Amelioration of spatial memory impairment by intrahippocampal grafts of mixed septal and raphe tissue in rats with combined cholinergic and serotonergic denervation of the forebrain

Previous studies in the rat have shown that a serotonergic depletion greatly potentiates the learning and memory impairments produced by pharmacological or lesion-induced cholinergic blockade in the forebrain. The impairment produced by combined serotonergic-cholinergic lesions is reminiscent of that seen in memory-impaired aged rats. In the present experiment, we investigated whether grafts of cholinergic septal tissue and serotonergic mesencephalic raphe tissue, placed in the hippocampus, could reverse the severe memory impairment produced by combined cholinergic-serotonergic lesions. Adult rats were given an intraventricular injection of 5,7-dihydroxytryptamine followed by a radiofrequency lesion of the septum 1-2 weeks later. Three weeks after lesion surgery, the rats were given bilateral intrahippocampal cell suspension grafts of either fetal septal or mesencephalic raphe tissue, or both. The rats were tested for spatial learning and memory in the Morris water maze task at 4 and 10 months after grafting. At 4 months, lesioned and grafted groups were all impaired compared to the normal controls in their swim time and distance swum to find the platform, and they did not show any spatially focussed search strategy in the spatial probe trial when the platform was removed from the tank. At 10 months, the rats with mixed cholinergic and serotonergic grafts were no longer impaired compared to normals in their swim time and distance to find the platform, and they were significantly improved compared to the other grafted groups. Moreover, in the spatial probe trial, the rats with mixed cholinergic and serotonergic grafts displayed a spatially focussed search behaviour over the previous platform site, which was not seen in the lesioned control rats or in the other graft groups. Morphological analysis of the hippocampus revealed that the septal grafts produced an acetylcholinesterase-positive innervation but were totally devoid of serotonin innervation. The raphe grafts produced mainly a serotonin innervation, of both acetylcholinesterase- and serotonin-positive fibres. The results suggest that a mixture of septal and raphe tissue is required when grafted to the hippocampal formation in order to ameliorate the severe spatial learning and memory impairments produced by a combined cholinergic and serotonergic denervation, and that each of these graft types separately are not sufficient to ameliorate such deficits.     

Intrahippocampal grafts containing cholinergic and serotonergic fetal neurons ameliorate spatial reference but not working memory in rats with fimbria-fornix/cingular bundle lesions

Three-month-old Long-Evans female rats sustained aspirative lesions of the dorsal septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts containing cells from the mesencephalic raphe, cells from the medial septum and the diagonal band of Broca, or a mixture of both. Lesion-only and sham-operated rats were used as controls. All rats were tested for locomotor activity 1 week, 3 and 5 months after lesion surgery, for spatial working memory in a radial maze from 5 to 9 months, and for reference and working memory in a water tank during the 9th month after lesioning. Determination of hippocampal concentration of acetylcholine, noradrenaline, and serotonin was made after completion of behavioral testing. Compared to sham-operated rats, all rats with lesions, whether grafted or not, exhibited increased levels of locomotor activity and made more errors in the radial maze. The lesioned rats were also impaired in the probe trial (30 first seconds) of the water-tank test made according to a protocol requiring intact reference memory capabilities. While rats with septal or raphe grafts were also impaired, the rats with co-grafts showed performances not significantly different from those of sham-operated rats. With a protocol requiring intact working memory capabilities, all lesioned rats, whether grafted or not, were impaired in the water-tank test. In the dorsal hippocampus of lesion-only rats, the concentration of acetylcholine and serotonin was significantly reduced. In rats with septal grafts or co-grafts, the concentration of acetylcholine was close to normal, as was that of serotonin in rats with raphe grafts or co-grafts. These results confirm previous findings showing that co-grafts enabled the neurochemical properties of single grafts to be combined. Data from the water-tank test suggest that cholinergic and serotonergic hippocampal reinnervations by fetal cell grafts may induce partial recovery of spatial reference, but not working memory capabilities in rats.     

