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

Detoxification Improves Multidomain Cognitive Dysfunction in High-Dose Benzodiazepine Abusers

Purpose

High-dose benzodiazepines (BZDs) abuse has been documented to cause multidomain cognitive dysfunction. We explored whether cognitive abnormalities to high-dose BZD abuse might be reversed by detoxification with slow subcutaneous infusion of flumazenil.

Methods

We recruited 96 patients consecutively admitted to the Department of Internal Medicine, Addiction Medicine Unit, Verona University Hospital, Italy for detoxification from high-dose BZD dependence. After selection for inclusion and exclusion criteria, 50 patients (23 men, 27 women; age 42.7 ± 10.3 years) were included. They underwent a comprehensive neuropsychological battery to explore verbal memory, visuospatial memory, working memory, attention, and executive functions 28–30 days prior to admission for detoxification (T0) and at the end of detoxification, i.e., 7 days after admission (T1). A group of 50 healthy adults (24 men, 26 women; mean age 44.5 ± 12.8 years) matched for age, sex, and education served as controls.

Results

At T0, patients scored significantly worse than healthy controls in all the neuropsychological tests. Depression and anxiety scores were associated with impaired verbal memory at T0 in patients. T1–T0 comparison showed improved performances in all neuropsychological tests after the end of detoxification in patients.

Conclusion

We confirmed that all neuropsychological domains were significantly and profoundly impaired by high-dose BZD abuse and documented that cognitive abnormalities improved after detoxification with slow subcutaneous infusion of flumazenil.

In vivo molecular imaging of the GABA/benzodiazepine receptor complex in the aged rat brain

The GABA-ergic system, known to regulate neural tissue genesis during cortical development, has been postulated to play a role in cerebral aging processes. Using in vivo molecular imaging and voxel-wise quantification, we aimed to assess the effects of aging on the benzodiazepine (BDZ) recognition site of the GABA(A) receptor. To visualize BDZ site availability, [(11)C]-flumazenil microPET acquisitions were conducted in young and old rats. The data were analyzed and region of interest analyses were applied to validate the voxel-wise approach. We observed decreased [(11)C]-flumazenil binding in the aged rat brains in comparison with the young control group. More specifically, clusters of reduced radioligand uptake were detected in the bilateral hippocampus, cerebellum, midbrain, and bilateral frontal and parieto-occipital cortex. Our results support the pertinence of voxel-wise quantification in the analysis of microPET data. Moreover, these findings indicate that the aging process involves declines in neural BDZ recognition site availability, proposed to reflect alterations in GABA(A) receptor subunit polypeptide expression.

Over-inhibition: a model for developmental intellectual disability

Developmental intellectual disability (DID) is a daunting societal problem. Although tremendous progress has been made in defining the genetic causes of DID, therapeutic strategies remain limited. In particular, there is a marked absence of a unified approach to treating cognitive impairments associated with DID. Here, we suggest that the brain in many DID-related disorders is subject to a basic imbalance in neuronal activity, with an increased contribution of inhibition to neural circuits. This over-inhibition, in turn, is predicted to lead to deficits in synaptic plasticity and learning and memory. We further discuss possibilities for pharmacological intervention in DID, focusing on the concept of drug-induced 'therapeutic neuroadaptation' as a means of stably enhancing constitutive circuit excitability and cognition over time.

The ameliorating effect of oroxylin A on scopolamine-induced memory impairment in mice

Oroxylin A is a flavonoid and was originally isolated from the root of Scutellaria baicalensis Georgi., one of the most important medicinal herbs in traditional Chinese medicine. The aim of this study was to investigate the ameliorating effects of oroxylin A on memory impairment using the passive avoidance test, the Y-maze test, and the Morris water maze test in mice. Drug-induced amnesia was induced by administering scopolamine (1 mg/kg, i.p.) or diazepam (1 mg/kg, i.p.). Oroxylin A (5 mg/kg) significantly reversed cognitive impairments in mice by passive avoidance and the Y-maze testing (P<.05). Oroxylin A also improved escape latencies in training trials and increased swimming times and distances within the target zone of the Morris water maze (P<.05). Moreover, the ameliorating effects of oroxylin A were antagonized by both muscimol and diazepam (0.25 mg/kg, i.p., respectively), which are GABA(A) receptor agonists. Furthermore, oroxylin A (100 microM) was found to inhibit GABA-induced inward Cl(-) current in a single cortical neuron. These results suggest that oroxylin A may be useful for the treatment of cognitive impairments induced by cholinergic dysfunction via the GABAergic nervous system.

