Cell loss in the locus coeruleus in senile dementia of Alzheimer type

Why patients with Alzheimer's disease may show increased sensitivity to tropicamide eye drops: role of locus coeruleus

RATIONALE

Patients suffering from Alzheimer's disease (AD) may show increased sensitivity to tropicamide, a muscarinic cholinoceptor antagonist. AD is associated with a severe loss of noradrenergic neurones in the locus coeruleus (LC), which can be "switched off" experimentally by the alpha(2)-adrenoceptor agonist clonidine. The possibility arises that increased pupillary sensitivity to tropicamide in AD may be due to diminished LC activity.

OBJECTIVE

To examine the hypothesis that clonidine may potentiate tropicamide-evoked mydriasis.

MATERIALS AND METHODS

Sixteen healthy male volunteers participated in two experimental sessions (0.2 mg clonidine or placebo) conducted 1 week apart. In each session tropicamide (0.01% 10 microl x 2) was applied to the left eye and artificial tear (10 microl x 2) was applied to the right eye. Pupillary functions (resting pupil diameter and light and darkness reflexes), alertness and non-pupillary autonomic functions (blood pressure, heart rate, core temperature and salivary output) were measured. Data were analysed by ANOVA, with multiple comparisons.

RESULTS

Tropicamide increased resting pupil diameter, velocity and amplitude of the darkness reflex response, and decreased recovery time of the light reflex response. Clonidine affected all these pupillary measures in the opposite direction with the exception of the recovery time. The mydriatic response to tropicamide was potentiated by pre-treatment with clonidine. Clonidine reduced critical flicker fusion frequency, subjective alertness, blood pressure, salivation and temperature.

CONCLUSIONS

The potentiation of tropicamide-evoked pupil dilatation by clonidine may be due to the abolition of the increase in parasympathetically mediated pupil constriction due to reduced LC activity.

Increased volume of the pigmented neurons in the locus coeruleus of schizophrenic subjects: a stereological study

The locus coeruleus is the largest cluster of noradrenaline-producing neurons in the brain and has been involved in regulating attention. The neurotransmitter system contributes to the initiation and maintenance of forebrain activity as well as modulation of the collection and processing of sensory information. This makes locus coeruleus a target of interest in the study of possible structural changes in the brains of subjects with chronic schizophrenia. Uniform sampling and optical disectors were used for estimation of total neuron numbers and the rotator principle for estimation of mean cell volume. This study estimated the bilateral total number of pigmented neurons in the locus coeruleus of schizophrenic and control subjects and found no difference between the two; schizophrenic subjects have 37,400 (coefficient of variation=CV=SD/mean=0.28), control subjects have 35,500 (CV=0.19), p=0.64. The average volume of the cell perikaryon of pigmented neurons was measured in both groups and showed a significant larger cell volume in the locus coeruleus of schizophrenic compared to control subjects; mean locus coeruleus cell volume was 58,400 microm(3) (CV=0.31) in schizophrenic subjects, which is 55% larger than the 37,600 microm(3) (CV=0.33) found in control subjects, a difference of 20,800 microm(3) (p=0.009). The fixation time was significantly longer for the schizophrenic brains with an average of 169 months compared to 88 months for the control brains. No relation was found between total numbers or geometric mean volume of the pigmented cells and fixation time.

The locus coeruleus in schizophrenia: a postmortem study of noradrenergic neurones

Despite evidence for an abnormality of noradrenergic function in schizophrenia, it remains unclear whether the number of noradrenergic neurones is normal in patients with the disorder. In postmortem, formalin-fixed tissue from 15 schizophrenic patients and 18 controls matched for age and gender, we made estimates of the number and size of tyrosine-hydroxylase-immunoreactive cells in the locus coeruleus (LC). No significant difference was detected between these groups in the cross-sectional area or diameter of immunoreactive cell profiles. Profile number was not significantly affected by gender, side of the brainstem (left or right), postmortem interval or time in formalin; however, the levels of immunoreaction product (optical density) correlated significantly with our profile counts, which were lower on average in the schizophrenic group. When optical density was included as a covariate in our comparison (a repeated-measures analysis of variance) of schizophrenic and control cases, we found no difference between these groups in the number of neurones counted. An age-related decrease in profile number was detected, but no effect of age on our estimates of cell size was apparent. Our results highlight the importance of accounting for potential confounding variables, including variations in the quality of immunostaining, in investigations of this type. The findings presented here concur with previous studies suggesting that noradrenergic dysfunction in schizophrenia is not associated with an anatomical abnormality at the level of the LC.

Postmortem locus coeruleus neuron count in three American veterans with probable or possible war-related PTSD

The authors investigated whether war-related posttraumatic stress disorder (WR-PTSD) is associated with a postmortem change in neuronal counts in the locus coeruleus (LC) since enhanced central nervous system (CNS) noradrenergic postsynaptic responsiveness has been previously shown to contribute to PTSD pathophysiology. Using postmortem neuromorphometry, the number of neurons in the right LC in seven deceased elderly male veterans was counted. Three veterans were classified as cases of probable or possible WR-PTSD. All three veterans with probable or possible WR-PTSD were found to have substantially lower LC neuronal counts compared to four comparison subjects (three nonpsychiatric veterans and one veteran with alcohol dependence and delirium tremens). To the authors' knowledge, this case series is the first report of LC neuronal counts in patients with PTSD or any other DSM-IV-TR anxiety disorder. Previous postmortem brain tissue studies of Alzheimer's Disease (AD) demonstrated an upregulation of NE biosynthetic capacity in surviving LC neurons. The finding reported is consistent with the similar upregulation of NE biosynthetic capacity of surviving LC neurons in veterans who developed WR-PTSD. Especially if replicated, this finding in WR-PTSD may provide further explanation of the dramatic effectiveness of propranolol and prazosin for the secondary prevention and treatment of PTSD, respectively. The LC neurons examined in this study are probably the origin of the first or second "leg" of what might be termed the PTSD candidate circuit. Larger neuromorphometric studies of the LC in veterans with WR-PTSD and in other development-stress-induced and fear-circuitry disorders are warranted, especially using VA registries.