Grafted septal neurons form cholinergic synaptic connections in the dentate gyrus of behaviorally impaired aged rats

A group of aged, behaviorally impaired rats received suspension grafts of fetal septal-diagonal band tissue into the otherwise intact hippocampal formation. Three months after grafting, behaviorally recovered rats were studied by immunocytochemistry by using monoclonal antibodies to choline acetyltransferase (ChAT) and electron microscopy. The innervation of the host dentate gyrus by graft-derived ChAT-positive fibres was unmasked by acute removal of the intrinsic septal cholinergic innervation by fimbria-fornix transection 5-7 days before perfusion. The pattern of termination and ultrastructural connectivity were compared with previous results obtained from both young nonoperated control animals and a group of young rats with intrahippocampal septal grafts that had been subjected to denervation of the intrinsic cholinergic input at the time of transplantation. Graft-derived, ChAT-immunoreactive terminals formed abundant synaptic specializations with neuronal elements in the host dentate gyrus. The predominant postsynaptic target (about 65% of all boutons) was dendritic shafts, whereas about 20% of the boutons contacted dendritic spines. Very few synapses onto neuronal perikarya were found in the grafted aged rats. In some of these cases, however, it was possible to identify the target as dentate granule cells. This situation is very similar to that seen in young control rats but significantly different than the distribution observed in the denervated young grafted group, where axosomatic contacts predominated. The results indicate that the graft-induced behavioral improvement seen in the aged rats may depend on the formation of functional cholinergic graft connections with neuronal elements in the host hippocampal formation.     

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

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

Conditionally immortal neuroepithelial stem cell grafts restore spatial learning in rats with lesions at the source of cholinergic forebrain projections cholinergic forebrain projections Conditionally immortal neuroepithelial stem cell grafts restore spatial leaming in rats with lesions at the source of cholinergic forebrain projections

Purpose: Loss of cholinergic projections from the basal forebrain (BF) to the cortex and from the medial septal area (MSA) to tbe hippocampus is a reliable correlate of cognitive deficits in aging and Alzheimer's disease (AD). We assessed the capacity of grafts of the conditionally immortal MHP36 clonal stem cell line to improve spatial learning in rats showing profound deficits after lesions to these projections. Methods: Rats were lesioned by infusions of S-AMPA unilaterally into BF or bilaterally into both BF and MSA. MHP36 cells were implanted ipsilaterally in cortex or basal forebrain two weeks after unilateral BF lesions, and in cortex and hippocampus bilaterally six months after bilateral BF-MSA lesions. Intact and lesion-only controls received vehicle. Six weeks later rats were assessed in spatial learning and memory tasks in the water maze, and then perfused for identification of grafted cells by beta-galactosidase immunohistocheniistry. Results: Lesioned rats with MHP36 grafts, whether implanted two weeks or six months after lesioning, learned to find a submerged platform in the water maze as rapidly as intact controls, and showed a strong preference for the platform quadrant on probe trials, whereas lesioned controls were impaired in all measures. Grafted cells of both neuronal and glial morphologies, migrated away from cortical implantation sites in BF Lesioned rats to the striatum, thalamus and basal forebrain lesion area. Cells implanted in basal forebrain showed a similar distribution. In rats with bilateral BF-MSA lesions, grafts implanted in the hippocampus migrated widely through all layers but cortical grafts largely escaped up the needle tract into the meninges. Conclusions: Although MHP36 grafts were functionally effective in both lesion models, the site and age of lesions and site of implantation influenced the pattern of engraftment. This flexibility encourages the development of conditionally immortal human stem cell lines with similar capacities for functional repair of variable neuronal degeneration in AD or aging.     

NGF improves spatial memory in aged rodents as a function of age.

