Influence of fetal hippocampal grafts on lesions induced by intraventricular infusion of N-methyl-D-aspartate (NMDA) into rats

Effects of fetal hippocampal transplants were evaluated following a prolonged intraventricular excitotoxic lesion (1.0 mg of N-methyl-D-aspartate over two weeks infusion) in F344 rats. The septum and ipsilateral hippocampus (CA1 and dentate regions) showed extensive cell loss, decreased acquisition of spatial memory was observed and a decrease in AChE positive fiber innervation to the hippocampus was noted following the lesion. Fetal hippocampal transplants into the posterior lateral ventricle resulted in moderate graft survival and physiological analysis of graft-host interconnection in vitro demonstrated evoked field potentials. However, the transplants did not lead to significant improvement in behavior, possibly due to poor synaptic integration of the intraventricular transplants into the host hippocampus. The prolonged intraventricular NMDA lesion may be helpful to understand a mixed lesion model of both septal areas and hippocampus and also as a background lesion in which to assess the connectivity and development of various types of neural grafts.     

Appropriate target interactions prevent abnormal cytoskeletal changes in neurons: a study with intra-sciatic grafts of the septum and the hippocampus.

Transplantation of embryonic CNS regions into the PNS provides an opportunity to study temporal and spatial changes in the cytoskeleton that are associated with aging and neurodegenerative diseases. In this study, the fetal septum was transplanted alone or with the hippocampus into the sciatic nerves of young adult rats to determine whether the proper central neural target could prevent the expression of abnormal cytoskeletal changes. The substantia nigra, a non-target area of the septum, served as control co-grafts. After 1, 3, 6, 12, and 18 months of survival, the grafts were examined by immunocytochemistry with antibodies to phosphorylated and nonphosphorylated neurofilaments, microtubule-associated proteins (MAPs), and glial fibrillary acidic protein (GFAP). Subpopulations of neurons in the septal transplants expressed CAT and the NGF receptor (192-IgG). Long-term (12-18 months) expression of these two markers was only observed when the septum was combined with the hippocampus. Although isolated single grafts of septum survived within the PNS substratum, significant neuronal loss, extensive graft shrinkage, and aberrant cytoskeletal immunoreactivity were prominent in the long-term group. Changes that reflected an aging process included the ectopic expression of phosphorylated neurofilaments in neuronal perikarya, swollen axons, and a loss of MAP2 immunoreactivity that paralleled dendrite regression. In addition, abnormal "curly" fibers in the neuropil were also immunolabeled with an antibody directed against tau (5E2). Introduction of hippocampal co-grafts increased the final size of the septal transplants and prevented the cytoskeletal changes that accompanied the degeneration in the single septal grafts. The degree of GFAP immunostaining in the septum corresponded with advancing graft age and was minimized when grafted with the hippocampal formation. When the septum was combined with the substantia nigra, the grafts also underwent shrinkage and no protective influence from aberrant cytoskeletal staining was observed. These experiments exemplify the importance of an appropriate CNS neural target on the maintenance of long-term cholinergic neuron survival and normal morphology at the cytoskeletal level and illustrate the usefulness of these CNS-PNS constructs to examine conditions that influence the cytoskeleton.     

Connective integration of hippocampal grafts in excitotoxic hippocampal lesions in adult rats: an anterograde axonal tracing study

Exchange of nerve connections between developing neural grafts and adult recipient brains is enhanced for grafts placed in excitotoxic lesions, which spare recipient brain afferent axons in otherwise neuron-depleted lesion areas. In previous studies of hippocampal grafts placed in such lesions, we have used anterograde axonal degeneration, histochemical Timm staining and acetylcholinesterase to demonstrate host-graft interconnectivity. In this study, we have now used three anterograde axonal tracers, Phaseoulus vulgaris-leukoaglutinin (PHA-L), biocytin and biotinylated dextran amine (BDA), which allow individual fibers to be traced. Adult male rats with 1-week-old axon-sparing ibotenic acid lesions of the dorsal CA3 region or fascia dentata were grafted into the respective lesions with suspensions of fetal (El8-19) CA3 cells or a block of neonatal fascia dentata tissue. One to twelve months later, recipients were injected with Phaseoulus vulgaris-leukoaglutinin or biocytin in the hippocampus contralateral to the graft to trace the possible ingrowth and distribution within the transplants of host commissural axons, or into the transplants with biotinylated dextran amine in order to trace outgrowing graft fibers. In rats with succesfull host Phaseoulus vulgaris-leukoaglutinin or biocytin injections, the CA3 and fascia dentata transplants were innervated by labelled host commissural fibers. In the dentate transplants, most commissural fibers projected as normally to the inner part of the molecular layer, with fewer aberrant fibers extending more superficially into the molecular layer. Following injections into the fascia dentata and CA3 grafts of biotinylated dextran amine, labelled graft fibers were traced into the ipsilateral host dentate hilus, CA3 and CA1. From some CA3 containing grafts, a few labelled fibers were also observed passing through the host fimbria-fornix to the lateral septum on the grafted side. A few fibers were projected as far as to the most septal levels of the contralateral CA1.     

