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Surface morphology of the ependyma and its specializations in the third and fourth ventricles of the rat brain as viewed by SEM
Micron. 1976, Vol. 7:309-311. Pergamon Press. Printed in Great Britain.
Surface m o r p h o l o g y o f the e p e n d y m a and its spec/a]l/zat/ons in the th;rd and fourth ventricles o f the rat brain as v/ewed by SEM* J. P. CARD and J. A. MITCHELL
Department of Anatomy, Wayne State University, Detroit, MI 48201, U.S.A.
The mammalian ventricular system and its numerous structural modifications have been the focus of a number of recent investigations. Studies at the light and electron microscopic level have revealed seven areas of strikingly similar regional specializations known as the circumventricular organs (CVO). The cellular and vascular organization of these areas have a number of features in common and many attempts have been made to relate them functionally. O f the seven, (neurohypophysis, median eminence, organum vasculosum of the lamina terminalis, subfornical organ, subcommissural organ, pineal recess and area postrema), the median eminence (ME) has been studied most extensively. These studies have clearly established a neuroendocrine role for the M E as well as an ability of the specialized ependymal cells in this area to transport substances from the cerebrospinal fluid (CSF) to the adjacent vasculature. Due to their structural similarities with the ME, attempts have also been made to demonstrate similar functional capabilities in the other six CVOs, however data reported up to the present is inconclusive in this
*Supported by NIH Grant RR-05387-13.
regard. This study is designed to elucidate the general surface morphology of the third (V-III) and fourth (V-IV) ventricles in the rat in preparation for more detailed functional studies of the CVOs. Fixation of tissue from adult female rats was accomplished through intracardiac perfusion of buffered glutaraldehyde-paraformaldehyde preceeded by a physiological saline wash. The desired area of the ventricular surface was exposed by midsaggital, coronal or horizontal sections. All tissue samples were post fixed in 2% OsO4 following a 0.24M PO4 buffer wash, dehydrated in ethanol and critically point dried in CO2. Each sample was then mounted and coated with 10-15nm of gold. Examination of the lateral wall of the V - I I I revealed the ependyma of the dorsal two-thirds to be heavily ciliated. This thick 'blanket' of cilia could be seen extending into the interventricular foramen, the cerebral aquaduct (CA) and the initial portion of the pineal recess. It is generally assumed that these cilia are at least in part responsible for the movement of CSF through the ventricular system. The ventral one-third of the V - I I I is characterized by a transition zone in which ciliated cells become sparse and intermixed with the nonciliated ependyma which comes to occupy the
Legendsfor Page 310 Fig. I. Non-ciliated ependyma in the region of the infundibular (IR) and premamillary (MR) recesses can be seen extending ventrally from the transition zone (T). × 130. Fig. 2. A view of the premamillary recess of a specimen exhibiting a number of spherical blebs which appear to be in varying states of degradation. × 2000. Fig. 3. The heavily ciliated ependyma typical of the dorsal wall of the third ventricle is modified in the region of the subfornical organ. Cilia are less dense in distribution and expose large portions of the apical cell surfaces. × 3400. Fig. 4. Cilia in the initial portion of the pineal recess (PR) are confined to the intercellular junctions with few evident on the apical cell surface. This sparcely ciliated ependyma gives way to non-ciliated ependyma within the confines of the recess. CP, choroid plexus; PC, posterior commissure. × 100. 309
:310
. I . P . Card and .l. ,X- Mitchell
Surface Morphology of the Ependyma most ventral aspect of the wall and floor. Spherical blebs and varying degrees of ependymal ciliation were also evident in other areas of V - I I I , most notably in the region of the CVOs (Figs. 1-4). Heavily ciliated ependyma persists through the CA into the V-IV. However, midway through the V - I V it gives way to ependyma in which the cilia are most prominent at intercellular junctions. The ependyma becomes
311
heavily ciliated once again in the posterior portion of the ventricle. Vesicles similar to those seen in the V - I I I are visible in the heavily ciliated areas. Detailed studies of the individual circumventricular organs during differing physiological states are presently in progress. The studies will hopefully be combined with T E M studies in an effort to delineate the function of these specialized areas of the ependyma.
