|Anatomical and histological study of the cerebellum in nocturnal raptor species (eagle owl). Bubo bubo
Shermean Abdullah Abd-Alrahman
Department of biology , college of Education Ibn Al-Haithum, university of Baghdad .
Morphological and histological aspects on the cerebellum of (eagle owl )was studied to describe the position , design and the structural variation. The large cerebellum was drive so far back , the ventral surface of the brain was turned upward and backword vertically . The cerebellum design was spade , its shape was cauliflower ,a set of gyri separated by sulci divided the overall internal structure into three lobes including ten primary folia . The folia lll , Vl , and lX were enlargement and subfoliated neither folium Vll nor Vlll were large . The folium X was obliquely oriented containing ventral lamella . The cerebellar cortex forms a series of deeply convoluted long single strip of gray matter , the later consist of three layers : the outer molecular layer (ML ) ,single middle large purkinje cell layer( PL) and the thick inner granular layer (GL ) ..
تناولت الدراسة الجوانب الشكلية والنسيجية لمخيخ طائر البوم Eagle owl )) من حيث الموقع والمظهر والاختلافات التركيبية . تميز المخيخ الكبير الحجم باندفاعه للخلف كما واتخذ السطح البطني للدماغ وضع شاقولي نحو الاعلى والاسفل . تميز المخيخ بالمظهر البسـتوني spade وبشكل اشبه بزهرة القرنابيطcauliflower لوجود التلافيف العديدة التي تنفصل عن بعضها البعض باخاديد تقسم المخيخ الى ثلاثة فصوص متضمنة عشرة ورقات اولية . تميزت الورقات الاولية الثالثة والسادسة والتاسعة باتساعها وتفرعها بخلاف الورقات الاولية السابعة والثامنة . تميزت الورقة الاولية العاشرة بكونها مائلة الاتجاه وتحوي صفائح بطنية . ظهرت قشـرة المخيخ بشكل شريط مفرد طولي كثير الطيات من المادة السنجابية ، وتضمنت الاخيرة ثلاث طبقات وهي: الطبقة الجزيئية الخارجية والطبقة الوسطية المفرده لخلايا بركنجي الكبيرة الحجم والطبقة الحبيبية الداخلية السـميكة .
Owls are unique birds , they are classified as raptors , they have large forward – facing eyes and ears and binocular vision , the facial disc
helps to funnel the sound of prey to their ears [ Kirk&Denning 2009 ;Rosemary 2006 ; Cholewiak 2008 ] . Much of the volume in raptors brain is taken up for visual acuity and processing including and especially gaze stabilization, the owls ability to be activeat night based only upon high sensory sensitivity perception [Kirk & Denning 2009 ;Martin 2008 ;Martin et al. 2007]. The highly folded cerebellum function involved sensory perception, coordination of voluntary motor movement , balance, equilibrium , muscle tones and cognitive function [Saladin 1998; Young et al. 2006; Bevelander&Ramaley 1979; Eroschenko 2005]. There are interspecific variation in the structure of the cerebellum in large – brained birds , they does not scale uniformly [ Sultan 2005; Pal et al. 2003 ;Sultan &Glickstein 2007 ;Iwaniuk et al. 2006c ,2007 ]. Our study has been made to find out the anatomical aspect of the cerebellum in nocturnal raptor species ( eagle owl) .This study maybe helpful for better understanding of the cerebellum structural variation related to owl behavioral habitats especially the high degree of territoriality, prey catching technique and their silently flying during night houres [Cholewiak 2008 ] .
Material and Methods
Three healthy adult (eagle owl)are used in this study , the brains were obtained from the skull by careful dissection, they were submersion fixed in 10% buffered formalin, bisected in sagittal plane. The cerebellum from one half of the brain are removed by cutting through the cerebellar penduncle to examine the cerebellar folia .Pieces of cerebellum made by a sharp knife were fixed in 10% buffered formalin, washed, dehydrated through ascending grades of alcohol, cleared and embeded in paraffin wax. Five –six microns thick sections were cut by using rotary microtome. The paraffin wax was removed by immersing the sllides in xylene. The slides were passed through descending grades of alcohol, the sections were stained with Haematoxylin and Eosin (H & E) as per standered procedures, the tissue sections were cleared, mounted with D.P.X. as per usual method [Humanson 1972; Drury 1980].
Result The cerebellum : Gross anatomy
The large cerebellum of the ( eagle owl ) is drive so far back by the big eyeballs that the ventral surface of the brain was turned upward vertically compared to the axis of the bill .The cerebellum is the largest part of the hindbrain . It is located at the lowerback of the brain . ( Fig . l )illustrates that the cerebellum is separated from the cerebrum by a deep tranverse fissure . The cerebellum design is spade and cauliflower shaped situated forwardly to cover the diencephalon dorsally and backwardly to cover the medulla oblongata (Fig.2) .
