Unilateral and bilateral nucleus basalis lesions: differences in neurochemical and behavioural recovery

Effect of chronic intraperitoneal aminoguanidine on memory and expression of Bcl-2 family genes in diabetic rats

Long-term hyperglycemia associates with memory defects via hippocampal cells damaging. The aim of the present study was to examine the effect of 1 month of i.p. injections of AG on passive avoidance learning (PAL) and hippocampal apoptosis in rat. Eighty male rats were divided into 10 groups: control, nondiabetics and STZ-induced diabetics treated with AG (50, 100, 200, and 400 mg/kg, i.p.). PAL and the Bcl-2 family gene expressions were determined. Diabetes resulted in memory and Bcl-2 family gene expression deficits. AG (50 and 100 mg/kg) significantly improved the learning and Bcl-2, Bcl-xl, Bax, and Bak impairment in diabetic rats. However, negative effects were indicated by higher doses of the drug (200 and 400 mg/kg). Present study suggests that 1 month of i.p. injections of lower doses of AG, may improve the impaired cognitive tasks in STZ-induced diabetic rats possibly by modulating Bcl-2 family gene expressions.

Employing Alzheimer disease animal models for translational research: focus on dietary components

BACKGROUND

Translational research needs valid animal models of disease to discover new pathogenetic aspects and treatments. In Alzheimer's disease (AD), transgenic models are of great value for AD research and drug testing.

OBJECTIVE

It was the aim of this study to analyze the power of dietary polyphenols against neurodegeneration by investigating the effects of oleuropein aglycone (OLE), the main phenol in the extra virgin olive oil (EVOO), a key component of the Mediterranean diet (MD), in a mouse model of amyloid-β deposition.

METHODS

TgCRND8 mice (3.5 months old), expressing the mutant KM670/671NL+V717F h-βAPP695 transgene, and wild-type (wt) mice were used to study in vivo the effects of an 8-week dietary supplementation with OLE (50 mg/kg of diet) [Grossi et al: PLoS One 2013;8:e71702], following the European Communities Council Directive 86/609 (DL 116/92) and National Guidelines (permit number: 283/2012-B).

RESULTS

OLE administration ameliorates memory dysfunction, raises a significant autophagic response in the cortex and promotes the proliferation of newborn cells in the subgranular zone of the dentate gyrus of the hippocampus.

CONCLUSIONS

Our findings support the beneficial effects of EVOO and highlight the possibility that continuous intake of high doses of OLE, both as a nutraceutical or as a food integrator, may prevent/delay the appearance of AD and reduce the severity of its symptoms.

The role of the nucleus basalis magnocellularis in fear conditioning consolidation in the rat

The nucleus basalis magnocellularis (NBM) is known to be involved in the memorization of several conditioned responses. To investigate the role of the NBM in fear conditioning memorization, this neural site was subjected to fully reversible tetrodotoxin (TTX) inactivation during consolidation in adult male Wistar rats that had undergone fear training to acoustic conditioned stimulus (CS) and context. TTX was stereotaxically administered to different groups of rats at increasing intervals after the acquisition session. Memory was assessed as the conditioned freezing duration measured during retention testing, always performed 72 and 96 h after TTX administration. In this way, there was no interference with normal NBM function during either acquisition or retrieval phases, allowing any amnesic effect to be due only to consolidation disruption. The results show that for contextual fear response memory consolidation, NBM functional integrity is necessary up to 24 h post-acquisition. On the other hand, NBM functional integrity was shown to be necessary for memory consolidation of the acoustic CS fear response only immediately after acquisition and not 24-h post-acquisition. The present findings help to elucidate the role of the NBM in memory consolidation and better define the neural circuits involved in fear memories.

Sensory experience determines enrichment-induced plasticity in rat auditory cortex

Our previous studies demonstrated that only a few days of housing in an enriched environment increases response strength and paired-pulse depression in the auditory cortex of awake and anesthetized rats [Engineer, N.D., Percaccio, C.R., Pandya, P.K., Moucha, R., Rathbun, D.L., Kilgard, M.P., 2004. Environmental enrichment improves response strength, threshold, selectivity, and latency of auditory cortex neurons. J Neurophysiol. 92, 73-82 and Percaccio, C.R., Engineer, N.D., Pruette, A.L., Pandya, P.K., Moucha, R., Rathbun, D.L., Kilgard, M.P., 2005. Environmental enrichment increases paired-pulse depression in rat auditory cortex. J Neurophysiol. 94, 3590-3600]. Multiple environmental and neurochemical factors likely contribute to the expression of this plasticity. In the current study, we examined the contribution of social stimulation, exercise, auditory exposure, and cholinergic modulation to enrichment-induced plasticity. We recorded epidural evoked potentials from awake rats in response to tone pairs and noise bursts. Auditory evoked responses were not altered by social stimulation or exercise. Rats that could hear the enriched environment, but not interact with it, exhibited enhanced responses to tones and increased paired-pulse depression. The degree to which enrichment increased response strength and forward masking was not reduced after a ventricular injection of 192 IgG-saporin. These results indicate that rich auditory experience stimulates physiological plasticity in the auditory cortex, despite persistent deficits in cholinergic activity. This conclusion may be beneficial to clinical populations with sensory gating and cholinergic abnormalities, including individuals with autism, schizophrenia, and Alzheimer's disease.

Role of substantia innominata in cerebral blood flow autoregulation

Ascending projections from the substantia innominata (SI) may have an important role in the regulation of cerebral blood flow (CBF). However, several reports have suggested that unilateral lesion of the SI does not affect CBF autoregulation. On the other hand, it is also reported that several cortical and subcortical functions may be regulated not only by ipsilateral SI, but also by contralateral SI. Thus, the objective of this study is to test the hypothesis that bilateral lesions of the SI affect CBF autoregulation. Experiments were performed on anesthetized male Sprague-Dawley rats. Ibotenic acid or physiological saline was microinjected into bilateral SI. Rats were classified into four groups as follows: bilateral SI lesion rats (ibotenic acid was injected bilaterally), left or right SI lesion rats (ibotenic acid was injected into the unilateral SI and saline into the contralateral SI), and control rats (saline was injected bilaterally). Ten days after injection, CBF in the left frontal cortex was measured by laser-Doppler flowmetry during stepwise controlled hemorrhagic hypotension. In bilateral SI lesion rats, CBF was started to decrease significantly at 80 mm Hg (p<0.01). In the other three groups, CBF was well maintained until 50 mm Hg. Changes in CBF through stepwise hypotension in bilateral SI lesion rats were significantly different from the other groups (p<0.01). These results suggest that bilateral SI regulates cortical vasodilator mechanisms during hemorrhagic hypotension. Under unilateral SI lesion, some compensatory effects from the contralateral SI may maintain CBF autoregulation.

Changes in acetylcholine extracellular levels during cognitive processes

Measuring the changes in neurotransmitter extracellular levels in discrete brain areas is considered a tool for identifying the neuronal systems involved in specific behavioral responses or cognitive processes. Acetylcholine (ACh) is the first neurotransmitter whose diffusion from the central nervous system was investigated and whose extracellular levels variations were correlated to changes in neuronal activity. This was done initially by means of the cup technique and then by the microdialysis technique. The latter, notwithstanding some technical limitations, makes it possible to detect variations in extracellular levels of ACh in unrestrained, behaving animals. This review summarizes and discusses the results obtained investigating the changes in ACh release during performance of operant tasks, exposition to novel stimuli, locomotor activity, and the performance of spatial memory tasks, working memory, and place preference memory tasks. Activation of the forebrain cholinergic system has been demonstrated in many tasks and conditions in which the environment requires the animal to analyze novel stimuli that may represent a threat or offer a reward. The sustained cholinergic activation, demonstrated by high levels of extracellular ACh observed during the behavioral paradigms, indicates that many behaviors occur within or require the facilitation provided by the cholinergic system to the operation of pertinent neuronal pathways.

