Basal Forebrain Transplants Research Articles

Nerve growth factor increases the size of intracortical cholinergic transplants.

The effects of continuous intracortical mouse Nerve Growth Factor on fetal rat basal forebrain transplants in denervated adult rat neocortex were investigated. Enzyme-linked immunoassay (ELISA) was used to measure the time course of endogenous NGF protein production in neocortex, hippocampus, and basal forebrain in a cohort of animals receiving unilateral ibotenic acid (IBO) lesions of the nucleus basalis magnocellularis (nBM). A second cohort of IBO-nBM lesioned animals received transplants of fetal basal forebrain followed by two to four weeks of continuous NGF or cytochrome-C infusion into the ipsilateral frontoparietal neocortex. To study the effects of abnormally high NGF doses on transplanted and host tissue, the cumulative dose of intracortical NGF was on the order of micrograms, compared with maximum picogram levels of neocortical NGF produced following IBO-nBM lesions. A four-fold increase in transplant size, and greater cell and fiber densities were observed in NGF-treated compared with NGF-untreated transplants. No adverse histological effects of long-term, high-dose NGF treatment were observed on transplanted basal forebrain or host neocortical tissue. These data indicate that cholinergic-rich mammalian brain tissue and intrinsic host tissue can be stimulated by high doses exogenous NGF without obvious deleterious effects.

Nerve growth factor increases stimulus-evoked metabolic activity in acetylcholine-depleted barrel cortex

Lesions of the basal forebrain deplete the neocortex of cholinergic fibers. Acetylcholine depletion in the somatosensory cortex of rats results in reduced stimulus-evoked activity in response to whisker stimulation. Previous studies demonstrate that embryonic basal forebrain transplants improve functional activity toward normal. It is not clear if the activity increase is due to cholinergic replacement or other factors present in the graft. In this study, we examined the possibility that nerve growth factor (NGF), a neurotrophin known as a survival factor and a specific protectant for cholinergic basal forebrain neurons, can preserve basal forebrain cells after a lesion and restore functional activity in the somatosensory cortex. We report that NGF alone is capable of restoring functional activity in the barrel cortex of animals with basal forebrain lesions, while vehicle injections of saline do not alter activity. Both high (10 mug) and low (5 mug) doses of NGF unilaterally injected into the lateral ventricle improved stimulus-evoked functional activity during bilateral whisker stimulation. The mechanism of NGF action is not clear since the restoration of functional activity in cortex was not accompanied by increased cholinergic activity as detected by acetylcholinesterase fiber staining. NGF may act directly on cortical neurons, although its site of action is not well defined.

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].

Plastic changes in the cholinergic innervation of the rat cerebral cortex after unilateral lesion of the nucleus basalis with alpha-amino-3-OH-4-isoxozole propionic acid (AMPA): effects of basal forebrain transplants into neocortex.

Unilateral AMPA lesions of the nucleus basalis magnocellularis (nbm) produced a nearly complete loss of cholinergic markers in the ipsilateral frontal and parietal cortices with no recovery at 6 months. The loss was associated with compensatory increases in AChE-positive fibre density in the contralateral cortex, in ipsilateral cortical regions not receiving their cholinergic innervation from the nbm and in the size of cholinergic magnocellular neurones in the contralateral nbm. The hypertrophy and increase in AChE-positive fibre density were apparent at 4-6 weeks after lesion and increased with time. Cholinergic transplants to cholinergically deafferented cortex prevented development of the compensatory increases in AChE-positive fibre density and restored AChE-positive fibre density and ChAT activity to control levels in ipsilateral cholinergically deafferented regions, partially after 6-8 weeks and completely after 6 months. In contrast, when cholinergic grafts were placed into unlesioned cortex, axonal outgrowth was localized to the vicinity of the transplant and did not develop with time. These results support the concept that vacant synapses promote and direct axonal outgrowth from transplanted neurones and that grafted cholinergic neurones integrate into the lesioned forebrain cholinergic projections system and prevent the lesion-induced changes in AChE-positive fibre density and ChAT activity.

Erratum for Jacobs et al., Cholinergic Basal Forebrain Transplants Restore Diminished Metabolic Activity in the Somatosensory Cortex of Rats with Acetylcholine Depletion

Due to a printing error, some data were left off of Figure 2C in “Cholinergic Basal Forebrain Transplants Restore Diminished Metabolic Activity in the Somatosensory Cortex of Rats with Acetylcholine Depletion” by S.E. Jacobs, A. Fine, and S.L. Juliano, which appeared in the February 1994 issue, pp. 697–711. The correct figure appears above.

