Alterations of the dopaminergic (DAergic) system are frequently reported in Alzheimer's disease (AD) patients and are commonly linked to cognitive and non-cognitive symptoms. However, the cause of DAergic system dysfunction in AD remains to be elucidated. We investigated alterations of the midbrain DAergic system in the Tg2576 mouse model of AD, overexpressing a mutated human amyloid precursor protein (APPswe). Here, we found an age-dependent DAergic neuron loss in the ventral tegmental area (VTA) at pre-plaque stages, although substantia nigra pars compacta (SNpc) DAergic neurons were intact. The selective VTA DAergic neuron degeneration results in lower DA outflow in the hippocampus and nucleus accumbens (NAc) shell. The progression of DAergic cell death correlates with impairments in CA1 synaptic plasticity, memory performance and food reward processing. We conclude that in this mouse model of AD, degeneration of VTA DAergic neurons at pre-plaque stages contributes to memory deficits and dysfunction of reward processing.

BackgroundIn man, many different events implying childhood separation from caregivers/unstable parental environment are associated with heightened risk for panic disorder in adulthood. Twin data show that the occurrence of such events in childhood contributes to explaining the covariation between separation anxiety disorder, panic, and the related psychobiological trait of CO2 hypersensitivity. We hypothesized that early interference with infant-mother interaction could moderate the interspecific trait of response to CO2 through genetic control of sensitivity to the environment.MethodologyHaving spent the first 24 hours after birth with their biological mother, outbred NMRI mice were cross-fostered to adoptive mothers for the following 4 post-natal days. They were successively compared to normally-reared individuals for: number of ultrasonic vocalizations during isolation, respiratory physiology responses to normal air (20%O2), CO2-enriched air (6% CO2), hypoxic air (10%O2), and avoidance of CO2-enriched environments.ResultsCross-fostered pups showed significantly more ultrasonic vocalizations, more pronounced hyperventilatory responses (larger tidal volume and minute volume increments) to CO2-enriched air and heightened aversion towards CO2-enriched environments, than normally-reared individuals. Enhanced tidal volume increment response to 6%CO2 was present at 16–20, and 75–90 postnatal days, implying the trait's stability. Quantitative genetic analyses of unrelated individuals, sibs and half-sibs, showed that the genetic variance for tidal volume increment during 6%CO2 breathing was significantly higher (Bartlett χ = 8.3, p = 0.004) among the cross-fostered than the normally-reared individuals, yielding heritability of 0.37 and 0.21 respectively. These results support a stress-diathesis model whereby the genetic influences underlying the response to 6%CO2 increase their contribution in the presence of an environmental adversity. Maternal grooming/licking behaviour, and corticosterone basal levels were similar among cross-fostered and normally-reared individuals.ConclusionsA mechanism of gene-by-environment interplay connects this form of early perturbation of infant-mother interaction, heightened CO2 sensitivity and anxiety. Some non-inferential physiological measurements can enhance animal models of human neurodevelopmental anxiety disorders.

Key factors driving eating behavior are hunger and satiety, which are controlled by a complex interplay of central neurotransmitter systems and peripheral stimuli. The lipid-derived messenger oleoylethanolamide (OEA) is released by enterocytes in response to fat intake and indirectly signals satiety to hypothalamic nuclei. Brain histamine is released during the appetitive phase to provide a high level of arousal in anticipation of feeding, and mediates satiety. However, despite the possible functional overlap of satiety signals, it is not known whether histamine participates in OEA-induced hypophagia. Using different experimental settings and diets, we report that the anorexiant effect of OEA is significantly attenuated in mice deficient in the histamine-synthesizing enzyme histidine decarboxylase (HDC-KO) or acutely depleted of histamine via interocerebroventricular infusion of the HDC blocker α-fluoromethylhistidine (α-FMH). α-FMH abolished OEA-induced early occurrence of satiety onset while increasing histamine release in the CNS with an H 3 receptor antagonist-increased hypophagia. OEA augmented histamine release in the cortex of fasted mice within a time window compatible to its anorexic effects. OEA also increased c-Fos expression in the oxytocin neurons of the paraventricular nuclei of WT but not HDC-KO mice. The density of c-Fos immunoreactive neurons in other brain regions that receive histaminergic innervation and participate in the expression of feeding behavior was comparable in OEA-treated WT and HDC-KO mice. Our results demonstrate that OEA requires the integrity of the brain histamine system to fully exert its hypophagic effect and that the oxytocin neuron-rich nuclei are the likely hypothalamic area where brain histamine influences the central effects of OEA.histamine receptors | behavioral satiety sequence | BSS | paraventricular hypothalamic nuclei | PVN E ating behavior is regulated by central neurotransmitter systems and peripheral stimuli that interact to change the behavioral state and concur to alter homeostatic aspects of appetite and energy expenditure. The fatty acid amide oleoylethanolamide (OEA) is released by the small intestine in a stimulus-dependent manner and suppresses food intake by activating peroxisome proliferator-activated receptor-α (PPAR-α) (1). Systemic administration of OEA induces c-Fos mRNA expression through the vagus nerve to the nucleus of the solitary tract (NST), supraoptic nuclei (SON), and paraventricular hypothalamic nuclei (PVN) and increases the expression of oxytocin (2, 3), which is involved in the central coordination of homeostatic signals and feeding behavior (4). However, it is not known whether OEA recruits other neurotransmitter systems in the brain to reduce food intake. Histaminergic neurons are clustered in the hypothalamic tuberomammillary nuclei (TMN). They send projections organized in functionally distinct circuits impinging on different brain regions (5), and their firing frequency changes according to the behavioral state (6). Brain histamin...