Cognitive impairment and chronic cerebral hypoperfusion: what can be learned from experimental models

The relation between chronic cerebral hypoperfusion and cognitive functions has not been completely clarified. The resolution of cerebral hypoperfusion states, such as those induced by arteriovenous malformations or carotid stenosis/occlusion, has been reported to improve mental decline in humans. Subcortical vascular dementia is another human condition supposed to be linked with chronic cerebral hypoxia/ischemia. The extent of this cause/effect relation is, however, difficult to be assessed in humans, where different factors, such as ageing or subtle degenerative processes, can coexist and interact influencing cognitive performances. Experimental studies can help to elucidate this relation because they can use models of pure chronic/moderate cerebral hypoperfusion. An experimental model of chronic ischemia is the bilateral common carotid artery occlusion in the rat. In this paper, we present a review of experimental studies that evaluated cognitive functions in the rat with bilateral common carotid artery occlusion. We then present an experimental model of bilateral common carotid artery occlusion in the rat modified with respect to previous papers regarding both the surgical procedure and the neurocognitive evaluation that is focused on cognitive domains depending on subcortical-frontal circuits. We propose this model to investigate subcortical vascular dementia.

Persistent impairment of gait performances and working memory after bilateral common carotid artery occlusion in the adult Wistar rat

BACKGROUND

The clinical and pathophysiological effects of a chronic reduction of cerebral blood flow in humans are not completely known. We investigated whether rats subjected to bilateral common carotid artery occlusion (bCCA-o) developed focal neurological deficits, gait dysfunction, and working memory alterations.

METHODS

Eighteen male Wistar rats were subjected to bCCA-o, 13 were sham-operated. We assessed sensorimotor functions, gait on a 60 cm-long elevated bridge, and working memory (object recognition and Y maze tests) before and 30, 60, and 90 days after surgery. Histological analysis was performed in a subgroup of 10 rats.

RESULTS

No rat showed sensorimotor alterations after surgery. Although gait performances of both bCCA-o and sham-operated rats declined over time, the differences reached statistical significance only for the bCCA-o group (mean+/-SE: 26.8+/-5.0; 22.4+/-4.9; 24.5+/-5.5 cm at 30, 60, and 90 days, respectively) in comparison with baseline (52.9+/-5.2 cm; P<0.05). At 60 and 90 days, bCCA-o rats in comparison with sham-operated rats showed decreased performances on object recognition (discrimination index: 0.15+/-0.03 vs. 0.29+/-0.05 at 60 days and 0.10+/-0.04 vs. 0.41+/-0.07 at 90 days; P<0.05) and on Y maze test (alternating rats: 9.9 vs. 85.7% at 60 days and 16.6 vs. 100% at 90 days; P<0.01). In none of the animals were cerebral infarcts detected. Selective neuronal necrosis was observed in the cortex and hippocampus of both bCCA-o and sham-operated rats without any obvious difference.

CONCLUSIONS

bCCA-o in the Wistar rat induces persistent and progressive gait and working memory impairment without producing sensorimotor deficit or cerebral infarcts. This model may help to elucidate some physiopathological aspects of neurological impairment associated with states of cerebral chronic ischemia.

Effect of Nucleus Basalis Magnocellularis Ablation on Local Brain Glucose Utilization in the Rat: Functional Brain Reorganization

After unilateral destruction of the nucleus basalis magnocellularis (NBM) in 3-month-old rats, which reduces cholinergic inputs to the ipsilateral frontoparietal neocortex, regional cerebral metabolic rates for glucose (rCMRglc) of denervated cortex are initially reduced, but nearly normalize by 2 weeks. To examine functional reorganization of the brain after unilateral destruction of the NBM, a correlation analysis of rCMRglc was performed on two groups of 16 young rats 2 weeks after stereotaxic ablation of the right NBM with ibotenate or sham surgery. rCMRglc was measured in 117 brain regions of awake rats with the [14C]deoxyglucose method. For each region pair, a partial correlation coefficient was calculated for rCMRglc across animals. Most correlations between cholinergic nuclei of both left and right forebrain (medial septum and diagonal band) and right (66/72, mean increase 0.44) but not left (39/72) frontoparietal cortical regions were larger (P < 0.001) in lesioned rats, as were those between most frontoparietal region pairs (516/630, P < 0.001). These results suggest that, after unilateral NBM ablation, (1) functional interactions are established between the remaining cholinergic forebrain and the deafferented cortex, (2) the neocortex becomes more integrated, and (3) functional reorganization involves both cortical hemispheres. These changes do not correspond to those reported to occur in Alzheimer's disease.

Overview and perspective on the therapy of Alzheimer's disease from a preclinical viewpoint

1. Drugs effective in Alzheimer's disease (AD) should have several aims: to improve the cognitive impairment, control the behavioural and neurological symptoms, delay the progression of the disease, and prevent the onset. In order to attain these targets, cell and animal models are needed on which to test pathogenetic hypothesis and demonstrate the potential effectiveness of new drugs. This overview examines the results obtained in animal models. They are the link between the molecular and biochemical studies on the disease and the reality of human pathology. 2. The development of animal models reproducing the complexity of AD pathogenetic mechanisms and clinical symptoms still represents a challenge for the preclinical investigators. Moreover, the succession of different animal models well documents the progressive widening of our knowledge of the disease with the identification of new therapeutic targets. 3. The main animal models are listed, and their contribution to the understanding of the pathogenic mechanisms and development of the drugs presently used in AD therapy is described. Moreover, their role in the study of future drugs is analysed 4. Preclinical studies on cholinesterases and animal models mimicking the cholinergic hypofunction occurring in AD have been instrumental in developing cholinesterase inhibitors, which are the only recognised drugs for the symptomatic treatment of AD. 5. Artificially created beta-amyloid (A beta) deposits in normal rats, and transgenic mice overexpressing amyloid precursor protein (APP) are the models on which the future treatment are tested. They are aimed to prevent formation of A beta deposits or its transformation in neuritic plaques. 6. Models of brain inflammation, aging animals, and models of brain glucose and energy metabolism impairment make it possible to identify and assess the activity of anti-inflammatory agents, antioxidants, ampakines and other potentially active agents. 7. It is concluded that the present level of information on AD could never have been reached without preclinical studies, and the development of new drugs will always require extensive preclinical investigations.

The effect of sequential lesioning in the basal forebrain on cerebral cortical glucose metabolism in rats. An animal positron emission tomography study

We studied the effect of the cortical projection from the basal forebrain on the cerebral cortical metabolism using positron emission tomography (PET) with [(18)F] fluorodeoxyglucose. Unilateral damage of the nucleus basalis magnocellularis (NBM) did not cause a permanent reduction of cortical metabolism: recovery was observed 4 weeks after the operation. Destruction of the contralateral side after recovery from unilateral damage produced persistent bilateral suppression of glucose metabolism, with partial recovery. We speculate that recovery from the unilateral NBM lesions is partly ascribable to the cholinergic projection from the contralateral NBM, and partly due to non-cholinergic systems, and conclude that bilateral damage might be responsible for persistent cortical glucose metabolism suppression.

