Exploring heart dissection techniques for enhancing anatomical education: a pilot study to replicate transthoracic echocardiography

PURPOSE

For novice learners, converting two-dimensional (2D) images of echocardiography to three-dimensional (3D) cardiac structures is deemed challenging. This study aimed to develop an accurate dissection method of the heart to reproduce the transthoracic echocardiographic views on cadavers and elucidate new educational methods in human anatomy dissection courses.

METHODS

A total of 18 hearts were used in this study. After reflecting the anterior thoracic wall inferiorly, the hearts were excised from embalmed cadavers. Thereafter, three landmarks were set on the heart for each plane of the incision, and the hearts were incised to observe the three different echocardiographic views, which include the apical four-chamber view (A4C), parasternal long axis (PLAX) view, and parasternal short axis (PSAX) view at the papillary muscle level. If all structures for observation during routine echocardiography are clearly observed in each view, a successful incision is considered. All procedures and incisions were performed by the medical students. After a successful incision, hearts were returned to the original position in the pericardial sac for further observation.

RESULTS

The success rates of incision for each view were 83.3% (5/6 success cases), 83.3% (5/6 success cases), and 66.7% (4/6 success cases) in the A4C view, PLAX view, and PSAX view at the papillary muscle level, respectively.

CONCLUSION

This dissection method could probably be employed to reproduce transthoracic echocardiographic views on cadaveric hearts, which is beneficial for novice learners for a deeper understanding of the anatomy.

Anatomical analysis of ligaments surrounding calcaneocuboid joint; implications for role in foot stability

PURPOSE

The calcaneocuboid joint is located in the lateral part of the foot and acts as a major stabilizer for the foot. Injuries to this joint often occur in association with ankle or foot injuries and are frequently overlooked, subsequently causing chronic pain or osteoarthritis. However, the relationship between ligaments surrounding the joint and joint instability remains unclear. Therefore, this study aimed to clarify the morphology and position of the ligaments surrounding the calcaneocuboid joint, and to reveal the relationship between the ligament structure.

METHODS

The position and morphology of the bifurcate ligament (subdivided into calcaneonavicular and calcaneocuboid ligaments), dorsal calcaneocuboid ligament, lateral calcaneocuboid ligament, long plantar ligament, and short plantar ligament were measured (N = 11 feet in 6 Japanese cadavers). The circumference of the joint was quartered, while the ligament-uncovered area and the estimated cross-sectional area of each ligament were compared between the four sides. Furthermore, the estimated cross-sectional area of each ligament was calculated as an index for the ligament strength.

RESULTS

The inferolateral side of the calcaneocuboid joint had the most uncovered area (54.63%) by the ligaments. In addition, the cross-sectional area of the ligaments on the lateral side was considerably smaller than that on the medial side.

CONCLUSION

Our results suggest that ligament weakness on the inferolateral side may cause instability of the calcaneocuboid joint, especially after an inversion sprain injury, and may decrease the lateral longitudinal arch function, which results in chronic foot pain.

Transforming Growth Factor α Evokes Aromatase Expression in Gastric Parietal Cells during Rat Postnatal Development

Estrogen, well known as a female hormone, is synthesized primarily by ovarian aromatase. However, extra-glandular tissues also express aromatase and produce estrogen. It is noteworthy that aromatase in gastric parietal cells begins expression around 20 days after birth and continues secreting considerable amounts of estrogen into the portal vein throughout life, supplying it to the liver. Estrogen, which is secreted from the stomach, is speculated to play a monitoring role in blood triglyceride, and its importance is expected to increase. Nevertheless, the regulatory mechanisms of the aromatase expression remain unclear. This study investigated the influence of transforming growth factor α (TGFα) on gastric aromatase expression during postnatal development. The administration of TGFα (50 μg/kg BW) to male Wistar rats in the weaning period resulted in enhanced aromatase expression and increased phosphorylated ERK1+2 in the gastric mucosa. By contrast, administration of AG1478 (5 mg/kg BW), a protein tyrosine kinase inhibitor with high selectivity for the epidermal growth factor receptor and acting as an antagonist of TGFα, led to the suppression of aromatase expression. In fact, TGFα expression in the gastric fundic gland isthmus began around 20 days after birth in normal rats as did that of aromatase, which indicates that TGFα might induce the expression of aromatase in the parietal cells concomitantly.

A novel categorization of the muscular branches of the tibial nerve within the popliteal fossa

BACKGROUND

The muscular branches of the tibial nerve within the popliteal fossa innervate the gastrocnemius, soleus, plantaris, and popliteus muscles. Various branching patterns have been described in textbooks; however, the underlying fundamental rules explaining the patterns remain unclear. Understanding the fundamental rule explaining the branching pattern of the innervating nerves is essential for understanding the ontogeny of skeletal muscles. Therefore, this study aimed at establishing a theory to explain the branching pattern of the muscular branches of the tibial nerve within the popliteal fossa.

METHODS

The branching patterns of the muscular branches of the tibial nerve within the popliteal fossa were examined macroscopically in 62 lower limbs derived from 31 adult cadavers (22 males and 9 females, aged 49-95 years).

RESULTS

The branch to the medial head of the gastrocnemius muscle invariably arose from the posteromedial side of the tibial nerve. The branches to the soleus muscle and lateral head of the gastrocnemius muscle had a common trunk in all the lower limbs and invariably arose from the posterolateral side. The branches to the plantaris and popliteus muscles arose anteriorly from the tibial nerve in this order (plantaris branch first, followed by the popliteus branch). These branches invariably arose more distally than the branch to both the heads of the gastrocnemius and soleus muscles.

CONCLUSIONS

Based on these fundamental branching patterns, we suggest a novel branching categorization. The branches could be categorized into a posterior group and an anterior group, which has independent branches to the plantaris and popliteus muscles. This fundamental branching pattern and novel categorization contribute to the understanding of the ontogeny of the skeletal muscles around the flexor compartment of the leg.

