AF64A (ethylcholine aziridinium ion), a cholinergic neurotoxin, selectively impairs working memory in a multiple component T-maze task

Imaging the Vesicular Acetylcholine Transporter in Schizophrenia: A Positron Emission Tomography Study Using [18F]-VAT

BACKGROUND

Despite longstanding interest in the central cholinergic system in schizophrenia (SCZ), cholinergic imaging studies with patients have been limited to receptors. Here, we conducted a proof-of-concept positron emission tomography study using [18F]-VAT, a new radiotracer that targets the vesicular acetylcholine transporter as a proxy measure of acetylcholine transmission capacity, in patients with SCZ and explored relationships of vesicular acetylcholine transporter with clinical symptoms and cognition.

METHODS

A total of 18 adult patients with SCZ or schizoaffective disorder (the SCZ group) and 14 healthy control participants underwent a positron emission tomography scan with [18F]-VAT. Distribution volume (VT) for [18F]-VAT was derived for each region of interest, and group differences in VT were assessed with 2-sample t tests. Functional significance was explored through correlations between VT and scores on the Positive and Negative Syndrome Scale and a computerized neurocognitive battery (PennCNB).

RESULTS

No group differences in [18F]-VAT VT were observed. However, within the SCZ group, psychosis symptom severity was positively associated with VT in multiple regions of interest, with the strongest effects in the hippocampus, thalamus, midbrain, cerebellum, and cortex. In addition, in the SCZ group, working memory performance was negatively associated with VT in the substantia innominata and several cortical regions of interest including the dorsolateral prefrontal cortex.

CONCLUSIONS

In this initial study, the severity of 2 important features of SCZ-psychosis and working memory deficit-was strongly associated with [18F]-VAT VT in several cortical and subcortical regions. These correlations provide preliminary evidence of cholinergic activity involvement in SCZ and, if replicated in larger samples, could lead to a more complete mechanistic understanding of psychosis and cognitive deficits in SCZ and the development of therapeutic targets.

Brain Factor-7® improves learning and memory deficits and attenuates ischemic brain damage by reduction of ROS generation in stroke in vivo and in vitro

Brain Factor-7® (BF-7), silk fibroin peptide, is known to be effective in improvement of memory and learning ability. In this study, the effects of BF-7 (10 mg/kg, p.o., pre-treatment for 7 days and post-treatment for 7 days) on neuroprotection and memory and learning functions were investigated in a rat model of transient focal cerebral ischemia and a gerbil model of transient global forebrain ischemia. Furthermore, to find the mechanism of BF-7, we examined the neuroprotective and antioxidative effects of BF-7 in vitro using neuroblastoma (SH-SY5Y) cells. In vivo model, treatment with BF-7 significantly reduced the number of errors in 8-arm maze test and significantly increased latency time in passive avoidance test at 7 days after focal ischemia compared to those in the vehicle-treated group. In addition, treatment with BF-7 significantly decreased the infarct size or neuronal death at 7 day following transient ischemia compared to that in the vehicle-treated group. In vitro model, 10 or 20 μg/ml of BF-7 treatment significantly increased cell viability in dose-dependent manner. In addition, oxidative stress was significantly attenuated in the ischemic cells, showing that 10 or 20 μg/ml of BF-7 treatment significantly reduced the generation of reactive oxygen species (ROS) compared to that in the ischemic cells. These results indicate that BF-7 treatment can attenuate ischemic damages and improve memory deficits via reduction of ROS generation.

Hippocampal-dependent appetitive control is impaired by experimental exposure to a Western-style diet

Animals fed a Western-style diet (WS-diet) demonstrate rapid impairments in hippocampal function and poorer appetitive control. We examined if this also occurs in humans. One-hundred and ten healthy lean adults were randomized to either a one-week WS-diet intervention or a habitual-diet control group. Measures of hippocampal-dependent learning and memory (HDLM) and of appetitive control were obtained pre- and post-intervention. HDLM was retested at three-week follow-up. Relative to controls, HDLM performance declined in the WS-diet group (d = 0.43), but was not different at follow-up. Appetitive control also declined in the WS-diet group (d = 0.47) and this was strongly correlated with HDLM decline (d = 1.01). These findings demonstrate that a WS-diet can rapidly impair appetitive control in humans-an effect that could promote overeating in consumers of a WS-diet. The study also suggests a functional role for the hippocampus in appetitive control and provides new evidence for the adverse neurocognitive effects of a WS-diet.

PKCα-mediated phosphorylation of LSD1 is required for presynaptic plasticity and hippocampal learning and memory

Lysine-specific demethylase 1 (LSD1) is a histone demethylase that participates in transcriptional repression or activation. Recent studies reported that LSD1 is involved in learning and memory. Although LSD1 phosphorylation by PKCα was implicated in circadian rhythmicity, the importance of LSD1 phosphorylation in learning and memory is unknown. In this study, we examined the roles of LSD1 in synaptic plasticity and memory using Lsd1 ^SA/SA knock-in (KI) mice, in which a PKCα phosphorylation site is mutated. Interestingly, short-term and long-term contextual fear memory as well as spatial memory were impaired in Lsd1 KI mice. In addition, short-term synaptic plasticity, such as paired pulse ratio and post-tetanic potentiation was impaired, whereas long-term synaptic plasticity, including long-term potentiation and long-term depression, was normal. Moreover, the frequency of miniature excitatory postsynaptic current was significantly increased, suggesting presynaptic dysfunction in Lsd1 KI mice. Consistent with this, RNA-seq analysis using the hippocampus of Lsd1 KI mice showed significant alterations in the expressions of presynaptic function-related genes. Intriguingly, LSD1n-SA mutant showed diminished binding to histone deacetylase 1 (HDAC1) compared to LSD1n-WT in SH-SY5Y cells. These results suggest that LSD1 is involved in the regulation of presynaptic gene expression and subsequently regulates the hippocampus-dependent memory in phosphorylation-dependent manner.

Altered reward sensitivity in female offspring of cocaine-exposed fathers

Recent rodent studies have demonstrated that parental cocaine exposure can influence offspring behavior, supporting the idea that environmental insults can impact subsequent generations. However, studies on the effects of paternal cocaine exposure are limited and multiple inconsistencies exist. In the current study, we behaviorally characterize the effects of paternal cocaine exposure in a C57BL/6J intergenerational mouse model. Male sires were administered cocaine hydrochloride (20mg/kg) or saline (0.01mL/g) once a day for 75days, and bred with drug naïve females twenty-four hours after the final injection. Offspring, separated by sex, were tested in a battery of behaviors. We found that paternal cocaine exposure altered sensitivity to the rewarding and stimulant effects of psychostimulants and natural reward (sucrose) in female offspring; female cocaine-sired offspring showed blunted cocaine preference using cocaine conditioned place preference (CPP) at a low dose (5mg/kg), but displayed similar preference at a higher dose (10mg/kg) compared to saline-sired controls. Additionally, cocaine-sired female offspring exhibited higher psychomotor sensitivity to cocaine (10mg/kg) and amphetamine (2mg/kg) and consumed more sucrose. Cocaine-sired males exhibited increased psychomotor effects of cocaine and amphetamine. Male offspring also displayed an anxiety-like phenotype. No effect of paternal cocaine exposure was observed on depressive-like, learning and memory or social behavior in male or female offspring. Collectively, our findings show that paternal, chronic cocaine exposure induces intergenerational behavioral effects in male and female offspring with greatest impact on sensitivity to psychostimulants and sucrose in females.

