[The hippocampus and neuro-transplantation]. / Gippokamp i neirotransplantatsiia.

A review of the author's histological and electron-microscopic studies of differentiation of hippocampal transplants with different levels of the graft/host integration. The grafts developing in the anterior eye chamber were the experimental model of complete isolation from the brain. The effects of various factors (age of the donor fetal tissue, host age and strain, degree of the integration with the recipient brain) on the growth and neural organization of grafts were studied. Analysis of fine structure of intraocular and intracortical grafts, as a rule, showed mature highly differentiated neurons and glia and normal density of typical synaptic contacts. However, morphological features suggesting both hyperactivity of some neurons and continuous growth of some neural processes were observed. The expression of nonsynaptic and transport-metabolic interactions between the cells was increased. The observed ultrastructural deviations can be regarded as a compensatory adaptation of the tissue to the deficit of specific afferent signals. It was shown that in the absence of normal cellular targets, axons of the grafted neurons establish functional synaptic contacts with improper neural elements in the host brain.

Effects of septal grafts on acetylcholine release from rat hippocampus after 192 IgG-saporin lesion.

The cholinergic inputs to the rat hippocampus were lesioned by intraseptal injections of 192 IgG-saporin. After 15 days, fetal septal cells were grafted into the hippocampus. Thirteen months later, hippocampal acetylcholine (ACh) release was studied by microdialysis. Lesioning reduced basal ACh release (100%) to 20% of normal, which was compensated for by the graft (71%). Infusion of the serotonin uptake inhibitor citalopram (100 microM) enhanced ACh release to the same extent (% of basal release) in all rat groups. Systemic injection of 8-OH-DPAT (0.5 mg/kg, SC), an agonist of 5-HT1A receptors, caused a smaller ACh release than citalopram. Acetylcholinesterase (AChE) staining and densitometric quantification revealed that the lesion-induced reduction of the AChE-staining density was compensated for by septal grafting. In conclusion, both histochemical and biochemical methods showed that cholinergic hippocampal parameters were drastically impaired by 192 IgG-saporin lesions, but were almost completely restored by septal grafting. The graft responded to intrinsic serotonergic regulation.

Pig fetal septal neurons implanted into the hippocampus of aged or cholinergic deafferented rats grow axons and form cross-species synapses in appropriate target regions.

The anatomical specificity of axon growth from fetal pig septal xenografts was studied by transplanting septal cells from E30-35 pig fetuses into cholinergic deafferented (192-IgG-saporin-infused) rats or into aged rats (> 18 months). Cell suspensions (100,000 cells/microl) were injected bilaterally into the dorsal and ventral hippocampus of immunosuppressed rats (10 mg/kg/day cyclosporine A). To assess axonal growth and synapse formation, acetylcholinesterase histochemistry, an antibody to choline acetyltransferase (ChAT), and three pig-positive/rat-negative antibodies: bovine 70kD neurofilament (NF70), human low-affinity NGF receptor (hNGFr), and human synaptobrevin (hSB) were used. In rats with surviving grafts at 6 months, NF70 axonal labeling was more extensive than either ChAT or hNGFr labeling. All three markers demonstrated graft axons extending selectively through the hippocampal CA fields and the molecular layer of the dentate gyrus. Graft axons did not extend into adjacent entorhinal cortex or neocortex. The distribution of pig hSB-positive synapses correlated with AChE-positive fiber outgrowth in to the host. Electron microscopic analysis of hSB-immunostained hippocampal sections revealed pig presynaptic terminals in contact with normal rat postsynaptic structures in the CA fields and the dentate gyrus. These data demonstrate target-appropriate growth of pig cholinergic axons and the formation of cross-species synapses in the deafferented or aged rat hippocampus.

Morris water maze analysis of 192-IgG-saporin-lesioned rats and porcine cholinergic transplants to the hippocampus.

