- Email: [email protected]
Fetal hypothalamic transplants in diabetic rats analysed by scanning electron microscopy
Neuroscience Letters, 61 (1985) 159-164 Elsevier Scientific Publishers Ireland Ltd.
159
NSL 03592 FETAL HYPOTHALAMIC TRANSPLANTS IN DIABETIC RATS ANALYSED BY S C A N N I N G E L E C T R O N M I C R O S C O P Y
DAVID E. SCOTT Department of Anatomy, University of Missouri - Columbia, School of Medicine, Columbia, MO 65212 (U.S.A.)
(Received March 4th, 1985; Revised version received and accepted July 29th, 1985)
Key words. neuronal transplantation - plasticity - hypothalamus - scanning-transmission electron mi-
croscopy - Brattleboro rat
Adult male Brattleboro rats with chronic diabetes insipidus underwent stereotaxic surgery wherein minced fragments of anterior hypothalamus from fetal rats, 17 days post-coitus, were stereotaxically positioned into the lumen of the host third cerebral ventricle. Host rats with fetal donor tissue were killed at various times following surgery and were prepared for correlative scanning-transmission electron microscopy. Examination with this technique revealed the presence of large neurografts which grew to occupy the entire lumen of the host third ventricle. Grafts were well vascularized and in addition exhibited remarkable numbers of supraependymal, cerebrospinal fluid-contacting neurons. The physical emergence of this cell line in proximity to viable grafts is discussed with respect to the biochemical influences that a neuropeptide producing fetal transplant has upon a peptide-deficient host.
The regional a n a t o m y o f the third cerebral ventricle has been an issue o f intense interest for m o r e t h a n a d e c a d e [3, 16-18]. A wealth o f literature n o w exists that describes the m o r p h o l o g y o f the cerebral ventricular wall in a n u m b e r o f m a m m a l i a n species, including h u m a n a n d s u b h u m a n p r i m a t e s [16-19]. H o w e v e r , little is k n o w n c o n c e r n i n g the n e u r o a n a t o m i c a l o r g a n i z a t i o n a n d the physical interaction(s) that occur between fetal h y p o t h a l a m i c t r a n s p l a n t s stereotaxically p o s i t i o n e d within the third cerebral ventricle o f B r a t t l e b o r o h o s t rats with a u t o s o m a l , h o m o z y g o u s d i a b e tes insipidus. T h e present r e p o r t is p a r t o f an o n g o i n g series o f investigations from this l a b o r a t o r y t h a t deals with the t r a n s p l a n t a t i o n o f n o r m a l fetal h y p o t h a l a m i c tissue into the b r a i n s o f B r a t t l e b o r o host rats with this congenital n e u r o p a t h y a n d the basic cellular events t h a t t r a n s p i r e following t r a n s p l a n t a t i o n . M a l e B r a t t l e b o r o rats o f the L o n g - E v a n s strain were e m p l o y e d as recipients in this c o m p o n e n t o f the investigation. Seventeen-day p o s t - c o i t u s (PC) fetal h y p o t h a l a m i represented the tissue d o n o r p o p u l a t i o n . E m p l o y i n g a technique described by G a s h a n d Sladek [4], m i n c e d f r a g m e n t s o f n o r m a l fetal a n t e r i o r h y p o t h a l a m u s were stereotaxically p o s i t i o n e d into the l u m e n o f the third cerebral ventricle. H o s t rats were then killed 30 a n d 60 d a y s p o s t - s u r g e r y a n d were p r e p a r e d for r o u t i n e t r a n s m i s s i o n - s c a n ning electron m i c r o s c o p y (EM). The d o m i n a n t feature o f the third cerebral ventricular lumen a n d floor o f recipient
160
Fig. 1. A: low-magnification scanning electron microgram (SEM) of large pleomorphic fetal hypothalamic graft (G) observed to reside upon the floor of the third cerebral ventricle of a Brattleboro host rat. Blood vessels (arrows) derived from the host routinely penetrate these grafts which often grow large enough to obliterate the lumen of the third cerebral ventricle, x 125. B: low-magnification SEM of host rat killed 30 days following stereotaxic placement of fetal hypothalamic neurograft. A remarkable number of SECs (stars) are seen to aggregate in close anatomical juxtaposition of the graft (G). The rapid emergence of these neuron-like cells that possess multiple processes that are interwoven into complex networks, suggest a remarkable degree of plasticity and potential for mechanical