Cognitive Impairment Associated with Parkinson's Disease: Role of Mitochondria

Parkinson's disease (PD) is a movement disorder and is associated with some of the intellectual disabilities like cognitive dysfunctions. PD associated cognitive dysfunctions have been proved well in both preclinical and clinical set ups. Like other neurodegenerative diseases, insults to mitochondria have a significant role in the pathobiology of PD associated dementia (PDD). Neurotoxins like MPTP, mutations of the mitochondrial genes, oxidative stress, imbalanced redox mechanisms and dysregulated mitochondrial dynamics have been implicated in mitochondrial dysfunctions and have paramount importance in the pathobiology of PDD. However, the extent of contribution of mitochondrial dysfunctions towards cognitive deficits in PD has not been characterized completely. In this review we highlight on the contribution of mitochondrial dysfunction to PDD. We also highlight different behavioural tests used in nonhuman primate and rodent models for assessing cognitive deficits and some common techniques for evaluation of mitochondrial dysfunction in PDD.

The supramammillary area: its organization, functions and relationship to the hippocampus

The supramammillary area of the hypothalamus, although small in size, can have profound modulatory effects on the hippocampal formation and related temporal cortex. It can control hippocampal plasticity and also has recently been shown to contain cells that determine the frequency of hippocampal rhythmical slow activity (theta rhythm). We review here its organization and anatomical connections providing an atlas and a new nomenclature. We then review its functions particularly in relation to its links with the hippocampus. Much of its control of behaviour and its differential activation by specific classes of stimuli is consistent with a tight relationship with the hippocampus. However, its ascending connections involve not only caudal areas of the cortex with close links to the hippocampus but also reciprocal connections with more rostral areas such as the infralimbic and anterior cingulate cortices. These latter areas appear to be the most rostral part of a network that, via the medial septum, hippocampus and lateral septum, is topographically mapped into the hypothalamus. The supramammillary area is thus diffusely connected with areas that control emotion and cognition and receives more topographically specific return information from areas that control cognition while also receiving ascending information from brain stem areas involved in emotion. We suggest that it is a key part of a network that recursively transforms information to achieve integration of cognitive and emotional aspects of goal-directed behaviour.

Protective effect of the heparin-derived oligosaccharide C3, on AF64A-induced cholinergic lesion in rats

Alzheimer's disease (AD) literature indicates that glycosaminoglycans (GAGs) may prevent proteoglycan-induced amyloid-beta (Abeta) aggregation, decrease Abeta-induced tau-2 immunoreactivity, and increase the axonal growth and arborization of hippocampal neurons. However, there is no information about the impact of GAGs on cholinergic lesions. Here, AF64A was administered stereotaxically into the lateral ventricles of rats, at doses that are selective for cholinotoxicity (1 and 2 nmol). The heparin-derived oligosaccharide (HDO), C3 (25mg/kg), was administered orally, once daily for 7 days before, and 7 days after AF64A administration. Choline acetyltransferase (ChAT) immunohistochemistry revealed that C3 administration reduced AF64A-induced cholinergic damage in the septum and cingulum bundle. Quantitative neuronal cell counts showed that C3 attenuated, by 60%, the decrease in cell number in the medial septum. Enzyme analysis showed that C3 also significantly restored ChAT (30%) and acetylcholinesterase (AChE) enzyme activity (45%), which had been diminished by AF64A. Our data suggest that, in addition to its effects of anti-Abeta aggregation, anti-Abeta-induced tau-2 immunoreactivity, and neurotrophic effects, C3 also effectively reduces AF64A-induced cholinergic damage; hence it may have potential therapeutic value in AD patients.

Lack of effect of moderate Purkinje cell loss on working memory

192 immunoglobulin G-saporin (192-sap) is an immunotoxin which targets the cholinergic basal forebrain after injection into either the ventricular system or the parenchyma of the rat brain. When injected by the i.c.v. route, 192-sap kills some cerebellar Purkinje cells in addition to its more extensive killing of the cholinergic basal forebrain. Behaviorally, i.c.v. injections of 192-sap result in impaired performance in a variety of experimental paradigms of learning and memory including a working memory task in the radial maze. The current study examined the contribution, if any, of immunotoxin-induced Purkinje cell loss to impaired performance in the radial maze. To meet this aim, we used i.c.v. injection of another immunotoxin, OX7-saporin (OX7-sap), at a dose that produced Purkinje cell loss of similar extent to that produced by i.c.v. 192-sap. We then compared these OX7-sap-injected rats with 192-sap-injected rats in a radial maze working memory task. We found a working memory impairment only in the 192-sap-injected rats. These data show that moderate Purkinje cell loss alone is insufficient to impair working memory. Furthermore, the data are consistent with the idea that the working memory deficit observed in 192-sap-injected animals is likely due to lesioning of the cholinergic basal forebrain.

Effects of AF64A on gene expression of choline acetyltransferase (ChAT) in the septo-hippocampal pathway and striatum in vivo

AF64A (ethylcholine mustard aziridinium ion) was stereotaxically administered bilaterally (1 nmol/side) into rat lateral cerebral ventricles. Choline acetyltransferase (ChAT) activity and ChAT mRNA levels were measured at predetermined time points in the septo-hippocampal pathway and striatum, both well identified as rich in cholinergic neurons. AF64A caused a rapid but transient increase in ChAT mRNA (167%, P < 0.05) and ChAT activity (164%, P < 0.01) in the septum. By day 7 post treatment, there was a significant decrease in ChAT mRNA (42.5% of control, P < 0.05) in the septum although the ChAT activity still stayed high. This decreased ChAT mRNA level in the septum lasted for at least four weeks, and was paralleled by a long-lasting decrease in ChAT activity in the hippocampus. In the striatum, on the other hand, there were no observed changes in either ChAT activity or ChAT mRNA. These data suggest that the long term effect of AF64A on the septo-hippocampal cholinergic pathway may, at least in part, be due to an action of AF64A on gene expression in the cholinergic neuron. The difference in the response to AF64A between the septo-hippocampal and striatal cholinergic systems might be due to their difference in neuron types.

