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Gray matter volume in medication-naïve individuals with ADHD : A systematic review of voxel-based morphometry MRI-studiesBaar, Linn January 2024 (has links)
Attention deficit hyperactivity disorder is one of the most common neurodevelopmental disorders, affecting around 7% of the worldwide population in their everyday life. It has been suggested that individuals with ADHD differ in gray matter volume from typically developing controls. However, findings on in which brain areas these differences are located, as well as how gray matter volume is affected by stimulant medication, remain inconclusive. Therefore, this systematic review aimed to investigate any potential differences in gray matter volume in medication-naïve individuals with ADHD compared to controls, focusing on studies using voxel-based morphometry applied to MRI-imaging data A keyword search in the databases Web of Science, Scopus and Medline EBSCO resulted in 349 studies, of which seven met the inclusion criteria and were included in the review. The results included a total of 169 participants diagnosed with ADHD and 148 typically developing controls. Findings suggested decreased cerebellar gray matter volume, potential gender-wise volume differences in the anterior cingulate cortex, and a decrease in caudate gray matter volume, specifically in adults with ADHD. Some limitations include small sample sizes, possible effects of age on gray matter volume, and the overall heterogeneous nature of the disorder. The present review agrees that individuals with ADHD exhibit differences in gray matter volume, but also highlights the importance of expanding research on medication-naïve subjects, to be able to draw more robust scientific conclusions about the neural correlates of ADHD in the future.
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A comparison of motility and head morphology of sperm using different semen processing methods and three different staining techniquesMcAlister, Debra Ann 12 1900 (has links)
Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2010. / Bibliography / ENGLISH ABSTRACT: Sperm morphology remains an important parameter in the prediction of fertility, both
in vivo and in vitro. However, there remains a considerable level of concern
surrounding the true potential of this parameter due to the lack of standardization of
differential staining techniques used for the evaluation of sperm morphology. This
study aimed at investigating two commonly used staining techniques, Rapidiff® (RD)
and Papanicolaou (PAP), along with a new commercially available stain, SpermBlue®
(SB), in the evaluation of sperm morphometry and morphology. Results indicated that
significant differences in sperm morphometry exist due to the use of the staining
techniques. Findings further indicated that RD causes sperm head swelling while PAP
causes sperm head shrinkage. Results obtained using the SB staining technique have
indicated measurements closest to that which would be obtained through the
evaluation of fresh, unstained sperm. The lack of standardization and the different
effects various stains have on sperm structure and overall sperm morphology
evaluation should raise a level of concern, particularly when evaluating patients with
borderline morphology. Based on this, the use of the SB staining technique is
recommended over RD and PAP for effective and accurate morphology evaluation. In
further support of this technique, SB was shown to be quick and simple in method,
and allowed for the easy detection of sperm by computer aided sperm analysis
(CASA) systems such as the Sperm Class Analyzer (SCA®).
The second aim of this study was to examine the concentration, morphology and
motility of the resultant sperm populations following semen preparation using the
PureSperm® density gradient and swim-up techniques. Semen preparation is an
essential step in any fertility treatment protocol, and it is important that the sperm
obtained following semen preparation has sperm morphology and motility
characteristics capable of improving assisted fertility success rates. Currently, the
PureSperm® density gradient and sperm swim-up are the most widely employed
techniques in fertility clinics. Although there is sufficient evidence to suggest they are
each effective at extracting sperm with improved quality from neat semen, there
remains insufficient evidence to suggest which of these two techniques is superior.