movement and displacement from the underlying neuropil of the host and transplant. × 600. host rats was the presence o f large, well-developed neurografts. As o b s e r v e d from a b o v e (dorsally), these grafts o b s c u r e d the underlying floor o f the third cerebral ventricle (Fig. I A). N u m e r o u s large b l o o d vessels were c o m m o n l y seen to p e n e t r a t e the surface o f these fetal explants a n d a r o s e from the h o s t ventricular well (Fig. 1A). The surfaces o f fetal explants were r o u t i n e l y covered b y n u m e r o u s blebs, r o u n d e d spherules a n d c e r e b r o s p i n a l fluid ( C S F ) - c o n t a c t i n g , n e u r o n - l i k e cells (Figs. 1B a n d 2A, B). In c o n t r a s t to c o n t r o l rats, B r a t t l e b o r o hosts that possessed viable, n e u r o g r a f t s d e m o n s t r a t e d unusually large p o p u l a t i o n s o f s u p r a e n d y m a l cells (SECs) (Figs. IB a n d 2A). These cells were often observed to be tightly a g g r e g a t e d t o g e t h e r in close a n a t o m i c a l j u x t a p o s i t i o n to fetal explants o r were o b s e r v e d individually a n d d e m o n strated c o m p l e x i n t e r d i g i t a t i o n o f their cell processes (Fig. 2B). The p o p u l a t i o n o f SECs varied significantly in their o r g a n i z a t i o n . S o m e were uni- o r b i p o l a r (Fig. 2A), whereas others were highly p l e o m o r p h i c a n d a p p e a r e d m u l t i p o l a r (Fig. 2B). Fine processes often arose f r o m n e i g h b o r i n g cells a n d established w h a t a p p e a r e d to be synaptic-like relationships between a d j a c e n t SECs (Figs. 2A a n d 3).
161
Fig. 2. A: high magnification SEM of cluster of neuron-like SEC (N) adjacent to a fetal hypothalamic transplant in a Brattleboro host rat killed 30 days following stereotaxic placement of a normal fetal hypothalamic fragment. These cells exhibit numerous delicate processes (arrows) that arborize over the surfaces of neighboring cells, x 1750. B: transmission electron microgram of isolated individual neuronlike SECs (N) on surface of fetal hypothalamic transplant (G) in a Brattleboro host rat killed 30 days post-surgery. The cytoplasm of this cell is filled with free ribonucleoprotein (polysomes), cisternae of rough endoplasmic reticulum (arrows) and mitochondria. Notable here are two presynaptic axonal profiles (stars) one of which demonstrates synaptic thickening. V, lumen, third cerebral ventricle. × 9000. Transplantational neurobiology has entered a new era o f growth and development with far greater emphasis directed towards the understanding o f pathophysiological mechanisms o f disease that specifically affect neuroendocrine transducers such as the median eminence and other circumventricular organs [7, 23]. A wealth o f new literature has emerged concerning the transplantation o f various h o m o l o g o u s or heterologous tissue into the m a m m a l i a n central nervous system. Specifically normal fetal hypothalamic preparations have been transplanted into various regions o f recipient hosts to include the anterior c h a m b e r o f the eye [1, 6], beneath the kidney capsule [14], and into the cerebral ventricles o f adult hosts [2, 4, 5, 9, 10, 12, 20-22]. A n u m b e r o f laboratories have described a return o f certain functional parameters in recipient hosts that, prior to transplantation with normal fetal tissue, did not possess such a physiological capacity and instead exhibited frank neuroendocrinepathies [4, 9, 10]. The present investigation confirms earlier observations from this and other laboratories which suggest that fetal hypothalamic transplants o f the same strain when introduced into the third cerebral ventricle m a y exert a potential biochemical influence upon the adjacent periventricular tissue o f the recipient host.
162
Fig. 3. SEM of SECs (stars) on the apical surfaces of tanycytes (T) that constitute the floor of third cerebral ventricle of Brattleboro host rat. These two prominent multipolar CSF-containing cells (N) exhibit multiple primary and secondary processes (arrows) that appear to interdigitate with one another. This complex arborization and physical interdigitation is characteristic of this cell line which in this and previous investigations has been identified as bonafide neurons. × 2250.
