Selective cholinergic neurotoxin: AF64A''s effects in rat striatum

The selective neurotoxic effects of the aziridinium ion of ethylcholine (AF64A) have been examined after stereotaxic injection into the rat striatum. In a dose-response study (2-26 nmol), 8 nmol caused a 46% decrease in striatal choline acetyltransferase (CAT) activity with minimal effects on the activities of glutamate decarboxylase (GAD) and tyrosine hydroxylase (TH) at 7 days. Maximal CAT reductions of 78-82% occurred with doses of 16-26 nmol which also caused dose-related decreases in GAD and TH activities that paralleled the progressive decrements in CAT. A time course study with 8 nmol indicated a rapid 20% reduction of CAT activity by 12 h and an additional gradual fall of 20% over the next week; TH and GAD activities were not significantly reduced. The selective inhibition of CAT activity persisted for at least 3 months. Histological examination of Nissl stained sections revealed an area of nonspecific damage at the injection site with an abrupt border surrounded by apparently normal striatal neuropil; however; neuronal perikarya staining intensely for acetylcholinesterase were not reduced. These preliminary findings strongly suggest that AF64A has selective neurotoxic effects against striatal cholinergic neurons while relatively sparing striatal GABAergic intrinsic neurons or dopaminergic afferents.     

AF64A, a cholinergic neurotoxin, selectively depletes acetylcholine in hippocampus and cortex, and produces long-term passive avoidance and radial-arm maze deficits in the rat

The behavioral and biochemical effects of AF64A, a presynaptic cholinergic neurotoxin, were investigated. Bilateral administration of this compound into the lateral cerebral ventricles produced transient and dose-related effects on sensorimotor function and long-term impairments of cognitive behavior. Male Fischer-F344 rats dosed with either 15 or 30 nmol of AF64A reacted 29–62% faster than CSF-injected controls in a hot-plate test 14 (but not 1, 7, 21 or 28) days following dosing. The group administered 15 nmol of AF64A was also significantly more active (41%) than controls 28 days following dosing. The activity level of this group was comparable to that of controls at other times and hyperactivity was never observed in the 30 nmol group. Retention of a step-through passive avoidance task, assessed 35 days after dosing, was impaired in both 15 and the 30 nmol groups. Their step-through latencies were significatlly shorter than the control latencies, and they exhibited more partial entries during the 24-h retention test. Radial-arm maze performance, measured 60–80 days following treatment, was markedly impaired in the treated groups. Animals treated with AF64A made fewer correct responses in their first 8 choices, required more total selections to complete the task, and had an altered pattern of spatial responding in the maze. The neurochemical changes produced by AF64A, determined 120 days after dosing, were specific to the cholinergic system and consisted of decreases of ACh in both the hippocampus (15 and 30 nmol groups) and the frontal cortex (30 nmol group). The concentrations of catecholamines, indoleamines, their metabolites and choline in various brain regions were not affected by AF64A. Furthermore, histological analysis revealed that the doses of AF64A used in the present study did not damage the hippocampus, the fimbria-fornix, the septum or the caudate nucleus. These data support the contention that cholinergic processes in the hippocampus, nd/or frontal cortex play an important role in learning and memory processes. Furthermore, based upon the behavioral and biochemical data presented, it is suggested that AF64A could be a useful pharmacological tool for examining the neurobiological substrates of putative cholinergic disorder such as senile dementia of the Alzheimer's type.     

Protection against inflammatory neurodegeneration and glial cell death by 7beta-hydroxy epiandrosterone, a novel neurosteroid

It has been demonstrated that neuroprotective effects of dehydroepiandrosterone (DHEA) may be mediated by its 7alpha- and 7beta-hydroxy derivatives. Epiandrosterone is also converted to 7beta-hydroxy epiandrosterone (7beta-OH EPIA) in numerous tissues. The aim of the present study was to establish whether treatment with 7beta-hydroxy epiandrosterone has a neuroprotective effect in animal models of Alzheimer's disease (AD) lesions. Intra-amygdaloid administration of amyloid beta [Abeta(25-35)] increased the number of tau-positive cells in the ipsilateral hippocampus. Intracerebroventricular administration of ethylcholine aziridinium (AF64A) caused cholinergic damage in the septum, and glial lesions in the lateral septal nucleus and in the lateral zones of the hippocampus. These effects were almost completely prevented when animals were treated subcutaneously (b.i.d.) for 10 days with 0.1 mg/kg 7beta-hydroxy epiandrosterone. These findings indicate that 7beta-hydroxy epiandrosterone has powerful cytoprotective effects suggesting that (a) this neurosteroid may have therapeutic potential in various neurodegenerative conditions such as Alzheimer's disease, and (b) 7beta-hydroxy steroids may constitute a novel class of endogenous neuroprotective agents.     

