Cyclic AMP-dependent regulation of tyrosine hydroxylase mRNA and immunofluorescence levels in rat retinal precursor cells

Yohimbine Ameliorates Temporomandibular Joint Chondrocyte Inflammation with Suppression of NF-κB Pathway

Local joint inflammation plays an important role in the pathogenesis of temporomandibular joint (TMJ) osteoarthrosis (TMJOA). Yohimbine, an alpha-2 adrenergic receptor antagonist, possesses anti-inflammatory properties; however, the ability of Yohimbine to protect against TMJOA-associated chondrocyte inflammation remains unclear. We conducted in vitro and in vivo analyses to investigate whether Yohimbine could ameliorate TMJOA-induced chondrocyte inflammation and to elucidate the mechanisms involved. Chondrocytes of TMJOA mice were stimulated with interleukin (IL)-1β or noradrenaline (NE), and the resulting production of inflammation-related factors was evaluated in the presence or absence of Yohimbine. Furthermore, two TMJOA mouse models were treated with Yohimbine and the therapeutic effect was quantified. NE (10^-6 M) triggered inflammatory cytokine secretion by TMJ chondrocytes, and Yohimbine suppressed IL-1β- or NE-induced IL-6 upregulation in TMJ chondrocytes with the nuclear factor (NF)-κB pathway inhibition. Yohimbine also ameliorated cartilage destruction in the TMJOA models. Interestingly, αmpT, a tyrosine hydroxylase inhibitor, reversed the effects of Yohimbine by activating the NF-κB pathway. Collectively, these findings show that Yohimbine ameliorated TMJ chondrocyte inflammation and the suppression of NF-κB pathway contributes to this effect.

Dopamine-2 receptor activation suppresses PACAP expression in gonadotrophs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed at a high level in the fetal pituitary and decreases profoundly between embryonic day 19 and postnatal day 1 (PN1), with a further decrease from PN1 to PN4. In this series of experiments, we investigated the hypothesis that dopamine 2 receptor (Drd2) activation interrupts a cAMP-dependent feed-forward loop that maintains PACAP expression at a high level in the fetal pituitary. Using single-cell RT-PCR of pituitary cell cultures from newborn rats, Drd2 mRNA was identified in gonadotrophs that were also positive for PACAP mRNA. PACAP expression in pituitary cultures from embryonic day 19 rats was suppressed by the PACAP6-38 antagonist and by the Drd2 agonist bromocriptine. Increasing concentrations of bromocriptine inhibited cAMP production as well as cAMP signaling based on cAMP response element-luciferase activity, decreased PACAP promoter activity, and decreased PACAP mRNA levels in αT3-1 gonadotroph cells. Furthermore, blockade of dopamine receptors by injecting haloperidol into newborn rat pups partially reversed the developmental decline in pituitary PACAP mRNA that occurs between PN1 and PN4. These results provide evidence that dopamine receptor signaling regulates PACAP expression under physiological conditions and lend support to the hypothesis that a rise in hypothalamic dopamine at birth abrogates cAMP signaling in fetal gonadotrophs to interrupt a feed-forward mechanism that maintains PACAP expression at a high level in the fetal pituitary. We propose that this perinatal decline in pituitary PACAP reduces pituitary follistatin which permits GnRH receptors and FSH-β to increase to facilitate activation of the neonatal gonad.