The three-dimensional morphology of the normal cerebral ventricular system as observed with scanning-transmission EM has been described in a number of mammalian species. Experimental manipulations such as gonadectomy, the intraventricular infusion of dopamine, or other physiological or pharmacologic manipulations [11, 13] have been followed by changes in the ultrastructural organization of the ventricular walls and floor not unlike those that transpire following fetal transplantation. The rapid invasion of blood vessels as observed with scanning EM from the host ventricular wall into the parenchyma of fetal neurografts is noteworthy and is consistent with the observations of Brightman et al. [2], who have demonstrated that fetal co-transplants of pineal gland and fragments of superior cervical sympathetic ganglia were rapidly invaded by host vessels within 9 h following placement into the lumen of the fourth cerebral ventricle of the mouse. The vascular invasion of fetal neurografts may involve two separate underlying mechanisms that provide for the fusion of extrinsic vessels from the host and intrinsic vascular anlage of the fetal transplant and has been the subject of an earlier report from this laboratory.
163
A striking accumulation of large numbers of CSF-contacting cells was noted. Many of such have been shown to be neurons in previous investigations [ 18,191. The origin of these cells at this point is uncertain. However, since they are observed to reside upon the surfaces of both the neurografts and the host ventricular wall, they may well arise from the underlying neuropil of both areas. Although SECs of neuronal or histiocytic origin are common to the cerebral ventricle of many species [3, 18, 191, they are never observed in the numbers that occur following transplantation or pharmacologic manipulation of the cerebral ventricular system. This emergence of neuron-like cells with complex cellular networks upon the cerebral ventricular wall or floor of the host, or for that matter, upon the surfaces of the explant itself, suggests a high degree of inherent plasticity and a migratory capacity classically associated with the other type of SEC, identified as histiocytes. The neuron-like cells observed in this investigation bear little resemblance to histiocytes and may function in an altogether different fashion. Previous observations of this phenomenon have led to the speculation that CSF-containing neurons may function as receptor cells in a short loop feedback mechanism that serves to monitor the composition of the CSF. A broad range of physiologically active substance have been detected in the mammalian CSF [18, 191 which has been characterized as a trophic mediator for the transport and movement of such. Although speculative, it is still an attractive theory that neuron-like SECs may function to monitor the composition of CSF and serve to feedback to either to inhibit or stimulate adjacent neuronal pools (supraoptic, periventricular, arcuate, etc.) that are responsible for the synthesis and secretion of neuropeptides or neurotransmitters that find their way into the CSF. Free nerve terminals have been observed to make entry into the lumen of the third cerebral ventricle [3, 18, 191and along with bulk flow from local cerebral capillaries, may constitute a mechanism by which biologically active substances such as catecholamines, indoleamines or peptides enter the CSF. However, the physical emergence of large numbers of neuron-like SECs in response to the fetal neurografts remains enigmatic and clearly may have little or nothing to do with basic neuroendocrine mechanisms. However, it could be argued that in rats which suffer with the congenital neuropathy of diabetes insipidus and which are essentially unable to synthesize sufficient intrinsic arginine-vasopressin (AVP), coupled to a normal neurophysin [ 151a functional peptide-producing explant may have a profound influence upon the local biochemical milieu of the third cerebral ventricle and surrounding ventricular walls. This alteration in local biochemistry of the CSF could conceivably trigger plastic and mechanical changes in adjacent neuronal pools which might trophically stimulate migration or rearrangement of the neuroanatomical organization of neurons adjacent to the fetal hypothalamic transplant. Hence, AVP arising from normal supraoptic neurons of the neurograft, coupled with other fetal nerve growth promoting factors from graft neurons and angiogenesis factors from invading blood vessels and glia, could function as chemotaxic agents that trigger this cellular response to a changing biochemical environment within the third cerebral ventricle of Brattleboro host rats. Supported by USPHS Grant NS 19197-03.