A bilateral third head of the gastrocnemius which is morphologically similar to the plantaris

PURPOSE

An extra muscle was observed on both sides of the popliteal fossa in the cadaver of a 78-year-old Japanese male during dissection. The aim of this case report was to identify whether this variant is a double plantaris or a third head of the gastrocnemius according to its morphological characteristics and innervation.

METHODS

The muscles were displayed by careful dissection and delineation of surrounding structures. The size of each of the muscle bellies and tendons of those extra muscles were measured manually by the vernier caliper.

RESULTS

The origin of each extra muscle was lateral to the tibial nerve and superior to the plantaris, and each extra muscle which transitioned to a descending tendon parallel to the plantaris had a cone-shaped belly. However, the tendon of the extra muscles was fused into the investing fascia of the gastrocnemius with a tendon length of 4.5 cm on the left and 4.6 cm on the right. The extra muscles were innervated by the branch of the tibial nerve to the medial head of the gastrocnemius on both sides.

CONCLUSION

Although they had an origin and shape similar to that of the plantaris, we identified the extra muscles in this case as a third head of the gastrocnemius, because of innervation to the plantaris arises directly from the tibial nerve. This case highlighted that the innervation is essential to understanding the myogenesis of extra muscles, especially in cases which are difficult to categorize based on the morphological features of the muscle.

Effects of various lengths of hypoglossal nerve resection on motoneuron survival

We employed stereological analyses for whole quantification of hypoglossal (XII) motoneurons in adult rats that received varying degrees of resection of the XII nerve. Various lengths of nerve gaps (0.0-13.3 mm) were made at the main trunk of the unilateral XII nerve, and the total number of XII neurons on the injured and uninjured sides was counted 12 weeks after nerve resection. The stereologically estimated total number of XII neurons decreased after various lengths of nerve resection, and survival rates ranged from 34.4% to 87.1%. Statistically significant negative correlations were observed between increasing length of the resected nerve and decreasing XII neuron survival. It was concluded that the total number of XII neurons decreased after nerve resection and that survival rates of XII neurons were related to distances between resected nerve stamps.

Acetyl-l-carnitine enhances myelination of regenerated fibers of the lateral olfactory tract

It is well known that acetyl-l-carnitine (ALC) has various neuroprotective effects against neurodegenerative diseases. In addition, it has been reported that ALC facilitates myelination of regenerated axons after peripheral nerve injuries. We previously reported that spontaneous regeneration of the lateral olfactory tract (LOT), the main fiber tract of the central olfactory system, consistently occurred in newborn rats and a majority of these regenerated fibers were unmyelinated in neonatally LOT-transected young adult rats. To investigate the effects of ALC treatment on myelination in LOT, neonatal rats were treated with ALC after LOT transection. Immunohistochemistry for myelin basic protein showed more positive areas in ALC-treated rats than in control rats. Moreover, the number of myelinated axons of regenerated fibers was assessed using electron microscopy and was found to be statistically higher in ALC-treated rats compared to control rats. The study revealed that ALC accelerates myelination of regenerated fibers in neonatally LOT-injured young adult rats.

Stereological assessment of the total number of hypoglossal neurons after repeated crush injuries to the hypoglossal nerve in adult rats

OBJECTIVE

Retrograde neuronal cell death does not occur in mature motoneurons following the axonal injury of peripheral nerves. However, a previous study suggested that retrograde neuronal cell death does occur in adult rats after the creation of double lesions on the hypoglossal (XII) nerve based on a substantial decrease in the number of XII neurons. Using stereological methods, we examined neuronal apoptosis in XII neurons and the total number of XII neurons following repeated crush injuries to the XII nerve.

METHODS

The right XII nerve of adult rats was crushed three times at one-week intervals with a brain aneurysm clip. At 4 weeks after the final crush, the total numbers of XII neurons on the injured right and uninjured left sides were estimated stereologically.

RESULTS

After repeated crush injuries, no apoptosis was evident in XII neurons as indicated by immunostaining for cleaved caspase-3. Moreover, immunohistochemistry for the vesicular acetylcholine transporter revealed axonal elongation in the tongue 4 weeks after repeated crush injuries. At 4 weeks, the total numbers of XII neurons were 7800 ± 290 on the injured right side and 8000 ± 230 on the uninjured left side, and no significant difference was evident between the injured and uninjured sides.

CONCLUSION

Neuronal cell death does not occur in XII neurons and the total number of XII neurons does not decrease after repeated crush injuries of the XII nerve in adult rats.

Morphological analysis of regenerated bulbar fibers in relation to neonatal olfaction

It was revealed that regeneration of the lateral olfactory tract (LOT) occurred in developing rats and the regenerated olfactory system was functional 4 weeks after transection. The aim of this study was to determine the earliest onset of functional recovery in LOT-injured rats and to quantify regenerated nerve components with functional correlation. Neonatal rats on postnatal day (P) 2 were subjected to unilateral transection of the left LOT and underwent unilateral removal of the right olfactory bulb on P11. Functional recovery of the tract injury was assessed by the suckling capability, which can be achieved by olfaction. Suckling capability was observed on P12 in most neonatally LOT-transected pups. Rat pups were subjected to unilateral transection of the left LOT on P2, and received injections of biotinylated dextran amine (BDA) into the bilateral olfactory bulb on P5 to quantify normal and regenerated nerve components in the olfactory cortices at the level of the olfactory tubercle. BDA(+) areas and density indices of the olfactory cortices in the neonatally LOT-transected P12 pups were 11.05×10⁵μm² and 0.35 on the normal right side and 4.34×10⁵μm² and 0.21 on the transected left side. We concluded that functional recovery of the LOT-transected neonatal rats occurred as early as 10days after tract transection and that areas and densities of regenerated nerve components essential for functional recovery were approximately 40% and 60% of the age-matched normal values in the olfactory cortices at the level of the olfactory tubercle.

