Cholinergic grafts, memory and ageing

Characterization of serum polyunsaturated fatty acid profile in patients with inflammatory bowel disease

Background:

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the digestive tract. The aetiology and pathogenesis of IBD are complex, which may lead to metabolic disorders. As a kind of metabolite, polyunsaturated fatty acid (PUFA) is closely related to IBD.

Objectives:

The aim of this study was to explore the correlation between the serum PUFAs and the pathogenesis of IBD.

Design:

The study is a hospital-based case-control study.

Methods:

The serum free PUFAs of all participants, including 104 patients with IBD and 101 normal controls, were detected by liquid chromatography–mass spectrometry (LC-MS).

Results:

Compared with the normal control, the levels of C18:2, α-C18:3 (ALA), ɤ-C18:3, C20:4 (AA), C20:5 (EPA), ω-3 C22:5, ω-6 C22:5 and C22:6 (DHA) PUFAs in patients with Crohn’s disease (CD) were obviously decreased. However, in patients with ulcerative colitis (UC), the levels of AA, EPA, ω-3 C22:5, ω-6 C22:5 and DHA were downregulated. The concentrations of seven PUFAs were significantly downregulated in the active CD group. In addition, four PUFAs had comparatively higher levels in the remission UC group.

Conclusion:

The present study revealed substantial differences in the levels of serum fatty acids between normal controls and patients with IBD. In detail, patients with CD were deficient in PUFAs, including the essential fatty acids. Moreover, as the disease activity aggravated, some PUFAs decreased dramatically.

Reconstruction of brain circuitry by neural transplants generated from pluripotent stem cells

Pluripotent stem cells (embryonic stem cells, ESCs, and induced pluripotent stem cells, iPSCs) have the capacity to generate neural progenitors that are intrinsically patterned to undergo differentiation into specific neuronal subtypes and express in vivo properties that match the ones formed during normal embryonic development. Remarkable progress has been made in this field during recent years thanks to the development of more refined protocols for the generation of transplantable neuronal progenitors from pluripotent stem cells, and the access to new tools for tracing of neuronal connectivity and assessment of integration and function of grafted neurons. Recent studies in brains of neonatal mice or rats, as well as in rodent models of brain or spinal cord damage, have shown that ESC- or iPSC-derived neural progenitors can be made to survive and differentiate after transplantation, and that they possess a remarkable capacity to extend axons over long distances and become functionally integrated into host neural circuitry. Here, we summarize these recent developments in the perspective of earlier studies using intracerebral and intraspinal transplants of primary neurons derived from fetal brain, with special focus on the ability of human ESC- and iPSC-derived progenitors to reconstruct damaged neural circuitry in cortex, hippocampus, the nigrostriatal system and the spinal cord, and we discuss the intrinsic and extrinsic factors that determine the growth properties of the grafted neurons and their capacity to establish target-specific long-distance axonal connections in the damaged host brain.

Cholinergic modulation of event-related oscillations (ERO)

The cholinergic system in the brain modulates patterns of activity involved in general arousal, attention processing, memory and consciousness. In the present study we determined the effects of selective cholinergic lesions of the medial septum area (MS) or nucleus basalis magnocellularis (NBM) on amplitude and phase characteristics of event related oscillations (EROs). A time-frequency based representation was used to determine ERO energy, phase synchronization across trials, recorded within a structure (phase lock index, PLI), and phase synchronization across trials, recorded between brain structures (phase difference lock index, PDLI), in the frontal cortex (Fctx), dorsal hippocampus (DHPC) and central amygdala (Amyg). Lesions in MS produced: (1) decreases in ERO energy in delta, theta, alpha, beta and gamma frequencies in Amyg, (2) reductions in gamma ERO energy and PLI in Fctx, (3) decreases in PDLI between the Fctx-Amyg in the theta, alpha, beta and gamma frequencies, and (4) decreases in PDLI between the DHPC-Amyg and Fctx-DHPC in the theta frequency bands. Lesions in NBM resulted in: (1) increased ERO energy in delta and theta frequency bands in Fctx, (2) reduced gamma ERO energy in Fctx and Amyg, (3) reductions in PLI in the theta, beta and gamma frequency ranges in Fctx, (4) reductions in gamma PLI in DHPC and (5) reduced beta PLI in Amyg. These studies suggest that the MS cholinergic system can alter phase synchronization between brain areas whereas the NBM cholinergic system modifies phase synchronization/phase resetting within a brain area.

Activation of α7 nicotinic acetylcholine receptors persistently enhances hippocampal synaptic transmission and prevents Aß-mediated inhibition of LTP in the rat hippocampus

Nicotinic acetylcholine receptors mediate fast cholinergic modulation of glutamatergic transmission and synaptic plasticity. Here we investigated the effects of subtype selective activation of the α7 nicotinic acetylcholine receptors on hippocampal transmission and the inhibition of synaptic long-term potentiation by the Alzheimer's disease associated amyloid ß-protein (Aß). The α7 nicotinic acetylcholine receptor agonist "compound A" ((R)-N-(1-azabicyclo[2.2.2]oct-3-yl)(5-(2-pyridyl))thiophene-2-carboxamide) induced a rapid-onset persistent enhancement of synaptic transmission in the dentate gyrus in vitro. Consistent with a requirement for activation of α7 nicotinic acetylcholine receptors, the type II α7-selective positive allosteric modulator PheTQS ((3aR, 4S, 9bS)-4-(4-methylphenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide) potentiated, and the antagonist methyllycaconitine (MLA) prevented the persistent enhancement. Systemic injection of the agonist also induced a similar MLA-sensitive persistent enhancement of synaptic transmission in the CA1 area in vivo. Remarkably, although compound A did not affect control long-term potentiation (LTP) in vitro, it prevented the inhibition of LTP by Aß1-42 and this effect was inhibited by MLA. These findings strongly indicate that activation of α7 nicotinic acetylcholine receptors is sufficient to persistently enhance hippocampal synaptic transmission and to overcome the inhibition of LTP by Aß.

Combining the cell-encapsulation technique and axon guidance for cell transplantation therapy

In cell transplantation therapy for the treatment of neurodegenerative disorders, encapsulation of implanted cells in a semipermeable membrane is a promising approach to protect the implanted cells from host immune rejection and inhibit the invasion of tumor into surrounding tissue if the implanted cells form a tumor after transplantation. However, implanted neurons isolated by capsules could not build connections with host neurons, preventing the implanted neurons from responding to stimuli from host neurons. In the present study, we focused on the passage of neurites and axons navigated by axon guidance molecules through membrane pores to enable encapsulated neurons and host neurons to form connections. The type of matrix coated on membranes and the pore size of the membranes greatly affected the successful passage of PC12 neurites through membrane pores. PC12 neurites preferably passed through collagen-coated membranes with pores greater than 0.8 μm in diameter, but the neurites did not pass through albumin- or fibronectin-coated membranes or membranes with pores less than 0.1 μm in diameter. We could navigate the direction of commissural neural axon extensions by utilizing the axon guidance molecules secreted from floor plate and make guided axons pass through the membrane pores. These results suggest the feasibility of building connections between encapsulated neurons and host neurons by encapsulating the implanted neurons and axon guidance molecules, which attract the axons of host neurons into the capsule, in the porous membranes with suitable pore size and matrix coating.