Analysis of the human locus coeruleus in perinatal and infant sudden unexplained deaths. Possible role of the cigarette smoking in the development of this nucleus

We investigated the immunohistochemical expression of the tyrosine hydroxylase (TH) enzyme and the morphometric parameters of the human locus coeruleus (LC) in the brainstems of 32 subjects aged from 17 gestational weeks to 12 postnatal month, died of unknown (sudden unexplained perinatal and infant deaths) and known causes. The goals of this study were: (1) to obtain basic information about the structure and physiology of the LC during the first phases of human nervous system development; (2) to evaluate whether there is altered expression of TH and/or structural alterations of the LC in cases of sudden perinatal and infant death; and (3) to verify if morphological and/or physiological abnormalities of the LC could be related to maternal cigarette smoking. Morphometric analysis showed homogeneous data in cases of sudden perinatal and infant death and in age-matched controls who had died of known aetiology. However, immunohistochemistry demonstrated in a wide subset of sudden and unexplained deaths a negativity or low positivity of TH. High distribution of TH protein were instead detectable in the LC neurons of foetuses aged 17-18 gestational weeks who had died of known causes. Therefore, we postulate the functional importance of the LC in the early phases of central nervous system development. Besides, the observation of a significant correlation between sudden unexplained death, negativity of TH staining and maternal smoking, prompted us to suppose a close relation between smoking in utero and a decrease of the noradrenergic activity of the LC, leading to sudden death in the last part of pregnancy and in the first year of life.

Noradrenergic innervation of the developing and mature septal area of the rat

The noradrenergic innervation of the developing and mature septal area of the rat was examined with light and electron microscopic immunocytochemistry using an antibody against dopamine-beta-hydroxylase. At birth, a small number of relatively thick noradrenergic fibers were found to innervate the lateral septum (mainly its intermediate part) and the nuclei of the vertical and horizontal limbs of the diagonal band of Broca. By postnatal day 7, a substantial increase in their density was observed. At this age some labeled fibers left the medial forebrain bundle and invaded the nucleus of the horizontal limb of the diagonal band. These fibers then ran in a ventrodorsal direction and innervated the nucleus of the vertical limb before entering the medial septum. Immunoreactive fibers were finer and more varicose than at birth. In the subsequent 2 weeks, the density of labeled fibers in the septal area was further increased. By postnatal day 21, the distribution pattern and density of the noradrenergic innervation appeared similar to the adult. In the adult, noradrenergic fibers exhibited more varicosities than in younger rats. Electron microscopic analysis revealed a low proportion (peaked at P7) of noradrenergic varicosities engaged in synaptic contacts throughout development. The overwhelming majority of these synapses were symmetrical, predominantly with small or medium-sized dendrites. The present findings provide the morphological basis for the functional interactions between noradrenergic afferents and neuronal elements in the septal area. The low proportion of synaptic contacts found in this study suggests that noradrenaline may exert its action in the septal area mainly through transmission by diffusion (volume transmission), as has been suggested for other areas of the developing and adult brain.

Hypothesis for a common basis for neuroprotection in glaucoma and Alzheimer's disease: anti-apoptosis by alpha-2-adrenergic receptor activation

Recent studies have suggested glaucomatous loss of retinal ganglion cells and their axons in Alzheimer's disease. Amyloid beta peptides and phosphorylated tau protein have been implicated in the selective regional neuronal loss and protein accumulations characteristic of Alzheimer's disease. Similar protein accumulations are not present on glaucomatous retinal ganglion cells. Neurons die in both Alzheimer's disease and glaucoma by apoptosis, although the signaling pathways for neuronal degradation appear to differ in the two diseases. Alzheimer's disease features a loss of locus ceruleus noradrenergic neurons, which send axon terminals to the brain regions suffering neuronal apoptosis and results in reductions in noradrenaline in those regions. Activation of alpha-2 adrenergic receptors reduces neuronal apoptosis, in part through a protein kinase B (Akt)-dependent signaling pathway. Loss of noradrenaline innervation facilitates neuronal apoptosis in Alzheimer's disease models and may act similarly in glaucoma. Alpha-2 adrenergic receptor agonists offer the potential to slow the neuronal loss in both diseases by compensating for lost noradrenaline innervation.

Cholinergic nicotinic systems in Alzheimer's disease: prospects for pharmacological intervention

Within the last few years, research into the cause and progression of Alzheimer's disease has made significant advances. Although there is still no preventative treatment or cure for this neurodegenerative illness, the development of drugs that may alleviate some of the cognitive symptoms associated with it is advancing. Cholinesterase inhibitors are at present the most effective form of treatment and have shown significant overall response rates in clinical trials. However, although some patients show substantial improvement when treated with this class of drugs, there is considerable variability in the amount of benefit gained in different individuals in terms of their cognitive and behavioural functioning. Furthermore, unfortunately some patients gain little or no benefit from these drugs. It would therefore be of great advantage to explore alternative therapeutic possibilities. This article reviews the potential involvement of the nicotinic cholinergic system in Alzheimer's disease and discusses the possibility of nicotinic pharmacotherapy. Substantial evidence indicates the involvement of the nicotinic cholinergic system in the pathology of Alzheimer's disease. Drugs targeting these sites may not only have a positive effect on cognitive function, but also have additional therapeutic benefits in terms of restoring the hypoactivity in the excitatory amino acid pyramidal system and even slowing the emergence of Alzheimer's disease pathology. The conclusion of this review is that nicotinic treatments are an important potential source of new therapeutic interventions in Alzheimer's disease.

Neural Transplantation in Animal Models of Dementia

Neural transplantation provides a powerful novel technique for investigating the neurobiological basis and potential strategies for repair of a variety of neurodegenerative conditions. The present review considers applications of this technique to dementia. After a general introduction (section 1), attempts to replace damaged neural systems by transplantation are considered in the context of distinct animal models of dementia. These include grafting into aged animals (section 2), into animals with neurotransmitter-selective lesions of subcortical nuclei, in particular involving basal forebrain cholinergic systems (section 3), and into animals with non-specific lesions of neocortical and hippocampal systems (section 4). The next section considers the alternative use of grafts as a source of growth/trophic factors to inhibit degeneration and promote regeneration in the aged brain (section 5). Finally, a number of recent studies have employed transplanted tissues to model and study the neurodegenerative processes associated with ageing and Alzheimer's disease taking place within the transplant itself (section 6). It is concluded (section 7) that although neural transplantation does not offer any immediate prospect of therapeutic repair in clinical dementia, the technique does offer a powerful neurobiological tool for studying the neuropathological processes involved in both spontaneous degeneration and specific diseases of ageing. New understandings derived from neural transplantation may be expected to lead to rational development of novel strategies to inhibit the neurodegenerative process and to promote regeneration in the aged brain.

