Cholinergic function and intellectual decline in Alzheimer's disease

Physiologic effects of nucleus basalis magnocellularis stimulation on rat barrel cortex neurons

Cholinergic neurons in the nucleus basalis magnocellularis (NBM) project to the cerebral cortex and are thought to play an important role in learning and memory, and other cognitive functions. In the present study, we examined the effects of NBM stimulation on the response properties of individual cortical neurons in layer V of the rat somatosensory cortex. Seventy-three neurons were studied before and after a brief electrical stimulation of NBM. Transient changes in spontaneous activity were observed in 60% of the cells, and in most cases this background activity decreased. Recordings lasting more than 1 h stimulation were obtained from 56 cells. Because some NBM stimulation-induced effects lasted several hours, neurons were evaluated in two groups, NBM1 and NBM2. NBM1 neurons were those exposed to either the first NBM stimulation of the day or an NBM restimulation following a more than 5 h stimulation-free period. Neurons exposed to NBM restimulation following a stimulation free interval of less than 5 h were classified as NBM2. Sixty-nine percent of the 32 NBM1 neurons displayed marked decreases in spontaneous activity and/or increases in the response evoked by deflecting a contralateral facial vibrissa. NBM1 stimulation caused some units to respond to previously minimally effective whisker stimuli. Stimulation effects often lasted several hours. By contrast, long-lasting changes were observed in only 25% of the 24 NBM2 neurons, and the only consistent effect was on spontaneous, not stimulus-evoked, activity. Systemic injection of atropine blocked NBM stimulation-induced changes in spontaneous and stimulus-evoked activities. Control neurons, studied without NBM stimulation, failed to display consistent alterations in their response properties during the course of 1 h or more. Results demonstrate that NBM activation produces long-lasting, cholinergically mediated alterations in the response properties of somatosensory cortical neurons. Effects were complex, being influenced by factors such as the time interval between successive stimulations during an experiment. The complexity of these NBM mediated effects should be considered when designing therapies for neurodegenerative disorders characterized by loss of NBM neurons.

Nicotinic and muscarinic modulations of excitatory synaptic transmission in the rat prefrontal cortex in vitro

The importance of the cholinergic innervation of the neocortex in cognitive functions has been shown in a number of clinical and animal studies. Until recently, attempts to study the mode of action of acetylcholine in the neocortex have concentrated on muscarinic effects, whereas cholinergic actions mediated by nicotinic receptors have been difficult to demonstrate. The present work was undertaken to study the mechanism of action of nicotinic agents on cortical neurons and compare it to muscarinic effects by means of intracellular recordings in a slice preparation. The study was performed in the prelimbic area of the rat prefrontal cortex, a cortical region particularly involved in cognitive processes. Recordings were made from pyramidal cells located in layers II/III and synaptic potentials were evoked by stimulation of superficial cortical layers. Iontophoretic applications of nicotinic agonists (nicotine, dimethylphenylpiperazinium, cytisine) increased the amplitude of the monosynaptic excitatory postsynaptic potential mediated by non-N-methyl-D-aspartate glutamate receptors in 14% (22/159) of cells. This effect was abolished by the selective nicotinic blocker, neuronal bungarotoxin (IC50 = 0.6-0.7 microM) and by dihydro-beta-erythroidine (IC50 = 20-30 microM), whereas hexamethonium, mecamylamine, curare and alpha-bungarotoxin were ineffective. The nicotinic agonists did not change resting membrane potential, input resistance or current-voltage relationship. They also did not affect the depolarizations produced by glutamate applied by iontophoresis in the somatic or dendritic area. In contrast, the muscarinic agonists (muscarine, acetyl-beta-methylcholine) decreased the amplitude of the excitatory postsynaptic potential in 100% of the neurons tested. Atropine was more effective (IC50 = 0.08 microM) than pirenzepine (IC50 = 2 microM) to antagonize the muscarinic action. These effects were observed in the absence of any direct postsynaptic change in membrane potential or input resistance, provided that the site of the iontophoretic application was more than 100 microM distant from the soma. The muscarinic agonists did not influence the actions of iontophoretically applied glutamate. These results suggest that nicotinic and muscarinic agonists modulate excitatory synaptic transmission mediated at dendritic sites by non-N-methyl-D-aspartate glutamate receptors, possibly through a presynaptic action. Thus ascending cholinergic systems may take part in information processing in the prefrontal cortex through the control of ongoing excitation to pyramidal cells.

Anticholinergic sensitivity in the aging rat septohippocampal system as assessed in a spatial memory task

The effects of central cholinergic blockade on spatial memory were tested in aged and basal forebrain-lesioned rats using the Morris Water Maze. In Experiment 1, aged rats (18-21 months old) were characterized as behaviorally impaired or nonimpaired based on water maze performance prior to an atropine sulfate challenge. In the atropine test (50 mg/kg, IP), both the impaired and the nonimpaired rats showed a severe disruption of their search behavior compared to young subjects. This effect was due to blockade of central receptors since peripheral cholinergic blockade using atropine methylbromide did not produce any impairments. Experiment 2 investigated effects of atropine on rats with septal lesions (SL), nucleus basalis lesions (NBL), and rats with both lesions combined (SL + NBL). Before drug treatment, the groups with septal lesions (SL and SL + NBL groups) displayed a moderate impairment in locating the platform site. However, similar to the aged rats, the septal-lesioned rats exhibited severe impairments in the water maze during atropine treatment. This effect was not seen in the normal controls or in the NBL rats. Aged rats, either impaired or nonimpaired in a spatial memory task, showed a pronounced sensitivity to pharmacological blockade of central cholinergic neurotransmission which resulted in severe deficits in spatial navigation in the water maze. Since the same behavioral deficit was produced by cholinergic blockade in young rats with septal lesions, we concluded that the impaired water maze performance seen in the aged rats during cholinergic blockade resulted from impaired function in the septohippocampal system.

Time gradient for post-test vulnerability to scopolamine-induced amnesia following the initial acquisition session of a spatial reference memory task in mice

The time course for vulnerability to the amnestic effects of the cholinergic antagonist, scopolamine, during the postacquisition period has been investigated. We have examined the effects of post-test injections of scopolamine (1 mg/kg ip) given at different times from 30 s for up to 6 h following the end of the first acquisition session of a concurrent spatial discrimination (reference memory) protocol in an 8-arm radial maze on subsequent long-term (24 h) retention performance in C57BL/6 mice. Results show that the immediate (30 s) post-test injection of scopolamine-HCl on Day 1 produces marked perturbation (amnesia) of long-term retention as attested to by significant deficits in various indices of spatial discrimination performance gain on Day 2 as compared to control subjects injected either with scopolamine-MBr or saline. The severity of this scopolamine-induced amnesia declines only slightly as a function of the treatment period 30 s-3 h post-test. However, no evidence for amnesia is observed if scopolamine-HCl injections are delayed for 6 h postsession. This important latter observation attests to the absence of any significant proactive effects of scopolamine on the ability of mice to perform the retention test via possible long-term effects on attention, motivation, or locomotor performance. These results thus constitute evidence for the existence of a limited (30 s-3 h) time gradient for vulnerability of the early memory trace to disruption by scopolamine. The present results are discussed in relation to our previous direct neurochemical observations describing the differential time courses of intervention of the ascending septohippocampal and nBM-cortical cholinergic pathways in the postlearning period. In particular, the presently observed time window concerning post-test vulnerability to scopolamine-induced amnesia corresponds more closely to the time course of the acute activation of the nBM-cortical cholinergic pathway, induced by testing with the same spatial memory protocol as used in the present study in mice.