Adults rats were lesioned with 192-IgG-saporin, an immunotoxin that targets cholinergic neurons in the basal forebrain expressing the low-affinity nerve growth factor receptor (p75). One month later, rats received E30-35 porcine cholinergic neurons bilaterally into the hippocampus, and were tested in the Morris water maze and the passive avoidance task 4.5-6 months after transplantation (in two experiments, rats were retested in the water maze) followed by histological and cellular analyses. The 192-IgG-saporin-lesioned animals displayed clear cognitive deficits in the Morris water maze. In all experiments the lesioned animals had spatial probe deficits on day 5 testing. A large variance was found among the transplanted animals, with individual animals exhibiting improved performance, but little overall improvement when compared to lesion-alone animals as a group. The relationships between behavioral performance and graft cholinergic factors were established by histological analyses. Grafted animals exhibited an increase in cholinergic innervation of the dentate gyrus (DG) region of the dorsal hippocampus when compared to lesion-alone animals. There was a significant correlation between the level of cholinergic innervation in the dentate gyrus and spatial navigation performance (latency and spatial probe) in the Morris water maze task. These data provide evidence of memory and spatial deficits following cholinergic denervation, and of target-specific growth of xenogeneic cholinergic neurons into the hippocampus. The lack of a clear treatment (transplant) effect in the behavioral measures leads us to believe that functional restoration of cognitive function would require cholinergic reinnervation of both the hippocampus and the neocortex in this 192-IgG-saporin animal model.

[Obtention and characterization of murine beta-NGF. Application in a model of cerebral aging]. / Obtención y caracterización del beta-NGF murino. Aplicación en un modelo de envejecimiento cerebral.

INTRODUCTION: beta-NGF is a basic protein of 118 aminoacids which acts are a trophic factor for sensory and sympathetic neurons of the peripheral nervous system, and on cholinergic neurons of the anterior basal cerebrum. OBJECTIVES: In view of the functional effect of beta-HGF and its possibilities as a therapeutic agent in neurodegenerative disease, including Alzheimer's disease in this study our aim was to obtain, characterize and show the main results of the application of beta-NGFm in a model of cerebral ageing in rats with cognitive disorders. MATERIAL AND METHODS: For the obtention of beta-NGFm we followed Mobley's method as modified by Ebendal and used mouse submaxillary gland as a source of raw material. The characterization studies were carried out by application of seven techniques which allowed physicochemical characterization and demonstration of the biological activity of the product. Application of beta-NGF obtained under these conditions was carried out in a mode of cerebral ageing and the effects of treatment were assessed by conduct studies, measurement of the activity of the enzyme acetyl cholinesterase and study of neural plasticity. CONCLUSIONS: Characterization studies carried out on the beta-NGFm showed that the protein obtained consists of a mixture of molecules of beta-NGFm which are intact at their extreme N-Terminal, and molecules which have lost the octapeptide of the N-terminal position and show some modification increasing hydrophobicity. All these species were recognized immunologically by the specific antibody anti-NGFm and showed biological activity.

Behavioral effects of GM1 ganglioside treatment and intrahippocampal septal grafts in rats with fimbria-fornix lesions.

The monosialoganglioside GM1 is a compound with neurotrophic properties found to foster functional recovery in various paradigms of brain damage. The present experiment examined whether systemic treatment with GM1 may facilitate behavioral recovery in rats with fimbria-fornix lesions and intrahippocampal grafts rich in cholinergic neurons. Among 68 Long-Evans female rats, 46 sustained a bilateral electrolytic lesion of the fimbria and the dorsal fornix and 22 were sham-operated. Fourteen days later, half the lesioned rats were subjected to intrahippocampal grafts of a fetal septal cell suspension. Starting a few hours after lesion surgery and over a 2-month period, half the rats of each surgical treatment group received a daily injection of GM1 (30 mg/kg i.p.), the other half being injected with saline as a control. All rats were subsequently tested for locomotor activity and radial maze learning. The lesions induced locomotor hyperactivity and impaired learning performances in both an uninterrupted and an interrupted radial maze testing procedure. In all rats with surviving grafts, the grafts had provided the hippocampus with a new and dense organotypic acetylcholinesterase-positive innervation pattern which did not differ between saline- and GM1-treated subjects. The scores/performances of the rats that had received only the grafts or only the GM1 treatment did not differ significantly from those of their respective lesion-only counterparts. However, in the radial-arm maze task, the grafted rats given GM1 showed improved learning performances as compared with their saline-treated counterparts: they used more efficient visit patterns under the uninterrupted testing conditions and made fewer errors under the interrupted ones. The results suggest that GM1 treatment or intrahippocampal grafts used separately do not attenuate the lesion-induced behavioral deficits measured in this experiment. However, when GM1 treatment and grafts are used conjointly, both may interact in a manner allowing part of these deficits to be attenuated.