Alzheimer's disease and the cerebellum: a morphologic study on neuronal and glial changes

Structural manifestations of Alzheimer's disease (AD) including neuronal loss were investigated in 12 cases of AD and in 10 healthy age-matched controls, with focus on the cerebellum. Linear Purkinje cell (PC) density was measured in the vermis and cerebellar hemispheres. Neurons were also counted in the inferior olivary nucleus. In vermis of the AD cases, the mean PC number was significantly lower (p = 0.019) than in the controls. The neurons in the inferior olive were similarly fewer, though not significantly (p = 0.13). Molecular layer gliosis and atrophy in the vermis was clearly severer in AD than in the controls. Features typical of cerebral Alzheimer encephalopathy (plaques, tangles and microvacuolization) were inconspicious. The structural cerebellar changes in the AD cases were thus neuronal loss, atrophy and gliosis, judged to represent the disease process, and with a main involvement in the vermis. This may be reflected in some of the symptoms and signs seen in AD, signs that are generally overlooked or judged to be of noncerebellar origin.

Tyrosine hydroxylase and norepinephrine transporter mRNA expression in the locus coeruleus in Alzheimer's disease

Despite the loss of locus coeruleus (LC) noradrenergic neurons in Alzheimer's disease (AD), cerebrospinal fluid norepinephrine (NE) levels are normal or increased in AD. This paradox suggests compensatory upregulation of NE synthetic capacity or downregulation of the NE transporter (NET) in the remaining LC neurons. LC tyrosine hydroxylase (TH) mRNA expression in the LC was measured in AD subjects (n=5) and in age and gender comparable non-demented subjects (n=6). When AD subjects were divided into those still ambulatory prior to death (CDR 3/4) and those in a prolonged 'vegetative' state prior to death (CDR 5), differences among groups became apparent at specific levels of the LC. In CDR 3/4 AD subjects there was increased TH mRNA expression per neuron compared to non-demented subjects in the caudal half of the LC. However, expression of NET mRNA in the same subjects was not significantly different at any level of the LC. These preliminary results suggest an upregulation of NE biosynthetic capacity in at least some LC neurons in AD prior to the very late stage of the disease.

Decreased exploratory activity and impaired passive avoidance behaviour in mice deficient for the alpha(1b)-adrenoceptor

There is growing evidence that a dysfunction of central noradrenergic neurotransmission is involved in age-related impairments of cognitive performance and the pathophysiology of Alzheimer's disease (AD). A reduction of density of central alpha(1)-adrenergic receptors (alpha(1)-AR) has been shown in aging and AD brains. Three alpha(1)-AR subtypes (alpha(1a), alpha(1b) and alpha(1d)) have been identified by molecular cloning. However, very little is known about the functional role of distinct alpha(1)-AR subtypes in the brain. This problem was specifically addressed using a model of knockout mouse deficient in alpha(1b)-AR (alpha(1B)-/-) because these animals show a 40% reduction of alpha(1)-AR density in the brain as already reported. In comparison to the wild-type mice (alpha(1B)+/+), alpha(1B)-/- mice showed significantly reduced square entries and a reduced rearing behaviour was observed over all sessions in the open field. In passive avoidance procedures, alpha(1B)-/- mice showed a tendency towards decreased short-term-latency and a significant decline in long-term-latency. The present results indicate that mutation of a single member of the alpha(1)-AR gene family creates a distinct phenotype and provide evidence that alpha(1B)-AR is possibly involved in modulation of memory consolidation and fear-motivated exploratory activity. Furthermore, this model of knockout mice may be useful in elucidating the role of alpha(1B)-AR in dementias involving deficits of the noradrenergic system.

[Expressions of depression in Alzheimer's disease. The current scientific debate]

This overview analyses findings coming from researches that considered the interaction between depression and Alzheimer's disease (AD).

METHOD

Information was collected from the Medline database and from a reasoned manual analysis of the published studies.

RESULTS

The prevalence of depressive symptoms in patients with AD is elevated (40-50%). The role of depression in the pathogenesis of AD (independent, prodromal symptom, factor of risk) still must be defined. Data on family history of depression suggest that AD could act as stimulus triggering depression from a basis of a genetic vulnerability. From a biological point of view the onset of depression could derive from an unbalance between cholinergic and noradrenergic systems. Psychological understanding sees depression as a reaction of mourning for the cognitive deficit. Current diagnostic instruments validated on patients with AD constitute a good aid for the clinician and the researcher. The identification of depression coexisting with AD is difficult, in absence of clear affective symptoms, since the cognitive, psychomotor and vegetative symptoms belong both to depression and to AD. The affective disorders most frequently reported are major depression and dysthymia. The use of antidepressant drugs with the lowest anticholinergic profile is strongly recommended. Good results have been obtained also using various psychotherapeutic interventions adapted for dementia sufferers.

CONCLUSIONS

The current scientific debate is based on information still limited and sparse. Future analyses should consider a better definition of the hypotheses related to psychopathology in AD, a standardised definition of cases and selection procedures and a prospective longitudinal design.

The role of norepinephrine in the pathophysiology of cognitive disorders: potential applications to the treatment of cognitive dysfunction in schizophrenia and Alzheimer's disease

The role of noradrenergic neurotransmission in normal cognitive functions has been extensively investigated, however, the involvement of noradrenergic functions in the cognitive impairment associated with schizophrenia and Alzheimer's disease has not been as intensively considered. The limited ability of atypical antipsychotics to treat the cognitive impairment of schizophrenia, and cholinomimetics to treat the cognitive impairment of Alzheimer's disease, may be related to the influence of a multiplicity of neurotransmitter abnormalities including noradrenergic dysfunction, which these treatments do not address. The evidence of noradrenergic dysfunction occurring concomitantly with dopamine dysfunction in schizophrenia and acetylcholine dysfunction in Alzheimer's disease supports therapeutic approaches using noradrenergic drugs in combination with neuroleptics and cholinesterase inhibitors, respectively, to enhance the treatment of cognitive impairment. Given the results of animal and human studies, it appears that alpha-2A agonists may be the optimal choice for this purpose.

