nBM Lesions Research Articles

Long-term effects of selective immunolesions of cholinergic neurons of the nucleus basalis magnocellularis on the ascending cholinergic pathways in the rat: A model for Alzheimer's disease

Alzheimer's disease is associated with a significant decrease in the cholinergic input to the neocortex. In a rat model of this depletion, we analyzed the subsequent long-term changes in cholinergic fiber density in two well-defined areas of the frontal and parietal cortices: Fr1, the primary motor cortex, and HL, the hindlimb area of the somatosensory (parietal) cortex, two cortical cholinergic fields that receive inputs from the nucleus basalis magnocellularis (nBM). A specific cholinergic lesion was induced by the intraparenchymal injection of 192 IgG-saporin into the nBM. Choline acetyltransferase (ChAT) immunohistochemistry was applied to identify the loss of cholinergic neurons in the nBM, while acetylcholinesterase (AChE) enzyme histochemistry was used to analyze the decreases in the number of cholinoceptive neurons in the nBM and the cholinergic fiber density in the Fr1 and HL cortical areas in response to the nBM lesion. The immunotoxin differentially affected the number of ChAT- and AChE-positive neurons in the nBM. 192 IgG-saporin induced a massive, irreversible depletion of the ChAT-positive (cholinergic) neurons (to 11.7% of the control level), accompanied by a less dramatic, but similarly persistent loss of the AChE-positive (cholinoceptive) neurons (to 59.2% of the control value) in the nBM within 2 weeks after the lesion. The difference seen in the depletion of ChAT- and AChE-positive neurons is due to the specificity of the immunotoxin to cholinergic neurons. The cholinergic fiber densities in cortical areas Fr1 and HL remained similarly decreased (to 62% and 68% of the control values, respectively) up to 20 weeks. No significant rebound in AChE activity occurred either in the nBM or in the cortices during the period investigated. This study therefore demonstrated that, similarly to the very extensive reduction in the number of ChAT-positive neurons in the nBM, cortical areas Fr1 and HL underwent long-lasting reductions in the number of AChE-positive fibers in response to specific cholinergic lesioning of the nBM.

The effect of peripheral administration of growth hormone on AD-like cognitive deficiency in NBM-lesioned rats

This study aimed to evaluate the peripheral administration of growth hormone (GH) on AD-like cognitive deficiency in NBM-lesioned rats induced by ibotenic acid (5 μg/μl, in each side). Forty-eight male Wistar rats (20–24 months old; weighing 330 ± 30 g) randomly divided into six groups ( n = 8). The groups include control group, which were intact rats; n-L + GH group: non-lesioned rats with GH treatment (1 mg/kg, 9.00 am, for 10 consecutive days); n-L + Veh group: non-lesioned rats with vehicle treatment; L group: NBM-lesioned rats; L + GH group: NBM-lesioned rats with GH treatment and L + Veh group: NBM-lesioned rats with same volume of vehicle treatment. Peripheral administration of GH in control had no effect on learning and memory, while in L + GH group produced a significant enhancement in spatial learning and memory comparing to L and L + Veh groups. The percent of time spent in goal quarter during probe trial has decreased significantly in L and L + Veh groups compared to n-L groups. While it has increased significantly in L + GH group compared to L and L + Veh groups. No significant difference in percent of time spent was seen between the control and n-L groups. The GH has known as a mediate that effect through IGF-1. As the IGF-1 itself is earlier shown to improve cognitive function it is likely that the observed effect of GH is mediated through release of IGF-1 from peripheral tissue into the circulation for further transport across the BBB. This mechanism may result in the improvement of learning and memory in rats with NBM lesion.

Glial alterations in the hippocampus of rats submitted to ibotenic-induced lesion of the nucleus basalis magnocellularis

Lesion of the nucleus basalis magnocellularis (nbm) is a suitable approach to study cognitive deficit and behavior alterations involving cholinergic dysfunction, which is associated with the major types of dementia. Cortical astrogliosis also has been described in this model, but it is not clear whether hippocampal astrocytes are activated. In this study, we investigated possible specific astrocyte alterations in the hippocampi of Wistar rats submitted to nbm damage with ibotenic acid, investigating the content and immunohistochemistry of glial fibrillary acidic protein (GFAP), as well as S100B protein content, glutamate uptake and glutamine synthetase activity on the 7th and 28th post-lesion days. Cognitive deficit was confirmed by the step-down inhibitory avoidance task. Interestingly, we found a decrease in GFAP content, S100B content and glutamate uptake activity in the hippocampus on the 28th day after nbm lesion. No alterations were observed in glutamine synthetase activity or in the cerebrospinal fluid S100B content. Although our data suggest caution in the use of nbm lesion with ibotenic acid as a dementia model, it is possible that these alterations could contribute to the cognitive deficit observed in these rats.