Age-dependent changes of pyridoxal phosphate synthesizing enzymes immunoreactivities and activities in the gerbil hippocampal CA1 region

In the present study, age-related changes of pyridoxal 5'-phosphate (PLP) synthesizing enzymes, pyridoxal kinase (PLK) and pyridoxine 5'-phosphate oxidase (PNPO), their protein contents and activities were examined in the gerbil hippocampus proper. Significant age-dependent changes in PLK and PNPO immunoreactivities were found in the CA1 region, but not in the CA2/3 region. In the postnatal month 1 (PM 1) group, PLK and PNPO immunoreactivities were detected mainly in the stratum pyramidale of the CA1 region. PLK and PNPO immunoreactivities and their protein contents were highest in the PM 6 group, showing that many CA1 pyramidal cells had strong PLK and PNPO immunoreactivities. Thereafter, PLK and PNPO immunoreactivities started to decrease and were very low at PM 24. Alterations in the change patterns in protein contents and total activities of PLK and PNPO corresponded to the immunohistochemical data, but their specific activities were not altered in any experimental group. Based on double immunofluorescence study, PLK and PNPO immunoreactive cells in the strata oriens and radiatum were identified as GABAergic cells. Therefore, decreases of PLK and PNPO in the hippocampal CA1 region of aged brains may be involved in aging processes related with gamma-aminobutyric acid (GABA) function.

Age-related changes of γ-aminobutyric acid transaminase immunoreactivity in the hippocampus and dentate gyrus of the Mongolian gerbil

We investigated the age-related changes of gamma-aminobutyric acid transaminase (GABA-T, a GABA degradation enzyme) in the hippocampus and dentate gyrus of the gerbil at postnatal month 1 (PM 1), PM 3, PM 6, PM 12, and PM 24. Age-related changes of GABA-T immunoreactivity were distinct in the hippocampal CA1 region and in the dentate gyrus. GABA-T immunoreactivity was weak at PM 1, but at PM 3, it had increased significantly, and then increased further. Between PM 6 and PM 12, strong GABA-T immunoreactivity was found in nonpyramidal cells (GABAergic) in the stratum pyramidale of the CA1 region, and at PM 6, strong GABA-T immunoreactivity was found in neurons of the dentate gyrus subgranular zone. At PM 24, CA1 pyramidal cells showed strong GABA-T immunoreactivity. Western blot analysis showed a pattern of GABA-T expression similar to that shown by immunohistochemistry at various ages. In conclusion, our results suggest that the age-related changes of GABA-T provide important information about the aged brain with GABA dysfunction.

Age-related modifications of the morphological organization of pituicytes are associated with alteration of the GABAergic and dopaminergic innervation afferent to the neurohypophysial lobe

Ageing is known to induce a marked activation of astrocytes within various regions of the central nervous system. To date, the age-related factors responsible for these modifications are unknown. The neural lobe of the hypophysis (NL) is a particular brain region which does not contain neurons but does contain specialized astrocytes, called pituicytes, and numerous terminals of afferent axons, including (i) peptidergic neurohypophysial axons which terminate on the NL blood vessels, and (ii) axons containing both gamma amino-butyric acid (GABA) and dopamine (DA) which form contacts with pituicytes. Because evidence has recently been provided that GABA signalling mediates the morphological organization of astrocytes, the present study was designed to determine whether modifications of pituicytes during ageing were associated with modifications of the GABAergic axons innervating the NL. We show here that, in adult rats, GABA/DA axons form preferential synaptic-like contacts with pituicytes which express both GABAA and D2 dopamine receptors. We then show that, during ageing, pituicytes undergo dramatic modifications of their morphology, correlatively with marked modifications of the GABA/DA fibres innervating the NL. Lastly, in vitro experiments indicate that modifications of the morphology of pituicytes similar to those observed during ageing were obtained by incubating isolated NL of adult rats with a GABAA receptor agonist and/or a D2 dopamine receptor antagonist, whereas inverse modifications were observed when NL of aged rats were incubated with a GABAA receptor antagonist and a D2 dopamine receptor agonist. Taken together, these data suggest that the age-related morphological changes of pituicytes result from the alteration of the GABA/DAergic innervation of the NL.