Topographical distribution in the adult rat brain of neurotrophic activities directed to central nervous system targets

Cortex, hippocampus, septum and striatum of day 18 rat embryos were grafted to several brain regions of young adult rats which had been lesioned in the chosen area 4 days earlier. Thirty days after transplantation, the grafts were fixed and morphometrically analysed under light microscope. The volumes, neuronal densities and total number of neurons of the transplants were compared. Each graft survived best when transplanted to its original region. Good survival was also achieved by heterotopic grafts between regions that are anatomically related. Striatal grafts showed reasonable survival only when transplanted to their original site. In a second series of experiences, the neurons from the same embryonic brain regions were cultured in a defined medium, to which was added tissue extracts from the lesioned regions of the adult brain. The neuronal survival was estimated. The in vitro results are closely related to those obtained in vivo. This experimental evidence agrees with the theory of the existence of a retrograde transport of NGF from the hippocampus to the septum, sustaining the survival of the latter. On the other hand, our results demonstrate the existence of other unidentified neurotrophic factors in the central nervous system which differ from one region to another.     

Septal and Hippocampal Release of Oxytocin, but not Vasopressin, in the Conscious Lactating Rat During Suckling

The central release of both oxytocin and vasopressin within the septum and dorsal hippocampus in response to suckling was studied in conscious, freely-behaving lactating rats. Three consecutive 30-min push-pull perfusions were carried out before, during and after suckling (suckled group) or without suckling (control group). As compared to control levels, suckling resulted in a significantly increased oxytocin release within both limbic brain areas (septum: to 140%, dorsal hippocampus: to 1,600%). After removal of the suckling pups, the oxytocin concentration in the final perfusates remained at the stimulation level (septum) or tended to return to control values (dorsal hippocampus). In contrast to oxytocin, the vasopressin perfusate levels did not differ significantly between unsuckled and suckled rats.     

Arginine vasopressin induces the expression of c-fos in the mouse septum and hippocampus

Arginine vasopressin is a neuropeptide that has been shown to modulate functional ethanol tolerance and memory processes. These actions of vasopressin in the CNS have been shown by us and others to be mediated by V1 receptors. Intracerebroventricular injection of vasopressin in mice resulted in a substantial increase in mRNA for the proto-oncogene c-fos in septum and hippocampus, but no increase in cerebral cortex. A V1-selective agonist also increased septal c-fos mRNA levels, while a V2-selective agonist was less effective. Similarly, the response to vasopressin was more effectively blocked by a V1- than a V2-selective antagonist. These results indicate that vasopressin acts specifically at V1 receptors in mouse septum and hippocampus to increase c-fos mRNA. The vasopressin metabolite, AVP(4-9), also increased c-fos mRNA levels in septum and hippocampus, while the response to oxytocin, which has different effects from vasopressin on memory and tolerance, was greater in hippocampus than in septum. Nerve growth factor, in contrast to the other peptides, had a more pronounced effect on c-fos mRNA levels in cerebral cortex than in the other brain areas. Increased c-fos expression has been hypothesized to play a role in neuroadaptation, and these results suggest that modulation of septal c-fos expression could be important for vasopressin effects on ethanol tolerance and/or memory.     