A comparison of behavioural effects and morphological features of grafts rich in cholinergic neurons placed in two sites of the denervated rat hippocampus.

This study compared the morphological characteristics and the behavioural effects of intrahippocampal septal cell suspension grafts injected either just above the pyramidal cell layer of the hippocampal region CA1 or within the dorsal leaf of the dentate gyrus (DG) in rats subjected to electrolytic fimbria-fornix lesions. The behavioural tests determined home-cage and open-field activity, as well as radial-maze performance. Cresyl-violet staining, acetylcholinesterase (AChE) histochemistry, and parvalbumin, glial fibrillary acidic protein and glutamic acid decarboxylase immunocytochemistry were used for morphological assessments. The cross-sectional area of the grafts was measured between 0.8 mm and 5.3 mm posterior to Bregma and used as an index of their development. Whether injected into CA1 or DG, the grafts provided the partially denervated hippocampus with a dense AChE-positive reinnervation. Both types of grafts were devoid of reactive astrocytes (although reactive astrocytes were found close to the graft-host interface), contained almost no parvalbumin-positive neurons and showed a high density of GAD-positive terminals. One of the main differences between the two groups of grafted rats was that the suspension injected into the DG yielded grafts that, in the vicinity of the injection sites (between 2.3 mm and 4.3 mm posterior to Bregma), had a cross-sectional area exceeding that of the grafts placed into CA1 by about 63-110% (average 79%), the latter being more dispersed than the former in the coronal plane. In addition, rats with grafts in the DG exhibited granule cell degeneration in the vicinity of the injection sites, whereas rats with grafts in region CA1 showed no damage near the injection sites. Concerning the behavioural data, we found that fimbria-fornix lesions induced hyperactivity in both the home cage and the open field and impaired radial-maze performance. Compared with the lesion-only rats, the grafted rats in both groups had further increased open-field and home-cage activity. While the grafts placed into region CA1 slightly, but significantly, accentuated the lesion-induced deficit in radial-maze performance, those placed into the DG had no effect. These results suggest that intrahippocampal grafts may, in some (still unspecified) conditions, produce adverse behavioural effects or no behavioural effects, despite an acceptable graft-induced cholinergic reinnervation of the hippocampus. They do not allow a clear answer to the question of whether intra-DG and intra-CA1 septal suspension grafts exhibiting almost comparable morphological features (except in their size and their dispersion in the vicinity of the injection sites) induce behavioural effects that would depend on intrahippocampal location of the grafts. They suggest, however, that the granule cell degeneration caused by the implantation procedure, in conjunction with the intragyral development of the graft, probably does not account for some of the reported adverse behavioural effects of intrahippocampal basal forebrain grafts. Finally, the finding that septal cell suspensions placed into the DG yielded larger grafts than when an equivalent number of cells was injected into CA1 might be explained by a larger lesion-induced neurotrophic activity in DG than in region CA1, although both regions had undergone a similar degree of cholinergic denervation.

The effect of basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on the survival of septal neurons transplanted into the third ventricle in rats.

Effects of short-term pretreatment with basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on the survival of neurons transplanted into the third ventricle in rats were studied. Septa from 16-day-old rat embryos were pretreated with growth factor containing medium for 30 min and transplanted into the third ventricle of adult rats. Twenty-one days after the operation, the recipient rats were perfused with 4% paraformaldehyde. Paraffin sections of the removed brains were made, and the sections were stained with cresylviolet. The number of neurons in the grafts was counted under a light microscope. Although pretreatment with NGF was not effect, bFGF at the concentration of 1 and 10 micrograms/ml enhanced the survival of transplanted septal neurons. These results suggest that short-term pretreatment with bFGF could increase the efficiency of neuronal transplantation.