A novel dehydroepiandrosterone analog improves functional recovery in a rat traumatic brain injury model

The purpose of this study was to investigate the efficacy of a novel steroid, fluasterone (DHEF, a dehydroepiandrosterone (DHEA) analog), at improving functional recovery in a rat model of traumatic brain injury (TBI). The lateral cortical impact model was utilized in two studies of efficacy and therapeutic window. DHEF was given (25 mg/kg, intraperitoneally) at the initial time point and once a day for 2 more days. Study A included four groups: sham injury, vehicle treated (n = 22); injured, vehicle treated (n = 30); injured, pretreated (5-10 min prior to injury, n = 24); and injured, posttreated (initial dose 30 min postinjury, n = 15). Study B (therapeutic window) included five groups: sham injury, vehicle treated (n = 17); injured, vehicle treated (n = 26); and three posttreatment groups: initial dose at 30 min (n = 18), 2 h (n = 23), or 12 h (n = 16) postinjury. Three criteria were used to grade functional recovery. In study A, DHEF improved beam walk performance both with pretreatment (79%) and 30-min posttreatment group (54%; p < 0.01, Dunnett vs. injured vehicle). In study B, the 12-h posttreatment group showed a 97% improvement in beam walk performance (p < 0.01, Dunnett). The 30-min and 12-h posttreatment groups showed a decreased incidence of falls from the beam, which reached statistical significance (p < 0.05, Dunnett). Tests of memory (Morris water maze) and neurological reflexes both revealed significant improvements in all DHEF treatment groups. In cultured rat mesangial cells, DHEF (and DHEA) potently inhibited interleukin-1beta-induced cyclooxygenase-2 (COX2) mRNA and prostaglandin (PGE2) production. In contrast, DHEF treatment did not alter injury-induced COX2 mRNA levels in the cortex or hippocampus. However, DHEF (and DHEA) relaxed ex vivo bovine middle cerebral artery preparations by about 30%, with an IC(50) approximately 40 microM. This was a direct effect on the vascular smooth muscle, independent of the endothelial cell layer. Fluasterone (DHEF) treatments improved functional recovery in a rat TBI model. Possible mechanisms of action for this novel DHEA analog are discussed. These findings suggest an exciting potential use for this agent in the clinical treatment of traumatic brain injury.

Gabaergic signaling mediates the morphological organization of astrocytes in the adult rat forebrain

Previous studies have provided evidence that the morphological organization of immature astrocytes is influenced by the inhibitory neuronal transmitter gamma amino-butyric acid (GABA). The present study was designed to determine whether the occurrence of differential organization of mature astrocytes throughout various regions of the adult brain is related to differential GABAergic signaling. For this we first used Western blotting and high-performance liquid chromatography to quantify the levels of the astrocytic protein glial fibrillary acidic protein (GFAP) and GABA, respectively, within the same tissue punches taken from different forebrain regions of the adult rat, as well as immunocytochemistry for GFAP, GABA, or glutamate decarboxylase to visualize the morphological organization of astrocytes and of GABAergic axons in these regions. These data indicate that GFAP and GABA contents are correlated throughout the different forebrain regions analyzed, and that the regions containing the highest densities in GABAergic terminals are those that contain astrocytes exhibiting the highest degree of stellation. Secondly, we chronically increased GABAergic signaling in vivo by the systemic administration of an inhibitor of GABA transaminase or by the intracerebroventricular infusion of muscimol, a potent agonist of GABA(A) receptors. Our data show that in both cases, the GFAP content of the different forebrain regions is significantly augmented, in close association with a marked increase in the number of astrocytic processes and with their degree of branching. Taken together, these data strongly suggest that GABAergic signaling mediates the morphological organization of astrocytes and their expression of GFAP in the adult brain.