Neuregulin Receptor ErbB2 Localization at T-tubule in Cardiac and Skeletal Muscle

Previous studies have indicated that ErbB receptors for neuregulins play an important role in cardiac development and muscle spindle formation during embryogenesis; however, little is known about their functions in adulthood. Recent reports indicate that breast cancer therapy with humanized monoclonal ErbB2 antibody induces cardiomyopathy, suggesting that ErbB2 serves as a crucial signaling receptor, even in the adult heart. Here, we examine ErbB2 expression and localization in both cardiac and skeletal muscle of adult mice via immunoblot and immunohistochemistry. ErbB2 was detected as a band ~185 kD molecular mass in each cardiac and skeletal muscle extraction. Confocal images of double labeling showed that ErbB2 was colocalized with caveolin-3 in cardiac muscle and with dihydropyridine receptor in skeletal muscle, suggesting that ErbB2 was localized at the T-tubule. In addition, immunoelectron micrographs clearly demonstrated that ErbB2 was located at the T-tubule in both types of muscle. Taken together, the results of the present study suggest that neuregulin-ErbB2 signaling plays a role in the physiological function of cardiac and skeletal muscle, even in adulthood.

Effect of graded nerve pressure injuries on motor function

OBJECT

The purpose of this study was to determine the minimum amount of nerve fibers required to maintain normal motor function after nerve injury in rats.

METHODS

The authors first confirmed that a common peroneal nerve injury caused more aggravating effects on lower limb motor function than tibial nerve injury, as assessed by the static sciatic index (SSI). Thereafter, rats were subjected to varying degrees of crush injury to the common peroneal nerve. At 48 hours after the injury, motor function was assessed using the SSI and slope-walking ability (with slope angles of 30° and 45°). The tibialis anterior muscle, a main muscle innervated by the common peroneal nerve, was removed. Muscle sections were co-labeled with neuronal class III β-tubulin polyclonal antibody to identify the presence of axons and Alexa Fluor 488-conjugated α-bungarotoxin to identify the presence of motor endplates.

RESULTS

The evaluation of neuromuscular innervation showed a correlation between SSI scores and ratios of residual axons (rs = 0.68, p < 0.01), and there was a statistically significant difference between slope-walking ability and ratios of residual axons (p < 0.01). Moreover, the ratios of residual axons in the nerve-crushed rats with normal motor function (SSI above -20) ranged from 36.5% to 88.7%, and those ratios in the success group with slope-walking angles of 30° and 45° ranged from 14.7% to 88.7% and from 39.8% to 88.7%, respectively.

CONCLUSIONS

In this study of rodents, less than half of the motor axons were sufficient to maintain normal motor function of the lower limb.

Two specific tongue regions receive bilateral hypoglossal innervation: a study in neonatal rat pups

OBJECTIVE

The purpose of this study was to investigate the functional role of bilateral hypoglossal (XII) nerve innervation of the tongue.

MATERIALS AND METHODS

The possibility of bilateral innervation of XII nerve in the tongue was examined using postmortem fibre tracing in normal neonatal rats. In addition, immunohistochemical testing for synaptophysin or vesicular acetylcholine transporter (VAChT) was carried out in unilaterally XII nerve-resected neonatal rats.

RESULTS

Postmortem fibre tracing revealed constant distribution of the nerve fibres extending across the midline and existence of bilateral innervated area in the rostroventral and caudodorsal regions of the tongue. Synaptophysin-positive and VAChT-positive nerve terminals were also distributed continuously from the XII nerve-intact to the nerve-resected side across the midline of the tongue. The contralaterally projecting VAChT-positive nerve terminals were more numerous in suckling P2 rats (6.6 ± 0.5/section) than those in non-suckling P2 rats (4.9 ± 0.3/section) 24 h after nerve resection. Furthermore, the contralaterally projecting VAChT-positive nerve terminals were more numerous in P7 rats with nerve resection on P1 (6.3 ± 0.2/section) than those in P7 rats with nerve resection on P6 (3.1 ± 0.8/section).

CONCLUSION

We concluded that neonatal rats have two specific tongue regions receiving bilateral XII innervation, which allowed suckling in unilaterally XII nerve-resected neonatal rats.

Stereological estimation of olfactory receptor neurons in rats

The total number of olfactory receptor neurons (ORNs) in the rat main olfactory epithelium (MOE) was estimated using stereological sampling. Skulls and noses of newborn (postnatal day 0), young adult (8 weeks), and adult (6 months) rats were decalcified, embedded in paraffin, cut into 10-μm thick sections serially at 100-μm intervals, and processed for immunohistochemistry for olfactory marker protein (OMP), a specific marker of mature ORNs with fiber connections to the olfactory bulb. The number of OMP (+) receptor neurons was measured using an optical fractionator with stereological software (Stereoinvestigator). The total number of OMP (+) receptor neurons in the unilateral MOE was 0.47 × 10(6) in newborns and 21 × 10(6) in young adults and adults. Our previous study showed that the corresponding unilateral total number of neurons was 5.2 × 10(6) in young adult mice. Accordingly, we concluded that rats had 4 times more OMP (+) receptor neurons than mice at the adult stage and that the number of these neurons increased approximately 45 times between birth and maturity.

Stereological quantification of olfactory receptor neurons in mice

The total number of olfactory receptor neurons (ORNs) in the mouse main olfactory epithelium (MOE) was estimated using stereological sampling. Noses and skulls of male and female 8-week-old C57BL/6J mice were de-calcified, embedded in paraffin, cut into 10-μm-thick sections serially at 100-μm intervals, and processed for immunohistochemistry for the olfactory marker protein (OMP), a specific marker for ORNs. The number of OMP (+) receptor neurons was measured using an optical fractionator with the Stereo-Investigator software. The mean values of the total number of OMP (+) receptor neurons in the unilateral MOE were 5,140,000±380,000 in males and 5,210,000±380,000 in females, with no significant differences between the sexes. We concluded that the total number of ORNs in the unilateral MOE is approximately 5×10(6) in mice.