Fetal hippocampal CA3 cell grafts enriched with FGF-2 and BDNF exhibit robust long-term survival and integration and suppress aberrant mossy fiber sprouting in the injured middle-aged hippocampus

Cell transplants that successfully replace the lost neurons and facilitate the reconstruction of the disrupted circuitry in the injured aging hippocampus are invaluable for treating acute head injury, stroke and status epilepticus in the elderly. This is because apt graft integration has the potential to prevent the progression of the acute injury into chronic epilepsy in the elderly. However, neural transplants into the injured middle-aged or aged hippocampus exhibit poor cell survival, suggesting that apt graft augmentation strategies are critical for robust integration of grafted cells into the injured aging hippocampus. We examined the efficacy of pre-treatment and grafting of donor fetal CA3 cells with a blend of fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF) for lasting survival and integration of grafted cells in the injured middle-aged (12 months old) hippocampus of F344 rats. Grafts were placed at 4 days after the kainic-acid-induced hippocampal injury and were analyzed at 6 months post-grafting. We demonstrate that 80% of grafted cells exhibit prolonged survival and 71% of grafted cells differentiate into CA3 pyramidal neurons. Grafts also receive a robust afferent input from the host mossy fibers and project efferent axons into the denervated zones of the dentate gyrus and the CA1 subfield. Consequently, the aberrant sprouting of the dentate mossy fibers, an epileptogenic change that typically ensues after the hippocampal injury, was suppressed. Thus, grafts of fetal CA3 cells enriched with FGF-2 and BDNF exhibit robust integration and dampen the abnormal mossy fiber sprouting in the injured middle-aged hippocampus. Because the aberrantly sprouted mossy fibers contribute to the generation of seizures, the results suggest that the grafting intervention using FGF-2 and BDNF is efficacious for suppressing epileptogenesis in the injured middle-aged hippocampus.     

Effects of delayed transplantation of cultured Schwann cells on axonal regeneration from central nervous system cholinergic neurons.

The introduction of transplants consisting of cultured Schwann cells and their associated extracellular matrix (Sc/ECM) into a central nervous system (CNS) lesion cavity facilitates axonal regeneration from injured, adult mammalian neurons with subsequent reinnervation of their appropriate target (Kromer and Cornbrooks: Proceedings of the National Academy of Sciences of the United States of America 82:6330-6334, 1985). In the present study, the effects of a delayed transplantation procedure on the time course of this regenerative response were evaluated. For these experiments, bilateral CNS lesions were created between the septum and hippocampus by removing the fimbria-fornix pathway. Lesion cavities received either no transplants, transplants of collagen, or Sc/ECM transplants at the time the lesion was created or 6 days later. When no transplants or transplants of collagen were used, axonal sprouts extended for very short distances into the lesion cavity. These axons were not preferentially associated with the collagen transplants nor maintained at long post-lesion survival times. In animals that received Sc/ECM transplants, the number of sprouting axons and the progression of axonal growth along the transplants was much more extensive than for the collagen transplants. Although more axons were detected in cavities that received transplants immediately after the fimbria-fornix lesion, axonal regeneration along the transplants was similar regardless of whether there was a delay in transplanting the Schwann cells. By using histochemical techniques to identify acetylcholinesterase (AChE), regenerating AChE-positive axons were first detected in the cavity at 3 days post-transplantation, were associated with the Sc/ECM transplants by 5 days, and crossed the cavity within 8 days post-transplantation. Regenerating, neurofilament-positive axons crossed the CNS-Sc/ECM transplant interfaces in association with laminin-positive, glial fibrillary acidic protein-positive cellular pathways. Upon reaching the caudal end of the Sc/ECM transplant, the cholinergic axons abandoned the transplant and oriented directly toward the adjacent hippocampus. Both the simultaneous and delayed transplantation paradigms demonstrated a similar reinnervation pattern of AChE-positive fibers in the hippocampus, but there was a more rapid penetration and more extensive arborization of fibers in animals receiving the delayed transplants. Cholinergic fibers initially invaded the dentate gyrus molecular layer and hilus between 8 and 14 days post-transplantation. By 45 days post-transplantation, AChE-positive axons were detected throughout the dentate gyrus and regio inferior, but few fibers were present in regio superior of the hippocampus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Background and evoked activity of septal and hippocampal neurons transplanted into the neocortex of the rat

Embryonic tissue of the septum and hippocampus was transplanted into a cavity made in parietal neocortex of adult rats. Extracellular recording 4-6 months after grafting revealed units with background spike activity in the grafted tissue. The activity (mean rate 3.6 +/- 0.4 spikes per s) had a random pattern without pathological features. About 90% of the graft cells responded to electrical stimulation of neighbouring cortical tissue with latencies 5-43 ms. The optimal frequencies for driving spike discharges were 5-10 Hz. Postactivatory suppression was observed in most units. The same proportion of the graft cells responded to tactile stimulation of the host animal. Phasic reactions of on-off type with latencies of 50-600 ms were observed. The normalization of the activity in intrabrain grafts as compared to intraocular ones and functional integration of graft units with the host brain are discussed.     