Aged rats were tested for place navigation in a circular water maze for spatial memory ability at 18 and 30 months of age; 45% of the 18-month-old rats displayed impaired place navigation performance relative to young control rats, while essentially all of the 30-month-old rats were impaired. The aged impaired rats were retested twice during NGF or vehicle infusion in the right lateral ventricle. In the 18-month-old group, NGF-infused rats showed improved retention of previously acquired place navigation performance and improved spatial acuity over the former platform site when the invisible platform was removed. NGF infusion also had a significant effect in the much more severely impaired 30-month-old rats: while the vehicle-infused aged rats showed a progressive decline in the performance between the first and second test weeks, the performance of the NGF-infused rats remained stable throughout the infusion period. The interpretation of these effects in the oldest animals, however, was confounded by a progressive decline in swim speed seen in the vehicle-infused animals. The 30-month-old vehicle-infused control rats showed a significant cell loss and cell shrinkage relative to the young control rats in the septal/diagonal band area, the striatum, and the nucleus basalis as assessed by NGF-receptor (NGFr) and ChAT double-label immunocytochemistry. A significant increase in the size but not in the number of cells was observed on the side of the NGF infusion in the 30-month-old NGF-infused rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Systemic treatment with GPI 1046 improves spatial memory and reverses cholinergic neuron atrophy in the medial septal nucleus of aged mice

Systemic treatment with GPI 1046, a non-immunosuppressive ligand of the immunophilin FKBP12 (FK-506-binding protein 12 kDa), has previously been shown to promote morphological recovery of the nigrostriatal dopaminergic projection after MPTP lesion in mice, and of lesioned sciatic nerve fibres after nerve crush in rats. In the present study, we investigated whether chronic systemic treatment with GPI 1046 could affect the decline of spatial learning and memory, and the atrophy of medial septal cholinergic neurons, associated with late senescence in C57 black mice. Three-month old (young) and 18-19-month old (aged) male C57BL/6N-Nia mice were first trained in a place learning task in the Morris water maze. Based on their performance relative to young controls, aged animals were then allocated to treatment groups (10 mg/kg GPI 1046, or vehicle). Retention of the spatial platform location was assessed after 3 weeks of dosing. We found that aged animals that had been dosed with GPI 1046 now performed at a significantly better level than their vehicle control group. Aged animals that had shown the greatest degree of impairment during training in the place learning task showed the greatest relative degree of improvement under treatment and were statistically indistinguishable from young, or aged unimpaired control animals. Cell volumes of cholinergic cells in the medial septal nucleus were assessed after an additional 10 months of dosing at 30 months of age, using stereological methods. We found that aged animals displayed a significant 34% decrease in volume of these cells relative to young controls. This atrophy was significantly reversed in aged GPI 1046-treated animals (13% shrinkage). We conclude that chronic systemic treatment with GPI 1046 positively affects memory mechanisms in the aged mouse, possibly by acting on the septohippocampal cholinergic system.     

Subcutaneous injection of carbachol enhances brain graft-induced recovery of memory-function by circumventing the blood-brain barrier

After bilateral neurotoxic hippocampectomy adult rats received bilateral fetal suspension grafts at the lesion sites. Functional efficacy of fetal grafted tissue was substantially improved by subcutaneous administration of carbachol at a dose of 0.01 mg/kg s.c. The drug caused an almost complete restitution of performance in grafted animals in a Morris water-maze test. The progress of behavioral recovery was studied over 3 months postoperatively. Grafts of fetal hippocampal neurons alone improved lesion-induced spatial learning deficits to a limited degree. These results suggest that peripheral administration of carbachol may be of use in the treatment of central lesions associated with cognitive impairments, allowing or enhancing the development of graft-induced amelioration of behavioral deficits. The data also support the view that grafts of embryonic neural tissue may produce a local opening of the blood-brain barrier allowing drugs which normally act only peripherally to exert central effects. These central effects are probably limited to the graft site because the rest of the brain has a blood-brain barrier which is still intact.     