Relationships among Sensory Responsiveness,Anxiety, and Ritual Behaviors in Children with and without Atypical Sensory Responsiveness

Aim: To explore relationships between sensory responsiveness, anxiety, and ritual behaviors in boys with typical and atypical sensory responsiveness. Method: Forty-eight boys, ages 5–9 participated in the study (28 boys with atypical sensory responsiveness and 20 controls). Atypical sensory responsiveness was defined as a score of ≤154 on the Short Sensory Profile. Parents completed the Sensory Profile, the Screen for Child Anxiety Related Emotional Disorders, and the Childhood Routines Inventory. Results: Children with atypical sensory responsiveness had significantly higher levels of anxiety and a higher frequency of ritual behaviors than controls. Atypical sensory responsiveness was significantly related to both anxiety and ritual behaviors, with anxiety mediating the relationship between sensory modulation and ritual behaviors. Conclusions: The findings elucidate the potential consequences of atypical sensory responsiveness and could support the notion that ritual behaviors develop as a coping mechanism in response to anxiety stemming from primary difficulty in modulating sensory input.     

Cholinergic lesion of the striatum impairs acquisition and retention of a passive avoidance response

Significant impairments in the acquisition and retention of a step-down passive avoidance task were found in rats with striatal lesions induced by the cholinergic neurotoxin AF64A. No significant differences between control and AF64A-injected rats were found in sensitivity to electric shock or in various measures of spontaneous locomotor activity. Striatal choline acetyltransferase (CAT) activity was significantly decreased in AF64A-treated rats compared with controls, whereas glutamic acid decarboxylase (GAD) activities were not. Furthermore, there were no significant differences between groups in activities of CAT and GAD in either the cortex or the hippocampus, results that support the specificity of the lesion to the striatum. The passive avoidance deficits found in these rats after intrastriatal injection of AF64A support a role for the striatal cholinergic system in complex behavioral processes.     

Pre-treatment neurotransmitter metabolites and response to imipramine or amitriptyline treatment

Preliminary data are presented from the NIMH Collaborative Study on the psychobiology of depression, biological studies, dealing with relationships between the pre-treatment levels of the neurotransmitter metabolites 3-methoxy-4-hydrophenethyleneglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) and the subsequent therapeutic response of depressed patients to imipramine or amitriptyline. Eighty-seven depressed patients were studied during pre-treatment and treatment periods. It has been found that (1) both low pre-treatment urinary MHPG and low CSF 5-HIAA values are associated with a response to imipramine; these relationships were not artefacts due to sex or age; (2) there were no significant relationships between pre-treatment urinary MHPG, CSF MHPG, 5-HIAA, or HVA values and the subsequent response, or failure of response, to amitriptyline; (3) there was not a bimodal distribution for CSF 5-HIAA. For both males and females, there were positive and statistically significant correlations between CSF MHPG and urinary MHPG; for the females, there were positive and significant correlations between both urinary and CSF MHPG and CSF 5-HIAA. The theoretical and practical implications of these findings are discussed.     

Hippocampal electrical activity in relation to behavior following ethylcholine aziridinium ion (AF64A) treatment

The effects of intracerebroventricular (ICV) injections of ethylcholine aziridinium ion (AF64A; 3 nmol/3 microliters/side) on the pattern of hippocampal electrical activity were studied in freely moving and urethane anesthetized rats. AF64A treated rats showed a significantly smaller increase in 6-12 Hz hippocampal rhythmical slow activity (RSA) with struggling in the no drug condition in comparison to the vehicle injected rats. However, neither AF64A treatment nor a control injection abolished the presumed cholinergic form of RSA that is present during urethane anesthesia. Systemic injection of atropine in waking rats did not significantly alter RSA in either the AF64A or vehicle injected rats. Analysis of histological brain sections revealed extensive damage to the fimbria-fornix, CA3 of the hippocampus, corpus callosum, neocortex and striatum. Acetylcholinesterase staining of the remaining hippocampus appeared normal in the AF64a treated rats. The data indicate that the depletion of cholinergic markers in the hippocampus following ICV administration of AF64A is not sufficient to disrupt the cholinergic form of RSA. Further, the question is discussed as to whether AF64A produces its cholinoselective effects via a specific pharmacological action or through a nonspecific destruction of the fimbria-fornix.     

Lateralization of brain morphologic and cholinergic abnormalities in Alzheimer's disease

The extent of left-right asymmetry in the densities of senile plaques and neurofibrillary tangles and the levels of the cholinergic enzymes choline acetyltransferase and acetylcholinesterase were quantified in the middle frontal and superior temporal cerebral cortex, entorhinal cortex, and prosubiculum of the hippocampus from 21 patients who died with Alzheimer's disease. Morphologic lesions were more asymmetrically distributed than deficits in the cholinergic enzymes. Neither cerebral hemisphere showed consistently higher densities of senile plaques and neurofibrillary tangles, or lower levels of choline acetyltransferase and acetylcholinesterase. Deficits in the cholinergic enzymes tended to colateralize, while asymmetries of senile plaques and neurofibrillary tangles did not. Finally, left-right asymmetry in the density of senile plaques diminished with increasing neuropathologic severity, while similar evidence for diminishing left-right asymmetry of neurofibrillary tangle density or cholinergic enzyme activity with increasing severity was not found.