NADPH-diaphorase histochemistry in the rat cerebral cortex and hippocampus: effect of electrolytic lesions of the nucleus basalis magnocellularis

Unilateral or bilateral electrolytic lesions of the nucleus basalis magnocellularis (NBM) increased NADPH-diaphorase in the fronto-parietal cortex and in the CA1-CA3 fields of the hippocampus. NBM is the cholinergic basal forebrain nucleus supplying the fronto-parietal cortex but not the hippocampus. This increase was more remarkable at 4 weeks than at 2 weeks after lesioning. Monolateral or bilateral lesioning of the NBM increased to a similar extent NADPH-diaphorase. The number of neurons expressing NADPH-diaphorase was not statistically different between sham-operated and NBM-lesioned rats. These results indicate that similarly as reported in experimental damage of several brain areas, lesions of the NBM induce NADPH-diaphorase. The induction of this marker for nitric oxide synthase occurs both in the target of projections arising from the NBM such as the frontal cortex and in an area not directly supplied by NBM such as the hippocampus. Lesion-induced NADPH-diaphorase increase may contribute to neurodegenerative changes caused by damage of the NBM area.

Morphological, biochemical and behavioural changes induced by neurotoxic and inflammatory insults to the nucleus basalis

Interest in the basal forebrain cholinergic system has greatly increased since neuropathological studies in humans provided evidence that this system is severely affected in Alzheimer's disease and other dementing disorders. In laboratory animals, disruption of the nucleus basalis cholinergic neurones has been produced by several neurotoxic insults in order to obtain a model reproducing the behavioural impairment related to the cholinergic deficits. The experiments reported in this review demonstrate that excitotoxic amino acids, beta-amyloid and lipopolysaccharide, injected directly in the nucleus basalis are toxic to the cholinergic neurones in the rat. The excitotoxin lesions of the nucleus basalis, although not selective, are a useful tool for producing experimental animals with cholinergic hypofunction and for investigating drugs able to ameliorate the cholinergic functions. Local injections of amyloid peptides in the rat nucleus basalis produced cholinergic hypofunction and some behavioural impairment. Finally, an intense glia reaction with a limited cholinergic hypofunction and no behavioural impairment was induced by a 4-week infusion of lipopolysaccharide in the nucleus basalis. In conclusion, all three models, in spite of their limitations, offer useful tools for the study of the pathogenetic mechanisms of Alzheimer's disease and for investigating potentially useful drugs.

Differential changes of nicotinic receptors in the rat brain following ibotenic acid and 192-IgG saporin lesions of the nucleus basalis magnocellularis

The basal forebrain cholinergic neurons are implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD). The nicotinic acetylcholine receptors (nAChRs) have been found to be significantly afflicted in AD. To study the underlying mechanisms for dysfunction of the basal forebrain cholinergic neurons development of suitable animal models is warranted. In this study we investigated the effects of bilateral lesions of the nucleus basalis magnocellularis on nAChRs in the rat brain using the cholinergic system selective immunotoxin 192-IgG saporin and non-selective excitotoxin ibotenic acid. Changes in nAChRs were measured by 3H-cytisine and 3H-epibatidine, two ligands with different selectivity for nAChRs subtypes. In the parietal cortex of ibotenic acid lesioned rates, the choline acetyltransferase activity (ChAT) was decreased by 24% while no changes were detected in the frontal cortex or hippocampus. Similarly, a 40% decrease was observed in the number of nAChRs labelled by 3H-cytisine, but not by 3H-epibatidine, in the parietal cortex, while no changes were found in the frontal cortex or hippocampus. Although the 192-IgG saporin induced lesions reduced the ChAT activity in the frontal cortex, parietal cortex and hippocampus by 77, 50 and 21%, respectively, no changes were observed in the number of nAChRs as studied by 3H-cytisine or 3H-epibatidine. The results indicate a difference in vulnerability of the cortical nAChR subtypes to experimental lesions of the nucleus basalis magnocellularis. The findings in this study suggest that a major portion of the nAChRs might be located on non-cholinergic neurons in the brain.

Effect of lesions of the nucleus basalis magnocellularis and of treatment with posatirelin on cholinergic neurotransmission enzymes in the rat cerebral cortex

The effect of 4 and 8 weeks of treatment with the thyrotropin releasing hormone (TRH), analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide), on the changes of cholinergic neurotransmission enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), caused by lesions of the nucleus basalis magnocellularis (NBM), was investigated in the rat frontal cortex. ChAT and AChE were demonstrated with immunohistochemical and histochemical techniques, respectively associated with image analysis and microdensitometry. Monolateral and bilateral lesions of NBM area caused a significant loss of ChAT-immunoreactive nerve cell bodies in the NBM, as well as a remarkable decrease of ChAT-immunoreactive fibres and of AChE reactivity in the frontal cortex ipsilateral to the lesion or of both sides, respectively. The number of ChAT-immunoreactive nerve cell bodies in the lesioned NBM was higher in posatirelin-treated rats for 8 weeks in comparison with control NBM-lesioned rats. Moreover, the compound increased the number of ChAT-immunoreactive fibres in the frontal cortex of monolaterally and bilaterally NBM-lesioned rats at 8 weeks after lesion, but was without effect on these fibres in sham-operated rats. The same is true for AChE reactivity, developed in the neuropil of the frontal cortex, which was restored in part by an 8-week treatment with posatirelin in NBM-lesioned rats. These findings suggest that treatment with posatirelin rescues cholinergic neurons of the NBM and cholinergic projections to the cerebral cortex affected by lesioning of the NBM. The functional relevance of these observations and their possible applications should be evaluated in future studies.

Short-term and complete reversal of NGF effects in rats with lesions of the nucleus basalis magnocellularis

Rats received bilateral quisqualic acid lesions of the nucleus basalis magnocellularis. Three weeks after lesioning, osmotic minipumps were implanted that released recombinant human nerve growth factor or cytochrome c at a dosage of 5.0 microg rat-1 day-1 through intracerebroventricular cannulas for 7 weeks. One quarter of the rats were sacrificed at the end of the treatment, while the rest of the animals were sacrificed 2, 8, and 12 weeks after termination of NGF/cc treatment. ICV administration of nerve growth factor (NGF) transiently reduced weight gain. NGF maximally increased choline acetyltransferase activity in all cortical regions, the olfactory bulb and the hippocampus between 20% and 56% at the end of the treatment. This increase linearly declined and completely regressed during the 12-week withdrawal period both in regions affected and unaffected by the lesion. Administration of NGF induced a short-lasting hypertrophy of low affinity NGF receptor immunoreactive neurons within the nucleus basalis magnocellularis (NBM), the horizontal limb of the diagonal band of Broca, and the medial septum. In contrast, QUIS-induced NBM lesions permanently reduced ChAT activity most pronounced in the frontal and parietal cortex up to 45%. Furthermore, QUIS induced a permanent loss of p75NGFr-immunoreactive neurons within the NBM and the DB without affecting the MS. These findings suggest that degenerating cholinergic neurons of the NBM and HDB do not spontaneously recover after lesioning and may require continuous neurotrophic support by NGF to ameliorate cholinergic hypofunctioning.

Effect of RGH-2716 on learning and memory deficits of young and aged rats in water-labyrinth

RGH-2716 is a novel 1-oxa-3,8-diazaspiro[4.5] decan 2-one, which was published to have potent inhibitory effect on neuronal Na and Ca movement and stimulatory action on nerve growth factor (NGF)-production, as well as to show significant antiamnesic activity in experimental amnesia models. The aim of the present experiments was to study the effect of the compound on the learning process and on the different stages of memory using water-labyrinth in normal and memory impaired young animals, as well as to study cognitive effect of RGH-2716 on aged animals. At the doses of 0.5 mg/kg i.p. or 3 mg/kg p.o. given before daily swimming, this compound improved the learning process of young animals impaired by either diazepam (DIA) or scopolamine (SCOP). In retrograde amnesia model RGH-2716 (3 mg/kg p.o.) significantly ameliorated consolidation process and retrieval of information impaired by SCOP or DIA. Nimodipine and vinpocetine (10 mg/kg p.o.) showed moderate effect compared to RGH-2716. Aged rats pretreated with daily i.p. RGH-2716 performed the tasks with significantly fewer errors and shorter swimming time than untreated aged rats. When aged animals had to solve a new labyrinth problem, treated aged rats showed significantly better learning ability than aged controls. One month of oral treatment of aged rats with 3 mg/kg dose of RGH-2716 two times daily resulted in a "tendency-like" improvement in learning of aged Fischer 344 and spontaneously hypertensive (SH) rats. The present results make RGH-2716 an interesting compound for the treatment of cognitive disorders.

