Effects of ganglioside treatment in rats with a lesion of the cholinergic forebrain nuclei

The effects of GM1 ganglioside (30 mg/kg i.p.) administration for 22 days on choline acetyltransferase (ChAT) activity and noradrenaline (NA) levels in the cerebral cortex and on the acquisition of active and passive avoidance-conditioned responses were investigated in both sham-operated rats and in rats with a unilateral electrolytic lesion of the magnocellular forebrain nuclei (MFN). A statistically significant ChAT decrease in cortical areas ipsilateral to the lesion was found in saline-treated lesioned rats. In the lesioned GM1-treated rats, ChAT activity was only reduced in the frontoparietal areas and was significantly increased in the ipsilateral parietooccipital areas as well as in both contralateral regions. NA levels in the cortex were neither significantly affected by the lesion nor by GM1 treatment. The lesion impaired the acquisition of active and passive conditioned avoidance responses. GM1 treatment improved acquisition of the active avoidance response in the lesioned rats as indicated by a larger number of avoidances and a smaller number of escape failures during training in comparison with saline treatment. Ganglioside had no effect on the passive avoidance responses. These results demonstrate that GM1 administration facilitates the recovery of the cortical cholinergic system and of behavioral responses impaired by an electrolytic lesion of the cholinergic forebrain nuclei.     

Generation of cortical event-related slow potentials in the rat involves nucleus basalis cholinergic innervation

These experiments were conducted to gather information regarding the role of cholinergic innervation to the cortex in the generation of event-related slow potentials. The effects of unilateral drug treatments or lesions on ipsilateral and contralateral frontal cortex slow potential (SP) responses were examined in rats. The SP responses were recorded with silver-silver chloride electrodes and were generated by a 2 sec light cue which preceded rewarding medial forebrain bundle stimulation. The following approaches were used: microinjection of GABA, procaine or saline into the nucleus basalis magnocellularis; microinjection of atropine or saline subdurally in the SP recording area; electrolytic lesion of the nucleus basalis area; and kainic acid lesion of the nucleus basalis area. The following bilateral measurements were obtained lesion studies: choline acetyltransferase (ChAT) in cortex and hippocampus; serotonin in cortex, hippocampus, striatum and nucleus accumbens; norepinephrine in cortex and hippocampus; dopamine in striatum and nucleus accumbens; and metabolites of serotonin, norepinephrine and dopamine in these areas. The cortical SP responses were reduced on the side ipsilateral to the injections of GABA and procaine into the nucleus basalis, and on the side of the subdural atropine injection. With either type of lesion, the SP responses on the lesioned side were significantly reduced as compared to the non-lesioned side. Reductions in cortical ChAT and other measures were observed ipsilateral to the electrolytic lesion, but only cortical ChAT activity was reduced in the kainic acid-lesioned animals. Thus, pharmacological depression of nucleus basalis neurons, blockade of cholinergic muscarinic receptors in the cortex, and nucleus basalis lesions that reduce cortical choline acetyltransferase activity depress event-related slow potentials in the rat frontal cortex. These results provide evidence that cortical slow potential responses in the rat are dependent upon cholinergic innervation from the nucleus basalis.     

Interaction between nerve growth factor and GM1 monosialoganglioside in preventing cortical choline acetyltransferase and high affinity choline uptake decrease after lesion of the nucleus basalis

Monosialoganglioside GM₁ and nerve growth factor (NGF) were administered alone or concomitantly to adult male rats with a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM). High-affinity choline uptake (HACU) rate and choline acetyltransferase (ChAT) activity were measured, 4 and 21 days after surgery, respectively, in the frontal and parietal cortices of both hemispheres. A 33–34% decrease in HACU rate and a 43-39% decrease in ChAT activity was found in the ipsilateral cortices 4 and 21 days, respectively, after the lesion. If the lesioned rats received NGF (10 μg i.c.v.) twice a week or daily administrations of GM₁ (30 mg/kg, i.p.), beginning immediately after surgery the decrease in HACU rate and ChAT activity was smaller. If NGF and GM, were given concomitantly no decrease in HACU rate and ChAT activity was detected in the lesioned hemisphere and a slight increase occurred in the contralateral hemisphere. However, after the concurrent administration of NGF (10 μg i.c.v.) and the inactive dose of GM₁ 10 mg/kg i.p. no decrease in HACU and ChAT activity was also found in the lesioned rats. The latter finding indicates a potentiation by GM₁ of NGF effects on the cholinergic neurons of the IBM. The two drugs may either antagonize the neurotoxic effects of ibotenic acid or stimulate a compensatory activity in the remaining neurons.     