Nucleus basalis lesions: implication of basoamygdaloid cholinergic pathways in memory

Previous studies have shown a lack of association between cortical choline acetyltransferase (ChAT) activity and severity of memory impairment following excitotoxic lesions of the nucleus basalis magnocellularis (NBM). It recently has been proposed that the differential effects of NBM injections of various excitotoxins on amygdaloid and cortical ChAT may explain this result. The present study evaluated the mnemonic effect of unilateral intra-NBM infusions of the excitotoxins phthalic acid and quisqualic acid, which decrease ChAT activity primarily in the amygdala and cortex, respectively. Rats were trained in a double Y-maze, lesioned, and allowed to recover for 1 week prior to memory assessment. Behavioral results showed impaired working but not reference memory following phthalic acid lesions, and no significant effect following quisqualic acid lesions. Biochemical analysis in a second group of subjects confirmed that phthalic acid lesions produced a large decrease in basolateral amygdaloid ChAT, but had little effect on cortical ChAT activity. Conversely, quisqualic acid lesions produced a large decrease in cortical, but not basolateral amygdaloid, ChAT activity. These results suggest that the NBM amygdalopetal cholinergic pathways play a role in mnemonic functioning.

Methyl mercury during late gestation affects temporarily the development of cortical muscarinic receptors in rat offspring

Pregnant Sprague-Dawley rats were treated by gavage with a single dose of 8 mg/kg of methyl mercury on gestational day 15. Offspring of control and treated rats were killed at 14, 21 and 60 days of age. The binding characteristics of muscarinic receptors labelled in cortical membrane preparation by 3H-L-quinuclidinyl benzilate were studied together with the assessment of mercury level in the same brain area. Furthermore, the performance in passive avoidance tasks was evaluated in 8 weeks old rats. Perinatal exposure to methyl mercury significantly reduced the maximum number of muscarinic receptors (Bmax) in the brain of 14 (53%) and 21 day old rats (21%), while this change was no more present in 60 day old rats. This phenomenon seems to be strictly related to the presence of mercury in the cortex since it disappeared with the normalization of mercury levels in the brain. Despite the recovery of muscarinic receptor densities in methyl mercury exposed rats at 8 weeks of age, the avoidance latency was reduced in passive avoidance test as an indication of learning and memory deficits in these animals. Results from this study indicate that prenatal methyl mercury exposure induces latent cognitive dysfunction which does not seem to be related to transient muscarinic receptor alteration found in the early period of postnatal life.

Long-term exposure to high levels of corticosterone aggravates AF64A-induced cholinergic hypofunction in rat hippocampus in vivo

Male Sprague-Dawley rats were bilaterally adrenalectomized and corticosterone (CORT) was substituted as subcutaneous pellets in two groups of animals: low- (L-CORT: 1 x 25 mg pellet) or high-level of CORT (H-CORT: 4 x 100 mg pellet). Between 14 and 19 days after CORT substitution, ethylcholine aziridinium (AF64A) was intracerebroventricularly (i.c.v.) injected in the CORT long-term exposed rats and the dose- and time-dependent effect of this treatment was measured on choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in hippocampus and septum and on serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and noradrenaline (NA) levels in hippocampus. Rats were killed at 2, 4, 7 and 14 days after AF64A treatment. Starting 4 days after the i.c.v. administration of 0.5 or 1.0 nmol of AF64A, an aggravation of the reduction of ChAT activity was measured in the hippocampus of the H-CORT animals compared to the L-CORT ones. In the septum of the H-CORT rats, the activity of ChAT increased within the first week after the infusion of the toxin, while no significant effect was observed in the L-CORT group. As we observed with ChAT, AF64A induced a severe inhibition of AChE activity in the hippocampus of the H-CORT rats compared to the L-CORT ones. In the septum, an increase of AChE activity was observed in both groups of CORT-exposed animals. In the hippocampus of H-CORT animals, the exacerbation of the inhibition of ChAT and AChE activity was accompanied by a parallel decrease in the content of 5-HT and 5-HIAA starting 4 days after AF64A injections. Finally, NA content in hippocampus was not affected by the toxin in the CORT-substituted animals. These data demonstrate that: (1) long-term exposure to supraphysiological levels of CORT enhances the cholinodisruption induced in hippocampus by AF64A, at doses of 0.5 and 1.0 nmol/side; (2) high circulating plasma CORT concentrations impair hippocampal cholinergic neuronal capacity to recover from damage; and (3) the degree of inhibition of the serotoninergic system is augmented in H-CORT animals, most probably due to an adaptation of the serotoninergic neurons to the larger withdrawal of cholinergic function observed in this group.

Facilitatory but nonessential role of the muscarinic cholinergic system in the generation of long-term potentiation of population spikes in the dentate gyrus in vivo

The role of the muscarinic cholinergic system in the generation of LTP in the medial perforant path-dentate granule cell synapses in vivo was investigated using anesthetized rats. Cholinergic denervation with AF64A, a cholinergic toxin, did not significantly affect LTP induced by a strong tetanus (100 pulses at 100 Hz), but attenuated the LTP induced by a weak tetanus (30 pulses at 60 Hz). The i.c.v. injection of scopolamine (1.5-50 nmol) did not significantly affect the LTP induced by the strong tetanus but attenuated the magnitude of LTP produced by the weak tetanus in a concentration-dependent manner. These results suggest that the cholinergic system is not essential for induction of LTP by strong stimuli but plays a role in facilitating the generation of LTP by weak stimuli. Furthermore, the induction of LTP by a weak tetanus was blocked by pirenzepine but affected by neither AF-DX116 nor 4-diphenylacetoxy-N-methylpiperidine. The LTP-facilitatory action of the cholinergic system is probably mediated by muscarinic M1 receptors.

Behavioral and neuroanatomical consequences of a unilateral intraventricular infusion of AF64A and limitations on the neuroprotective effects of nimodipine

The monoethylcholine aziridinium ion, AF64A, (3 nmol in 1 microliter) or artificial CSF (1 microliter) was infused unilaterally into the right dorsal lateral ventricle of male adult rats. Treatment with the L-type calcium channel antagonist, nimodipine (70 micrograms/kg b.wt.) or its vehicle was administered beginning before and for seven days following surgery. The infusion of AF64A reduced spontaneous alternation rates in the T-maze when compared to CSF and sham infused animals. AF64A-treated animals also took longer to reach the goal area in a complex maze task on specific trials relative to CSF and sham-infused animals. Locomotion and habituation to the open field did not differ between surgery groups. Unilateral AF64A significantly depleted acetylcholinesterase (AChE) positive terminals in the ipsilateral hippocampus and cell bodies in the ipsilateral medial septal area (MSA). Receptors for nerve growth factor (NGF-R), often colocalized with cholinergic cell bodies and terminals, also were depleted in the ipsilateral MSA of AF64A infused animals. Treatment with nimodipine did not have a neuroprotective effect on AF64A animals in either behavioral or histological results. However, some degree of protection was found in the vehicle-treated rats. This effect was likely a consequence of the stress of the injection procedure rather than the content of the vehicle, largely polyethylene glycol 400. Nimodipine-treated animals, regardless of surgery group, exhibited fewer emotional responses and had lower spontaneous alternation rates than untreated animals. The behavioral alterations found in the nimodipine groups are most easily explained in terms of altered emotionality. Overall our findings indicate that AF64A is a potent cholinotoxin that can selectively eliminate the ipsilateral septohippocampal cholinergic system when unilaterally infused into the lateral ventricle. It is possible that the mechanism of action of AF64A, like other nitrogen mustard analogues, involves disruption of basic processes involved in protein synthesis and DNA activities. Because of this, the toxic effects of the aziridinium mustard are independent of extracellular calcium and thus may not be susceptible to protection by calcium channel antagonists.