Plasticity of GABA(a) system during ageing: focus on vestibular compensation and possible pharmacological intervention

The lesion of the vestibular end organ evokes static and dynamic symptoms, which spontaneously regress during a complex process known as 'vestibular compensation'. Vestibular compensation is age-dependent and involves several transmitter-identified pathways in the central nervous system. In this paper we studied the time course of vestibular compensation in adult (3 months) and old (24 months) rats and correlated behavioral recovery with modifications of glutamic acid decarboxylase (GAD) mRNA expression and benzodiazepine receptor density in different brain areas. Compensation in adult rats was complete 28 days after hemilabyrinthectomy, whereas old rats still showed significant behavioral impairment. A higher GABAergic tone was found in old rats, as indicated by higher benzodiazepine receptor density in lateral vestibular nucleus and higher mRNA level for glutamic acid decarboxylase in cerebral cortex and medial vestibular nucleus. In adult, compensated rats, benzodiazepine receptor density in the vestibular nuclei was normal 28 days after lesion, whereas GAD mRNA level was higher in anterior cingulate cortex, only. On the contrary, these parameters were still altered in anterior cingulate and somatosensory cortex, basal ganglia, vestibular nuclei and cerebellum in old rats 28 days after vestibular lesion. We also evaluated the effect of the ergoline derivative nicergoline on behavioral and neurochemical correlates of vestibular compensation in old rats. Nicergoline treatment attenuated the severity of oculomotor and postural symptoms after vestibular lesion and reversed most of these age- and lesion-induced alterations in GAD mRNA expression. Thus, lesion-related alterations of the GABAergic transmission and behavioral profile after vestibular lesion are age-dependent.

Sex differences in neurochemical markers that correlate with behavior in aging mice

Sex differences in neurochemical markers that correlate with behavior in aging mice NEUROBIOL AGING. We examined whether the enzymatic activities of choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) were altered similarly with age in male and female mice, and whether these changes were correlated with age-related alterations in memory and anxiety. ChAT and GAD activities were measured in neocortex, hippocampus, and striatum of behaviorally characterized male and female C57BL/6 mice (5, 17, and 25 months). Generally, ChAT activity was increased, and GAD activity decreased, with age. However, disparate changes were revealed between the sexes; activities of both enzymes were decreased in 17-month males, whereas alterations in females were not observed until 25-months. Furthermore, enzyme-behavior correlations differed between the sexes; in males, ChAT activity was related to one behavioral task, whereas in females, activities of both enzymes were correlated with multiple tasks. Significant enzyme-behavior correlations were most evident at 17 months of age, likely the result of behavioral and enzymatic sex differences at this age. These data represent the first comprehensive report illustrating differential alterations of ChAT and GAD activities in aging male and female mice.

Sulfated and unsulfated steroids modulate gamma-aminobutyric acidA receptor function through distinct sites

Sulfated and unsulfated neurosteroids such as pregnenolone sulfate, dehydroepiandrosterone sulfate (DHEAS), pregnanolone, and allopregnanolone, modulate ionotropic amino acid neurotransmitter receptors, and may function as endogenous neuromodulators. The gamma-aminobutyric acid type A (GABAA) receptor exhibits both negative and positive modulation by neurosteroids, but the interaction between negative and positive modulators is not well-understood. For a number of neuroactive steroids, sulfation at C-3 reverses the direction of modulation from positive to negative, suggesting that sulfation could be an important control point for the activity of endogenous neurosteroids. Modulation by endogenous and synthetic steroids of the response to exogenous or synaptically released GABA was examined in primary chick spinal cord and rat hippocampal neurons, and in Xenopus laevis oocytes expressing alpha1beta2gamma2S GABAA receptors. Inhibitory activity is retained when hemisuccinate is substituted for sulfate at C-3, suggesting that it is the negative charge, rather than the sulfate group, that confers inhibitory efficacy. The interaction between steroid negative and positive modulators is not competitive, indicating that steroid negative and positive modulators act through distinct sites. Some steroids, such as 11-ketopregnenolone sulfate, appear to act at both negative and positive modulatory sites, as indicated by an 'off-response' upon washout. A similar off-response is also observed after co-application of the negative modulator DHEAS and the positive modulator allopregnanolone. The observation that simultaneous application of sulfated and unsulfated steroids, such as DHEAS and allopregnanolone, act at distinct sites implies that steroid negative and positive modulators can act independently or coordinately to regulate GABA-mediated inhibition in the central nervous system.