Interaction between nerve growth factor and GM1 monosialoganglioside in preventing cortical choline acetyltransferase and high affinity choline uptake decrease after lesion of the nucleus basalis

Monosialoganglioside GM₁ and nerve growth factor (NGF) were administered alone or concomitantly to adult male rats with a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM). High-affinity choline uptake (HACU) rate and choline acetyltransferase (ChAT) activity were measured, 4 and 21 days after surgery, respectively, in the frontal and parietal cortices of both hemispheres. A 33–34% decrease in HACU rate and a 43-39% decrease in ChAT activity was found in the ipsilateral cortices 4 and 21 days, respectively, after the lesion. If the lesioned rats received NGF (10 μg i.c.v.) twice a week or daily administrations of GM₁ (30 mg/kg, i.p.), beginning immediately after surgery the decrease in HACU rate and ChAT activity was smaller. If NGF and GM, were given concomitantly no decrease in HACU rate and ChAT activity was detected in the lesioned hemisphere and a slight increase occurred in the contralateral hemisphere. However, after the concurrent administration of NGF (10 μg i.c.v.) and the inactive dose of GM₁ 10 mg/kg i.p. no decrease in HACU and ChAT activity was also found in the lesioned rats. The latter finding indicates a potentiation by GM₁ of NGF effects on the cholinergic neurons of the IBM. The two drugs may either antagonize the neurotoxic effects of ibotenic acid or stimulate a compensatory activity in the remaining neurons.     

Recovery of choline acetyltransferase activity without sprouting of the residual acetylcholine innervation in adult rat cerebral cortex after lesion of the nucleus basalis

In view of the divergent literature concerning the long-term effects of ibotenic acid lesions of the nucleus basalis of Meynert (NBM) on the choline acetyltransferase (ChAT) activity in adult rat cerebral cortex, we have critically reassessed the issue of an eventual recovery of this enzymatic activity by sprouting of the residual acetylcholine (ACh) innervation. At short (1 week) and long survival time (3 months) after unilateral ibotenic acid lesion, ChAT activity was biochemically measured in the ipsi and contralateral fronto-parietal cortex of several rats in which the extent of ACh neuronal loss in NBM was also estimated by counts of ChAT-immunostained cell bodies on the lesioned vs. non-lesioned side. In other lesioned rats, particular attention was paid to the distribution of the residual cortical ACh (ChAT-immunostained) innervation, and that of immunostained vasoactive intestinal polypeptide (VIP) axon terminals known to belong in part to intrinsic cortical ACh neurons which co-localize this peptide. One week after NBM lesion, profound decreases of ipsilateral cortical ChAT activity were tightly correlated with the extent of ACh cell body loss in the nucleus. A significant recovery of cortical ChAT activity could be documented after 3 months, despite persistence of NBM cell body losses as severe as after 1 week. At both survival times, the number of ChAT-immunostained axons was markedly reduced throughtout the ipsilateral fronto-parietal cortex, demonstrating that most ACh fibers of extrinsic origin had been permanently removed. This result also indicated that the long-term recovery of ChAT activity had occurred without sprouting of the residual ACh innervation. The laminar distribution and number of VIP-immunostained terminals remained the same on the lesioned and intact side and comparable to normal, ruling out an extensive sprouting of intrinsic ACh/VIP or VIP alone fibers. The return to a near normal cortical ChAT activity in severely ACh-denervated cortex suggested that the intrinsic ACh innervation was primarily responsible for this recovery.     

A protective effect of lithium on rat behaviour altered by ibotenic acid lesions of the basal forebrain cholinergic system

Lithium was tested on an animal model of a brain cholinergic excitotoxic lesion. Male Wistar rats received unilaterally 50 nmol ibotenic acid in the nucleus basalis magnocellularis. Some were treated intraperitoneally with LiCl from two days before to six days after lesioning. Such treated rats showed less deficits than untreated lesioned animals on passive avoidance, ambulatory behaviour and choline acetyltransferase activity in the lesioned cortex. Lithium protection against excitatory amino acid neurotoxicity is suggested.     

Are the neurochemical and behavioral changes induced by lesions of the nucleus basalis in the rat a model of Alzheimer's disease?