The facilitative effects of glucose ingestion on memory retrieval in younger and older adults: is task difficulty or task domain critical?

The ingestion of a glucose-containing drink has been shown to improve cognitive performance, particularly memory functioning. However, it remains unclear as to the extent to which task domain and task difficulty moderate the glucose enhancement effect. The aim of this research was to determine whether boosts in performance are restricted to particular classes of memory (episodic v. semantic) or to tasks of considerable cognitive load. A repeated measures (25g glucose v saccharin), counterbalanced, double-blind design was used with younger and older adults. Participants performed a battery of episodic (e.g. paired associate learning) and semantic memory (e.g. category verification) tasks under low and high cognitive load. Electrophysiological measures (heart rate and galvanic skin response) of arousal and mental effort were also gathered. The results indicated that whilst glucose appeared to aid episodic remembering, cognitive load did not exaggerate the facilitative effect. For semantic memory, there was little evidence to suggest that glucose can boost semantic memory retrieval even when the load was manipulated. One exception was that glucose facilitated performance during the difficult category fluency task. Regardless, the present findings are consistent with the domain-specific account in which glucose acts primarily on the hippocampal region, which is known to support episodic memory. The possible contribution of the hippocampus in semantic memory processing is also discussed.

Optimising plasticity: environmental and training associated factors in transplant-mediated brain repair

With progressively ageing populations, degeneration of nerve cells of the brain, due to accident or disease, represents one of the major problems for health and welfare in the developed world. The molecular environment in the adult brain promotes stability limiting its ability to regenerate or to repair itself following injury. Cell transplantation aims to repair the nervous system by introducing new cells that can replace the function of the compromised or lost cells. Alternatives to primary embryonic tissue are actively being sought but this is at present the only source that has been shown reliably to survive grafting into the adult brain and spinal cord, connect with the host nervous system, and influence behaviour. Based on animal studies, several clinical trials have now shown that embryonic tissue grafts can partially alleviate symptoms in Parkinson's disease, and related strategies are under evaluation for Huntington's disease, spinal cord injury, stroke and other CNS disorders. The adult brain is at its most plastic in the period following injury, offering a window of opportunity for therapeutic intervention. Enriched environment, behavioural experience and grafting can each separately influence neuronal plasticity and recovery of function after brain damage, but the extent to which these factors interact is at present unknown. To improve the outcome following brain damage, transplantation must make use of the endogenous potential for plasticity of both the host and the graft and optimise the external circumstances associated with graft-mediated recovery. Our understanding of mechanisms of brain plasticity subsequent to brain damage needs to be associated with what we know about enhancing intrinsic recovery processes in order to improve neurobiological and surgical strategies for repair at the clinical level. With the proof of principle beginning to emerge from clinical trials, a rich area for innovative research with profound therapeutic application, even broader than the specific context of transplantation, is now opening for investigation.

Aging and subcellular localization of m2 muscarinic autoreceptor in basalocortical neurons in vivo

By using immunohistochemical approaches at the light and electron microscopic levels, we have shown that aging modifies the subcellular distribution of the m2 muscarinic autoreceptor (m2R) differentially at somato-dendritic postsynaptic sites and at axonal presynaptic sites in cholinergic basalocortical neurons, in vivo. In cholinergic perikarya and dendrites of the nucleus basalis magnocellularis (NBM), aging is associated with a decrease of the density of m2R at the plasma membrane and in the cytoplasm, suggesting a decrease of the total number of m2R in the somato-dendritic field. In contrast, the number of substance P receptors per somato-dendritic surface was not affected. In the frontal cortex (FC), we have shown a decrease of cytoplasmic m2R density also leading to a decrease of the number of m2R per surface of varicosities but with no change of the density of m2R at the membrane. Our results suggest that the decrease of m2R in the somato-dendritic field of the NBM, but not a modification of the number of presynaptic m2 autoreceptors at the plasma membrane in the FC, could contribute to the decrease of the efficacy of cholinergic transmission observed with aging in the rat.

The newly synthesized linoleic acid derivative FR236924 induces a long-lasting facilitation of hippocampal neurotransmission by targeting nicotinic acetylcholine receptors

The newly synthesized linoleic acid derivative, FR236924, induces a long-lasting facilitation of hippocampal neurotransmission based on a persistent enhancement in the activity of presynaptic nicotinic ACh receptors via a PKC pathway and the ensuing increase in glutamate release, not only in vitro but in vivo at a low dosage (2mg/kg, ip), which suggested the possibility of its use as a promising anti-dementia drug.

Fimbrial control of bidirectional synaptic plasticity of medial perforant path-dentate transmission

Lesions of the fimbria-fornix (FF) tract cause profound impairments of cognitive ability in animals. Our previous study showed that spatial performance correlates with long-term potentiation (LTP) of the dentate gyrus (DG), but not of the CA1 region, in rats with bilateral FF lesions, suggesting that FF lesions selectively inhibited LTP in the DG. The cortical input to the DG is anatomically and physiologically divided into two types of afferents, i.e., the medial perforant path (MPP) and the lateral perforant path (LPP), which show distinct synaptic properties. To elucidate the difference in the FF modulation of these two inputs, field responses were recorded from MPP- or LPP-DG synapses in anesthetized rats. MPP-DG synapses of rats with FF lesions displayed neither LTP in response to theta-burst stimulation nor long-term depression (LTD) in response to low-frequency burst stimulation. In contrast to the MPP, LPP-DG synapses showed normal LTP in rats with FF lesions. The low-frequency burst stimulation could not induce LTD at LPP-DG synapses in either intact or FF-lesioned rats. These results suggest that the FF pathway selectively supports the mechanisms of bidirectional synaptic plasticity at MPP-DG synapses. This study provides new insights into external control of information processing in the hippocampus.

Reduced [125I]-Bolton Hunter substance P binding (NK1 receptors) in the basal forebrain nuclei of aged rats

1. Quantitative autoradiography and homogenate radioligand binding of [125I]-Bolton Hunter substance P ([125I]-BHSP) were used to compare brain NK1 receptors in young (2 months) and aged (18-20 months) rats. 2. The autoradiographic distribution and density of [125I]-BHSP binding sites was similar in all cortical regions of young and aged rats. In contrast, the density of [125I]-BHSP binding sites was significantly (P < 0.05) lower in the basal forebrain nuclei (intermediate part of the lateral septal nuclei, medial septal nucleus and horizontal and vertical nuclei of the diagonal band) of aged rats. In all other brain regions examined, binding densities were almost identical in young and aged rats. 3. Because a population of NK1 receptors ([125I]-BHSP binding sites) in the basal forebrain nuclei is associated with cholinergic neurons, the decrease in NK1 receptors in aged rats may reflect degeneration of cholinergic neurons and contribute to the motor and cognitive deficiencies that occur with ageing.