Enhanced acetylcholine release in the hippocampus and cortex during acquisition of an operant behavior

The activity of the septo-hippocampal and nucleus basalis-cortical cholinergic pathways was investigated by measuring changes in the extracellular acetylcholine levels in the hippocampus and parietal cortex, by means of transversal microdialysis, during the acquisition and recall of a positively reinforced operant behavior. Adult male Wistar rats were trained in a sound-isolated operant chamber equipped with a single lever. The positive reinforcement was represented by food pellets and the number of cumulative reinforced responses was recorded every 30 min. Five groups of rats were used. Unoperated animals were used as controls. In two groups of untrained animals, the microdialysis tubes were transversally implanted in the parietal cortex, and hippocampus and the training in the operant behavior chamber began 24 h after surgery. In two further groups the microdialysis tubes were implanted in the parietal cortex, and hippocampus after training for 15 days in the operant chamber. Food was removed 12 h before training. The time needed by the control rats to reach a stable baseline of reinforced responses was 83 +/- 12 min, while in the untrained rats implanted with dialysis probes in the cerebral cortex and in the hippocampus was 621 +/- 129 and 521 +/- 126 min, respectively, and in those pretrained and implanted in cerebral cortex and in the hippocampus was 116 +/- 38 and 217 +/- 59 min, respectively. In the untrained operated rats, both cortical and hippocampal extracellular acetylcholine levels remained constant until the number of reinforced responses was low but increased significantly (+156% in the cortex and +183% in the hippocampus) in the first 30 min period in which there was a sharp rise in the reinforced responses. In the pretrained operated rats, neither in the cortex nor in the hippocampus was the increase in response rate accompanied by a statistically significant increase in extracellular acetylcholine levels. Our findings demonstrate that activation of the forebrain cholinergic pathways occurs during the acquisition of a rewarded operant responses, while recall of the same behavior is not associated with the activation of the cholinergic system.

beta-Amyloid 25-35 and/or quinolinic acid injections into the basal forebrain of young male Fischer-344 rats: behavioral, neurochemical and histological effects

beta-Amyloid peptides have been shown to potentiate the neurotoxic effect of excitatory amino acids in vitro. In order to determine if this occurs in vivo, four experiments were performed. We injected beta-amyloid 25-35 (beta A 25-35) and/or quinolinic acid (QA) bilaterally into the ventral pallidum/substantia innominata (VP/SI) of rats. Control rats received vehicle infusions. A high dose of QA (75.0 nmol/3 microliters) increased open field activity and impaired spatial learning in the Morris water maze, but did not affect the acquisition of a one-way conditioned avoidance response. These changes were associated with histological evidence of neurotoxicity and a reduction in amygdaloid but not frontal cortical or hippocampal choline acetyltransferase (ChAT) activity. A lower dose of QA (37.5 nmol/3 microliters) produced no behavioral effects. It reduced amygdaloid ChAT activity to a lesser extent than the higher dose (15% vs. 29-37%), and caused less histological damage. beta A 25-35 (1.0 or 8.0 nmol/3 microliters) failed to produce behavioral, histological or neurochemical signs of toxicity. Neither dose of beta A 25-35 potentiated the effects of QA (37.5 nmol) on behavior or amygdaloid ChAT activity, and did not appear to increase the histological damage caused by QA. These results suggest that in vivo beta A 25-35 is not neurotoxic and does not potentiate the neurotoxicity of QA in the VP/SI. Further, the histological effects of a high dose of beta A 25-35 (8.0 nmol/3 microliters; a cavitation containing a Congo red positive proteinaceous material) are quite distinct from those produced by a high dose of QA (75.0 nmol/3 microliters; widespread neuronal loss and gliosis).

Neuroprotection against NMDA induced cell death in rat nucleus basalis by Ca2+ antagonist nimodipine, influence of aging and developmental drug treatment

In the current study the neuroprotective effect of the L-type calcium channel antagonist nimodipine in rat brain was investigated in N-methyl-D-aspartate-induced neuronal degeneration in vivo. In the present model NMDA was unilaterally injected in the magnocellular nucleus basalis and the neurotoxic impact assessed by measuring cortical cholinergic fibre loss as a percentage of fibre density of the intact control hemisphere. This procedure proved to be a reproducible model in which the degree of damage was almost linearly proportional to the NMDA dose. Neuroprotection by nimodipine was determined in a number of conditions. First, the effect of nimodipine treatment in adult animals starting two weeks prior to neurotoxic injury was compared with neuroprotection provided by perinatal treatment of the mother animals with the calcium antagonist. Surprisingly, the degree of protection was in both cases similar, yielding almost 30% reduction of fibre loss. The neuroprotective effect in adulthood of perinatal nimodipine treatment may be explained by developmentally enhanced calcium binding proteins or persistent developmental changes in calcium channel characteristics. Protection by nimodipine was also investigated in aged, 26 month old rats. Compared to young adult cases, aged animals proved to be less vulnerable to NMDA exposure, while nimodipine application was more potent, thus yielding a reduction of nearly 50% in nerve fibre damage induced by NMDA infusions. Possible mechanisms of differential calcium influx in the various experimental conditions will be discussed.

Differential effects of amyloid peptides beta-(1-40) and beta-(25-35) injections into the rat nucleus basalis

The nucleus basalis of male Charles River Wistar rats was injected with 10 micrograms of the beta-amyloid peptides beta-(1-40) and beta-(25-35) and changes in the morphology of the lesioned area, the release of acetylcholine from the cortex, and in behavior were investigated. Injections of saline and a scrambled (25-35) peptide were used as controls. One week after lesioning, a Congo Red-positive deposit of aggregated material was found at the beta-peptides injection site, which lasted for about 21 days in the case of the beta-(25-35) peptide and at least two months for beta-(1-40). No deposit was detected after scrambled peptide injection. At one week post injection, an extensive glial reaction surrounded the injection site of all peptides and saline as well. Such a reaction was still present but rather attenuated after two months. A decrease in the number of cholinergic neurons was detected in the nucleus basalis after one week with all treatments except saline. After two months, a reduction in the number of choline acetyltransferase-immunopositive neurons was still detectable in the rats injected with beta-(1-40) but not in the beta-(25-35)-or scrambled-injected. The reduction in choline acetyltransferase immunoreactivity was closely paralleled by a decrease in basal acetylcholine release from the parietal cortex ipsilateral to the lesion. Disruption of object recognition was observed in the first weeks after beta-(25-35) peptide injection, whereas the beta-(1-40) peptide impaired the performance only two months after lesion. Rats with lesions induced by beta-peptides may be a useful animal model of amyloid deposition for investigation of the pathogenetic mechanisms leading to Alzheimer's disease.