164 I Bernstein, M.F. and Moore, R.Y., Differentiation of anterior hypothalamus transplanted to eye anterior chamber. In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 2 Brightman, M., Markey, S. and Klein, D., Co-transplants of pineal and superior cervical ganglian of the IV ventricle. In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 3 Card, J.R. and Mitchell, J.A., Electron microscopic demonstrations of a supraependymal cluster of neuronal cells and processes in the hamster third ventricle, J. Comp. Neurol., 180 (1978) 430~458. 4 Gash, D.M. and Sladek, J.E., Jr., Vasopressin neurons grafted into Brattleboro rats: viability and activity, Peptides, 1 (1980) 1-14. 5 Gash, D.M. and Scott, D.E., Fetal hypothalamic transplants in the third ventricle of the adult brain, Cell Tiss. Res., 211 (1980) 191-206. 6 Henderson, S.R., Bethea, C.L. and Monroe, S.E., Hypothalamic transplants: dopamine, norepinephfine and gonadotropin releasing hormone contents. In Abstracts of the 61st Annual Endocrine Society Meeting, Anaheim, CA, Endocrine Society, Rockville Pike, MD, 1979, p. 464. 7 H6fer, H., Zur morphologie der circumventrieularen organe des Zwischenhirnes der Saugetiere, Vorh. Deutsch. Zool., Ges. (Frankfort) (1958) 202-251. 8 Johansson, B.B., Farenkrug, J., W.K. Kelso, C., Anderson, O. and Bloomstrand, C , Vasoactive intestinal polypeptide in human cerebrospinal fluid. In Frontiers of Hormone Research, Karger, Basel, 1982, pp. 179 188. 9 Kreiger, D.T., Perlow, M.J., Davies, T.F., Zimmerman, E.A., Ferin, M. and Charlton, M., Brain grafts reverse hypogonadism of gonadotropic releasing hormone deficiency, Nature (Lond.), 298 (1982) 468 471. 10 Kreiger, D., Gibson, M.J., Perlow, J., Davies, T., Perlow, M., Ferin, M. and Charlton, M., Correction of genetic gonadotropin-releasing (GNRH) deficiency by grafts of fetal preoptic area (POA) tissue: In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 11 Paull, W.K., Martin, H. and Scott, D.E., Third ventricular floor surface alterations following the intraventricular administration of dopamine, Scanning Electron Microsc., 2 (1978) 817-882. 12 Perlow, M., Functional brain transplants, Peptides, Suppl. 1 (1980) 101 110. 13 Saland, L.C. and M unger, A.T., Emergence of supraependymal cells in rat third ventricle of the administration ofp-chloroamphetamine, Brain Res. Bull., 6 (198 l) 517-524. 14 Schecter, J., Gash, D.M. and Ahmad, N., Neuroembryogenesis of ventral hypothalamus transplanted to kidney capsule, Cell Tiss. Res., 190 (1978) 247 254. 15 Schmale, H. and Richter, D., Single base delection in the vasopressin gene is the cause of diabetes insipidus in Brattleboro rats, Nature (Lond.), 308 (1984) 705-709. 16 Scott, D.E., Krobish-Dudley, G. and Paull, W.K., A comparative scanning electron microscopic analysis of the human cerebral ventricular system. I. The third ventricle, Z. Zellforsch., 132 (1972) 203 215. 17 Scott, D.E., Van Dyke, D.H., Paull, W.K. and Kozlowski, G.P., Ultrastructural analysis of human cerebral ventricular system. III. The choroid plexus, Cell Tiss. Res., 608 (1974) 1-11. 18 Scott, D.E., Krobish-Dudley, G., Paull, W.K. and Ribas, J., The primate medi,n eminence. I. Correlative scanning/transmissionelectron microscopy, Cell Tiss. Res., 162 (1975) 61-73. 19 Scott, D.E., Krobish-Dudley, G., Paull, W.K. and Kozlowski, G.P., The ventricular system in neuroendocrine mechanisms. III. Supraependymal neuronal networks in the primate brain, Cell Tiss. Res., 179 (1977) 235-254. 20 Scott, D.E. and Sherman, D., Neurological transplants. I. Neuronal and neurovascular integration following transplantation of the fetal hypothalamus into the third cerebral ventricle of Brattleboro rats. Brain Res. Bull., 12 (1984) 453467. 21 Scott, D.E., Fetal hypothalamic transplants: neuronal and neurovascular interrelationships, Neurosci. Lett., 51 (1984) 93 98. 22 Stenevi,U., Bjorklund, A., Kromer, L.F. Kromer, Paden, C.M., Gerlach, J.L., McEwen B.S. and Silverman A.J., Differentiation of embryonic hypothalamic transplants cultured on the choroidal pia of the brains of a~tult rats, Cell Tiss. Res., 205 (1980) 217 228. 23 Weindl, A., Neuroendocrine aspects of circumventricular organs. In F. Ganong and L. Marini (Eds.). Frontiers in Neuroendocrinology, Oxford University Press, London, 1973, pp. 1 32.