Muscimol injections in the medial septum impair spatial learning

These experiments examined the role of GABAergic systems in modulating septohippocampal cholinergic influences on learning. Microinjections of the GABA(A) agonist muscimol (0.5, 1.0 or 5.0 nmol) or physiological saline were administered (0.5 microliters) into the medial septum of rats via chronically implanted cannulae just prior to daily training in the Morris water maze spatial learning task. The animals received 3 training trials on each of 4 days. The escape latencies of rats trained with a submerged escape platform at a fixed location were significantly shorter than those trained with a randomly located platform. Rate of learning of the fixed location was significantly impaired in rats given pretraining muscimol injections in the medial septum at doses (1.0 and 5.0 nmol) that significantly reduced hippocampal high-affinity choline uptake (HACU). Analyses of responses on a probe trial with no pretraining injections and no platform revealed that, in comparison with controls, animals that had received muscimol prior to each training session were likely to swim in the region where the platform had been located. The finding that muscimol-injected rats were subsequently able to learn the task when trained without muscimol injections indicates that the acquisition impairment was not due to a lasting effect of the drug injections. Our results are consistent with the view that the septal GABAergic modulation of the septohippocampal cholinergic pathway is involved in regulating the acquisition of spatial information.     

Behavioral effects of photothrombotic ischemic cortical injury in aged rats treated with the sedative-hypnotic GABAergic drug zopiclone

Sedative-hypnotic drugs commonly used in the elderly may affect functional recovery following cerebrovascular events. Previous research has shown that prolonged exposure to diazepam can interfere with recovery of function and exaggerate tissue loss after brain injury. The present study evaluated the effect of zopiclone, a widely used hypnotic drug, on functional and histological outcome after cortical photothrombosis in aged rats, which might be particularly vulnerable to brain insults and inhibitory sedative-hypnotic drugs. Aged Wistar rats were treated with zopiclone at a dose of 3 mg/kg (i.p., once a day) beginning 4 days before ischemia induction and continuing for 23 days. Sensorimotor recovery was assessed by a new ledged beam-walking test and spatial learning by the Morris water-maze. After a 7-day washout period all rats were administered a single dose of zopiclone (3 mg/kg, i.p.) and retested. Infarct volumes were measured from nitroblue tetrazolium-stained sections at the end of the experiment. Beam-walking data showed that ischemic rats treated with zopiclone were not more impaired than untreated rats. Indeed, they showed fewer faults with the impaired hindlimb than ischemic controls on post-operative day 16. Water-maze performance was not affected by zopiclone. After the washout period a single dose of zopiclone did not worsen forelimb or hindlimb function, but seemed to improve performance in the water-maze test. Cortical infarct volumes were similar in ischemic controls and ischemic rats treated with zopiclone. In conclusion, zopiclone was not detrimental and even seemed to improve behavioral outcome without affecting ischemic damage in aged rats subjected to cortical photothrombosis.     

Effects of implantation site of dead stem cells in rats with stroke damage

Searching for valid control grafts, we assessed the performance of rats subjected to middle cerebral artery occlusion (MCAO) and grafted with freeze-thawed dead stem cells into sites previously used for active grafts (ipsilateral and contralateral striatum and ventricle) on bilateral asymmetry and water maze tests. We expected to find that sham grafted groups had impairments equivalent to those of MCAO-only controls, relative to intact controls. This proved to be the case for contralateral and intraventricular grafts, and for asymmetry in rats with ipsilateral grafts. However, spatial learning was substantially impaired and lesion volume was increased by 55% with ipsilateral dead cell grafts. Exacerbation of stroke effects indicates potential hazards in the use of dead cells for sham grafts.     

Behavioral and histological effects of chronic antipsychotic and antidepressant drug treatment in aged rats with focal ischemic brain injury

Psychotropic drugs are commonly used in the elderly, including those who may sustain ischemic attacks. Concomitant CNS medication may interfere with functional recovery. The present study evaluated the effect of risperidone, an atypical neuroleptic, and fluoxetine, a selective serotonin reuptake inhibitor, on histological and functional outcome after experimental stroke in aged rats, which might be more vulnerable to brain insults. Aged Wistar rats were treated with risperidone at a dose of 1 mg/kg (i.p., once a day), fluoxetine at a dose of 5 mg/kg (i.p., once a day), or their combination. Drug treatment was started 7 days before focal cortical photothrombosis (Rose Bengal, 20 mg/kg) and continued for 28 days thereafter. Sensorimotor recovery was assessed by a new beam-walking test and spatial learning by the Morris water-maze before cortical stroke, immediately after stroke, and at the end of follow-up. Infarct volumes were measured from nitroblue tetrazolium-stained sections at the end of follow-up. The high slip ratio for the contralateral hindlimb in ischemic rats treated with risperidone indicated sensorimotor impairment when tested 2 h after drug administration. Sensorimotor impairment was not observed, however, when the rats were tested 24 h after risperidone administration. Similarly, water-maze performance was impaired 2 h after risperidone. Fluoxetine did not affect sensorimotor or water-maze performance. Cortical infarct volumes were not different in ischemic controls and ischemic rats treated with antipsychotic drugs. The present study showed that an atypical neuroleptic, risperidone, acutely impairs behavioral performance, but does not affect histological or functional outcome in aged rats subjected to cortical photothrombosis.     