L-type calcium channels in the hippocampus and cerebellum of Alzheimer's disease brain tissue

There is growing evidence that the selective neuronal cell death observed in Alzheimer's Disease (AD) is the result of dysregulation of intracellular calcium (Ca2+) homeostasis. In the present study, L-type voltage sensitive calcium channels (L-VSCCs) were examined in the cerebellum and hippocampus of AD (n = 6; postmortem interval less than 5 h) and age-matched control (n = 6) tissue by homogenate binding techniques and quantitative in vitro receptor autoradiography using [3H]isradipine (PN200-110). Saturation analyses of the cerebellum revealed unaltered [3H]isradipine binding parameters (Kd and Bmax) between AD and control subjects. Analysis of AD and control hippocampus demonstrated significant differences as [3H]isradipine binding increased (62%) in AD, whereas hippocampal cell density decreased (29%) in AD, relative to control subjects. Moreover, AD differentially affected L-VSCC in area CA1 and dentate gyrus. The dentate gyrus had greatly increased binding (77%) with little cell loss (16%) in AD brains, whereas area CA1 had increased binding (40%) with significant cell loss (42%) in AD brains, relative to controls. The results of the present study suggest that hippocampal area CA1 may experience greater cell loss in response to increased L-VSCCs in AD relative to other brain regions.

Increased activity of surviving locus ceruleus neurons in Alzheimer's disease

In Alzheimer's disease (AD) there is neuronal loss in the locus ceruleus (LC), and the noradrenergic system may be even more affected in depressed AD patients. However, this neuronal loss may go together with an increase in activity of the remaining noradrenergic neurons. We prospectively evaluated 16 AD patients (6 depressed, 5 transiently depressed, and 5 nondepressed) and 10 controls. We determined norepinephrine and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in various brain areas, and compared these data with previously established neuron numbers in the LC in the same patients. We could not confirm earlier studies reporting lower norepinephrine concentrations in depressed than in nondepressed dementia patients. The mean norepinephrine concentrations in AD patients were significantly lower than those in control patients, whereas the mean concentrations of MHPG were not different. Moreover, we found significant inverse relationships between the number of remaining pigmented LC neurons and the MHPG/norepinephrine ratio in the frontal cortex and LC. These data are the first to provide direct evidence for the hypothesis that remaining LC neurons are activated to compensate for decreased cerebral norepinephrine levels in AD, by demonstrating that the MHPG/norepinephrine ratio is significantly higher in AD, indicating increased metabolism.

Inflammation and Alzheimer's disease: relationships between pathogenic mechanisms and clinical expression

During the past 15 years a variety of inflammatory proteins has been identified in the brains of patients with Alzheimer's disease (AD) postmortem. There is now considerable evidence that in AD the deposition of amyloid-beta (A beta) protein precedes a cascade of events that ultimately leads to a local "brain inflammatory response." Here we reviewed the evidence (i) that inflammatory mechanisms can be a part of the relevant etiological factors for AD in patients with head trauma, ischemia, and Down's syndrome; (ii) that in cerebral A beta disorders the clinical symptoms are determined to a great extent by the site of inflammation; and (iii) that a brain inflammatory response can explain some poorly understood characteristics of the clinical picture, among others the susceptibility of AD patients to delirium. The present data indicate that inflammatory processes in the brain contribute to the etiology, the pathogenesis, and the clinical expression of AD.

Transgenic mouse models of Alzheimer's disease and amyotrophic lateral sclerosis

Over the past several years, there has been enormous progress in generating transgenic mice that model aspects of human neurodegenerative diseases. These studies build upon the efforts of molecular geneticists who have identified a number of genes that, when mutated, cause familial forms of these diseases. In this review, we focus on the mutations that cause familial forms of Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), and transgenic mouse models that develop clinical and pathological abnormalities resembling those occurring in the human diseases.

Importance of immunological and inflammatory processes in the pathogenesis and therapy of Alzheimer's disease

The contribution of autoimmune processes or inflammatory components in the etiology and pathogenesis of Alzheimer's disease (AD) has been suspected for many years. The presence of antigen-presenting, HLA-DR-positive and other immunoregulatory cells, components of complement, inflammatory cytokines and acute phase reactants have been established in tissue of AD neuropathology. Although these data do not confirm the immune response as a primary cause of AD, they indicate involvement of immune processes at least as a secondary or tertiary reaction to the preexisting pathogen and point out its driving-force role in AD pathogenesis. These processes may contribute to systemic immune response. Thus, experimental and clinical studies indicate impairments in both humoral and cellular immunity in an animal model of AD as well as in AD patients. On the other hand, anti-inflammatory drugs applied for the treatment of some chronic inflammatory diseases have been shown to reduce risk of AD in these patients. Therefore, it seems that anti-inflammatory drugs and other substances which can control the activity of immunocompetent cells and the level of endogenous immune response can be valuable in the treatment of AD patients.

The value of REM sleep parameters in differentiating Alzheimer's disease from old-age depression and normal aging

Pseudodementia as a common trait in elderly depressives presents a major problem in gerontopsychiatry, especially for the differential diagnosis between Old-Age Depression (OAD) and Dementia of the Alzheimer Type (DAT). The present polysomnographic study examined parameters of sleep continuity, sleep architecture, and REM sleep to differentiate DAT from OAD. The investigation was based on the theoretical framework of the cholinergic-aminergic imbalance model of depression, the cholinergic deficit hypothesis of Alzheimer's disease and the reciprocal interaction model of Non-REM/REM sleep regulation, according to which REM sleep parameters should have high discriminative value to differentiate OAD and DAT. We investigated 35 DAT patients, 39 OAD patients and 42 healthy controls for two consecutive nights in the sleep laboratory. The DAT patients were in relatively early/mild stages of the disease, the severity of depression in the OAD group was moderate to severe. Depressed patients showed characteristic 'depression-like' EEG sleep alterations, i.e. a lower sleep efficiency, a higher amount of nocturnal awakenings and decreased sleep stage 2. Sleep continuity and architecture in DAT was less disturbed. Nearly all REM sleep measures differentiated significantly between the diagnostic groups. OAD patients showed a shortened REM latency, increased REM density and a high rate of Sleep Onset REM periods (SOREM), whereas in DAT REM density was decreased in comparison to control subjects. REM latency in DAT was not prolonged as expected. To assess the discriminative power of REM sleep variables a series of discriminant analyses were conducted. Overall, 86% of patients were correctly classified, using REM density and REM latency measures. Our findings suggest that REM density as an indicator of phasic activity appears to be more sensitive as a biological marker for the differential diagnosis of OAD and DAT than REM latency. The results support the role of central cholinergic neurotransmission in REM sleep regulation and the pathogenesis of DAT and OAD.