159
NSL 03592 FETAL HYPOTHALAMIC TRANSPLANTS IN DIABETIC RATS ANALYSED BY S C A N N I N G E L E C T R O N M I C R O S C O P Y
DAVID E. SCOTT Department of Anatomy, University of Missouri - Columbia, School of Medicine, Columbia, MO 65212 (U.S.A.)
(Received March 4th, 1985; Revised version received and accepted July 29th, 1985)
Key words. neuronal transplantation - plasticity - hypothalamus - scanning-transmission electron mi-
croscopy - Brattleboro rat
Adult male Brattleboro rats with chronic diabetes insipidus underwent stereotaxic surgery wherein minced fragments of anterior hypothalamus from fetal rats, 17 days post-coitus, were stereotaxically positioned into the lumen of the host third cerebral ventricle. Host rats with fetal donor tissue were killed at various times following surgery and were prepared for correlative scanning-transmission electron microscopy. Examination with this technique revealed the presence of large neurografts which grew to occupy the entire lumen of the host third ventricle. Grafts were well vascularized and in addition exhibited remarkable numbers of supraependymal, cerebrospinal fluid-contacting neurons. The physical emergence of this cell line in proximity to viable grafts is discussed with respect to the biochemical influences that a neuropeptide producing fetal transplant has upon a peptide-deficient host.
The regional a n a t o m y o f the third cerebral ventricle has been an issue o f intense interest for m o r e t h a n a d e c a d e [3, 16-18]. A wealth o f literature n o w exists that describes the m o r p h o l o g y o f the cerebral ventricular wall in a n u m b e r o f m a m m a l i a n species, including h u m a n a n d s u b h u m a n p r i m a t e s [16-19]. H o w e v e r , little is k n o w n c o n c e r n i n g the n e u r o a n a t o m i c a l o r g a n i z a t i o n a n d the physical interaction(s) that occur between fetal h y p o t h a l a m i c t r a n s p l a n t s stereotaxically p o s i t i o n e d within the third cerebral ventricle o f B r a t t l e b o r o h o s t rats with a u t o s o m a l , h o m o z y g o u s d i a b e tes insipidus. T h e present r e p o r t is p a r t o f an o n g o i n g series o f investigations from this l a b o r a t o r y t h a t deals with the t r a n s p l a n t a t i o n o f n o r m a l fetal h y p o t h a l a m i c tissue into the b r a i n s o f B r a t t l e b o r o host rats with this congenital n e u r o p a t h y a n d the basic cellular events t h a t t r a n s p i r e following t r a n s p l a n t a t i o n . M a l e B r a t t l e b o r o rats o f the L o n g - E v a n s strain were e m p l o y e d as recipients in this c o m p o n e n t o f the investigation. Seventeen-day p o s t - c o i t u s (PC) fetal h y p o t h a l a m i represented the tissue d o n o r p o p u l a t i o n . E m p l o y i n g a technique described by G a s h a n d Sladek [4], m i n c e d f r a g m e n t s o f n o r m a l fetal a n t e r i o r h y p o t h a l a m u s were stereotaxically p o s i t i o n e d into the l u m e n o f the third cerebral ventricle. H o s t rats were then killed 30 a n d 60 d a y s p o s t - s u r g e r y a n d were p r e p a r e d for r o u t i n e t r a n s m i s s i o n - s c a n ning electron m i c r o s c o p y (EM). The d o m i n a n t feature o f the third cerebral ventricular lumen a n d floor o f recipient
160
Fig. 1. A: low-magnification scanning electron microgram (SEM) of large pleomorphic fetal hypothalamic graft (G) observed to reside upon the floor of the third cerebral ventricle of a Brattleboro host rat. Blood vessels (arrows) derived from the host routinely penetrate these grafts which often grow large enough to obliterate the lumen of the third cerebral ventricle, x 125. B: low-magnification SEM of host rat killed 30 days following stereotaxic placement of fetal hypothalamic neurograft. A remarkable number of SECs (stars) are seen to aggregate in close anatomical juxtaposition of the graft (G). The rapid emergence of these neuron-like cells that possess multiple processes that are interwoven into complex networks, suggest a remarkable degree of plasticity and potential for mechanical movement and displacement from the underlying neuropil of the host and transplant. × 600. host