The present investigation revealed that both sperm preparation methods were effective at improving sperm morphology and motility, however to varying degrees. The swimup
method yielded a population of sperm with superior motility and morphology
when assessed according to World Health Organisation (WHO) criteria, while the
PureSperm® density gradient technique isolated a higher percentage of normal sperm,
according to both WHO and Tygerberg strict criteria, with motility better than that of
neat semen. Although results obtained via the swim-up method suggest it would be
best for use in in vitro fertilization (IVF), the very low concentration of sperm isolated
via this method remains a significant draw-back. The PureSperm® density gradient
separation technique on the other hand is capable of isolating larger quantities of
sperm, which is likely to be of more benefit with fertility treatments requiring larger
quantities of sperm. Based on these findings, the use of PureSperm® density gradient
technique is recommended, due to its ability to isolate large quantities of good quality
sperm. However, a swim-up may still be of use when performing fertility treatment
using a sperm sample which possesses a high concentration and motility. / AFRIKAANSE OPSOMMING: Sperm morfologie bly ‘n belangrike parameter in die voorspelling van vrugbaarheid,
beide in vivo en in vitro. Tog is daar nogsteeds ‘n aansienklike vlak van kommer
rondom die ware potensiaal van hierdie parameter weens die gebrek aan
standardisering van verskillende kleuringstegnieke wat gebruik word vir die
evaluering van spermmorfologie. Hierdie studie is daarop gemik om ondersoek in te
stel na twee algemeen gebruikte kleurings tegnieke naamlik, Rapidiff® (RD) en
Papanicolaou (PAP), asook ‘n nuwe kommersiëel beskikbare kleurstof, SpermBlue®
(SB), vir die evaluering van spermmorfometrie en morfologie. Resultate dui aan dat
beduidende verskille in sperm morfometriese afmetings ontstaan as gevolg van die
gebruik van die verskillende kleurstowwe. Bevindinge dui verder daarop dat RD
swelling van die sperm se kop versoorsaak, terwyl PAP die spermkop laat krimp.
Resultate wat verkry is met behulp van die SB kleuringstegniek dui daarop dat hierdie
kleurstof aanleiding gegee het tot afmetings naaste aan die verkry tydens die
beoordeling van vars, ongekleurde sperme. Die gebrek aan standardisasie en die
uiteenlopende effekte wat verskillende kleurstowwe het op die spermstruktuur en die
evaluering van sperm morfologie ingeheel is kommerwekkend, veral tydens die
evaluering van pasiënte met grensgeval morfologie. Op grond van hierdie resultate,
word die gebruik van die SB kleuringstegniek, bo die gebruik van RD en PAP, vir
effektiewe en akkurate morfologie evaluering aanbeveel. Verdere ondersteuning vir
die gebruik van die SB kleuringstegniek is die feit dat daar bevind is dat SB ‘n
vinnige en eenvoudige metode is, wat toelaat vir maklike visualisering van sperme
deur rekenaargesteunde sperm analise sisteme soos die Sperm Class Analyzer
(SCA®).
Die tweede doel van hierdie studie was om die konsentrasie, morfologie en die
motiliteit van spermpopulasies te ondersoek, soos verkry tydens die voorbereiding van
semen deur gebruik te maak van die PureSperm® digtheidsgradiënt en op-swem
tegnieke. Die voorbereiding van semen is ‘n noodsaaklike stap in enige
vrugbaarheidsbehandeling protokol, aangesien dit belangrik is dat die sperme wat
deur hierdie prosesse verkry word oor die nodige morfologiese en motiliteit
eienskappe beskik wat in staat is om die sukses van vrugbaarheidsbehandelings te
verbeter. Huidiglik is die PureSperm® digtheidsgradiënt en op-swem tegnieke die mees algemeen gebruikte tegnieke in vrugbaarheidsklinieke. Alhoewel daar
voldoende bewyse is wat voorstel dat elke tegniek effektief is vir die ekstraksie van
sperme met beter kwaliteit vanuit semen, bly daar steeds onvoldoende bewyse wat
daarop dui dat een van hierdie twee tegnieke beter is as die ander een. Huidige
navorsing het getoon dat beide sperm voorbereidings metodes daarin geslaag het om
sperme met normale morfologie en beter motiliteit te selekteer. Die opswem metode
het ‘n spermpopulasie met beter motiliteit en verbeterde morfologie gelewer, soos
getoets volgens die WGO kriteria, terwyl die PureSperm digtheidsgradiënt tegniek
sperme met verbeterde morfologie, volgens beide die WGO en Tygerberg Streng
Kriteria, en ‘n redelike verbetering in sommige motiliteits parameters geselekteer het.