Basal forebrain stimulation facilitates tone-evoked responses in the auditory cortex of awake rat

The effects of unilateral basal forebrain stimulation on the tone-evoked responses recorded in the auditory cortex ipsilateral and contralateral to the stimulation site, were investigated in fully awake rats. After 10 tone alone presentations, 20 pairing trials were given during which the basal forebrain stimulation was followed by the tone 30 ms later. Ten test-tones were presented immediately, 15 min and 1 h after pairing. Immediately after pairing, the short-latency "on" and "off" tone-evoked responses were enhanced in the ipsilateral but not in the contralateral cortex. This enhancement did not persist 15 min later. Systemic atropine injection prevented the ipsilateral facilitation. The responses to the tone were not modified when tested after 20 basal forebrain stimulations delivered in the absence of the tone. These results are the first demonstration in awake animals that an activation of the auditory cortex by cholinergic neurons of the basal forebrain is able to facilitate cortical responsiveness. A temporal contiguity between the cholinergic activation and the neuronal discharges elicited by the sensory stimulus is required for the facilitation to take place. The results are compared to previous ones obtained in anesthetized animals, and the functional role of cholinergic activation from the basal forebrain in cortical processing is discussed.

Neurochemical alterations in Rett syndrome

The Rett syndrome (RS) is a neurological disorder associated with severe mental deficiency and neurological manifestations of cortical and extrapyramidal dysfunction. The present report is (1) a postmortem brain study that compares the levels of choline acetyltransferase (ChAT) activity and the binding density of selected neurotransmitter receptors in four cases of RS and five normal controls of similar age and (2) a study of cerebrospinal fluid (CSF) concentrations of the endogenous tridecapeptide neurotensin in 12 RS patients and 8 controls of similar age. The level of ChAT activity was lower in many cortical and subcortical regions in the RS brains as compared to control levels. The number of NMDA, AMPA, mu opioid and neurotensin binding sites, as well as CSF concentrations of neurotensin, did not differ significantly from control levels. The results suggest that changes in specific neurotransmitter systems, particularly cholinergic neurons, in the thalamus, cerebellum and basal ganglia may underlie the progressive deterioration in motor and cognitive function characteristic of this disorder.

Effects of excitotoxic lesions of the nucleus basalis magnocellularis on conditioned taste aversion and inhibitory avoidance in the rat

The role of the nucleus basalis magnocellularis (NBM) in a variety of learning tasks is well known. Lesions of this nucleus result in a reduction of cholinergic transmission throughout a vast portion of the cortex. Because cholinergic transmission in the insular cortex seems to be important for the acquisition of conditioned taste aversion, the aim of the present work was to study the effects of bilateral chemically induced lesions of the NBM on this conditioning, as correlated with some cholinergic markers in the insular cortex. The effect on inhibitory avoidance was also studied. Lesions prevented the acquisition of the aversion and disrupted retention of the task in previously trained animals. Learning in the inhibitory avoidance paradigm was also notably affected. Postlesion reductions of choline acetyltransferase and acetylcholinesterase activities and of K(+)-stimulated [3H]acetylcholine release were found in the insular cortex. Further, in intact rats labeling of NBM neurons was observed by retrograde tracing after injection of Fluoro-Gold into the insular cortex. These findings indicate that the NBM is involved in the neural integration of feeding behavior and that its cholinergic projection to the insular cortex is one of the implicated neurotransmitter systems.

The effects of tacrine and zacopride on the performance of adult rats in the working memory task

1. The present study investigated the effects of tacrine (an inhibitor of acetylcholinesterase) and zacopride (the antagonist of 5-HT3 receptors) on the performance of adult rats in a continuous operant delayed non-matching to position task assessing spatial working memory. 2. Adult rats had a decline in the percent correct responses at the longest delays (16 and 30 sec) in this task. Tacrine (1.0 mg/kg) or zacopride (0.0025, 0.05, 1.0 mg/kg) did not increase the percent correct responses at any time delays. The higher dose of tacrine reduced behavioural activity (e.g. the decreased number of trials completed and increased sample press latency) of rats during memory testing, and it slightly increased choice accuracy across all the delays. 3. The combination of zacopride (1.0 mg/kg) and tacrine (1.0 mg/kg) increased the percent correct responses at the shortest delays, but not at the longest delays. 4. These results indicate a non-mnemonic improvement in the accuracy performance of rats, and they suggest that the effects of acute, systemic administrations of zacopride (which is thought to increase the release of acetylcholine) or/and tacrine (which inhibits the breakdown of acetylcholine) do not improve spatial working/short-term memory in rats.

Glucocorticoid receptor gene expression is unaltered in hippocampal neurons in Alzheimer's disease

Excessive glucocorticoid levels increase the metabolic vulnerability of hippocampal neurons to a wide variety of insults. Since glucocorticoid hypersecretion occurs in Alzheimer's-type dementia it has been proposed that a primary reduction in hippocampal glucocorticoid receptor expression leads to failure of feedback, hypercortisolemia and hence further neuronal loss. However, we have recently found that lesions of the cholinergic innervation of the hippocampus--known to be severely affected in Alzheimer's disease--increase corticosteroid receptor gene expression in the rat hippocampus. We have now examined both glucocorticoid (GR) and mineralocorticoid (MR) receptor gene expression in individual neurons in human postmortem hippocampus, using in situ hybridization histochemistry in 5 patients with Alzheimer's disease (81 +/- 3 years) and 7 controls (81 +/- 7 years) without neurological disease. The distribution and intensity of MR and GR mRNA expression in the hippocampus of Alzheimer's disease were similar to that in control tissue, with high expression in dentate gyrus and CA2-4, but significantly lower expression in CA1. In a separate group of patients with Alzheimer's disease we found significantly increased 24 h integrated plasma cortisol levels (59% greater than age-matched controls) and reduced cortisol-binding globulin (21% lower). These data do not suggest a primary deficiency of biosynthesis of hippocampal corticosteroid receptors in Alzheimer's disease. The maintenance of hippocampal GR and MR gene expression, in the face of an increased glucocorticoid feedback signal, may reflect loss of the cholinergic innervation.