Conditioned blocking is re-established by neurotransplantation in mature rats

Aging has been associated with a decay of hippocampal function that may begin well before senescence. Conditioned blocking is a complex learning phenomenon that requires an intact hippocampus in young-adult rats and is absent in middle-aged rats. The aim of the present study was to test the possibility of re-establishing conditioned blocking in 17-month-old Wistar rats by neurotransplantation. Solid embryonic hippocampal or nigral tissue was bilaterally transplanted in the proximity of the dorsal hippocampus (lateral ventricle and alveus). Conditioned blocking of an aversion to a cider vinegar (3%) solution presented in compound with a previously conditioned saccharin solution (0.1%) appeared 14 days after transplantation and persisted 3 months later only in the hippocampal grafted group, showing the possibility of restoring age-related cognitive deficits.

Selective cholinergic denervation inhibits expression of long-term potentiation in the adult but not infant rat hippocampus

The present study assessed the role of the cholinergic systems on the expression of perforant path long-term potentiation (LTP) in rat hippocampal slices from the infant and adult brain. To denervate the cholinergic systems, 192 IgG--saporin was injected into the lateral ventricle of the infant (2-weeks-old) and adult (6-weeks-old) rat brain. There, choline acetyltransferase-immunoreactive fibers were barely detectable 2 weeks and 2 months after injection for both the groups. For the infant rats, perforant path LTP was not affected by selective cholinergic denervation; the probability of LTP development was 0.83 (five out of six slices) and 0.78 (seven out of nine slices) at 2 weeks and 2 months later in 192 IgG--saporin-treated slices, as compared with 0.83 at each period in control saline-treated slices. In contrast, the expression of the LTP was blocked by selective cholinergic denervation for the adult rats; the probability of LTP development was 0 (zero out of 10 slices) and 0.38 (three out of eight slices) at 2 weeks and 2 months later in 192 IgG--saporin-treated slices, as compared with 0.8 (eight out of 10 slices) and 0.83 (five out of six slices) at each period in control saline-treated slices. The results of the present study thus suggest that the cholinergic systems play a crucial role in the expression of LTP in the adult brain and that the denervated systems in the infant brain could be compensated by the sprouting of non-cholinergic fibers.

Presynaptic nicotinic acetylcholine receptors as a functional target of nefiracetam in inducing a long-lasting facilitation of hippocampal neurotransmission

Nefiracetam (1-10 microM), a nootropic (or cognition-enhancing) agent, persistently potentiated currents through Torpedo acetylcholine (ACh) receptors expressed in Xenopus oocytes as a result of interacting with a protein kinase C pathway and the ensuing protein kinase C phosphorylation of the receptors. A similar effect was found in neuronal nicotinic ACh receptors (alpha4beta2 and alpha7). In contrast, the other nootropic agents such as piracetam and aniracetam had no potentiating action on the receptors. A sustained enhancement in the activity of nicotinic ACh receptors induced by nefiracetam caused a marked increase in the glutamate release, leading to a long-term potentiation-like facilitation of hippocampal synaptic transmissions. One of the consistent neuropathologic features of the Alzheimer brain is a loss of nicotinic ACh receptors. This fact, together with the results of our study, raises the possibility that the loss of nicotinic ACh receptors may be a key factor in the decline of cognitive function observed in Alzheimer disease and that agents targeting neuronal nicotinic ACh receptors like nefiracetam could, therefore, be of great therapeutic importance.

The anti-dementia drug nefiracetam facilitates hippocampal synaptic transmission by functionally targeting presynaptic nicotinic ACh receptors

Nefiracetam, a pyrrolidone derivative developed as an anti-dementia drug, persistently potentiated currents through neuronal nicotinic acetylcholine (ACh) receptors (alpha7, alpha4beta2) expressed in Xenopus oocytes, and the potentiation was blocked by either the selective protein kinase C (PKC) inhibitors, GF109203X and staurosporine, or co-expressed active PKC inhibitor peptide. In primary cultures of rat hippocampal neurons, nefiracetam increased the rate of nicotine-sensitive miniature excitatory postsynaptic currents, without affecting the amplitude, and the increase was inhibited by GF109203X. In addition, the drug caused a marked increase in the glutamate release from electrically stimulated guinea pig hippocampal slices, and the effect was abolished by the nicotinic ACh receptor antagonists, alpha-bungarotoxin and mecamylamine. Nefiracetam induced a long-lasting facilitation of synaptic transmission in both the CA1 area and the dentate gyrus of rat hippocampal slices, and the facilitation was inhibited by alpha-bungarotoxin and mecamylamine. Such facilitatory action was still found in the hippocampus with selective cholinergic denervation. The results of the present study, thus, suggest that nefiracetam enhances activity of nicotinic ACh receptors by interacting with a PKC pathway, thereby increasing glutamate release from presynaptic terminals, and then leading to a sustained facilitation of hippocampal neurotransmission. This may represent a cellular mechanism underlying the cognition-enhancing action of nefiracetam. The results also provide the possibility that nefiracetam could be developed as a promising therapeutic drug for senile dementia or Alzheimer's disease.

Nefiracetam facilitates hippocampal neurotransmission by a mechanism independent of the piracetam and aniracetam action

Nefiracetam, a nootropic (cognition-enhancing) agent, facilitated neurotransmission in the dentate gyrus of rat hippocampal slices in a dose-dependent manner at concentrations ranged from 1 nM to 1 microM, being evident at 60-min washing-out of the drug. The facilitatory action was blocked by the nicotinic acetylcholine (ACh) receptor antagonists, alpha-bungarotoxin and mecamylamine. A similar facilitation was induced by the other nootropic agents, piracetam and aniracetam, but the facilitation was not inhibited by nicotinic ACh receptor antagonists and it did not occlude the potentiation induced by nefiracetam. In the Xenopus oocyte expression systems, nefiracetam potentiated currents through a variety of neuronal nicotinic ACh receptors (alpha 3beta 2, alpha 3beta 4, alpha 4 beta 2, alpha 4 beta 4, and alpha 7) to a different extent. In contrast, neither piracetam nor aniracetam had any potentiating action on alpha 7 receptor currents. While aniracetam delayed the decay time of currents through the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor, GluR1, -2, -3, expressed in oocytes, nefiracetam or piracetam had no effect on the currents. Nefiracetam, thus, appears to facilitate hippocampal neurotransmission by functionally targeting nicotinic ACh receptors, independently of the action of piracetam and aniracetam.