Microanatomical and electrophysiological changes of the rat dentate gyrus caused by lesions of the nucleus basalis magnocellularis

The effect of unilateral or bilateral lesions of the nucleus basalis magnocellularis (NBM) on the dentate gyrus of the hippocampus were assessed using microanatomical and electrophysiological techniques. NBM is the main cholinergic basal forebrain nucleus that supplies the fronto-parietal cortex. Lesions were induced using the neurotoxin ibotenic acid or a radio-frequency system and did not affect glutamic acid decarboxylase activity both in the frontal cortex and in the hippocampus. At 4 weeks after lesioning, a loss of choline acetyltransferase (ChAT) activity and of ChAT-immunoreactive fibres was observed in the frontal cortex but not in the hippocampus and no changes in the density of granule neurons of the dentate gyrus or in the hippocampal long-term potentiation (LTP) were noticeable. At 8 weeks after lesioning the loss of both ChAT activity and of ChAT-immunoreactive fibres persisted in the frontal cortex of NBM-lesioned rats. Moreover, at this time a significant decrease in the density of granule neurons in the dentate gyrus accompanied by a reduced probability of dentate LTP induction were observed in both ibotenic acid- and radio-frequency-lesioned rats. These findings have shown that although NBM does not send direct cholinergic projections to the hippocampus, lesions of this cholinergic nucleus are accompanied by delayed neurodegenerative changes involving the dentate gyrus. This suggests the occurrence of indirect connections between NBM and the hippocampus, the functional relevance of which should be explored.

Pyritinol facilitates the recovery of cortical cholinergic deficits caused by nucleus basalis lesions

The effect of a nootropic, Pyritinol, on the recovery of cortical cholinergic deficits induced by injury of the nucleus basalis has been tested on two groups of unilateral quisqualic acid nbM-lesioned rats. The first group had a 30 nmol lesion producing a cortical cholinergic impairment at 21 days, with a spontaneous recovery at 45 days. The second group had a 50 nmol lesion that produced a deeper cholinergic deficit, which did not recover at 45 days. Pyritinol enhanced the recovery in the 30 nmol group of animals on the 21st day after surgery. The recovery was measured as an increase in the activities of acetylcholinesterase (AChE), choline acetyltransferase (ChAT) and the high affinity choline uptake system, and the histochemical densities of the cortical AChE network and the M2 receptor. Histochemical analysis of the nbM enabled cortical recovery to be related to the number of surviving neurons and also to their hypertrophy and AChE-ChAT hyperactivity. Pyritinol enhanced recovery in 30 nmol lesioned animals but in the other group, with a lower number of surviving neurons and a lower ability of the cells to become hypertrophic, the drug was unable to promote cortical recovery.

Effect of nerve growth factor and GM1 ganglioside on the recovery of cholinergic neurons after a lesion of the nucleus basalis in aging rats

A unilateral ibotenic acid lesion was placed in the nucleus basalis magnocellularis of 3- and 18-month-old rats. In the lesioned aging rats, the number of choline acetyltransferase-immunoreactive neurons of the nucleus basalis magnocellularis was markedly reduced in the ipsilateral side and to a lesser extent in the contralateral side. Twenty-one days after the lesion, the activity of choline acetyltransferase in the ipsilateral cortex was reduced by 40% in both groups of rats and by 24% in the contralateral frontal cortex of the aging rats. Intracerebroventricular administration of nerve growth factor (10 micrograms twice a week) to aging lesioned rats for 3 weeks after surgery resulted in a complete recovery in the number of choline acetyltransferase-immunoreactive neurons in the nucleus basalis of both sides, and choline acetyltransferase activity in the contralateral cortex, with little effect on the ipsilateral cortex. No potentiation was seen after the concurrent administration of GM1 ganglioside and nerve growth factor. Complete recovery in cortical choline acetyltransferase activity was only observed in the lesioned rats treated with nerve growth factor for 1 week before and 3 weeks after lesioning. Nerve growth factor treatment, both after the lesion, and before and after the lesion, improved the passive avoidance performance disrupted by the lesion. In young lesioned rats daily intraperitoneal administration of GM1 (30 mg/kg) for 21 days after surgery promoted both the recovery of choline acetyltransferase activity and passive avoidance performance. In aging rats GM1, even at a dose twice as large, failed to reverse the biochemical and morphological deficits and behavioral impairment induced by the lesion. Only when GM1 administration was started 3 days before the lesion, were a complete recovery in choline acetyltransferase activity in the contralateral cortex and a partial recovery in the ipsilateral cortex obtained. Our results indicate that nerve growth factor and, to some extent, GM1 facilitate the recovery of the cholinergic neurons after a lesion of the nucleus basalis in aging rats, but their efficacy is reduced. The lower efficacy of GM1 as compared to NGF might be due to the different routes of administration used.

Post-training nucleus basalis magnocellularis functional tetrodotoxin blockade effects on passive avoidance consolidation in the rat

The tetrodotoxin (TTX) functional ablation technique was employed in order to evaluate the temporal coordinates of the rat's nucleus basalis magnocellularis (NBM) involvement in memory trace processing. Under ketamine general anesthesia, TTX (10 ng in 1 microliter saline) was stereotaxically administered to rats, either in one or both NBMs. TTX was injected to different groups of rats, respectively 15 min, 6, 24, 48, 96 h after passive avoidance acquisition testing. The rats underwent retrieval testing 48 h later, i.e. after full recovery from TTX effects. Results show that: (1) monolateral TTX blockade significantly impairs PAR conditioned responding if induced up to 6 h but not 24 h after acquisition testing; (2) bilateral TTX blockade dramatically impairs passive avoidance responding up to a 48-h delay but not 96 h after acquisition testing. The results indicate a very profound involvement of NBM in passive avoidance response consolidation. The experimental evidence is discussed together with previous functional ablation findings concerning amygdala, parabrachial nuclei and neocortex.

Dysfunction of the brain cholinergic system during aging and after lesions of the nucleus basalis of Meynert

In order to establish how closely the models mimic aging and Alzheimer's disease, a comparison was made, using the extensive literature available, between brain cholinergic dysfunction in aging animals and man, and between that in animals with lesions of the nucleus basalis of Meynert and in subjects affected by Alzheimer's disease. It is concluded that cholinergic dysfunction in the aging rat closely resembles that in aging man. A similarity can also be found between the cortical dysfunction induced by lesions of the nucleus basalis and that occurring in patients with Alzheimer's disease. However, cholinergic dysfunction only represents a limited aspect of the neorotransmitter deficits and neuropathological alterations of the disease.

Effect of ipsilateral lesioning of the nucleus basalis magnocellularis and of L-alpha-glyceryl phosphorylcholine treatment on choline acetyltransferase and acetylcholinesterase in the rat fronto-parietal cortex

The present study assesses the effect of unilateral lesions of the nucleus basalis magnocellularis (NBM) and of treatment with L-alpha-glyceryl phosphorylcholine (GFC, choline alfoscerate) on the acetylcholine-synthesizing (choline acetyltransferase (ChAT)), and acetylcholine-degradating (acetylcholinesterase (AChE)) enzymes in the rat fronto-parietal cortex ipsilateral to the lesion. Ibotenic acid injections in the right NBM area caused a significant decrease of both ChAT and AChE activities as well as of histochemically reactive stores of AChE in the right fronto-parietal cortex. Treatment with GFC restored in part the loss of ChAT and AChE activities. Moreover, AChE reactivity is restored in the fronto-parietal cortex of NBM-lesioned rats treated with GFC. GFC is a precursor in the biosynthesis of brain phospholipids which increases the bioavailability of acetylcholine in the nervous tissue. The possible relevance of the restoration of the marker enzymes of cholinergic neurotransmission by GFC in an animal model of cholinergic hypofunction is considered.

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 throughout 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.