Hoewel die resultate wat verkry word via die op-swem metode voorstel dat dit die
beste metode vir die gebruik tydens in vitro bevrugting sou wees, bly die baie lae
konsentrasie van sperme wat met hierdie metode verkry word ‘n belangrike nadeel.
Die PureSperm® skeidingstegniek laat egter toe vir die isolering van groter
hoeveelhede sperme, wat waarskynlik meer voordelig sal wees vir
bevrugtingsbehandelings wat meer sperme benodig. Gebaseer op hierdie bevindinge,
word die gebruik van die PureSperm® digtheidsgradiënt tegniek aanbeveel, as gevolg
van hierdie tegniek se vermoë om groot hoeveelhede goeie gehalte sperm te isoleer.
Daar kan egter nogsteeds van op-swem metodes gebruik gemaak word tydens
vrugbaarheidsbehandeling indien die semenmonster beskik oor ‘n hoë konsentrasie
sperme met goeie beweeglikheid.
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Structural Brain Abnormalities in Temporomandibular DisordersMoayedi, Massieh 18 December 2012 (has links)
Temporomandibular disorders (TMD) are a family of prevalent chronic pain disorders affecting masticatory muscles and/or the temporomandibular joint. There is no unequivocally recognized peripheral aetiology for idiopathic TMD. The central nervous system (CNS) may initiate and/or maintain the pain in idiopathic TMD due to sustained or long-term nociceptive input that induces maladaptive brain plasticity, and/or to inherent personality-related factors that may reduce the brain's capacity to modulate nociceptive activity. The main aim of this thesis is to determine whether there are structural neural abnormalities in patients with TMD, and whether these abnormalities are related to TMD pain characteristics, or to neuroticism. The specific aims are to delineate in TMD: (1) gray matter (GM) brain abnormalities and the contribution of pain and neuroticism to abnormalities; (2) the contribution of abnormal brain GM aging in focal cortical regions associated with nociceptive processes; and (3) abnormalities in brain white matter and trigeminal nerve and the contribution of pain. In groups of 17 female patients with TMD and 17 age- and sex- matched controls, magnetic resonance imaging revealed that patients with TMD had: (1) thicker cortex in the somatosensory, ventrolateral prefrontal and frontal polar cortices than controls, (2) cortical thickness in motor and cognitive areas that was negatively related to pain intensity, orbitofrontal cortical thickness that was negatively correlated to pain unpleasantness, and thalamic GM volume correlated to TMD duration, (3) an abnormal relationship between neuroticism and orbitofrontal cortical thickness, (4) abnormal GM aging in nociceptive, modulatory and motor areas, (5) widespread abnormalities in white matter tracts in the brain related to sensory, motor and cognitive functions, (6) reduced trigeminal nerve integrity related to pain duration, and (7) abnormal connectivity in cognitive and modulatory brain regions. In sum, this thesis demonstrates for the first time abnormalities in both peripheral nerve and CNS in patients with TMD.