Correlation between motor function and axonal morphology in neonatally sciatic nerve-injured rats

The present study was conducted to investigate the correlation between motor function and axonal morphology in neonatally sciatic nerve-injured rats. The left sciatic nerve of newborn rats was transected or crushed, and functionality of the sciatic nerve was assessed by the static sciatic index after 8 weeks. After functional assessment, the common peroneal nerves in the control, nerve-transected, and nerve-crushed rats were removed and prepared for morphometric examinations. The cross-sectional area of the nerve, total number of myelinated axons, and size of each myelinated axon were analyzed for each group. The control rats showed normal motor function, whereas the nerve-transected rats showed severe motor dysfunction. The cross-sectional area of the nerve and total number of myelinated axons were reduced after nerve transection. Moreover, the percentage per size class of myelinated axons was almost uniform in the control rats, while the distribution was shifted to the left in the nerve-transected rats. Furthermore, no large myelinated axons were observed in the nerve-transected rats. The nerve-crushed rats showed various gait functions with various distribution patterns of axonal size, and the rats were divided into two groups with and without uninjured residual large axons. The results showed that the importance of regenerated medium-sized axons in cases without large axons and of residual large axons in cases with large axons in motor function. It was revealed that motor function was related closely to axonal size in neonatally nerve-injured rats.

Quantitative analysis of survival of hypoglossal neurons in neonatally nerve-injured rats: Correlation with milk intake

INTRODUCTION

Tongue movement innervated by the hypoglossal (XII) nerve is essential for the survival of neonatal rats. The pups with bilateral XII nerve resection failed to suckle milk and did not survive, and the pups with unilateral XII nerve resection showed disturbed suckling capability and lower survival rates. The present study was performed to investigate the relation between neuronal population and milk intake of developing rats that had received various degrees of crush injuries to the unilateral XII nerve during the neonatal period.

METHODS

The right XII nerve of postnatal day 1 (P1) pups was crushed and milk intake was estimated at 3 days and 6 days after the nerve injury. As nerve injury at the neonatal stage results in death of axotomized neurons, varying degrees of crushing was estimated by the number of survived motor neurons.

RESULTS

In nerve-crushed rats, the populations of XII motor neurons and amounts of milk intake were reduced in a varied manner. Statistically significant positive correlations were observed between increasing XII neuron survival and increasing milk intake at 3 (r=0.62) and 6 (r=0.71) days after the nerve injury.

CONCLUSION

The results indicate that there is a strong relationship between the number of XII motor neurons and the amount of milk intake in neonatally XII nerve-injured rats.

Cell bodies of the trigeminal proprioceptive neurons that transmit reflex contraction of the levator muscle are located in the mesencephalic trigeminal nucleus in rats

Since the levator and frontalis muscles lack interior muscle spindles despite being antigravity mixed muscles to involuntarily sustain eyelid opening and eyebrow lifting, this study has proposed a hypothetical mechanism to compensate for this anatomical defect. The voluntary contraction of fast-twitch fibres of the levator muscle stretches the mechanoreceptors in Müller's muscle to evoke proprioception, which continuously induces reflex contraction of slow-twitch fibres of the levator and frontalis muscles. This study confirmed the presence of cell bodies of the trigeminal proprioceptive neurons that transmit reflex contraction of the levator and frontalis muscles. After confirming that severing the trigeminal proprioceptive fibres that innervate the mechanoreceptors in Müller's muscle induced ipsilateral eyelid ptosis, Fluorogold was applied as a tracer to the proximal stump of the trigeminal proprioceptive nerve in rats. Fluorogold labelled the cell bodies of the trigeminal proprioceptive neurons, not in any regions of the rat brain including the trigeminal ganglion, but in the ipsilateral mesencephalic trigeminal nucleus neighbouring the locus ceruleus. Some Fluorogold particles accumulated in the area of the locus ceruleus. The trigeminal proprioceptive neurons could be considered centrally displaced ganglion cells to transmit afferent signal from the mechanoreceptors in Müller's muscle to the mesencephalon, where they may be able to make excitatory synaptic connections with both the oculomotor neurons and the frontalis muscle motoneurons for the involuntary coordination of the eyelid and eyebrow activities, and potentially to the locus ceruleus.

Analysis of spontaneous regeneration of olfactory structures with emphasis on myelination and re-innervation of cortical areas

Regeneration of the lateral olfactory tract (LOT) occurs spontaneously after transection in developing rats. In neonatally LOT-transected rats, we observed a newly formed myelinated tract near the rhinal sulcus. The aim of this study was to analyze the precise re-innervated cortical areas and to demonstrate ectopic LOT myelination in neonatally LOT-transected rats. Neonatal rats were subjected to unilateral LOT transection and simultaneous injection of a retrograde fluorescent tracer into the posterior olfactory cortex to evaluate the degree of transection. After 8 weeks, bilateral olfactory bulbs of the rats were subjected to multiple injections of an anterograde neuronal tracer to determine the extent of the regenerated fibers. In the completely LOT-transected rats, the regenerated fibers were distributed in the anterior olfactory cortices; the anterior olfactory nucleus, the olfactory tubercle, and the rostral part of the piriform cortex. Ectopic myelination of LOT was evident immediately below the rhinal sulcus in the completely and incompletely LOT-transected rats. We concluded that the regenerated bulbar fibers were confined to the regions of the anterior olfactory cortices and that ectopic myelination of the regenerated LOT occurred only at a specific site near the rhinal sulcus.

Effects of repeated crush injuries on motor functional recovery of the sciatic nerve

OBJECTIVES

The present study was conducted to examine whether repeated crush injuries have significant effects on motor functional recovery of peripheral nerves.

METHODS

Repeated crush injuries of the sciatic nerve were inflicted on adult rats at 1-week intervals, and functionality of the sciatic nerve was assessed by the static sciatic index each week for 8 weeks after the final injury. To determine the effects of repeated crush injuries on motor functional recovery of the sciatic nerve, tibialis anterior muscle fibers from single and triple crush injuries were examined, and fiber size and fiber reinnervation during the 2- to 4-week period after the final injury were measured.