The systemic administration of tacrine or selegiline facilitate spatial learning in aged fisher 344 rats

Summary When compared to young Fisher 344 rats, aged Fisher 344 rats were impaired in their acquisition of the water maze task as indicated by longer escape latencies and distances to find a hidden platform. In a free swim trial which was performed after the training period, young rats had a better spatial bias, since they spent more time swimming in the previous training quadrant. Tacrine 3mg/kg, an anticholinesterase, and selegiline 0.25mg/kg, a MAO-B inhibitor, partially reversed the acquisition deficit in aged rats when administered on their own, and drug-treated aged rats swam more in the previous training quadrant than vehicle-treated aged rats during the free swim trial. Aged rats also swam slower than young rats. Tacrine, but not selegiline, increased swimming speed in aged rats. Taken as a whole, these data support the proposal that tacrine may be effective at alleviating age-related learning impairment and confirm the role of cholinergic dysfunction in the spatial learning deficit in aged rats.     

Intrahippocampal grafts of cholinergic-rich striatal tissue ameliorate spatial memory deficits in rats with fornix lesions.

Previous studies have shown that cholinergic grafts derived from the medial septal nucleus are capable of restoring behavioral function in rats with lesions that sever the cholinergic inputs to the hippocampal formation. In this study, we demonstrate that intrahippocampal grafts of cholinergic-rich striatal tissue also ameliorate spatial memory deficits of rats with fornix lesions. We also found that atropine administration dramatically disrupted spatial navigation performance of rats with striatal grafts and control rats, thus suggesting that the striatal graft effects are mediated by cholinergic mechanisms of action. Measurements of high affinity choline uptake (HACU) and muscarinic receptor binding revealed that intrahippocampal striatal grafts increased HACU and normalized muscarinic receptor binding in animals with fornix lesions. Regression analyses demonstrated significant correlations between the amelioration of spatial memory deficits and hippocampal HACU and receptor binding. We conclude that intrahippocampal grafts of cholinergic-rich striatal tissue can ameliorate spatial memory deficits and that this amelioration is associated with the reinstatement of functional cholinergic terminations.     

Physiological and behavioral consequences of delayed septal grafts in the subcortically denervated hippocampus

The present experiments examined whether cholinergic grafts reverse the physiological and behavioral deficits of the damaged hippocampus. Fimbria-fornix lesions were performed in young rats and 3 months later half of the lesioned rats received cholinergic-rich basal forebrain transplants. Eight months after grafting we tested the animals behaviorally in the water maze. Following the behavioral experiments, the animals were implanted with chronic recording and stimulating electrodes and the electrical properties of the hippocampus, including spontaneous EEG, interictal spikes, evoked responses, long-term potentiation, and sensitivity to induced seizures were examined. Grafted rats did not show statistically reliable behavioral recovery (swim latencies, swim path lengths) and their performance was identical to the lesion-only group. Acetylcholinesterase reinnervation of the host hippocampus in grafted animals was similar to intact rats; the grafts also contained numerous parvalbumin-immunoreactive neurons. The most striking physiological change was the significant elevation of seizure threshold in the grafted group, but other physiological parameters did not improve consistently. The findings suggest that the presence of septal tissue grafts and restoration of cholinergic reinnervation in animals with previous subcortical denervation of the hippocampus are not sufficient to restore normal hippocampal electrical patterns or to improve behavioral performance.     