Spatial, temporal and numeric analysis of Alzheimer changes in the nucleus coeruleus

The distribution of neurofibrillary tangles in the nucleus coeruleus was topographically and quantitatively analyzed. The topographical analysis showed statistically significant differences with regard to the distribution of neurofibrillary tangles in the dorsal-ventral and medial-lateral axes. More neurofibrillary tangles were found to be located in the dorsal and medial regions than in ventral and lateral areas. No significant difference in neurofibrillary tangle content was found between the rostral and the caudal areas of the nucleus coeruleus. Neurofibrillary tangle formation begins in the central parts of the nucleus coeruleus. The total number of neuromelanized neurons in the nucleus coeruleus was determined using a modern, unbiased sampling scheme and related to the cortical stage of Alzheimer's disease-related neurofibrillary changes present. A statistically significant reduction (50%) in nucleus coeruleus neurons was evident only in cases meeting the histopathological criteria for Alzheimer's disease. The extent of reduction in the total number of neurons in the nucleus coeruleus did not correlate with the number of neurofibrillary tangles observed. Our data suggest that despite the relatively early susceptibility of the nucleus coeruleus to neurofibrillary tangle formation, significant neuronal loss appears to occur much later, with an estimated average delay time of at least 25 years. Nonetheless, comparison of the topographical pattern of neurofibrillary tangle formation and cell loss indicates that neuronal loss is tangle-related.

Collateral sprouting of central noradrenergic neurons during aging: histochemical and neurochemical studies in intraocular triple transplants

The sprouting capacity of aged noradrenergic neurons of the brain-stem nucleus locus coeruleus (LC) was examined using intraocular transplants of fetal tissues. Fetal hippocampal tissue (E18) and LC tissue (E15) were transplanted together as a double transplant into the anterior chamber of the eye of young adult Fischer 344 rats. The double transplants were allowed to mature for 14-18 months, after which an additional fetal hippocampal transplant was placed next to the LC graft. The triple transplants were monitored for overall growth and vascularization for an additional 2-6 months. Immunohistochemical examinations showed that both young (2-6 months old) and aged (16-24 months old) hippocampal cografts contained a plexus of thin varicose tyrosine hydroxylase (TH)-immunoreactive fibers extending throughout the grafted hippocampal tissues. However, the aged hippocampal grafts contained a denser uniform plexus of TH-positive fibers compared to the young transplants. Immunohistochemistry with synapsin antibodies demonstrated that both the young and the aged hippocampal transplants contained much higher densities of synaptic elements than the LC grafts. In vivo electrochemical measurements of potassium-evoked overflow of norepinephrine (NE) in the grafts showed that similar amounts of NE overflow were detected in both the young and the aged hippocampal grafts. HPLC-EC measurements of NE levels in the grafts revealed that there were similar amounts of NE in the young and the aged grafts, and the grafts did not contain serotonin or dopamine. In summary, the findings of the present study show that aged LC neurons are capable of undergoing collateral sprouting producing a functional NE neuronal system when introduced to an appropriate young target.

Alzheimer's disease, Lewy body disease and aging: a comparative study of the perforant pathway

The relationship between Alzheimer's disease (AD) and Lewy body disease (LBD) is poorly understood. In AD there is severe loss of neurons comprising the perforant pathway. To assess perforant pathway integrity in pure LBD we compared neuronal counts in layer II of the entorhinal cortex (ERC) in 11 cases of pure LBD that did not meet CERAD pathologic criteria for AD with ERC neuronal counts from seven AD cases with a similar disease duration and six cognitively normal individuals. We counted cell bodies/island in layer II of the ERC using formalin-fixed, paraffin-embedded, tau/cresyl violet-stained sections at the level of the rostral-most body of the hippocampus. There was marked variability in neuronal counts among cases in the LBD group; LBD data overlapped with data from both normal and AD groups. Overall, perforant pathway perikaryal counts in LBD differed significantly from those in AD, but not from those in aged normals (mean perikarya/island = 30.09 +/- 8.95, 7.57 +/- 6.08, and 38.83 +/- 8.98, respectively; F = 26.131, P < 0.001). The percent of remaining neurons bearing neurofibrillary tangles in LBD also overlapped with AD and control groups (16.17 = 13.85%, 87.86 +/- 11.81%, and 24.36 +/- 13.30% of remaining neurons, respectively, F = 65.62, P < 0.001). We conclude that although perforant pathway neuronal loss may occur in LBD, it is more often milder and more variable than that seen in AD.

Direct catecholaminergic-cholinergic interactions in the basal forebrain. I. Dopamine-beta-hydroxylase- and tyrosine hydroxylase input to cholinergic neurons

Immunocytochemical double-labeling techniques were used at the light and electron microscopic levels to investigate whether dopamine-beta-hydroxylase and tyrosine hydroxylase-containing axons contact basal forebrain cholinergic neurons. Dopamine-beta-hydroxylase- and tyrosine hydroxylase-positive fibers and terminals were found in close proximity to cholinergic neurons throughout extensive basal forebrain areas, including the vertical and horizontal limb of the diagonal band nuclei, the sublenticular substantia innominata, bed nucleus of the stria terminalis, ventral pallidum, and ventrolateral globus pallidus. Cholinergic cells in some aspects of the globus pallidus appeared to be contacted by tyrosine hydroxylase-positive but not dopamine-beta-hydroxylase-positive fibers, suggesting dopaminergic input to cholinergic neurons in these regions. Direct evidence for the termination of dopamine-beta-hydroxylase and tyrosine hydroxylase-positive fibers on cholinergic neurons was obtained in electron microscopic double-immunolabeling studies. Using high magnification light microscopic screening, both qualitative and quantitative differences were noted in the catecholaminergic innervation of forebrain cholinergic neurons. For example, while many cholinergic neurons were in close proximity to single dopamine-beta-hydroxylase-positive varicosities, others, particularly those located in the substantia innominatabed nucleus of the stria terminalis continuum, were apparently contacted by labeled fibers in repetitive fashion. The findings of the present study, together with our preliminary biochemical experiments (Zaborszky et al. [1993] Prog. Brain Res. 98:31-49) suggest that catecholaminergic afferents can differentially modulate forebrain cholinergic neurons. Such interactions may be important in learning and memory processes, and their perturbations may contribute to the cognitive decline seen in aging and in disorders such as Alzheimer's and Parkinson's diseases.

