Cholinergic Cells In Basal Forebrain Research Articles

Transcriptional Profiling of Cholinergic Neurons From Basal Forebrain Identifies Changes in Expression of Genes Between Sleep and Wake.

To assess differences in gene expression in cholinergic basal forebrain cells between sleeping and sleep-deprived mice sacrificed at the same time of day. Tg(ChAT-eGFP)86Gsat mice expressing enhanced green fluorescent protein (eGFP) under control of the choline acetyltransferase (Chat) promoter were utilized to guide laser capture of cholinergic cells in basal forebrain. Messenger RNA expression levels in these cells were profiled using microarrays. Gene expression in eGFP(+) neurons was compared (1) to that in eGFP(-) neurons and to adjacent white matter, (2) between 7:00 am (lights on) and 7:00 pm (lights off), (3) between sleep-deprived and sleeping animals at 0, 3, 6, and 9 hours from lights on. There was a marked enrichment of ChAT and other markers of cholinergic neurons in eGFP(+) cells. Comparison of gene expression in these eGFP(+) neurons between 7:00 am and 7:00 pm revealed expected differences in the expression of clock genes (Arntl2, Per1, Per2, Dbp, Nr1d1) as well as mGluR3. Comparison of expression between spontaneous sleep and sleep-deprived groups sacrificed at the same time of day revealed a number of transcripts (n = 55) that had higher expression in sleep deprivation compared to sleep. Genes upregulated in sleep deprivation predominantly were from the protein folding pathway (25 transcripts, including chaperones). Among 42 transcripts upregulated in sleep was the cold-inducible RNA-binding protein. Cholinergic cell signatures were characterized. Whether the identified genes are changing as a consequence of differences in behavioral state or as part of the molecular regulatory mechanism remains to be determined.

A primate model of Alzheimer's disease

Animal models of Alzheimer's Disease (AD) are designed to duplicate a subset of selected neuropathological, biochemical and behavioral changes that are associated with AD. One well-studied model is based upon the assumption that the destruction of basal forebrain cholinergic neurons by injection of a neurotoxin, such as ibotenic acid, is sufficient to reproduce the cognitive impairments associated with AD. Monkeys have been trained and tested in a variety of behavioral tasks that are selective for learning and memory deficits. Typically, performance was only slightly impaired, and usually recovered to control levels with continued testing. Monkeys with basal forebrain lesions were sensitive to cholinergic antagonists but did not show a consistent benefit from treatment with cholinergic agonists. Furthermore, the memory deficits did not correlate with the degree of cholinergic cell loss. Electrophysiological studies suggest that cholinergic basal forebrain cells may help to evaluate afferent sensory stimuli for degree of novelty or familiarity, or the association of the stimuli with a subsequent reward. Consistent with these findings, monkeys with basal forebrain lesions were significantly impaired in an attention task that tested spatial orienting ability. These recent studies suggest that monkeys with basal forebrain lesions may be useful as models of the attentional deficits associated with AD.

BDNF protection of basal forebrain cholinergic neurons after axotomy: complete protection of p75NGFR-positive cells.

To elucidate the role of brain derived neurotrophic factor (BDNF) in the protection of cholinergic neurons in the basal forebrain, recombinant human BDNF and as a positive control, human recombinant nerve growth factor (NGF), were infused for 20 days into the lateral ventricle of adult rats with fimbrial transections. BDNF and NGF administration protected cholinergic basal forebrain cells from degenerative changes after axotomy, as assessed with immunohistochemical analysis of the two cholinergic marker proteins ChAT and p75NGFR. Both BDNF and NGF treatment completely prevent the lesion induced loss of p75NGFR-positive cells in the septal area of animals with fimbrial transections. This finding contrasts with the result obtained with ChAT immunohistochemistry, where BDNF treatment protects only part of the population of neurons which disappear following the transections. These findings are compatible with the view that there is a cascade of events induced in cholinergic neurons by the transections, so that ChAT expression is lost before p75NGFR expression, and that BDNF reduces degenerative events in the entire population of cholinergic neurons, maintaining some of them as p75NGFR-positive but ChAT-negative cells.

Galaninergic Innervation of the Cholinergic Vertical Limb of the Diagonal Band (Ch2) and Bed Nucleus of the Stria terminalis in Aging, Alzheimer's Disease and Down's Syndrome (Part 2 of 2)

The galanin (GAL) containing peptide fiber system circuit which innervates acetylcholine containing basal forebrain neurons has been shown to hypertrophy and hyperinnervate remaining cholinergic Ch4 perikarya in Alzheimer's disease (AD). The present study examined whether a similar hyperinnervation occurs within the cholinergic vertical limb of the diagonal band nucleus (Ch2), a portion of the basal forebrain which, unlike Ch4, exhibits only modest degeneration in AD. Furthermore, we evaluated whether GAL hyperinnervation occurs within the basal forebrain in Down's syndrome, a genetic disorder with extensive AD-like pathology including cholinergic basal forebrain neuron degeneration. The present study revealed that virtually all Ch2 neurons were GAL immunonegative. However, this region was innervated by GAL immunoreactive (ir) interneurons and fibers associated with a major galaninergic pathway which travels through the substantia innominata enroute to the hypothalamus, bed nucleus of the stria terminalis as well as vertical limb of diagonal band nucleus. GAL-ir fibers coursing within this fiber bundle hypertrophied in AD relative to age matched controls and the Down's cases. Within the putative Ch2 terminal zones in AD, many of the remaining cholinergic neurons were hyperinnervated by GAL despite the modest reduction in Ch2 neurons. In contrast, GAL-ir fibers were not hypertrophied in Down's syndrome despite extensive cholinergic cell loss within Ch4. Taken together these findings suggest that extensive cholinergic basal forebrain cell loss alone is not sufficient to trigger the basal forebrain GAL plasticity response found in AD.