Functional activity of intrahippocampal septal grafts is regulated by catecholaminergic host afferents as studied by microdialysis of acetylcholine.

Previous microdialysis experiments have shown that acetylcholine (ACh) release from septal grafts in the hippocampus of awake rats is influenced by the behaviour of the animals, which strongly suggests that the host brain can exert a regulatory control over the activity of the grafted neurons. Since the activity of the normal septo-hippocampal cholinergic system is likely to be regulated, in part, by brainstem catecholaminergic afferents, we wished to study the effect of catecholaminergic drugs on ACh release in the hippocampus reinnervated by septal grafts. Rats were subjected to a unilateral aspirative fimbria-fornix (FF) transection and grafted with tissue from the fetal septal-diagonal band area, either as a cell suspension injection into the depth of the hippocampus or as a solid implant in the FF lesion cavity. Microdialysis of ACh release was carried out 17-20 months after transplantation in awake, freely-moving animals. The reduction in steady-state ACh overflow induced by the FF lesion (-81%) was restored to normal or above normal levels in rats with either solid or suspension grafts. In normal rats, systemic administration of apomorphine (2.0 mg/kg, s.c.) or amphetamine (2.5 mg/kg, i.p.) caused a 3.7 (+189%) or 7.8 (+301%) pmol/15 min increase in ACh overflow compared to the previous baseline level, respectively. The drug-induced increases in ACh levels in the FF-lesioned controls was substantially lower than normal (86-89% reduction). Both apomorphine and amphetamine resulted in an approximately two-fold increase in hippocampal ACh release in rats with suspension grafts. These responses were significantly increased over those seen in rats with FF lesions only, but they tended to be lower and more variable than normal. Rats with solid septal grafts responded significantly stronger than FF lesion controls to amphetamine with two-fold increased ACh overflow, whereas the response to apomorphine was less clear-cut. Pretreatment with the catecholamine synthesis blocker alpha-methyl-p-tyrosine (AMPT; 200 mg/kg x 3) did not affect steady-state or apomorphine-stimulated release of ACh in any of the groups, whereas the effect of amphetamine was abolished in both normal and grafted rats. The results suggest that ACh release derived from septal grafts in the hippocampus, similar to the normal septo-hippocampal system, can be affected by manipulations of the host catecholaminergic systems. This mechanism may, at least in part, underlie the ability of the host brain to influence and control the activity of grafted cholinergic neurons.

[The dynamics of phenotypically and genotypically determined high brain seizure activity in the intracerebral allografting of embryonic nerve tissue]. / Dinamika fenotipicheski i genotipicheski obuslovlennoi vysokoi sudorozhnoi aktivnosti mozga pri vnutrimozgovoi allotransplantatsii émbrional'noi nervnoi tkani.

Experiments were made on rats of two lines during 120-140 days. A study was made of the effect of transplanting the embryonal hippocamp tissue and the septum (E 18) on the phenotypically (mechanical destruction in Wistar rats of the areas CA1 and CA4 of the fields of the hippocamp and dentate gyrus) and genotypically (Krushinskii-Molodkina rats, all responding to graded acoustic stimulations (86 dB) by audiogenic convulsive fits) determined high convulsive activity of the brain. It has been shown that from days 4-6, in 19 out of 23 Wistar rats, the transplantation was followed by a steady increase of the threshold of convulsive activity. As to the threshold of convulsive activity in K-M rats, it was affected by the transplantation to a slightly less measure. Out of 17 K-M rats, 9 stopped reacting to acoustic stimulations by audiogenic convulsive fits from days 39-44. In 5 more animals, convulsive fits failed to occur after every acoustic stimulation, the duration of the clonic and tonic phases of convulsive fit and the duration of the post-paroxysmal motor excitation declined.

Application of a fluorescent dye to study connectivity between third ventricular preoptic area grafts and host hypothalamus.