RESULTS

Compared to single crush injuries, which completely recovered by post-injury week 4, double crush injuries resulted in retarded, but complete recovery by post-injury week 6, whereas triple crush injuries resulted in marked retardation in the regenerative process with incomplete recovery during week 8 of the experimental period. Muscle fiber size for rats with triple crush did not recover to normal range at post-injury week 4, despite its normal size for rats with single crush. The rate of reinnervation increased prominently between post-injury weeks 2 and 3 in both injuries, but the rate with triple crush was lower than that with single crush at post-injury week 3.

DISCUSSION

These results, which contradict those of a previous study that reported early functional recovery, indicate that repeated crush injuries inhibit motor functional recovery of the damaged sciatic nerve, as evidenced by delayed and incomplete regeneration, atrophied muscle fibers, and delayed reinnervation.

Determination of functionally essential neuronal population of the olfactory epithelium for nipple search and subsequent suckling behavior in newborn rats

Neuronal population of the olfactory epithelium required for nipple search and subsequent suckling behavior was examined in newborn rats. After unilateral ablation of the olfactory bulb, different concentrations of ZnSO(4) were contralaterally injected into the nasal cavity to produce varying degrees of neuronal degeneration in the olfactory epithelium. The ZnSO(4)-treatment resulted in two populations of pups. One exhibited suckling while the other did not, and intact olfactory receptor neurons were quantified immunohistochemically using an antibody for olfactory marker protein (OMP), a marker protein for olfactory receptor neurons. The total numbers of the OMP (+) cells in the ZnSO(4)-treated pups with suckling capability ranged between 2457 and 4615, whereas those in the ZnSO(4)-treated pups without suckling capability ranged between 112 and 2398. With the mean value (4969) of the total numbers of the OMP (+) cells of the normal/control pups assumed to represent 100%, the total numbers of the OMP (+) cells accounted for 49-93% in the suckling (+) group and 2-48% in the suckling (-) group. From these findings, we conclude that approximately 50% of neuronal population of the olfactory epithelium is a critical value to distinguish between the two groups with and without suckling capability in the unilateral olfactory system of newborn rats.

Tyrosine hydroxylase-immunoreactive fibers in the human vagus nerve

Sympathetic catecholaminergic fibers in the vagus nerve were immunohistochemically examined in formalin-fixed human cadavers using an antibody against the noradrenalin-synthetic enzyme tyrosine hydroxylase (TH). TH-positive fibers were extensively distributed in the vagal nerve components, including the superior and inferior ganglia, the main trunk and the branches (superior and recurrent laryngeal, superior and inferior cardiac, and pulmonary branches). The inferior ganglion and its continuous cervical main trunk contained numerous TH-positive fibers with focal or diffuse distribution patterns in each nerve bundle. From these findings, we conclude that sympathetic fibers are consistently included in the human vagus nerve, a main source of parasympathetic preganglionic fibers to the cervical, thoracic and abdominal visceral organs.

Neural plasticity of neonatal hypoglossal nerve for effective suckling

The adaptive movement of the tongue after unilateral lesion of the hypoglossal (XII) nerve during the early postnatal days is essential for recovery of milk intake. The present study investigated the basic mechanisms underlying such adaptation, focusing on the neural plasticity that allows effective suckling. After resection of the ipsilateral XII nerve on P1, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlolate (DiI), a postmortem neuronal tracer, was applied to the contralateral uninjured XII nerve on P4 and P7. DiI-labeled fibers were traced successfully within the tongue and showed gradually increased extension over the XII nerve-injured side in the central core portion of the denervated tongue between P4 and P7. Systematic neuroanatomic experiments showed that contralateral axonal sprouting occurred as early as 1 day after nerve injury (P2), and that such axonal sprouting occurred exclusively from the medial branch of the XII nerve responsible for tongue protrusion, an essential movement for suckling. These findings provide direct evidence of functional neural plasticity that allows effective suckling in XII nerve-injured newborns with suckling disturbance.

Increased stem cell proliferation in the spinal cord of adult amyotrophic lateral sclerosis transgenic mice

Harnessing the regenerative potential of the central nervous system to repopulate depleted cellular populations from endogenous stem cells would be a novel approach for the treatment of neurological diseases resulting from cell death. Consequently, understanding if and how the central nervous system is capable of such regeneration would determine if such an approach is feasible. In this report, we provide evidence of widespread regenerative response in the spinal cord of amyotrophic lateral sclerosis transgenic mice. However, this regenerative response appears to be largely unproductive. We demonstrate that there is significantly increased gliogenesis, but an absence of convincing neurogenesis. The fact that the neurodegenerative process stimulates a regenerative response suggests that the adult spinal cord has at least limited ability for regeneration. Further studies will determine if this endogenous regenerative process can be enhanced and directed so as to slow or even reverse the natural progression of this devastating disease.

Functional role of lingual nerve in breastfeeding

Functional role of lingual nerve in breastfeeding was investigated in rat pups during the suckling period. DiI, a postmortem neuronal tracer, was used to confirm the immature lingual nerve (LN) responsible for tongue sensation and resulted in successful fiber labeling anterogradely to the tongue, which showed different distribution patterns from fiber labeling derived from the hypoglossal nerve. Unilaterally LN-injured pups did not show suckling disturbance with absence of any shortening (P11 pups: 559+/-16s; 105% of the control value) in nipple attachment time and the survival rate remained high (P11: 100%). Bilaterally LN-injured pups showed suckling disturbance with marked shortening (P11 pups: 220+/-54 s; 42% of the control value) in nipple attachment time and a low survival rate (P1: 33%; P11: 41%). Bilaterally infraorbital nerve-injured or bilaterally bulbectomized pups did not show any nipple attachment at all and there were no survivors, confirming the crucial roles of upper lip sensation and olfaction in suckling. Based on these findings, we conclude that tongue sensation is very important, but not essential for suckling.