Further analysis of the effects of immunotoxic lesions of the basal nucleus of Meynert reveals substantial impairment on visual discrimination learning in monkeys

In this paper we undertake a combined analysis of several studies in which marmoset monkeys received immunotoxic lesions of the cortical cholinergic projections from the basal nucleus of Meynert (NBM) bilaterally and/or in combination with immunotoxic lesions of other parts of the cholinergic system or ablations of the target inferotemporal neocortical area. Analysis of the mean learning scores across all visual discriminations learning tasks for each lesion combination revealed highly significant impairments where the NBM was lesioned bilaterally or where an NBM lesion in one hemisphere was crossed with an inferotemporal cortical ablation in the other hemisphere. This demonstrates that the cholinergic projection from the NBM to the major target area of neocortex involved in visual discrimination learning, i.e. the inferotemporal cortex, makes an important contribution to the perceptuo-mnemonic processes necessary for this type of learning. A new study demonstrates a significant effect of a subtotal bilateral cholinergic lesion confined to the NBM on a concurrent object-reward association task using black objects which is perceptually and mnemonically demanding. These results do not preclude the possibility that cholinergic projections from the NBM to other parts of the neocortex make a contribution to other cortical functions which are not mnemonic. It is well established that lesions of the cholinergic projection from the diagonal band of Broca disrupts the mnemonic functions of the hippocampus. The results described here suggest that degeneration of the cholinergic projections in Alzheimer's disease and other dementias will contribute to the loss of those mnemonic functions which are dependent on the neocortex.

No facilitation of amphetamine- or cocaine-induced hyperactivity in adult rats after various 192 IgG-saporin lesions in the basal forebrain

Lesions of basal forebrain cholinergic neurons by intracerebroventricular (i.c.v.) injections of 192 IgG-saporin increased the locomotor response to 0.5 and 1.5 mg/kg of d-amphetamine in adult rats [A. Mattsson, S.O. Őgren, L. Olson, Facilitation of dopamine_mediated locomotor activity in adult rats following cholinergic denervation, Exp Neurol. 174 (2002) 96–108.]. In the present study, adult male rats were subjected to bilateral injections of 192 IgG-saporin either into the septum (Sp), the nucleus basalis magnocellularis (Nbm), both structures (SpNbm) or i.c.v. Locomotor activity was assessed in the home cage 23 days after surgery, and, subsequently, thrice after an intraperitoneal injection of d-amphetamine (1 mg/kg) and twice after an injection of cocaine (15 mg/kg). Analysis of AChE-stained material showed that Sp lesions induced preferentially hippocampal denervation, Nbm lesions induced preferentially cortical denervation, while both SpNbm and i.c.v. lesions deprived the hippocampus and the cortex of almost all AChE-positive reaction products. The spontaneous and drug-induced locomotor activity of all lesioned rats did not differ significantly from that of control rats, except in rats subjected to i.c.v. injections, in which the locomotor response was significantly increased after the second administration of cocaine. In addition, in Nbm and SpNbm rats, the locomotor reaction to cocaine was weaker right after the second injection. The present results do not confirm the report by Mattsson et al. on the potentiation of amphetamine-induced locomotion by i.c.v. injections of 192 IgG-saporin, but suggest that cocaine-induced locomotion can be increased by such lesions and, to some respect, attenuated by cholinergic damage in the Nbm.

