (SMA), M. Sartorius (SRT), M. pectineus (PCT), M. adductor magnus (AM)] were collected after animals euthanasia and examined by light microscopy. Three muscle fiber types (I, IIB and IIA) were found in these muscles using enzyme histochemical techniques [myosine adenosine triphosphatase (ATPase) and nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR)]. Ten of these eleven muscles are composed by 89% to 100% of fast contracting fibers (types IIA and IIB), while the SMA was almost exclusively formed by slow contracting fibers.

Changes in contractile properties of muscles receiving repeat injections of botulinum toxin (Botox)

Botulinum toxin type A (BTX-A) is a frequently used therapeutic tool to denervate muscles in the treatment of neuromuscular disorders. Although considered safe by the US Food and Drug Administration, BTX-A can produce adverse effects in target and non-target muscles. With an increased use of BTX-A for neuromuscular disorders, the effects of repeat injections of BTX-A on strength, muscle mass and structure need to be known. Therefore, the purpose of this study was to investigate the changes in strength, muscle mass and contractile material in New Zealand White (NZW) rabbits. Twenty NZW rabbits were divided into 4 groups: control and 1, 3 and 6 months of unilateral, repeat injections of BTX-A into the quadriceps femoris. Outcome measures included knee extensor torque, muscle mass and the percentage of contractile material in the quadriceps muscles of the target and non-injected contralateral hindlimbs. Strength in the injected muscles was reduced by 88%, 89% and 95% in the 1, 3 and 6 months BTX-A injected hindlimbs compared to controls. Muscle mass was reduced by 50%, 42% and 31% for the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM), respectively, at 1 month, by 68%, 51% and 50% at 3 months and by 76%, 44% and 13% at 6 months. The percentage of contractile material was reduced for the 3 and 6 months animals to 80-64%, respectively, and was replaced primarily by fat. Similar, but less pronounced results were also observed for the quadriceps muscles of the contralateral hindlimbs, suggesting that repeat BTX-A injections cause muscle atrophy and loss of contractile tissue in target muscles and also in non-target muscles that are far removed from the injection site.

Pain following the repair of an abdominal hernia

Pain and other types of discomfort are frequent symptoms following the repair of an abdominal hernia. After 1 year, the incidence of light to moderate pain following inguinal hernia repair is as high as 10% and 2% for severe disabling chronic pain. Postoperative chronic pain not only affects the individual patient, but may also have a great impact on relatives and society, and may be a cause of concern for the responsible surgeon. This paper provides an overview of the anatomy, surgical procedures, and disposing factors (age, gender, ethnicity, genotype, previous hernia repair, pain prior to surgery, psychosocial characteristics, and surgical procedures) related to the postoperative pain conditions. Furthermore, the mechanisms for both acute and chronic pain are presented. We focus on inguinal hernia repair, which is the most frequent type of abdominal hernia surgery that leads to chronic pain. Finally, the paper provides an update on the diagnostic and treatment routines for postoperative pain.

Anatomy and histochemistry of hindlimb flight posture in birds. I. The extended hindlimb posture of shorebirds

Birds utilize one of two hindlimb postures during flight: an extended posture (with the hip and knee joints flexed, while the ankle joint is extended caudally) or a flexed posture (with the hip, knee, and ankle joints flexed beneath the body). American Avocets (Recurvirostra americana) and Black-necked Stilts (Himantopus mexicanus) extend their legs caudally during flight and support them for extended periods. Slow tonic and slow twitch muscle fibers are typically found in muscles functioning in postural support due to the fatigue resistance of these fibers. We hypothesized that a set of small muscles composed of high percentages of slow fibers and thus dedicated to postural support would function in securing the legs in the extended posture during flight. This study examined the anatomy and histochemical profile of eleven hindlimb muscles to gain insight into their functional roles during flight. Contrary to our hypothesis, all muscles possessed both fast twitch and slow twitch or slow tonic fibers. We believe this finding is due to the versatility of dynamic and postural functions the leg muscles must facilitate, including standing, walking, running, swimming, and hindlimb support during flight. Whether birds use an extended or flexed hindlimb flight posture may be related to the aerodynamic effect of leg position or may reflect evolutionary history.

