According to TCM theory, the herbal combination was believed to enhance the therapeutic efficacy of single herb via herbal compatibility [
19]. Synergistic works among different herbs had been well illustrated in DBT [
4]. For example, the boiling AR and ASR together could generate a perfect decoction having the best chemical and biological properties [
1,
10]. Traditionally, DBT is prescribed to improve menopausal symptoms [
2]. In addition, the efficacies of DBT have been revealed and confirmed in different aspects, i.e. estrogenic effect, bone development, blood enhancement, immune stimulation and cardiovascular function [
1,
2,
16]. Here, we proposed a possible function of DBT in the brain.
The neuro-functions of AR and ASR, two herbs making up DBT, had been verified in enhancing memory and in promoting synaptic plasticity [
20]. In particular, the flavonoids derived from AR, such as calycosin and formononetin, are regarded as an important and effective constituent within DBT. These flavonoids were shown to be absorbable by cells [
10]. Several types of flavonoids are believed to show beneficial effects on neural stem cell for its differentiation and survive. Hesperidin was able to increase survival rate of neural crest cells [
20]. Pre-treatment of quercetin, a flavonol, was capable to prevent H
2O
2-induced cellular viability [
21]. Furthermore, Baicalein, a flavone, was shown to protect neural progenitor cells from irradiation-induced necrotic cell apoptosis by elevating the BDNF-mediated signaling in hippocampus [
22]. It also reported that flavonoids, and their known physiologically relevant metabolites, were able to cross the blood–brain barrier using well-established in vitro models, i.e. brain endothelial cell lines and ECV304 monolayers co-cultured with C6 glioma cells [
23]. The intake of isoflavonoid-enriched herbal decoction in rat could induce productions of neurotrophic factors, and subsequently the decoction rescued cognitive impairment associated with N-methyl-D-aspartate (NMDA) receptor antagonism [
24], promoted hippocampal neurogenesis [
25] and attenuated depressive symptoms [
26]. Aging and Alzheimer’s disease (AD) are characterized by deficiency of learning and memory. The close relationship between AD and aging plays a critical role in elucidating the pathophysiological mechanism in each event, e.g. the involvement of neurotrophic factors in both processes [
27]. BDNF is important in neuronal growth and neuronal survival, in particular the effect in synaptic processes of memory. Indeed, a decreased level of pro-BDNF was shown in mild cognitive impairment (MCI) patients [
25]. The intake of NGF in AD patients showed improvements in cognitive functions, as well as a low level of amyloid β in cerebrospinal fluid [
28]. Moreover, a reduced level of GDNF led to excess glutamate release and deregulation of glutamate transporter-1, which caused the excitotoxicity in nervous system [
29].
Neurons are responsible to process and transmit information within human body. MAPK/Erk pathway is a key factor of NMDA receptor signaling transduction in regulating neuronal development, synaptic communications and neuroplasticity. The stimulated MAPK/Erk mechanism is believed to contribute AD pathogenesis via multiple mechanisms, e.g. up-regulation of neuronal apoptosis, transcriptional and translational activations of β- and γ-secretases, and stabilization and phosphorylation of amyloid precursor protein [
30]. In fact, the initiation of MAPK/Erk signaling can trigger the activation of cAMP response element binding protein (CREB) [
31]. CREB activation is important in gene transcriptions, in particular during the promotion of cell survival [
32]. Here, the application of this ancient herbal formula was capable of inducing the activations of Erk and CREB in a time-dependent manner. More importantly, the activations of Erk1/2 and CREB could be blocked by U0126. Thus, we believed that MAPK/Erk might involve in regulating neurotrophic expressions.