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Structural Brain Abnormalities in Temporomandibular DisordersMoayedi, Massieh 18 December 2012 (has links)
Temporomandibular disorders (TMD) are a family of prevalent chronic pain disorders affecting masticatory muscles and/or the temporomandibular joint. There is no unequivocally recognized peripheral aetiology for idiopathic TMD. The central nervous system (CNS) may initiate and/or maintain the pain in idiopathic TMD due to sustained or long-term nociceptive input that induces maladaptive brain plasticity, and/or to inherent personality-related factors that may reduce the brain's capacity to modulate nociceptive activity. The main aim of this thesis is to determine whether there are structural neural abnormalities in patients with TMD, and whether these abnormalities are related to TMD pain characteristics, or to neuroticism. The specific aims are to delineate in TMD: (1) gray matter (GM) brain abnormalities and the contribution of pain and neuroticism to abnormalities; (2) the contribution of abnormal brain GM aging in focal cortical regions associated with nociceptive processes; and (3) abnormalities in brain white matter and trigeminal nerve and the contribution of pain. In groups of 17 female patients with TMD and 17 age- and sex- matched controls, magnetic resonance imaging revealed that patients with TMD had: (1) thicker cortex in the somatosensory, ventrolateral prefrontal and frontal polar cortices than controls, (2) cortical thickness in motor and cognitive areas that was negatively related to pain intensity, orbitofrontal cortical thickness that was negatively correlated to pain unpleasantness, and thalamic GM volume correlated to TMD duration, (3) an abnormal relationship between neuroticism and orbitofrontal cortical thickness, (4) abnormal GM aging in nociceptive, modulatory and motor areas, (5) widespread abnormalities in white matter tracts in the brain related to sensory, motor and cognitive functions, (6) reduced trigeminal nerve integrity related to pain duration, and (7) abnormal connectivity in cognitive and modulatory brain regions. In sum, this thesis demonstrates for the first time abnormalities in both peripheral nerve and CNS in patients with TMD.
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The Neural Correlates of Auditory Processing in Adults and Children who StutterBeal, Deryk Scott 05 August 2010 (has links)
This dissertation is comprised of four studies investigating the hypothesis that adults and children who stutter differ from their same-age fluent peers in the neuroanatomy and neurophysiology underlying auditory speech processing. It has been consistently reported that adults who stutter demonstrate unique functional neural activation patterns during speech production, including reduced auditory activation, relative to nonstutterers. The extent to which these functional differences are accompanied by abnormal morphology of the brain in stutterers is unclear. The first study in this dissertation examined the neuroanatomical differences in speech-related cortex between adults who do and do not stutter using magnetic resonance imaging and voxel-based morphometry analyses. Adults who stutter were found to have localized grey matter volume increases in auditory and motor speech related cortex. The second study extended this line of research to children who stutter, who were found to have localized grey matter volume decreases in motor speech related cortex. Together, these studies suggest an abnormal trajectory of regional grey matter development in motor speech cortex of people who stutter. The last two studies investigated the mechanism underlying the repeated findings of reduced auditory activation during speech in people who stutter in more detail. Magnetoencephalography was used to investigate the hypothesis that people who stutter have increased speech induced suppression of early evoked auditory responses. Adults and children who stutter demonstrated typical levels of speech induced suppression relative to fluent peers. However, adults and children who stutter showed differences from peers in the timing of cortical auditory responses. Taken together, the studies demonstrate structural and functional abnormalities in brain regions related to auditory processing and point to the possibility that people who stutter have difficulty forming the neural representations of speech sounds necessary for fluent speech production.
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Hydrologický režim vybraných jezer Vysokých Tater / Hydrological regime of selected lakes in the High Tatra Mts.Sankotová, Tereza January 2015 (has links)