Lesions and Dysfunctions of the Nucleus Basalis as Alzheimers Disease Models: General and Critical Overview and Analysis of the Long-Term Changes in Several Excitotoxic Models

The cholinergic hypothesis of Alzheimer's Disease (AD) has led to a number of animal models to study in vivo the pathogeny of cortical cholinergic involution. The lesion of the cholinergic neurons of the basal forebrain, especially of the nucleus basalis magnocellularis (nbm) of rodents, has been the most utilized method for obtaining these models. Toxic substances such as quinolic, kainic, NMDA, ibotenic and quisqualic acids, the specific cholinergic toxin AF64, amyloid, and antibodies to neurotrophic factors; etc, have been used to produce such lesions. These investigations have helped our understanding of the role of cerebral cholinergic innervation in cognitive disorders and their treatments. However, this research has provided conflicting results, and much controversy has developed surrounding the role of the cholinergic systems and the suitability of these models. It is very important to take into account the exact type of nbm/cortical lesion produced, and its evolution, if meaningful results are to be obtained. This review covers the theoretical and practical use of nbm lesion models, and examines the main positive and negative results obtained by different authors in the light of our own observations on the long-term (3 years) morphological and biochemical changes that occur in several kinds of nbm-lesion model rats. The changes seen were very different, but many of them were increased up to the end of life with no clear relationship with the development of the original lesion.

Immunotoxin Lesion of the Cholinergic Nucleus Basalis Causes Aβ Deposition: Towards a Physiologic Animal Model of Alzheimers Disease

Transgenic βAPP mice are valid and useful models of Alzheimers disease (AD) as they effectively recreate Aβ deposition, which is widely regarded as the central pathogenic event in the disease. Transgenic mice do not, however, replicate the initial pathogenic event of the most common form of AD. The majority of AD is not caused by any of the gene mutations employed to create these mice. As cortical Aβ deposition is a common, if not universal, occurrence in many mammalian species, its cause is likely to lie within the physiologic process of aging. We have created an animal model of Aβ deposition by inducing cortical cholinergic deafferentation, a well-known aging change, in the brains of young rabbits. Lesioning the cholinergic nucleus basalis magnocellularis (nbm) results in cortical cholinergic deafferentation and cortical Aβ deposition. The Aβ deposits are primarily vascular, with occasional perivascular plaques. The specificity of this change for cholinergic processes has been demonstrated by the reduction of lesion-induced Aβ deposition by cholinergic therapy with AF267B, an m1-selective muscarinic agonist, and physostigmine, an acetylcholinesterase inhibitor, and by showing that lesioning of the noradrenergic locus ceruleus does not cause Aβ deposition. Significant decreases in cortical synaptic antigen density occur at 6 months post-lesion. Examination of longer survival periods has been complicated by regeneration of cortical cholinergic afferents but repetitive nbm lesions are expected to overcome this obstacle. Agerelated degeneration of the nbm in humans may be a major contributor to Aβ deposition in normal aging and AD. Keywords: immunotoxin lesion, cholinergic nucleus, deposition, cholinergic differentiation

Multiple injections of thyrotropin releasing hormone fail to reverse learning and memory deficits in rats with lesions of the nucleus basalis of meynert

The learning and memory enhancing effects of thyrotropin releasing hormone (TRH) was examined in an animal model of Alzheimer's disease. Adult rats were prepared with either sham surgeries or cholinergic lesions of the nucleus basalis of Meynert (nbM). Subjects were injected (ip) with one of three doses of TRH (0, 5, 10 mg/kg) starting on the day of surgery and continuing once every other day for a total of four injections. Performance (four trials/day for 4 days, 30 m inter-trial interval) in a Morris water maze was assessed one week after the last TRH injection (i.e., 2 weeks postoperatively). Latency to find the hidden platform served as the dependent variable. Results indicated that damage to the nbM impaired task performance in that animals with nbM lesions generally required more time to find the platform and showed less trial-to-trial improvement. Treatment with TRH failed to reverse this lesion-induced deficit. These results suggest that multiple injections of TRH do not provide residual protection against the deleterious effects on learning and memory produced by cholinergic lesions of the basal forebrain. Other doses and administration parameters, however, need to be studied in order to determine the generalizability of these findings.