Effects of grafts containing cholinergic and/or serotonergic neurons on cholinergic, serotonergic and noradrenergic markers in the denervated rat hippocampus

Long-Evans female rats sustained aspirative lesions of the septohippocampal pathways and, 2 weeks later, received intrahippocampal suspension grafts prepared from the regions including either the medial septum and the diagonal band of Broca (group S), or the mesencephalic raphe (group R), or from both these regions together (group S + R). Sham-operated (group SHAM) and lesion-only (group LES) rats were used as controls. Six months after grafting, high affinity synaptosomal uptake of choline (HACU) and serotonin (HASU), choline acetyltransferase (ChAT) activity and, using HPLC, the content of serotonin ([5-HT]), 5-hydroxyindolacetic acid ([5-HIAA]) and noradrenaline ([NA]) were determined in three rostro-caudal segments of the hippocampus (designated hereafter as the dorsal, the 'middle' and the ventral segments). In all three segments of the dorsal hippocampus, septohippocampal lesions decreased HACU, ChAT activity, HASU and [5-HT]; [5-HIAA] was decreased only in the middle and ventral hippocampal segments. The lesions also resulted in an above normal increase of [NA]. Septal grafts increased HACU and ChAT in the three hippocampal regions, had no effect on serotonergic markers and attenuated the lesion-induced increase of [NA] in only the dorsal and middle hippocampal segments. Raphe grafts increased HASU, [5-HT] and [5-HIAA] in the dorsal and middle hippocampal segments, had no effects on cholinergic markers and did not affect the lesion-induced increase of [NA]. Co-grafts increased HACU, ChAT activity, HASU, [5-HT] and [5-HIAA], and attenuated the lesion-induced increase in [NA]. These data demonstrate that grafts of fetal neurons placed into the denervated hippocampus may induce a neurochemical recovery which depends upon the anatomical origin of the grafted cells. They also show that co-grafting allows to combine the neurochemical properties of two fetal brain regions grafted separately. Furthermore, our findings suggest that graft-derived cholinergic reinnervation of the hippocampus prevents the lesion-induced increase of noradrenaline concentration which is likely to result from sympathetic sprouting. Thus, our data confirm the results of a previous experiment carried out at a post-grafting delay of 10-11 months, and show that the graft-induced effects reported previously are already massively present by 6 months after surgery.

Effect of chronic ethanol on the septohippocampal system: a role for neurotrophic factors?

The mechanisms by which chronic ethanol exposure produces neuronal damage have not been established. Potentially ethanol may reduce normal neurotrophic influences necessary for neuronal survival, growth, and function. We hypothesized that chronic ethanol exposure might produce a decrease in the synthesis, availability, upregulation, delivery, and/or the biological activity of normally occurring neurotrophic factors, or may alter the capacity of target neurons to respond to these factors. The available evidence leading to this hypothesis and supporting data from our laboratory are discussed.

Cholinergic regulation of hippocampal brain-derived neurotrophic factor mRNA expression: evidence from lesion and chronic cholinergic drug treatment studies

Quantitative in situ hybridization and northern blot analysis techniques were used to determine the effects of removal of the cholinergic input on levels and topographical distribution of brain-derived neurotrophic factor mRNA in the hippocampus of adult rats. First, the effects of partial and full fimbrial transections, which result in partial and near-total cholinergic deafferentation respectively, were compared. Twenty-one days after partial unilateral fimbrial transections, there were significant decreases in brain-derived neurotrophic factor mRNA expression throughout the hippocampal formation. Decreased expression of brain-derived neurotrophic factor mRNA was evident in all areas of localization within the hippocampal formation. The decreases amounted to 22-36% reductions compared with unlesioned control animals. Brain-derived neurotrophic factor mRNA levels were decreased to a greater extent (50-69%) following full unilateral fimbrial transections. Quantitative northern blot analysis indicated that hippocampal BDNF mRNA was decreased by 29 and 68%, three weeks after partial or full unilateral fimbrial transections, respectively. The extent of the reductions in brain-derived neurotrophic factor mRNA levels correlated with reductions in acetylcholinesterase staining density and cholinergic terminal density determined by quantitative autoradiographic analysis of [3H]vesamicol binding sites. Second, we found that chronic treatment with atropine (20 mg/kg per day for 14 days) decreased (by 54%) brain-derived neurotrophic factor mRNA levels in all areas of localization within the hippocampus. In contrast, chronic treatment with nicotine (1.18 mg/kg per day for 14 days), a treatment known to desensitize nicotinic receptors, did not affect brain-derived neurotrophic factor mRNA expression in the hippocampal formation. The findings provide evidence for cholinergic muscarinic regulation of brain-derived neurotrophic factor mRNA expression in the adult rat hippocampal formation and they suggest the existence of a tonic stimulation of brain-derived neurotrophic factor synthesis by the cholinergic afferents.

Chronic treatments with cholinoceptor drugs influence spatial learning in rats

Nicotine, scopolamine, oxotremorine, diisopropyl-fluorophosphate (DFP) and tetrahydroaminoacridine (THA) were administered chronically to different groups of rats in doses reported to alter central muscarinic and/or nicotinic receptor numbers. Beginning 24 h after final drug injection, the groups were compared to a vehicle control group on acquisition of a hidden platform position in the Morris water maze over 20 trials with a 30-min inter-trial interval. Chronic treatment with either nicotine or scopolamine significantly improved the rate of learning, but oxotremorine and DFP retarded learning and THA had no effect on learning. The chronic drug effects on behaviour were consistent with known effects of the injected drugs on muscarinic and nicotinic binding in the forebrain and on the sensitivity of frontal cortex neurones to iontophoretically applied cholinoceptor agonists. However, alternative explanations for the observed changes cannot be ruled out, since the drugs used are known to have a wide range of effects on other neurotransmitters.

Attenuation of scopolamine-induced spatial memory deficits in the rat by cholinomimetic and non-cholinomimetic drugs using a novel task in the 12-arm radial maze

The effects of cholinomimetic and non-cholinomimetic agents on spatial memory using a novel task in the 12-arm radial maze were investigated. The task was designed to reduce the tendency to use non-spatial strategies. Animals were repeatedly trained to retrieve food rewards from three arms, until a criterion level of performance was reached. Scopolamine (0.03 and 0.1 mg/kg SC), but not N-methylscopolamine (0.1 mg/kg SC) disrupted performance of this task. Physostigmine (0.3 mg/kg SC) and pilocarpine (30 mg/kg SC) completely reversed the deficit of performance produced by scopolamine. Furthermore, the ACE inhibitor Hoe 288 (10 nmol ICV) and the angiotensin AT1 receptor antagonist losartan (10 mg/kg SC) also significantly attenuated the scopolamine-induced deficit. These results show that this novel task in the radial maze is sensitive to the disruptive effects of scopolamine and can identify cognitive enhancing effects of both cholinomimetic and non-cholinomimetic drugs. Thus, this maze task provides a useful model for the evaluation of novel cognitive enhancing agents.