Differential effect of functional ablation of thalamic reticular nucleus on the acquisition of passive and active avoidance

The possible contribution of inadvertent damage of the thalamic reticular nucleus to memory impairment caused by lesion of nucleus basalis magnocellularis (NBM) was examined. Rats carrying chronically implanted cannulae received unilateral injection of 3 ng tetrodotoxin (TTX) into the reticular nucleus either 60 min before (PRE) or 2 min after (POST) acquisition of a combined passive avoidance (PAR)--active avoidance (AAR) task. Three days later retrieval was tested during unilateral TTX blockade of the reticular nucleus in the same (IPSI) or in the opposite (CONTRA) hemisphere. Unilateral inactivation of the reticular nucleus affected neither acquisition nor retrieval of PAR, but interfered with AAR acquisition under the PRE conditions. AAR reacquisition was impaired in the PRE-CONTRA but not in the other groups. The effects of reticular nucleus blockade (AAR disruption without PAR impairment) contrast with AAR facilitation and PAR disruption after NBM lesions. It is concluded that the consequences of NBM damage are not enhanced by unintentional thalamic encroachment.

Long-term ethanol consumption by rats: effect on acetylcholine release in vivo, choline acetyltransferase activity, and behavior

The extent and duration of cholinergic hypofunction induced by long-term ethanol consumption was investigated in the rat. Ethanol (20% v/v) was administered to male adult Wistar rats as a sole source of fluid for three or six months. Control rats received tap water. The body weight, food and fluid intake in ethanol-treated rats were lower than in control rats throughout the treatment. After three months of ethanol consumption, and one week withdrawal, acetylcholine release in freely moving rats, investigated by microdialysis technique coupled to high-performance liquid chromatography quantification, was significantly decreased by 57 and 32% in the hippocampus and cortex, respectively, while choline acetyltransferase activity was significantly decreased (-30%) only in the hippocampus. A complete recovery of choline acetyltransferase activity and acetylcholine release was found after four ethanol-free weeks. Conversely, after four weeks of withdrawal following six months of ethanol treatment, the recovery in acetylcholine release was not accompanied by that in choline acetyltransferase activity, which remained significantly lower than in control rats in both cortex and hippocampus. The ability of rats to negotiate active and passive avoidance conditioned response tasks, tested after four ethanol-free weeks, was strongly impaired in both three- and six-month ethanol-treated rats. In conclusion, our experiments demonstrate that the development of a long-lasting cholinergic hypofunction requires at least six months of ethanol administration. The hypofunction affects choline acetyltransferase activity and acetylcholine release differently, and undergoes a remarkable recovery.

Sustained cortical metabolic responsivity to physostigmine after nucleus basalis magnocellularis ablation in rats

Unilateral nucleus basalis magnocellularis (NBM) ablation, which causes partial cholinergic denervation of the ipsilateral anterior neocortex, results in an acute but transient depression of regional cerebral metabolic rates for glucose (rCMRglc) in deafferented areas; rCMRglc normalizes within 2 weeks. To seek possible compensatory changes in cholinergic mechanisms following NBM ablation that could lead to rapid metabolic normalization, we studied rCMRglc responses to the receptor agonists nicotine and arecoline and the cholinesterase inhibitor physostigmine in rats at 2 weeks after unilateral NBM destruction. Physostigmine increased rCMRglc in 10 of 30 cortical areas contralateral to the NBM lesion. Compared to the unlesioned side, rCMRglc after physostigmine in the lesioned cortex was significantly lower in 2, significantly higher in 1 and not different (P < 0.05) in 27 areas. Neither arecoline nor nicotine treatment produced rCMRglc asymmetry in lesioned rats. These results demonstrate that responsivity to physostigmine is maintained in most regions of the rat neocortex after extrinsic cholinergic denervation by NBM ablation. This adaptive response appears not to result from cholinergic receptor upregulation and may reflect instead reorganization of cholinergic synapses.

Differential alterations of cortical cholinergic and neurotensin markers following ibotenic acid lesions of the nucleus basalis magnocellularis

The present study determined whether cortical cholinergic neurons recover functionally following the loss of afferent projections from the nucleus basalis magnocellularis (nbm). At various time points following ibotenic acid lesions of the nbm, choline acetyltransferase (ChAT) activity or the capacity of cortical cholinergic neurons to synthesize [3H]acetylcholine (ACh) from the precursor molecule [3H]choline were measured in the frontoparietal cortex. First, cortical ChAT activity was decreased by 21% and 35% on the side ipsilateral to the lesion at 1 and 2 weeks following the nbm lesion, respectively. By 6 weeks following nbm lesions, cortical ChAT activity returned to control levels and remained at control levels at 10 weeks following nbm lesions. However, by 13 weeks following nbm lesions, we observed a 21% increase in ChAT activity on the side ipsilateral to the lesion. ChAT activity in the nbm remained unchanged over the time course studied. Secondly, there was a parallel reduction (by 43%) in the capacity of frontoparietal cortex slices from the side ipsilateral to the lesion to synthesize [3H]ACh by 2 weeks following nbm lesions. By 13 weeks following the lesion there was a significant increase (29%) in the synthetic capacity of cortical cholinergic neurons compared to the 2 week time point. Third, the content of neurotensin in the frontoparietal cortex was significantly decreased by 25% and 36%, at 2 weeks and 13 weeks following nbm lesions, respectively. Neurotensin levels in the nbm were not affected by ibotenic acid lesions. In contrast, [125I]neurotensin binding sites in the frontal or parietal cortex were not altered at 2 weeks following nbm lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Lesions of the nucleus basalis magnocellularis in immature rats: short- and long-term biochemical and behavioral changes

Short- and long-term effects of unilateral lesions of the nucleus basalis magnocellularis (NBM) on cortical choline acetyltransferase (ChAT) activity and passive avoidance conditioned responses were examined in immature rats. The lesions were made by stereotaxic injection of quisqualic acid on postnatal days 14 (P14), 17 (P17), and 21 (P21). A marked loss of ChAT activity was found 7 days after surgery in all age groups of lesioned rats. Unoperated P14 rats were unable to perform the passive avoidance conditioned responses. Acquisition began on P17. Lesions made on P17 and P21 strongly impaired the acquisition and retention of the task, evaluated 7 days postoperation. No biochemical but a partial behavioral recovery was observed 3 months after surgery in rats lesioned on P14. On the contrary, despite a persistent decrease in cortical ChAT activity, rats lesioned on P21 were able to acquire and retain the passive avoidance conditioned response. These results indicate that destruction of NBM cholinergic neurons shortly after birth is not compensated for by the developmental plasticity of the residual neurons but results in permanent cholinergic hypofunction. They also demonstrate that cholinergic NBM neurons play an important role in the acquisition and retention of a passive avoidance task; nevertheless, a behavioral recovery may take place 3 months after the lesion, even in the presence of a persistent cholinergic hypofunction.

Age-dependent cerebral metabolic effects of unilateral nucleus basalis magnocellularis ablation in rats

To investigate the age-dependent functional importance of cholinergic neocortical inputs, and to explore whether cortical cholinergic denervation in aged animals might better model the cerebral metabolic changes of Alzheimer's disease, the effects of unilateral ablation of the nucleus basalis magnocellularis (NBM) on cerebral glucose metabolism were studied in young and aged rats. Regional cerebral metabolic rates for glucose (rCMRglc) were determined, using the [14C]deoxyglucose method, in 48 brain regions of 3- and 24-month old Fischer-344 rats at 3, 7, 14 and 28 days after stereotaxic injection of ibotenate into the right NBM, and in sham-operated animals at 3 and 14 days later. For both ages the peak effect of unilateral NBM ablation occurred 3 days later: in young rats, rCMRglc was significantly reduced (compared to the contralateral side) in all 24 anterior cortical areas examined (mean decline 20%), whereas in aged animals, only 9 of 24 areas showed a significant decline in glucose utilization, and the magnitude of rCMRglc reduction (9%) was smaller. Near complete recovery of rCMRglc occurred by 7 days in young and old rats. We conclude that the basalocortical cholinergic projection plays a smaller role in neocortical function of aged rats, possibly because its tonic activity is reduced. Both young and aged rats undergo cortical metabolic normalization after unilateral NBM ablation; hence the NBM-lesioned aged rat is not a better model of the progressive decline in rCMRglc that occurs in Alzheimer's disease.