The mutant hypogonadal (hpg) mouse lacks a functioning gene for the neurohormone gonadotropin releasing hormone (GnRH). Previous studies from our laboratory had indicated that the initiation and maintenance of reproductive function in these mice could be brought about by the implantation of normal fetal grafts into adult hosts. Testicular or ovarian growth and other indicators of normal neurosecretory output were always accompanied by survival of GnRH neurons and growth of GnRH axons into the host median eminence where such axons terminate on the hypophysial portal capillaries. To determine if other connections exist between graft and the host hypothalamus, small crystals of the carbocyanine dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) were applied to either graft or host after fixation of the brain. Tissue sections were analyzed for retrograde and and anterograde movement of the dye. When crystals were placed on the graft, labeled axons were found in the host median eminence or in the host hypothalamus taking an arching trajectory toward the median eminence. Retrogradely labeled neurons in the host were few in number and largely confined to the host arcuate nucleus. With DiI crystals applied to the basal hypothalamus, labeled axons were distributed widely in the host but much sparser in the graft. Axons appeared to enter primarily at sites where the graft and host interface lacked an ependymal lining. Small numbers of retrogradely labeled neurons were also seen in the graft. Most were cells of very simple morphology and were distributed randomly in the graft. When double label experiments were carried out most DiI positive cells in the graft contained GnRH. These results indicate the connectivity between host hypothalamus and the third ventricular preoptic area grafts exists but is limited in nature.

Transplantation of fetal CNS tissue into the peripheral nervous system: a model to study aberrant changes in the neuronal cytoskeleton.

Defined regions (septum, substantia nigra) of the embryonic central nervous system (CNS) were transplanted into the sciatic nerves of young adult rats. Immunocytochemical techniques were used to examine the expression of neurotransmitter related enzymes and neuronal cytoskeletal proteins in the grafts. The origin of the septal grafts was confirmed by immunoreactivity in neurons to choline acetyltransferase and the beta-nerve growth factor receptor (192-IgG). In substantia nigra grafts, neuronal perikarya and processes were identified with an antibody directed against tyrosine hydroxylase. Typical spatial distributions of phosphorylated (Mr 200,000) and non-phosphorylated (Mr 168,000 & 200,000) neurofilaments were observed in the short term (1-2 months) grafts with the monoclonal antibodies RT97 and SMI-32 respectively. Dense dendrite arbors and neuronal cell bodies were immunostained with an antibody that recognizes a high molecular weight microtubule associated protein (MAP2). In the long term (1 year) transplants, prominent cytoskeletal changes in the somata, axons and dendrites of neurons were evident. The cells showed a shift in phosphorylated neurofilament staining from the axon to the soma accompanied by a reduction in axonal immunoreactivity in the adjacent neuropil. Other abnormal features included swollen perikarya, hypertrophied axonal segments and short segments of kinked axons. Regression of the dendrite trees in the long standing grafts was also apparent when sections were reacted with the MAP2 antibody. These experiments indicate that grafted fetal neurons, isolated in the peripheral nervous system, differentiate and express markers like their counterparts in situ. After extended time periods under these circumstances, cytoskeletal modifications become apparent in the neurons. These aberrant changes are similar to morphological characteristics associated with aging and neurodegenerative disorders. This experimental paradigm offers a new approach to study cytoskeletal disturbances in neurons and provides a unique opportunity to examine conditions that may modulate the abnormal changes.

Graft-induced behavioral recovery from subcallosal septohippocampal damage in rats depends on maturity stage of donor tissue.