Intrahippocampal cholinergic-rich transplants restore lead-induced deficits: a preliminary study in rats

In the present study restorative potential of fetal cholinergic rich cell suspensions in ameliorating cognitive deficits in rats perinatally exposed to lead was studied. Lactating dams with 1-day old litters were given 0.2% (w/v) lead acetate in drinking water throughout lactation from postnatal day (PND) 1 to PND21 at the end of which the treatment was stopped and the animals were weaned. On PND42 lead exposed rats were given bilateral, intrahippocampal, cholinergic rich fetal neural transplants (approximately 60,000 cells per site) and subsequently assessed 3 and 6 months posttransplantation. Control animals (Sham operated and transplanted) were also run in parallel. Lead exposed rats exhibited a decreased learning ability and locomotor activity. A significant decrease in the levels of acetylcholinesterase and sodium potassium ATPase Na+,K+-ATPase activity was observed in hippocampal region of lead exposed rats. The levels of lead were increased by fivefold in the hippocampal region of lead exposed rats. Transplantation showed marginal improvement in the above impairments at 3 months which were more marked at 6 months. Lead levels at 6 months were not significantly higher in lead exposed rats as compared with the control. Results confirm previous findings that fetal neural transplants help in restoring the lost functional deficits and demonstrate their restorative potential in case of lead induced deficits.

A 'long-term-potentiation-like' facilitation of hippocampal synaptic transmission induced by the nootropic nefiracetam

Nefiracetam, a nootropic agent, enhanced the slope of field excitatory postsynaptic potentials in the CA1 region of rat hippocampal slices to about 170% of basal levels, being evident still at 4-h washing-out of the drug. A similar sustained enhancement (>/=16 h after i.m. injection with nefiracetam) was observed in the population spikes recorded from the granular cell layer of the intact mouse hippocampus. Saturation of the enhancement in the synaptic strength occluded potentiation obtained with long-term potentiation (LTP) induced by high-frequency (tetanic) stimulation, and vice versa. Interestingly, the facilitatory action of nefiracetam was blocked by either the nicotinic acetylcholine (ACh) receptor antagonists, alpha-bungarotoxin and mecamylamine, or the selective protein kinase C (PKC) inhibitor, GF109203X, but in contrast, it was not affected by D-2-amino-5-phosphonovaleric acid (APV), a selective N-methyl-D-aspartate (NMDA) receptor antagonist. The results of the present study suggest that nefiracetam, whereas the action is independent of NMDA receptors, induces an 'LTP-like' facilitation of hippocampal synaptic transmission as a consequence of modulation of nicotinic ACh receptors and PKC. This may represent a likely mechanism underlying the cognition-enhancing actions of nefiracetam.

Control of resolution and perception in working memory

Mechanisms underlying and controlling resolution and perception in working memory are studied by means of a pulse-coupled network model. It is shown that the adaptivity, i.e. the degree to which previous activity affects the ability to fire, of the excitatory units can control several aspects of the network dynamics in a coordinated way to enable multiple items to be resolved and perceived in working memory. One basic aspect is the complexity of the dynamics that regulates the temporal resolution of several items. The slow NMDA-receptor-mediated component of synaptic couplings to excitatory units facilitates successive activations of a given item. The dimension of the activated subspace of the complete available neural representation space is gradually decreased as adaptivity is reduced. It is also shown that the formation of perception by sufficiently intense and coherent activation of different features of an object can be controlled concurrently with resolution by the adaptivity. The mechanisms derived can account for the observed capacity of working memory with respect to number of items consciously resolved and also for the observed temporal separation of different items. Numerous observations link neuromodulators to cognitive functions and to various brain disorders involving working memory. Based on the influence of various neuromodulators on neuronal adaptivity, the model can also account for neuromodulatory regulation of working memory functions.

Modelling recovery of cognitive function after traumatic brain injury: spatial navigation in the Morris water maze after complete or partial transections of the perforant path in rats

The Morris water maze (MWM) has been used to assess cognitive function in rats after a variety of lesions designed to model brain damage and to assess the effects of drugs, growth factors, and neural transplants on post-operative deficits. The present study examined recovery of spatial navigation in the MWM over time in order to model the spontaneous recovery of cognitive function seen in humans. Diffuse axonal injury, a neuropathology commonly associated with traumatic brain injury (TBI), was modelled by transecting the perforant path (PP) bilaterally, either caudal to the hippocampus or dorsal to it at the decussation of the dorsal hippocampal commissure. Both groups with PP cuts showed substantial deficits initially, but spatial performance recovered with time and training. Recovery of platform finding was nearly complete within 14 days of testing, but recovery of platform searching did not occur for 2 or 3 more weeks. When the platform was moved to a new location, a continuing deficit in learning rate was revealed. When the platform was moved to a new position every day, this deficit was even more evident. These results illustrate the multi-faceted nature of recovery after brain injury and provide a new model for assessing the effects of manipulations designed to modulate recovery.

High potassium enhances secretion of neurotrophic factors from cultured astrocytes

Elevation of extracellular potassium concentration ([K+]o) in the central nervous system (CNS), which is observed such after physiological stimuli and during ischemia, is known to be regulated by astrocytes. We suspected that in response to increased [K+]o, astrocytes might secrete some neurotrophic factor(s) to promote the survival of active and/or ischemically damaged neurons. In the present study, we examined neurotrophic activity contained in HK-ACM, i.e., astrocyte-conditioned medium (ACM) obtained after culturing astrocytes in 40 mM potassium-containing medium (HK medium). Addition of HK-ACM to basal forebrain cultures from postnatal 2-week-old (P2w) rats increased both the choline acetyltransferase (ChAT) activity (4.40-fold) and the number of ChAT-positive neurons (2.01-fold) as compared with non-conditioned HK medium. On the other hand, the neurotrophic effects of LK-ACM, i.e., ACM collected after culturing astrocytes in 4 mM potassium-containing medium (LK medium), were much weaker (2.85- and 1.41-fold for ChAT activity and number of ChAT-positive neurons, respectively) than those of HK-ACM. The neurotrophic effects of ACMs increased in a manner dependent on potassium concentration and on astrocyte culture time. Addition of an antibody against nerve growth factor (NGF) neutralized the neurotrophic effects of HK- and LK-ACMs. Direct quantification of NGF protein in ACMs by the two-site ELISA method demonstrated that a high concentration of potassium enhanced NGF secretion from cultured astrocytes. These results suggested that astrocytes secrete NGF in response to [K+]o elevation in the CNS.