Description and First Clinical Application of AirWay Scope for Tracheal Intubation

We have developed a novel airway apparatus, AirWay Scope, which we have used in the orotracheal intubation of 10 consecutive patients requiring general anesthesia before neurosurgical procedures. The characteristic shape of the introducer (INTLOCK), the tube guiding function and the sighting device of the AirWay Scope has possibility to facilitate tracheal intubation. Here, we report the first clinical application of this system and describe potential advantages of the apparatus.

Differential effects of hypoglossal and facial nerve injuries on survival and growth of rats at different developmental stages

The hypoglossal (XII) nerve is made up of functionally different nerve branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. The present study was performed to determine the effects of facial (VII) and XII nerve injuries on the survival and growth of rats in which the unilateral or bilateral VII and XII nerve components (main trunk, XII-trunk; medial branch, XII-med; lateral branch, XII-lat) had been resected at different developmental stages. In the suckling period, unilateral as well as bilateral injuries in the XII-trunk or XII-med nerve produced disturbed milk intake, lower survival rates and growth retardation in the nerve-injured rats. In the transition and mastication periods, only bilateral injury in the XII-trunk or XII-med nerve produced disturbed food intake followed by lower survival rates and growth retardation in those animals. The unilateral XII-lat nerve injury did not have significant effects on milk and food intake, whereas the bilateral injury caused disturbance in milk intake especially at the early neonatal stage. The unilateral VII nerve injury at the early neonatal stage caused deteriorating effects on food intake resulting in lower survival rate and severe growth retardation in the nerve-injured rats. The results indicate that the survival and growth of XII and VII nerve-resected rats differ considerably depending on the nerves injured and the developmental ages of the animals at the time of nerve insult.

Effects of hypoglossal and facial nerve injuries on milk-suckling

Functional roles of the perioral anatomical structures involved in breastfeeding were examined in newborn rat pups in which the hypoglossal (XII) and facial (VII) nerves had been resected at the neonatal stage. The XII nerve controls tongue movement and is comprised of two functionally distinct branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. Newborn rat pups with bilateral resection of either of the XII nerve components (main trunk: XII-trunk; medial branch: XII-med; lateral branch: XII-lat) failed to suckle milk and did not survive. Unilateral XII nerve-resected neonates showed different milk-suckling capabilities, which thus resulted in differences in survival rate (XII-trunk: 38%; XII-med: 24%; XII-lat: 92%) and postnatal growth during the postnatal 3 weeks until P21. Unilateral and bilateral resections of the VII nerve innervating the buccolabial musculature produced lowered suckling capabilities and retarded postnatal growth, although all pups showed 100% survival. The results indicate a crucial role of the tongue, especially of protruding muscular elements innervated by the XII-med nerve, in breastfeeding. The results also indicate differential effects of the VII and XII nerve components on suckling capability, survival, and postnatal growth of newborn rat pups.

Effect of maternal deprivation on milk intake in normal and bilaterally facial nerve-injured developing rats

We examined effect of maternal deprivation (2, 4 and 6h) on milk intake in developing rats. Milk intake was obtained by body weight gain after 1h lactation. The amounts of milk intake significantly differed depending on the duration of the deprived periods at P7 and P14 with proportional increase by longer deprivation. Further, milk intake was measured in the bilaterally facial nerve-injured neonatal rats. The results show that milk intake is increased during development affected by maternal deprivation, and that milk intake of the facial nerve-injured group is decreased by 35% (2h), 7% (4h) and 7% (6h) at P7, and 25% (2h), 20% (4h) and 27% (6h) at P14 compared to that of the control group.

The minimum number of facial motor neurons essential for minimal whisker movement in neonatally nerve-transected young adult rats

OBJECT

This study was performed to provide quantitative data on the number of surviving facial motor neurons that extend regenerated nerve fibers through the nerve-injured site and to reveal the relationship between facial function and the number of those motor neurons in which the facial nerve has been transected or resected in neonatal rats.

METHODS

After transection of facial nerves in 1-day-old rat pups, facial function was estimated on postoperative Day 56 and a retrograde neuronal tracer was applied to the specific facial nerve branch responsible for the whisker movement. The mean number of the tracer-labeled neurons in the control rats was 2623+/-31 (mean+/-standard error of the mean) and that of the nerve-transected rats was 74+/-11 (range 0-221). Based on whisker movement, the nerve-transected rats were divided into two groups: clear spontaneous whisker movement and no whisker movement. The mean number of the tracer-labeled neurons in the nerve-transected rats with mobile whiskers was (106+/-12, range 44 [2% of the control value]-221 [8%]), whereas that in the nerve-transected rats with nonmobile whiskers was 24+/-6 (range 0-54 [2% of the control value]). The nerve-resected rats produced no labeled neurons.

CONCLUSIONS

It was concluded that axotomized neonatal facial motor neurons extended regenerated nerve fibers through the nerve-transected site with the maximum value of 8% of the control value and that minimal whisker movement was preserved with a very small population of motor neurons (2%).

Efferent and afferent innervations of Mueller's muscle related to involuntary contraction of the levator muscle: important for avoiding injury during eyelid surgery

Because stretching of Mueller's muscle induces involuntary contraction of the levator muscle, we hypothesised that Mueller's muscle functions as a serial kind of muscle spindle of the levator muscle. To confirm the presence and location of efferent and afferent innervations of Mueller's muscle, cadavers' eyelids were microscopically and macroscopically examined, and the resultant findings were physiologically confirmed in patients' eyelids during surgery. Fine neural myelinated structures acting as a mechanoreceptor were found in the proximal Mueller's muscle. Mueller's muscle is doubly innervated by the unmyelinated sympathetic efferent nerve and the myelinated trigeminal proprioceptive afferent nerve, both of which run transversely on the proximal Mueller's muscle to join the lacrimal nerve. Electrical stimulation of the transverse nerve fibres induced involuntary contraction of both the levator muscle as the Hoffmann reflex and Mueller's muscle. Surgical injury to these nerve fibres should be avoided to preserve involuntary contraction of the levator muscle.