GABAergic deafferentation hypothesis of brain aging and Alzheimer's disease revisited

Considering the mechanisms responsible for age- and Alzheimer's disease (AD)-related neuronal degeneration, little attention was paid to the opposing relationships between the energy-rich phosphates, mainly the availability of the adenosine triphosphate (ATP), and the activity of the glutamic acid decarboxylase (GAD), the rate-limiting enzyme synthesizing the gamma-amino butyric acid (GABA). Here, it is postulated that in all neuronal phenotypes the declining ATP-mediated negative control of GABA synthesis gradually declines and results in age- and AD-related increases of GABA synthesis. The Ca2+-independent carrier-mediated GABA release interferes with Ca2+-dependent exocytotic release of all transmitter-modulators, because the interstitial (ambient) GABA acts on axonal preterminal and terminal varicosities endowed with depolarizing GABA(A)-benzodiazepine receptors; this makes GABA the "executor" of virtually all age- and AD-related neurodegenerative processes. Such a role of GABA is diametrically opposite to that in the perinatal phase, when the carrier-mediated GABA release, acting on GABA(A)/chloride ionophore receptors, positively controls chemotactic migration of neuronal precursor cells, has trophic actions and initiates synaptogenesis, thereby enabling retrograde axonal transport of target produced factors that trigger differentiation of neuronal phenotypes. However, with advancing age, and prematurely in AD, the declining mitochondrial ATP synthesis unleashes GABA synthesis, and its carrier-mediated release blocks Ca2+-dependent exocytotic release of all transmitter-modulators, leading to dystrophy of chronically depolarized axon terminals and block of retrograde transport of target-produced trophins, causing "starvation" and death of neuronal somata. The above scenario is consistent with the following observations: 1) a 10-month daily administration to aging rats of the GABA-chloride ionophore antagonist, pentylenetetrazol, or of the BDZ antagonist, flumazenil (FL), each forestalls the age-related decline in cognitive functions and losses of hippocampal neurons; 2) the brains of aging rats, relative to young animals, and the postmortem brains of AD patients, relative to age-matched controls, show up to two-fold increases in GABA synthesis; 3) the aging humans and those showing symptoms of AD, as well as the aging nonhuman primates and rodents--all show in the forebrain dystrophic axonal varicosities, losses of transmitter vesicles, and swollen mitochondria. These markers, currently regarded as the earliest signs of aging and AD, can be reproduced in vitro cell cultures by 1 microM GABA; the development of these markers can be prevented by substituting Cl- with SO4(2-); 4) the extrasynaptic GABA suppresses the membrane Na+, K+-ATPase and ion pumping, while the resulting depolarization of soma-dendrites relieves the "protective" voltage-dependent Mg2+ control of the N-methyl-D-aspartate (NMDA) channels, thereby enabling Ca2+-dependent persistent toxic actions of the excitatory amino acids (EAA); and 5) in whole-cell patch-clamp recording from neurons of aging rats, relative to young rats, the application of 3 microM GABA, causes twofold increases in the whole-cell membrane Cl- conductances and a loss of the physiologically important neuronal ability to desensitize to repeated GABA applications. These age-related alterations in neuronal membrane functions are amplified by 150% in the presence of agonists of BDZ recognition sites located on GABA receptor. The GABA deafferentation hypothesis also accounts for the age- and AD-related degeneration in the forebrain ascending cholinergic, glutamatergic, and the ascending mesencephalic monoaminergic system, despite that the latter, to foster the distribution-utilization of locally produced trophins, evolved syncytium-like connectivities among neuronal somata, axon collaterals, and dendrites, to bidirectionally transport trophins. (ABSTRACT TRUNCATED)

Depression: immunological resignation of the will to live?

Evolution is assumed to promote the survival of the fittest by the greater success of the reproductive potential of those with the characteristics most suited to their environment. Little thought is given to how those least adapted fail to survive to reproduce. If the species, rather than the individual, has a drive to adaptation and survival, there should be a specific mechanism for those least adapted to withdraw from life. The immunological changes accompanying depression may facilitate heart disease, infection, parasitic infestation or other ill health, so that depression is a mechanism for those least resilient, or faced with most adversity, to succumb to illness. If depression is a state facilitating withdrawal from competition for reproductive success, major depressive illness may be the inappropriate and spontaneous occurrence of a mental state which has advantages for the species in allowing those 'least fit' to fail to survive. This hypothesis gives an empirically testable challenge to the view that the species has no evolutionary drive to survival and increased adaptedness to the environment, as well as explaining the more and more frequent occurrence of a specific mental state and its associated changes in the immune system.