Behavior-related cortical activity and swim-to-platform performance in the aged rat

Aged rats (26 months) usually retained normal acetylcholine-dependent and serotonin-dependent forms of neocortical low-voltage fast activity and serotonin-dependent hippocampal rhythmical slow-wave activity. In a simple swim-to-platform test, aged rats (23 and 26 months) performed normally in acquisition and in retention over a 7-day period. The results are discussed in relation to the common assumption that aged rats provide a valid model of human senile dementia.

AF102B, a novel M1 agonist, enhanced spatial learning in C57BL/10 mice with a long duration of action

Orally administered AF102B, a selective muscarinic M1 cholinergic agonist, improved spatial learning in C57BL/10 mice in the Morris water maze. In four experiments in which all drug-treated animals received only one single administration of AF102B, improvement of acquisition depended on two factors: pretreatment time (tp) and dose. When a standard tp of 1 h was used, AF102B exhibited a U-shaped dose-response curve that is characteristic of many nootropic agents: learning was significantly improved by dose levels ranging from 0.1 to 1 mg/kg p.o. When the tp was extended out to as long as 8 days, two new effects emerged: (a) 1 mg/kg, the dose that had been the peak active dose at 1 h, exhibited a biphasic time course of action, being active at 1 h or at all tp intervals from 3 h to 5 days, but not at 1.5 h; (b) 0.03 mg/kg, a dose that had been inactive at a tp of 1 h, was active at all tp intervals from 3 h to 5 days, but not at shorter (1 and 2 h) or longer (6-8 days) tp intervals. In another experiment, animals received 0.03 mg/kg for 1-5 consecutive days: this dose level was active if the tp interval between the last dose and the learning session was 24-120 h, but not if it was only 1 h. Thus AF102B enhanced cognition in mice with a longer duration of action than reported for traditional muscarinic agonists.

Brain and cerebrospinal fluid cholinesterases in Alzheimer's disease, Parkinson's disease and aging. A critical review of clinical and experimental studies

Acetylcholinesterase (AChE), an enzyme responsible for the break-down of acetylcholine, is found both in cholinergic and non-cholinergic neurons in the central nervous system. In addition to its role in the catabolism of acetylcholine, AChE have other functions in brain, e.g. in the processing of peptides and proteins, and in the modulation of dopaminergic neurons in the brain stem. Several clinical and experimental studies have investigated AChE in brain and cerebrospinal fluid (CSF) in aging and dementia. The results suggest that brain AChE and its molecular forms show interesting changes in dementia and aging. However, CSF-AChE activity is not a very reliable or sensitive marker of the integrity and function of cholinergic neurons in the basal forebrain complex. Additional work is needed to clarify the role of AChE abnormality in the formation of pathology changes in patients with Alzheimer's disease.

Effect of scopolamine and nootropic drugs on rewarded alternation in a T-maze

The effects of different doses of scopolamine, and of the nootropic drugs oxiracetam and aniracetam, were investigated on the performance of male Wistar rats in a T-maze requiring a spatial discrimination in the stem (reference memory) and an alternate discrimination in the arms (working memory). Criterion (90% correct responses) was reached within 3 days of daily training for stem and 9 days for arm discrimination. Scopolamine (0.1, 0.2, 0.6, and 1.0 mg/kg, SC, 60 min before session) significantly impaired working memory, as shown by a decrease in the number of correct alternations, without affecting reference memory. Both nootropic drugs (25-50 and 100 mg/kg PO) 30 min before scopolamine) attenuated the working memory impairment induced by scopolamine.

Tyrosine hydroxylase-immunoreactive neurons in the nucleus basalis of the common marmoset (Callithrix jacchus)

In the course of characterizing the distribution of putative catecholaminergic neurons in the brain of the common marmoset, we encountered a population of such cells in the basal forebrain. Tyrosine hydroxylase-immunoreactive neurons are abundant within the nucleus basalis magnocellularis throughout its entire rostrocaudal extent, but not in other cholinergic basal forebrain nuclei. Most tyrosine hydroxylase-immunoreactive cells are large and multipolar. Double staining with antibodies to choline acetyltransferase or nerve growth factor receptor confirmed that these tyrosine hydroxylase-immunoreactive neurons are cholinergic, and compose at least 40% of the nucleus basalis cholinergic cells. The presence of a catecholamine-synthesizing enzyme in the neurons that provide the major cholinergic input to the neocortex may have important consequences for cortical function, and may be relevant to the vulnerability of the nucleus basalis in certain neurodegenerative disorders.

Comparison of the concentration of messenger RNA encoding four muscarinic receptor subtypes in control and Alzheimer brains

We determined the concentration of the messenger RNA species which encode four (m1-m4) of the five cloned muscarinic receptors in brains of Alzheimer's disease patients as compared to age-matched controls. Assays were performed using the quantitative method of DNA-excess solution hybridization in the cerebral cortex (frontal, temporal and occipital), hippocampus, nucleus basalis of Meynert and brainstem. The results suggest a statistically significant decrease in the m1 muscarinic receptor message in the temporal and occipital cortex, with no change in other regions. There was no change in the level of mRNA encoding the m2, m3 or m4 receptors in any of the brain regions studied.

The effects of p-chlorophenylalanine-induced serotonin synthesis inhibition and muscarinic blockade on the performance of rats in a 5-choice serial reaction time task

The effects of serotonergic dysfunction induced by treatment with p-chlorophenylalanine (PCPA), an inhibitor of serotonin synthesis, and cholinergic dysfunction induced by scopolamine on the performance of adult rats in the 5-choice serial reaction time task measuring selective attention were studied. Food-deprived rats were trained to detect and respond to brief flashes of light presented randomly in one of five locations, until they reached a stable level of performance (about 4 months). Scopolamine 0.2 mg/kg produced a marked variation in the performance but did not, however, induce any consistent impairment in the discriminative accuracy. Other doses of scopolamine (0.05 and 0.1 mg/kg) or N-methyl-scopolamine 0.2 mg/kg, a peripheral muscarinic receptor antagonist, did not affect discriminative accuracy. Furthermore, scopolamine as well as N-methyl-scopolamine produced a number of other performance deficits, such as significantly decreased overall probability of responding and significantly increased response latencies. PCPA treatment induced an almost total depletion (> 99%) of frontal cortical serotonin and its major metabolite 5-HIAA and reduced the frontal cortical concentrations of noradrenaline (-30%) and dopamine (-42%). During baseline testing conditions, there was a trend for the discriminative accuracy to be decreased by PCPA, although this effect failed to reach significance (P = 0.07). Presenting the stimuli at unpredictable intervals or reducing the intensity of the visual stimulus impaired discriminative accuracy in both PCPA-treated and control rats. The decrease in discriminative accuracy induced by PCPA reached statistical significance when the stimuli were presented faster than normally or the intensity of the visual stimulus was reduced. PCPA treatment did not make the rats more susceptible to the effects of scopolamine on discriminative accuracy. However, PCPA treatment also induced a number of other performance deficits, resulting in a decreased overall tendency to respond. In summary, there is a statistically non-significant trend for the discriminative accuracy to be decreased by PCPA treatment under normal testing conditions, and as the discrimination task is made more difficult (stimulus intensity reduction, presentation of the stimuli at faster than normal rates), the deficit in discriminative accuracy produced by PCPA treatment is revealed. The results suggest a role for brain serotonin in the general organization of behavior.