Messenger RNA levels of chromogranin B, secretogranin II, and VGF in rat brain after AF64A-induced septohippocampal cholinergic lesions

The mRNA levels of secretogranin II, chromogranin B, and VGF were compared in brains of control and AF64A-treated rats. This toxin induces specific lesions of the septohippocampal cholinergic pathway. As a consequence of this treatment, the chromogranin B message was elevated in the dentate gyrus granule cells of the hippocampus. In the paraventricular nucleus of the hypothalamus, a concomitant elevation of the messages of secretogranin II and corticotropin-releasing factor occurred in the parvocellular neurons, and an increase of those of secretogranin II and VGF occurred in a subgroup of magnocellular neurons. Further increases for secretogranin II were seen in the amygdaloid nuclei and the reticular thalamic nuclei and increases for chromogranin B in the temporal cortex, substantia nigra compacta, and ventral tegmental area. These results indicate that the toxin-induced lesion of the cholinergic pathway innervating the hippocampus apparently leads to the stimulation of several defined groups of neurons that react with an increase in the mRNA levels of their secretory peptides. We suggest that changes in mRNA expression of these peptides are useful parameters for defining neurons under chronic stimulation.

Improving effect of acetylcholine receptor agonists on a deficit of 2-deoxyglucose uptake in cerebral cortical and hippocampal slices in aged and AF64A-treated rats

The aim of the present study was to determine whether the facilitation of 2-deoxyglucose (2-DG) uptake in the cerebral and hippocampal slices by nicotinic and muscarinic receptor agonists is compromised in the aged rat brain. For this, the effects of the nicotinic receptor agonist nicotine, the muscarinic receptor agonists oxotremorine and McN-A-343, and the ACh esterase inhibitors physostigmine and NK247 on 2-DG uptake in the brain slices of young (2-month-old) and aged (24-26-month-old) rats were tested. The decrements of 2-DG uptake in the cortical slices of aged rats were significantly attenuated by treatment with oxotremorine, nicotine and amiridine. In contrast, the metabolic responsivity of hippocampal slices to these drugs was reduced. To assess whether age-related changes in 2-DG uptake may be due to deficits in cholinergic function, we tested these drugs on the decrements of 2-DG uptake in ethylcholine aziridinium (a neurotoxic analog of choline) injected rats. The reductions of 2-DG uptake by injection of ethylcholine aziridinium was attenuated by oxotremorine but not by physostigmine. The present results reveal that metabolic decrements in the cerebral cortex from aged or ethylcholine aziridinium-injected rats were attenuated by muscarinic and nicotinic receptor agonists, suggesting that the muscarinic and nicotinic receptor mechanism in the cerebral cortex may be involved in cholinergic drug-induced functional recovery in aged rats.

Behavioural, biochemical and histological effects of AF64A following injection into the third ventricle of the mouse

Behavioural, biochemical and histological effects were assessed following AF64A injected into the third ventricle of female NMRI mice. Doses from 3 to 7 nmol produced significant changes in behaviour, causing hyperactivity, reduced hole-board exploration, rotational behaviour in a symmetrical Y-maze corresponding to a loss of alternation, abnormal behaviour in a plus-maze task of fear/anxiety with markedly increased exploration of the open arms and finally deficits in passive avoidance responding and spatial orientation in a Morris-type water maze. In this latter test, a cue learning deficit was noted for the two highest doses only. No histological changes of consequence were observed up to 5 nmol. Beyond this dose, at 6 and particularly 7 nmol, necrosis of parts of the hippocampus and septum was apparent. ChAT and AChE activity were decreased in the hippocampus but not in the cortex although the decreases were smaller than generally reported for AF64A-treated rats. ChAT and AChE reductions correlated highly with hyperactivity in the open-field and to a lesser extent, with spatial learning deficits. Monoaminergic activity was also affected in the hippocampus, but not in the cortex, at 4 nmol and above. NE and particularly 5-HT and 5-HIAA levels were reduced although the rate of 5-HT turnover was unaltered. A highly significant correlation was obtained between 5-HT effects and the increased open arm exploration in the plus-maze task of fear/anxiety. The behavioural effects and biochemical changes lasted at least 8-9 weeks postop.

Behavioural, biochemical and histological effects of trimethyltin (TMT) induced brain damage in the rat

To assess the nature and extent of behavioural, biochemical and histological changes induced by trimethyltin (TMT), rats were treated with a single injection of TMT over a dose range of 6, 7 and 8 mg/kg i.p. Behavioural observations were performed at a minimum of 21 days after the administration of TMT. The behavioural consequences of TMT were hyperactivity in the open-field test, increased locomotor activity and deficits in passive and active avoidance behaviour, T-maze alternation and Morris Water Maze behaviour. The behavioural changes were dose dependent and were accompanied by a degree of pathological damage to the hippocampal pyramidal cells which was particularly apparent at the highest dose. The main biochemical effects of TMT involved deficits in the serotonergic and GABA-ergic systems and a decrease in M1 and M2 binding sites in the hippocampus. These results suggest that the toxic interaction of TMT with the hippocampus and other limbic brain regions may be responsible for its effect on learning and memory.

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.

Effects of the acute administration of a new trimethylxanthine derivative, S 9977-2, on local cerebral blood flow and glucose utilization in the rat

S 9977-2 is a new trimethylxanthine derivative with promnesic properties. Its effects on cerebral glucose utilization and blood flow were studied by means of quantitative autoradiography. S 9977-2 was injected intravenously into adult rats at doses of 0.1, 1.0 and 10 mg/kg. At 0.1 mg/kg, S 9977-2 induced a significant increase in cerebral glucose utilization over control values in two white matter areas and in the vestibular nucleus. At 1.0 mg/kg, glucose utilization was affected in 14 areas out of the 63 studied, mainly limbic regions such as the hippocampus, raphe nuclei and locus coeruleus, as well as some posterior areas. Conversely, after the injection of 10 mg/kg S 9977-2, cerebral glucose utilization was similar to that of control rats. At the three doses tested, S9977-2 did not induce any significant variation in local rates of cerebral blood flow compared to those of controls. Likewise, S 9977-2 did not change the level of coupling between cerebral blood flow and metabolism, except at 10 mg/kg, where a relative hypoperfusion at a constant metabolic level was recorded. These data show that, at 1.0 mg/kg, S 9977-2 increased glucose utilization in hippocampal areas, an effect which may be related to the promnesic properties of this compound at the same dose. Moreover, at low doses, the lack of change in the level of coupling between cerebral blood flow and metabolism is indicative of the rather selective action of this compound, compared to that of caffeine. Thus S9977-2 should have therapeutic effects, mainly via its promnesic properties, without having many side effects.