Selegiline in treatment of behavioral and cognitive symptoms of Alzheimer disease

OBJECTIVE

To evaluate the effects of selegiline on behavioral and cognitive symptoms of patients with Alzheimer disease.

DATA SOURCES

An English-language MEDLINE search (1982-1995) was used to identify the review articles and human clinical trials discussed in this article.

STUDY SELECTION

Double- and single-blind and open-label trials were reviewed. Studies were also reviewed if selegiline was evaluated comparatively with other agents. Review articles were used for background information.

DATA EXTRACTION

Data were evaluated from human studies. Studies were critiqued on the basis of design, methodology, duration, sample size, and the degree to which neuropsychological tests used in each study were compared.

DATA SYNTHESIS

Selegiline is a selective, irreversible inhibitor of monoamine oxidase type B. Eight of 11 controlled trials showed selegiline had a positive effect on cognition (e.g., word fluency, delayed recall, total recall). Two of 5 controlled trials evaluating selegiline's effect on behavior (e.g., anxiety, tension, excitement, depression) showed a positive effect.

CONCLUSIONS

The role of selegiline remains to be determined by large well-controlled long-term clinical trials. Selegiline may be a useful agent in managing behavioral and cognitive symptomatology associated with Alzheimer disease. Given that the management of Alzheimer disease is symptomatic and no standard treatment exists, selegiline should be considered among the various options.

The basis for behavioural disturbances in dementia

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The messenger RNAs for the N-methyl-D-aspartate receptor subunits show region-specific expression of different subunit composition in the human brain

The expression of the messenger RNAs encoding N-methyl-D-aspartate receptor subunits in neurologically normal post-mortem human brain was studied by in situ hybridization. In the caudate, putamen and nucleus accumbens strong hybridization signals were observed for N-methyl-D-aspartate R1-1 messenger RNA but much weaker signals for N-methyl-D-aspartate R1-3 and N-methyl-D-aspartate R1-4, N-Methyl-D-aspartate R1-2 was not detectable. N-methyl-D-aspartate R2B was the only N-methyl-D-aspartate R2 subunit detected in these nuclei. In the hippocampus the messenger RNAs for both N-methyl-D-aspartate R1-1 and N-methyl-D-aspartate R1-4 were strongly expressed in the dentate gyrus, CA3-CA1 pyramidal cells, subiculum, entorhinal cortex and perirhinal cortex. Much lower expression was seen for N-methyl-D-aspartate R1-2 and N-methyl-D-aspartate R1-3. The messenger RNAs for both N-methyl-D-aspartate R2A and N-methyl-D-aspartate R2B, but not N-methyl-D-aspartate R2C, subunits were expressed in the hippocampus. In the temporal cortex all N-methyl-D-aspartate RI isoforms were expressed (N-methyl-D-aspartate R1-1 and N-methyl-D-aspartate R1-4 being the most abundant) and N-methyl-D-aspartate R2A and N-methyl-D-aspartate R2B but not N-methyl-D-aspartate R2C were also moderately expressed. In the brain stem N-methyl-D-aspartate R1-4 was strongly expressed in various nuclei including the locus coeruleus, nucleus centralis superior and deep pontine nuclei. Only weak expression was seen for N-methyl-D-aspartate RI-1 and N-methyl-D-aspartate R1-3 but not N-methyl-D-aspartate RI-2; of the N-methyl-D-aspartate R2 subunits only N-methyl-D-aspartate R2C was found to be expressed in these nuclei. In the cerebellum all the N-methyl-D-aspartate I isoforms were expressed (mostly N-methyl-D-aspartate R1-4) in the Purkinje layer which also expressed N-methyl-D-aspartate R2A and N-methyl-D-aspartate R2C. In the molecular layer cells were found expressing N-methyl-D-aspartate R1-4 and N-methyl-D-aspartate R2B and cells in the granule layer were found to express N-methyl-D-aspartate R1-1, N-methyl-D-aspartate R1-3 and N-methyl-D-aspartate R1-4 and N-methyl-D-aspartate R2C only. Preliminary studies indicated that the messenger RNA for the N-methyl-D-aspartate R2D subunit was not expressed in the above areas of brain. These results give the first demonstration of the distribution of N-methyl-D-aspartate receptor subunit messenger RNAs in the human brain. The region-specific expression of subunit combinations suggests a heterogeneity of N-methyl-D-aspartate receptors with diverse physiological/pathophysiological roles and provides a rationale for the development of discriminatory N-methyl-D-aspartate receptor antagonists to target selective neuronal populations.

Double-blind placebo-controlled study of velnacrine in Alzheimer's disease

The present study assessed the safety and efficacy of the cholinesterase inhibitor, velnacrine, for treating the cognitive symptoms of Alzheimer's disease. Patients (N = 236) meeting NINCDS-ADRDA criteria for Alzheimer's disease entered a double-blind, placebo-controlled dose-ranging protocol (30, 75, 150, 225 mg/day each for one week) to identify velnacrine responders (> or = four point improvement on the cognitive subscale of the Alzheimer's Disease Assessment Scale [ADAScog]). After a two week drug washout, velnacrine responders were randomly assigned to their best velnacrine dose or placebo in a six week dose-replication protocol employing the ADAScog and the Clinical Global Improvement scale as primary outcome measures. During dose-replication, intent-to-treat analysis revealed that velnacrine patients scored significantly better than placebo patients on the ADAScog after two (p < 0.004), four (p < 0.025) and six (p < 0.001) weeks of treatment. No significant treatment effect on Clinical Global Improvement scores was observed. The primary adverse event was an asymptomatic elevation of liver transaminases found among 28% of the 236 treated patients. Cholinergic side effects including diarrhea (14%), nausea (11%) and vomiting (5%) were observed and 8% of patients experienced skin rash. The present study identified a subgroup of Alzheimer's patients who demonstrated a significant, but modest, improvement during velnacrine treatment on structured cognitive testing.