Effect of kainic acid administration to prepubescent rats on cholinergic markers in selected brain regions of adult rats

Systemic kainic acid administration to prepubescent rats, in a convulsant dose, results in permanent changes in behaviour, learning and memory in adulthood (Holmes et al., 1988, Epilepsia 29, 721-730). With regard to the hypothesis that cholinergic mechanisms play a crucial role in cognitive processes, M1- and M2-muscarinic acetylcholine receptors, choline acetyltransferase, and high-affinity choline uptake as well as benzodiazepine receptors were studied in selected cortical regions (frontal, temporal, somatosensory, visual, piriform cortex), in amygdala, hippocampus, and in the nucleus basalis of Meynert from adult rats, which received at the age of 25 days a single dosage of 11 mg/kg, s.c. kainic acid. Kainic acid treatment of prepubescent rats resulted in the adult brain in decreased numbers of the total population of muscarinic acetylcholine receptors in frontal (by 27%, P < 0.05, two-tailed Student's t-test), temporal (22%, P < 0.05), and piriform cortex (31%, P < 0.05), in amygdala (24%, P < 0.05), and nucleus basalis of Meynert (39%, P < 0.02). The binding affinity was unchanged in these regions. However, in the hippocampus, the dissociation constant was significantly increased following kainic acid treatment, while the receptor numbers remained unchanged. Analysis of competition experiments with the muscarinic antagonist pirenzepine revealed that the reductions of muscarinic acetylcholine receptors in the cortical regions after kainic acid treatment are mainly due to decreases in the number of the muscarinic M1-receptor subtype. In the amygdala, the numbers of both M1- and M2-receptor subtypes are reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Septo-hippocampal and nBM-cortical cholinergic neurones exhibit differential time-courses of activation as a function of both type and duration of spatial memory testing in mice

We previously showed that the initial acquisition session of a spatial discrimination (mixed reference/working memory) test in an 8-arm radial maze induced differential activations in the ascending cholinergic septo-hippocampal and nBM-cortical pathways in mice. This data showed that the duration of post-test cholinergic activation was longer in the nBM-cortical pathway than in the septo-hippocampal projection. Moreover, the post-test durations but not the immediate post-test amplitudes of activation in each pathway decreased progressively as a function of repeated daily acquisition sessions. In the present study we have thus tested the hypotheses that the time-courses of post-test cholinergic activation in the septo-hippocampal and nBM-cortical pathways may vary both as a function of the type of memory used (working vs. reference) and according to the duration of repeated daily testing. Cholinergic activity in vivo in the hippocampus or frontal cortex of mice was quantified using measures of sodium-dependent high-affinity choline uptake at two different times (30 s and 15 min) following specific spatial working or reference memory testing in an 8-arm radial maze. The memory tests were administered daily over a 13-day period to attain high levels of performance in each type of task. In comparison to control groups both types of memory testing induced significant post-test cholinergic activations in each brain region on Day 15. However, cholinergic activity remained elevated in frontal cortex at 15 min post-test following reference memory testing, whereas significantly shorter durations of cortical and hippocampal cholinergic activation were observed following working memory testing using short (1 min) retention intervals. The possible significance of these differential modifications to the time-course of the post-test activations in these cholinergic pathways in working and reference memory processes and the putative transsynaptic mechanisms involved are discussed.

GABAergic mediation of indirect transsynaptic control over basal and spatial memory testing-induced activation of septo-hippocampal cholinergic activity in mice

A neurochemical study of the transsynaptic interactions established between septal GABAergic interneurones and cholinergic septo-hippocampal neurones was conducted using mice. The effects of acute in vivo injections of either muscimol (20-500 ng/0.2 microliter), bicuculline (100 ng-1 micrograms/0.2 microliter) or saline vehicle (0.2 microliter) into the medial septum on septo-hippocampal cholinergic activity were evaluated using measures of hippocampal high affinity choline uptake at 30 min post-injection in two main groups of mice. The first (quiet control) remained in their home cages during the post-injection period whereas the second (active) were submitted, 10 min following injection to a 20-min period of spatial working memory testing in an 8-arm radial maze. Intraseptal injections of either muscimol or bicuculline produced significant (25-50%) inhibition of hippocampal cholinergic activity in quiet conditions (basal) as compared to intact or saline-injected mice. In the active groups, whereas memory testing induced significant cholinergic activation (+15-20%) in intact and saline injected mice at 30 s post-test no significant memory testing-induced activation was observed in either muscimol or bicuculline-injected mice at any dose. The role of septal GABAergic interneurones in the indirect transsynaptic control over the basal and activated states of septo-hippocampal cholinergic activity is discussed with respect to the concept that these complex neuronal interactions contribute to the physiological mechanisms involved in the modulation of working memory performance.

Persistence of chronic nicotine-induced cognitive facilitation

Nicotine has been found in a variety of species and behavioral paradigms to improve memory performance. The beneficial effect of nicotine has been seen after both acute and chronic administration. Interestingly, improved performance has been seen 24 h after acute injection and for at least 2 weeks after chronic administration. However, it is not clear from previous studies whether the persistence of the improved performance represents a true carryover of the drug effect or is due to the behavioral experience while under nicotine's effect. The current study was conducted to determine whether the facilitating effect of nicotine on learning and memory performance could be seen after withdrawal even if there was no behavioral training during the period of chronic nicotine administration. Rats were administered nicotine chronically for 3 weeks but were not tested during that time. Starting 1 week after withdrawal they were trained on a working memory paradigm in an eight-arm radial maze. The nicotine-treated rats started out at control-like levels of performance, but showed significantly faster learning as detected by three different measures of choice accuracy. By the final phase of testing the control subjects had caught up with the nicotine-treated rats. After the acquisition phase, acute challenges with the nicotinic and muscarinic antagonists, mecamylamine and scopolamine, did not elicit any differential effects in the nicotine-treated and control groups. The current study demonstrated that nicotine-induced cognitive facilitation persists for at least 4 weeks after withdrawal and does not depend upon behavioral test experience under the influence of the drug. The mechanism for this persisting effect is not currently understood.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of septal and/or raphe cell suspension grafts on hippocampal choline acetyltransferase activity, high affinity synaptosomal uptake of choline and serotonin, and behavior in rats with extensive septohippocampal lesions