Shift in the performance of 24-month-old Wistar rats in the Morris water escape task: a comparison across 36 experiments

Spatial discrimination learning in aged rats serves as an animal model of cognitive aging. We assessed the replicability of spatial discrimination performance in the standard Morris water escape task. To this end the learning curves and the performance in a probe trial of 24-month-old outbred Wistar (HsdWin:Wu) control rats from 36 experiments were compared. These experiments had been performed at our laboratory under strictly controlled conditions over a period of 71 weeks. There was a very high variability in the learning curves between experiments. The initial performance level, i.e. the performance during the first session, did not change systematically across the 36 experiments. In contrast, the final performance level, i.e. the level reached in the fifth training session, decreased over the 71 week period, when the platform escape latency and the distance swam to reach the platform, measured as number of line crossings, were considered. In the last experiments of the series, learning curves were no longer seen: the rats did not improve their performance across the acquisition sessions. By contrast, the swimming speed and, in the probe trial, the bias for the quadrant where the platform had been positioned during training, did not change. This indicates that a decrease across experiments occurred predominantly with respect to spatial orientation performance, whereas the motor performance appeared to be unchanged. Explanations for this observation, such as differences in viability between shipments and the possible occurrence of genetic drift, are discussed.

Effects of intraseptal injection of 192-IgG-saporin in mature and aged Long-Evans rats

In this study, the effects intraseptal injections of the selective cholinergic immunotoxin, 192-IgG-saporin, were investigated in mature (6-month-old) and aged (24-26-month-old) male Long-Evans rats. Ten days following intraseptal injection of either 192-IgG-saporin or saline, testing began in a battery of behavioral tests modulated by the septohippocampal system including two versions of the Morris water maze (i.e. submerged platform task, and 2-platform spatial discrimination), inhibitory avoidance, and pre-pulse inhibition of acoustic startle. In both mature and aged rats, intraseptal injection of 192-IgG-saporin selectively reduced ChAT activity in the hippocampus and posterior cingulate cortex, without affecting ChAT activity of amygdala or parietal cortex. In general, in all of the behavioral tests analyzed, intraseptal 192-IgG-saporin treatment had no effect in mature animals. Age-related deficits were observed in the spatial memory tasks, however this impairment was largely a function of the poor performance of aged rats treated with the toxin. In addition, an increase in the response to an acoustic startle was found in aged rats treated with 192-IgG-saporin. Thus, although intraseptal injection of 192-IgG-saporin produced similar reductions of ChAT activity, performance of mature and aged rats in tasks believed to be modulated by the septohippocampal pathway tended to be differentially affected in mature and aged rats.

GABAergic deafferentation hypothesis of brain aging and Alzheimer's disease; pharmacologic profile of the benzodiazepine antagonist, flumazenil