rats was the presence o f large, well-developed neurografts. As o b s e r v e d from a b o v e (dorsally), these grafts o b s c u r e d the underlying floor o f the third cerebral ventricle (Fig. I A). N u m e r o u s large b l o o d vessels were c o m m o n l y seen to p e n e t r a t e the surface o f these fetal explants a n d a r o s e from the h o s t ventricular well (Fig. 1A). The surfaces o f fetal explants were r o u t i n e l y covered b y n u m e r o u s blebs, r o u n d e d spherules a n d c e r e b r o s p i n a l fluid ( C S F ) - c o n t a c t i n g , n e u r o n - l i k e cells (Figs. 1B a n d 2A, B). In c o n t r a s t to c o n t r o l rats, B r a t t l e b o r o hosts that possessed viable, n e u r o g r a f t s d e m o n s t r a t e d unusually large p o p u l a t i o n s o f s u p r a e n d y m a l cells (SECs) (Figs. IB a n d 2A). These cells were often observed to be tightly a g g r e g a t e d t o g e t h e r in close a n a t o m i c a l j u x t a p o s i t i o n to fetal explants o r were o b s e r v e d individually a n d d e m o n strated c o m p l e x i n t e r d i g i t a t i o n o f their cell processes (Fig. 2B). The p o p u l a t i o n o f SECs varied significantly in their o r g a n i z a t i o n . S o m e were uni- o r b i p o l a r (Fig. 2A), whereas others were highly p l e o m o r p h i c a n d a p p e a r e d m u l t i p o l a r (Fig. 2B). Fine processes often arose f r o m n e i g h b o r i n g cells a n d established w h a t a p p e a r e d to be synaptic-like relationships between a d j a c e n t SECs (Figs. 2A a n d 3).
161
Fig. 2. A: high magnification SEM of cluster of neuron-like SEC (N) adjacent to a fetal hypothalamic transplant in a Brattleboro host rat killed 30 days following stereotaxic placement of a normal fetal hypothalamic fragment. These cells exhibit numerous delicate processes (arrows) that arborize over the surfaces of neighboring cells, x 1750. B: transmission electron microgram of isolated individual neuronlike SECs (N) on surface of fetal hypothalamic transplant (G) in a Brattleboro host rat killed 30 days post-surgery. The cytoplasm of this cell is filled with free ribonucleoprotein (polysomes), cisternae of rough endoplasmic reticulum (arrows) and mitochondria. Notable here are two presynaptic axonal profiles (stars) one of which demonstrates synaptic thickening. V, lumen, third cerebral ventricle. × 9000. Transplantational neurobiology has entered a new era o f growth and development with far greater emphasis directed towards the understanding o f pathophysiological mechanisms o f disease that specifically affect neuroendocrine transducers such as the median eminence and other circumventricular organs [7, 23]. A wealth o f new literature has emerged concerning the transplantation o f various h o m o l o g o u s or heterologous tissue into the m a m m a l i a n central nervous system. Specifically normal fetal hypothalamic preparations have been transplanted into various regions o f recipient hosts to include the anterior c h a m b e r o f the eye [1, 6], beneath the kidney capsule [14], and into the cerebral ventricles o f adult hosts [2, 4, 5, 9, 10, 12, 20-22]. A n u m b e r o f laboratories have described a return o f certain functional parameters in recipient hosts that, prior to transplantation with normal fetal tissue, did not possess such a physiological capacity and instead exhibited frank neuroendocrinepathies [4, 9, 10]. The present investigation confirms earlier observations from this and other laboratories which suggest that fetal hypothalamic transplants o f the same strain when introduced into the third cerebral ventricle m a y exert a potential biochemical influence upon the adjacent periventricular tissue o f the recipient host.
162
Fig. 3. SEM of SECs (stars) on the apical surfaces of tanycytes (T) that constitute the floor of third cerebral ventricle of Brattleboro host rat. These two prominent multipolar CSF-containing cells (N) exhibit multiple primary and secondary processes (arrows) that appear to interdigitate with one another. This complex arborization and physical interdigitation is characteristic of this cell line which in this and previous investigations has been identified as bonafide neurons. × 2250.