At 31 days of age, Long-Evans female rats sustained aspirative lesions of the septohippocampal pathways and, 14 days later, received intrahippocampal suspension grafts prepared from the region including the medial septum and the diagonal band of Broca (Group S, n = 11), from the region including the mesencephalic raphe (Group R, n = 11) or from both regions together (Group S+R, n = 11). Sham-operated (Group Sham, n = 9) and lesion-only (Group Les, n = 11) rats served as non-grafted controls. Seven Sham, 7 Les and 8 rats from each transplant group were tested for home cage activity (6 months after grafting) and radial maze performance (between 7.5 and 8.5 months post-grafting). One month after completion of behavioral testing, the dorsal hippocampi of these rats were prepared for measuring choline acetyltransferase (ChAT) activity and high affinity synaptosomal uptake of both [3H]choline and [3H]serotonin. The remaining rats were used for histological verifications on brain sections stained for acetylcholinesterase (AChE). The lesions increased locomotor activity, impaired radial maze learning and, in the dorsal hippocampus, reduced AChE positive staining, decreased ChAT activity (-73%) as well as high affinity uptake of both choline (-81%) and serotonin (-82%). Neither type of transplant produced any significant behavioral recovery. However, septal transplants increased hippocampal AChE positivity, restored ChAT activity and enhanced choline uptake to 116% and 70% of the values found in sham-operated rats, respectively; they had no significant effect on uptake of serotonin. Transplants from the raphe region had weak effects on hippocampal AChE positivity, increased both the ChAT activity and the choline uptake to 70% ad 38% of the sham-operated rats, respectively, and produced an (over)compensation of the serotonin uptake which reached 324% of the values found in sham-operated rats. The co-transplantation of both regions resulted in restoration of ChAT activity (113% of sham-operated rats values), choline uptake (83% of sham-operated rats) and serotonin uptake (129% of sham-operated rats). Our neurochemical data show that after extensive denervation of the hippocampus, intrahippocampal grafts of fetal neurons may foster a neurotransmitter-specific recovery which depends upon the anatomical origin of the grafted cells: a graft rich in serotonergic neurons overcompensates the serotonergic deficit, a graft rich in cholinergic neurons attenuates the cholinergic deficit, whereas a mixture of both types of grafts produces recovery from both types of deficits. Thereby, both the feasibility and the interest of the co-grafting technique are confirmed.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of noradrenergic DSP4 lesion on the effectiveness of pilocarpine in reversing scopolamine-induced amnesia

We studied the effectiveness of pilocarpine in reversing the scopolamine-induced water maze learning deficit (increase in escape latencies, decrease in spatial bias) in control and DSP4- (a noradrenergic neurotoxin) lesioned rats. The water maze acquisition deficit (escape latency, first spatial bias) induced by scopolamine 0.8 mg/kg was augmented by DSP4 treatment. The water maze performance deficit induced by scopolamine was reversed by pilocarpine 4 mg/kg in both DSP4-lesioned and control rats. A smaller dose of pilocarpine (1 mg/kg) did not reverse scopolamine-induced acquisition deficit in either control or DSP4-lesioned rats. Analysis of the second spatial bias test measured 2 weeks after training revealed that pilocarpine 4 mg/kg reversed scopolamine-induced retention deficit in control and DSP4-lesioned rats. Pilocarpine 1 mg/kg reversed scopolamine-induced retention performance deficit during the second spatial bias test in control but not in DSP4-lesioned rats. The present results suggest that 1) noradrenergic and cholinergic systems may interact in the regulation of spatial acquisition and retention and 2) the effectiveness of cholinergic drugs in reversing scopolamine-induced spatial retention deficit may be affected by noradrenergic lesioning.

Reduced density of NMDA receptors and increased sensitivity to dizocilpine-induced learning impairment in aged rats

About 20 min prior to training in a shock-motivated 14-unit T-maze, young (3-4 months) and aged (24-25 months) male Fischer-344 rats were given s.c. injections of either saline or dizocilpine (MK-801, 0.02 or 0.04 mg/kg), a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. The aged rats showed a dose-dependent impairment in maze performance. Deficiencies were manifested as increases in errors, in runtime from start to goal, and in the number and duration of shocks received. In contrast, young rats exhibited no detrimental effects of dizocilpine on maze performance. Analysis of [3H]glutamate binding in these rats revealed a marked age-related decline in NMDA receptor binding in hippocampus. A significant correlation was observed between errors in the maze and hippocampal [3H]-glutamate binding, but the correlation was positive, i.e., rats that made the most errors had the highest level of NMDA receptor binding. Thus, compared to young rats, aged rats were more sensitive to the behavioral effects of NMDA receptor antagonism and they showed a hippocampal loss of [3H]glutamate in binding, which may be related to the increased sensitivity to dizocilpine. The positive correlation between poor maze performance and NMDA receptor binding suggests that the behaviors assessed involve complex interactions between NMDA receptors and other neuronal systems in the hippocampus.

Cholinergic fiber aberrations in nucleus basalis lesioned rat and Alzheimer's disease

Innervation density and morphological aberrations of cholinergic fibers were studied with choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry in 30-35 month-old aged rats and rats with long-term bilateral lesions of the magnocellular basal nucleus (MBN). In addition, AChE histochemistry was performed on human cortical sections derived from autopsy brains of normal aged and Alzheimer's disease (AD) patients. A limited but variable number of morphological alterations were observed in ChAT-immunoreactive fibers in the cortex and the hippocampus of the aged control rats. The aged MBN-lesioned rats displayed a severely reduced number of cholinergic fibers in the denervated areas of the neocortex, whereas the surviving fibers showed a strongly increased number of aberrations. Fiber anomalies were also observed in the cortex of the aged human subjects and Alzheimer patients, the latter showing a higher incidence of such aberrations. Only a part of these distended profiles were seen in close association with senile plaques as detected in the AChE-stained material. These findings suggest that experimental MBN lesions combined with aging share with AD the induction of large quantities of fiber malformations. Implications of possible mechanisms in both conditions are discussed.

Medial septal cholinergic lesions increase hippocampal mineralocorticoid and glucocorticoid receptor messenger RNA expression

Loss of the cholinergic innervation of the hippocampus and failure of central (presumably hippocampal) suppressive control of hypothalamic-pituitary-adrenal axis activity are important features of Alzheimer's dementia. We have examined the effects of electrolytic lesions of the medial septal cholinergic innervation on mineralocorticoid (MR) and glucocorticoid (GR) receptor mRNA expression in rat hippocampus using in situ hybridization histochemistry. Expression of both MR and GR mRNA was significantly increased in a subregions of the hippocampus, but not neocortex, with the greatest increase in the CA1 area for MR mRNA and dentate gyrus for GR mRNA. Since glucocorticoids potentiate the effects of neurotoxins in the hippocampus, the increased expression of receptors following loss of cholinergic inputs in Alzheimer's disease may increase hippocampal neuronal vulnerability.