Modulation of memory processing by neuropeptide Y varies with brain injection site

Neuropeptide Y (NPY) is a 36 amino acid peptide which was shown to enhance memory retention, recall and prevent amnesia induced by either scopolamine or anisomycin. In this study, we examined the effects of NPY administration into 6 areas of the mouse brain on memory retention for footshock avoidance training in a T-maze. NPY was injected into the rostral and caudal hippocampus, amygdala, caudate, septum and thalamus shortly after training. NPY improved retention when injected into the rostral portion of the hippocampus and septum, impaired retention in the caudal portion of the hippocampus and amygdala and had no effect in the thalamus and caudate. NPY was ineffective at either improving or impairing retention when injected 24 h after training, thus demonstrating that the effects of NPY on retention were time-dependent and not due to proactive effects on retention test performance per se. In addition, NPY had no effect on retention when injected into overlying cortical areas. NPY antibody impaired retention when administered into the rostral hippocampus and septum; it improved retention in the caudal hippocampus and amygdala. Thus NPY antibody had the opposite effect to that of NPY on memory retention suggesting that NPY has a physiological role as a modulator of memory processing within specific anatomical areas of the central nervous system.     

Collateral projections from the supramammillary nucleus to the medial septum and hippocampus

Previous reports have shown that the supramammillary nucleus projects to the medial septum and to the hippocampus, and specifically to the dentate gyrus and the CA2/CA3a region of the hippocampus. The aim of the present study was to examine collateral projections from the supramammillary nucleus to the septum and hippocampus. The fluorescent retrograde tracers, Fluororuby and Fluorogold, were injected into regions of the septum and hippocampus, respectively, and the supramammillary nucleus was examined for the presence of single- and double-labeled neurons. The main findings were: 1) pronounced numbers of single-labeled cells (about 40-60/section) were present in the supramammillary nucleus following retrograde tracer injections in either the septum or hippocampus; 2) single and double retrogradely labeled neurons were intermingled within the supramammillary nucleus and mainly localized to the lateral two-thirds of the supramammillary nucleus; 3) approximately 5-10% of supramammillary cells were double-labeled, ipsilaterally, and 2-4%, contralaterally, with injections in medial or lateral parts of the medial septum and the dentate gyrus of the hippocampus; and 4) approximately 3-5% of supramammillary cells were double-labeled, ipsilaterally, and 1-2%, contralaterally, with injections in the medial septum and CA2/CA3a of the dorsal hippocampus. Cells of the supramammillary nucleus have been shown to fire rhythmically in bursts synchronous with the hippocampal theta rhythm and have been implicated in the generation of the theta rhythm. The supramammillary cells that we identified with collateral projections to the septum and hippocampus may be directly involved in generation of the theta rhythm.     

Inhibitory influence of GABA on central serotonergic transmission. Raphé nuclei as the neuroanatomical site of the GABAergic inhibition of cerebral serotonergic neurons

Acute injection of the gamma-aminobutyric acid (GABA) mimetics progabide, aminooxyacetic acid, gamma-acetylenic GABA and dipropylacetamide reduced 5-hydroxytryptophan (5-HTP) accumulation in serotonergic nerve terminal regions (prefrontal cortex, olfactory tubercle, septum, striatum, hypothalamus, hippocampus, substantia nigra, cerebellum and spinal cord) as well as in corresponding cell body areas (raphé dorsalis, medianus, pontis and magnus). This effect was antagonized by bicuculline. The inhibition of serotonin (5-HT) synthesis induced by a single progabide administration was accentuated on repeated treatment in the striatum, prefrontal cortex and cerebellum but was similar to that seen after acute treatment in the other areas. Local infusion of high concentrations of GABA or GABA mimetics into the striatum, septum or substantia nigra failed to modify 5-HTP accumulation in these areas. Cerebral hemitransection antagonized the ability of progabide (1200 mg/kg i.p.) to diminish 5-HTP accumulation in the striatum, hippocampus and prefrontal cortex. Intra-raphé dorsalis infusion of muscimol (0.1-100 ng) or GABA (1-100 micrograms) decreased 5-HT synthesis in the corresponding projection areas (e.g. striatum, substantia nigra, cortex) but not in the hippocampus or cerebellum. Conversely, intra-raphé medianus infusion of these drugs diminished 5-HTP accumulation in the corresponding projection areas (e.g. hippocampus, septum, cortex) but not in the striatum or cerebellum. Intra-raphé dorsalis or medianus injection of GABA antagonists (bicuculline, picrotoxinin, RU-5135) was without effect on cerebral 5-HT synthesis but antagonized the diminution of the amine synthesis observed in corresponding projection areas after intra-raphé dorsalis or medianus infusion of muscimol or GABA. These results suggest that GABA exerts an inhibitory (non-tonic) control over central serotonergic neurons which is mediated via GABA receptors located in the raphé nuclei.     

