Laus M. Broersen

Docosahexaenoic Acid Reduces Amyloid β Production via Multiple Pleiotropic Mechanisms

Alzheimer disease is characterized by accumulation of the β-amyloid peptide (Aβ) generated by β- and γ-secretase processing of the amyloid precursor protein (APP). The intake of the polyunsaturated fatty acid docosahexaenoic acid (DHA) has been associated with decreased amyloid deposition and a reduced risk in Alzheimer disease in several epidemiological trials; however, the exact underlying molecular mechanism remains to be elucidated. Here, we systematically investigate the effect of DHA on amyloidogenic and nonamyloidogenic APP processing and the potential cross-links to cholesterol metabolism in vivo and in vitro. DHA reduces amyloidogenic processing by decreasing β- and γ-secretase activity, whereas the expression and protein levels of BACE1 and presenilin1 remain unchanged. In addition, DHA increases protein stability of α-secretase resulting in increased nonamyloidogenic processing. Besides the known effect of DHA to decrease cholesterol de novo synthesis, we found cholesterol distribution in plasma membrane to be altered. In the presence of DHA, cholesterol shifts from raft to non-raft domains, and this is accompanied by a shift in γ-secretase activity and presenilin1 protein levels. Taken together, DHA directs amyloidogenic processing of APP toward nonamyloidogenic processing, effectively reducing Aβ release. DHA has a typical pleiotropic effect; DHA-mediated Aβ reduction is not the consequence of a single major mechanism but is the result of combined multiple effects.

DHA and cholesterol containing diets influence Alzheimer-like pathology, cognition and cerebral vasculature in APPswe/PS1dE9 mice.

Cholesterol and docosahexenoic acid (DHA) may affect degenerative processes in Alzheimers Disease (AD) by influencing Abeta metabolism indirectly via the vasculature. We investigated whether DHA-enriched diets or cholesterol-containing Typical Western Diets (TWD) alter behavior and cognition, cerebral hemodynamics (relative cerebral blood volume (rCBV)) and Abeta deposition in 8- and 15-month-old APP(swe)/PS1(dE9) mice. In addition we investigated whether changes in rCBV precede changes in Abeta deposition or vice versa. Mice were fed regular rodent chow, a TWD-, or a DHA-containing diet. Behavior, learning and memory were investigated, and rCBV was measured using contrast-enhanced MRI. The Abeta load was visualized immunohistochemically. We demonstrate that DHA altered rCBV in 8-month-old APP/PS1 and wild type mice[AU1]. In 15-month-old APP/PS1 mice DHA supplementation improved spatial memory, decreased Abeta deposition and slightly increased rCBV, indicating that a DHA-enriched diet can diminish AD-like pathology. In contrast, TWD diets decreased rCBV in 15-month-old mice. The present data indicate that long-term dietary interventions change AD-like pathology in APP/PS1 mice. Additionally, effects of the tested diets on vascular parameters were observed before effects on Abeta load were noted. These data underline the importance of vascular factors in the APP/PS1 mouse model of AD pathology.

Changes in cerebral blood volume and amyloid pathology in aged Alzheimer APP/PS1 mice on a docosahexaenoic acid (DHA) diet or cholesterol enriched Typical Western Diet (TWD).

High dietary cholesterol and low dietary docosahexaenoic acid (DHA) intake are risk factors for Alzheimers disease (AD). However, it is unclear how these components influence the course of the disease. We investigated the effects of dietary lipids on beta-amyloid deposition and blood circulation in the brains of 18-month-old APP/PS1 mice. Starting at 6 months of age, mice were fed a regular rodent chow, a Typical Western Diet (TWD) containing 1% cholesterol, or a diet with a high (0.5%) level of DHA for 12 months. Relative cerebral blood volume (rCBV) and flow (CBF) were determined with (2)H MR spectroscopy and gradient echo contrast enhanced MRI. Deposition of beta-amyloid was visualized in fixed brain tissue with immunohistochemistry. The TWD diet increased plaque burden in the dentate gyrus of the hippocampus, but did not significantly reduce rCBV. In contrast, the DHA-enriched diet increased rCBV without changing blood flow indicating a larger circulation in the brain probably due to vasodilatation and decreased the amount of vascular beta-amyloid deposition. Together, our results indicate that the long-term intake of dietary lipids can impact both brain circulation and beta-amyloid deposition, and support the involvement of hemodynamic changes in the development of AD.

Combined uridine and choline administration improves cognitive deficits in spontaneously hypertensive rats.