The three-dimensional morphology of the normal cerebral ventricular system as observed with scanning-transmission EM has been described in a number of mammalian species. Experimental manipulations such as gonadectomy, the intraventricular infusion of dopamine, or other physiological or pharmacologic manipulations [11, 13] have been followed by changes in the ultrastructural organization of the ventricular walls and floor not unlike those that transpire following fetal transplantation. The rapid invasion of blood vessels as observed with scanning EM from the host ventricular wall into the parenchyma of fetal neurografts is noteworthy and is consistent with the observations of Brightman et al. [2], who have demonstrated that fetal co-transplants of pineal gland and fragments of superior cervical sympathetic ganglia were rapidly invaded by host vessels within 9 h following placement into the lumen of the fourth cerebral ventricle of the mouse. The vascular invasion of fetal neurografts may involve two separate underlying mechanisms that provide for the fusion of extrinsic vessels from the host and intrinsic vascular anlage of the fetal transplant and has been the subject of an earlier report from this laboratory.
163
A striking accumulation of large numbers of CSF-contacting cells was noted. Many of such have been shown to be neurons in previous investigations [ 18,191. The origin of these cells at this point is uncertain. However, since they are observed to reside upon the surfaces of both the neurografts and the host ventricular wall, they may well arise from the underlying neuropil of both areas. Although SECs of neuronal or histiocytic origin are common to the cerebral ventricle of many species [3, 18, 191, they are never observed in the numbers that occur following transplantation or pharmacologic manipulation of the cerebral ventricular system. This emergence of neuron-like cells with complex cellular networks upon the cerebral ventricular wall or floor of the host, or for that matter, upon the surfaces of the explant itself, suggests a high degree of inherent plasticity and a migratory capacity classically associated with the other type of SEC, identified as histiocytes. The neuron-like cells observed in this investigation bear little resemblance to histiocytes and may function in an altogether different fashion. Previous observations of this phenomenon have led to the speculation that CSF-containing neurons may function as receptor cells in a short loop feedback mechanism that serves to monitor the composition of the CSF. A broad range of physiologically active substance have been detected in the mammalian CSF [18, 191 which has been characterized as a trophic mediator for the transport and movement of such. Although speculative, it is still an attractive theory that neuron-like SECs may function to monitor the composition of CSF and serve to feedback to either to inhibit or stimulate adjacent neuronal pools (supraoptic, periventricular, arcuate, etc.) that are responsible for the synthesis and secretion of neuropeptides or neurotransmitters that find their way into the CSF. Free nerve terminals have been observed to make entry into the lumen of the third cerebral ventricle [3, 18, 191and along with bulk flow from local cerebral capillaries, may constitute a mechanism by which biologically active substances such as catecholamines, indoleamines or peptides enter the CSF. However, the physical emergence of large numbers of neuron-like SECs in response to the fetal neurografts remains enigmatic and clearly may have little or nothing to do with basic neuroendocrine mechanisms. However, it could be argued that in rats which suffer with the congenital neuropathy of diabetes insipidus and which are essentially unable to synthesize sufficient intrinsic arginine-vasopressin (AVP), coupled to a normal neurophysin [ 151a functional peptide-producing explant may have a profound influence upon the local biochemical milieu of the third cerebral ventricle and surrounding ventricular walls. This alteration in local biochemistry of the CSF could conceivably trigger plastic and mechanical changes in adjacent neuronal pools which might trophically stimulate migration or rearrangement of the neuroanatomical organization of neurons adjacent to the fetal hypothalamic transplant. Hence, AVP arising from normal supraoptic neurons of the neurograft, coupled with other fetal nerve growth promoting factors from graft neurons and angiogenesis factors from invading blood vessels and glia, could function as chemotaxic agents that trigger this cellular response to a changing biochemical environment within the third cerebral ventricle of Brattleboro host rats. Supported by USPHS Grant NS 19197-03.