This diploma thesis deals with morphometric analysis and hydrological regime of Skalnaté pleso lake and Hincové Oká lakes, especially the lake level fluctuation, during the period 2011 - 2014. One of the tasks was the bathymetric mapping of observed locations. For Hincové Oká lakes was it the first mapping of bathymetry at all. The hydrological regime and lake level fluctuation regime of observed locations shows interesting differences from the other Tatra lakes whose hydrological regime is controlled by precipitation amounts. The annual culmination of Hincové Oká lakes (the largest lake) is shifted into the spring caused by melting snowpack. When there is no rainfall for a couple of days Skalnaté pleso lake often dries up, even during summer months, when levels of most Tatra lakes reach their maximum values. However summer drying is shortterm. Lake level fluctuation regime is very dynamic. After a strong rainfall event its level rises very steeply, up to 0,14 m per hour. Powered by TCPDF (www.tcpdf.org)
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Kraniometrická studie středoevropských populací bělozubek Crocidura suaveolens a C. leucodon (Mammalia: Soricomorpha) / Craniometric study of Central European populations of the white-toothed shrews Crocidura suaveolens and C. leucodon (Mammalia: Soricomorpha)Milerová, Petra January 2014 (has links)
Interspecific and intraspecific size variability of the skull, mandibles and teeth of the lesser white- toothed shrew Crocidura suaveolens and the bicolored white-toothed shrew C. leucodon was studied on material of 350 skulls and 465 mandibles of white-toothed shrews obtained by analysis of the barn owl pellets originating from four regions in the Czech Republic and one region in the southern Slovakia. C. suaveolens was present in all regions under study, while sympatric C. leucodon occurred in three regions only. In total, 21cranial and dental measurements and 4 mandibular measurements were investigated. It was found that the most reliable measurement enabling discrimination between skulls of both species in the whole studied material is the lenght of the lower dental row. If skulls of both species were evaluated separately for each area of their sympatry it was possible to use also the distance between second molars M2 and the width of premolar P4 . Skulls of these two species can also be distinguished by bivariate graphs using the length and width of premolar P4 and the palatal length. We studied relationships between cranial measurements of both species and geoclimatic factors such as longitude, latitude, mean annual temperature and mean annual percipitation. It was found that variability of...
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Taxonomies moléculaire et morphologique chez les foraminifères planctoniques : élaboration d'un référentiel et cas particuliers de Globigerinoides sacculifer et Neogloboquadrina pachyderma / Morphological and molecular taxonomies of planktonic foraminifera : design of a taxonomic framework and special cases of Globigerinoides sacculifer and Neogloboquadrina pachydermaAndré, Aurore 14 November 2013 (has links)
Les morpho-espèces de foraminifères planctoniques sont composées d'éco-génotypes parfois différentiables sur la base de la morphologie de leur coquille. Cette découverte récente d'une diversité ainsi qualifiée de « pseudo-cryptique » ouvre des perspectives d'amélioration de la précision des reconstructions paléocéanographiques. Malheureusement, ces génotypes ont été définis de façon subjective et ne sont pas homogènes quant à leur rang taxonomique, ce qui est pourtant un pré-requis pour leur intégration dans les modèles de reconstruction. Grâce à l'application de méthodes quantitatives de délimitation d'unités taxinomiques sur les séquences partielles de la petite sous-unité ribosomale (SSU) disponibles chez l'ensemble des morpho-espèces de foraminifères planctoniques, nous montrons que 49 de ces génotypes sont suffisamment divergents pour constituer d'authentiques espèces. Deux morpho-espèces clefs de la paléocéanographie sont étudiées plus en détail. Chez Neogloboquadrina pachyderma, l'obtention des premières séquences complètes de la SSU et la comparaison morphogénétique de spécimens (sub)polaires permettent de proposer un nouveau scénario évolutif et de montrer que les variations morphologiques sont ici d'origine éco-phénotypique, et donc indépendantes de la diversité génétique. Chez Globigerinoides sacculifer, caractérisé par une forte diversité morphologique, il existe au contraire une seule et unique espèce cosmopolite dans les eaux (sub)tropicales de l'Océan mondial. Ces