Muscimol infused into the medial septal area impairs long-term memory but not short-term memory in inhibitory avoidance, water maze place learning and rewarded alternation tasks

These experiments investigated the effects of injections of muscimol (1 or 5 nmol), administered into the medial septal area prior to training, on memory tested at different retention delays after training in 3 tasks: an inhibitory avoidance task, a one-trial place learning task, and a rewarded alternation task. In all 3 tasks, intraseptal injections of muscimol did not impair memory performance at short retention delays, but impaired memory at the longer retention delays. These findings are consistent with the view that GABAergic regulation of the septohippocampal cholinergic system plays a selective role in the establishment of long-term memory.

Reversal by 3,3?,5-triido-l-thyronine of the working memory deficit, and the decrease in acetylcholine, glutamate and ?-aminobutyric acid induced by ethylcholine aziridinium ion in mice

The effect of 3,3',5-triiodo-L-thyronine (T3) on working memory in ethylcholine aziridinium ion (AF64A)-treated mice was studied in a delayed non-matching to sample task using a T-maze. After behavioural testing was completed, mice were killed by microwave irradiation and regional brain levels of acetylcholine, aspartate, glutamate, glutamine, glycine, taurine, and gamma-aminobutyric acid (GABA) were measured by high-performance liquid chromatography with electrochemical detection. Treatment with AF64A (7 nmol, i.c.v.) produced a deficit in working memory performance in the non-matching to sample task at 30 s delay, and decreased acetylcholine, glutamate, and GABA levels in the hippocampus, but not in the septum and cerebral cortex. Administration of T3 (0.3 mg/kg, p.o., once daily for 6 days) to AF64A-treated animals improved the deficit in working memory performance and reversed the decrease in acetylcholine, glutamate, and GABA levels in the hippocampus. These results indicate that the deficit in performance induced by AF64A can be improved by T3 administration.

A simple T-maze method for estimating working memory in mice. Effect of ethylcholine mustard aziridinium ion (AF64A)

Mice were housed in a cage containing a T maze. A watering place was located at the entrance of the maze. The right and left arms of the maze each had two exits, one of which led to the home cage where food was placed, while the other led to the watering place via a bypass. The exit leading to the home cage in either the right or left arm was alternately closed every 90 min. One-way swinging doors were inserted at the entrance to each arm and between each bypass and the watering place. The mice were given a cholinergic neurotoxin--ethylcholine mustard aziridinium ion (AF64A)--(8 nmol) or saline as a control into the left ventricle 2 weeks before they were housed in the apparatus. Those mice housed in this apparatus mastered the alternation task at a 5-sec delay on day 3 in the sham group and on day 4 in the AF64A group. When a longer delay (5-90 sec) was introduced for the mice that mastered the alternation task at 5-sec delay, the AF64A group made significantly more errors than did the sham group at 60- and 90-sec delays. These results show that the apparatus is useful in estimating working memory in mice with little effort.

Protective effect of WEB 1881 FU on AF64A (ethylcholine aziridinium ion)-induced impairment of hippocampal cholinergic neurons and learning acquisition

The effect of continuous administration of 4-aminomethyl-1-benzylpyrrolidin-2-one-hemifumarate (WEB 1881 FU) on cerebral cholinergic neurons was studied using rats treated with ethylcholine aziridinium ion (AF64A), a neurotoxic choline analog. AF64A (2.0 nmol, administered i.c.v.) caused a significant decrease in the hippocampal acetylcholine (ACh) content. This decrease in hippocampal ACh content was accompanied by a reduction of choline acetyltransferase (CAT) activity. Under these experimental conditions, the latency of the passive avoidance response of rats, determined with a step-through method, was strongly decreased as compared with that of sham-operated rats. Although treatment with WEB 1881 FU (50 mg/kg per day, administered orally for 7 days) from immediately after the administration of AF64A did not affect the AF64A-induced decrease of ACh in the hippocampus, 100 mg/kg per day of WEB 1881 FU (orally for 7 days) significantly suppressed the AF64A-induced declines in hippocampal ACh content and CAT activity. The AF64A-induced reduction in latency of the passive avoidance response was also significantly antagonized by the treatment with 100 mg/kg per day of WEB 1881 FU (administered orally for 7 days) from immediately after the administration of AF64A. Continuous administration of WEB 1881 FU (100 mg/kg per day, orally for 7 days) from 7 days after the treatment with AF64A also had a significant inhibitory effect on the AF64A-induced decrease in ACh content in the hippocampus. These results suggest that WEB 1881 FU may have protective actions on the destruction of hippocampal cholingergic neurons as well as memory impairment induced by AF64A administration.

Involvement of the septohippocampal cholinergic system in representational memory

To develop an animal model for testing muscarinic agonists, we examined the effects of cholinergic lesions with the ethylcholine aziridinium ion (AF64A) on two types of memory tasks. The tasks provided a distinction between representational and dispositional memory that could be measured in a single paradigm. Young, male Long-Evans rats were trained in a modified T-maze to learn both a discrimination task and a paired-run alternation task. Once animals learned the tasks, they were administered either saline or AF64A (5 nmol into each hippocampus) via stereotaxic technique. One week following surgery, saline-treated animals exhibited comparable performances (P greater than 0.2) on both the discrimination task (90.0 +/- 2.6% correct) and the alternation task (79.5 +/- 5.7%). In contrast, animals treated with AF64A showed a significant impairment of performance (P less than 0.005) on the alternation task (56.1 +/- 1.7%) as compared to the discrimination task (81.6 +/- 5.0%). Performance of the alternation task was significantly lower for AF64A-treated animals than for controls (P less than 0.02). AF64A-treated animals subsequently injected with pilocarpine (1.0 mg/kg, i.p.) showed moderate improvements in performance on the alternation task, while performance on the discrimination task remained unaffected. Immunocytochemical studies of choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) immunoreactivity indicated a loss of ChAT-positive cells in the septal region in AF64A-injected animals while TH-positive cells in the ventral tegmental area were unaffected by the treatment. The data suggest that AF64A can be used to produce selective lesions of the septohippocampal cholinergic system, which plays a greater role in representational memory than in dispositional memory.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose- and delay-dependent working/episodic memory impairments following intraventricular administration of ethylcholine aziridinium ion (AF64A)

The present study examined the effects of intraventricular administration of the cholinergic neurotoxin ethylcholine aziridinium ion (AF64A) on performance of a radial arm maze task. Male Sprague-Dawley rats were trained to perform a delayed-nonmatch to sample radial arm maze task in which a 1-h delay was imposed between the fourth and fifth arm selections. Following acquisition, animals were injected bilaterally with AF64A (1.5 or 0.75 nmol/side) or artificial cerebrospinal fluid into the lateral cerebral ventricles and allowed 7 days to recover before behavioral testing resumed. Significant dose- and delay-dependent impairments in the radial maze performance were observed in AF64A-treated rats as evidenced by fewer correct choices following the delay and by more errors to complete the task. Long-term testing in this task revealed significant recovery of memory performance. These findings indicate dose-dependent impairments in memory following intraventricular administration of AF64A and spontaneous behavioral recovery following such insult.