A review of the work on the neurochemical, electroencephalographic and behavioral changes induced in the rat by lesions of the nucleus basalis is presented. The similarities and differences between the effects of the lesions and the neurochemical and clinical alterations characterizing senile dementia of Alzheimer type are pointed out. The decrease in choline acetyltransferase (ChAT) activity in the cortex following unilateral or bilateral electrolytic or neurotoxic lesions of the nucleus basalis are described and compared with the decrease in ChAT activity found in the cortex and hippocampus of patients affected by senile dementia. At variance with the latter condition, in rats with lesions of the nucleus basalis a spontaneous recovery in cortical ChAT activity has been observed 3-6 months after the lesion. The lesions of the nucleus basalis decrease high affinity choline uptake activity which, however, undergoes a rapid recovery. Lesions also decrease spontaneous and drug-stimulated ACh release from the cerebral cortex. Transitory changes in the number of muscarinic binding sites have been reported in the cerebral cortex of the lesioned rats while a decrease in the number of muscarinic binding sites has generally been found in the cerebral cortex of patients with senile dementia. [3H] glutamate uptake in the striatum of the lesioned rats was not affected. In both lesioned rats and patients affected by senile dementia, a decrease of low voltage high frequency electrocortical activity has been reported. Unilateral and bilateral lesions of the nucleus basalis bring about an impairment of the acquisition of active and passive avoidance responses and of the rewarded alternation discriminatory tasks involving working memory and spatial memory. On the other hand, memory impairment is a typical symptom of senile dementia. In conclusion, the lesions of the nucleus basalis only partly mimic the complex clinical picture of senile dementia of Alzheimer type. They offer, nevertheless, a useful tool for understanding the critical role of the central cholinergic pathways in some of the cognitive processes and identifying potentially useful pharmacological treatments.     

Effect of nerve growth factor on the lesioned septohippocampal cholinergic system of aged rats

Nerve growth factor (NGF) was injected intraventricularly into aged (24 months) rats with unilateral lesions of the lateral fimbria. The activity of choline acetyltransferase (ChAT) was determined in the septum and hippocampus from the normal unlesioned rats, lesioned and cytochrome c-treated rats (controls), and lesioned and NGF-treated rats at different times after the lesion. NGF-injection for 15 days after the lesion resulted in an increase of the ChAT activity in both the contralateral hippocampus and the entire septum, to about 130% of that in the normal animals, but resulted in a slight increase in the ipsilateral lesioned hippocampus, when compared to the activity in the ipsilateral side of the cytochrome c-treated controls. NGF-injection for 30 days after the lesion resulted in a 48% increase of the ChAT activity in the ipsilateral hippocampus as compared to cytochrome c-treated controls, but failed to result in a significant increase in the contralateral hippocampus. These findings indicate that atrophic cholinergic neurons in aged animals are similarly responsive to NGF treatment, like these in the young animals. Moreover, these findings suggest that the responses of basal forebrain cholinergic neurons to NGF treatment varies with time after the lesion and imply that the NGF administration can promote the collateral sprouting from spared cholinergic fibers after the lesion in the aged forebrain.     

Effects of unilateral lesion of the nucleus basalis of Meynert on brain glucose utilization in callosotomized baboons: a PET study

Prior work has demonstrated that unilateral lesions of the nucleus basalis of Meynert (NbM) in baboons induce a marked reduction in glucose utilization of the ipsilateral cerebral cortex, linearly proportional to the depression in cortical choline acetyltransferase (ChAT) activity achieved. Unexpectedly, there was also marked hypometabolism of the contralateral cerebral cortex, and glucose utilization recovered gradually on both sides despite persistent deficit in cortical ChAT activity. To investigate the role of the corpus callosum (CC) in this bilateral metabolic effect and subsequent recovery, three baboons were subjected to unilateral electrolytic NbM lesion greater than 3 months following section of the anterior CC. Brain glucose utilization was sequentially studied by positron emission tomography; ChAT activity was measured and histological sections obtained after death. In these animals, the NbM lesion also induced significant metabolic depression over the ipsilateral cortex, proportional to the reduction in ChAT activity. Corpus callosotomy did not prevent the contralateral metabolic effects, suggesting that the latter do not normally operate through the CC. However, there was no significant recovery of glucose utilization, suggesting that, following unilateral NbM lesion, the CC normally mediates, at least in part, the recovery of cortical glucose utilization.     