Extensive reinnervation of the hippocampus by embryonic basal forebrain cholinergic neurons grafted into the septum of neonatal rats with selective cholinergic lesions

Reconstruction of the septohippocampal pathways by axons extending from embryonic cholinergic neuroblasts grafted into the neuron-depleted septum has been explored in the neonatal rat by using a novel lesioning and grafting protocol. Neonatal ablation of the basal forebrain cholinergic projection neurons, accompanied by extensive bilateral cholinergic denervation of the hippocampus and neocortex, was produced at postnatal day (PD) 4 by 192 immunoglobulin (IgG)-saporin intraventricularly. Four days later, cholinergic neuroblasts (from embryonic day 14 rats) were implanted bilaterally into the neuron-depleted septum by using a microtransplantation approach. The results show that homotopically implanted septal neurons survive and integrate well into the developing septal area, extending axons caudally along the myelinated fimbria-fornix and supracallosal pathways that are able to reach the appropriate targets in the denervated hippocampus and cingulate cortex as early as 4 weeks postgrafting. Moreover, the laminar innervation patterns established by the graft-derived axons closely resembled the normal ones and remained essentially unchanged up to at least 6 months, which was the longest postoperative time studied. The reinnervating fibers restored tissue choline acetyltransferase activity (up to 50% of normal) in the dorsal hippocampus and the parietooccipital cortex. Retrograde labeling with Fluoro-Gold from the host hippocampus combined with immunocytochemistry confirmed that most of the projecting neurons, indeed, were cholinergic. The results suggest that the graft-host interactions that are necessary for target-directed axon growth are present in the septohippocampal system during early postnatal maturation. Thus, the present approach may contribute to overcome the functional limitations inherent in the use of ectopically placed intrahippocampal transplants. © 1996 Wiley-Liss, Inc.     

NIH-3T3 fibroblast transplants enhance host regeneration and improve spatial learning in ventral subicular lesioned rats

Transplants, besides providing neural replacement, also stimulate host regeneration, which could serve as a powerful means to establish functional recovery in CNS insults. Earlier, we have reported the H3-GFP transplant mediated recovery of cognitive functions in the ventral subicular lesioned rats. In the present study, we demonstrate the efficacy of a non-neural fibroblast transplants in mediating host regeneration and functional recovery in ventral subicular lesioned rats. Adult male Wistar rats were lesioned with ibotenic acid in the ventral subiculum (VSL) and were transplanted with NIH-3T3 fibroblast cells into CA1 region of the hippocampus. Ventral subicular lesioning impaired the spatial task performances in rats and produced considerable degree of dendritic atrophy of the hippocampal pyramidal neurons. Two months following transplantation, the transplants were seen in the dentate gyrus and expressed BDNF and bFGF. Further, the VSL rats with fibroblast transplants showed enhanced expression of BDNF in the hippocampus and enhanced dendritic branching and increased spine density in the CA1 hippocampal pyramidal neurons. Transplantation of fibroblast cells also helped to establish functional recovery and the rats with transplants showed enhanced spatial learning performances. We attribute the recovery of cognitive functions to the graft mediated host regeneration, although the mechanisms of functional recovery remain to be elucidated.     

Development of synapsin I and synapsin II in intraocular hippocampal transplants.