Galaninergic innervation of the cholinergic vertical limb of the diagonal band (Ch2) and bed nucleus of the stria terminalis in aging, Alzheimer's disease and Down's syndrome.

The galanin (GAL) containing peptide fiber system circuit which innervates acetylcholine containing basal forebrain neurons has been shown to hypertrophy and hyperinnervate remaining cholinergic Ch4 perikarya in Alzheimer's disease (AD). The present study examined whether a similar hyperinnervation occurs within the cholinergic vertical limb of the diagonal band nucleus (Ch2), a portion of the basal forebrain which, unlike Ch4, exhibits only modest degeneration in AD. Furthermore, we evaluated whether GAL hyperinnervation occurs within the basal forebrain in Down's syndrome, a genetic disorder with extensive AD-like pathology including cholinergic basal forebrain neuron degeneration. The present study revealed that virtually all Ch2 neurons were GAL immunonegative. However, this region was innervated by GAL immunoreactive (ir) interneurons and fibers associated with a major galaninergic pathway which travels through the substantia innominata enroute to the hypothalamus, bed nucleus of the stria terminalis as well as vertical limb of diagonal band nucleus. GAL-ir fibers coursing within this fiber bundle hypertrophied in AD relative to age matched controls and the Down's cases. Within the putative Ch2 terminal zones in AD, many of the remaining cholinergic neurons were hyperinnervated by GAL despite the modest reduction in Ch2 neurons. In contrast, GAL-ir fibers were not hypertrophied in Down's syndrome despite extensive cholinergic cell loss within Ch4. Taken together these findings suggest that extensive cholinergic basal forebrain cell loss alone is not sufficient to trigger the basal forebrain GAL plasticity response found in AD.

Immunocytochemical localization of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat: A correlated light and electron microscopic study

The cholinergic circuitry in the nucleus basalis magnocellularis of the rat was investigated in a correlated light and electron microscopic study by using monoclonal antibodies against the acetylcholine-synthesizing enzyme, choline acetyltransferase, following the unlabelled antibody peroxidase-antiperoxidase immunocytochemical procedure. After the immunocytochemical approach, large cholinergic cells and a few immunoreactive fibres exhibiting a varicose appearance, were detected by light microscopy in portions of the nucleus basalis magnocellularis located within the anatomical limits of the globus pallidus, mostly in its ventromedial part. Cholinergic neurons and fibre-like structures were also found within the substantia innominata on the edge of globus pallidus.The same material studied by light microscopy was analysed with the electron microscope. At the ultrastructural level, the immunopositive neurons showed the same cytological characteristics and pattern of synaptic input as cholinergic basal forebrain cells. Additionally, scarce immunoreactive preterminal axons and terminal boutons were detected in the region. The immunoreactive terminals were scattered or formed occasional clusters and appeared as heavily immunostained vesicle-filled boutons making exclusively axodendritic synaptic contacts principally with immunonegative distal dendrites. Both symmetric and asymmetric synaptic contacts established between these structures were detected, although the symmetric contacts were the more numerous. The surface of postsynaptic immunonegative dendrites in asymmetric synaptic contact with immunoreactive terminals was generally covered by terminals that lacked detectable immunoreactivity. In contrast, those in symmetric synaptic contact with labelled terminals showed much sparser input from immunonegative terminals, suggesting that they may belong to interneurons. Very rarely, cholinergic terminals were detected in asymmetric synaptic contact with dendrites which also contained positive immunoreaction product. Asymmetric contracts were frequently characterized by the presence of subjunctional dense bodies.The detection of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat indicates that this region not only contains cholinergic projecting neurons, but receives a cholinergic input itself. Results of this study provide evidence of the existence of a cholinergic transmission in the basal forebrain of the rat, and also that acetylcholine might play a role in the regulation of the extrinsic cortical cholinergic innervation. The possible sources of this innervation are discussed.

Parenterally administered GM 1 ganglioside prevents retrograde degeneration of cholinergic cells of the rat basal forebrain

The effect of daily intraperitoneal injections of GM1 ganglioside on retrograde degeneration in the basal forebrain has been examined, using a monoclonal antibody directed against choline acetyltransferase to identify the cholinergic neurones. Rats underwent extensive damage of the cerebral cortex and underlying hippocampus. From the day of operation on, they received daily injections of ganglioside. After a survival of 30 days, the animals were killed and the cholinergic cells of the basal forebrain were examined. These were compared with material treated in the same way from animals who had received the injections of ganglioside but no lesion, animals who had been operated upon but without the ganglioside treatment, and normal animals. Intraperitoneal ganglioside administration markedly reduces the retrograde death of the cholinergic neurones of the medial septal nucleus and abolishes the shrinkage of the remaining neurones following hippocampal damage.