The histopathological, behavioral and neurochemical effects of intraventricular injection of ethylcholine mustard aziridinium (AF64A) in the neonatal rat

This study investigated the histopathological, behavioral and neurochemical effects of bilateral injection of 2.0, 0.5 and 0.1 nmol/ventricle ethylcholine aziridinium (AF64A) on postnatal day (PND) 2. The rats showed a significant, but non-dose-related reduction of choline acetyltransferase (ChAT) in the hippocampus but not the cerebral cortex or the caudate nucleus when sacrificed on PND 16. No effect on ChAT was found in any region at PND 58. The group given 2 nmol/ventricle were hyperactive and showed a deficit in spatial learning when tested on the Morris water maze at PND 38-43. No such differences were observed for the rats injected with 0.1 or 0.5 nmol/ventricle AF64A. This spatial learning impairment in the 2 nmol group was associated with non-specific tissue damage seen only in animals from this group that were sacrificed at PND 40. This tissue damage was most evident in the left medial frontal cortex, the caudate nuclei and the anterior dorsal hippocampus.

Transplantation of ventral forebrain cholinergic neurons to the hippocampus ameliorates impairment of radial-arm maze learning in rats with AF64A treatment

Two types of cholinergic neurons were transplanted into the hippoccampus of adult rats chemically damaged by lateral ventricular administration of AF64A, a cholinergic neurotoxin, and the effects were compared with respect to their ability to reinnervate the hippocampus and to repair behavioral deficit. Pieces of brain tissue containing the nucleus basalis magnocellularis (NBM) or the striatum were taken for grafting from 17-day rat fetuses. About 3 months after transplantation, the rats with bilateral NBM grafts showed significant amelioration in radial-arm maze performance and habituation to a novel environment in an open field box, although they had not recovered to the control level. In rats with NBM grafts that showed a good performance, there were surviving grafts and many ingrowths of AChE-positive fibers in the hippocampus. By contrast, rats with striatal grafts showed hardly any significant improvement in these behavioral measures. The AChE staining revealed poor outgrowth of the striatal grafts into the hippocampus. These results indicate that grafting of NBM cholinergic neurons, which are anatomically similar to septal neurons, into the hippocampus produces a partial restorative effect on the cognitive impairment associated with hypofunction of the septohippocampal system.

The biochemical and ultrastructural examinations in central cholinergic damage of the rat induced by the intraperitoneal administration of AF64A

Ethylcholine mustard aziridinium ion (AF64A), a synthesized cholinergic neurotoxin, was administered via intraperitoneal injection to the rat to study its effect on the central cholinergic nervous system. A single or consecutive daily injection of AF64A for 10 days resulted in a persistent reduction of acetylcholine (ACh) content in the several tested regions of the brain in the following order: hippocampus greater than cerebral cortex = striatum, the degree was the greatest in the hippocampus. Both resting and K(+)-stimulated release of ACh from the hippocampus were also significantly reduced 24 hr after a single injection of AF64A. Furthermore, daily injection of AF64A for 10 days induced a significant reduction of choline acetyltransferase (ChAT) activity in the homogenate obtained from the hippocampus but not from the cerebral cortex and striatum. ChAT activity in the crude synaptosomal fraction of the cerebral cortex was also significantly decreased. These results suggest that intraperitoneal administration of AF64A could induce cholinergic hypofunction more selectively in the nerve terminals. The high affinity choline uptake, which is located mainly on cholinergic nerve terminals, was not affected by the administration of AF64A. Any notable changes of ultrastructure in the cholinergic nerve terminals after the administration were not observed in all three regions examined. The present findings suggested that intraperitoneal administration of AF64A induces a specific damage of cholinergic nerve terminals by inhibiting ChAT activity. The cholinergic damage was most prominent in the hippocampus.

Ganglioside AGF2 promotes task-specific recovery and attenuates the cholinergic hypofunction induced by AF64A

Ganglioside AGF2 attenuated both the cognitive impairments and the cholinergic hypofunction induced by ethylcholine aziridinium ion (AF64A). Adult male rats were initially trained to perform a standard radial arm maze (RAM) task. Following training, they were injected intraperitoneally with 10 mg/kg AGF2 (AF/AGF2, CSF/AGF2) or the saline vehicle (AF/SAL, CSF/SAL) for 3 days prior to and for 14 days following bilateral injection of AF64A (3 nmol/side) or artificial CSF into the lateral ventricles. AF64A (AF/SAL) impaired performance of the standard RAM task and a working memory version of the task in which various delays were imposed between the fourth and fifth arm choices. In contrast, animals that received AGF2 and AF64A (AF/AGF2) were initially impaired on the standard RAM task but rapidly recovered and were performing as well as the control groups (CSF/SAL, CSF/AGF2) by the end of training. The AF/AGF2 group, however, exhibited persistent deficits on the working memory version of the RAM task. These data demonstrate that AGF2 promotes behavioral recovery in a task-dependent manner in this model system. Neurochemical analysis revealed that AF64A produced a significant 37% decrease in hippocampal ChAT activity that was significantly attenuated, but not prevented, by prior treatment with AGF2. Thus the behavioral recovery afforded by AGF2 might be related to increased cholinergic activity in the hippocampus that is sufficient for the performance of tasks which either lack or have a minimal working memory component. An analysis of the temporal profile of AGF2-induced neurochemical recovery revealed that ChAT activity was enhanced at 20, but not 2 or 11, weeks following AF64A. Since AGF2 did not attenuate the cholinergic cell loss (35%) induced by AF64A in the medial septum these data indicate that AGF2 might have (1) enhanced sprouting of cholinergic terminals following the initial insult, (2) directly increased ChAT activity in surviving neurons, or (3) induced behavioral and neurochemical recovery through a combination of these or other mechanisms.