Rationale. Hypertension is considered a risk factor for the development of cognitive disorders, because of its negative effects on cerebral vasculature and blood flow. Genetically induced hypertension in rats has been associated with a range of cognitive impairments. Therefore, spontaneously hypertensive rats (SHR) can potentially be used as a model for cognitive deficits in human subjects. Consecutively, it can be determined whether certain food components can improve cognition in these rats. Objective. The present study aimed to determine whether SHR display specific deficits in attention, learning, and memory function. Additionally, effects of chronic uridine and choline administration were studied. Methods. 5-7 months old SHR were compared with normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats. (a) The operant delayed non-matching-to-position (DNMTP) test was used to study short-term memory function. (b) The five-choice serial reaction time (5-CSRT) task was used to assess selective visual attention processes. (c) Finally, the Morris water maze (MWM) acquisition was used as a measure for spatial learning and mnemonic capabilities. Results. (1) SHR exhibited significantly impaired performance in the 5-CSRT test in comparison with the two other rat strains. Both the SHR and WKY showed deficits in spatial learning when compared with the SD rats. (2) Uridine and choline supplementation normalized performance of SHR in the 5-CSRT test. (3) In addition, uridine and choline treatment improved MWM acquisition in both WKY and SHR rats. Conclusion. The present results show that the SHR have a deficiency in visual selective attention and spatial learning. Therefore, the SHR may provide an interesting model in the screening of substances with therapeutic potential for treatment of cognitive disorders. A combination of uridine and choline administration improved selective attention and spatial learning in SHR.

The role of the medial prefrontal cortex of rats in short-term memory functioning: further support for involvement of cholinergic, rather than dopaminergic mechanisms

The putative involvement of the dopaminergic innervation of the medial part of the prefrontal cortex (PFC) in short-term memory functioning was investigated by evaluating the effects of local infusions of dopaminergic drugs into the ventral part of the medial PFC of rats in an operant delayed-matching-to-position (DMTP) task. Two separate groups of rats were tested after bilateral microinfusion of several doses of either the dopamine receptor agonist apomorphine (APO) or the dopamine receptor antagonist cis-flupenthixol (FLU) into the ventromedial PFC. In addition, all animals were tested after infusion of several doses of the muscarinic receptor antagonist scopolamine (SCO) and the dopamine DI receptor antagonist SCH-23390 (SCH). The drugs tested affected DMTP performance differentially. APO had no effect on response accuracy, although it dose-dependently affected nose poke activity and response latencies. FLU and SCH both induced a dose-dependent, but delay-independent deterioration of response accuracy that was paralleled by increases in response latencies and decreases in nose poke frequencies, causing some animals to stop responding after infusion of the highest doses of both drugs. In contrast, SCO infusions into the ventromedial PFC induced a dose- and delay-dependent deterioration of response accuracy, that was accompanied by an increase in response latencies only. Taken together, these results provide additional support for the involvement of cholinergic, rather than dopaminergic mechanisms in short-term memory supported by the medial PFC of the rat, and they are not in favor of a functional dissociation between the dorsomedial PFC and the ventromedial PFC in the role.

Role of the prefrontal cortex of the rat in learning and decision making: effects of transient inactivation

Publisher Summary This chapter describes the role of the prefrontal cortex of the rat in learning and decision making. Depending on the authors reviews of prefrontal cortex (PFC) functions in rats have provided lists of behavioral deficiencies following damage of the PFC. They include deficient performance in various delay-type tasks, spatial tasks, inhibition, attention, along with abnormalities in social behavior. When rats with PFC damage are examined for their spatial learning skills in a Morris water maze, no impairments in spatial learning could be detected; however, when the task was changed from an allocentric one to a visual-cued one, rats with damage of the medial PFC were initially impaired. It is assumed that with prefrontal damage, it was more difficult to shift between tasks with different task demands. Evidence supporting this assumption has been obtained, when rats are trained either in a cheeseboard task, or a visual-cued version of that task. Transient inactivation of the medial PFC did not interfere with task acquisition. However, such an inactivation impaired learning when the rats were switched from one version of the task to the other one. It is tempting to relate these findings with the well-known deficiencies described in humans with PFC damage.

Operant learning and differential-reinforcement-of-low-rate 36-s responding in 5-HT1A and 5-HT1B receptor knockout mice.

Previous studies with mice lacking 5-HT(1A) (1AKO) and 5-HT(1B) (1BKO) receptors in hippocampus-dependent learning and memory paradigms, suggest that these receptors play an important role in learning and memory, although their precise role is unclear. In the present study, 1AKO and 1BKO mice were studied in operant behavioural paradigms of decision making and response inhibition, to further study the putative involvement of these receptors in prefrontal cortex-dependent learning and memory. Moreover, because 1AKO mice have been shown to exhibit an antidepressant-like phenotype and 1BKO mice to be more impulsive in ethological studies, mice were trained in a differential-reinforcement-of-low-rates (DRL) procedure. Overall, results indicate that 1AKO and 1BKO mice display subtle differences in operant paradigms of decision making and response inhibition compared to wild type (WT) mice. In addition, when responding under a DRL 36-s schedule had stabilised, 1BKO mice showed a phenotype indicative of increased impulsivity, whereas 1AKO mice did not differ from WT mice. In conclusion, 5-HT(1B) receptors appear to play an important role in impulsivity and a minor role in prefrontal cortex-dependent learning and memory as shown by the results obtained in serial reversal learning and extinction. In contrast, 5-HT(1A) receptors appear to be involved in facilitation of autoshaping, but their role in impulsivity and prefrontal cortex-dependent learning and memory appears to be limited.