Neurotrophin-mediated neuroprotection by solid fetal telencephalic graft in middle cerebral artery occlusion: a preventive approach

In the present study, embryonic rat neocortex was implanted into the parietal subcortical area of adult naive animals. On the 7th day, the middle cerebral artery was permanently occluded ipsilateral to the graft. Twenty-four hours after middle cerebral artery occlusion, the extent of infarct was visualized by means of 2,3,5-triphenyltetrazolium chloride histochemistry and quantified in four different standardized coronal plains. Subsequently, the effects of fetal tissue grafting and those of transplantation were identified by using glial fibrillary acidic protein and nerve growth factor immunocytochemistry. The grafts integrated well into their new environment and significantly reduced the size of infarct in middle cerebral artery-occluded animals compared with both sham-operated and control rats 24 h postoperation. The underlying mechanism of this phenomenon might be an increased neurotrophic, particularly nerve growth factor, release by the grafted fetal tissue. Moreover, reactive astroglial cells may also trigger the neuroprotection by additional ischemia-induced nerve growth factor release. The present data demonstrate the potential neurotrophin-mediated protective effects of fetal brain tissue implanted into the adult rat brain before unilateral middle cerebral artery occlusion and the beneficial effects of astrocyte activation.

Amelioration of spatial navigation and short-term memory deficits by grafts of foetal basal forebrain tissue placed into the hippocampus and cortex of rats with selective cholinergic lesions

Impairments in learning and memory, induced by surgical or excitotoxic lesions of the septo-hippocampal or basalo-cortical pathways, can be ameliorated by grafts of cholinergic-rich foetal basal forebrain tissue into the hippocampus and/or neocortex. However, the effects of such grafts have been only partial, which may be due to the non-specific nature of the lesioning procedures used in these studies, known to destroy both cholinergic and non-cholinergic neuronal projections. In the present study, we have explored the effects of cholinergic-rich grafts in rats subjected to selective cholinergic lesions, induced by intraventricular injections of the immunotoxin 192 IgG-saporin. This lesion, which selectively destroyed 85-95% of the cholinergic neurons in both the septal-diagonal band and nucleus basalis, produced a long-lasting, substantial impairment in both the acquisition of spatial reference memory in the Morris water maze task and delay-dependent short-term memory performance, as seen in a delayed matching-to-position test. Foetal cholinergic grafts (but not control grafts of cerebellar tissue) implanted at multiple sites into both the hippocampus and fronto-parietal neocortex, bilaterally, completely reversed the acquisition deficit in place navigation in the water maze, to an extent that greatly exceeded that previously seen in animals with non-selective lesions. Most notably, however, the impairment in short-term memory was only partially and inconsistently affected, and only at the longest delay times. The morphological analysis, performed at about 7 months after transplantation, showed that the grafts had re-established a close to normal cholinergic innervation in the initially denervated cortical and hippocampal territories. It is proposed that the differential effects of cholinergic-rich transplants on different aspects of cognitive performance may define intrinsic limitations to the functional capacity of the ectopically placed grafts, which may be due to incomplete integration of the grafted cholinergic neurons into functional regulatory circuitries normally available to the basal forebrain cholinergic system.

GM1 and the aged brain

Aging is associated with the loss of brain neurotransmitter function, which apparently is the substrate for an adverse constellation of age-associated symptoms. In particular, cholinergic deficits have been associated with cognitive impairment in aging. Systemic administration of GM1 ganglioside, 30 mg/kg, i.p., for 30 days, enhances the cholinergic neurochemical presynaptic markers, choline acetyltransferase, choline uptake, and acetylcholine, in the brain and spinal cord of aged 22-24-month-old Sprague-Dawley rats. In addition to correcting cholinergic neurochemistry, it improves spatial learning and memory impairment, and restores the number and the size of the cholinergic neurons in the basal forebrain and striatum. The induced neuronal recovery by GM1 is long-lasting.

Cholinergic modulation, visual function and Alzheimer's dementia

Electrophysiological evidence at a cellular level and in vivo macroelectrode recordings converge in indicating a degree of specificity of acetylcholine action in vision. Acetylcholine (ACh) function is also thought to play a significant role in memory, learning and other cognitive processes. In this respect, ACh action is suggested to serve in both sensory and cognitive processes. The pharmacological blocking of brain muscarinic transmission has been proposed as a model of geriatric memory impairment and Alzheimer's dementia. Visual electrophysiological testing is deemed of diagnostic specificity for this disease. ACh brain neurotransmission, however, mostly contributes to the modulation of nonspecific aspects of cognition, such as arousal or attention. Alzheimer's dementia results from complex neuron alterations [which also affect muscarinic receptors among other (sub)cellular structures] rather than simply reflecting ACh impoverishment. A substantial loss of retinal ganglion cells is documented in patients with Alzheimer's disease and is consistent with electrophysiological observations. However, it is unclear to what extent the dysfunction of the visual system observable in Alzheimer's dementia is qualitatively different from that occurring spontaneously during aging. The dissimilarities between the effect of acute muscarinic blocking (e.g. by scopolamine) and dementia outnumber the similarities. Accordingly, the conventional ACh agonist-antagonist model of dementia now appears questionable, and replacement treatment with compounds enhancing ACh function proved disappointing. It is suggested that (nonspecific) ACh action becomes function-specific, as determined by the architecture of local brain circuits in which it is involved.

Fetal hippocampal transplants restore conditioned blocking in rats with dorsal hippocampal lesions: effect of age

Previous studies have shown that conditioned blocking of taste aversion learning in 3-month-old Wistar rats depends on the hippocampal system integrity. Thus, the aim was to demonstrate that enough connectivity would develop after a graft to support the attention mechanism required for conditioned blocking. In the first experiment, bilateral homotopic grafts of 16-17 day-old hippocampal fetal tissue applied to 3-month-old male Wistar rats after electrolytical lesions of the dorsal hippocampus reinstated conditioned blocking tested 5 months after the transplantation. Unexpectedly, an early age-dependent impairment of conditioned blocking, similar to that induced by hippocampal lesions, was found in the 8-month-old control group. This finding was further supported by the results of the second experiment. Non-operated 3-month-old but not 8-month-old Wistar rats showed conditioned blocking. The results are discussed in terms of early hippocampal vulnerability, prevented by fetal grafts.

A neural mechanism of the generation of meaning in cognitive processes

A neural mechanism for control of computational dynamics underlying the generation of meaning in cognitive processes is demonstrated. Meaning derives from recognition of connections between items in related conceptual classes of the neural representation in the brain. It is generated from a stimulated item in one conceptual class by an associative process in which linked items in related conceptual classes are activated in parallel. The complexity of the dynamics of this process varies between exploratory and direct retrieval modes. It is shown that the dynamics mode of the generation of meaning can be controlled by the neuronal adaptivity, i.e., the coupling strength between neuronal activity and excitability. Neuronal adaptivity in turn is controlled by neuromodulators in the brain. An autonomous regulation of the dynamics can be accomplished by an activity-dependent release of neuromodulators. The generation of a sequence of bifurcations from an initial exploratory phase to a final retrieval of appropriate item in each conceptual class is demonstrated. The time required for retrieval is shown also to depend on synaptic coupling strengths. The involvement of neuromodulatory systems in cognitive processes has long been observed but the underlying mechanisms not known. The present model describes a mechanism based on the primary effect observed of neuromodulators, viz. that on neuronal adaptivity, and is shown to be consistent with many neuroanatomical, neurophysiological and behavioural observations.