164 I Bernstein, M.F. and Moore, R.Y., Differentiation of anterior hypothalamus transplanted to eye anterior chamber. In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 2 Brightman, M., Markey, S. and Klein, D., Co-transplants of pineal and superior cervical ganglian of the IV ventricle. In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 3 Card, J.R. and Mitchell, J.A., Electron microscopic demonstrations of a supraependymal cluster of neuronal cells and processes in the hamster third ventricle, J. Comp. Neurol., 180 (1978) 430~458. 4 Gash, D.M. and Sladek, J.E., Jr., Vasopressin neurons grafted into Brattleboro rats: viability and activity, Peptides, 1 (1980) 1-14. 5 Gash, D.M. and Scott, D.E., Fetal hypothalamic transplants in the third ventricle of the adult brain, Cell Tiss. Res., 211 (1980) 191-206. 6 Henderson, S.R., Bethea, C.L. and Monroe, S.E., Hypothalamic transplants: dopamine, norepinephfine and gonadotropin releasing hormone contents. In Abstracts of the 61st Annual Endocrine Society Meeting, Anaheim, CA, Endocrine Society, Rockville Pike, MD, 1979, p. 464. 7 H6fer, H., Zur morphologie der circumventrieularen organe des Zwischenhirnes der Saugetiere, Vorh. Deutsch. Zool., Ges. (Frankfort) (1958) 202-251. 8 Johansson, B.B., Farenkrug, J., W.K. Kelso, C., Anderson, O. and Bloomstrand, C , Vasoactive intestinal polypeptide in human cerebrospinal fluid. In Frontiers of Hormone Research, Karger, Basel, 1982, pp. 179 188. 9 Kreiger, D.T., Perlow, M.J., Davies, T.F., Zimmerman, E.A., Ferin, M. and Charlton, M., Brain grafts reverse hypogonadism of gonadotropic releasing hormone deficiency, Nature (Lond.), 298 (1982) 468 471. 10 Kreiger, D., Gibson, M.J., Perlow, J., Davies, T., Perlow, M., Ferin, M. and Charlton, M., Correction of genetic gonadotropin-releasing (GNRH) deficiency by grafts of fetal preoptic area (POA) tissue: In A. Bjorklund and U. Stenevi (Eds.), Transplantation in the Mammalian CNS, Elsevier, Amsterdam, in press. 11 Paull, W.K., Martin, H. and Scott, D.E., Third ventricular floor surface alterations following the intraventricular administration of dopamine, Scanning Electron Microsc., 2 (1978) 817-882. 12 Perlow, M., Functional brain transplants, Peptides, Suppl. 1 (1980) 101 110. 13 Saland, L.C. and M unger, A.T., Emergence of supraependymal cells in rat third ventricle of the administration ofp-chloroamphetamine, Brain Res. Bull., 6 (198 l) 517-524. 14 Schecter, J., Gash, D.M. and Ahmad, N., Neuroembryogenesis of ventral hypothalamus transplanted to kidney capsule, Cell Tiss. Res., 190 (1978) 247 254. 15 Schmale, H. and Richter, D., Single base delection in the vasopressin gene is the cause of diabetes insipidus in Brattleboro rats, Nature (Lond.), 308 (1984) 705-709. 16 Scott, D.E., Krobish-Dudley, G. and Paull, W.K., A comparative scanning electron microscopic analysis of the human cerebral ventricular system. I. The third ventricle, Z. Zellforsch., 132 (1972) 203 215. 17 Scott, D.E., Van Dyke, D.H., Paull, W.K. and Kozlowski, G.P., Ultrastructural analysis of human cerebral ventricular system. III. The choroid plexus, Cell Tiss. Res., 608 (1974) 1-11. 18 Scott, D.E., Krobish-Dudley, G., Paull, W.K. and Ribas, J., The primate medi,n eminence. I. Correlative scanning/transmissionelectron microscopy, Cell Tiss. Res., 162 (1975) 61-73. 19 Scott, D.E., Krobish-Dudley, G., Paull, W.K. and Kozlowski, G.P., The ventricular system in neuroendocrine mechanisms. III. Supraependymal neuronal networks in the primate brain, Cell Tiss. Res., 179 (1977) 235-254. 20 Scott, D.E. and Sherman, D., Neurological transplants. I. Neuronal and neurovascular integration following transplantation of the fetal hypothalamus into the third cerebral ventricle of Brattleboro rats. Brain Res. Bull., 12 (1984) 453467. 21 Scott, D.E., Fetal hypothalamic transplants: neuronal and neurovascular interrelationships, Neurosci. Lett., 51 (1984) 93 98. 22 Stenevi,U., Bjorklund, A., Kromer, L.F. Kromer, Paden, C.M., Gerlach, J.L., McEwen B.S. and Silverman A.J., Differentiation of embryonic hypothalamic transplants cultured on the choroidal pia of the brains of a~tult rats, Cell Tiss. Res., 205 (1980) 217 228. 23 Weindl, A., Neuroendocrine aspects of circumventricular organs. In F. Ganong and L. Marini (Eds.). Frontiers in Neuroendocrinology, Oxford University Press, London, 1973, pp. 1 32.