Excitatory amino acids and memory: evidence from research on Alzheimer's disease and behavioral pharmacology

The excitatory amino acid transmitter (EAA) system is believed to play a crucial role in a variety of physiological processes related to neuronal plasticity. Substantial neurophysiological evidence suggests that, under normal physiological conditions. EAAs may be involved in mechanisms underlying learning and memory. However, overactivity of this system produces excitotoxic damage to neurons which is believed to be an etiological factor in various neurological conditions, such as epilepsy, and stroke-induced impairments. The fact that EAAs have been implicated in both, normal cognitive function and in degenerative neurological conditions suggests that they may contribute to the etiology of Alzheimer's disease (AD), because AD is characterized by memory deficits and specific histopathological signs of neuronal damage. This paper summarizes information regarding 1) the involvement of EAAs in Alzheimer's disease and 2) results from psychopharmacological studies of EAAs in laboratory animal models of learning. Investigations of the pathophysiology of AD indicate that glutamatergic deficits are associated with this syndrome. However, there is controversy concerning the nature of this defect. As a result, it is unclear whether it is a consequence of excitotoxic changes produced by glutamatergic overactivity or result from a decrease in glutamatergic function. Evidence from behavioral studies is consistent with the conclusion that EAAs may be involved in the acquisition of conditioned responses. However, in parallel with the clinical findings, learning impairments have been produced by treatments which either increase or decrease activity within this transmitter system. Therefore, although present results suggest that the EAAs play a role in cognition and in clinical syndromes in which such function is compromised, the specific nature of that role needs to be elucidated by future research.

Assessment of a cholinergic contribution to chlordiazepoxide-induced deficits of place learning in the Morris water maze

This investigation sought to characterize the interaction between benzodiazepine and cholinergic systems in place learning in the Morris water maze. In the first experiment, rats were treated with scopolamine (1 mg/kg) alone or concomitantly with one of two doses of flumazenil (15 and 30 mg/kg) or with chlordiazepoxide (5 mg/kg) alone or concomitantly with flumazenil (15 mg/kg). Chlordiazepoxide and scopolamine severely impaired place learning but not cue learning. The low dose of flumazenil completely reversed the impairment produced by chlordiazepoxide and both high and low doses of flumazenil attenuated the place learning deficit produced by scopolamine. Neither dose of flumazenil affected place learning when administered alone. In the second experiment, rats were administered chlordiazepoxide (5 mg/kg) or scopolamine (1 mg/kg) alone or concomitantly with one of four doses of physostigmine (0.05, 0.10, 0.25, and 0.5 mg/kg). Once again, both chlordiazepoxide and scopolamine impaired place but not cue learning. Physostigmine reversed the impairment produced by scopolamine in a dose-dependent manner but failed at every dose to attenuate the impairment produced by chlordiazepoxide. The higher doses of physostigmine impaired place learning when administered alone. None of the drug treatments impaired cue learning. Together, these results suggest that the scopolamine-induced impairment of place learning is due to an increase in benzodiazepine/GABA activity, and contradict the notion that benzodiazepines impair memory by cholinergic mechanisms.

Effects of tetrahydroaminoacridine on spatial navigation of nucleus-basalis- and frontal-cortex-lesioned rats

The present study investigates the effects of tetrahydroaminoacridine (THA: 1 and 3 mg/kg) on water maze (WM) spatial learning performance of intact, nucleus-basalis- (NB) lesioned, frontal-cortex- (FR) lesioned, or NB + FR-lesioned rats. NB lesions did not impair WM learning and had no effect on the WM performance deficit in FR-lesioned rats. THA at 1 or 3 mg/kg did not improve WM spatial memory of intact, NB-, FR-, or NB + FR-lesioned rats. These results suggest that 1) the cholinergic NB system is not a prerequisite for frontally mediated acquisition of WM performance, 2) THA treatment does not enhance spatial memory, and 3) THA is not effective in alleviating cognitive deficits induced by degeneration of the frontal cortex.

Age-related deficits of central muscarinic cholinergic receptor function in the mouse: partial restoration by chronic piracetam treatment

The effect of aging on muscarinic cholinergic receptor function in dissociated cell aggregates of the mouse brain was investigated using two biochemical models, i.e., carbachol-induced accumulation of inositol monophosphates and carbachol-induced desensitization of muscarinic cholinergic receptors as measured by the sequestration of specific 3H-N-methyl-scopolamine binding. While aging strongly reduced carbachol-induced inositol monophosphate accumulation, desensitization was not affected in the brains of aged animals. Chronic treatment of aged mice with the nootropic drug piracetam (500 mg/kg daily PO) significantly elevated the agonist-induced accumulation of inositol monophosphates possibly by increasing the available number of muscarinic cholinergic receptors not being in a desensitized state. The results support the hypothesis that nootropics like piracetam might act in part by restoring age-related deficits of central muscarinic cholinergic receptor function.

Alterations in cortical muscarinic receptors following cholinotoxin (AF64A) lesion of the rat nucleus basalis magnocellularis

Cortical choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH), muscarinic receptors and sodium-dependent, high-affinity, choline uptake (SDHACU) sites were examined in the rat brain following unilateral stereotaxic injection of the cholinotoxin, AF64A, into the nucleus basalis magnocellularis (NBM). Injection of AF64A resulted in a significant loss of presynaptic cholinergic markers in the cortex without alteration in TH and TPH activity. The binding to SDHACU sites was reduced to background values in the NBM and increased in the central amygdala (Ce) and cortex. The increase in cortical [3H]QNB binding was the result of a change in muscarinic receptor number (BMAX) and not a change in receptor affinity (KD). Examination of muscarinic receptor subtypes demonstrated a reduction of M1 receptor binding in the cortex and NBM without any alteration in the Ce. Non-M1 binding was significantly increased in all the laminae of the cortex and in the Ce, but decreased in the NBM. These data suggest that there exists a population of M1 receptors on NBM projections to the cortex and that NBM projections influence a population of postsynaptic receptors in the cortex and Ce which are not of the M1 subtype.

Septal cholinergic afferents regulate expression of brain-derived neurotrophic factor and beta-nerve growth factor mRNA in rat hippocampus

In situ hybridization was used to study the expression of members of the nerve growth factor family of trophic factors in rat hippocampus following stimulation of afferent cholinergic and glutamatergic pathways with quisqualate. A transient increase in brain-derived neurotrophic factor (BDNF) and beta-nerve growth factor (NGF) mRNA expression in the hippocampus was seen 4 h after a quisqualate injection into the medial septal nucleus. Both BDNF and NGF mRNA levels increased more than 4-fold in the granule layer of the dentate gyrus and for BDNF mRNA also in the pyramidal cells of CA1, while the levels of BDNF mRNA in CA3 increased 2-fold. The increase in BDNF and NGF mRNA levels were completely prevented by pretreatment with systemic injections of either scopolamine or diazepam. A quisqualate injection into the entorhinal cortex, containing glutamatergic afferents to the hippocampus, resulted in a 15-, 5- and 17-fold increase in the expression of BDNF mRNA in the ipsilateral granule cells, CA3 and CA1 pyramidal cells, respectively. Similar increases were also seen in the hippocampus contralateral to the injections. In contrast, the level of NGF mRNA did not increase significantly in any of the subfields in the hippocampus. The increase in BDNF mRNA after cortex injections was attenuated by diazepam but not by scopolamine. These findings imply that increased activity in afferent cholinergic and glutamatergic pathways to the hippocampus differentially regulate expression of the NGF family of neurotrophic factors in the hippocampus.