Recent experiments have shown that: 1) A chronic 10 month daily administration to rats of the benzodiazepine (BDZ) receptor antagonist, flumazenil (FL; 4 mg/kg in drinking water), from the age of 13 through 22 months, significantly retarded the age-related loss of cognitive functions, as ascertained by the radial arm maze tests conducted two months after FL withdrawal. 2) An equal number of 8 rats died in the control and FL-treated group before the behavioral tests were completed and the animals were sacrificed; the life span of the FL-treated 8 rats equaled 24.0 (+/- 0.6 SEM) months, while that of the control 8 rats equaled 22.3 months (+/- 0.7 SEM), and the group difference was marginally significant (p = 0.04 Mann-Whitney test). 3) In rats sacrificed 3 months after FL withdrawal and behavioral testing, the protective action of FL, relative to age-matched controls, was revealed by a significant reduction in the age-related loss of neurons in the hippocampal formation. 4) In the time period of 3 months between the drug withdrawal and sacrificing of the animals, stress experienced by the aging rats during behavioral testing, related to excessive daily handling of the animals and partial food deprivation to motivate them to perform in the radial arm maze, apparently had excitotoxic effects on the hippocampal neurons, as indexed by the presence of 30% neurons in a state of moderate pyknosis found both in the FL group and the age-matched controls. In the 6 months "young" control group, the number of pyknotic neurons equaled only 3.5%. It was concluded that the drug withdrawal and stress of behavioral testing unleashed the previously FL-controlled age-related degeneration. On the basis of these results and the literature, showing that the tone of the GABAergic system increases with age, and particularly in Alzheimer's disease (AD), the hypothesis of brain aging was formulated. It postulates that in mammals, with growing age, and prematurely in humans with AD, the increasing tone of the BDZ/GABAergic system interferes with antero- and retrograde axonal transport through a chronic depolarizing block of preterminal axon varicosities of the ascending aminergic and cholinergic/peptidergic systems, which are indispensable for normal metabolic/trophic glial-neuronal relationships. Such a state leads to discrete anatomic deafferentation of forebrain systems, and particularly of the neocortex, where block of the anterograde axonal transport results in induction of the cortical mRNA responsible for synthesis of the beta-amyloid precursor protein (beta APP). The simultaneous block of retrograde transport from chronically depolarized preterminal axon varicosities may account for toxic accumulation in cortex of the nerve growth factor (NGF) and other trophins, without which the basal forebrain cholinergic neurons degenerate. The general pharmacologic profile of FL has been discussed on the basis of FL administration to animals and healthy and diseased humans. This profile shows that FL: 1) increases brain metabolic functions; 2) reduces emotional responses, thereby stabilizing the functions of the autonomic system in both humans and animals challenged by adverse environmental stimuli; 3) improves cognitive and coordinated motor functions in both humans and animals; 4) uniquely combines anxiolytic, vigilance and cognitive enhancing, i.e. nootropic, properties, which may, in part, stem from FL-induced emotional imperturbability (ataraxy); 5) facilitates habituation of healthy humans and animals to novel but inconsequential environmental stimuli, and promotes non-aggressive interactions among animals; 6) in single i.v. doses, and administered chronically to humans, FL has antiepileptic actions in the Lennox-Gastaut syndrome and other forms of epilepsy characterized by "spike-and-dome" EEG patterns; these actions are likely to depend on FL's disinhibition of the serotonin system; 7) administered in single i.v...

Involvement of endogenous benzodiazepine receptor ligands in brain disorders: therapeutic potential for benzodiazepine antagonists?

Many therapeutic effects of benzodiazepines are mediated by neuronal high-affinity binding sites, i.e. benzodiazepine receptors (BR), located on GABAA receptors. Recently, endogenous BR ligands have partially been identified which, as agonists, either increase or, as inverse agonists, decrease GABAergic inhibition in the brain. BR antagonists, previously described as intrinsically inactive, induce effects in animals and humans under particular circumstances emphasizing a functional relevance of endogenous BR ligands. Several brain disorders, e.g. anxiety, insomnia, epilepsy, spasticity, alcoholism, coma, dementia, may be associated with a disequilibrium of opposing endogenous BR ligands changing the excitability of neurons implicated in aforementioned diseases. It is proposed that, depending on the relative role endogenous BR ligands play in the pathophysiology of these disorders, BR antagonists might demonstrate a variable efficacy in improving their symptomatology. In fact, such therapy would restore the homeostatic balance among various endogenous BR ligands being disturbed during an illness.

A comparison of age-related deficits in memory and frontal lobe function following oral lorazepam administration

Differential responses on cognitive function of young (18-45 years, n = 17) and elderly (60-75 years, n = 9) subjects were compared before and after a challenge with lorazepam (2 mg oral) or placebo. Tests of memory and frontal lobe function were administered to determine the specificity of the amnesic deficit produced and the interaction of drug and the aging brain. Anterograde amnesia, as assessed by recall of a word list, was noted in both groups and was greater in the elderly. Whereas lorazepam produced only impaired recall in the young group, the elderly group manifested a further range of cognitive impairments, including decreased verbal fluency on the controlled oral word association test and reduced performance on the Wisconsin card-sorting test. These impairments in the elderly group could not be attributed to performance deficits pre-drug. Short-term memory, as evidenced by digit span and the copy trial of the Rey figure, was not impaired by lorazepam. It is concluded that whilst lorazepam produces a relatively `pure' amnesia in young to middle aged adults, in the elderly there is an admixture of deficits in some frontal lobe functions. This is presumed to reflect age-related changes in the brain and may be analogous to the spectrum of results noted in Korsakoff's psychosis as opposed to 'pure' diencephalic amnesia.