Effects of lesion of the cholinergic basal forebrain nuclei on the activity of glutamatergic and GABAergic systems in the rat frontal cortex and hippocampus

The effects of cholinergic basal forebrain lesions on the activity of the glutamatergic and GABAergic systems were investigated in the rat frontal cortex and hippocampus. Bilateral quisqualic acid injections in the nucleus basalis magnocellularis (NBM) at the origin of the main cholinergic innervation to the neocortex induced a cholinergic deficit in the cerebral cortex 15 days later, as shown by the marked selective decrease in cortical choline acetyltransferase (CAT) activity observed. Concurrent alterations in the kinetic parameters of high affinity glutamate uptake consisting mainly of a decrease in the Vmax were observed in the cerebral cortex. These changes presumably reflect a decreased glutamatergic transmission and provide support for the hypothesis that cortical glutamatergic neurons may undergo the influence of cholinergic projections from the NBM. Surprisingly, similar alterations in the glutamate uptake process were found to occur at hippocampal level in the absence of any significant change in the hippocampal cholinergic activity. These data indicate that the NBM may contribute to regulating hippocampal glutamatergic function without interfering with the hippocampal cholinergic innervation that mainly originates in the medial septal area-diagonal band (MSA-DB) complex. No change in parameters of GABAergic activity, namely the glutamic acid decarboxylase (GAD) activity and high affinity GABA uptake, were observed in any of the structures examined. In a second series of experiments involving bilateral intraventricular injections of AF64A, marked survival time-dependent decreases in CAT and high affinity choline uptake activities but no significant change in the high affinity glutamate uptake rate were observed in the hippocampus. No significant change in either parameters of cholinergic activity or in the glutamate uptake was concurrently observed in the cerebral cortex. The GABAergic activity was again unaffected whatever the survival time and the structure considered. Taken as a whole, these data suggest that basal forebrain projections originating in the NBM may play a major role in regulating glutamatergic but not GABAergic function in both the cerebral cortex and the hippocampus; whereas the glutamatergic and GABAergic activities in these two structures may not be primarily under the influence of the cholinergic projections from the MSA-DB complex.

High-affinity transport of choline and amino acid neurotransmitters in synaptosomes from brain regions after lesioning the nucleus basalis magnocellularis of young and aged rats

Bilateral lesion of the nucleus basalis with ibotenic acid infusions in young and aged rats results in the degeneration of cholinergic neurons which innervate the cortex. As expected, high-affinity uptake of choline was decreased in the frontal cortex subsequent to the lesion. Twenty one days after surgery there was a significantly decrease of the transport rate of GABA, glutamate and glycine in the frontal cortex of young rats, but those activities showed a recovery six months after lesion. On the contrary, 12-month old rats lesioned with the same experimental protocol showed no recovery of the transport rates in the frontal cortex. Uptake of choline, GABA, glutamate and glycine has also been studied in other areas of the brain, namely, hippocampus, olfactory bulb and cerebellum. The present results suggest that lesioning the nucleus basalis of rats led to a more effective and permanent impairment of some biochemical functions of the brain, when compared to young lesioned animals, and also suggest a functional relationship between the nucleus basalis and other areas of the brain.

Inhibition of high affinity choline uptake in the rat brain by neurotoxins: effect of monosialoganglioside GM1

Mustard derivatives of ethyl-choline and hemicholinium-3 have been suggested as possible specific cholinergic neurotoxins. In this study a structural analog of hemicholinium-3, a,a'-bis[di(2-chloroethyl)amino]-4,4'-2-biacetophenone (toxin 7), was added to synaptosomes prepared from the cortex, striatum or hippocampus of rat brain. Synaptosomal high affinity choline uptake (HACU) was significantly decreased in a dose-dependent manner by addition of toxin 7, while synaptosomal uptake of GABA or dopamine was not changed. Incubation of cortical synaptosomes with the monosialoganglioside GM1 prevented the decrease in HACU seen following administration of toxin 7. This preventative effect of GM1 was greater if GM1 was added prior to or concomitant with toxin 7, than if GM1 was added following toxin 7. Two newly synthesized hemicholinium-3 analogs, 4-[3'-di(2-chloroethyl)aminopropionyl]biphenyl (toxin 5) and 4-[3'-di(2-bromoethyl)aminopropionyl]biphenyl (toxin 6) caused a large decrease in HACU when added to cortical synaptosomes, this decrease was significantly greater than that seen with the same dose of toxin 7 or ethyl-choline aziridinium (AF64A). Ultrastructural changes in the synaptosomal membrane following incubation with toxin 7 or toxin 7 with GM1 were examined by electron microscopy. Development of a compound which is both a potent neurotoxin, and is specific for cholinergic neurons will allow new insights into the normal function of the cholinergic system in the CNS and provide animal models of disease states in which cholinergic degeneration is an important element.

Cholinergic deafferentation after focal cerebral infarct in rats

BACKGROUND AND PURPOSE

For a better understanding of neuronal network disturbances after stroke, we investigated the changes in the cholinergic system after experimental focal infarct.

METHODS

We quantitatively evaluated the highly sensitive acetylcholinesterase histochemistry and local glucose utilization 7 days after left middle cerebral artery occlusion in Wistar rats.

RESULTS

In all rats with occlusion, the ipsilateral frontal cortex and the nucleus basalis Meynert developed no infarct, whereas the subcortical striatum did. In the frontal cortex on the occlusion side, the acetylcholinesterase-positive fiber density was significantly (p less than 0.05) reduced; a computer-assisted image-analyzing system quantified approximately 1.0 m/mm3 brain cortex acetylcholinesterase-positive fibers in the ipsilateral frontal cortex layers II-IV and approximately 9.7 m/mm3 brain cortex acetylcholinesterase-positive fibers in the contralateral frontal cortex layers II-IV. Local glucose utilization was also significantly (p less than 0.05) decreased in the ipsilateral frontal cortex compared to the contralateral side and sham-operated animals.

CONCLUSIONS

These results suggest that functional disturbances and disruption of the cholinergic pathway between the frontal cortex and the nucleus basalis Meynert occur after middle cerebral artery occlusion in rats.

Stimulation of mono- and diacylglycerol lipase activities in ibotenate-induced lesions of nucleus basalis magnocellularis

Ibotenic acid was injected into the nucleus basalis magnocellularis region of rat brain in order to study whether an elevation of lipase activities was associated with the degeneration of cholinergic neurons in this potential animal model of Alzheimer's disease. Two plasma membrane fractions were prepared from different regions of ibotenate injected (right hemisphere) and non-injected (left hemisphere) rat brain. One plasma membrane fraction was from synaptosomes (SPM) and the other from glial and neuronal cell bodies (PM). Activities of mono- and diacylglycerol lipases in these plasma membrane fractions were markedly increased (3- to 5-fold) in hippocampus, midbrain and frontal cortical regions of rat brain at 10 days after the injection of ibotenate. The activity of choline acetyltransferase was decreased in frontal cortex but unchanged in hippocampus and midbrain. Our results suggest that the increase in lipase activity is much more widespread and non-specific than is the decrease in cholinergic function.

Local action of the diabetogenic drug, streptozotocin, on glucose and energy metabolism in rat brain cortex

Glucose is the principal source for energy production in the brain, and undisturbed glucose metabolism is pivotally significant for normal function of this organ. Peripheral glucose metabolism is impaired by streptozotocin (STZ), which induces diabetes mellitus. In this investigation, we have studied the local effects of intracerebroventricular (i.c.v.) STZ on glucose and energy metabolism in cerebral cortex. Three weeks after one single i.c.v. administration of STZ, ATP and phosphocreatine (CrP) concentrations as well as the ATP/ADP ratio and the energy charge potential were decreased, while the concentrations of glucose and ADP were increased, in cerebral cortex. Arterial blood glucose levels were not altered by i.c.v. STZ. It is concluded that brain energy metabolism is locally impaired by i.c.v. STZ. We propose that the disturbance of brain energy metabolism by i.c.v. STZ administration may provide a model for the study of prolonged metabolic neuronal stress.