Surface m o r p h o l o g y o f the e p e n d y m a and its spec/a]l/zat/ons in the th;rd and fourth ventricles o f the rat brain as v/ewed by SEM* J. P. CARD and J. A. MITCHELL
Department of Anatomy, Wayne State University, Detroit, MI 48201, U.S.A.
The mammalian ventricular system and its numerous structural modifications have been the focus of a number of recent investigations. Studies at the light and electron microscopic level have revealed seven areas of strikingly similar regional specializations known as the circumventricular organs (CVO). The cellular and vascular organization of these areas have a number of features in common and many attempts have been made to relate them functionally. O f the seven, (neurohypophysis, median eminence, organum vasculosum of the lamina terminalis, subfornical organ, subcommissural organ, pineal recess and area postrema), the median eminence (ME) has been studied most extensively. These studies have clearly established a neuroendocrine role for the M E as well as an ability of the specialized ependymal cells in this area to transport substances from the cerebrospinal fluid (CSF) to the adjacent vasculature. Due to their structural similarities with the ME, attempts have also been made to demonstrate similar functional capabilities in the other six CVOs, however data reported up to the present is inconclusive in this
*Supported by NIH Grant RR-05387-13.
regard. This study is designed to elucidate the general surface morphology of the third (V-III) and fourth (V-IV) ventricles in the rat in preparation for more detailed functional studies of the CVOs. Fixation of tissue from adult female rats was accomplished through intracardiac perfusion of buffered glutaraldehyde-paraformaldehyde preceeded by a physiological saline wash. The desired area of the ventricular surface was exposed by midsaggital, coronal or horizontal sections. All tissue samples were post fixed in 2% OsO4 following a 0.24M PO4 buffer wash, dehydrated in ethanol and critically point dried in CO2. Each sample was then mounted and coated with 10-15nm of gold. Examination of the lateral wall of the V - I I I revealed the ependyma of the dorsal two-thirds to be heavily ciliated. This thick 'blanket' of cilia could be seen extending into the interventricular foramen, the cerebral aquaduct (CA) and the initial portion of the pineal recess. It is generally assumed that these cilia are at least in part responsible for the movement of CSF through the ventricular system. The ventral one-third of the V - I I I is characterized by a transition zone in which ciliated cells become sparse and intermixed with the nonciliated ependyma which comes to occupy the
Legendsfor Page 310 Fig. I. Non-ciliated ependyma in the region of the infundibular (IR) and premamillary (MR) recesses can be seen extending ventrally from the transition zone (T). × 130. Fig. 2. A view of the premamillary recess of a specimen exhibiting a number of spherical blebs which appear to be in varying states of degradation. × 2000. Fig. 3. The heavily ciliated ependyma typical of the dorsal wall of the third ventricle is modified in the region of the subfornical organ. Cilia are less dense in distribution and expose large portions of the apical cell surfaces. × 3400. Fig. 4. Cilia in the initial portion of the pineal recess (PR) are confined to the intercellular junctions with few evident on the apical cell surface. This sparcely ciliated ependyma gives way to non-ciliated ependyma within the confines of the recess. CP, choroid plexus; PC, posterior commissure. × 100. 309
:310
. I . P . Card and .l. ,X- Mitchell
Surface Morphology of the Ependyma most ventral aspect of the wall and floor. Spherical blebs and varying degrees of ependymal ciliation were also evident in other areas of V - I I I , most notably in the region of the CVOs (Figs. 1-4). Heavily ciliated ependyma persists through the CA into the V-IV. However, midway through the V - I V it gives way to ependyma in which the cilia are most prominent at intercellular junctions. The ependyma becomes
311
heavily ciliated once again in the posterior portion of the ventricle. Vesicles similar to those seen in the V - I I I are visible in the heavily ciliated areas. Detailed studies of the individual circumventricular organs during differing physiological states are presently in progress. The studies will hopefully be combined with T E M studies in an effort to delineate the function of these specialized areas of the ependyma.