MRNA expression alterations of inward rectifier potassium channels in rat brain with cholinergic impairment

Potassium channel dysfunction has been indicated in Alzheimer's disease. In the present study, spatial memory, the activity of cortical acetylcholinesterase (AChE) and the expressions of inward rectifier potassium channels (Kir) were measured after ibotenic acid lesions of nucleus basalis magnocellularis (nbm) in rats. Expressions of Kir (Kir2.1, Kir3.1, Kir6.1 and Kir6.2) at mRNA level were assessed using reverse transcription-polymerase chain reaction. At 28 days after ibotenic acid injection, the spatial memory of rats was significantly impaired accompanied by a 32% reduction of cortical AChE activity. Furthermore, the expression of Kir6.2 was increased by 79.3% in cortex, and that of Kir6.1 was increased by 172.1% in hippocampus, while no obvious changes in the mRNA expression of Kir2.1 and Kir3.1 were detected. This study indicated that the expression of adenosine triphosphate-sensitive potassium channel was area and channel subtype specifically increased following nbm lesions.

Behavioral and Morphological Consequences of Primary Astrocytes Transplanted into the Rat Cortex Immediately After Nucleus Basalis Ibotenic Lesion

Adult male rats received transplants of dissociated 30-day old cultured cortical astrocytes into the ipsilateral frontal and parietal cortex immediately after unilateral ibotenic acid lesion of the NBM or after sham injury. We hypothesized that transplants of astrocytes into the acetylcholine-deprived cortex might provide trophic support to terminals arising from damaged NBM neurons. Twenty four hours after transplantation and every other day for 11 days post surgery, the animals were tested for locomotion and habituation in an open field. NBM lesion reduced vertical movements on ly as compared to no lesion and no transplant counterparts. Nine days after surgery rats with NBM lesion and astrocyte-transplants into the cortex were as impaired in the acquisition of a passive avoidance (PA) task as untreated counterparts. Animals with no lesions and transplants into the cortex also had significant PA acquisition deficits. All rats with ibotenic lesion were significantly impaired on PA retention as compared to rats with no lesions. Astrocyte-transplants survived up to 2 months after cortical implantation but these transplants produced severe laminar disruption and gliosis. This effect was greater in rats with NBM lesion than in intact animals with transplants into the cortex. These data show that astrocyte-transplants do not promote functional recovery after NBM lesion and suggest an immune rejection of the astrocyte transplants by the host brain.

Effects of Antimuscarinic Drugs on Both Urinary Frequency and Cognitive Impairment in Conscious, Nonrestrained Rats

Recent studies indicate a risk of learning and memory impairments when patients with senile dementia are treated with antimuscarinic drugs. In this study, we compared the effectiveness of propiverine hydrochloride (propiverine) and oxybutynin chloride (oxybutynin) on the increased urinary frequency and cognitive impairment induced by nucleus basalis magnocellularis (nBM) lesioning in conscious and non-restrained rats. For examination of bladder function, nBM-lesioned rats were given total parenteral nutrition regimens for 8 days. Propiverine administered orally at 0.3, 3 and 30 mg /kg on the postoperative day 7 significantly lessened the increase in the frequency of voiding caused by the nBM lesion, whereas oxybuty-nin administration did not show any improvement at 0.1 or 1 mg/kg but did so at 10 mg /kg. To examine the memory impairment, we trained nBM-lesioned rats in an 8-arm radial maze task for 20 days and then evaluated the effectiveness of oral drug administration on 19th and 20th radial maze performance. The higher rate of errors caused by nBM lesioning was significantly aggravated by oxybutynin at 30 and 100 mg/kg. Propiverine showed slight aggravation of errors, but with no statistical significance at any dose, 30, 100 or 300 mg/kg. These results suggest that propiverine has comparatively less effect on the cognitive impairment than oxybutynin.

The effects of nucleus basalis magnocellularis lesions in Long-Evans hooded rats on two learning set formation tasks, delayed matching-to-sample learning, and open-field activity.

Rats with quisqualic acid lesions of the nucleus basalis magnocellularis (nBM) and control rats were compared in discrimination reversal learning set (DRLS) and olfactory discrimination learning set (ODLS) tasks, a delayed matching-to-sample task (DMTS), and open-field activity. Evidence of learning set formation was seen in control rats but not in nBM-lesioned rats in both the DRLS and ODLS tasks. Better-than-chance performances were seen for both groups in DMTS, indicating no impairment after nBM lesions. There were no group differences in open-field activity. These findings suggest that the nBM is important for higher cognitive processing such as "learning to learn" and thus is important for a complex form of reference memory. In addition, perseverational, working memory, and attentional deficits could not explain learning set impairment after nBM lesions.