Testing the importance of the caudal retrosplenial cortex for spatial memory in rats

Although there is evidence to suggest that the retrosplenial cortex is involved in spatial learning and memory, many lesion studies have left the more caudal part of this region intact so leaving its role untested. In the first experiment, rats with neurotoxic lesions of the caudal half of the retrosplenial cortex (RspC1) were tested on a reference memory task in the water-maze. The RspC1 animals were impaired on initial acquisition although they performed normally on a subsequent probe test. The second experiment looked at working memory in the radial-arm maze and water-maze. Animals with caudal retrosplenial lesions (RspC2) were unimpaired on the acquisition stage of the radial-arm maze task but were impaired when the task involved maze rotation to control for the possible use of intramaze cues. The RspC2 animals also took longer to learn the platform position on a delayed matching-to-place task in the water-maze. These results show a subtle impairment in spatial memory performance that is not as severe as that seen when more complete lesions of the retrosplenial cortex are made.     

The effects of cholinergic drugs and cholinergic-rich foetal neural transplants on alcohol-induced deficits in radial maze performance in rats.

Chronic alcohol (20% v/v in drinking water for 28 weeks) impaired acquisition of radial maze spatial and associative tasks by increasing both within-trial working and long-term reference memory errors; animals with high (above the median of 100 mg/100 ml) blood alcohol concentrations (BACs) during treatment were significantly more impaired than those with BACs below the median. Alcohol-treated rats showed improvements in radial maze performance after treatment with cholinergic agonists (arecoline and nicotine) and disruption with antagonists (scopolamine and mecamylamine) at low doses which did not affect controls. These effects were more pronounced for working than reference memory, and not manifest with the peripherally acting antagonists hexamethonium and N-methylscopolamine. Transplants into cortex and hippocampus of cholinergic-rich basal forebrain (BF) and ventral mesencephalon (VM) foetal neural tissue improved radial maze performance of alcohol-treated rats to control level over a period of 9-12 weeks after grafting. Cholinergic-poor foetal hippocampal (HC) grafts were without effect. BF and VM, but not HC, grafts showed dense acetylcholinesterase (AChE) staining, tyrosine-hydroxylase staining was most pronounced in VM sections and dopamine-beta-hydroxylase staining was minimal in all grafts. Choline acetyltransferase (ChAT) activity was significantly reduced in cortex and hippocampus of alcohol-treated rats, except those given cholinergic-rich transplants. Alcohol treatment also significantly reduced AChE-positive cell counts in the nucleus basalis, medial septal and diagonal band brain areas, at the sources of the forebrain cholinergic projection system (FCPS). Cortical levels of noradrenaline were significantly reduced in all alcohol-treated rats, regardless of transplant, whereas cortical dopamine content was significantly elevated in all rats receiving transplants, regardless of behavioural effect, but not in alcohol-treated controls. Forebrain serotonin levels were not significantly altered by grafting or alcohol treatment. These results suggest that damage to the FCPS, as shown by reduced ChAT activity in target areas, and reduced AChE cell counts in projection areas, played an important part in the radial maze deficits displayed by alcohol-treated rats, since these animals were sensitive to cholinergic drug challenge, and cholinergic-rich transplants from two different sites in foetal brain elevated ChAT activity and restored cognitive function. In contrast alcohol- or graft-induced alterations in other transmitter systems did not correlate with the pattern of behavioural deficit and recovery.     