Modifications in the cortical regional distribution of choline acetyltransferase, somatostatin and somatostatin binding sites in the normal rat and following lesion of the nucleus basalis

The regional distribution of choline acetyltransferase activity, somatostatin levels and 125I-CGP 23996 (a somatostatin agonist analog) specific binding sites in 10 separate zones of the cerebral cortex was analyzed. The study was performed in normal rats as well as 15 days after unilateral excitotoxic lesion of the nucleus basalis. A significant correlation was found in the controls between the regional distribution of choline acetyltransferase activity and somatostatin concentrations, both most highly concentrated in the piriform and entorhinal cortex. In contrast, the regional density of 125I-CGP 23996 binding sites correlated neither with choline acetyltransferase activity nor with somatostatin levels. Unilateral lesions of the basal forebrain decreased choline acetyltransferase activity in the frontal and parietal cortex, while 125I-CGP 23996 binding decreased in frontal and occipital regions. No decrease in somatostatin content was observed. The results suggest that, in rats, cortical somatostatin receptors could be associated with cholinergic afferents from the nucleus basalis in the frontal cortex only.     

Recovery of nucleus basalis cholinergic neurons by grafting NGF secretor fibroblasts.

The effects of nerve growth factor (NGF) secreted from genetically modified fibroblasts was studied in vitro, using dissociated septal cells and in vivo, in rats bearing unilateral cortical devascularizing lesions. Transfected fibroblasts expressing nerve growth factor (NGF) were co-cultured with rat embryonic cholinergic cells of the septal region. This in vitro system showed that NGF secretor cells produce biologically active NGF, as determined by increasing choline acetyltransferase (ChAT) activity in septal culture after seven days. The potential therapeutic value of applying grafts of transfected fibroblasts expressing NGF in the model of retrograde atrophy of cholinergic neurons of the nucleus basalis magnocellularis (NBM) was assessed following partial devascularizing lesions of the cerebral cortex. We observed an increase in ChAT activity in the remaining cortex and a partial protection of the ipsilateral NBM, as determined by morphometric and biochemical studies.     

Changes in high affinity choline uptake in rat cortex following lesions of the magnocellular forebrain nuclei

High affinity choline uptake (HACU) and choline acetyltransferase (CAT) were measured in the cerebral cortex of rats 4 and 20 days after placing electrolytic lesions in the magnocellular forebrain nuclei (MFN) or in the pallidum.Four days after MFN lesion a 40–50% decrease in ipsilateral cortical HACU was found and a slightly smaller decrease was found 4 days after the pallidum lesion. Twenty days after the lesion, HACU activity returned to control values in the ipsilateral parietal cortex, its decrease was smaller than 4 days postlesion in the ipsilateral frontal cortex and a significant increase was found in the contralateral cortex.CAT activity showed a 40% decrease in the frontal, parietal and occipital ipsilateral cortex 4 days after MFN lesion. The same decrease was found 20 days postlesion. However, at this time a significant increase in CAT activity was detected in the contralateral cortex.The ipsilateral recovery of HACU activity 20 days after the lesions and the contralateral increase in HACU and CAT activity demonstrate the remarkable and widespread functional adjustment associated with discrete brain lesions. The existence of a large cholinergic pathway projecting to the neocortex from the basal forebrain region is also confirmed.     

Partial reversal of lesion-induced deficits in cortical cholinergic markers by nerve growth factor

Nerve growth factor (NGF) was injected into the lateral ventricle (5 μg on 4 occasions) of rats which had previously sustained ibotenic acid-induced lesions of the nucleus basalis of Meynert. Lesioned, but vehicle-injected and sham-lesioned and vehicle-injected rats were run as controls. Infusion of NGF led to a significant recovery of cortical choline acetyltransferase and acetylcholinesterase activity 6 weeks, but not two weeks after the lesion.     

Maintenance of cortical somatostatin and monoamine levels in the rat does not require intact cholinergic innervation

Levels of somatostatin, noradrenaline, dopamine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were unchanged in rat neocortex 3 or 6 months after ibotenic acid lesion of the ipsilateral nucleus basalis that reduced cortical choline acetyltransferase levels by over 60%. These results render unlikely the possibility that non-cholinergic neurotransmitter deficits in Alzheimer's disease cortex are the consequence of cholinergic degeneration.     

Effects of chronic infusion of nerve growth factor (NGF) in AF64A-Lesioned rats

We report here the behavioral and biochemical recovery induced by the nerve growth factor (NGF) administration in AF64A-treated rats. Retention in the passive avoidance test was affected by lesion but it was significantly improved after the NGF treatment. Similar results were observed in the performance during the Morris water maze (MWM) task. Remarkable losses in the ChAT activity were detected in some brain regions from lesioned rats. The NGF-induced alleviation of choline acetyltransferase (ChAT) activity losses and cognitive functions suggest a trophic and protective action on the remaining cholinergic neurons after the lesion. Thus NGF therapy could be considered as a possibility mainly in the early course of Alzheimer disease.     