Immunohistochemical determination of the sympathetic pathway in the orbit via the cranial nerves in humans

Object.The present study was undertaken to elucidate the extent and precise distribution of the postganglionic sympathetic fibers in the cranial nerves projecting to the orbit and to reconstruct sympathetic routes in the orbit in humans. For this purpose, the authors made an immunohistochemical determination of the sympathetic fibers by using an antibody against norepinephrine-synthetic enzyme, tyrosine hydroxylase (TH).

Methods.Specimens containing the orbit and the cavernous sinus were obtained from formalin-fixed human cadavers. First, it was confirmed that the superior cervical ganglion contained strongly immunostained TH-positive neuronal cell bodies and fibers. After careful dissection of the cranial nerves projecting to the orbit, different segments of each cranial nerve were processed for immunohistochemical analysis for TH. All of the intraorbital cranial nerves contained TH-positive sympathetic fibers, although the amounts were very different in each cranial nerve. At the proximal site of the common tendinous ring, TH-positive fibers were found mainly in the abducent and trochlear nerves. At the distal site of this ring, TH-positive fibers were lost or markedly reduced in number in the abducent and trochlear nerves and were distributed mostly in the ophthalmic and oculomotor nerves. Among the cranial nerves projecting to the orbit, the ophthalmic nerve and its bifurcated nerves—frontal, lacrimal, and nasociliary—contained numerous TH-positive fibers.

Conclusions.The authors conclude that the postganglionic sympathetic fibers are distributed to all cranial nerves projecting to the orbit and that the ophthalmic nerve provides a major sympathetic route in the orbital cavity in humans.

Effects of bilateral resection of facial nerves on suckling in developing rats

The purpose of the present study is to investigate functional role of the facial nerve on suckling in developing rats. The bilateral resection of facial nerves on postnatal day 1 (P1) resulted in cell loss of facial motoneurons and complete facial paralysis without any whisker movement or nictitating reflex at the end of the postnatal 3 weeks. Although the body weight of the nerve-resected rats increased gradually for the postnatal 3 weeks, they weighed less than the control rats without nerve resection. The nerve-resected rats contained less milk (0.25 +/- 0.02 g) than the control rats (0.35 +/- 0.02 g) in the stomach on P17. On P21, the body weight of the nerve-resected rats (25.33 +/- 0.32 g) was decreased by 28% compared to that of the control rats (35.08 +/- 0.57 g). Although their growth was substantially more retarded than that of the control animals, most (92%) of the nerve-resected pups could survive without facial nerve innervation. The orofacial musculature innervated by the facial nerve plays an important role in breastfeeding, but the present study shows that these muscles are not essential for the survival of neonatal rats.

Neurotrophic effect of hepatocyte growth factor on neonatal facial motor neurons

The neurotrophic effect of hepatocyte growth factor (HGF) on axotomized facial motor neurons was examined after local application of HGF to the proximal facial nerve stump of the neonatal rat on post-natal day one (P1). Motor neuron survival was expressed as the neuronal cell count on the injured side as a percentage of that on the noninjured side. Motor neuron survival of the control group was 76% on P3, 54% on P5 and 23% on P8, that of the HGF-treated group 78% on P3, 69% on P5 and 31% on P8, and that of the brain-derived neurotrophic factor (BDNF)-treated group 91% on P5 and 45% on P8. The motor neuron survival rates were then adjusted by deducting the facial motor neurons corresponding to the uninjured retroauricular branch (20%) of the facial nerve. The adjusted values were 70% (P3), 42% (P5) and 4% (P8) for the control group, 72% (P3), 61% (P5) and 14% (P8) for the HGF-treated group, and 88% (P5) and 32% (P8) for the BDNF-treated group. These findings demonstrate that HGF has a neuroprotective effect on injured facial motor neurons and suggest that HGF has neurotrophic properties distinct from those of BDNF.

Proliferating cell populations in experimentally-induced hydrocephalus in developing rats

To examine the fate of proliferating brain cells in hydrocephalus (Hydro), experimental Hydro was induced in neonatal rats by intracisternal injection of kaolin and, 3 weeks later, the rats were injected with bromodeoxyuridine (BrdU). The BrdU (+) cells were immunohistochemically analyzed by using antibodies against neural (nestin), neuronal (NeuN) and glial (GFAP and MBP) markers in the posterior cerebrum. The percentage of nestin expression for the BrdU (+) cells was 8% in control and increased from 17% in the Hydro to 33% in the Hydro at an earlier stage after the shunt procedure, but was restored to 6% in the Hydro at a later stage after the shunt procedure. The percentages of GFAP expression showed a similar tendency to those of nestin expression. The BrdU (+) cells did not express either NeuN or MBP throughout the experiments.

Great potentiality of neonatal facial motor neurons for neural plasticity as determined by functionally essential neuronal population

The present study was undertaken to determine the neuronal population essential for normal and minimal facial function of young adult rats that had received various degrees of crush injuries to the facial nerve in the neonatal period. Using a neuronal tracer, it was found in young adult rats receiving neonatal injuries that the minimum number of tracer-labeled facial motor neurons necessary for normal facial function corresponded to 13-14% of the neurons (2540+/-64) of the age-matched control animals, whereas the minimum number of neurons necessary for minimal facial function corresponded to 5%. On the other hand, the minimum numbers of tracer-labeled facial motor neurons necessary for normal and minimal facial function of young adult rats that received various degrees of crush injuries corresponded to 61 and 27-30%, respectively, of the neurons (2540+/-64) of the uninjured control animals. These results indicate that the facial function of animals with nerves crushed at the neonatal stage can be adequately maintained by a very small population of neurons, implying a great potential of neonatal neurons for neural plasticity.