Cholinergic basal forebrain transplants restore diminished metabolic activity in the somatosensory cortex of rats with acetylcholine depletion [published erratum appears in J Neurosci 1994 Mar;14(3): following table of contents

It has been known for several years that stimulus-evoked metabolic activity is reduced in the somatosensory cortex of animals with basal forebrain lesions that deplete the neocortex of acetylcholine (ACh). During 2-deoxyglucose (2-DG) experiments, animals with unilateral basal forebrain lesions demonstrate a decreased response to somatic stimulation, while background metabolic activity in the surrounding cortical regions remains normal. In an attempt to ameliorate these deficits, we examined the ability of embryonic cholinergic basal forebrain transplants inserted into neocortex to innervate surrounding cortical regions and restore functional 2-DG activity in adult host rats previously depleted of ACh by basal forebrain lesions. To accomplish this goal, a series of experiments were conducted in which we (1) depleted the cerebral cortex of ACh by injecting an excitotoxin into the rat basal forebrain, (2) transplanted embryonic basal forebrain or embryonic neocortical (control) tissue into the ACh-depleted cortex and, (3) 6-12 months later, used the 2-DG metabolic mapping technique to examine effects of the transplants on metabolic activity evoked by whisker stimulation in rat somatosensory (barrel) cortex. Histochemical analysis revealed that acetylcholinesterase (AChE) staining within 2 mm of the basal forebrain transplants was similar in density to the contralateral normal hemisphere. AChE staining farther than 2 mm from the basal forebrain transplants and throughout hemispheres containing neocortical (control) transplants was greatly reduced, with few AChE-positive fibers present, a finding typical of cerebral cortex in basal forebrain-lesioned animals. Stimulus-evoked 2-DG uptake in barrels adjacent to the basal forebrain transplants, and therefore within AChE-rich territory, was similar to that in corresponding barrels identically activated in the contralateral hemisphere. 2-DG activity was reduced, however, in stimulated barrels outside the region of dense AChE-positive staining, as well as in all activated barrels in hemispheres containing control transplants of embryonic neocortex. These results indicate that transplantation of cell suspensions containing embryonic cholinergic basal forebrain, but not neocortex, can ameliorate basal forebrain lesion-induced deficits in functional activity, and that the restoration of activity is influenced by proximity to the transplant.

Intracortical grafts of purified astrocytes ameliorate memory deficits in rat induced by chronic treatment with ethanol

Chronic intake of ethanol in rat results in a substantial and permanent impairment in memory function which can be ameliorated by intracortical grafting of fetal tissue derived from the primordial basal forebrain. The present study demonstrates that grafting of purified astrocytes is equally effective in improving the performance in the eight-arm radial maze. In comparison, the rate of behavioral recovery is even more accelerated after grafting of astrocytes than after fetal basal forebrain transplants. The improvement in memory function can be detected as early as 2 weeks after operation and is accompanied by an increase in the activity of choline acetyltransferase in the basal forebrain previously reduced after ethanol treatment. Graft-induced behavioral recovery in the present paradigm is most likely due to a neurotrophic influence of astrocytes mediated via the cholinergic basal forebrain system.

Changes in Sensitivity of Rat Front Cortex Neurons to Acetylcholine (ACh) after α‐Amino‐3‐Hydroxy‐4‐Isoxozole Propionic Acid (AMPA) Lesions of Nucleus Basalis Magnocellularis and After Embryonic Basal Forebrain Transplants

