When food is available during a restricted and predictable time of the day, mammals exhibit food-anticipatory activity (FAA), an increase in locomotor activity preceding the presentation of food. Although many studies have attempted to locate the food-entrainable circadian oscillator in the central nervous system, the pathways that mediate food entrainment are a matter of controversy. The present study was designed to determine the role of dopaminergic and histaminergic systems on FAA. Mice were given access to food for 2 h (ZT12-ZT14), and FAA was defined as the locomotor activity that occurred 2 h before the availability of food. Dopamine D(1) receptor (R), D(2)R, and histamine H(1)R-specific antagonists were used to clarify the role of dopamine and histamine receptors in FAA induced by food restriction (FR). FAA was monitored by infrared locomotor activity sensors. Mice were sacrificed at ZT12 on the 14th day of FR, and monoamine concentrations were determined by high-performance liquid chromatography coupled to electrochemical detection (HPLC-ECD). The results showed that pretreatment with the D(1)R antagonist SCH23390 at 1, 3, or 10 µg/kg significantly reduced FAA by 19% (p < 0.05), 26% (p < 0.05), or 19% (p < 0.01), respectively, and the D(2)R antagonist raclopride at 22, 67, or 200 µg/kg significantly reduced FAA by 16% (p < 0.05), 36% (p < 0.01), or 41% (p < 0.01), respectively, as compared with vehicle control. Moreover, coadministration of SCH23390 (10 µg/kg) and raclopride (200 µg/kg) synergistically inhibited FAA by 57% (p < 0.01) as compared with vehicle control. Consistently, the levels of dopamine and its metabolites in the striatum and midbrain were significantly increased during FAA, even with the pretreatment of D(1)R and D(2)R antagonists. However, pretreatment with pyrilamine at 2.5, 5, or 10 mg/kg did not significantly reduce FAA, although it reduced the locomotor activity during the dark period in ad libitum mice. These results strongly indicate that the dopaminergic system plays an essential role in the FAA in mice.

Microglia-mediated neuroinflammation plays a critical role in the pathological development of Parkinson's disease (PD). Orphan nuclear receptor Nur77 (Nur77) is abundant in neurons, while its role in microglia-mediated neuroinflammation remains unclear. The present data demonstrated that the expression of Nur77 in microglia was reduced accompanied by microglia activation in response to lipopolysaccharide (LPS) in vitro and in experimental 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-PD mouse model. Nur77 over-expression or application of Nur77 agonist cytosporone B suppressed the expression of proinflammatory genes, such as inducible nitric oxide NOS, cyclooxygenase-2, IL-1β, and tumor necrosis factor-α in the activated microglia, while silenced Nur77 exaggerated the inflammatory responses in microglia. Moreover, activation of Nur77 suppressed the LPS-induced NF-κB activation which was partly dependent on p38 MAPK activity, since inhibition of p38 MAPK by SB203580 abolished the LPS-activated NF-κB in microglia. On the other hand, inhibition of p38 MAPK attenuated LPS-induced Nur77 reduction. Furthermore, in a microglia-conditioned cultured media system, Nur77 ameliorated the cytotoxicity to MN9D dopaminergic cells. Lastly, cytosporone B attenuated microglia activation and loss of dopaminergic neuron in the substantia nigra pars compacta (SNpc) of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-PD mouse model. Taken together, these findings revealed the first evidence that Nur77 was an important modulator in microglia function that associated with microglia-mediated dopaminergic neurotoxicity, and thus modulation of Nur77 may represent a potential novel target for treatment for neurodegenerative disease.

These findings indicate that safranal enhances NREM sleep in pentobarbital-treated mice. The hypnotic effects of safranal may be related to the activation of the sleep-promoting neurons in the VLPO and the simultaneous inhibition of the wakefulness-promoting neurons in the TMN, suggesting that safranal may be a hypnotic substance.