The role of cholinergic projections from the nucleus basalis in memory

The behavioral effects of lesions of the nucleus basalis magnocellularis (NBM) are reviewed, focusing on the anatomical extent of the lesion, the involvement of neurotransmitter systems and the alterations in memory processes. Most behavioral deficits after NBM lesions can be attributed to damage to the NBM itself, although during spontaneous or pharmacologically induced recovery, other brain structures might play a role. The neurochemical deficit underlying the behavioral impairments is most likely the decrease in cholinergic functioning, since, for example, enhancement of cholinergic functioning is sufficient for behavioral improvement. However, since the lesions are not specific for cholinergic neurons, the extent to which noncholinergic damage causes behavioral deficits is still unclear. Finally, lesions of the NBM impair memory, but affect also other behavioral processes, such as discrimination and habituation. A common process underlying these various impairments could be that of insufficiently focused processing of stimuli.

Long-term changes in phosphoinositide hydrolysis following colchicine lesions of the nucleus basalis magnocellularis

The effect of bilateral colchicine lesions of the nucleus basalis magnocellularis (NBM) on agonist-stimulated phosphoinositide (PI) hydrolysis was examined in cortical slices 1, 3, or 14 months after surgery. Colchicine lesions resulted in a loss of acetylcholinesterase staining in the cortex which recovered to control levels by 14 months. Choline acetyltransferase activity in the cortex was decreased by 43% one month after lesioning, but returned to control levels by 3 months. In vitro stimulation with carbachol produced a concentration-dependent increase in PI hydrolysis, which was enhanced 3 and 14 months after NBM lesions. Norepinephrine and quisqualate-stimulated PI hydrolysis was also enhanced 14 months after NBM lesions. These results suggest a slow up-regulation of postsynaptic receptor function following presynaptic loss of transmitter.

Serotonin influences the behavioral recovery of rats following nucleus basalis lesions

The present study investigated the effects of serotonergic depletion upon the performance of rats with lesions of the nucleus basalis magnocellularis (NBM) in a nonspatial memory task. NBM lesions were made by injections of ibotenic acid. Serotonin was depleted by systemic injections of p-chloroamphetamine (PCA). After four weeks of testing, the choice accuracy of PCA rats was not different from that of control rats (CON), while the choice accuracy of NBM rats and rats with combined treatment (NBM + PCA) was significantly lower than CON rats, but not different from each other. After prolonged testing, performance improved in NBM rats, but not in NBM + PCA rats indicating that simultaneous loss of both cholinergic and serotonergic neurotransmission produced a significantly longer lasting behavioral deficit than the loss of cholinergic neurotransmission alone.

Role of nucleus basalis in cholinergic control of cortical blood flow

The present investigation was designed to determine the effect of lesions localized to the nucleus basalis/substantia innominata (NB) on resting and cholinergically activated regional cerebral cortical blood flow (rCBF). Ibotenic acid (10 micrograms) was infused locally at 1 mm caudal to bregma, 3 mm lateral to the midline, and 8 mm below the cortical surface. Effectiveness of lesions was demonstrated by histological verification of lesion sites and determination of choline acetyltransferase activity in cerebral cortex homogenates. rCBF was measured with the autoradiographic iodo-14C-antipyrine technique. Resting rCBF was similar in the hemisphere that received the NB lesion and in the contralateral (intact) side in all regions examined. Physostigmine intravenous infusion (3.3 micrograms.kg-1.min-1) enhanced rCBF in frontal, parietal, occipital, and temporal cortex. The increase was symmetrical, however, indicating inability of NB lesion to affect this phenomenon. It is concluded that the cortical cholinergic afferents originating in the NB are not involved in the control of rCBF.

Sprouting of cholinergic axons does not occur in the cerebral cortex after nucleus basalis lesions

Different doses of the excitotoxin quisqualate were used to make lesions in the caudal part of the ferret nucleus basalis, i.e. the part that projects to the visual cortex. The higher doses of the excitotoxin destroyed all nerve growth factor receptor-immunoreactive cells in the caudal nucleus basalis and gave rise to up to 75% loss of acetylcholinesterase-containing axons in the visual cortex. In sections stained for Nissl substance there was generalized tissue damage around the injection sites and extensive loss of all neuron types in areas surrounding the caudal nucleus basalis. Lower doses of the excitotoxin damaged only a proportion of the nerve growth factor receptor-immunoreactive neurons in the caudal nucleus basalis and produced a much lower depletion of acetylcholinesterase-positive fibres in the visual cortex. The only damage seen in sections stained for Nissl substance was a loss of magnocellular neurons in the vicinity of the injection sites. A quantitative morphological approach was used to show that either one week or three months after the lesions there was a linear correlation between the proportion of acetylcholinesterase-positive axons lost in the visual cortex and the proportion of nerve growth factor receptor-immunoreactive cells that had disappeared from the caudal nucleus basalis. Since the correlation lines for the short-term (one week) survival and the long-term (three months) survival experiments coincided, this indicated that no collateral sprouting of cholinergic axons had occurred in the visual cortex of the long-term survival animals regardless of size of the lesion in the nucleus basalis.

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.

Effects of nucleus basalis lesions on cerebral cortical concentrations of corticotropin-releasing hormone (CRH)-like immunoreactivity in the rat

The present study was designed to determine the effects of partial cholinergic denervation on parietal cortical corticotropin-releasing hormone-like immunoreactivity (CRH-LI) in the rat at different ages. Young adult rats received either unilateral or bilateral ibotenic acid infusions into their nucleus basalis, destroying most of the acetylcholinesterase-positive neurons in that region. Parietal cortical levels of CRH-LI were assayed 2.5, 10, 14 and 19 months after placement of nucleus basalis lesions. Parietal CRH-LI was elevated at 10, 14 and 19 months in bilaterally lesioned animals, while unilateral lesions had no effect on CRH-LI.

Chronic infusion of GABA and saline into the nucleus basalis magnocellularis of rats: II. Cognitive impairments

In order to assess sensorimotor and/or cognitive modifications following chronic inhibition of nucleus basalis magnocellularis (NBM) neurons, rats trained in two radial maze paradigms (the classical version of the test and a modified version introducing a one-hour delay between the fourth and the fifth choice) received chronic infusion of gamma-aminobutyric acid (GABA) into the NBM area. GABA (10 and 50 micrograms/microliters/h) was infused for 3 days into the NBM contralateral to their preferred turning direction in the radial maze. Simultaneously, saline (NaCl 0.9%; 1 microliter/h) was infused into the contralateral NBM. GABA and saline infusions were alternated for the subsequent 3-day period. One week later, we investigated the rats' ability to learn a multiple trial passive avoidance task. At the dose of 50 micrograms/microliters, GABA infusion produced (1) a turning bias ipsilateral to the side first infused with GABA, (2) transitory cognitive impairments in radial maze tasks and (3) a deficit in the acquisition of the passive avoidance task. At the dose of 10 micrograms/microliters, the same behavioral deficits were observed except that (1) the turning bias was reversed by the contralateral GABA infusion and (2) cognitive impairments in the radial maze were observed only when a delay was inserted between the fourth and the fifth choice. Histologically, we found a dose-dependent gliosis in the NBM area first infused with GABA. These data suggest a reactivity of the NBM to GABAergic manipulations and the intervention of this structure in both sensorimotor and cognitive processes involved in the radial maze paradigms.