Long-term effects of aluminium on the fetal mouse brain

Potentially noxious substances may act as fetal teratogens at levels far lower than those required to produce detectable effects in adults, and behavioural teratogenicity may occur at levels lower than those which produce morphological teratogenesis. Aluminium (Al) is a potential neurotoxin in adults. Since pregnant women may be exposed to untoward levels of Al compounds under certain conditions, we have examined the long-term effects of treating the pregnant mouse with intraperitoneal or oral aluminium sulphate on brain biochemistry and behaviour of the offspring. The cholinergic system, as evaluated by the activity of choline acetyltransferase (ChAT), was affected differentially in different regions of the brain, and still showed significant effects in the adult. Differences between the intraperitoneal and oral series in the magnitude of effect seen in the regions of the brain probably reflect differences in the effective level of exposure. Growth rate and psychomotor maturation in the pre-weaning mouse were affected in the intraperitoneal series only, showing a marked post-natal maternal effect.

Nicotinic systems and cognitive function

Nicotinic acetylcholine receptors have been found to be important for maintaining optimal performance on a variety of cognitive tasks. In humans, nicotine-induced improvement of rapid information processing is particularly well documented. In experimental animals nicotine has been found to improve learning and memory on a variety of tasks, while the nicotinic antagonist mecamylamine has been found to impair memory performance. Nicotine has been found to be effective in attenuating memory deficits resulting from lesions of the septohippocampal pathway or aging in experimental animals. Nicotinic receptors are decreased in the cortex of patients with Alzheimer's disease. Preliminary studies have found that some aspects of the cognitive deficit in Alzheimer's disease can be attenuated by nicotine. Nicotine may prove to be useful therapeutic treatment for this and other types of dementia.

Chronic treatment with phosphatidylserine restores muscarinic cholinergic receptor deficits in the aged mouse brain

Chronic treatment (21 days) with phosphatidylserine (BC-PS) partially restored the reduced density of muscarinic cholinergic receptors in several regions of the aged (18 months) mouse brain. The effect was similar whether 3H-QNB or 3H-NMS was used as radioligand. The affinity of both radioligands was not altered by BC-PS treatment. Similar treatment of young (3 months) animals was without any effect on muscarinic cholinergic receptor density in all brain regions investigated. The effect was dose-dependent with elevations of receptor density between 15 and 28% for daily IP doses between 10 and 40 mg/kg, respectively. Similar treatment of aged mice with phosphatidylcholine (40 mg/kg) was without any effect. The data give further evidence that chronic treatment of aged animals with BC-PS reverses a variety of aged-related deficits of brain function.

Effect of piracetam administration on 3H-N-methylscopolamine binding in cerebral cortex of young and old rats

Piracetam, a nootropic drug, has been used for some time in Alzheimer's disease for its facilitatory effect on learning and memory. Rats treated with piracetam (500 mg/kg, p.o.) daily, during 1 and 2 weeks, showed a significant increase in muscarinic receptor number (Bmax) and in the dissociation constant values (Kd) in the cerebral motor cortex, in binding studies using 3H-NMS as ligand. The effect was observed not only in young rats (control- Bmax = 663.4 fmol/mg protein, Kd = 0.45 nM; treated- Bmax = 961.9 fmol/mg protein, Kd = 0.82 nM) but also in aged animals (control- Bmax = 628.0 fmol/mg protein, Kd = 0.47 nM; treated-Bmax = 747.6 fmol/mg protein, Kd = 0.84 nM). Since piracetam does not interact with muscarinic receptors, the reason for its effect expressed as the enhanced number of brain muscarinic receptors is not clear but could be the result of stimulation of phospholipid synthesis and thus would represent an indirect action of the drug.

Scopolamine impairs delayed matching in an olfactory task in rats

The action of the cerebral cholinergic system seems to be important for remembering events over short time intervals. We decided to test this hypothesis in the rat by developing an original model of short term memory based on the olfactory sensory modality which is a major determinant in the animal behaviour. The principle of the experiment was a "delayed match-to-sample" test performed in a classical T maze divided into two compartments. In the first compartment, rats received an odorant stimulation, then, in the second, they had to discriminate between the two arms odorized differently. To receive a food reinforcement, the animals had to enter the arm signaled by the odor presented in the first part of the maze. The test was performed with (Short-term memory condition) or without (Immediate memory condition) a variable delay between the first odor sampling and the discrimination task. Both tests were performed with control and scopolamine-treated animals (0.5, 0.125 and 0.0625 mg/kg IP). An injection of scopolamine (0.5 mg/kg) impaired performances, even when no retention of the odor was required. However, lower doses (0.125, 0.0625 mg/kg) selectively altered performances in the short term memory condition. These results suggest that intact muscarinic transmission is required for an olfactory cue to be used over a short time after its presentation.

Behavioral screening for cognition enhancers: from indiscriminate to valid testing: Part I

Preclinical efforts to detect and characterize potential cognition enhancers appear to have been dominated by a strategy of demonstrating a wide variety of apparently beneficial behavioral effects with little attention given to the specific psychological mechanisms underlying behavioral enhancement. In particular, the question of whether or not behavioral facilitation is based on relevant mnemonic mechanisms and is independent of the stimulus properties and/or the motivational and attentional components of a task is not often considered. As a result, an overwhelming number of compounds have failed to produce the clinical effects predicted for them on the basis of preclinical research. The available data suggest that a more successful approach requires deductive research strategies rather than the indiscriminate accumulation of apparently beneficial effects in a variety of behavioral tasks and animal models. The first step towards such an approach is a systematic and rigorous evaluation of the different aspects of validity for the models most frequently used in preclinical research. It is concluded that a combination of good construct validity and good face validity represents a necessary condition for screening tests with predictive validity, and that the most popular paradigms fail to fulfil these criteria. Future screening programs for cognition enhancers will probably be characterized by a depreciation of "fast and dirty tests" in favor of approaches focussing on the validity of the effects of potential cognition enhancers.

A semiautomated flow injection procedure for acetylcholinesterase and cholinesterase activities

A stopped-flow FIA adaptation of the classical Ellman's colorimetric procedure for the measurement of acetylcholinesterase or cholinesterase activity is described. The samples are injected into a flow analytical system which is provided with an electronic timer and an electrovalve in order to stop the flow when the sample is inside the measurement cell. In this way, the absorbance-time relationship is obtained with a savings of sample, time, and reagents.