Targeting synaptic dysfunction in Alzheimer's disease by administering a specific nutrient combination.

Synapse loss and synaptic dysfunction are pathological processes already involved in the early stages of Alzheimers disease (AD). Synapses consist principally of neuronal membranes, and the neuronal and synaptic losses observed in AD have been linked to the degeneration and altered composition and structure of these membranes. Consequently, synapse loss and membrane-related pathology provide viable targets for intervention in AD. The specific nutrient combination Fortasyn Connect (FC) is designed to ameliorate synapse loss and synaptic dysfunction in AD by addressing distinct nutritional needs believed to be present in these patients. This nutrient combination comprises uridine, docosahexaenoic acid, eicosapentaenoic acid, choline, phospholipids, folic acid, vitamins B12, B6, C, and E, and selenium, and is present in Souvenaid, a medical food intended for use in early AD. It has been hypothesized that FC counteracts synaptic loss and reduces membrane-related pathology in AD by providing nutritional precursors and cofactors that act together to support neuronal membrane formation and function. Preclinical studies formed the basis of this hypothesis which is being validated in a broad clinical study program investigating the potential of this nutrient combination in AD. Memory dysfunction is one key early manifestation in AD and is associated with synapse loss. The clinical studies to date show that the FC-containing medical food improves memory function and preserves functional brain network organization in mild AD compared with controls, supporting the hypothesis that this intervention counteracts synaptic dysfunction. This review provides a comprehensive overview of basic scientific studies that led to the creation of FC and of its effects in various preclinical models.

Effects of local application of dopaminergic drugs into the dorsal part of the medial prefrontal cortex of rats in a delayed matching to position task: comparison with local cholinergic blockade

Lesions of the medial prefrontal cortex (mPFC) disrupt performance in a variety of delay tasks, which suggests that the mPFC supports short-term memory processes. The putative involvement of the dopaminergic innervation of the mPFC in these mnemonic processes was investigated by evaluating the effects of local infusions of dopaminergic drugs into the mPFC of rats in an operant delayed-matching-to-position (DMTP) task. Trained animals were provided with bilateral guide cannulae aimed at the dorsal part of the mPFC. Two separate groups of rats were tested after microinfusion of several doses of either the dopamine agonist apomorphine (APO) or the dopamine antagonist cis-flupenthixol (FLU). In addition, all animals were tested after infusion of several doses of the muscarinic antagonist scopolamine (SCO). Animals were tested 0 and 135 min after each infusion. At the 0 min interval, neither APO nor FLU affected accuracy of DMTP performance, while both drugs dose-dependently increased response latencies and decreased nosepoke frequencies. At the 135 min interval, APO had almost no effect, whereas the effects of FLU were very prominent. A number of animals no longer responded after infusion of the highest doses of FLU and those that did showed a delay-independent decrease in response accuracy. In contrast, SCO infusions into the mPFC induced a dose- and delay-dependent deterioration of DMTP performance. Taken together, these results support a direct involvement of the rat mPFC in short-term memory processes, although they implicate cholinergic rather than dopaminergic mechanisms in this function.

Effects of local application of dopaminergic drugs into the medial prefrontal cortex of rats on latent inhibition

The involvement of the dopamine (DA) innervation of the medial prefrontal cortex (PFC) in attention was studied in a latent inhibition (LI) paradigm in rats. LI becomes evident by a retardation of conditioning to a stimulus after nonreinforced preexposure to that stimulus. LI is thought to reflect an animals ability not to attend to irrelevant stimuli and is often used as an animal paradigm modeling schizophreniclike attentional deficits. In the present study the effects of bilateral infusions of the DA receptor agonist apomorphine (APO, 9.0 micrograms/side) and the DA receptor antagonist cis-flupenthixol (FLU, 12.0 micrograms/side) into the medial PFC on LI were assessed. Although in comparison with vehicle both APO and FLU infusions attenuated response suppression in nonpreexposed animals, the drugs differentially affected LI in preexposed animals. After infusions of APO animals failed to show conditioned suppression, whereas FLU-treated animals displayed as much suppression of responding as nonpreexposed animals. The abolition of LI induced by FLU infusions into the medial PFC suggests that prefrontal DA is involved in attentional processes in a way opposite to the established role of subcortical DA systems in these processes.