Long-Evans female rats sustained electrolytic lesions of the fimbria and the dorsal fornix and, 10-14 days later, received intrahippocampal suspension grafts of septal-diagonal band tissue from either 14-day-old (Group S14, n = 8) or 16-day-old fetuses (Group S16, n = 10), or of parietal cortex from 16-day-old fetuses (Group Cx, n = 10). Sham-operated (Group S, n = 10) and lesion-only (Group Fifo, n = 21) rats served as non-grafted controls. Spontaneous alternation was assessed in a T-maze at three weeks and two months post-grafting. Home cage and open field activity as well as radial maze learning were assessed from two months post-grafting onwards. Fimbria-fornix lesions induced lasting hyperactivity in both the open field and the home cage, impaired radial maze learning and transiently reduced spontaneous alternation rates. Neither type of graft significantly affected home cage activity. Septal-diagonal band grafts improved open field habituation (within trial decline of ambulatory activity) and radial maze learning; the former was observed only in S16 rats, whereas the latter was observed only in S14 rats. Acetylcholinesterase histochemistry revealed an initial lesion-induced depletion of hippocampal acetylcholinesterase (eight days post-surgery) which was no longer observed at the end of the experiment. Acetylcholinesterase positivity was similar in S14 and S16 grafts, which also contained many choline acetyltransferase-positive neurons. Cortical grafts were found to be almost devoid of acetylcholinesterase positivity and no well-stained choline acetyltransferase-positive neurons could be identified. Septal-diagonal band grafts from 14-day-old fetuses and cortical grafts contained more parvalbumin-positive neurons than septal-diagonal band grafts provided by 16-day-old fetuses. These results suggest that grafts rich in cholinergic neurons may promote behavioral recovery from fimbria-fornix lesion-induced deficits. However, such a recovery may concern different behavioral deficits as a function of the age of the implanted tissue, suggesting that the maturity stage of the donor may critically influence the functional expression in the lesioned recipient. Also, such a recovery does not appear to be related solely to cholinergic hippocampal (re)innervation and might depend on the presence, not only of cholinergic neurons, but also of non-cholinergic neuronal populations, such as parvalbumin-positive (probably GABAergic) neurons.

Normalization of subtype-specific muscarinic receptor binding in the denervated hippocampus by septodiagonal band grafts.

Unilateral fimbria-fornix lesions were made by aspiration in female Sprague-Dawley rats. In a group of these rats, fetal septal tissue was transplanted into the lesion cavity. Lesion of the fimbria-fornix resulted in a reduction of cholinergic input to the hippocampal formation as indicated by the loss of acetylcholinesterase (AChE)-positive staining in all ipsilateral hippocampal laminae and a loss of [3H]hemicholinium-3 binding to cholinergic terminals in the strata oriens (82% reduction) and radiatum (77% reduction) of areas CA2 and CA3 and in the molecular layer of the dentate gyrus (83% reduction). In contrast, the density of muscarinic receptor binding ([3H]QNB) increased in the strata oriens (80% increase) and radiatum (70% increase) in areas CA2-CA4. This was shown to be due to an actual increase in receptor number (Bmax) and not to a change in affinity (KD). Analysis of muscarinic receptor subtypes indicated that the increase in receptor binding in the stratum radiatum was of the M-1 subtype ([3H]-pirenzepine) and in the stratum oriens was of the M-2 subtype ([3H]QNB + 100 nM pirenzepine). In the host hippocampus after fetal septal graft, the staining for AChE, the binding of [3H]hemicholinium-3, and the binding of muscarinic receptors (both the M-1 and M-2 receptor subtypes) were all comparable to nonlesioned control values. These data indicate that the fetal septal grafts have reinnervated the host hippocampus and have made synaptic contact with host cells in a manner capable of regulating postsynaptic muscarinic receptors.

Septal transplants ameliorate spatial deficits and restore cholinergic functions in rats with a damaged septo-hippocampal connection.

Behavioral effects of septal lesion and fornix-fimbria transection were compared in absence and presence of a septal transplant in the hippocampus. The transplant grew in the hippocampus and projected acetylcholinesterase (AChE)-containing fibers throughout the extent of the denervated hippocampus. There were no differences in graft size or AChE reinnervation pattern after septal lesion or fornix transection. An increase in the density of M1 binding sites seen in hippocampal CA3 region after a cholinergic lesion, was restored back to normal after reinnervation of the hippocampus by the graft. Fornix-transected rats were more impaired in water maze acquisition than septal-lesioned rats which were impaired compared to controls. Septal-grafted rats were not different from lesioned rats in the behavioral tasks. However, an injection of physostigmine improved their performance relative to lesioned non-grafted rats. These experiments indicate that grafts can ameliorate behavioral deficits when the efficacy of acetylcholine of graft origin is enhanced.

Regulation of muscarinic receptors in hippocampus following cholinergic denervation and reinnervation by septal and striatal transplants.