Septal transplants restore maze learning in rats with fornix-fimbria lesions

In a study of the capacity of neural grafts to promote functional recovery in rats with fimbria-fornix lesions, 5 groups of rats were studied behaviourally and with acetylcholinesterase (AChE) histochemistry: (1) sham-operated controls; (2) bilateral fimbria-fornix lesions; (3) bilateral lesions plus bilateral solid embryonic septal grafts to the lesion cavity; (4) bilateral lesions plus bilateral embryonic septal suspension injections into the hippocampus; and (5) bilateral lesions plus bilateral solid embryonic locus coeruleus grafts to the lesion cavity. Seven months were allowed for growth of the grafts and reinnervation of the host hippocampus prior to behavioural testing.The control rats were able to rapidly learn a rewarded alternation task, while the performance of animals with bilateral fimbria-fornix lesions alone remained at a chance level. Both types of septal grafts (rich in cholinergic neurones) but not the locus coeruleus grafts (rich in noradrenergic neurones) reversed the impairment. Behavioural recovery correlated significantly with AChE-positive fibre ingrowth from the grafts into the denervated host hippocampus. However, the septal grafts did not ameliorate the lesion-induced disturbances in spontaneous activity or spontaneous alternation. Thus, the observed behavioural recovery appears specific to the conditioned alternation task and dependent upon cholinergic reinnervation of the hippocampus.     

NGF Deprivation of Adult Rat Brain Results in Cholinergic Hypofunction and Selective Impairments in Spatial Learning

Cholinergic hypofunction has often been correlated with a variety of behavioural impairments. In the present study, adult Wistar rats were intraventricularly infused with antibodies to nerve growth factor (anti-NGF) to examine the effects on cholinergic neurons of the basal forebrain, and on behavioural performance. Immunocytochemical techniques indicated that chronically infused anti-NGF penetrates into the basal forebrain, cortex, striatum, corpus callosum and hippocampus, confirming previous findings after a single injection. Treatment with anti-NGF for 1 or 2 weeks resulted in a significant decrease of 27-33% in density of choline acetyltransferase immunostaining of the cholinergic cell bodies in the medial septum and vertical diagonal band, and a 26% reduction in choline acetyltransferase enzyme activity in the septal area. An array of spatial learning Morris water maze tasks was used to distinguish between acquisition skills and the flexible use of learned information in novel tests. Rats subjected to the spatial learning paradigm received anti-NGF infusion for 2 weeks prior to and for another 2 weeks during the behavioural testing. The anti-NGF-treated animals were found to be no different from those receiving control serum in the Morris water maze acquisition task, either in the latency to find the platform or in the time spent searching in the training quadrant when the platform was removed. However, in consecutive extinction trials, anti-NGF rats continued to search in the empty training quadrant, suggesting the occurrence of perseveration; control rats expanded their search over other areas of the pool. This inflexibility of the anti-NGF rats was also evident from their difficulty in learning to find a relocated platform in the reversal task. Finally, the anti-NGF-treated animals demonstrated hyperactivity in the open field, resembling in this respect the behaviour of animals after septal and fimbria fornix lesions, and during pharmacological cholinergic blockade. While these data support a role for NGF in cholinergic function and spatial learning behaviour, they indicate that deficits in the latter, e.g. those demonstrated in impaired aged rats, may not be attributable selectively to deficits in the function of NGF-sensitive cholinergic neurons of the basal forebrain.     

Intrahippocampal transplants of septal cholinergic neurons: high-affinity choline uptake and spatial memory function

Recent studies have demonstrated that intrahippocampal cholinergic septal grafts can ameliorate deficits in spatial memory function and hippocampal cholinergic neurochemical activity in animals with disruptions of the septohippocampal system. However, no study has determined if the restoration of spatial memory function is correlated to the restoration of cholinergic activity, as measured by high-affinity choline uptake (HACU). The present study was designed to determine if such a correlation between behavioral and neurochemical restoration exists. Male Sprague-Dawley rats received either sham lesions (SHAM), bilateral lesions of the septohippocampal pathway (LES), or bilateral lesions along with intrahippocampal septal grafts (SG). After 8 months, rats were tested for their ability to perform spatial reference, spatial navigation and working memory tasks. Upon completion of the behavioral testing, neurochemical activity of the hippocampus was measured by HACU. The results indicate that animals in the SG group had significantly higher behavioral scores and hippocampal HACU rates than animals in the LES group. Regression analysis indicates that a significant correlation exists between performance on each behavioral task and HACU rates. These results demonstrate that hippocampal cholinergic activity, as measured by HACU, correlates significantly with performance on tests of spatial memory function.