Isoform diversity of giant proteins in relation to passive and active contractile properties of rabbit skeletal muscles

The active and passive contractile performance of skeletal muscle fibers largely depends on the myosin heavy chain (MHC) isoform and the stiffness of the titin spring, respectively. Open questions concern the relationship between titin-based stiffness and active contractile parameters, and titin's importance for total passive muscle stiffness. Here, a large set of adult rabbit muscles (n = 37) was studied for titin size diversity, passive mechanical properties, and possible correlations with the fiber/MHC composition. Titin isoform analyses showed sizes between ∼3300 and 3700 kD; 31 muscles contained a single isoform, six muscles coexpressed two isoforms, including the psoas, where individual fibers expressed similar isoform ratios of 30:70 (3.4:3.3 MD). Gel electrophoresis and Western blotting of two other giant muscle proteins, nebulin and obscurin, demonstrated muscle type–dependent size differences of ≤70 kD. Single fiber and single myofibril mechanics performed on a subset of muscles showed inverse relationships between titin size and titin-borne tension. Force measurements on muscle strips suggested that titin-based stiffness is not correlated with total passive stiffness, which is largely determined also by extramyofibrillar structures, particularly collagen. Some muscles have low titin-based stiffness but high total passive stiffness, whereas the opposite is true for other muscles. Plots of titin size versus percentage of fiber type or MHC isoform (I-IIB-IIA-IID) determined by myofibrillar ATPase staining and gel electrophoresis revealed modest correlations with the type I fiber and MHC-I proportions. No relationships were found with the proportions of the different type II fiber/MHC-II subtypes. Titin-based stiffness decreased with the slow fiber/MHC percentage, whereas neither extramyofibrillar nor total passive stiffness depended on the fiber/MHC composition. In conclusion, a low correlation exists between the active and passive mechanical properties of skeletal muscle fibers. Slow muscles usually express long titin(s), predominantly fast muscles can express either short or long titin(s), giving rise to low titin-based stiffness in slow muscles and highly variable stiffness in fast muscles. Titin contributes substantially to total passive stiffness, but this contribution varies greatly among muscles.

The influence of timing on the functional and morphological result after nerve grafting: an experimental study in rabbits

Clinical experience and experimental work in sheep have shown that a two-stage approach to restoring muscle function with a long nerve graft and free muscle grafting seems to be more beneficial than a one-stage approach. Based on a standardised experimental protocol, one-stage and two-stage nerve grafting approaches in rabbits were compared, and the actual differences in muscle force, together with morphological data, were calculated. In 20 rabbits the saphenous nerve was used as a 7 cm nerve graft. Animals were separated into two groups. In group 1, 10 rabbits underwent a one-stage approach to reinnervate the rectus femoris muscle. In the left hindlimb, the proximal end of the graft was coapted to the cut motor nerve branch of the vastus medialis muscle, and the distal end was coapted to the nerve branch of the rectus femoris muscle. In group 2, 10 rabbits underwent a two-stage approach, leaving the distal end of the nerve graft unconnected to the rectus femoris muscle in the first stage. In the second stage, this end was coapted to the freshly cut motor nerve branch of the rectus femoris muscle. After 15 months, the maximum tetanic tensions in the reinnervated rectus femoris muscle and the contralateral unoperated muscle were determined. The graft and the motor branch distal to the graft were biopsied in order to count the number of regenerated myelinated nerve fibres. The mean+/-s.d. maximum tetanic tensions in the reinnervated rectus femoris muscles were 10.6+/-4.9 N in group 1 and 21.4+/-1.1 N in group 2. Compared with the unoperated side, the muscle force following denervation and reinnervation was 38.3% in group 1 and 58.9% in group 2 (P=0.01). The mean+/-s.d. numbers of regenerated myelinated nerve fibres distal to the graft in the rectus femoris muscle branch were 737+/-340 in group 1 and 1487+/-1004 in group 2 (P=0.05). These results show that the neurotrophic effect of an immediately connected target organ is far outweighed by the adverse effect of the longer period of muscle denervation. Therefore, nerve grafting and muscle transplantation should not be performed in the same operation.