Synthesis and structure-activity relationships of N-propyl-N-(4-pyridinyl)-1H-indol-1-amine (besipirdine) and related analogs as potential therapeutic agents for Alzheimer's disease

A series of novel N-(4-pyridinyl)-1H-indol-1-amines and other heteroaryl analogs was synthesized and evaluated in tests to determine potential utility for the treatment of Alzheimer's disease. From these compounds, N-propyl-N-(4-pyridinyl)-1H-indol-1-amine (besipirdine, 4c) was selected for clinical development based on in-depth biological evaluation. In addition to cholinomimetic properties based initially on in vitro inhibition of [3H]quinuclidinyl benzilate binding, in vivo reversal of scopolamine-induced behavioral deficits, and subsequently on other results, 4c also displayed enhancement of adrenergic mechanisms as evidenced in vitro by inhibition of [3H] clonidine binding and synaptosomal biogenic amine uptake, and in vivo by reversal of tetrabenazine-induced ptosis. The synthesis, structure-activity relationships for this series, and the biological profile of 4c are reported.

GDNF prevents degeneration and promotes the phenotype of brain noradrenergic neurons in vivo

The locus coeruleus (LC), the main noradrenergic center in the brain, participates in many neural functions, as diverse as memory and motor output, and is severely affected in several neurodegenerative disorders of the CNS. GDNF, a neurotrophic factor initially identified as dopaminotrophic, was found to be expressed in several targets of central noradrenergic neurons in the adult rat brain. Grafting of genetically engineered fibroblasts expressing high levels of GDNF prevented > 80% of the 6-hydroxydopamine-induced degeneration of noradrenergic neurons in the LC in vivo. Moreover, GDNF induced a fasciculated sprouting and increased by 2.5-fold both tyrosine hydroxylase levels and the soma size of lesioned LC neurons. These findings reveal a novel and potent neurotrophic activity of GDNF that may have therapeutic applications in neurodegenerative disorders affecting central noradrenergic neurons, such as Alzheimer's, Parkinson's, and Huntington's diseases.

Locus coeruleus cell loss in the aging human brain: a non-random process

Quantitative neuroanatomical techniques were used to determine whether with aging there is random or systematic loss of locus coeruleus (LC) neurons in the human brain. The cells were identified by immunohistochemical staining for the catecholaminergic enzyme tyrosine hydroxylase and/or by neuromelanin pigment content. Cell locations were mapped, using computer imaging procedures, in horizontal sections spaced 0.5 to 0.8 mm throughout the rostrocaudal extent of the nucleus in 17 cases, from 1 to 104 years of age. Neuromelanin pigment accumulated within the neurons with aging. In brains less than 25 years of age there were many fewer pigment-containing neurons than tyrosine hydroxylase-containing neurons; however, by the fifth decade the number of cells identified by the two markers was comparable. From the first to the tenth decade of life there is over a 50% loss of LC neurons: in four cases from "young" individuals (1-28 years of age) there were 21,084 +/- 653 tyrosine hydroxylase immunostained cells (mean +/- standard error of the mean) on one side of the brain; in seven cases from "old" individuals (60-82 years of age) there were 16,502 +/- 921 pigment-containing cells; and in the three cases from the "oldest" individuals (103-104 years of age) there were 9,493 +/- 1,236 pigment-containing neurons. In both the "old" and "oldest" groups, compared to the "young," there was significantly greater loss of rostral cells than caudal cells. These data indicate a systematic loss of cells such that the rostral, forebrain-projecting neurons decrease in number with aging to a greater extent than do the caudal, spinal cord-projecting neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer's-associated phospho-tau epitope in human neuroblastoma cell cultures: up-regulation by fibronectin and laminin

Alzheimer's-afflicted neurons contain phosphorylated forms of tau that are not present in healthy adults. these can be recognized with great specificity by monoclonal antibodies such as paired helical filament-1 (PHF-1) [Greenberg S. G. and Davies P. (1990) Proc. natn. Acad. Sci. U.S.A. 87, 5827-5831; Greenberg S. G. et al. (1992) J. biol. Chem. 267, 564-569]. The PHF-1 phospho-tau epitope is also present in immature neurons undergoing axodendritic differentiation [Pope W. B. et al. (1993) Expl Neurol. 120, 106-113]. Analogous to its presence in immature neurons, we report here that the PHF-1 tau epitope spontaneously occurs in the human neuroblastoma cell line SHSY5Y, where its level can be regulated by differentiation and by molecules found in the extracellular matrix. Confocal immunofluorescence studies showed PHF-1 epitope to be constitutively expressed in the somatic cytoplasm as well as in short neurites typical of undifferentiated SHSY5Y cells. Induction of differentiation with retinoic acid produced cells with a neuronal morphology and a redistribution of the expression of PHF-1 tau in the long neurites. Protracted exposure to retinoic acid decreased the levels of PHF-1 immunofluorescence without a loss of neurites, similar to the developmental down-regulation seen in situ. The effects of retinoic acid on PHF-1 immunofluorescence were modifiable by fibronectin, which can be released by some neuroblastoma cell lines [Ciccarone V. et al. (1989) Cancer Res. 49, 219-225; Yoshihara T. et al. (1992) Int. J. Cancer 51, 620-626]. Exogenous human fibronectin caused a marked up-regulation of PHF-1 immunofluorescence. Quantitative analysis of 15 multicellular areas, from six different cultures, per experimental condition showed a 16-fold increase compared to untreated controls. Up-regulation by fibronectin was also evident in undifferentiated cells. Cell counts indicated no proliferative effects of the fibronectin under the conditions used. Laminin also caused an increase of PHF-1 tau in retinoic acid-treated cells. Data obtained from immunoblots verified the results observed with immunofluorescence. The data show that the PHF-1 tau epitope is spontaneously expressed by non-degenerating human neuroblastoma cells, down-regulated by cellular differentiation, induced by retinoic acid and up-regulated by the extracellular matrix components fibronectin and laminin. One explanation of the data is that fibronectin maintains a population of SHSY5Y cells in a biochemical state of differentiation in which PHF-1 tau is expressed.(ABSTRACT TRUNCATED AT 400 WORDS)