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Palatable food can be seductive and hedonic eating can become irresistible beyond hunger and negative consequences. This is witnessed by the subtle equilibrium between eating to provide energy intake for homeostatic functions, and reward-induced overeating. In recent years, considerable efforts have been devoted to study neural circuits, and to identify potential factors responsible for the derangement of homeostatic eating toward hedonic eating and addiction-like feeding behavior. Here, we examined recent literature on “old” and “new” players accountable for reward-induced overeating and possible liability to eating addiction. Thus, the role of midbrain dopamine is positioned at the intersection between selected hormonal signals involved in food reward information processing (namely, leptin, ghrelin, and insulin), and lipid-derived neural mediators such as endocannabinoids. The impact of high fat palatable food and dietary lipids on endocannabinoid formation is reviewed in its pathogenetic potential for the derangement of feeding homeostasis. Next, endocannabinoid signaling that regulates synaptic plasticity is discussed as a key mechanism acting both at hypothalamic and mesolimbic circuits, and affecting both dopamine function and interplay between leptin and ghrelin signaling. Outside the canonical hypothalamic feeding circuits involved in energy homeostasis and the notion of “feeding center,” we focused on lateral hypothalamus as neural substrate able to confront food-associated homeostatic information with food salience, motivation to eat, reward-seeking, and development of compulsive eating. Thus, the lateral hypothalamus-ventral tegmental area-nucleus accumbens neural circuitry is reexamined in order to interrogate the functional interplay between ghrelin, dopamine, orexin, and endocannabinoid signaling. We suggested a pivotal role for endocannabinoids in food reward processing within the lateral hypothalamus, and for orexin neurons to integrate endocrine signals with food reinforcement and hedonic eating. In addition, the role played by different stressors in the reinstatement of preference for palatable food and food-seeking behavior is also considered in the light of endocannabinoid production, activation of orexin receptors and disinhibition of dopamine neurons. Finally, type-1 cannabinoid receptor-dependent inhibition of GABA-ergic release and relapse to reward-associated stimuli is linked to ghrelin and orexin signaling in the lateral hypothalamus-ventral tegmental area-nucleus accumbens network to highlight its pathological potential for food addiction-like behavior.

Despite the knowledge of the molecular mechanisms is still a work in progress, the clinical relevance of the manipulation of dietary fats is well acknowledged and such manipulations are in fact currently in use for the treatment of brain diseases.

Recent evidence suggest that antagonism of adenosine A 2A receptors represent an alternative therapeutic approach to Parkinson's disease (PD). Coactivation of A 2A and the glutamate subtype 5 metabotropic receptors (mGlu 5 ) synergistically stimulates DARPP-32 phosphorylation and c-fos expression in the striatum. This study therefore tested the effects of a joint blockade of these receptors to alleviate the motor dysfunction in a rat model of PD. 6-Hydroxydopamine infusions in the striatum produced akinetic deficits in rats trained to release a lever after a stimulus in a reaction time (RT) task. At 2 weeks after the lesion, A 2A and mGlu 5 receptors selective antagonists 8-(3-chlorostyryl)caffeine (CSC) and 2-methyl-6-(phenylethynyl)-pyridine (MPEP) were administered daily for 3 weeks either as a single or joint treatment. Injections of CSC (1.25 mg/kg) and MPEP (1.5 mg/kg) separately or in combination reduced the increase of delayed responses and RTs induced by 6-OHDA lesions, while the same treatment had no effect in controls. Furthermore, coadministration of lower doses of 0.625 mg/kg CSC and 0.375 mg/kg MPEP noneffective as a single treatment promoted a full and immediate recovery of akinesia, which was found to be more efficient than the separate blockade of these receptors. These results demonstrate that the combined inactivation of A 2A and mGlu 5 receptor potentiate their beneficial effects supporting this pharmacological strategy as a promising anti-Parkinsonian therapy.