Immune response to murine cell lines of glial origin transplanted into the central nervous system of adult mice

Temperature-sensitive simian virus 40 (SV40) T antigen-transformed central nervous system (CNS)-derived murine cell lines were used to analyse the host response to transplantation in the mouse adult brain. The cell lines were shown to be susceptible to immune recognition in vitro by cytotoxic effector cells indicating that tissue-specific privilege was not in operation. Histological examination at time points post-implantation showed characteristic responses similar to those seen during graft rejection. Astrocytosis and up-regulation of major histocompatibility complex (MHC) class I and MHC class II activation of resident microglia and recruitment of macrophages were observed in both allogeneic and syngeneic hosts 10 days post-implantation suggesting a trauma-induced response. However, the response in allogeneic hosts was more widespread and evident when the syngeneic responses had returned to normal levels. Evidence of T-cell infiltration was also more pronounced in the allogeneic hosts. Despite quite extensive host reactions to these cellular grafts at early time-points the implants appeared to survive in the host CNS long after the responses had abated and could be detected at the maximum time-point studied of 40 days.

GM1 ganglioside improves spatial learning and memory of aged rats

GM1 ganglioside, 30 mg/kg, i.p., was administered to cognitively impaired aged rats for 30 days, and spatial learning and memory evaluated in a Morris water maze paradigm. During treatment with GM1, aged animals improved both the acquisition and retention of place navigation, as reflected by reduced escape latencies and swim distances to a hidden platform, and persistently performed better than the aged control animals. Furthermore, the GM1-treated animals showed improved spatial acuity in a spatial probe test when the hidden platform was removed. The improved performance in place navigation was not lost if GM1 treatment was discontinued and the animals tested up to 15 days later. GM1 treatment had no effect on the performance of young rats in the water maze. These results indicate that memory deficits associated with aging can be attenuated by treatment with GM1 ganglioside.

Nitric oxide synthase in ventral forebrain grafts and in early ventral forebrain development

Embryonic ventral forebrain (VFB) grafts to cortex contain neurons that synthesize acetylcholine and partially ameliorate behavioral deficits caused by excitotoxic damage to the nucleus basalis magnocelullaris in rats. An additional neurotransmitter, nitric oxide (NO), is synthesized by a subset of cholinergic neurons in rat ventral forebrain. If this neurotransmitter is expressed also by grafted cholinergic neurons (which include the embryonic medial septum and diagonal band), its functional contribution should be considered. Six to twelve months after transplantation of embryonic VFB tissue rats were sacrificed. Brain tissue was processed either for in situ hybridization of nNOS and neuropeptide Y (NPY) or for immunohistochemistry of choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS). Quantification of messenger ribonucleic acid (mRNA) for nNOS was performed with radioactively labeled probes (silver grains were counted) and a preliminary comparison was made of graft sections to sections of the ventral forebrain of developing rats. Plots of silver grain counts against cell size revealed similar patterns in the grafts and in the ventral forebrain of developing rats. The rates of expression of mRNA for nNOS in the grafts were intermediate between those of the ventral forebrain of postnatal day 19 and those of postnatal day 12. Double immunohistochemical labeling revealed that 45.87 + 8.26% of cells expressing ChAT also expressed nNOS in the grafts, significantly higher than 33.16 + 3.9% which was the rate of co-expression observed in the adult ventral forebrain. This study suggests that possible contribution of NO to graft-associated modulation of behavior should be examined.

Ionic mechanisms of muscarinic depolarization in entorhinal cortex layer II neurons

The mechanisms underlying direct muscarinic depolarizing responses in the stellate cells (SCs) and non-SCs of medial entorhinal cortex layer II were investigated in tissue slices by intracellular recording and pressure-pulse applications of carbachol (CCh). Subthreshold CCh depolarizations were largely potentiated in amplitude and duration when paired with a short DC depolarization that triggered cell firing. During Na+ conductance block, CCh depolarizations were also potentiated by a brief DC depolarization that allowed Ca2+ influx and the potentiation was more robust in non-SCs than in SCs. Also, in non-SCs, CCh depolarizations could be accompanied by spikelike voltage oscillations at a slow frequency. In both SCs and non-SCs, the voltage-current (V-I) relations were similarly affected by CCh, which caused a shift to the left of the steady-state V-I relations over the entire voltage range and an increase in apparent slope input resistance at potentials positive to about -70 mV. CCh responses potentiated by Ca2+ influx demonstrated a selective increase in slope input resistance at potentials positive to about -75 mV in relation to the nonpotentiated responses. K+ conductance block with intracellular injection of Cs+ (3 M) and extracellular Ba2+ (1 mM) neither abolished CCh depolarizations nor resulted in any qualitatively distinct effect of CCh on the V-I relations. CCh depolarizations were also undiminished by block of the time-dependent inward rectifier Ih, with extracellular Cs . However, CCh depolarizations were abolished during Ca2+ conductance block with low-Ca2+ (0.5 mM) solutions containing Cd2+, Co2+, or Mn2+, as well as by intracellular Ca2+ chelation with bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid. Inhibition of the Na+-K+ ATPase with strophanthidin resulted in larger CCh depolarizations. On the other hand, when NaCl was replaced by N-methyl-D-glucamine, CCh depolarizations were largely diminished. CCh responses were blocked by 0.8 microM pirenzepine, whereas hexahydro-sila-difenidolhydrochloride,p-fluoroanalog (p-F-HHSiD) and himbacine were only effective antagonists at 5- to 10-fold larger concentrations. Our data are consistent with CCh depolarizations being mediated in both SCs and non-SCs by m1 receptor activation of a Ca2+-dependent cationic conductance largely permeable to Na+. Activation of this conductance is potentiated in a voltage-dependent manner by activity triggering Ca2+ influx. This property implements a Hebbian-like mechanism whereby muscarinic receptor activation may only be translated into substantial membrane depolarization if coupled to postsynaptic cell activity. Such a mechanism could be highly significant in light of the role of the entorhinal cortex in learning and memory as well as in pathologies such as temporal lobe epilepsy.

Effects of combined ventral forebrain grafts to neocortex and amygdala on behavior of rats with damage to the nucleus basalis magnocellularis

In rats with damage to the nucleus basalis magnocellularis, transplantation of the embryonic ventral forebrain to the neocortex improves behavioral performance in some behavioral tasks. The present investigation focuses on improvement of behavioral performance by combined graft placement to both neocortex and amygdala. Male rats received unilateral microinjections of quisqualate to the nucleus basalis magnocellularis to produce cell damage. Embryonic ventral forebrain cell suspensions were placed in one group of rats in the frontal and parietal neocortex, in a second group in the amygdala, and in a third group in the frontal and parietal neocortex and in the amygdala. These groups were compared to a group of nonoperated rats and a group of rats with damage but with no grafts. Quisqualate-induced damage to the nucleus basalis magnocellularis reduced cholinergic innervation in the ipsilateral cortical hemisphere, impaired performance in the one-trial training version of passive avoidance, an increased motility and time spent in the open arms of the elevated plus maze. Combined graft placement to neocortex and amygdala normalized performance of passive avoidance and restored the normal time spent in the open arms of an elevated plus maze. These results suggest that after damage to the nucleus basalis magnocellularis, modulation of function in multiple brain regions may be necessary for optimization of adaptive behavior in situations involving induction of fear.

