Brain-derived neurotrophic factor (BDNF) plays a fundamental role in neuronal synaptic plasticity. A decrease of plasticity in the brain may be related to the pathogenesis of neurodegenerative or psychiatric disorders. Pyrethroid insecticides, which affect sodium channels in neurons, are widely used to control insect pests in agriculture and in the home. We previously found that deltamethrin (DM), a type II pyrethroid, increased Bdnf mRNA expression in cultured rat cortical neurons. However, the cyano group at the α-position of type II pyrethroids is likely susceptible to hydrolytic degradation and, its degraded product, hydrogen cyanide, could generate a cellular toxicity in the human body. To determine if the cyano group is required for the Bdnf exon IV-IX (Bdnf eIV-IX) mRNA expression induced by type II pyrethroids, for this study we synthesized a series of derivatives, in which the cyano group at the α-position was replaced with an ethynyl group. Then we added various substituents at the terminal position of the ethynyl group, and biologically evaluated the effects of these derivatives on Bdnf eIV-IX mRNA expression. These ethynyl derivatives induced the Bdnf eIV-IX mRNA expression in a concentration-dependent manner, at varying levels but lower levels than that evoked by DM. The mechanisms for the Bdnf induction and the morphological changes of neurons were the same whether the cyano or ethynyl group was included in the compounds.

Valproic acid (VPA), a drug used to treat epilepsy and bipolar mood disorder, inhibits histone deacetylase (HDAC), which is associated with the epigenetic regulation of gene expression. Using a microarray, we comprehensively examined which genes are affected by stimulating cultured rat cortical neurons with VPA, and found that the VPA-treatment markedly altered gene expression (up-regulated; 726 genes, down-regulated; 577 genes). The mRNA expression for brain-derived neurotrophic factor (BDNF) and the α4 subunit of the GABAA receptor (GABAARα4), known to be involved in epileptogenesis, was up-regulated, with the increase in BDNF exon I–IX mRNA expression being remarkable, whereas that for GABAARγ2, GAD65 and 67, and the K+/Cl− co-transporter KCC2, which are responsible for the development of GABAergic inhibitory neurons, was down-regulated. The number of GAD67-positive neurons decreased upon VPA-treatment. Similar changes of up- and down-regulation were obtained by trichostatin A. VPA did not affect the intracellular Ca2+ concentration and the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), suggesting its direct action on HDAC. The acetylation of histones H3 and H4 was increased in the promoters of up-regulated but not down-regulated genes. Thus, VPA may disrupt a balance between excitatory and inhibitory neuronal activities through its epigenetic effect.

Although dynorphins are widely involved in the control of not only nociceptive neurotransmission but also a variety of brain functions such as memory and emotion, no natural regulator for inducing the mRNA expression of prodynorphin (Pdyn), a precursor protein of dynorphins, is known. Using primary cultures of rat cortical neurons, we found that pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon neuropeptide family, markedly induces Pdyn mRNA expression. PACAP was much more effective than VIP, indicating a major role for PAC1 in the PACAP-induced Pdyn mRNA expression. The increase in Pdyn mRNA expression was independent of de novo protein synthesis. Administration of forskolin, an activator for adenylate cyclase/protein kinase A (PKA), but not TPA, an activator for protein kinase C (PKC), induced Pdyn mRNA expression, suggesting a major role for PKA. The involvement of PKA was supported by the inhibition of PACAP-induced Pdyn mRNA expression upon addition of H89, an inhibitor for PKA. The PACAP-induced potentiation of NMDA-R was involved in the mRNA expression of Bdnf or c-fos but not Pdyn. These results suggest PACAP to be an upstream regulator for inducing Pdyn mRNA expression through PKA.Research highlights▶ PACAP induces prodynorphin (Pdyn) mRNA expression in cultured rat cortical neurons. ▶ PACAP had much more of an effect than VIP on Pdyn mRNA expression. ▶ De novo protein synthesis is not necessary for the PACAP-induced Pdyn mRNA expression. ▶ The PACAP-induced Pdyn mRNA expression is dependent on a PACAP/PAC1/PKA pathway.