Differential neurogenesis and gliogenesis by local and migrating neural stem cells in the olfactory bulb

The rostral migratory stream (RMS) is a unique forebrain structure that provides a long-distance migratory route for the neural stem cells of the periventricular region towards the olfactory bulb (OB). The purpose of the study presented here is to examine the extent of neurogenesis and gliogenesis by the neural stem cells of different origins (periventricular vs. intrabulbar) in the OB. After the RMS had been subjected to injury, the rats received intraperitoneal injections of 5-bromodeoxyuridine (BrdU) and were further reared for 2 weeks. Neuronal and glial differentiations of the BrdU(+) cells in the olfactory bulbar granule cell (OB-GCL) and the olfactory glomerular (OB-GL) layers were examined immunohistochemically using antibodies against neuronal (NeuN, neuronal nuclei) and glial (GFAP, glial fibrillary acidic protein) markers in the OBs with injured and uninjured (control) RMS. In the completely RMS-lesioned OB, where migration of the periventricular neural stem cells was inhibited, a small number of BrdU(+) NeuN(+) cells were found in both the OB-GCL and OB-GL. The BrdU(+) NeuN(+) cells accounted for a much higher percentage of the BrdU(+) cells on the control side (OB-GCL, 36.7%; OB-GL, 8.8%) than on the completely RMS-lesioned side (OB-GCL, 3.7%; OB-GL, 0.6%). The percentage of the BrdU(+) GFAP(+) cells relative to the BrdU(+) cells did not show any major difference between the control and completely RMS-lesioned sides. This study revealed differences in neurogenesis and gliogenesis between the local and migrating neural stem cells in the OB of the adult rodent.

Cell dynamics of calretinin-immunoreactive neurons in the rostral migratory stream after ibotenate-induced lesions in the forebrain

It is now apparent that adult neurogenesis is taking place during life in the olfactory bulb (OB) of the rodent brain. In the olfactory nervous system, the precursor cells of the subventricular zone are known to continually proliferate, migrate through the rostral migratory stream (RMS) and differentiate into the bulbar neurons. The RMS, consisting of heterogeneous cell populations of the neural and neuronal precursor cells, is the unique forebrain structure that provides a long-distance migratory route for the precursor cells. The present study was undertaken to examine whether neuronal regeneration, focusing on calretinin-immunoreactive (+) cells, may proceed in the RMS following lesions induced by an excitotoxin. Two days after ibotenate injections, massive degeneration of calretinin (+) cells occurred in the RMS and its adjacent forebrains. Thereafter, calretinin (+) cells gradually increased in the RMS and reached above their control value 2 weeks after ibotenate injections. Removal of the OB also produced a marked increase in calretinin (+) cells in the RMS. Autoradiographic experiments using (3)H-thymidine showed that calretinin (+) cells were continually generated in the RMS and underwent neuronal turnover within 8 weeks in a normal condition. The results indicate that, in terms of calretinin (+) cells, neuronal differentiation and replacement is continually taking place within the RMS, and that the RMS is capable of repopulating those cells which were injured by ibotenate.

The minimum number of neurons in the central olfactory pathway in relation to its function: a retrograde fiber tracing study

The present study was aimed at determining the functionally essential size of the neuronal population in the central olfactory nervous system. Using conditioned rats who had learnt to avoid repellent (cycloheximide) solution by olfaction, varying degrees of injuries were made to the lateral olfactory tract, a major central olfactory pathway connecting the olfactory bulb to the olfactory cortex. After examining their olfactory ability to discriminate cycloheximide solution from water, intact bulbar projection neurons (mitral cells) with fiber connections to the olfactory cortex were quantified using a retrograde fiber tracing technique. The numbers of retrogradely labeled mitral cells from the rats with normal olfaction ranged between 20 and 92% of the control value, while those numbers from the anosmic rats ranged between 0 and 22%. We conclude that the functionally essential neuronal population is approximately one-fifth of the total in the central olfactory pathway, a presumed threshold value in terms of the ability to avoid cycloheximide solution by olfactory discrimination.

Continual replacement of newly-generated olfactory neurons in adult rats

It has been known that stem cells do exist in the central nervous system, and adult neurogenesis is continually taking place in the olfactory bulb during life. We report here, with the combined method of autoradiography using (3)H-thymidine and immunohistochemistry for a neuronal marker, that 65.3-76.9% of calretinin-immunoreactive bulbar neurons are replaced during the short period of 6 weeks in the adult rodent. The results indicate that neuronal replacement is a common phenomenon in the olfactory bulb during life.

Fate of newly formed periglomerular cells in the olfactory bulb

It is well established that olfactory receptor cells are replaced during life. Periglomerular (PG) cells of the olfactory bulb have recently been demonstrated to be produced following proliferation and migration of periventricular neuronal precursor cells even in adulthood. The purpose of the present study was to examine the fate of newly formed PG cells in adult rodents. Using 5-bromodeoxyuridine (BrdU), we carried out a quantitative immunohistochemical analysis of BrdU-positive cells in the bulbar glomerular layer at different survival periods. Each number of BrdU-positive PG cells per 100 olfactory glomeruli was 34.1 +/- 3.3 (1 week), 57.2 +/- 2.7 (2 weeks), 28.0 +/- 4.7 (4 weeks) and 25.9 +/- 1.6 (8 weeks). These results indicate that bulbar PG cells, similar to olfactory receptor cells, are mostly replaced during life, and that the olfactory system is composed of disposable neuronal networks centrally as well as peripherally.

Calretinin-immunoreactive neurons in rostral migratory stream: neuronal differentiation

The purpose of the present study was to examine immunohistochemically the expression of nestin and polysialylated neural cell adhesion molecule in calretinin-immunoreactive neurons of the rostral migratory stream, the restricted pathway through which neuronal precursor cells migrate towards the olfactory bulb. Using mirror sectioning, calretinin-immunoreactive neurons of the rostral migratory stream were shown to co-express nestin (20.8%) and polysialylated neural cell adhesion molecule (61.8%). The results show that calretinin-immunoreactive neurons in the rostral migratory stream still express immature neural and neuronal phenotypes.