There are a set of numerous folds named gyri separated by deep sulci divided the overall structure of the cerebellum into three lobes including ten primary folia . The small anterior lobe is above the primary fissure , the large posterior lobe is above the secondary fissure and the smallest third lobe at the base named flocculonodular lobe which consists of transverse thickenings continues laterally with the flocculus on each side . The folia lll ,Vl ,and lX are enlargement and subfoliated , neither folium Vll nor Vlll are large . The folium X is obliquely oriented and contains ventral lamella as seen in ( Fig . 2 )
The cerebellum: Microscopic anatomy
The cerebellar cortex formes a series of deeply convoluted long single strip of gray mattersupported by a branching central medulla of white matter (Fig.3) . At higher magnification of ( Fig. 4 ) the cortex is seen to consist of three layers : the outer molecular (ML ) which contains relatively few neurons , the superficial stellate cells and the larger basket cells that distributed through great numbers of nerve fibers . The inner thick granular cell layer (GL ) was extremely cellular , this layer composed of numerous granular cells and Golgi cells , the later are scattered in the superficial parts , between the two layers there is a single layer of huge neurons with extraordinary dendritic system named the purkinje cells layer (PL) .As seen at the higher magnification of (Fig . 5) these cells has very large cell bodies and relatively fine axon extending down through the granular cell layer (GL) and an extensively branching dendritic system which arborises into the outer molecular layer (ML) .
The eagle owl have large cerebellum, this findings is inagreement with [Pal et al. 2003; Cook 2000 ;Iwaniuk 2003] in birds. The domestic pigeons and chicken like birds do not have large cerebellum [Iwaniuk 2003 ; Rehkmpera et al. 2008] . The cerebellum position in eagle owl was drive so far back by the big eyeballs, the brain was turned upwared and backward compared to the axis of the bill . This position was the similar in snipe and was different in other birds which their brain and bill axises were nearly parallel [Kirk & Denning 2009 ; Cholewiak 2008] . The cerebellum design in eagle owl was, situated forward to cover the diencephalons dorsally and backward to cover the medulla oblongata , while it was rounded in outline in fowl as stated by [Pal et al. 2003] and it was accommodated to wide rostral surface in other birds [Cook 2000] . According to [Sultan &Glickstein 2007; Iwaniuk et al. 2006c,2007 ] birds cerebellum generally divided into three cerebellar lobes but one of the most prominent differences among birds was the relative size of the cerebellar lobes which due to the enlargement or reduction of individual ten primary folia which was related to specific functional and behavioral differences among birds . Eagle owl have small anterior lobe this finding was the same in apodiformes , camprimulgiformes birds and was different in nightjars and humming birds , they have reduced or absent anterior lobes as stated by [Iwaniuk et al. 2006c] . Folium lll within the anterior lobe in eagle owl was enlargement and subfoliated this folium responded tactile stimulation of the tail and leg , while in pigeon it responded deep somatosensory stimulation of the wings as stated by [Iwaniuk et al. 2006a,b] . In eagle owl folia Vl and lX within the large posteriorlobe were expanded and subfoliated , neither folium Vll nor Vlll within the same lobe are large . Folium Vll is primarily visual although Vlll appears tobe primarily auditory , they were large in night jars and oilbirds as stated by [Iwaniuk et al. 2006a,c;2007] . According to [Sultan 2005] there was extenstive overlap among tactile , auditory and visual stimuli within folia Vl and lX In eagle owl folium X within the third lobe have obliquely oriented and has ventral lamella but in apodiformes this folium doesnot have ventral lamella , also it was vertically oriented as mentioned by [Iwaniuk et al. 2006a] . The cerebellum which involved sensory perception ,muscular activity coordination and the maintains of the posture and the equilibrium [Saladin 1998 ; Young et al. 2006; Bevelander&Ramaley 1979; Eroschenko 2005] consistsof a cortex of gray matter with central core of white matter containing pairs of deep cerebellar nuclei. The outer long single strip of cortex in eagle owl divided into three layers i.e. the outer molecular layer (ML) , Purkinje cell layer (PL) and the inner thick granular layer (GL). [Sultan 2005 ;Sultan &Glickstein 2007] stated that the extention of the cerebellar cortical strip varies in different birds species and that was associated with the length and design of the cerebellum . The cortical layer was greater and highly developed in strong fliers compared to the flightless [Pal et al. 2003] .The cerebellar cortex of adult hens contain dense plexus nerve fibers which innervate more than one class of the cerebellar neurons [Mugnain&Dahl 2004]
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