TLR4 and CD14 receptors expressed in rat pineal gland trigger NFKB pathway.

Nuclear factor-kappa B (NFKB), a pivotal player in inflammatory responses, is constitutively expressed in the pineal gland. Corticosterone inhibits pineal NFKB leading to an enhancement of melatonin production, while tumor necrosis factor (TNF) leads to inhibition of Aa-nat transcription and the production of N-acetylserotonin in cultured glands. The reduction in nocturnal melatonin surge favors the mounting of the inflammatory response. Despite these data, there is no clear evidence of the ability of the pineal gland to recognize molecules that signal infection. This study investigated whether the rat pineal gland expresses receptors for lipopolysaccharide (LPS), the endotoxin from the membranes of Gram-negative bacteria, and to establish the mechanism of action of LPS. Here, we show that pineal glands possess both CD14 and toll-like receptor 4 (TLR4), membrane proteins that bind LPS and trigger the NFKB pathway. LPS induced the nuclear translocation of p50/p50 and p50/RELA dimers and the synthesis of TNF. The maximal expression of TNF in cultured glands coincides with an increase in the expression of TNF receptor 1 (TNFR1) in isolated pinealocytes. In addition, LPS inhibited the synthesis of N-acetylserotonin and melatonin. Therefore, the pineal gland transduces Gram-negative endotoxin stimulation by producing TNF and inhibiting melatonin synthesis. Here, we provide evidence to reinforce the idea of an immune-pineal axis, showing that the pineal gland is a constitutive player in the innate immune response.

Melatonin, the Hallmark of Darkness Modulates Nicotinic Acetylcholine Receptors Sensitive to alfa Bungarotoxin

Melatonin, known as the hallmark of darkness, is released during the dark by pineal glands and retina of adult animals. In neonates melatonin is secreted in a tonic manner by extra-pineal sources, including retina. Here we show that melatonin modulates the density and functional response of nicotinic acetylcholine receptors (nAChRs) in central and peripheral nervous system. Melatonin effect is restricted to α-bungarotoxin sensitive nAChRs in all models tested: rat sympathetic nerve terminals, cerebellum, and chick retina. In addition, it is shown that in adult animals, where the pineal gland releases melatonin in a rhythm manner, this hormone imposes a daily rhythm in the cholinergic function, whereas during the development of the retina, when melatonin is produced in a tonic manner, it is essential for the appearance of function nAChRs sensitive to α-bungarotoxin. This common pattern of action on different cell models that express α-bungarotoxin-sensitive receptors probably reflects a more general mechanism of regulation of these receptors.

P2Y(1) receptor activation enhances the rate of rat pinealocyte-induced extracellular acidification via a calcium-dependent mechanism.

Pineal gland G-protein coupled P2Y(1) receptors potentiate noradrenaline-induced N'-acetylserotonin production, a long term response which occurs after 5 h incubation. In the current study we show that a short-term effect of stimulation of P2Y(1) receptors is the increase in extracellular acidification rate (ECAR), which is mediated by an increase in intracellular calcium concentration ([Ca(2+)](i)). The pD(2) values for ATP (3.06 +/- 0.12)-induced ECAR increase was significantly smaller (p < 0.01) than that for ADP (3.64 +/- 0.18), 2MeSATP (3.56 +/- 0.02) and 2MeSADP (3.65 +/- 0.13). The selective P2Y(1) receptor antagonists A3'P-5'P and A3'P-5'PS inhibited the increase in ECAR-induced by ADP. Clamping [Ca(2+)](i) with BAPTA (30 and 50 micromol/l) led to inhibition of ADP-induced increase in ECAR. Agonist and antagonist data indicate P2Y(1) activation leads to a [Ca(2+)](i)-dependent acidification of the extracellular medium.