deux cas particuliers montrent que, contrairement à ce que suggéraient les études précédentes, la spéciation pseudo-cryptique n'a pas valeur de règle chez les foraminifères planctoniques / Morphospecies of planktonic foraminifera are clusters of eco-genotypes that show small but significant shell morphological differences (pseudo-cryptic species).This discovery opens a new perspective for improving the accuracy and resolving power of paleoceanographic reconstructions. Unfortunately, current genetic type delimitations suffer subjectivity, inducing non-homogenous taxonomic status while homogenous taxonomic status is a prerequisite for including genetic types in reconstruction models. By applying quantitative and complementary methods for taxonomic units delimitation to the available dataset of partial sequences of SSU (ribosomal small sub-unit), we delimited 49 genuine (pseudo)cryptic species of planktonic foraminifera. We studied two paleoceanographic key-species. Complete sequencing of the SSU and morpho-genetic comparison within austral (sub)polar genetic types of Neogloboquadrina pachyderma lead to a new phylogeographic hypothesis and showed that morphological variations are the result of ecophenotypic effects and are not related with genetic types. The morphologically diverse Globigerinoides sacculifer is the first case of a planktonic foraminifera morphospecies corresponding to a single genetic type distributed world-wide in (sub) tropical waters. These two cases show that, contrary to previous studies conclusions, pseudo-cryptic speciation is not a rule within planktonicForaminifera
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Vývoj pleistocénního zalednění české části Šumavy (Případová studie z okolí Černého a Čertova jezera) / Development of Pleistocene glaciation of the Czech part of the Šumava Mts. (Case study of the Černé and Čertovo Lakes)Vočadlová, Klára January 2011 (has links)
This Ph.D. thesis presents new facts about a paleoenvironmental development of the northern part of the Bohemian Forest (area of Černé Lake and Čertovo Lake) in the Late Pleistocene and Early Holocene. The main goals of the research are: characterize the glacier landforms in the Bohemian Forest and define the variance of these landforms; determine factors influencing formation and development of the glaciation in the study area; describe environmental settings and its changes during deglaciation and in Early Holocene by using environmental proxies. This research proceeds from original data obtained by geomorphological mapping, morphometric analysis and proxy data analyses originated from a sediment sequence in a peat bog in the Černé Lake vicinity. The common attributes of the Bohemian Forest cirques and cirque variability was determined using morphometric and morphologic characteristics of the cirques on the Bavarian and Czech side of the mountain range. These characteristics were compared with other cirques of the Bohemian Massif and other chosen mountain ranges of the world. The cirque overdeepening was defined on the basis of headwall shapes and it emerged that overdeepening of the cirques in the Bavarian Forest and in the High Sudetes reflects a different extent of the Pleistocene glaciation....
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Aspectos descritivos e quantitativos da anatomia macroscópica e microscópica do nervo vestíbulo-coclear de cobaias / Descriptive and Quantitative Aspects of macroscopic and microscopic anatomy of the vestibulocochlear nerve of guinea pigsVasconcelos, Carlos Augusto Carvalho de 20 June 2005 (has links)
O nervo vestíbulo-coclear da cobaia possui peculiaridades não encontradas em outros nervos periféricos. Não foram encontradas informações detalhadas sobre os aspectos morfométricos do VIII nervo craniano em cobaias adultas na literatura. A avaliação descritiva e quantitativa no presente estudo, evidencia informações que precedem o estudo das alterações que ocorrem em modelos experimentais de neuropatias do VIII nervo craniano e as doenças ou lesões que possam afetar o homem. Foram utilizadas 8 cobaias adultas, perfundidas com glutaraldeído a 2,5% em tampão cacodilato de sódio (0,025 M). Seus nervos direito e esquerdo (n=6, 4 nervos direito e 2 esquerdos) foram dissecados na região mediana do nervo e pós fixado com tetróxido de ósmio (OsO4) a 1% e incluídos em resina epóxi Poly/Bed 812®. Os fragmentos foram cortados em secções transversais semifinas seriadas (6 nervos) com uma espessura de 0,5 μm e corados com azul de toluidina para a microscopia de luz. Foram analisados os aspectos histológicos descritivos e topográficos do nervo vestíbulo-coclear em