Irit Gordon

Memory deficits and cholinergic impairments in apolipoprotein E-deficient mice ☆

Apolipoprotein E-deficient mice provide a useful system for studying the role of apolipoprotein E (apoE) in the function of distinct neuronal systems. In the present study we focused on the cholinergic system of these mice. This was pursued by measurements of specific biochemical, physiological and cognitive parameters. Morris Water Maze tasks revealed impairments in working memory but not in reference memory of the apoE-deficient mice. Measurements of brain choline acetyltransferase activities revealed them to be markedly lower in the hippocampus and frontal cortex of the apoE-deficient mice than in the corresponding brain areas of the controls, but unaltered in other brain areas. In addition, hypothermia induced by the centrally acting muscarinic agonist, oxotremorine, was reduced in the apoE-deficient mice as compared to controls. These results show that apoE-deficient mice have cholinergic deficits and highlight the importance of this mouse model for studying the interactions between apoE and the cholinergic nervous system.

Modulatory effect of agents active in the presynaptic dopaminergic system on the striatal dopamine transporter

We have investigated the effects of agents active in the presynaptic dopaminergic system on the characterization of the rat striatal dopamine transporter. The dopamine transporter was characterized by high-affinity [3H]GBR 12935 (1-[2-diphenylmethoxy)-ethyl]-4-(3-phenylpropyl)-piperazine) binding to a membrane preparation and by [3H]dopamine uptake into striatal synaptosomes. Subchronic treatment with reserpine (2.5 mg/kg, 4 days), a monoamine depletor, caused a significant decrease in both [3H]GBR 12935 binding (20%) and [3H]dopamine uptake (51%). In contrast, amantadine (a dopamine releaser) treatment (20 mg/kg, 21 days) induced an increase (28%) in the maximal number of [3H]GBR 12935 sites. Chronic levo-dopa (dopamine precursor) treatment combined with carbidopa (50 mg/kg and 5 mg/kg respectively, 21 days) as well as benztropine (dopamine uptake inhibitor) treatment (10 mg/kg, 21 days) did not affect the striatal dopamine transporter characteristics. The present results showed that the striatal dopamine transporter is sensitive to changes in dopaminergic neurotransmission caused by agents that do not interact directly with the dopamine carrier.

Phosphorylation of tau in apolipoprotein E-deficient mice

It has been suggested that the deleterious effects of the allele E4 of apolipoprotein E (apoE) in Alzheimers disease (AD) are related to its inability to interact with the microtubule associated protein tau and to thereby prevent its hyperphosphorylation. In the present study we investigated the effects of apoE on tau phosphorylation by immunoblot analysis of the levels and extents of phosphorylation of tau of apoE-deficient mice. This revealed that mAb AT8, which is directed against a phosphorylated tau epitope, labels tau of the apoE-deficient mice more intensely than that of control mice and that the opposite occurs with mAb Tau1, which is directed against dephosphorylated tau epitopes. mAb ALZ50 also labeled the tau enriched preparations of the apoE-deficient mice more intensely than those of the controls, whereas the extents of their labeling by the phosphorylation insensitive anti-tau mAb 134 were similar. These results suggest that tau of apoE-deficient mice is hyperphosphorylated.

Biochemical and cognitive studies of apolipoprotein-E-deficient mice

Apolipoprotein-E-deficient mice provide a useful model system for studying the role of apolipoprotein E (apoE) in brain function. In the present study, we characterization the cholinergic function of these mice and the extent of phosphorylation of their cytoskeletal protein τ. Morris water maze tasks revealed deficits in working memory that were accompanied by a specific decrease in hippocampal and cortical choline acetyltransferase activities. Immunoblot experiments utilizing native and dephosphorylated τ and antibodies directed against specific phosphorylated and unphosphorylated τ epitopes revealed that τ of the apoE-deficient mice is hyperphosphorylated. These results show that apoE-deficient mice have cognitive cholinergic and cytoskeletal derangements and point out the importance of this model for studying the role of apoE in neuronal function.

Derangement in stress response of apolipoprotein E-deficient mice☆

Apolipoprotein E (apoE) is associated with familial and sporadic Alzheimers disease (AD). Stress has been identified as a putative risk factor of AD. Thus, in the present study we examined the susceptibility of apoE-deficient mice to stress. The results obtained revealed that the elevation of corticosterone levels in apoE-deficient mice following restraint stress is markedly lower than in controls, and that these mice differ in their behavioral pain response to noxious stimuli in both stress and non-stress conditions. These findings suggest an interplay between apoE and the response to stressful stimuli and provide a model for elucidating the relationship between apoE and susceptibility to stress.