AF64A depletes hippocampal high-affinity choline uptake but does not alter the density of alpha-bungarotoxin binding sites or modify the effect of exogenous choline

Sodium-dependent, high-affinity choline uptake (HACU) and the density of alpha-bungarotoxin (BuTX) receptor-binding sites were measured in the hippocampus following the intraventricular infusion of ethylcholine aziridinium ion (AF64A), a neurotoxin that competes with choline at high-affinity choline transport sites and may result in the degeneration of cholinergic axons. Eight days after the infusion of AF64A into the lateral ventricles (2.5 nmol/side), HACU was depleted by 60% in the hippocampus of experimental animals in comparison with controls, but the density of BuTX-binding sites was not altered. The administration of 15 mg/ml of choline chloride in the drinking water increased the density of BuTX-binding sites, as previously reported by this laboratory. The administration of AF64A did not prevent the effect of exogenous choline on the density of binding sites, nor did choline treatment alter the effect of AF64A on HACU. These data indicate that the density of BuTX-binding sites in the hippocampus is not altered following a substantial decrease in HACU and presumed degeneration of cholinergic axons. Since the effect of exogenous choline was not prevented by AF64A treatment, the data are interpreted to support the hypothesis that the increase in the density of BuTX-binding sites following dietary choline supplementation is attributable to a direct effect of choline on receptor sites.

AF64 depletes hypothalamic high-affinity choline uptake and disrupts the circadian rhythm of locomotor activity without altering the density of nicotinic acetylcholine receptors

Ethylcholine aziridinium ion (AF64) was synthesized from acetylethylcholine mustard hydrochloride and 5 nmol was infused into the third ventricle of rats. Seven days after AF64 treatment, sodium dependent high-affinity choline (HACU) uptake was decreased by 54% in the hypothalamus. The density of hypothalamic (-)-[3H]nicotine binding sites and [alpha-125I]bungarotoxin sites in AF64-treated animals did not differ significantly from controls. A second experiment was performed to elucidate the effect of AF64 treatment on HACU and determine the effect of AF64 on entrained circadian rhythms. Animals were infused with artificial CSF or 5 nmol AF64. Locomotor activity and body temperature were recorded for 3 weeks before and 3 weeks after treatment. Ten of 14 AF64-treated animals showed a decrease in the ratio of dark cycle:light cycle locomotor activity. The decrease in dark-cycle activity was correlated with a disruption of a predominant circadian rhythm. The circadian rhythm (CR) of core body temperature was disrupted only transiently, but the CR of locomotor activity remained disrupted for the duration of the experiment in several AF64-treated animals. HACU was decreased by 48% in animals with disrupted rhythms in comparison with controls but was not significantly decreased in AF64-treated animals with normal dark-cycle activity and circadian activity. These data suggest that the AF64-treated animal may be a good model for studying the role of acetylcholine in maintaining the integrity of certain circadian rhythms.

Hemicholinium-3 prevents the working memory impairments and the cholinergic hypofunction induced by ethylcholine aziridinium ion (AF64A)

The present study examined whether intraventricular administration of the potent high affinity choline transport (HAChT) inhibitor hemicholinium-3 (HC-3) would attenuate the memory impairments and the neurochemical deficits induced by i.c.v. ethylcholine aziridinium ion (AF64A). Male Sprague-Dawley rats were trained to perform a delayed-non-match to sample radial arm maze (RAM) task in which a 1-h delay was imposed between the fourth and fifth arm selections. Following 30 acquisition trials, animals were bilaterally injected with AF64A (3 nmol/side) or AF64A preceded by HC-3 (20 micrograms/side) into the lateral ventricles and allowed 7 days to recover before behavioral testing resumed. Control animals received either artificial cerebrospinal fluid or HC-3. AF64A-treated rats were significantly impaired in their performance of the RAM task as evidenced by fewer correct choices following the delay and more total errors to complete the task. This behavioral deficit was associated with a significant (32%) decrease in HAChT in the hippocampus. In contrast, animals pretreated with HC-3 exhibited no significant decreases in HAChT or decrements in RAM performance. These findings indicate that the memory deficits resulting from intraventricular administration of AF64A are a consequence of the compound's cholinotoxic properties and in particular its interaction with the HAChT carrier. Furthermore they demonstrate that a select alteration of septohippocampal cholinergic activity is sufficient to disrupt working memory processes.

Intraseptal administration of muscimol produces dose-dependent memory impairments in the rat

The present study examined the effects of intraseptal administration of the GABAergic agonist muscimol on performance of a radial-arm maze (RAM) task. Male Long-Evans rats were trained to perform a RAM task in which a 1-h delay was imposed between the sample and the test session. In this task rats have access to four out of eight maze arms during a predelay session. Following a 1-h delay, rats are returned to the maze and allowed to freely choose among all eight arms. Arms not blocked during the predelay session are baited, and entry into an arm chosen during the predelay session or a repeated entry into a postdelay chosen arm constitutes an error. Following acquisition, animals were implanted with a single cannula aimed at the medial septum. A within-subjects design was utilized to examine the effects of intraseptal administration of muscimol (0.0, 0.75, 1.5 or 3.0 nmol) on performance in this task. All drugs or artificial cerebrospinal fluid were administered immediately following the predelay session. Muscimol, a GABA-A agonist, produced a dose-dependent impairment in maze performance as evidenced by fewer correct choices in the first four postdelay choices and an increase in the number of errors. Intraseptal administration of muscimol did not significantly alter latency per choice on the RAM task nor did it affect locomotor activity levels. Muscimol-induced impairments were also observed when a 4-h delay was imposed between the fourth and the fifth maze selection, suggesting that the behavioral deficit represents an inability to store or retain spatial working memories rather than a general performance deficit. These data indicated that pharmacological manipulation of GABA-A receptors within the medial septum modifies working memory processes. The potential interaction of GABAergic and cholinergic mechanisms in the modulation of working memory processes is discussed.

Transplantation of septal cholinergic neurons to the hippocampus improves memory impairments of spatial learning in rats treated with AF64A

Embryonic septal neurons were transplanted into damaged hippocampus in adult rats which had received lateral ventricular administration of AF64A, a cholinergic neurotoxin. About 3 months after transplantation, the rats with bilateral septal grafts showed significant improvement in the radial maze and T-maze tasks. Many ingrowths of acetylcholinesterase (AChE)-positive fibers originating from the grafts were observed in the hippocampus of the rats which showed good performance in these learning tasks. These results indicate that transplantation of septal cholinergic neurons into the AF64A-treated hippocampus may induce at least partial recovery in learning tasks believed to involve the hippocampus.