The effects of unilateral S-AMPA lesions of nucleus basalis magnocellularis (nbm) and of subsequent ipsilateral embryonic basal forebrain transplants on the sensitivity of pyramidal cells in the frontal cortex to iontophorized acetylcholine (ACh) and carbachol were studied in anaesthetized rats. Each drug was applied with an ejection current of 30 nA for 20 s and the average response of 3 applications (separated by 1 min recovery periods) was obtained. Neurons were considered to be sensitive when their firing rate increased or decreased (Wilcoxon, P<0.05), either during or within 20 s of drug application. Neuronal firing rates were significantly reduced in the frontal cortex 8-10 weeks postlesion, when acetylcholinesterase (AChE)positive fibre staining was almost completely absent, but the percentage of ACh-sensitive neurons increased (68/82 neurons from 7 rats compared with 72/144 neurons from 12 control rats, P<0.0001); the duration of ACh’s action also significantly increased. Comparison with controls showed that this enhanced sensitivity to ACh after lesion could be explained solely by an increase in the proportion of neurons excited by ACh (Table 1). The modulatory effects of ACh were also studied on responses of cortical neurons evoked by afferent electrical stimulation (single square wave pulses, 5 ms duration, 1-3 mA, were delivered at intervals of not less than 10 s and 10 stimulations used for each procedure). ACh modulation of neuronal responses evoked by sensory stimulation was not significantly changed after the lesion. Sensitivity to carbachol and glutamate was unchanged after lesion. In normal rats, acute administration of an AChE-inhibitor, di-isopropyl fluorophosphate (DFP) significantly increased the frontal cortex neurons’ responsiveness to ACh from 50% in the control group to 87.4% in the DFP treated group (P<0.0001). DFP also decreased the latency and increased the duration of ACh action without changing the frontal cortex firing rate. The sensitivity of frontal cortex to carbachol and glutamate was not changed after DFP. Chronic administration of scopolamine (10 mg/kg s.c. in 0.9% NaC1 daily for 16 days) significantly increased the sensitivity of frontal cortex neurons to both ACh and carbachol. It also significantly increased the neuronal firing rate, prolonged the duration of ACh and carbachol action and decreased the latency of action of both drugs. In contrast, chronic administration of oxotremorine (0.5 mg/kg s.c. in 0.9% NaC1 twice daily for 11 days and 10 mg/kg in sesame oil for 9 days) significantly decreased the frontal cortex neurons’ sensitivity to both ACh and carbachol. It also significantly decreased the neuronal firing rate, decreased the duration and increased the latency of ACh and carbachol action. Cholinergic-rich transplants to the frontal cortex normalised neuronal sensitivity to ACh and its duration of action but did not restore the firing rate. Non-cholinergic transplants or cholinergie-rich transplants to the somatosensory cortex were ineffective. Histological examination showed a sprouting of ChAT and AChE from the transplant into the neocortex of

Autoradiographic analysis of muscarinic receptors and choline-uptake mechanisms within foetal basal forebrain transplants

The pharmacological characteristics of both muscarinic receptors and high-affinity choline uptake sites were examined within intracerebral implants of foetal basal forebrain cell suspensions. Approximately 12 weeks after implantation, the transplants were identified by acetylcholinesterase histochemistry. Muscarinic receptors were labelled by [3H]quinuclidinyl benzylate (QNB) autoradiography. The M1 and M2 receptor components of QNB binding were differentiated by pirenzepine competition. The distribution of the high-affinity choline uptake site was examined using [3H]hemicholinium-3 (HC3) autoradiography. Unilateral lesion of the nucleus basalis reduced [3H]QNB (8-25%) and [3H]HC3 (19-43%) binding throughout host frontoparietal cortex ipsilateral to the lesion but did not significantly alter these cholinergic markers within cingulate cortex, subcortical white matter, striatum or septum. Saturation analysis of the implanted tissue revealed the presence of a single population of [3H]QNB and [3H]HC3 binding sites with affinities similar to those of the host tissue (KD = 0.43 nM and 20.4 nM respectively). However, the receptor profile which developed appeared to be intrinsic to the implant; it was unaffected by the site of implantation and was dissimilar to that which ultimately developed in the donor tissue when left in situ.

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.

Electrophysiological and pharmacological properties of neurons within solid basal forebrain transplants in the rat brain

Electrophysiological and pharmacological properties of neurons within solid basal forebrain transplants were studied in adult rats anesthetized with urethane. No specific topography of the neurons recorded was observed within the graft. The mean spontaneous activity of the grafted neuronjs (GNs) was relatively low (4.9 implulse/s) but not unlike that of other central neurons in situ. A large proportion of GNs fired with regular discharges, but other modes of discharge were also observed. A few rhythmically bursting GNs were recorded having a discharge pattern very much like that of the rhythmically bursting medial septal neurons. The responses of GNs to glutamate, γ-aminobutyric acid, acetylcholine, serotonin and norepinephrine was fairly similar to those described in other central structures.