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.

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.

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.

A low-noise preamplifier for multisite recording of brain multi-unit activity in freely moving animals.

A novel FET instrumentation amplifier is described which, as compared to most traditional operational FET preamplifiers, is characterized by an about 7-10 times lower intrinsic electronic noise and a higher common mode rejection. This allows discrimination of single units from multi-unit recording, even if the action potential amplitudes are as small as 20-30 microV and the units are located more than 100 microns away from the electrode tips. Such a distant and chronic recording may be expected to reduce the possibility of mechanical interference with functions of neuronal membrane and its immediate environment, and may be suitable for studying changes in functional connectivities among neurons during the animal's behavior and learning.

Benzodiazepines inhibit neutrophil chemotaxis and superoxide production in a stimulus dependent manner; PK-11195 antagonizes these effects.

Diazepam, which binds both central (neuronal) and peripheral (non-neuronal) benzodiazepine binding sites, and Ro5-4864, a ligand selective for benzodiazepine peripheral binding sites (PBS), both inhibited the FMLP induced chemotaxis in human neutrophils at concentrations as low as 10(-8) M. A selective peripheral benzodiazepine antagonist, PK-11195 (10(-5) M), partially reversed the benzodiazepine inhibition of chemotaxis. Diazepam also inhibited the superoxide production induced by FMLP, NaF, and A23187, but not that induced by PMA whose stimulant action was insensitive even to 10(-4) M diazepam.

Chronic administration of flumazenil (Ro 15-1788) enhances non-appetitive exploratory behavior of rats.

The effects of chronic administration of the benzodiazepine receptor antagonist, flumazenil (Ro 15-1788; 4 mg/kg/day for 14 days in drinking water) on the performance of adult rats in the 12-arm radial maze were studied. Relative to controls, the animals treated with flumazenil showed an increase (P less than 0.002) in non-appetitively motived exploratory behavior, so called because it occurred in 88% of instances in non-baited alleys, facing the well-illuminated "enriched environment" of the center of the room, as opposed to the baited alleys, facing the "dull" corner of the room.

Chronic Ro 15-1788 treatment increases REM sleep in rats.

Administration of Ro 15-1788, a benzodiazepine antagonist (3.6 mg/kg/day in drinking water for 14 days), increased total sleep and rapid eye movement (REM) sleep in rats. Standard six-hour EEG recording periods were obtained on day 0, 1, 3, 7, 10, 14, as well as 24 and 72 hours following withdrawal.

Chronic exposure to flumazenil: anxiolytic effect and increased exploratory behavior.

The aim of the present study was to define the behavioral correlates of chronic exposure of adult rats to flumazenil (4 mg/kg/day X 21 days in drinking water). In the holeboard test, performed on day 13 of drug treatment, the animals showed a significantly greater interest for the holes under which objects were placed than for the holes without objects (p less than 0.03), while there was no such difference in the control group.

Chronic flumazenil (Ro 15-1788) facilitates acquisition and retention of a swim-escape response in rats.

Since chronic flumazenil treatment was previously found to stimulate exploratory behavior in rodents, the aim of this study was to test the effect of chronic exposure to flumazenil on acquisition and retention of escape behavior. Adult rats were treated with flumazenil (Ro 15-1788; 4 mg/kg/day in drinking water) for 21 days (experiment 1) and for 17 days (experiment 2). In experiment 1 (a round water tank with one escape rope) conducted 24 h after drug/vehicle withdrawal, the time the animals needed to resolve a swim-escape task was significantly shorter in the drug group, compared to the controls.

Chronic exposure to Ro 15-1788: differential effect on flunitrazepam binding to cortex and hippocampus.

The time course of changes in specific [3H]flunitrazepam binding following 2 weeks of treatment with the benzodiazepine antagonist Ro 15-1788 (2.7 and 4 mg/kg per day in drinking water) was studied in the rat neocortical and hippocampal synaptosomal membranes. Such a treatment produced regional increases in the density of benzodiazepine sites, which remained for up to 24 and 48 h after drug withdrawal in the hippocampus and cortex, respectively; the dissociation constant (Kd) was unchanged.

Adenosine presynaptic inhibition and transmitter "spillover": a new hypothesis of etiopathogenesis of narcolepsy.

Neurobiologic and clinical evidence has been discussed in order to propose a new hypothesis explaining the precipitous nature of narcoleptic attacks. It is postulated that narcoleptic episodes are triggered by a surge in the tone of the arousal system which temporarily overcomes the abnormal tonic inhibitory influences of adenosine on presynaptic terminals of the arousal system. As a result, abnormally high levels of accumulated transmitters "spillover" onto supersensitive postsynaptic receptors both in the brain and spinal cord.

Animal models of chronic anxiety and "fearlessness".

Three behavioral animal models have been described: a feline and a rodent model of chronic anxiety, and a rodent model of "fearless" behavior. The models have been obtained by pre- or perinatal exposure to diazepam (DZ) or RO 15-1788 which produced enduring postnatal deficits or enrichment, respectively, of brain benzodiazepine (BDZ) receptors. The receptor-deficient one-year-old cat progenies showed hyperarousal, unabated restless behavior, delayed acquisition of instrumentally conditioned behavior, bizarre escape responses and absence or reduced alpha-like EEG activity.

