Molecular Insights of CREB and MAP-K Phosphorylation by Modafinil in Wake-Related Brain Areas.

BACKGROUND: Modafinil (MOD) is a waking-promoting compound that is used for the treatment of sleep disorders such as sleepiness and narcolepsy. Despite its efficiency, there are missing pieces of evidence regarding the mechanism of action of MOD at molecular level. For example, current data have demonstrated that MOD induces alertness by activating several wake-related neurotransmitter receptors, including dopamine 1 (D1) receptor. Nevertheless, an intriguing point highlights that MOD might be activating intracellular elements bounded to D1 receptor, such as cAMP response element-binding (CREB) or mitogen-activated protein kinase (MAP-K) expression. OBJECTIVE: We tested whether administrations of MOD induce phosphorylation of either CREB or MAPK in wake-related brain areas, such as dorsomedial hypothalamic nucleus (DM) and tuberomammillary nucleus (TMN) in rats. METHODS: Rats that received a systemic injection of MOD (30 or 150 mg/Kg) were sacrificed and brains were processed for immunohistochemical analysis of phospho-CREB or phospho-MAP-K staining. RESULTS: MOD dose-dependently enhanced phospho-CREB and phospho-MAP-K immunoreactivity in DM and TMN. Moreover, the statistical analysis revealed that MOD increased the number of phospho- CREB and phospho-MAP-K immunoreactive neurons in these brain areas studied. CONCLUSION: These findings provide significative insights regarding the possible molecular mechanism of action of MOD engaging the activation of phospho-CREB and phospho-MAP-K in wake-linked brain areas. Indeed, further studies are required to fully understand the molecular mechanism of action of MOD.

Regulation of differentiation flux by Notch signalling influences the number of dopaminergic neurons in the adult brain.

Notch signalling is a well-established pathway that regulates neurogenesis. However, little is known about the role of Notch signalling in specific neuronal differentiation. Using Dll1 null mice, we found that Notch signalling has no function in the specification of mesencephalic dopaminergic neural precursor cells (NPCs), but plays an important role in regulating their expansion and differentiation into neurons. Premature neuronal differentiation was observed in mesencephalons of Dll1-deficient mice or after treatment with a Notch signalling inhibitor. Coupling between neurogenesis and dopaminergic differentiation was indicated from the coincident emergence of neuronal and dopaminergic markers. Early in differentiation, decreasing Notch signalling caused a reduction in NPCs and an increase in dopaminergic neurons in association with dynamic changes in the proportion of sequentially-linked dopaminergic NPCs (Msx1/2+, Ngn2+, Nurr1+). These effects in differentiation caused a significant reduction in the number of dopaminergic neurons produced. Accordingly, Dll1 haploinsufficient adult mice, in comparison with their wild-type littermates, have a consistent reduction in neuronal density that was particularly evident in the substantia nigra pars compacta. Our results are in agreement with a mathematical model based on a Dll1-mediated regulatory feedback loop between early progenitors and their dividing precursors that controls the emergence and number of dopaminergic neurons.