Behavioural and histological effects of low concentrations of intraventricular AF64A

The effects of ethylcholine mustard aziridinium ion (AF64A; 0.3, 1.0 and 3.0 nmol), injected into each lateral ventricle in the rat, were determined in a range of behavioural tests, each involving a learning component. Effects were observed at 1.0 and 3.0 nmol/side and, to a lesser extent, at 0.3 nmol/side. Habituation of locomotor activity was impaired and deficits in learning were obtained using a variety of mazes including the Morris swimming maze. Slight, non-significant impairments occurred in shock reinforced behaviours. Histologically, marginal effects were observed at 0.3 nmol/side, and slight ventricular dilatation with necrosis of the hippocampus, restricted to the site of injection at 1.0 nmol/side; at 3.0 nmol/side more widespread necrosis was apparent. Biochemical efficacy of the lesions in terms of cholinergic changes was confirmed by analysis of acetylcholinesterase (AChE) levels showing decreases in the hippocampus and the cortex; no studies were carried out with respect to other neurotransmitters. Cognitive deficits can therefore be obtained by i.c.v. injection of AF64A at doses which cause significant cholinergic changes with minimal histological disturbances.

The cholinergic neurotoxin ethylcholine mustard aziridinium (AF64A) induces an increase in MAO-B activity in the rat brain

Recently it was reported that there is an increase in monoamine oxidase B (MAO-B) activity in post-mortem brains of patients with Alzheimer's disease. It was postulated that this increase in MAO-B activity was due to gliosis associated with neuronal degeneration. The aim of the present investigation was to evaluate the effect on MAO of neuronal degeneration primarily affecting the cholinergic system. The specific cholinergic toxin AF64A (3 and 4.5 nmol) was injected bilaterally into the cerebral ventricles of rats. We then estimated MAO-A, MAO-B, dopamine (DA) uptake rates and choline acetyltransferase (ChAT) activities in hippocampus, striatum and cortex, 1, 2.5 and 4.5 weeks after the injection. Marked long-lasting reduction in ChAT activities appeared only in hippocampus, consistent with previous reports. The MAO-A activity was unchanged as were DA uptake rates. Neither was there any change in MAO-B activity found 1 week after the injection. However, a significant increase in MAO-B activity appeared after 2.5 weeks and persisted after 4.5 weeks in all 3 brain regions investigated. This result is likely to reflect progressive gliosis after cholinergic neuronal degeneration. Previous results have shown an increased MAO-B activity with age and a further accelerated increase in Alzheimer's disease. Experimentally, hemitransection and injection of kainic acid have been shown to cause a similar increase. The present results show that changes in MAO-B activity also reflect degenerative processes in brain mainly affecting the cholinergic system.

Selective working memory impairments following intradentate injection of colchicine: attenuation of the behavioral but not the neuropathological effects by gangliosides GM1 and AGF2

Bilateral injection of 3.5 micrograms of colchicine into the dentate gyrus produced specific learning and memory impairments together with a selective pattern of neuropathology. Animals injected with colchicine exhibited a significant impairment in their ability to perform the working memory, but not the reference memory, component of a multiple component T-maze task. These deficits were transient and over time all animals were able to reaquire the task to preoperative levels of performance. Histological analyses revealed that intradentate injection of colchicine produced 1) a significant decrease in the width of both the superior and inferior blades of the dentate gyrus reflecting the extensive loss of granule cells, 2) a related decrease in the size of the dentate molecular layer, and 3) a decrease in the number of cholinergic neurons in the medial septum. The second phase of the experiment demonstrated that gangliosides GM1 and AGF2 did not prevent the initial impairments in working memory performance induced by colchicine but rather accelerated the rate at which it recovered. The gangliosides did not decrease the extent of neuronal damage; there was no sparing of granule cells in the dentate gyrus or cholinergic neurons in the medial septum. These data further support a role for the hippocampus in working memory processes and they also indicate that gangliosides GM1 and AGF2 might be useful for treating the behavioral deficits induced by hippocampal damage.

Non-specific effects of the putative cholinergic neurotoxin ethylcholine mustard aziridinium ion in the rat brain examined by autoradiography, immunocytochemistry and gel electrophoresis

Autoradiographic localisation of [3H]-ethylcholine mustard aziridinium ion (ECMA) after microinjection into the rat striatum has revealed intracellular sequestration of the toxin by glial and endothelial cells; fewer neuronal cells were labelled. Intrastriatal injection of 200 pmol ECMA caused severe cavitation of the tissue, extensive gliosis and permanent damage to myelinated structures, as revealed by immunocytochemical detection of glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP). These non-specific effects are in addition to ECMA's irreversible action on the choline carrier associated with cholinergic neurons, and only marginally protected by concomitant administration of the reversible choline transport inhibitor hemicholinium-3. They may instead be attributed to the powerful alkylating action that ECMA has on tissue proteins, as shown by fluorography of synaptosomal proteins treated with [3H]ECMA and separated by SDS-PAGE.

AF64A-induced working memory impairment: behavioral, neurochemical and histological correlates

The present studies examined the behavioral, neurochemical and histological consequences of intraventricular administration of ethylcholine aziridinium ion (AF64A). Male Long-Evans rats were trained to perform a radial arm maze task in which a one hour delay was imposed between the fourth and fifth arm selections. Following acquisition, animals were bilaterally injected with AF64A (3 nmol/side) or CSF into the lateral ventricles and allowed 14 days to recover before behavioral testing resumed. AF64A-treated animals were markedly impaired in their ability to perform this working/episodic memory task at a variety of delay intervals. In contrast to a long-lasting impairment on the radial maze task, these animals showed no impairment in their ability to acquire a simple discrimination task (reference/skill memory). Neurochemical analysis revealed a significant (50%) decrease in choline acetyltransferase (ChAT) activity in the hippocampus (HPC) 90 days following surgery. ChAT activity was not affected in the striatum, frontal and parietal cortices, cingulate or amygdala. Regional concentrations of catecholamines and indoleamines were not affected in any of these brain regions. Histological analysis of animals receiving unilateral injections of AF64A (3 nmol) into the right lateral ventricle revealed decreases in ChAT-immunoreactive (ChAT-IR) cells within the medial septum/vertical limb diagonal band (MS/VLDB), but not in nucleus accumbens, striatum or basal nucleus regions. These data suggest that: (1) intraventricular administration of AF64A can markedly impair working/episodic, as opposed to reference/skill memory, processes; (2) AF64A can be used to selectively alter presynaptic cholinergic indices within the hippocampus; and (3) the behavioral deficits resulting from AF64A administration are most likely a consequence of altered septohippocampal cholinergic function.

AF64A(ethylcholine aziridinium ion)-induced basal forebrain lesion impairs maze performance

Rats were given bilateral injections of ethylcholine aziridinium ion, AF64A (1 nmol/side) into the basal forebrain (BF). One month later, choline acetyltransferase activity was reduced by 25% in the frontal cortex (FC). There was a marked decrease in cortical uptake of [3H]choline, but [3H]GABA and [3H]dopamine uptake was not affected by the injection. Histological analysis confirmed that this dose of AF64A caused acetylcholinesterase staining in the FC to disappear. Acquisition and retention of a T-maze task were impaired in the rats with BF lesions one month after the injection. Acquisition of the water-filled multiple T-maze task was also impaired by AF64A. These observations suggest that the cholinergic component in the BF is involved in spatial memory.