Potassium, but not atropine-stimulated cortical acetylcholine efflux, is reduced in aged rats

Using in vivo microdialysis, cortical acetylcholine (ACh) efflux was measured in freely moving Brown Norway/Fischer 344 F1 rats, aged 4 or 22 months. The effects of local, intracortical perfusion of atropine (1.0 or 100.0 microM) via the dialysis probe were compared to local K+ (100.0 mM) stimulation in the presence of elevated extracellular Ca2+ (2.5 mM). Basal cortical ACh efflux in aged rats was similar to that of young animals. Administration of atropine (1.0 or 100.0 microM) via the cortical dialysis probe substantially increased cortical ACh efflux, but did not differentially stimulate ACh efflux in young and aged rats. In contrast, ACh efflux stimulated locally with K+ and Ca2+ was significantly reduced in aged rats relative to young adults. The implications of the dissociable effects of K(+)-depolarization and muscarinic blockade for local regulation of cortical ACh efflux in aged animals are discussed.

Glial cell transplants: experimental therapies of myelin diseases

Transplantation of cells into the CNS of human patients with neurodegenerative disorders offers a radical new approach to the treatment of previously incurable diseases. Considerable success has been achieved in Parkinson's disease following transplantation of human fetal dopaminergic neurons. Disorders of myelination of the brain, of either inherited or acquired origin, might also be treated by glial cell transplantation although there are additional challenges. Cells of the oligodendrocyte lineage have been found to be capable of myelinating axons on transplantation into numerous experimental pathological environments, including the CNS of myelin mutants and focal areas of demyelination in normal animals made by injection of myelinotoxic chemicals. In general, primary cells and progenitors are likely to have the greatest myelinating capacity. Cell lines can also be used, but those driven by oncogenes may produce little myelin, and tumor formation is likely. Schwann cells are also a potential source of cells, possibly as a homograft, and may be primed by treatment ex vivo with glial growth factors. The variable CNS milieu seen in human myelin disease will mean that transplanted cells must be able to migrate appropriately and myelinate axons in an adult, pathological environment, and this awaits experimental confirmation. Physiological analysis of transplants in such situations in adult animals will provide the functional data which may expedite clinical trials.

Atropine suppresses associative LTP in the CA1 region of rat hippocampal slices

The effect of the muscarinic antagonist atropine on associative long-term potentiation (aLTP) of the CA1 population EPSPs was studied in rat hippocampal slices. Local application of atropine (10(-4) M) significantly suppressed aLTP in a 'weak' radiatum input, measured 40-60 min after the tetanization (128 +/- 10% vs. 168 +/- 9% during control, P < 0.03) provided that a 'strong' supporting tetanization was applied to the stratum oriens. LTP in the 'strong' stratum oriens input itself was not suppressed and even tended to be enhanced by atropine (158 +/- 4% vs. 137 +/- 13 during control). The results suggest that synaptically released endogenous acetylcholine supports induction of aLTP in the 'weak' input and does not support induction of homosynaptic LTP in the 'strong' input. A possible physiological role of the cholinergic neuromodulatory system in the hippocampal CA1 region hence could consist in 'equalising' LTP-like changes of synaptic conductivity in pathways with high and low level of activity.

Microencapsulation and the grafting of genetically transformed cells as therapeutic strategies to rescue degenerating neurons of the CNS

A number of approaches have been developed to deliver growth factors within the central nervous system of adult mammals. Initially a variety of neurotrophic factors were administered either by single intracerebroventricular or local injections directly into brain tissues or via permanently installed cannulae for chronic administrations. More recently delivery systems including conjugates, biodegradable and non-biodegradable implants and microspheres as well as genetically engineered cells have been introduced in order to provide a prolonged supply of neurotrophic factors and to prevent their enzymatic degradation. In this review we examine a variety of means of delivering neurotrophic factors (mainly nerve growth factor) with the primary focus upon the use of microencapsulated neurotrophins and cells genetically modified to produce them. In addition, this review highlights some difficulties and future trends in the development of novel delivery systems hopefully more suitable for investigations in different areas of neuroscience.

Behavioral effects of basal forebrain grafts after dorsal septo-hippocampal pathway lesions

There are many reports that basal forebrain grafts ameliorate behavioral impairments produced by dorsal septo-hippocampal pathway lesions, but several studies have either found that this recovery may be unrelated to concomitant restitution of cholinergic markers, may be modest and depend on certain experimental conditions or instead that grafts may actually exacerbate lesion-induced impairments. In this study, rats received one of three lesions of the dorsal septo-hippocampal pathways or a sham lesion, at 32 days of age, and intrahippocampal basal forebrain grafts or the vehicle control 10 days later. In grafted rats with total aspirative lesion of the fimbria-fornix, there was a substantial AChE-positive hippocampal reinnervation but no improvement of the severe lesion-induced spatial learning deficits, either reference memory or working memory, whether tested at 1 or 5 months post-grafting. In rats with bilateral medial fimbria lesions, grafts were successful, normal in appearance and produced substantial hippocampal cholinergic reinnervation; relative to non-grafted counterparts, however, grafted medial fimbria rats showed an early reference memory impairment and a persistent exacerbation of a working memory deficit. Exacerbation of learning impairments was also apparent in grafted rats with partial hippocampal denervation due to lesion of the cingulate and adjacent cortex above the fimbria-fornix. Nonetheless, basal forebrain grafts normalised general activity in these lesion groups, irrespective of whether the lesion-induced change was an increase or a decrease relative to controls. Graft-derived lesion groups, irrespective of whether the lesion-induced change was an increase or a decrease relative to controls. Graft-derived AChE-positive innervation was more marked than expected in both grafted cingulate-lesioned rats and grafted sham-lesioned rats, while control grafts of fetal cortex (above the septum) produced little or no AChE-positive innervation. Size of basal forebrain grafts, originally 3 microliters at two dorsal sites per hippocampus, increased markedly from rostral to caudal dorsal hippocampus in all groups but did not differ significantly across grafted groups, even with respect to non-lesioned rats. This study adds further evidence that basal forebrain grafts, successful with respect to cholinergic reinnervation, do not always enhance cognitive functions in rat hippocampal lesion models, and confirms that these grafts may have adverse effects after partial septo-hippocampal system lesions. It is important to attend to both the potential negative and positive effects of neural grafts.