Perinatal upregulation of benzodiazepine receptor ontogenesis: "fearless" and more efficient goal-directed behavior of adult rat progenies.

Pregnant and subsequently lactating rats had ad lib access to drinking water which contained either a benzodiazepine antagonist, Ro 15-1788 or diazepam (DZ). On the average, the rats consumed 2.9 mg/kg/day of Ro 15-1788 or 5.

Prenatal exposure to diazepam: late postnatal teratogenic effect.

During the last 5 days of gestation, pregnant Sprague-Dawley rats were treated daily with SC diazepam (DZ) injections (average dose 6 mg/kg of body weight). The control pregnant rats were treated with corresponding volumes of the vehicle. The progenies were examined for the occurrence of neoplastic and non-neoplastic lesions for up to 20 months.

Prenatal diazepam: chronic anxiety and deficits in brain receptors in mature rat progeny.

Pregnant rats were treated with daily doses (5.0 to 7.5 mg/kg, SC) of the benzodiazepine (BDZ) receptor agonist, diazepam (DZ) between day 15 through day 20 of gestation, i.

Enduring effects of prenatal diazepam on the behavior, EEG, and brain receptors of the adult cat progeny.

Pregnant cats were treated with a benzodiazepine receptor agonist, diazepam (DZ; Valium; average dose of 0.4 mg/kg/day, i.m.

Prenatal exposure to diazepam results in enduring reductions in brain receptors and deep slow wave sleep.

After prenatal exposure to diazepam (Valium), mature rats at 4 months of age displayed slow wave sleep (SWS) electroencephalographic patterns indicating impaired synchronization and SWS mechanisms. These animals spent a much greater portion of their SWS in the lighter SWS I, as compared to the control group which showed a predominance of the deeper SWS II. At one year of age, the diazepam-exposed rats had much fewer diazepam-specific binding sites in the thalamus than the vehicle-exposed controls.

Sleep and purposive behavior: inverse deviations from randomness of neuronal firing patterns in the feline thalamus. A new form of homeostasis?

In behaving cats trained to press a bar for small aliquots of milk reward, single neuronal firing patterns were monitored from the nucleus reticularis (NR) thalami during bar bressing (BP), subsequent quiet wakefulness with EEG spindles (S- QW ), grooming behavior (GR) and slow-wave sleep (SWS). The temporal patterns in the neuronal spike trains were analyzed using a non-parametric method based on relative relations between sequential spike intervals. The deviations of pattern occurrences from the random model were quantified.

Sleep-wakefulness: inverse deviation from randomness of neuronal firing patterns in the feline thalamus. A new form of homeostasis?

During stereotypic goal-directed behavior, neurons in the feline nucleus reticularis thalami emitted specific temporal patterns, while other patterns occurred much less often than predicted by the random model. During subsequent slow wave sleep, the mean firing rate increased, but the patterns that were emitted during behavior were eliminated or suppressed far below chance level, while those that were previously suppressed became dominant.

Visual attention and neuronal firing patterns in the feline pulvinar nucleus of thalamus.

In behaving cats, temporal patterns of neuronal firing were studied during slow wave sleep (SWS), motionless quiet wakefulness (QW) coupled with specific direction of the animal's attention, and during bar pressing performance (BP) for milk reward. The analysis was based on relative relations between sequential spike intervals. The strength of the method is based on the fact that the probabilities of occurrence of patterns are determined by the history of a spike train.

Phasic loss of constraints in timing of neuronal spikes in the feline centrum medianum during EEG alpha-like activity.

In unrestrained cats, temporal patterns of single neuronal firing in the centrum medianum-parafascicular complex (CM-Pf) of thalamus were studied during a state of motionless quiet wakefulness. The spike trains from each neuron were electronically divided into episodes that occurred during desynchronized EEG and those that occurred during bursts of 6-14 Hz EEG spindles or alpha-like activity over the parieto-occipital cortex and in the CM-Pf. Contrary to expectations based on the theory of inhibitory phasing of neuronal activity, the episodes of synchronized quiet wakefulness (S-QW) were associated with independent and random distribution of spike intervals, although they tended to occur in clusters.

The magnitude of post-reinforcement EEG synchronization (PRS) in cats reflects learning ability.

Electrocortical alpha-like activity, termed post-reinforcement synchronization (PRS), observed during operantly behavior, was quantified in 25 cats and plotted against the number of training sessions required for each to learn to press a lever for milk reward. A significant correlation (r = 0.77; P less than 0.

Neuronal firing patterns in the feline hippocampus during sleep and wakefulness.

The study addressed the problem of information transmission in mammalian brain as reflected in the emergence or disappearance of temporal patterns in extracellularly monitored single action potentials from the dorsal hippocampus of unrestrained cats during slow wave sleep (SWS), rapid eye movement sleep (REM), and motionless quiet wakefulness (QW). The spike trains were analyzed with a nonparametric technique. Chi-square statistics were used to measure deviation of firing patterns from the theoretical model which is based on the assumption that the intervals are random and/or independent from each other.