The regulation of hippocampal muscarinic M1 and M2 receptors was studied by autoradiographic methods following cholinergic denervation and reinnervation from embryonic septal transplant. In young adult male rats the density of M1 sites, labeled either with 3H-pirenzepine (PZ) or 3H-N-methylscopolamine (NMS, in the presence of excess carbachol), exceeded by 4- to 5-fold the density of M2 sites, labeled with 3H-NMS in the presence of excess PZ. Both receptors appeared to be densest in hippocampal regions lowest in acetylcholinesterase or 3H-hemicholinium-3 binding. The distribution of M1 receptors did differ from the distribution of M2 receptors within subregions of the hippocampus. Along the mediolateral axis from the subiculum to the lateral CA 1, the density of M1 receptors is uniform, but the density of M2 receptors decreases. Also apparent is the relatively small difference in density between the CA1 and dentate gyrus for M1 receptors but a significantly greater difference for M2 receptors. However, the response of M1 and M2 receptors to long-term cholinergic denervation following fimbriafornix transection of the septal cholinergic input and to cholinergic innervation by embryonic septal transplants was similar. Long-term denervation (40-60 d) resulted in a 30-60% increase in both M1 and M2 receptors within regions of the hippocampal formation. Receptor levels were reduced to normal in regions innervated by septal transplants. For both receptors, the changes in the density of sites were due to alterations in the Bmax and not the Kd for the radioligands. The specificity of this regulation is supported by the evidence that (1) the degree and topography of the normalization of muscarinic receptor density was entirely dependent on the degree and pattern of cholinergic reinnervation by the fibers of the septal transplant, (2) cholinergic fiber reinnervation by embryonic striatal grafts also down-regulated the density of M1 and M2 receptors, and (3) successfully surviving transplants (e.g., cerebellar and striatal) that did not provide innervation to the hippocampus did not induce down-regulation of muscarinic receptors. Changes in the density of sites were not related to changes in the width of the hippocampus following denervation and reinnervation. The data support the view that the majority of M1 and M2 receptors are located postsynaptically on neurons within the hippocampus and not presynaptically on cholinergic fibers.

Interactions between donor and host tissue following cross-species septohippocampal transplants.

Interactions between donor and host tissues following xenogeneic transplantation were studied using the neural cell surface antigen, Thy 1.2, as a marker for the donor tissue. Dissociated septal cells from Thy 1.2-positive fetal mice were transplanted to the dentate gyrus of Thy 1.2-negative adult rats. At post-transplantation survival times between 1 and 5 months, an antibody to Thy 1.2 was used to identify donor tissue. The results demonstrate that the donor tissue was capable of migrating and developing within the host following transplantation. Thy 1.2-positive cells and processes were consistently found within the supragranular, infragranular, and molecular layers of the dentate gyrus, and occasionally within the hilus, suggesting that mechanisms existed within the host which influenced the development of the transplanted tissue. Additionally, the survival and growth of the Thy 1.2-positive neurons differed from previous reports describing the growth of acetylcholinesterase (AChE)-positive fibers from xenogeneic transplants. This finding suggested that in addition to growing within the host, xenogeneic transplants may also stimulate a compensatory sprouting response from the host.

Restoration of memory following septo-hippocampal grafts: a possible treatment for Alzheimer's disease.

The present paper outlines the reasons for the current interest in work on septo-hippocampal grafts. It examines the role of cholinergic dysfunction in the memory deficits associated with Alzheimer's disease, the effects of hippocampal lesions on memory in infra-human animals, and the anatomy of the hippocampus. Methodological aspects of neural grafting are then examined, including the source, nature and site of the graft. A review of the tasks employed to determine functional recovery following septo-hippocampal grafts suggests that although recovery is evident its nature is unclear. An experiment is described which suggests that grafts from embryonic septum bring about recovery of working memory in rats. Different bases of the recovery of function are discussed, including the role of the graft in eliciting release of trophic factors from the host brain; the possibility that the graft acts by providing a pool of neurotransmitter; and finally that the graft may replace the damaged circuitry of the host. Some problems of the grafting procedure are outlined. It is concluded that grafting may provide a viable treatment technique in the absence of other forms of treatment for Alzheimer's disease.