Previous studies have indicated that the appearance of synaptic vesicle-associated proteins known as the synapsins is one indicator of synapse formation. In this study, the levels and morphological distribution of synapsin I and synapsin IIa and IIb were studied in intraocular hippocampal transplants and in situ in the intact hippocampus. No detectable levels of either synapsin I or synapsin II were found in the fetal brain. The in situ levels of the synapsins exhibited parallel increases rapidly after birth, reaching peak levels at 8 weeks, after which a slight decline was noted in synapsin I and synapsin IIb. In hippocampal transplants, a comparable increase in the synapsins was seen during the first 8 weeks in oculo. It is likely that the synapse formation in the hippocampal transplants represents synapses from neurons within the transplant, as well as from various peripheral ganglia that send collaterals into the graft. Peripheral and central synapses express different synapsin I: synapsin IIa and IIb ratios. When the ratios of the synapsin proteins in hippocampal transplants were examined ratios essentially identical to those seen in the normal hippocampus were found, despite the numerous peripheral neurites innervating the grafts. Immunohistochemical studies supported the immunoblot data, showing no detectable immunofluorescence with synapsin antibodies in fetal or newborn hippocampal formation. The density of immunoreactive profiles increased substantially both in transplants and in the hippocampal formation in situ during the first 2 postnatal months. In conclusion, the present data demonstrate that hippocampal transplants in oculo can develop significant levels of the synapsins and that there is no time lag in development in these levels compared to the hippocampal formation in situ.     

Methylmercury induced alterations in the nerve growth factor level in the developing brain.

Pre- and early postnatal stages in the development of the central nervous system (CNS) are very sensitive to the toxic effects of methylmercury. The influence of methylmercury on the level of nerve growth factor (NGF) during the development of CNS was studied. Sprague-Dawley rats were exposed indirectly throughout the fetal and suckling periods until weaning on postnatal day 25 (P 25) via their dams given methylmercury in the diet (3.9 mg/kg diet). In addition, after weaning offsprings were exposed directly to methylmercury via the diet until postnatal day 50 (P 50). The level of NGF was analyzed in cortical areas and in the septum with a sensitive enzyme immunoassay. The pups exposed to MeHg exhibited a 50% elevation in the level of NGF in the hippocampus on P 25 and P 50 compared to control animals. Concomitantly, the level of NGF decreased by 30% in the septum on P 25 and P 50, suggesting that the retrograde transport of NGF from hippocampus to septum could be affected by the exposure of methylmercury. The exact mechanism by which the low level of mercury is affecting the NGF concentration in the developing brain is yet unknown. The increase of NGF in the hippocampus and the decrease of NGF measured in the septum could reflect altered conditions for neurotrophic support in these areas of the brain as a result of the exposure to heavy metal. Thus, this finding might indicate a connection between exposure of heavy metals and neurodegeneration, such as that found in the basal forebrain in Alzheimer's disease.     

Cytoarchitecture and efferent projections of the nucleus incertus of the rat

The nucleus incertus is located caudal to the dorsal raphe and medial to the dorsal tegmentum. It is composed of a pars compacta and a pars dissipata and contains acetylcholinesterase, glutamic acid decarboxylase, and cholecystokinin-positive somata. In the present study, anterograde tracer injections in the nucleus incertus resulted in terminal-like labeling in the perirhinal cortex and the dorsal endopyriform nucleus, the hippocampus, the medial septum diagonal band complex, lateral and triangular septum medial amygdala, the intralaminar thalamic nuclei, and the lateral habenula. The hypothalamus contained dense plexuses of fibers in the medial forebrain bundle that spread in nearly all nuclei. Labeling in the suprachiasmatic nucleus filled specifically the ventral half. In the midbrain, labeled fibers were observed in the interpeduncular nuclei, ventral tegmental area, periaqueductal gray, superior colliculus, pericentral inferior colliculus, pretectal area, the raphe nuclei, and the nucleus reticularis pontis oralis. Retrograde tracer injections were made in areas reached by anterogradely labeled fibers including the medial prefrontal cortex, hippocampus, amygdala, habenula, nucleus reuniens, superior colliculus, periaqueductal gray, and interpeduncular nuclei. All these injections gave rise to retrograde labeling in the nucleus incertus but not in the dorsal tegmental nucleus. These data led us to conclude that there is a system of ascending projections arising from the nucleus incertus to the median raphe, mammillary complex, hypothalamus, lateral habenula, nucleus reuniens, amygdala, entorhinal cortex, medial septum, and hippocampus. Many of the targets of the nucleus incertus were involved in arousal mechanisms including the synchronization and desynchronization of the theta rhythm.     