Long-term evolution of local, proximal and remote astrocyte responses after diverse nucleus basalis lesioning (an experimental Alzheimer model): GFAP immunocytochemical study

A study on long-term astrocytic responses (from 1 day to 20 months after lesioning in 4-month-old rats, and from 1 day to 6 months in 20-month-old rats) to diverse unilateral damage of the nucleus basalis (nbM) by injection of 40 nmol of ibotenic acid, or 50 or 100 nmols of quisqualic acid was performed using a histochemical method (immunoreactivity against the glial fibrillary acidic protein GFAP). Glial reactivity (i.e., isolated or clustered hypertrophic and/or hyper-reactive astrocytes) was evaluated in several ipsilateral and contralateral brain regions: the ‘local response’ within the damaged nbM region; the ‘proximal response’ (a new concept proposed by us) in the non-damaged structures neighbouring the nbM; and the ‘remote response’ in the ipsilateral brain cortex and in the contralateral cortex and nbM. In 4-month-old animals, the remote cortical glial responses, independent of the involution of cortical cholinergic activity and randomly located in layers I–V of motor and somatosensory cortical regions, were similar in appearance over a long period (13–20 months), with the highest reactivity 45 days after lesioning. The proximal response lasted from 1 day to 13 months and afterwards tended to disappear. Contralateral reactivity and ipsilateral cortical scars were observed. The local (nbM) glial response was maintained throughout the period studied. Subsets of astrocytes of different reactivities were observed, most of their elements being highly intermeshed. In 20-month-old animals, nbM lesions produced less positive, but similar, glial reactive patterns. This glial reactivity was superposed onto the glial reactivity of old age. All these results are discussed. The maintenance of reactive astrocytes many months after lesioning suggests the existence of cellular factors other than those produced by damaged nbM neurons. Taking into account the role of glial cells under pathological conditions, it is possible that these reactive astrocytes in humans could promote neurodegenerative processes, such as amyloid plaque formation and neurodegeneration (Alzheimer’s disease). Along this line, nbM cholinergic involution could then originate cortical involution through induced reactive astrocytosis.

Severe learning impairment caused by combined immunotoxic lesion of the cholinergic projections to the cortex and hippocampus in monkeys

Monkeys with immunotoxic lesions of both the basal nucleus of Meynert and the vertical limb of the diagonal band of Broca (NBM+VDB) lost cholinergic innervation throughout the cortex and hippocampus. They were impaired at learning discriminations between objects differing in either few, or many, attributes and at learning visuospatial conditional discriminations. Monkeys with immunotoxic lesions of the NBM lost cholinergic innervation of the neocortex only. Initially, they were unable to learn a simple visual discrimination where the stimuli differed in a limited number of attributes but they were unimpaired at learning discriminations between objects that differed in more attributes. They were mildly impaired at learning a visuospatial conditional task. The impairment exhibited by monkeys with lesions of the NBM alone ameliorated with time but that following NBM+VDB lesions did not. Previous experiments have shown that monkeys with immunotoxic lesions of the VDB alone are impaired at learning visuospatial conditional discriminations but are unimpaired at learning simple visual discriminations. When monkeys with NBM lesions were given excitotoxic lesions of the CA1 field of the hippocampus the learning impairment on discriminations between objects which differed in few attributes was reinstated. Pretreatment with a cholinergic agonist improved learning ability on visual discrimination learning in all monkeys but this improvement was significantly greater in monkeys with lesions of the NBM. On conditional discrimination learning, which is particularly sensitive to hippocampal damage, pilocarpine produced a significant improvement in monkeys with NBM+VDB lesions (where the hippocampal dysfunction was cholinergic) but not in monkeys with NBM+CA1 lesions (where the hippocampal damage was structural).

Different effects on learning ability after injection of the cholinergic immunotoxin ME20.4IgG-saporin into the diagonal band of Broca, basal nucleus of Meynert, or both in monkeys.