Dendritic reorganisation in the basal forebrain under degenerative conditions and its defects in Alzheimer's disease. III. The basal forebrain compared with other subcortical areas

The distribution of the reticular neuronal type in the human brain and its involvement in both degeneration and dendritic reorganisation under the conditions of ageing, Korsakoff's disease (KD), Alzheimer's disease (AD), and Parkinson's disease (PD) was comparatively investigated after Golgi impregnation. Reticular neurones are distributed throughout different areas along the brain axis. The cholinergic basal forebrain nuclei, i.e., the basal nucleus of Meynert, the nucleus of the diagonal band, and the medial septal nucleus form the most rostral part of this network of "open nuclei," which is collectively referred to as the "reticular core." Reticular neurones of the following areas were quantitatively investigated by a computer-based three-dimensional analysis: caudate nucleus, globus pallidus, medial septal nucleus, nucleus of the vertical limb of the diagonal band, basal nucleus, medial amygdaloid nucleus, reticular thalamic nucleus, lateral hypothalamic area, subthalamic nucleus, substantia nigra, locus coeruleus, pedunculopontine tegmental nucleus, and raphe magnus nucleus. There are three major findings. First, neurones that were found to be susceptible to degeneration in AD were largely part of the same neuronal populations prone to degeneration during ageing, in KD and PD. Thus, areas could be classified according to their overall degree of vulnerability under the present degenerative conditions as being highly vulnerable (basal forebrain nuclei, caudate nucleus, locus coeruleus), moderately vulnerable (medial amygdaloid nucleus, raphe magnus nucleus, lateral hypothalamic area, substantia nigra, pedunculopontine tegmental nucleus), or marginally vulnerable (globus pallidus, subthalamic nucleus, reticular thalamic nucleus). Second, neuronal populations that are particularly vulnerable to degenerative changes show a high degree of structural plasticity. Third, the degree of this dendritic plasticity is inversely related to the complexity of dendritic arborisation of the neurone. It is concluded that the sparsely ramified reticular type of neurone forms a pool of pluripotent neurones that have retained their plastic capacity throughout life, which makes them vulnerable to a variety of perturbations.

Effects of SDZ ENA 713, novel acetyl cholinesterase inhibitor, on learning of rats with basal forebrain lesions

1. The effects of SDZ ENA 713, a novel acetyl cholinesterase inhibitor, on rat learning was studied using a step-down avoidance paradigm. 2. Injection of ibotenic acid into the caudolateral part of the basal forebrain (BF) innervating cholinergic neurons to the cerebral cortex, resulted in an increase in the number of trials required to obtain 300-second-latency, and also a decrease in the latency period after attaining 300-second-latency. 3. It is shown that the BF-lesioned rats are impaired in both acquisition and retention of learning. 4. Intraperitoneal injection of 0.10-0.05 mg/kg/day SDZ ENA 713 to the BF-lesioned rats showed amelioration of the learning impairment, with a decreased number of trials required to obtain 300-second-latency as well as an increase in the latency time after repeated training. 5. These results indicate that SDZ ENA 713 improves acquisition and retention impairment in BF-lesioned rats, and that this drug may be useful for demented patients with cholinergic dysfunction, such as Alzheimer's disease.

Absolute number and size of pigmented locus coeruleus neurons in young and aged individuals

Significant loss of noradrenergic neurons of the locus coeruleus in aging and Alzheimer's disease has been reported. The interpretation of these analyses, however, is problematic because of the model- and assumption-based nature of conventional sampling and estimation techniques. In the present study, unbiased stereological methods were used to estimate the total number and mean cell volume of pigmented neurons of the locus coeruleus in the brains of young and aged nondemented persons. No side-to-side differences are seen, and there is no change in pigmented cell number or size in the locus coeruleus of nondemented older persons as compared with that of young individuals. In light of previous studies that show severe locus coeruleus cell loss in Alzheimer's disease, these data support further critical investigations into the possible protective role of noradrenaline in normal cognitive functions and emphasize the importance of avoiding methodological bias in quantitative neuroanatomical studies.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

Chronic administration of flumazenil increases life span and protects rats from age-related loss of cognitive functions: a benzodiazepine/GABAergic hypothesis of brain aging

Under barrier condition and with ad lib access to food and water, 20 Fischer-344 rats were chronically treated for 10 months with the benzodiazepine (BDZ) antagonist, flumazenil (FL; 4 mg/kg/day in drinking water acidified to pH = 3.0), beginning at the age of 13 months, while the group of 20 control age-matched rats received plain acidified water. The life span of the first 8 deceased rats treated with FL was significantly longer than that of the first 8 deceased rats in the age-matched control group. In tests for spontaneous ambulation and exploratory behavior in the Holeboard apparatus, conducted during the 3rd and the 8th month of treatment, the FL group, relative to controls, had significantly higher scores for the ambulation and exploratory behavior. In tests for unrewarded spontaneous alternation in the T maze, conducted at days 7, 39, 42, and 47 through 54 after drug withdrawal, i.e., at the age of 24-25 months, the FL-exposed group, compared to age-matched controls, showed a significantly higher percent of alternating choices, a behavior that was statistically comparable to that of the "young" 6-month-old controls. In the Radial Maze tests conducted 2 months after drug withdrawal, the FL group made significantly less "working memory" errors and "reference memory" errors, relative to the age-matched 25-month-old control group, a performance that was comparable to that of the young 7-month-old control group. In conclusion, chronic FL significantly protected rats from age-related loss of cognitive functions. It is postulated that the age-related alterations in brain function may be attributable to the negative metabolic/trophic influences of the "endogenous" benzodiazepine (BDZ) ligands and/or those ingested with food. A BDZ/GABAergic hypothesis of brain aging has been formulated which assumes that age-related and abnormally strong BDZ/GABAergic influences promote neurodegeneration by suppressing trophic functions of the aminergic and peptidergic neurons through opening of chloride channels in soma membrane and axon terminals, causing excessive hyperpolarizing and depolarizing inhibition, respectively. The review of human clinical and animal data indicates that FL has nootropic actions by enhancing vigilance cognitive and habituation processes.