cobaias adultas, bem como os aspectos histométricos na parte mediana do nervo, no referente a densidade de fibras mielínicas, a distribuição dos diâmetros de tal tipo de fibras mielínicas, ao cálculo da razão G e o número de vasos sangüíneos encontrados dentro da área de cada nervo. O nervo coclear é envolvido pelo vestibular na porção inicial da junção de ambos. O conjunto, nervos coclear e vestibular e nervo vestíbulo-coclear têm a aparência bifurcada da letra Y, na horizontal com os ramos lateralizados, possuindo em média 5 mm de comprimento. É ricamente vascularizado e documenta uma completa interposição das fibras dos nervos coclear e vestibular, quando o fascículo do VIII nervo está completamente constituído. As suas fibras mielínicas dispõem-se paralelamente em seu sentido longitudinal e são circundadas por escasso tecido endoneural. Não foram evidencias fibras amielínicas no VIII nervo. A distribuição das fibras mielínicas no segmento mediano do VIII nervo craniano foi unimodal, havendo predomínio de fibras com 3,5 m de diâmetro. O número de fibras foi de 5.390 ± 1.504 fibras. O diâmetro das fibras variou de 1,5 a 6 m de diâmetro. Os axônios com 2,5 m de diâmetro foram predominantes quantitativamente: 6.757 ± 1.922 axônios. O diâmetro axonal variou entre 1 a 4,5 m. A densidade média das fibras do VIII nervo em seu segmento mediano foi de 41.474 ± 4384 fibras/mm2. O diâmetro fascicular foi de 0,77 ± 0,04 mm. A razão G varia de 0,2 a 0,9. O maior número de fibras tem razão G de 0,7 e 0,6, respectivamente, predominando as fibras com 0,7. Os resultados descritos neste trabalho científico são originais, contendo alguns resultados inéditos e pouco estudados na literatura científica sobre a anatomia e morfometria do VIII nervo craniano em cobaia. O nervo vestíbulo-coclear da cobaia é um nervo sensitivo aferente especial, e bem diferente em sua anátomo-fisiologia de todos os outros nervos sensitivos e motores encontrados nos mamíferos. A cobaia adulta é um excelente modelo experimental para o estudo do nervo vestíbulo-coclear, semelhantes aos de humanos. / The vestibulocochlear (VIIIth cranial nerve) nerve of guinea pigs have special features not common for peripheral nerves in general. There are no detailed reports on the morphometric characteristics of the VIII nerve in adult guinea pigs. This is a descriptive and qualitative study that shows normal parameters that are useful in experimental models of the VIIIth nerve neuropathy. Eight adult guinea pigs were perfused with 2.5% glutaraldehyde in isotonic cacodilate buffer (0.025M). The right (N=4) and left (N=2) nerves were dissected in the median region, post-fixed in 1% osmuin tetroxide and embedded in epoxy resin. Semithin (0.5 µm) serial transverse sections were stained with 1% toluidine blue for light microscopy study. The descriptive histology and the topographical and histometric aspects of the median region of the nerve were analyzed, including myelinated fiber density, myelinated fiber diameter distribution, g ratio and number of endoneural capillary vessels. The cochlear nerve is enveloped by the vestibular nerve when they join together. Both, the cochlear and the vestibular nerves join to form the vestibulocochlear nerve with a Y shape, with approximately 5 mm in length. The nerve is widely vascularized and presents a complete mixture of the vestibular and cochlear myelinated fibers when the VIII nerve fascicle is constituted. The myelinated fibers are longitudinally oriented and present few endoneural connective tissue in between. No unmyelinated fibers were evidenced in the VIII nerve. The myelinated fiber diameter distribution was unimodal, with a peak at 3.5, and intervals between 1,5 and 6 m. The average number of fibers was 5.390 ± 1.504. The myelinated axon diameter distribution was also unimodal, with a peak at 2.5 µm of diameter were predominant quantitatively: 6.757 ± 1.922, and intervals between 1 and 4.5 µm. The average myelinated fiber density was 41.474 ± 4384 mm2, spread in a fascicular diameter of 0.77 ± 0.04 mm. The g ratio values varied from 0.2 to 0.9 and most of the myelinated fibers showed g ratio values of 0.7. Our results are original and only few parameters studied here were described in the literature. The vestibulocochlear nerve of the guinea pigs is a special afferent nerve, differing from other peripheral nerves (sensitive and motor) in its main anatomic and physiological characteristics, compared to other nerves from mammals. The adult guinea pig is an excellent model for the vestibulocochlear nerve neuropathy studies once it is similar to the human nerve.
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