Developmental and age-related alterations in rat brain presynaptic dopaminergic mechanisms.

Age-related changes in both pre- and post-synaptic components of dopamine neurons have been demonstrated in humans as well as in animals. Our study was designed to examine the effects of age on presynaptic DA neurons. To assess the developmental changes in rat striatal dopamine carrier, we used [3H]GBR 12935, which binds selectively to this transporter. In addition we monitored changes in amphetamine- and KCl-induced [3H]DA release from rat striatal slices. We were able to demonstrate age dependent changes in DA transporter density, which reached a peak at age 3 months. Amphetamine-induced released of stored DA was exactly reversed, with a nadir at age 3 months. We assumed that the combination of low DA transporter level with increased transporter-mediated DA release may have a major compensatory role with respect to the maintenance of dopaminergic transmission during normal development, aging and neuro-degenerative diseases.

Bilateral imbalance in striatal DA-uptake controls rotation behavior

We tested the relation between bilateral imbalance in striatal DA uptake and asymmetric rotation behavior. Rats were screened for either spontaneous or amphetamine-induced preferred direction of rotation and the presynaptic DA transporter in the ipsi- and contralateral striatum was characterized in vitro by measuring [3H]DA uptake or [3H]GBR-12935 binding. DA uptake was lower in the striatum contralateral to either the spontaneous or amphetamine-induced preferred direction of rotation. Similar imbalance in the density of the transporter was confirmed by the binding experiments. These results support the hypothesis that striatal imbalance in DA uptake produces asymmetric behavior during spontaneous rotation. Further studies are required to assess the involvement of DA transporter imbalance in amphetamine-induced behavioral asymmetry.

Long-term effects of amygdaloid kindling on striatal dopaminergic terminals.

The present study assessed the effects of kindling on striatal DA terminals. Kindled and control rats were tested for DA transporter density using [3H]GBR-12935 binding to striatal membranes and for amphetamine and KCl-induced [3H]DA release from striatal slices. Kindling decreased the maximal number of [3H]GBR-12935 binding sites in the dorsal striatum of rats sacrificed either 2 h or 4 weeks after the last seizure but had no effect on stimulated fractional [3H]DA release. These findings suggest a minor damage to DA terminals in the dorsal striatum. At the same postseizure time points, kindling augmented the hyperlocomotion associated with novel environment. Explanation of this effect requires in vivo measures of striatal DA functioning.

Behavioral and biochemical studies in rats following prenatal treatment with β-adrenoceptor antagonists

Abstract Increased motor activity and poor performance in the active avoidance test were observed in the offspring of rats treated with d1-propranolol or sotalol during pregnancy, but not with atenolol and d-propranolol. All substances were administered in drinking water from days 8–22 of gestation. A significant increase in the density of muscarinic acetylcholine receptors in the hippocampus was found for dl-propranolol and sotalol, at 35 and 20 days of age, respectively. Twenty-day-old pups bom to dl-propranolol-treated rats exhibited a non-significant decrease in the number of β-adrenoceptors in the frontal cortex. Assuming that all the β-adrenoceptor antagonists tested had access to the developing fetal brain, the effect of dl-propranolol and sotalol on behavior could stem from central β 2 -adrenoceptor blockade. In view of the lack of behavioral changes after atenolol, a β 1 -selective adrenoceptor antagonist, it is suggested that the clinical use of β 1 -selective adrenoceptor antagonists during pregnancy might be safer for the fetus than β 2 -adrenoceptor antagonists.

The effect of repeated amphetamine treatment on striatal DA transporter and rotation in rats

The effect of repeated amphetamine treatment on the involvement of the striatal DA transporters in rotation behavior was tested in rats. Repeated amphetamine treatment had no effect on [3H]DA uptake or [3H]GBR-12935 binding density. However, unlike the naive rats who rotated away from the striatum with a lower density of DA transporters, rats sensitized to amphetamine rotated toward the striatum with a lower density of DA transporters. These findings imply that repeated amphetamine augments the subcortical involvement in behavioral output.