Effects of chronic infusion of nerve growth factor (NGF) in AF64A-Lesioned rats

We report here the behavioral and biochemical recovery induced by the nerve growth factor (NGF) administration in AF64A-treated rats. Retention in the passive avoidance test was affected by lesion but it was significantly improved after the NGF treatment. Similar results were observed in the performance during the Morris water maze (MWM) task. Remarkable losses in the ChAT activity were detected in some brain regions from lesioned rats. The NGF-induced alleviation of choline acetyltransferase (ChAT) activity losses and cognitive functions suggest a trophic and protective action on the remaining cholinergic neurons after the lesion. Thus NGF therapy could be considered as a possibility mainly in the early course of Alzheimer disease.     

Effects of microencapsulated monosialoganglioside GM1 on cholinergic neurons

The preparation, physical characterization and effects of microcapsules containing the monosialoganglioside GM1 in an in vivo rat model are described herewith. Several preparations of microcapsules were obtained differing in physical and chemical properties. Human serum albumin (HSA) microcapsules with or without GM1 are spherical in shape, have a consistent particle size (8-10 microns in diameter) and are devoid of large pores. In agreement with our previous work, we now provide further evidence that GM1 can prevent shrinkage and the decrease of choline acetyltransferase activity in the nucleus basalis magnocellularis (NBM) of the rat following a unilateral cortical lesion. In the present study we examined the effect of microencapsulated GM1 in this in vivo rat model. Local application of HSA-microencapsulated GM1 (in doses comparable to those obtained by i.c.v. administration) onto the surface of the lesioned cortex prevents both the biochemical and morphological degenerative changes in the NBM of rats with unilateral devascularizing cortical lesions. The results from these studies show that microencapsulated GM1 can be applied successfully and a prolonged controlled release of this drug obtained, thus avoiding surgical implantation of a cannula.     

Sciatic nerve axotomy in aged rats: response of motoneurons and the effect of GM1 ganglioside treatment

The number, size, and staining intensity of choline acetyltransferase (ChAT)-immunopositive cells in the retrodorsal lateral nucleus (RDLN) of the spinal cord were studied in young (3-5 months old) and aged (22-24 months old) rats following left sciatic nerve distal transection (axotomy) and treatment with GM1 ganglioside. The cell size and the ChAT immunostaining density were decreased in the RDLN of non-manipulated as well as in the contralateral intact side of axotomized aged rats. Axotomy had no effect on the number of RDLN motoneurons in both aged and young rats. In the young rats, there was a decrease in the size of motoneurons 7 days post-axotomy and a partial spontaneous recovery occurred by 21 days. Axotomy did not reduce further the size of aged motoneurons, however. The ChAT staining intensity of the axotomized RDLN declined in both age groups after 7 days, and there was spontaneous near normal recovery by 21 days. In the aged rats, GM1 administration for 7 days corrected the cell size and ChAT immunoreactivity of the contralateral intact RDLN. With regard to axotomized RDLN neurons, 7 days of GM1 restored the cell size but not the ChAT immunostaining in young animals. The same treatment schedule, however, corrected both cell size and staining in aged rats. Administration of GM1 for 21 days had no further effect on the morphometric parameters of the axotomized motoneurons in aged rats, but slightly enhanced the recovery of ChAT immunostaining in young rats. Thus, it appears that GM1 facilitates the phenotypic recovery of RDLN motoneurons during aging and after axotomy.     

GM1 ganglioside protects nucleus basalis from excitotoxin damage: Reduced cortical cholinergic losses and animal mortality

Ten days after bilateral injections of ibotenic acid into the nucleus basalis, rats injected daily (i.m.) with ganglioside GM1 were protected from anterograde degeneration of cholinergic projections to the frontolateral cortex. This protection was reflected by reduced losses (associated with ibotenic acid lesions) of cortical acetylcholinesterase, choline acetyltransferase, and lowered animal mortality.     

Neurochemical recovery in the neocortex after colchicine lesions of the nucleus basalis magnocellularis in rats

Neurochemical recovery was investigated in male, Fischer-344 rats up to 3 months after lesions of the nucleus basalis. Bilateral injections of colchicine (1.0 micrograms/site) into the nucleus basalis magnocellularis (NBM) resulted in a 30% decrease in choline acetyltransferase (ChAT) activity in frontal cortex 4 weeks after surgery, compared to unlesioned controls. ChAT activity in the frontal cortex gradually recovered to control levels by 12 weeks. The loss of ChAT-immunoreactive neurons in the NBM observed 4 weeks after surgery was still evident 12 weeks after surgery. These results suggest that surviving cholinergic neurons in the NBM contribute to recovery of ChAT activity in the neocortex.