Neuropeptides in Alzheimer type dementia

Five neuropeptides (cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP), somatostatin (SRIF), neurotensin (NT) and substance P (SP)) were measured in 14 brain areas (4 cortical areas, hippocampus, amygdala, 3 striatal areas, 2 thalamic areas and 3 subcortical areas-- septum, substantia innominata and hypothalamus) in 12 brains with neuropathologically confirmed Alzheimer type change and in 13 control brains. Choline acetyltransferase (CAT) activity was assessed in 6 of these areas. Levels of SRIF, but not those of the other peptides, were reduced in several cortical areas in Alzheimer-type dementia (ATD). The distribution and magnitude of the reduction in SRIF were less than that of CAT activity and the temporal cortex was the only region in which there was a significant relationship between CAT and SRIF deficits. Peptide levels were unchanged in hippocampus, amygdala, thalamus, hypothalamus and striatum (except for an increase in SP in the putamen). SRIF levels were increased in substantia innominata in ATD. NT and SRIF were significantly, and VIP and SP non-significantly, reduced in the septum in ATD. Thus, apart from these alterations in the septum, SRIF was the only neuropeptide for which major changes were identified and these did not follow either the pattern of neuropathological change (e.g. in amygdala and hippocampus) or of CAT deficits (e.g. in substantia innominata).     

Analysis of acetylcholinesterase synthesis and transport in the rat hippocampus: recovery of acetylcholinesterase activity in the septum and hippocampus after administration of diisopropylfluorophosphate

The site and rate of synthesis, as well as the transport dynamics, of newly synthesized acetylcholinesterase (AChE) has been studied in the septum and hippocampus of the rat. Histochemical and biochemical techniques were employed to study time-dependent changes in AChE activity of the medial septal nucleus and hippocampus following systemic administration of the anticholinesterase diisopropyl-fluorophosphate. In both septum and hippocampus, an initially rapid phase of recovery was followed by a slower recovery with similar rate constants for the two regions. Analysis of AChE synthesis in the septo-hippocampal system revealed that recovery of activity in the septum(t_1/2for recovery= 140h) preceded that in the hippocampus(t_1/2for recovery= 400h). The data suggested that the bulk of septal AChE in the hippocampus is transported via the slow component of axoplasmic flow (about 2 mm/day). A fast component may exist, but the experimental arrangement did not permit the clear demonstration of any rapid axoplasmic flow.     

Neural grafts attenuate behavioral deficits produced by early radiation-induced hypoplasia of fascia dentata granule cells

Localized X-irradiation of the mitotic cells in the neonatal rat hippocampus produces a discrete hypoplasia of the fascia dentata granule cell layer. This brain damage inhibits the acquisition of a passive avoidance task, and stimulates spontaneous perseverative turning (without reversals) in a plastic hemisphere apparatus. Here we report how transplantation of fetal brain tissue can attenuate these radiation-induced behavioral deficits. The partially shielded cerebral hemispheres of neonatal rats received fractionated exposures to 13 Gray (Gy) of X-rays during the first 16 days post partum. This procedure depleted 90% of the hippocampal granule cells while sparing other brain areas. Control animals were sham irradiated. Baseline behavioral tests were conducted when subjects reached an average age of 147 +/- 4 days. We recorded behavioral parameters known to be sensitive to hippocampal damage: (1) passive avoidance performance, and (2) perseverative spontaneous turning without reversals. Irradiated subjects later (average age = 182 +/- 4 days) received intracerebral transplants of either fetal (E20-21) neurons/neuronal precursors from the fascia dentata or cerebral cortex (control grafts). Additional controls (both irradiated and sham-irradiated) experienced sham surgical procedures or received no surgical manipulation. Two post-surgical behavioral retests were accomplished when rats were 265 +/- 5 and 351 +/- 6 days old. Rats were then sacrificed and brains were treated histologically to assess radiation-induced brain damage, graft survivability and graft locus. Both hippocampal and cerebral cortex grafts generally facilitated performance on the passive avoidance task. This effect was most prominent during the first post-surgical test. Hippocampal transplants (especially those found to reside in the damaged hippocampus) also significantly attenuated perseverative spontaneous rotation at the time of the final post-surgical test series. Cortex grafts found within the damaged hippocampus did not ameliorate perseverative movements, while cortex grafts located outside the hippocampus significantly reduced this behavioral deficiency. These data suggest that selected behavioral deficits may be attenuated by transplanting fetal neural tissue long after early radiation-induced brain damage. The success of these procedures depends on a number of factors including: (1) the behaviors chosen for analysis, (2) the time after transplantation that behavioral tests are conducted, and (3) the source and final location of the donor neural tissue.