Immunotoxic lesions of the diagonal band of Broca (VDB) in monkeys disrupted cholinergic input to the hippocampus, producing impaired learning of visuospatial conditional discriminations but not simple visual discriminations. Immunotoxic lesions of the basal nucleus of Meynert (NBM) deprived the cortex of most of its cholinergic input, producing impaired learning of simple visual discriminations but not visuospatial conditional discriminations. Combined lesions of the NBM + VDB resulted in impaired learning of both types of task. The impairment after NBM lesions ameliorated with time but could be reinstated by a low dose of the glutamate blocking drug MK801, which, at this dose, did not impair simple visual discrimination learning in normal monkeys. The cholinergic projections from the NBM and VDB may sustain the function of the glutamatergic pyramidal cell pathways within the cortex and hippocampus, respectively.

Sexually dimorphic responses to neonatal basal forebrain lesions in mice: I. Behavior and neurochemistry.

The nucleus basalis magnocellularis (nBM) provides the primary source of cholinergic input to the cortex. Neonatal lesions of the nBM produce transient reductions in cholinergic markers, persistent abnormalities in cortical morphology, and spatial navigation impairments in adult mice. The present study examined sex differences in the effects of an electrolytic nBM lesion on postnatal day 1 (PND 1) in mice on behavior and neurochemistry in adulthood. Mice were lesioned on PND 1 and tested at 8 weeks of age on a battery of behavioral tests including passive avoidance, cued and spatial tasks in the Morris water maze, simple and delayed nonmatch to sample versions of an odor discrimination task, and locomotor activity measurements. Following behavioral testing, mice were sacrificed for either morphological assessment or neurochemical analysis of a cholinergic marker or catecholamines. There were no lesion or sex differences in acquisition or retention of passive avoidance, performance of the odor discrimination tasks, or activity levels. Control mice showed a robust sex difference in performance of the spatial water maze task. The lesion produced a slight cued but more dramatic spatial navigation deficit in the water maze which affected only the male mice. Neurochemical analyses revealed no lesion-induced changes in either choline acetyltransferase activity or levels of norepinephrine or serotonin at the time of testing. The subsequent report shows a sex difference in lesion-induced changes in cortical morphology which suggests that sexually dimorphic cholinergic influences on cortical development are responsible for the behavioral deficits seen in this study.

Sexually dimorphic responses to neonatal basal forebrain lesions in mice: II. Cortical morphology

Previous studies in the mouse have shown that neonatal lesions to the cholinergic basal forebrain (nBM) areas result in transient cholinergic depletion of neocortex and precipitate altered cortical morphogenesis. Lesion-induced morphological alterations in cortex persist into adulthood and are accompanied by behavioral changes, including spatial memory deficits. The current study investigated whether neonatal nBM lesions affect male and female mice differently in adulthood. Quantitative morphometry of cortical layer width was employed to assess alterations in cytoarchitecture in neonatally nBM-lesioned and littermate control mice of both sexes following behavioral testing. Our results showed significant decreases in cortical layer IV and V widths across somato/motor cortex in neonatally nBM lesioned mice of both sexes. Sexually dimorphic responses were observed in cortical layer II/III and total cortical width, limited to the area containing the "barrel cortex" representation of the whisker hairs. In lesioned females, layer II/III and total cortical width were decreased relative to female controls, and in lesioned males, layer II/III was increased relative to controls, whereas total cortical width was unchanged. In male but not female mice we observed significant correlations between decreased widths in layer IV and V and impaired performance on a spatial memory task. The current data further support a role of developing cholinergic cortical afferents in the modulation of cortical morphogenesis and cortical circuits involved in cognitive behaviors. In addition, our observations provide further evidence for sexually dimorphic development and function in cognitive centers of the rodent brain.

P300-like potential disappears in rabbits with lesions in the nucleus basalis of Meynert.

The nucleus basalis of Meynert (nbM, substantia innominata) in the basal forebrain provides a single major source of cholinergic innervation for the entire cerebral cortex. We tested the effects of nbM lesions on rabbit P300-like potentials. The P300-like event-related potential (ERP) was recorded in 14 female adult white rabbits using a conventional auditory oddball paradigm. The probability of occurrence for the 2-kHz and 1-kHz stimulus tones was 90% (frequent) and 10% (rare), respectively. The nbM was destroyed bilaterally in seven rabbits referred to as the nbM (+) group. In the other seven rabbits [nbM (-) group], putamen nuclei (n=6) or amygdaloid nuclei (n=1) were destroyed bilaterally. The evoked responses were recorded before and 1 week after the destruction. In the nbM (+) group, P300 amplitude to rare stimuli significantly decreased after the lesion. In the nbM (-) group, no component of ERPs showed changes after the lesions. These results indicate that the nbM might be involved in the generation of the rabbit P300.