Human neural transplantation

Great advances in neurobiology have resulted from 100 years of neural transplantation research. In the last 20 years, there has been a focus on using neural transplantation to repair the damaged central nervous system (CNS) utilising experimental animal models of various human neurodegenerative disease and CNS injury. Since 1985, there has been a rapid proliferation of adrenal medullary autograft transplantation to the caudate nucleus of humans with Parkinson's disease. However, this operation proved to be unsuccessful and was associated with unacceptable morbidity. Implantation of human fetal mesencephalon into patients with severe parkinsonism has supplanted the adrenal operation and has produced promising results, with some patients reported to improve markedly and some evidence of graft survival noted on positron emission tomography (PET). Host tissue recovery appears to be an important mechanism for this clinical improvement. The optimal technique is to use three to four fetuses from induced abortions of 6.5 to 8 weeks gestation, with multiple stereotactic implants into the putamen and caudate nucleus. Many biological questions still remain and the community remains troubled by the ethical problems of using fetal tissue obtained from abortions. This procedure is still experimental and should be restricted to a few centres with excellence in cell and molecular biology. A multicentre study is needed to more carefully evaluate CNS transplantation. Cloned neural precursor cells or immortalized embryonic cell lines genetically modified to manufacture selected growth factors or neurotransmitters may offer an alternative to the use of human fetal tissue. Much more experimental animal research is necessary before transplantation can be used to treat other CNS maladies.

Fimbria-fornix lesions impair spatial performance and induce epileptic-like activity but do not affect long-term potentiation in the CA1 region of rat hippocampal slices

Groups of rats were given bilateral fimbria-fornix lesions and one month later grafted into the hippocampus with fetal cholinergic and non-cholinergic (hippocampal) neural tissue. Three weeks and 3 months after transplantation the animals were trained to find and then to retain the location of a hidden platform in the Morris water maze. After the final behavioral testing phase, electrophysiological studies of the short- and long-term potentiation (STP and LTP) and epileptiform activity of evoked responses were performed in vitro in the CA1 region of the hippocampus. The lesions produced a marked deficit in spatial function in the early testing phase which showed some recovery at the three month time point. Neither the cholinergic nor the non-cholinergic grafts improved spatial performance; indeed, on some measures these groups showed a significantly greater deficit than the lesion-alone group. Epileptiform activity, which was defined as the ratio of the sum of amplitudes of second and third population spikes to the amplitude of the first, before tetanization was not significantly different for all groups. After tetanization of the radiatum input, however, the epileptiform activity in the FFL group was significantly higher in comparison to that of the control groups. Grafting of cholinergic tissue decreased this parameter to the control level, but non-cholinergic grafts did not modify the lesion-induced epileptiform activity. Epileptiform activity after tetanization of the oriens input was approximately equal for all groups. There were no significant differences between surgical groups in STP and LTP for both the oriens and radiatum inputs.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic innervation in the human hippocampal formation including the entorhinal cortex

The cholinergic innervation of the hippocampal formation is thought to play an important role in memory processes, but its organization in humans has not been described in detail. We studied the cholinergic innervation of the human hippocampal formation by means of immunohistochemistry with polyclonal antisera directed against acetylcholinesterase (AChE), choline acetyltransferase (ChAT), and the low-affinity (p75) nerve growth factor receptor (NGFR). The density of ChAT-like immunoreactive (ChAT-li) fibers differed substantially among the various regions, in general paralleling the pattern of AChE-li staining. One notable exception was the presence of AChE-li cell bodies. In contrast, ChAT immunoreactivity was associated only with fibers and terminals. NGFR-li staining corresponded closely to the ChAT-li fiber pattern. ChAT-li fibers in the CA fields diffusely filled the stratum pyramidale and extended into the stratum oriens and radiatum as well. The highest density was consistently observed in CA4 and CA3 subfields. Staining decreased from CA4 to CA1 and was substantially less dense in the subicular complex. In the entorhinal cortex, the ChAT- and NGFR-li fiber innervation displayed a laminar pattern, most intense over the nests of cells in layer II. There was a trend towards an age-related reduction in the density of ChAT- and AChE-li fibers and terminals. Nonetheless, we also found a surprisingly conserved NGFR-li innervation and the presence of occasional NGFR-li pyramidal cells, providing evidence of a plastic response in the brains of the elderly patients.

Cholinergic treatment of an amnestic man with a basal forebrain lesion: theoretical implications

Cholinergic deficient states, such as in Alzheimer's disease, are associated with amnesia. Therapeutic trials with cholinergic augmentation in Alzheimer's disease have had only equivocal results, but mechanisms other than cholinergic deficiency may contribute to the memory deficit. Normally the diagonal band of Broca provides much of the hippocampal cholinergic input. To learn if amnesia secondary to cholinergic deficiency can be ameliorated by cholinergic augmentation, we treated an amnestic man who had a lesion located primarily in the right diagonal band of Broca with physostigmine and lecithin. During the initial best-dose-finding phase, he demonstrated an inverted U-shaped curve for immediate recall of word lists, with peak performances at 3.0 and 3.5 mg of physostigmine. Single photon emission tomography showed decreased blood flow in the medial temporal region ipsilateral to the lesion at baseline, with a reversal of the asymmetry on 3.5 mg of physostigmine. A follow-up double-blind, placebo-controlled study on 3.5 mg of physostigmine, however, failed to demonstrate that cholinergic treatment improved memory.

Regional patterns of cholinergic and glutamate activity in the developing and aging human brain

The levels of choline acetyltransferase (ChAT) and the binding activity of N-methyl-D-aspartate (NMDA) and non-NMDA receptors have been measured in the hippocampus, entorhinal cortex, frontal cortex and cerebellum, in a series of human brains from 24 weeks gestation to 100 years. The patterns of ChAT and glutamate receptor activity during aging and development were strikingly different in the different brain areas. In the hippocampus and associated cortex, ChAT activity did not reach a peak until middle age, when it almost immediately started to decline by 50-60% to the 10th decade, whereas in the frontal cortex ChAT peaked transiently in the infant and then stayed constant during aging. In the cerebellum ChAT activity was very high in the foetus and fell in the neonate to maintain a constant level more in line with the concentrations found in the other brain areas through the rest of life. The high levels of ChAT in the foetal cerebellum were not associated with high acetylcholinesterase (AChE) content, which tended to increase during development, and was present initially in Purkinje cells (foetus and neonate) and the molecular layer in the adult. In the hippocampus and entorhinal cortex, autoradiographic [3H]MK-801 binding was relatively constant throughout life, however, [3H]CNQX binding rose from the perinatal period up to a peak in the 1st or 2nd decade and then tended to fall with age. In the cerebellum, autoradiographic binding of both ligands rose from the foetal period to reach a plateau by the age of 10 years and there was no apparent further change during aging. These data on cholinergic and glutamatergic phenotypic changes during development and senescence reflect marked variations in regional plasticity and aging within and between the two transmitter systems and are likely to contribute to our understanding of their role in the different brain areas investigated.