Astrocytes Grafted Into Rat Nucleus Basalis Magnocellularis Immediately After Ibotenic Acid Injection Fail to Survive and Have no Effect on Functional Recovery

In order to determine if the “trophic” properties of astrocytes makes them appropriate for use as a therapeutic agent to excitotoxic brain damage, adult male rats received grafts of cultured cerebral cortical astrocytes into the NBM immediately after infusion of ibotenic acid into the same structure. Twenty four hours after grafting and every other day for 11 days post surgery, the animals were tested for locomotor activity and habituation in an open field. Animals with NBM lesions had significantly reduced rearing activity as compared to counterparts with no lesions. Nine days after surgery, rats with NBM lesions and astrocyte grafts were as impaired in the acquisition of passive avoidance (PA) as their untreated counterparts. AH animals with ibotenic lesions were impaired on PA retention compared to rats with no lesions. There was no difference between animals that had received grafts and those that had not. Fourteen days after grafting, all brains were processed for Nissl stain, acetylcholinesterase (AChE) histochemistry, GFAP immunocytochemistry, and bisben-zamide fluorescent microscopy. Decreases in the number of neurons in the NBM as well as decreases in the density of AChE staining in the ipsilateral cortex (the area of innervation of the NBM cholinergic neurons) was evident in all animals with NBM lesions. In addition, a large number of host reactive astrocytes were seen within the NBM, its vicinity, and in the ipsilateral neocortex. Grafted astrocytes survived and integrated into the host tissue when they were grafted into the brain of intact animals but no living grafted astrocytes were found in animals injected with ibotenate. In this latter case, two weeks after grafting, instead of surviving astrocytes only fluorescent tissue ‘masses’ were seen in the NBM. surrounded by a cavity. Grafted astrocytes did not have any effect on the extension of the lesion caused by ibotenic acid infusion. These results suggest that the concentration of ibotenic acid used to injure the NBM killed not only the host cholinergic neurons but also the grafted astrocytes. The failure of astrocytes to ameliorate the behavioral deficits caused by ibotenic acid lesions of the NBM may be due to the ibotenic acid creating a lethal environment for the grafted and freshly dissociated, cultured astrocytes.

Changes in the Sensitivity of Frontal Cortical Neurones to Acetylcholine After Unilateral Lesion of the Nucleus Basalis with α-Amino-3-OH-4-Isoxozole Propionic Acid (AMPA): Effects of Basal Forebrain Transplants Into Neocortex

Unilateral S- α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) lesions of the nucleus basalis magnocellularis (nbm), which produced persistent and extensive ChAT-positive cell loss within the nbm and depletion of cortical cholinergic markers in the frontal cortex, increased both the number and sensitivity of individual frontal cortical neurones responding to iontophoretic administration of ACh. The lesion also increased the sensitivity of individual neurones to carbachol but the increase in the number of neurones responding to carbachol was transient and had returned to normal 4 weeks after lesion. The sensitivity of individual neurones to glutamate was unchanged by the lesion. The percentage of cortical neurones responding to ACh, but not the sensitivity of individual neurones was restored to the prelesion level, 6–8 weeks after cholinergic transplants to the lesioned frontal cortex; cholinergic transplants to the more distant parietal cortex were only effective after 6 months whereas noncholinergic transplants were ineffective at both time intervals. Cholinergic transplants placed in the frontal cortex 6–8 weeks or 6 months before nbm lesion offered some protection from the effects of the lesion, particularly at 6 months but were ineffective when placed into the parietal cortex. Lesion of the nbm also reduced basal firing rate of spontaneously active neurones and this was not restored by any of the transplants. The results are discussed in the light of quantitative measurements of acetylcholinesterase-positive fibre outgrowth from the transplant into the recording area, which are described in the preceding manuscript [20].